Langley Memoir on Mechanical Flight, Parts I and II - Smithsonian Contributions to Knowledge, Volume 27 Number 3, Publication 1948, 1911

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Title: Langley Memoir on Mechanical Flight, Parts I and II - Smithsonian Contributions to Knowledge, Volume 27 Number 3, Publication 1948, 1911
Author: Langley, S. P. (Samuel Pierpont), Manly, Charles M. (Charles Matthews)
Language: English
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Smithsonian Contributions to Knowledge
Volume 27 Number 3

LANGLEY MEMOIR ON MECHANICAL FLIGHT

PART I. 1887 TO 1896

SAMUEL PIERPONT LANGLEY

Edited by Charles M. Manly

PART II. 1897 TO 1903

CHARLES M. MANLY

Assistant in Charge of Experiments

[Illustration]

(Publication 1948)

City of Washington
Published by the Smithsonian Institution
1911

Commission to whom this Memoir
has been referred:
Otto Hilgard Tittman,
George Owen Squier,
Albert Francis Zahm.

The Lord Baltimore Press
Baltimore, MD., U. S. A.
67009

[page iii]

The present work, entitled “Langley Memoir on Mechanical Flight,” as
planned by the late Secretary Samuel Pierpont Langley, follows his
publications on “Experiments in Aerodynamics” and “The Internal Work
of the Wind” printed in 1891 and 1893, respectively, as parts of
Volume 27 of the Smithsonian Contributions to Knowledge.

This Memoir was in preparation at the time of Mr. Langley’s death
in 1906, and Part I, recording experiments from 1887 to 1896, was
written by him. Part II, on experiments from 1897 to 1903, has been
written by Mr. Charles M. Manly, who became Mr. Langley’s Chief
Assistant in June, 1898. The sources of information for this Part
were the original carefully recorded accounts of the experiments
described.

It is expected later to publish a third part of the present memoir,
to consist largely of the extensive technical data of tests of the
working of various types of curved surfaces, propellers, and other
apparatus.

It is of interest here to note that experiments with the Langley type
of aerodrome[1] did not actually cease in December, 1903, when he
made his last trial with the man-carrying machine, but as recently
as August 6, 1907, a French aviator made a flight of nearly 500 feet
with an aerodrome of essentially the same design. (See Appendix.)

In accordance with the established custom of referring to experts
in the subject treated, all manuscripts intended for publication in
the Smithsonian Contributions to Knowledge, this work was examined
and recommended by a Commission consisting of Mr. O. H. Tittman,
Superintendent of the United States Coast and Geodetic Survey, who
witnessed some of the field trials, George O. Squier, Ph. D. (Johns
Hopkins), Major, Signal Corps, U. S. Army, and Albert Francis Zahm,
Ph. D., of Washington City.

CHARLES D. WALCOTT,
‹Secretary of the Smithsonian Institution›.

FOOTNOTES:

[1] The name “aerodrome” was given by Secretary Langley to the flying
machine in 1893, from ἀεροδρομέω (to traverse the air) and ἀεροδρόμος
air runner.--Internal Work of the Wind, p. 5.

PREFACE

The present volume on Mechanical Flight consists, as the title-page
indicates, of two parts. The first, dealing with the long and
notable series of early experiments with small models, was written
almost entirely by Secretary Langley with the assistance of Mr. E.
C. Huffaker and Mr. G. L. Fowler in 1897. Such chapters as were not
complete have been finished by the writer and are easily noted as
they are written in the third person. It has been subjected only to
such revision as it would have received had Mr. Langley lived to
supervise this publication, and has therefore the highest value as an
historical record. The composition of the second part, dealing with
the later experiments with the original and also new models and the
construction of the larger aerodrome, has necessarily devolved upon
me. This is in entire accordance with the plan formed by Mr. Langley
when I began to work with him in 1898, but it is to me a matter of
sincere regret that the manuscript in its final form has not had the
advantage of his criticism and suggestions. If the reader should feel
that any of the descriptions or statements in this part of the volume
leave something to be desired in fullness of detail, it is hoped that
some allowance may be made for the fact that it has been written in
the scanty and scattered moments that could be snatched from work
in other lines which made heavy demands upon the writer’s time and
strength. It is believed, however, that sufficient data are given to
enable any competent engineer to understand thoroughly even the most
complicated phases of the work.

Persons who care only for the accomplished fact may be inclined to
underrate the interest and value of this record. But even they may
be reminded that but for such patient and unremitting devotion as is
here enregistered, the now accomplished fact of mechanical flight
would still remain the wild unrealized dream which it was for so many
centuries.

To such men as Mr. Langley an unsuccessful experiment is not a
failure but a means of instruction, a necessary and often an
invaluable stepping-stone to the desired end. The trials of the
large aerodrome in the autumn of 1903, to which the curiosity of the
public and the sensationalism of the newspapers gave a character of
finality never desired by Mr. Langley, were to him merely members of
a long series of experiments, as much so as any trial of one of the
small aerodromes or even of one of the earliest rubber-driven models.
Had his health and strength been spared, he would have gone on with
his experiments undiscouraged by these accidents in launching and
undeterred by criticism and misunderstanding.

Moreover, it is to be borne in mind that Mr. Langley’s contribution
to the solution of the problem is not to be measured solely by
what he himself accomplished, important as that is. He began his
investigations at a time when not only the general public but even
the most progressive men of science thought of mechanical flight
only as a subject for ridicule, and both by his epoch-making
investigations in aerodynamics and by his own devotion to the subject
of flight itself he helped to transform into a field of scientific
inquiry what had before been almost entirely in the possession of
visionaries.

The original plans for this publication provided for a third part
covering the experimental data obtained in tests of curved surfaces
and propellers. Owing to the pressure of other matters on the writer,
the preparation of this third part is not yet complete and is
reserved for later publication.

CHARLES M. MANLY.
NEW YORK CITY.

CONTENTS

PART I

I. Introductory … 1

II. Preliminary … 5

Experiments with small models … 6

Abbreviations and symbols employed … 14

Experiments with Aerodromes Nos. 30 and 31 … 16

III. Available motors … 21

India rubber … 21

Steam engine … 24

Gunpowder, hot-water, compressed air … 25

Gas, electricity … 26

Carbonic-acid gas … 28

IV. Early steam motors and other models … 30

V. On sustaining surfaces … 41

Experiments in the open wind … 42

Relation of air to weight and power … 43

VI. Balancing the aerodrome … 45

Lateral and longitudinal stability … 45

VII. History of construction of frame and engines of
aerodromes … 53

1893 … 53

1894 … 64

1895 … 75

1896 … 79

VIII. History of construction of sustaining and guiding
surfaces of aerodromes 4, 5, and 6 … 80

Introduction … 80

1893, 1894 … 81

1895 … 85

1896 … 89

IX. History of launching apparatus and field trials of
aerodromes 4, 5, and 6 … 92

1892 … 92

1893 … 93

Field trials … 93

1894 … 96

1895 … 101

1896 … 106

X. Description of the launching apparatus of aerodromes
Nos. 5 and 6 … 110

Description of Aerodrome No. 5 … 111

Description of Aerodrome No. 6 … 120

PART II

I. Introductory … 123

II. General considerations … 128

III. Experiments with models … 133

Condensed record of flights of aerodromes Nos. 5 and 6,
from June 7 to August 3, 1899 … 135

June 7--aerodrome No. 6 … 135

June 13--aerodrome No. 6 … 137

June 22--aerodrome No. 6 … 139

June 23--aerodrome No. 6 … 140

June 27--aerodrome No. 5 … 140

June 30--aerodrome No. 5 … 141

July 1 to July 8 … 142

July 11 to July 14--aerodrome No. 5 … 143

July 19--aerodrome No. 5 … 144

July 27--aerodrome No. 6 … 145

July 28--aerodrome No. 6 … 146

July 29--aerodrome No. 5 … 147

August 1--aerodrome No. 5 … 148

August 3--aerodrome No. 5 … 149

IV. House-boat and launching apparatus … 156

V. Construction of frame of large aerodrome … 164

Transverse frame … 174

Propellers … 178

Aviator’s car … 185

VI. Construction of supporting surfaces … 188

VII. Equilibrium and control … 207

VIII. The experimental engine … 218

IX. The quarter-size model aerodrome … 226

X. Construction and tests of the large engine … 234

XI. Shop tests of the aerodrome … 251

XII. Field trials in 1903 … 255

Statement made by Mr. Manly to associated press … 266

Report of War Department, January, 1904 … 276

Langley aerodrome, Official Report of Board of Ordnance,
October, 1904 … 278

Statement to the Press … 280

Present status of the work … 281

Blériot Machine of 1907 on Langley type … 283

Appendix. Study of American Buzzard and “John Crow” … 285

Instructions to assistants … 294

Data sheets 1 to 12 … 297

Index … 309

LIST OF PLATES

1. Rubber-motor model aerodromes Nos. 11, 13, 14, 15, 26,
30, 31 … 16

2. Rubber-motor model aerodromes Nos. 11, 13, 14 … 16

3. Rubber-motor model aerodromes Nos. 15, 24 … 16

4. Rubber-motor model aerodrome No. 26 … 16

5. Rubber-pull model aerodrome … 24

6. Rubber-pull model aerodrome … 24

7. Rubber-pull model aerodrome … 24

8. Rubber-pull model aerodrome … 24

9. Rubber-pull model aerodrome … 24

10. Steel frames of aerodromes Nos. 0, 1, 2, 3, 1891 and
1892 … 33

11. Steel frames of aerodromes Nos. 4, 5, 6, 1893, 1895,
and 1896 … 53

12. Burners, aeolipiles, and separators … 56

13. Boilers of aerodromes … 56

14. Aerodrome No. 5, December 3, 1895. Plan view. Rudder
removed … 78

15. Aerodrome No. 5, December 3, 1895. Side view … 78

16. Early types of wings and systems of guying … 81

17. Aerodrome No. 5. Plan of wings and system of guying …
89

18. House-boat with overhead launching apparatus, 1896 …
106

19. Paths of aerodrome flights, May 6 and November 28,
1896, near Quantico, Va., on the Potomac River … 108

20. Instantaneous photograph of the aerodrome at the
moment after launching in its flight at Quantico on the
Potomac River, May 6, 1896. Enlarged ten times … 108

21. Instantaneous photograph of the aerodrome at a
distance in the air during its flight at Quantico on the
Potomac River, May 6, 1896. Enlarged ten times … 108

22. Instantaneous photograph of the aerodrome at a
distance in the air during its flight at Quantico on the
Potomac River, May 6, 1896. Enlarged ten times … 108

23. Overhead launching apparatus … 108

24. Overhead launching apparatus … 108

25. Side view of steel frame of aerodrome No. 5 suspended
from launching-car, October 24, 1896 … 112

26A. Dimensioned drawing of boiler coils, burners, pump,
needle valve, and thrust bearing … 116

26B. Dimensioned drawing of engine No. 5 … 116

27A. Side and end elevations of aerodrome No. 5, May 11,
1896 … 116

27B. Aerodrome No. 5. Plan view. October 24, 1896 … 116

28. Steel frame of aerodrome No. 6 on launching car … 120

29A. Plan view of aerodrome No. 6. October 23, 1896 … 122

29B. Side elevation of aerodrome No. 6. October 23, 1896 …
122

30. Plan view of steel frames and power plants of
aerodromes Nos. 5 and 6 … 122

31. Details of aerodrome No. 5 … 122

32. Drawings of proposed man-carrying aerodrome, 1898 … 130

33. Path of flight of aerodrome No. 6, June 7, 1899 … 136

34. Paths of flight of aerodrome No. 6, June 13 and 23,
1899 … 140

35. Aerodrome No. 5 on launching-ways … 142

36. Paths of flights of aerodrome No. 5, July 29, 1899 …
148

37. Experimental forms of superposed surfaces, 1898, 1899.
(See also plates 64 and 65.) … 153

38. House-boat and launching apparatus, 1899 … 156

39. Method of attaching guy-wires to guy-posts to relieve
torsional strain … 158

40. General plan and details of launching-car … 160

41. Aerodrome on launching-car … 160

42. Details of clutch-post for launching-car … 160

43. Front end of track just preparatory to launching
aerodrome … 160

44. Resistance of wires at given velocities … 166

45. Frame of aerodrome A, January 31, 1900 … 168

46. Frame of aerodrome A, January 31, 1900 … 168

47. Frame of aerodrome A, February 1, 1900 … 168

48. Frame of aerodrome A, February 1, 1900 … 168

49. Guy-wire system, July 10, 1902 … 170

50. Guy-wire system, July 10, 1902 … 170

51. Guy-wire system, July 10, 1902 … 170

52. Scale drawing of aerodrome A. End elevation … 170

53. Scale drawing of aerodrome A. Side elevation … 170

54. Scale drawing of aerodrome A. Plan … 170

55. Frame fittings and guy-wire attachments, etc. … 174

56. Frame fittings and guy-wire attachments, etc. … 174

57. Frame fittings and guy-wire attachments, etc. … 174

58. Bed plate gears, etc. … 176

59. Wing clamps … 183

60. Hoisting aerodrome to launching-track … 184

61. Aerodrome on launching-car; front wings in place,
guy-wires adjusted … 184

62. Details of guy-posts … 184

63. Guy-post and pin on launching-car … 184

64. Experimental type of superposed wings, March 2, 1899 …
192

65. Experimental type of superposed wings, March 2, 1899 …
192

66. Details of ribs and fittings for wings … 200

67. Cross-section of ribs … 201

68. Automatic equilibrium devices … 212

69. Mechanism of control … 212

70. Plan view of quarter-size model aerodrome, June 1,
1900 … 232

71. Plan view of quarter-size model aerodrome … 232

72. End, side, and three-quarter elevations of
quarter-size model aerodrome … 232

73. Launching-car with floats … 232

74. Launching-car with floats … 232

75. Quarter-size model aerodrome equipped with superposed
surfaces, June 11, 1901. Side view … 232

76. Quarter-size model aerodrome equipped with superposed
surfaces, June 11, 1901. End view … 232

77. Cylinders of engine of quarter-size model aerodrome …
233

78. Engine of aerodrome A. Section through cylinder and
drum … 236

79. Engine of aerodrome A. End elevation, port side … 236

80. Engine of aerodrome A. Top plan … 236

81. Engine of aerodrome A. Elevation starboard bed plate,
sparking mechanism … 236

82. Dynamometer tests of large engine … 248

83. Dynamometer tests of large engine … 248

84. Dynamometer tests of large engine … 248

85. Location of house-boat in center of Potomac River,
July 14, 1903 … 256

86. Quarter-size model aerodrome mounted on launching-car
… 260

87. Quarter-size model aerodrome in flight, August 8, 1903
… 260

88. Quarter-size model aerodrome in flight, August 8, 1903
… 260

89. Quarter-size model aerodrome in flight, August 8, 1903
… 260

90. Quarter-size model aerodrome in flight, August 8, 1903
… 260

91. Quarter-size model aerodrome in flight, August 8, 1903
… 260

92. Quarter-size model aerodrome in flight, August 8, 1903
… 260

93. Quarter-size model aerodrome at end of flight, August
8, 1903 … 260

94. Hoisting wing of full-size aerodrome … 263

95. Flight of large aerodrome, October 7, 1903 … 266

96. Flight of large aerodrome, October 7, 1903 … 266

97. Aerodrome being recovered, October 7, 1903 … 270

98. Aerodrome in water, October 7, 1903 … 270

99. Aerodrome in water, October 7, 1903 … 270

100. Aerodrome in water, October 7, 1903 … 270

101. Attempted launching of aerodrome, December 8, 1903 …
274

REFERENCES

Aerodynamics. ‹See› Langley, S. P. Experiments in
Aerodynamics.

L’Aéronaute. ‹See› Pénaud, A.

Aeronautical Society. ‹See› Harting, P.

Aéroplane automoteur. ‹See› Pénaud, A.

Balancing of Engines, Steam, Gas, and Petrol. ‹See› Sharp,
A.

Century Magazine. ‹See› Maxim, H. S.

Comptes Rendus, of the Sessions of the Academy of
Sciences. ‹See› Langley, S. P. Description du vol
méchanique.

Encyclopædia Britannica. ‹See› Flight and Flying Machines.

Experiments in Aerodynamics. ‹See› Langley, S. P.

Flight and Flying Machines. Encyclopædia Britannica, 9th
ed., Vol. 9, 1879, Edinburgh, pp. 308–322, figs. 1–45.

Harting, P. Observations of the relative size of the wings
and the weight of the pectoral muscles in the vertebrated
flying animals. Annual Report of the Aeronautical Society
of Great Britain, No. 5, 1870, Greenwich, pp. 66–77.

Il nuovo aeroplano Blériot, Bollettino della Società
Aeronautica Italiana, Anno IV, N. 8, Agosto 1907, Roma,
pp. 279–282, figs. 4.

Langley, Bollettino della Società Aeronautica Italiana,
Anno II, Num. 11–12, Nov.–Dic. 1905, Roma, pp. 187–188,
figs. 10.

Langley, S. P. Description du vol méchanique. Comptes
Rendus de l’Académie des Sciences, T. 122, Mai 26, 1896,
Paris, pp. 1177–1178.

Langley, S. P. Experiments in Aerodynamics. Smithsonian
Contributions to Knowledge, Vol. 27, 1891, Washington, D.
C., pp. 115, pl. 10.

Langley, S. P. Le travail intérieur du vent. Revue de
l’Aéronautique, 6e année, 3e livraison, 1893, Paris, pp.
37–68.

Langley, S. P. The Flying Machine. McClures Magazine, Vol.
9, No. 2, June, 1897, N. Y., pp. 647–660.

Langley, S. P. The Internal Work of the Wind. Smithsonian
Contributions to Knowledge, Vol. 27, 1893, Washington, D.
C., pp. 23, pl. 6.

McClure’s Magazine. ‹See› Langley, S. P. The Flying
Machine.

Maxim, H. S. Aerial navigation. The power required.
Century Magazine, Vol. 42, No. 6, Oct., 1891, N. Y., pp.
829–836, figs. 1–6.

Pénaud, A. Aeroplane automoteur. L’Aéronaute, 5e année,
No. 1, Jan., 1872, Paris, pp. 2–9, figs. 1–4.

Revue de l’Aéronautique. ‹See› Langley, S. P. Le travail
intérieur du vent.

Sharp, A. Balancing of Engines, Steam, Gas, and Petrol.
New York, Longmans, Green & Co., 1907.

Wellner, Georg. Versuche ueber den Luftwiderstand
gewölbter Flächen im Winde und auf Eisenbahnen.

Zeitschrift für Luftschiffahrt, Bd. 12, Beilage, 1893,
Berlin, pp. 1–48.

Zeitschrift für Luftschiffahrt. ‹See› Wellner, Georg.

[p001]

LANGLEY MEMOIR ON MECHANICAL FLIGHT

PART I. 1887 TO 1896

BY S. P. LANGLEY

EDITED BY CHARLES M. MANLY

CHAPTER I
INTRODUCTORY

I[2] announced in 1891,[3] as the result of experiments carried on by
me through previous years, that it was possible to construct machines
which would give such a velocity to inclined surfaces that bodies
indefinitely heavier than the air could be sustained upon it, and
moved through it with great velocity. In particular, it was stated
that a plane surface in the form of a parallelogram of 76.2 cm.×12.2
cm. (30×4.8 inches), weighing 500 grammes (1.1 lbs.), could be driven
through the air with a velocity of 20 metres (65.6 feet) per second
in absolutely ‹horizontal› flight, with an expenditure of 1/200
horse-power, or, in other terms, that 1 horse-power would propel and
sustain in horizontal flight, at such a velocity (that is, about 40
miles an hour), a little over 200 pounds weight of such surface,
where the specific gravity of the plane was a matter of secondary
importance, the support being derived from the elasticity and inertia
of the air upon which the body is made to run rapidly.

It was further specifically remarked that it was not asserted that
planes of any kind were the best forms to be used in mechanical
flight, nor was it asserted, without restrictions, that mechanical
flight was absolutely possible, since this depended upon our ability
to get ‹horizontal› flight during transport, and to leave the earth
and to return to it in safety. Our ability actually to do this, it
was added, would result from the practice of some unexplored art or
science which might be termed Aerodromics, but on which I was not
then prepared to enter.

I had at that time, however, made certain preliminary experiments
with flying models, which have been continued up to the present
year,[4] and at the same time I have continued experiments distinct
from these, with the small whirling-table established at Washington.
The results obtained from the latter being supplemental to those
published in “Experiments in Aerodynamics,” and [p002] being more or
less imperfect, were at first intended not for publication, but for
my own information on matters where even an incomplete knowledge was
better than the absence of any.

It is to be remembered that the mechanical difficulties of artificial
flight have been so great that, so far as is known, never at any
time in the history of the world previous to my experiment of May,
1896, had any such mechanism, however actuated, sustained itself in
the air for more than a few seconds—never, for instance, a single
half-minute—and those models which had sustained themselves for
these few seconds, had been in almost every case actuated by rubber
springs, and had been of such a size that they should hardly be
described as more than toys. This refers to actual flights in free
air, unguided by any track or arm, for, since the most economical
flight must always be a horizontal one in a straight line,[5] the
fact that a machine has lifted itself while pressed upward against
an overhead track which compels the aerodrome to move horizontally
and at the proper angle for equilibrium, is no proof at all of real
“flight.”

I desire to ask the reader’s consideration of the fact that even ten
years ago,[6] the whole subject of mechanical flight was so far from
having attracted the general attention of physicists or engineers,
that it was generally considered to be a field fitted rather for
the pursuits of the charlatan than for those of the man of science.
Consequently, he who was bold enough to enter it, found almost
none of those experimental data which are ready to hand in every
recognized and reputable field of scientific labor. Let me reiterate
the statement, which even now seems strange, that such disrepute
attached so lately to the attempt to make a “flying-machine,” that
hardly any scientific men of position had made even preliminary
investigations, and that almost every experiment to be made was
made for the first time. To cover so vast a field as that which
aerodromics is now seen to open, no lifetime would have sufficed.
The preliminary experiments on the primary question of equilibrium
and the intimately associated problems of the resistance of the
sustaining surfaces, the power of the engines, the method of their
application, the framing of the hull structure which held these, the
construction of the propellers, the putting of the whole in initial
motion, were all to be made, and could not be conducted with the
exactness which would render them final models of accuracy.

I beg the reader, therefore, to recall as he reads, that everything
here has been done with a view to putting a trial aerodrome
successfully in flight within a few years, and thus giving an early
demonstration of the only kind which is conclusive in the eyes of the
scientific man, as well as of the general public—a demonstration
that mechanical flight is possible-—by actually flying.

All that has been done, has been with an eye principally to this
immediate [p003] result, and all the experiments given in this book
are to be considered only as approximations to exact truth. All were
made with a view, not to some remote future, but to an arrival within
the compass of a few years at some result in actual flight that could
not be gainsaid or mistaken.

Although many experimenters have addressed themselves to the problem
within the last few years--and these have included men of education
and skill--the general failure to arrive at any actual flight has
seemed to throw a doubt over the conclusions which I had announced as
theoretically possible.

When, therefore, I was able to state that on May 6, 1896, such a
degree of success had been attained that an aerodrome, built chiefly
of steel, and driven by a steam engine, had indeed flown for over
half a mile--that this machine had alighted with safety, and had
performed a second flight on the same day, it was felt that an
advance had been made, so great as to constitute the long desired
experimental demonstration of the possibility of mechanical flight.
These results were communicated to the French Academy in the note
given below.[7]

Independently of the preliminary experiments in aerodynamics already
published, I had been engaged for seven years in the development of
flying models. Although the work was discouraging and often resulted
in failure, success was finally reached under the conditions just
referred to, which obviously admitted of its being reached again, and
on a larger scale, if desired. [p004]

In view of the great importance of these experiments, as
demonstrating beyond question the practicability of the art of
mechanical flight, and also in view of the yet inchoate state of this
art, I have thought it worth while to publish an account of them
somewhat in detail, even though they involve an account of failures;
since it is from them, that those to whom it may fall to continue
such constructions, will learn what to avoid, as well as the ‹raison
d’etre› of the construction of the machines which have actually flown.

In an established art or science, this description of the essays
and failures which preceded full knowledge would have chiefly an
historical interest. Here almost nothing is yet established beyond
the fact that mechanical flight has actually been attained. The
history of failure is in this case, then, if I do not mistake, most
necessary to an understanding of the road to future success, to which
it led, and this has been my motive in presenting what I have next to
say so largely in narrative form.

[p005]

CHAPTER II
PRELIMINARY

Part I of the present work is intended to include an account of
the experiments with actual flying models, made chiefly at or
near Washington, from the earliest with rubber motors up to the
construction of the steam aerodromes that performed the flights of
May 6 and November 28, 1896.

An account of some observations conducted at Washington, with the
whirling table, on the reaction of various surfaces upon the air, is
relegated to a later part.

The experiments with working models, which led to the successful
flights, were commenced in 1887, and it has seemed to me preferable
to put them at first in chronological order, and to present to
the reader what may seem instructive in their history, while not
withholding from him the mistaken efforts which were necessarily made
before the better path was found. In this same connection, I may say
that I have no professional acquaintance with steam engineering,
as will, indeed, be apparent from the present record, but it may
be observed that none of the counsel which I obtained from those
possessing more knowledge was useful in meeting the special problems
which presented themselves to me, and which were solved, as far as
they have been solved, by constant “trial and error.”

I shall, then, as far as practicable, follow the order of dates in
presenting the work that has been done, but the reader will observe
that after the preliminary investigations and since the close of
1893, at least four or five independent investigations, attended with
constant experiment and radically distinct kinds of construction,
have been going on simultaneously. We have, for instance, the work in
the shop, which is of two essentially different kinds: first, that
on the frames and engines, which finally led to the construction
of an engine of unprecedented lightness; second, the experimental
construction of the supporting and guiding surfaces, which has
involved an entirely different set of considerations, concerned with
equilibrium and support in flight. These constructions, however
successful, are confined to the shop and are, as will be seen later,
useless without a launching apparatus. The construction of a suitable
launching apparatus itself involved difficulties which took years to
overcome. And, finally, the whole had to be tested by actual flights
in free air, which were conducted at a place some 30 miles distant
from the shop where the original construction went on. [p006]

Simultaneously with these, original experiments with the
whirling-table were being conducted along lines of research, which
though necessary have only been indicated. We have, then, at least
five subjects, so distinct that they can only be properly treated
separately, and accordingly they will be found in Chapters VII, VIII,
IX and X, and in Part Third [in preparation].

It is inevitable that in so complex a study some repetition should
present itself, especially in the narrative form chosen as the
best method of presenting the subject to the reader. Each of these
chapters, then, will contain its own historical account of its own
theme, so that each subject can be pursued continuously in the order
of its actual development, while, since they were all interdependent
and were actually going on simultaneously, the order of dates which
is followed in each chapter will be a simple and sufficient method of
reference from one to the other.

EXPERIMENTS WITH SMALL MODELS

In order to understand how the need arises for such experiments in
fixing conditions which it might appear were already determined in
the work “Experiments in Aerodynamics,”[8] it is to be constantly
borne in mind, as a consideration of the first importance, that the
latter experiments, being conducted with the whirling-table, force
the model to move in horizontal flight and at a constant angle. Now
these are ideal conditions, as they avoid such practical difficulties
as maintaining equilibrium and horizontality, and for this reason
alone give results more favorable than are to be expected in free
flight.

Besides this, the values given in “Aerodynamics” were obtained
with rigid surfaces, and these surfaces themselves were small and
therefore manageable, while larger surfaces, such as are used in
actual flight, would need to be stiffened by guys and like means,
which offer resistance to the air and still further reduce the
results obtained. It is, therefore, fairly certain, that nothing
like the lift of 200 pounds to the horse-power for a rate of 40
miles an hour,[9] obtained under these ideal conditions with the
whirling-table, will be obtained in actual flight, at least with
plane wings.

The data in “Aerodynamics” were, then, insufficient to determine the
conditions of free flight, not alone because the apparatus compels
the planes to move in horizontal flight, but because other ideally
perfect conditions are obtained by surfaces rigidly attached to the
whirling-table so as to present an angle to the wind of advance
which is invariable during the course of the experiment, whereas
the surfaces employed in actual flight may evidently change this
angle and cause [p007] the aerodrome to move upward or downward,
and thus depart from horizontal flight so widely as to bring prompt
destruction.

To secure this balance, or equilibrium, we know in theory, that
the center of gravity must be brought nearly under the center of
pressure, by which latter expression we mean the resultant of all
the forces which tend to sustain the aerodrome; but this center
of pressure, as may in fact be inferred from “Aerodynamics,”[10]
varies with the inclination of the surface. It varies also with the
nature of the surface itself, and for one and the same surface is
constantly shifted unless the whole be rigidly held, as it is on the
whirling-table, and as it cannot be in free flight.

Here, then, are conditions of the utmost importance, our knowledge of
which, as derived from ordinary aerodynamic experiments, is almost
nothing. A consideration of this led me to remark in the conclusion
of “Aerodynamics”:

“I have not asserted, without qualification, that mechanical flight
is practically possible, since this involves questions as to the
method of constructing the mechanism, of securing its safe ascent
and descent, and also of securing the indispensable condition
for the economic use of the power I have shown to be at our
disposal--the condition, I mean, of our ability to guide it in the
desired ‹horizontal› direction during transport--questions which, in
my opinion, are only to be answered by further experiment and which
belong to the inchoate art or science of ‹aerodromics› on which I do
not enter.”

It is this inchoate art of aerodromics which is begun in the
following experiments with actual flying machines.

In all discussions of flight, especially of soaring flight, the first
source to which one naturally looks for information is birds. But
here correct deductions from even the most accurate of observations
are very difficult, because the observation cannot include all of
the conditions under which the bird is doing its work. If we could
but see the wind the problem would be greatly simplified, but as
the matter stands, it may be said that much less assistance has
been derived from studious observations on bird-flight than might
have been anticipated, perhaps because it has been found thus far
impossible to reproduce in the flying machine or aerostatic model
the shape and condition of wing with its flexible and controllable
connection with the body, and especially the instinctive control of
the wing to meet the requirements of flight that are varying from
second to second, and which no automatic adjustment can adequately
meet.

At the time I commenced these experiments, almost the only
flying-machine which had really flown was a toy-like model, suggested
by A. Pénaud, a young Frenchman of singular mechanical genius, who
contributed to the world many most original and valuable papers on
Aeronautics, which may be found in the journal “L’Aeronaute.” His
aeroplane is a toy in size, with a small propeller [p008] whose
blades are usually made of two feathers, or of stiff paper, and whose
motive power is a twisted strand of rubber. This power maintains it
in the air for a few seconds and with an ordinary capacity for flight
of 50 feet or so, but it embodies a device for automatically securing
horizontal flight, which its inventor was the first to enunciate.[11]

Although Pénaud recognized that, theoretically, two screws are
necessary in an aerial propeller, as the use of a single one tends to
make the apparatus revolve on itself, he adopted the single screw on
account of the greater simplicity of construction that it permitted.
One of these little machines is shown as No. 11, Plates 1 and 2.

‹AB› is a stem about 2.5 mm. in diameter and 50 cm. long. It is bent
down at each end, with an offset which supports the rubber and the
shaft of the screw to which it is hooked. The screw ‹HH›^1 is 21
cm. in diameter, and has two blades made of stiff paper; two are
preferable, among other reasons, because they can be made so that
the machine will lie flat when it strikes in its descent. About the
middle of ‹AB› there is a “wing” surface ‹DC›, 45 cm. long and 11
cm. broad, the ends ‹C› and ‹D› being raised and a little curved.
In front of the screw is the horizontal rudder ‹GK› having a shape
like that of the first surface, with its ends also turned up, and
‹inclined at a small negative angle with this wing surface›. Along
its center is a small fin-like vertical rudder that steers the device
laterally, like the rudder of a ship.

The approximately, but not exactly, horizontal rudder serves to
hold the device in horizontal flight, and its operation can best be
understood from the side elevation. Let ‹CD› be the wing plane set
nearly in the line of the stem, which stem it is desired to maintain,
in flying, at a small positive angle, α, with the horizon, α being
so chosen that the tendency upward given by it will just counteract
the action of gravity. The weight of the aeroplane, combined with
the resistance due to the reaction of the air caused by its advance
would, under these conditions, just keep it moving onward in a
horizontal line, if there were no disturbance of the conditions.
There is, however, in the wing no power of self-restoration to the
horizontal if these conditions are disturbed. But such a power
resides in the rudder ‹GK›, which is not set parallel to the wing,
but at a negative angle (α^1) with it equal to the positive angle
of the wing with the horizon. It is obvious that, in horizontal
flight, the rudder, being set at this angle, presents its edge to
the wind of advance and consequently offers a minimum resistance as
long as the flight is horizontal. If, however, for any reason the
head drops down, the rear edge of the rudder is raised, and it is
at once subjected to the action of the air upon its upper surface,
which has a tendency to lower the rear of the machine and to restore
horizontality. Should the head rise, the lower [p009] surface of the
rudder is subjected to the impact of the air, the rear end is raised,
and horizontality again attained. In addition to this, Pénaud appears
to have contemplated giving the rudder-stem a certain elasticity,
and in this shape it is perhaps as effective a control as art could
devise with such simple means.

Of the flight of his little machine, thus directed, Pénaud says:

“If the screw be turned on itself 240 times and the whole left free
in a horizontal position, it will first drop; then, upon attaining
its speed, rise and perform a regular flight at 7 or 8 feet from the
ground for a distance of about 40 metres, requiring about 11 seconds
for its performance. Some have flown 60 metres and have remained
in the air 13 seconds.[12] The rudder controls the inclination to
ascend or descend, causing oscillations in the flight. Finally the
apparatus descends gently in an oblique line, remaining itself
horizontal.”

The motive power is a twisted hank of fine rubber strips, which
weighs 5 grammes out of a total of 16 grammes for the whole machine,
whose center of gravity should be in advance of the center of surface
‹CD›, as will be demonstrated in another place. This device attracted
little notice, and I was unfamiliar with it when I began my own first
constructions at Allegheny, in 1887.

My own earliest models employed a light wooden frame with two
propellers, which were each driven by a strand of twisted rubber.[13]
In later forms, the rubber was enclosed and the end strains taken
up by the thinnest tin-plate tubes, or better still, paper tubes
strengthened by shellac.

Little was known to me at that time as to the proper proportions
between wing surface, weight and power; and while I at first sought
to infer the relation between wing surface and weight from that of
soaring birds, where it varies from 1/2 to 1 sq. ft. of wing surface
to the pound, yet the ratio was successively increased in the earlier
models, until it became 4 sq. ft. to 1 pound. It may be well to add,
however, that the still later experiments with the steam-driven
models, in which the supporting surface was approximately 2 sq.
ft. to the pound, proved that the lack of ability of these early
rubber-driven models to properly sustain themselves even with 4 sq.
ft. of wing surface to the pound, was largely due to the fact that
the wings themselves had not been stiff enough to prevent their being
warped by the air pressure generated by their forward motion.

During the years I presently describe, these tentative constructions
were [p010] renewed at intervals without any satisfactory result,
though it became clear from repeated failures, that the motive power
at command would not suffice, even for a few seconds’ flight for
models of sufficient size to enable a real study to be made of the
conditions necessary for successful flight.

In these earliest experiments everything had to be learned about the
relative position of the center of gravity, and what I have called
the center of pressure. In regard to the latter term, it might at
first seem that since the upward pressure of the air is treated as
concentrated at one point of the supporting surface, as the weight
is at the center of gravity, this point should be always in the same
position for the same supporting surface. This relation, however,
is never constant. How paradoxical seems the statement that, if
‹ab› be such a supporting surface in the form of a plane of uniform
thickness and weight, suspended at ‹c› (‹ac› being somewhat greater
than ‹cb›) and subjected to the pressure of a wind in the direction
of the arrow, the pressure on the lesser arm ‹cb› will overpower that
on the greater arm ‹ac›! We now know, however, that this must be so,
and why, but as it was not known to the writer till determined by
experiments published later in “Experiments in Aerodynamics,” all
this was worked out by trial in the models.

[Illustration: FIG. 1. Diagram of suspended plane showing position of
C. P.]

It was also early seen that the surface of support could be
advantageously divided into two, with one behind the other, or one
over the other, and this was often, though not always, done in the
models.

At the very beginning another difficulty was met which has proved a
constant and ever-increasing one with larger models--the difficulty
of launching them in the air. It is frequently proposed by those
unfamiliar with this difficulty, to launch the aerodrome by placing
it upon a platform car or upon the deck of a steamer, and running
the car or boat at an increasing speed until the aerodrome, which is
free to rise, is lifted by the wind of advance. But this is quite
impracticable without means to prevent premature displacement, for
the large surface and slight weight renders any model of considerable
size unmanageable in the least wind, such as is always present in the
open air. It is, therefore, necessary in any launching apparatus that
the aerodrome be held rigidly until the very moment of release, and
that instant and simultaneous release from the apparatus be made at
all the sustaining points at the proper moment. [p011]

There is but a very partial analogy in this case to the launching
of a ship, which is held to her ways by her great weight. Here, the
“ship” is liable to rise from her ways or be turned over laterally at
any instant, unless it is securely fastened to them in a manner to
prevent its rising, but not to prevent its advancing.

The experiments with rubber-driven models commenced in April,
1887, at the Allegheny Observatory, were continued at intervals
(partly there, but chiefly in Washington) for three or four years,
during which time between thirty and forty independent models
were constructed, which were so greatly altered in the course of
experiment that more nearly one hundred models were in reality tried.
The result of all this extended labor was wholly inconclusive,
but as subsequent trials of other motors (such as compressed air,
carbonic-acid gas, electric batteries, and the like) proved futile,
and (before the steam engine) only the rubber gave results, however
unsatisfactory, in actual flight, from which anything could be
learned, I shall give some brief account of these experiments, which
preceded and proved the necessity of using the steam engine, or other
like energetic motor, even in experimental models.

An early attempt was made in April, 1887, with a model consisting
of a frame formed of two wooden pieces, each about 1 metre long and
4 centimetres wide, made for lightness, of star-shaped section,
braced with cross-pieces and carrying two long strips of rubber, each
about 1 mm. thick, 30 mm. wide, 2 metres long, doubled, weighing 300
grammes. Each of these strips could be wound to about 300 turns,
one end being made fast to the front of the frame, the other to the
shaft of a four-bladed propeller 30 cm. in diameter. The wings were
made of lightest pine frames, over which paper was stretched, and
were double, one being superposed upon the other. Each was 15 cm.
wide, and 120 cm. long. The distance between them was 12 cm. and the
total surface a little more than 3600 sq. cm. (4 square feet). In
flying, the rubber was so twisted that the propellers were run in
opposite directions. The weight of the whole apparatus was not quite
1 kilogramme, or about 1 pound to 2 feet of sustaining surface, which
proved to be entirely too great a weight for the power of support.
When placed upon the whirling-table, it showed a tendency to soar
at a speed of about ten miles an hour, but its own propellers were
utterly insufficient to sustain it.

In this attempt, which was useful only in showing how much was to
be learned of practical conditions, the primary difficulty lay in
making the model light enough and sufficiently strong to support its
power. This difficulty continued to be fundamental through every
later form; but besides this, the adjustment of the center of gravity
to the center of pressure of the wings, the disposition of the wings
themselves, the size of the propellers, the inclination and number
of their blades, and a great number of other details, presented
themselves for examination. [p012] Even in the first model, the
difficulty of launching the machine or giving it the necessary
preliminary impulse was disclosed—a difficulty which may perhaps not
appear serious to the reader, but which in fact required years of
experiment to remove.

By June, 1887 two other models, embodying various changes that had
suggested themselves, had been constructed. Each of these had a
single propeller (one an 18-1/2-inch propeller with eight adjustable
blades, the other a 24-inch propeller with four adjustable blades)
and was sustained by two pairs of curved wings 4 feet 7 inches long.
It is, however, unnecessary to dwell further on these details, since
these models also proved altogether too heavy in relation to their
power, and neither of them ever made an actual flight.

At this period my time became so fully occupied with the experiments
in aerodynamics (which are not here in question) that during the next
two years little additional was done in making direct investigations
in flight.

In June, 1889, however, new rubber-driven models were made in which
the wooden frames were replaced by tubes of light metal, which,
however, were still too heavy, and these subsequently by tubes of
paper covered with shellac, which proved to be the lightest and best
material in proportion to its strength that had been found. The
twisted rubber was carried within these tubes, which were made just
strong enough to withstand the end-strain it produced. The front end
of the rubber being made fast to an extremity of the tube, the other
end was attached directly to the shaft of the propeller, which in the
early models was still supplied with four blades.

A detailed description of one of these early models, No. 26, shown in
Plates 1 and 4, follows:

In each of the two tubes of paper, stiffened with shellac, which form
a part of the framing, is mounted a hank of twisted rubber, which
connects with a propeller at the rear. There are two pairs of wings,
superposed and inclined at an angle, the one above, the other below
the frame. A light stem connected with the frame bears a triangular
Pénaud tail and rudder.

Length of model 105 cm.
Spread of wings 83 "
Width of upper wings 14 "
Width of lower wings 19 "
Diameter of propeller 29 "
Area of upper wings 1134 sq. cm.
Area of lower wings 1548 "
Area of tail 144 "
Weight of wings 51 grammes
Weight of tail 7 "
Weight of frame 38 "
Weight of wheels 20 "
Weight of rubber (.09 pound) 40 "
Total weight 156 "
No. of turns of rubber 100
Time of running down 8 seconds
Horse-power from preceding data 0.001 HP

The aerodromes made at this time were too heavy, as well as too
large, to be easily launched by hand, and it was not until 1891 that
the first one was constructed light enough to actually fly. This
first flight was obtained from the north window of the dome of the
Allegheny Observatory, on March 28, 1891, and imperfect as it was,
served to show that the proper balancing of the aerodrome which would
bring the center of gravity under the center of pressure, so as to
give a horizontal flight, had yet to be obtained.

From this time on until 1893, experiments continued to be made with
rubber-driven models, of which, as has been stated, nearly 40 were
constructed, some with two propellers, some with one; some with one
propeller in front and one behind; some with plane, some with curved,
wings; some with single, some with superposed, wings; some with
two pairs of wings, one preceding and one following; some with the
Pénaud tail; and some with other forms. A few of these early forms
are indicated on the accompanying Plates 1 to 4, but it does not seem
necessary to go into the details of their construction.

No. 11 with which an early flight was made, closely resembles the
Pénaud model.

No. 13 has two propellers, one in front and one behind, with a
single wing.

No. 14 has two propellers, nearly side by side, but one slightly in
advance, with a single wing and a flat horizontal tail.

No. 15 has one leading propeller and two broad wings, placed one
behind the other.

No. 30 has the propeller shafts at an angle, and one pair of wings.

No. 31 has the propeller shafts at an angle, and two pairs of wings
superposed.

The wings in general were flat, but in some cases curved. The rubber
was usually wound to about 100 turns, and trouble continually arose
from its “kinking” and unequal unwinding, which often caused most
erratic flights.

It is sufficient to say of these that, rude as they were, much
was learned from them about the condition of the machines in free
air, which could never be learned from the whirling-table or other
constrained flight.

The advantages and also the dangers of curved wings as compared with
plane ones, were shown, and the general disposition which would
secure an even balance, was ascertained; but all this was done with
extreme difficulty, since the brief flights were full of anomalies,
arising from the imperfect conditions of observation. For instance,
the motor power was apparently exhausted more rapidly when the
propellers were allowed to turn with the model at rest, than when it
was in motion, though in theory, in the latter case more power would
seem to be expended and a greater speed of revolution obtained in
a given time. The longest flights obtainable did not exceed 6 or 8
seconds in time, nor 80 to 100 feet in distance, and were not only
so brief, but, owing to the spasmodic action of the rubber and other
causes, so irregular, that it was extremely difficult to obtain even
the imperfect results which were actually deduced from them. [p014]

ABBREVIATIONS AND SYMBOLS EMPLOYED

The following rules and symbols were adopted for determining the
relative position of points on the aerodrome, some of them during
1891, and some of them since. All are given here for convenience of
reference, though their chief application is to the larger steam
aerodromes described later. Those which immediately follow were meant
to give some of the notation of descriptive geometry in untechnical
language for the use of the workmen employed. Let ‹X›, ‹Y› and ‹Z›
be three lines at right angles to each other, and passing through
the same point in space, ‹O›, lying at any convenient distance above
the floor of the work-shop. The line ‹X› lies North and South; the
line ‹Y› lies East and West, and the line ‹Z› points to the zenith.
Now place the aerodrome on the floor so that its principal axis lies
horizontally in the plane ‹XZ›, with its head pointing North, and
in such a position that a line passing through the center of the
propellers shall coincide with the line ‹Y›.

[Illustration: FIG. 2. Diagram showing mensural coordinates.]

When measurements are made on or parallel to the line ‹X›, the point
of intersection ‹O› will be marked 1500 centimetres, and distances
toward the South will be less than, and distances toward the North
greater than 1500 centimetres.

When measurements are made on or parallel to the line ‹Z›, the point
‹O› will be considered to be marked 2500 centimetres, and distances
above will be greater than, and distances below will be less than
2500 centimetres. [p015]

Lastly, when measurements are made on or parallel to the line ‹Y›,
the point ‹O› will be marked 3500 centimetres, and distances toward
the East will be greater than, and distances toward the West will be
less than 3500 centimetres. Measurements in these latter directions
will be comparatively infrequent because the center of gravity and
center of pressure both lie in the plane ‹XZ›.

EXAMPLE

In the figure the point ‹T› in the tail, if 15 centimetres to the
South of ‹O›, would be graduated 1485 centimetres. A weight (‹W›)
25 centimetres below the axis, would be graduated 2475 centimetres.
A point 50 centimetres above the axis would be graduated 2550
centimetres, etc.

‹CG› represents the Center of Gravity of the aerodrome, or (with
subscript letters) of any specially designated part, or with
reference to some indicated condition.

‹CG›_1 ‹CG›_2 represent the Center of Gravity as referred to
the first, or horizontal, and to the second, or vertical plane,
respectively.

‹CP› represents the Center of Pressure[14] of the whole aerodrome, or
(with a subscript) of any specially designated part.

‹CF› represents the Center of Figure of the aerodrome, or of any
specially designated part.

Subscripts:

“‹fw›” refers to the front wings. “1” refers to the plane ‹XY›.
“‹rw›” refers to the rear wings. “2” refers to the plane ‹XZ›.
“‹r›” refers to a state of rest. “3” refers to the plane ‹YZ›.
“‹m›” refers to a state of motion.

“‹A›” represents the total area of the supporting surface; “‹a›”
represents the total area of the tail; ‹HP› represents the
horse-power by Prony brake measurement. “Horse-power by formula” is
given by Maxim’s formula:[15]

rev.×diam. of propeller×pitch×thrust
‹HP› = ------------------------------------.
33,000

(This formula was not in use at the time of the rubber-motor
experiments, for which the thrust was not taken. It appears to assume
the conditions where the screws from a fixed position move a mass
of still air, are the same as those of free flight. Its results,
however, are in better agreement with experiment than might be
anticipated.)

“Flying-weight” means everything borne in actual flight, including
fuel and water. [p016]

Remembering that the principal object of all these experiments is to
be able to predict that setting of the wings and tail with reference
to the center of gravity which will secure horizontal flight, we must
understand that in the following tables (see No. 30) the figures
‹CP›_m = 1516.5 cm. mean a prediction that the center of pressure
of the sustaining surfaces in motion (‹CP›_m) is to be found in a
certain position 1516.5; that is, 16.5 cm. in advance of the line
joining the propeller shafts. This prediction has been made by means
of previous calculation joined with previous experimental adjustment.
We know in a rough way where the ‹CP› will fall on the wings when
they are exposed independently if flat, and at a certain angle, and
where it will fall on the tail. From these, we can find where the
resulting ‹CP› of the whole sustaining surface will be.

It would seem that when we have obtained the center of gravity by a
simple experiment, we have only to slide the wings or tail forward
and back until the (calculated) center of pressure falls over this
observed center of gravity. But in the very act of so adjusting the
wings and tail, the center of gravity is itself altered, and the
operation has to be several times repeated in order to get the two
values (the center of pressure and center of gravity) as near each
other as they are found in the above-mentioned table, our object
being to predict the position which will make the actual flight
itself horizontal. How far this result has been obtained, experiment
in actual flight alone can show, and from a comparison of the
prediction with the results of observation, we endeavor to improve
the formula.

The difficulties of these long-continued early experiments were
enhanced by the ever-present difficulty which continued through later
ones, that it was almost impossible to build the model light enough
to enable it to fly, and at the same time strong enough to withstand
the strains which flight imposed upon it. The models were broken
up by their falls after a few flights, and had to be continually
renewed, while owing to the slightness of their construction, the
conditions of observation could not be exactly repeated; and these
flights themselves, as has already been stated, were so brief in
time (usually less than six seconds), so limited in extent (usually
less than twenty metres), and so wholly capricious and erratic,
owing to the nature of the rubber motor and other causes, that very
many experiments were insufficient to eliminate these causes of
mal-observation.

It is not necessary to take the reader through many of them, but not
to pass over altogether a labor which was so great in proportion
to the results, but whose results, such as they were, were the
foundation of all after knowledge, I will, as illustrations, take
from an almost unlimited mass of such material the observations of
November 20, 1891, which were conducted with Model No. 30 with a
single pair of wings, shown in Plate 1, and with another one, No.
31, also shown [p018] in Plate 1, with superposed wings, which was
used for the purpose of comparison. S. P. Langley was the observer,
the place of observation the larger upper hall of the Smithsonian
building, at Washington, the time being taken by a stop-watch, and
the distance by a scale laid down upon the floor. The models were in
every case held by an assistant and launched by hand, being thrown
off with a slight initial velocity. In the case of No. 30, the
preliminary calculation of the position of the center of pressure had
been made by the process already described; the center of gravity,
with reference to the horizontal plane, was determined by simply
suspending the whole by a cord.

[Illustration: PL. 1

RUBBER-MOTOR MODEL AERODROMES NOS. 11, 13, 14, 15, 26, 30, 31]

[Illustration: PL. 2

RUBBER-MOTOR MODEL AERODROMES NOS. 11, 13, 14]

[Illustration: PL. 3

RUBBER-MOTOR MODEL AERODROMES NOS. 15, 24]

[Illustration: PL. 4

RUBBER-MOTOR MODEL AERODROME NO. 26]

OBSERVATION OF NOVEMBER 20, 1891.
OBSERVER, S. P. L.
LOCALITY, UPPER HALL, SMITHSONIAN BUILDING.

------------------------+----------------------+----------------------
| No. 30. | No. 31.
| Single wings. | Superposed wings.
------------------------+----------------------+----------------------
‹CP›_m 1516.5 cm.
‹CG›_1 1515 cm. 1517 cm.
‹CF›_w 1528 cm.
Length (without fender) 120 cm. = 3.94 ft. 120 cm. = 3.94 ft.
Width over wing tips 120 cm. = 3.94 ft. 120 cm. = 3.94 ft.
Weight of rubber (72
grammes in each tube) 144 gr. = 0.32 lbs. 144 gr. = 0.32 lbs.
Total flying weight
(including tail) 432 gr. = 0.95 lbs. 506 gr. = 1.11 lbs.
Turns of rubber 30 30
Diameter of propellers 37 cm. = 1.21 ft. 37 cm. = 1.21 ft.
Width of propellers 7 cm. = 0.23 ft. 7 cm. = 0.23 ft.
Pitch of propellers 50 cm. = 1.64 ft. 50 cm. = 1.64 ft.

Each pair 1984 sq. cm.
Area of wings (each 1984 sq. cm. = 2.13 sq. ft.
992 sq. cm.) = 2.13 sq. ft. Total 3968 sq. cm.
= 4.26 sq. ft.

Area of tail 373 sq. cm. 373 sq. cm.
= 0.40 sq. ft. = 0.40 sq. ft.
------------------------+----------------------+----------------------
Area of wings and tail in No. 30, 2357 sq. cm. = 2.53 sq. ft.
2.53 sq. ft. ÷ .95 = 2.7. Therefore, there are 2.7 or nearly
3 square feet of sustaining area to the pound.

-------+----------+---------------------------------------------------
Flight.|Aerodrome.| Results.
-------+----------+---------------------------------------------------
1 No. 30 With 30 turns of the rubber, flew low through
10 metres.

2 No. 30 Flew heavily through 12 metres.

3 No. 31 Flew high and turned to left; distance not noted.

4 No. 31 The right wing having been weighted (to depress it
and correct the tendency to turn to the left),
model flew high, but the rubber ran down when it
had obtained a flight of 10 metres.

5 No. 31 The wings were moved backward until the ‹CP›
stood at 1493. The model still turned to the left;
flight lasted three and a-half seconds; distance
not noted.

6 No. 31 Vertical tail was adjusted so as to further increase
the tendency to go to the right. In spite of all
this, the model turned sharply to the left, flying
with a nearly horizontal motion; time of flight
not noted; distance not noted.

7 No. 30 Straight horizontal flight; time three and
three-fifth seconds, when rubber ran down;
distance 13 metres.

8 No. 30 Straight flight as before; time two and four-fifth
seconds; distance 13 metres.

9 No. 30 With a curved wing in the same position as the flat
wing had previously occupied, model flew up and
struck the ceiling (nearly 30 feet high), turning
to right, with a flight whose curtate length was
10 metres.

10 No. 30 Wing having been carried back 5 centimetres, model
still flew up, but not so high, and still turned
to the right.

11 No. 30 Wings carried back 5 centimetres more; model still
flew high; time two and two-fifths seconds;
distance 13 metres.

12 No. 30 Wings carried back 4 centimetres more; model still
flew high during a flight of 13 metres.
-------+----------+---------------------------------------------------
The observations now ceased, owing to the breaking up of the model.

The objects of these experiments, as of every other, were to find the
practical conditions of equilibrium and of horizontal flight, and to
compare the calculated with the observed positions of the center of
pressure. They enable us to make a comparison of the performances
given by earlier ones with a light rubber motor, with the relatively
heavy motors used to-day, as well as a comparison of single flat,
single curved, and superposed flat wings.

The average time of the running down of the rubber in flight was
something like three seconds, while the average time of its running
down when standing still was but one and a half seconds. It might
have been expected from theory that it would take longer to run
down when stationary, than in flight, and this was one of the
many anomalies observed, whose explanation was found later in the
inevitable defects of such apparatus.

The immediate inferences from the day’s work were:

1. That the calculated position of the ‹CP› at rest, as related to
the ‹CG›, is trustworthy only in the case of the plane wing.

2. The formula altogether failed with the curved wing, for which the
‹CP› had to be carried indefinitely further backward.

On comparing the previous flights of November 14, with these, it
seems that with the old rubber motor of 35 grammes and 50 turns,
the single wing, either plane or curved, is altogether inferior to
the double wing; while with the increased motor power of this day,
the single wing, whether plane or curved, seems to be as good as
the double wing. It also seems that the curved wing was rather more
efficient than the plane one.

The weight of the rubber in each tube was 72 grammes, or 0.16 pounds;
mean speed of flight in horizontal distance 4-1/2 metres (about 15
feet) per second.[16]

From experiments already referred to, there were found available
300 foot-pounds of energy in a pound of rubber as employed, and in
0.16 of a pound, 48 foot-pounds of energy were used; 48/33,000 or
0.00145 = the horse-power exerted in [p019] one minute, but as the
power was in fact expended in 1/20 of that time we have 20×0.00145 =
0.029; that is, during the brief flight, about 0.03 of a horse-power
was exerted, and this sustained a total weight of only about a pound.

In comparing this flight with the ideal conditions of horizontal
flight in “Aerodynamics,” it will be remembered that this model’s
flight was so irregular and so far from horizontal, that in one
case it flew up and struck the lofty ceiling. The angle with the
horizon is, of course, so variable as to be practically unknown, and
therefore no direct comparison can be instituted with the data given
on page 107 of “Experiments in Aerodynamics,” but we find from these
that at the lowest speed there given of about 35 feet per second,
0.03 of a horse-power exerted for three seconds would carry nearly
one pound through a distance of somewhat over 100 feet in horizontal
flight.

The number of turns of the propellers multiplied by the pitch
corresponds to a flight of about 16 metres, while the mean actual
flight was about 12. It is probable, however, that there was really
more slip than this part of the observation would indicate. It
was also observed that there seemed to be very little additional
compensatory gain in the steering of No. 30 for the weight of the
long rudder-tail it carried. It may be remarked that in subsequent
observations the superiority of the curved wing in lifting power
was confirmed, though it was found more liable to accident than
the flatter one, tending to turn the model over unless it was very
carefully adjusted.

It may also be observed that these and subsequent observations show,
as might have been anticipated, that as the motor power increased,
the necessary wing surface diminished, but that it was in general an
easier and more efficient employment of power to carry a surface of
four feet sustaining area to the pound than one of three, while one
of two feet to the pound was nearly the limit that could be used with
the rubber motor.[17]

It may be remarked that the flights this day, reckoned in horizontal
distance, were exceptionally short, but that the best flights at
other times obtained with these models (30 and 31) did not exceed
25 metres. Such observations were continued in hundreds of trials,
without any much more conclusive results. [p020]

The final results, then, of the observations with rubber-driven
models (which were commenced as early as 1887, continued actively
through the greater portion of the year 1891 and resumed, as will
be seen later, even as late as 1895), were not such as to give
information proportioned to their trouble and cost, and it was
decided to commence experiments with a steam-driven aerodrome on a
large scale.

[p021]

CHAPTER III
AVAILABLE MOTORS

In the introductory chapter to “Experiments in Aerodynamics,” it was
asserted that

“These researches have led to the result that mechanical
sustentation of heavy bodies in the air, combined with very great
speeds, is not only possible, but within the reach of mechanical
means we actually possess.”

It was, however, necessary to make a proper selection in order to
secure that source of power which is best adapted to the requirements
of mechanical flight. Pénaud had used india rubber as the cheapest
and at the same time the most available motor for the toys with
which he was experimenting, but when models were constructed that
were heavier than anything made prior to 1887, it appeared, after
the exhaustive trials with rubber referred to in the preceding
chapter, that something which could give longer and steadier flights
must be used as a motor, even for the preliminary trials, and the
construction of the large steam-driven model known as No. 0, and
elsewhere described, was begun. Even before the completion of this,
the probability of its failure grew so strong that experiments were
commenced with other motors, which it was hoped might be consistent
with a lighter construction.

These experiments which commenced in the spring of 1892 and continued
for nearly a twelvemonth, were made upon the use of compressed air,
carbonic-acid gas, electricity in primary and storage batteries, and
numerous other contrivances, with the result that the steam engine
was finally returned to, as being the only one that gave any promise
of immediate success in supporting a machine which would teach the
conditions of flight by actual trial, though it may be added that the
gas engine which was not tried at this time on account of engineering
difficulties, was regarded from the first as being the best in
theory and likely to be ultimately resorted to. All others were
fundamentally too heavy, and weight was always the greatest enemy.

It is the purpose of this chapter to pass in brief review the work
that was done and the amount of energy that was obtained with
these several types of motors, as well as the obstacles which they
presented to practical application upon working aerodromes.

INDIA RUBBER

India rubber is the source of power to which the designer of a
working model naturally turns, where it is desirable that it shall
be, above all, light and free from the necessity of using complicated
mechanism. Rubber motors were, [p022] therefore, used on all of
the earlier models, and served as the basis of calculations made
to determine the amount of power that would be required to propel
aerodromes with other sources of energy.

Some of the disadvantages inherent in the use of rubber are at
once apparent, such as the limited time during which its action is
available, the small total amount of power, and the variability in
the amount of power put forth in a unit of time between the moment of
release and the exhaustion of the power. In addition, serious, though
less obvious difficulties, present themselves in practice.

There are two ways in which rubber can be used; one by twisting a
hank of strands, and, while one end is held fast, allowing the other
to revolve; the other, by a direct longitudinal stretching of the
rubber, one end being held fast and the other attached to the moving
parts of the mechanism. The former method was adopted by Pénaud,
and was also used in all of my early constructions, but while it is
most convenient and simple in its (theoretical) application, it has,
in addition to the above drawbacks, that of knotting or kinking,
when wound too many turns, in such a way as to cause friction on
any containing tube not made impracticably large, and also that of
unwinding so irregularly as to make the result of one experiment
useless for comparison with another.

In 1895, some experiments were made in which the latter method was
used, but this was found to involve an almost impracticable weight,
because of the frame (which must be strong enough to withstand the
end pull of the rubber) and the mechanism needed to convert the pull
into a movement of rotation.

As the power put forth in a unit of time varies, so there is a
corresponding variation according to the original tension to which
the rubber is subjected. Thus in some experiments made in 1889 with
a six-bladed propeller 18.8 inches in diameter, driven by a rubber
spring 1.3 inches wide, 0.12 inch thick and 3 feet long, doubled, and
weighing 0.38 pound, the following results were obtained:

Number of twists of rubber 50 75 100
Time required to run down 7 sec. 10 sec. 12 sec.
Foot-pounds developed 37.5 63.0 124.6
Foot-pounds developed per min. 321.4 378.0 623.0
Horse-power developed 0.0097 0.0115 0.0189

Thus we see that, with twice the number of turns, more than three
times the amount of work was done and almost twice the amount of
power developed, giving as a maximum for this particular instance 328
foot-pounds per pound of rubber.

The usual method of employing the twisted rubber was to use a number
of fine strands formed into a hank looped at each end. One of these
hanks, consisting of 162 single or 81 double strands of rubber, and
weighing 73 grammes, when given 51 turns developed 55 foot-pounds
of work, which was put out in 4 seconds. This corresponds to 0.01
horse-power per minute for one pound of rubber. [p023]

The results of a large number of tests show that one pound of twisted
rubber can put forth from 450 to 500 or more foot-pounds of work,
but at the cost of an overstrain, and that a safe working factor can
hardly be taken at higher than 300 foot-pounds, if we are to avoid
the “fatigue” of the rubber, which otherwise becomes as marked as
that of a human muscle.

While twisting is an exceedingly convenient form of application
of the resilience of rubber to the turning of propelling wheels,
the direct stretch is, as has been remarked, much more efficient
in foot-pounds of energy developed by the same weight of rubber.
It was found that rubber could not, without undue “fatigue,” be
stretched to more than four and a half times its original length,
though experiments were made to determine the amount of work that a
rubber band, weighing one pound, was capable of doing, the stretching
being carried to seven times its original length. The results varied
with the rubber used and the conditions of temperature under which
the experiments were tried, ranging from 1543 foot-pounds to 2600
foot-pounds. The tests led to the conclusion that, for average
working, one pound of rubber so stretched, is capable of doing 2000
foot-pounds of work, but, owing to the weight of the supporting
frame and of the mechanism, this result can be obtained only
under conditions impracticable for a flying machine. In the more
practicable twisted form it furnishes, as has been said, less than a
fifth of that amount.

The conclusions reached from these experiments are:

1. The length of the unstretched rubber remaining the same, the
sustaining power will be directly proportional to the weight of
rubber;

2. With a given weight of rubber, the end strain is inversely
proportional to the length of the unstretched rubber;

3. With a given weight of rubber, the work done is constant, whatever
the form; hence if we let ‹w› = the work in foot-pounds, ‹g› = the
weight of the rubber in pounds, and ‹k› = a constant taken at 2000 as
given above, we have

‹w› = ‹kg› = 2000 ‹g› foot-pounds.

This is for an extension of seven units of length, so that for a unit
of extension we would have approximately

‹w› = 300 ‹g› foot-pounds

which for four units of extension corresponds very closely to the
1300 foot-pounds which Pénaud claims to have obtained.

4. The end strain varies with the cross-section for a given unit of
extension.

These results can lead to but one conclusion; that for the
development of the same amount of power when that amount shall be
1 horse-power or more, rubber weighs enormously more than a steam
engine, besides being less reliable [p024] for a sustained effort,
and, therefore, cannot be used for propelling aerodromes intended for
a flight that is to be prolonged beyond a few seconds.[18]

It may be desirable to present a tabular view of the ‹theoretical›
energy of available motors, which it will be noticed is a wholly
different thing from the results obtained in practice. Thus, we
represent the weight of rubber only, without regard to the weight
of the frame required to hold it. In the steam engine, we consider
the theoretical efficiency per pound of fuel, without regarding the
enormous waste of weight in water in such small engines as these,
or the weight of the engine itself. We treat the hot-water engine
in like manner, and in regard to carbonic acid and compressed air,
we take no note of the weight of the containing vessel, or of the
cylinders and moving parts. In the same way we have the theoretical
potency of electricity in primary and storage batteries, without
counting the weight of the necessary electromotors; and of the
inertia-engine without discussing that of the mechanism needed to
transmit its power.

Foot-pounds of energy in one pound of

Gasoline 15,625,280

Alcohol 9,721,806

Gunpowder 960,000

Hot water, under pressure of 100 atmospheres 383,712

Air, under pressure of 100 atmospheres, isothermal
expansion 120,584

Liquid carbonic acid, at temperature of 30° and pressure
of 100 atmospheres 78,800

Electric battery; short-lived, thin walled; chromic acid
and platinum 75,000

Steel ring, 8 inches in diameter, at speed of 3000 turns
per minute 19,000

Storage battery 17,560

Rubber, pulled 2,000

Rubber, twisted 300

It may be interesting to consider next, in even a roughly approximate
way, what may be expected from these various sources of energy in
practice.

STEAM ENGINE

The steam engine on a small scale, and under the actual restrictions
of the model, must necessarily be extremely wasteful of power. If we
suppose it to realize 2 per cent of the theoretical energy contained
in the fuel, we shall be assuming more than was actually obtained.
The energy of the fuel cannot be obtained at all, of course, without
boiler and engine, whose weight, for the purpose of the following
calculation, must be added to that of the fuel; and if we suppose
the weight of the boilers, engines and water, for a single minute’s
flight, to be collectively ten pounds, we shall take an optimistic
view of what may be expected under ordinary conditions. We have
in this view 1/500 of the [p025] theoretical capacity possibly
realizable under such conditions, but if we take 1/1000 we shall
probably be nearer the mark. Even in this case we have, when using
gasoline as fuel, 15,625 foot-pounds per minute, or nearly 0.50
horse-power, as against .0091 horse-power in the case of the rubber,
so that even with this waste and with the weight of the engines
necessary for a single minute’s service, the unit weight of fuel
employed in the steam engine gives 55 times the result we get with
rubber.

[Illustration: PL. 5

RUBBER-PULL MODEL AERODROME]

[Illustration: PL. 6

RUBBER-PULL MODEL AERODROME]

[Illustration: PL. 7

RUBBER-PULL MODEL AERODROME]

[Illustration: PL. 8

RUBBER-PULL MODEL AERODROME]

[Illustration: PL. 9

RUBBER-PULL MODEL AERODROME]

With alcohol we have about 2/3 the result that is furnished by
gasoline, since nearly the same boiler and engine will be used
in either case. Certain difficulties which at first appeared to
be attendant on the use of gasoline on a small scale induced me
to make the initial experiments with alcohol. This was continued
because of its convenience during a considerable time, but it was
finally displaced in favor of gasoline, not so much on account of
the superior theoretical efficiency of the latter, as for certain
practical advantages, such as its maintaining its flame while exposed
to wind, and like considerations.

GUNPOWDER

Although there are other explosives possessing a much greater energy
in proportion to their weight than gunpowder, this is the only one
which could be considered in relation to the present work, and the
conclusion was finally reached that it involved so great a weight
in the containing apparatus and so much experiment, that, although
the simplicity of its action is in its favor where crude means are
necessary, experiments with it had better be deferred until other
things had been tried.

HOT-WATER ENGINE

A great deal of attention was given to the hot-water engine, but it
was never put to practical use in the construction of an aerodrome,
partly on account of the necessary weight of a sufficiently strong
containing vessel.

COMPRESSED AIR

Compressed air, like the other possible sources of power, was
investigated, but calculations from well-authenticated data showed
that this system of propelling engines would probably be inadequate
to sustain even the models in long flights. As the chief difficulty
lies in the weight, not of the air, but of the containing vessel,
numerous experiments were made in the construction of one at once
strong and light. The best result obtained was with a steel tube
40 mm. in diameter, 428 mm. in length, closed at the ends by heads
united by wires, which safely contained 538 cubic cm. of air at an
initial pressure of 100 atmospheres for a weight of 521 grammes.
[p026]

If we suppose this to be used, by means of a proper reducing valve,
at a mean pressure of 100 pounds, for such an engine as that of
Aerodrome No. 5, which takes 60 cubic cm. of air at each stroke, we
find that (if we take no account of the loss by expansion) we have
18,329 foot-pounds of energy available, which on the engine described
will give 302 revolutions of the propellers.

There are such limits of weight, and the engines must be driven at
such high speeds, that the increased economy that might be obtained
by re-heating the air would be out of the question. The principal
object in using it would have been the avoidance of fire upon the
aerodrome, and the expansion of the unheated air would probably
have caused trouble with freezing, while the use of hot (i. e.
superheated) water was impracticable. So when, after a careful
computation, it was found that, having regard to the weight of the
containing vessel, only enough compressed air could be stored at 72
atmospheres and used at 4, to run a pair of engines with cylinders
0.9 inch in diameter by 1.6 inches stroke, at a speed of 1200
revolutions per minute for 20 seconds, all further consideration of
its adaptation to the immediate purpose was definitely abandoned.
This course, however, was not taken until after a model aerodrome
for using compressed air had been designed and partially built.
Then, after due consideration, it was decided to make the test with
carbonic-acid gas instead.

GAS

The gas engine possesses great theoretical advantages. At the time
of these experiments, the gas engine most available for the special
purposes of the models was one driven by air drawn through gasoline.
As the builders could not agree to reduce the weight of a one
horse-power engine more than one-half of the then usual model, and
as the weight of the standard engine was 470 pounds, it was obvious
that to reduce this weight to the limit of less than 3 pounds was
impracticable under the existing conditions, and all consideration
of the use of gas was abandoned provisionally, although a gasoline
engine of elementary simplicity was designed but never built. I
purposed, however, to return to this attractive form of power if I
were ever able to realize its theoretical advantages on the larger
scale which would be desirable.

ELECTRICITY

As it was not intended to build the model aerodromes for a long
flight, it was thought that the electric motor driven by a primary
or storage battery might possibly be utilized. It therefore occurred
to me that a battery might be constructed to give great power in
proportion to its weight on condition of being short-lived, and that
in this form a battery might perhaps advantageously take the place
of the dangerous compressed-air tubes that were at the time (1893)
[p027] under consideration for driving the models. I assumed that
the longest flight of the model would be less than five minutes. Any
weight of battery, then, that the model carried in consumable parts
lasting beyond this five minutes would be lost, and hence it was
proposed to build a battery, the whole active life of which would be
comprised in this time, to actuate a motor or motors driving one or
two propellers.

According to Daniell, when energy is stored in secondary batteries,
over 300,000 megergs per kilogramme of weight can be recovered and
utilized if freshly charged.

300,000 megergs = 0.696 horse-power for 1 min.
300,000 megergs = 0.139 horse-power for 5 min.

In a zinc and copper primary battery with sulphuric acid and water,
one kilogramme of zinc, oxidized, furnishes at least 1200 calories as
against 8000 for one kilogramme of carbon, but it is stated that the
zinc energy comes in so much more utilizable a form that the zinc,
weight for weight, gives practically, that is in work, 40 per cent
that of carbon. The kilogramme of carbon gives about 8000 heat units,
each equal to 107 kilogrammetres, or about 6,176,000 foot-pounds.
Of this, in light engines, from 5 to 10 per cent, or at least
308,800 foot-pounds, is utilized, and 2/5 of this, or about 124,000
foot-pounds, would seem to be what the kilogramme of zinc would give
in actual work. But to form the battery, we must have a larger weight
of fluid than of zinc, and something must be allowed for copper. If
we suppose these to bring the weight up to 1 kilogramme, we might
still hope to have 50,000 foot-pounds or 1.5 horse-power for one
minute, or 0.3 horse-power for 5 minutes.

Storage batteries were offered with a capacity of .25 horse-power for
5 minutes per kilogramme, but according to Daniell one cannot expect
to get more than 0.139 horse-power from a freshly charged battery of
that weight for the same time.

The plan of constructing a battery of a long roll of extremely thin
zinc or magnesium, winding it up with a narrower roll of copper or
platinized silver, insulating the two metals and then pouring over
enough acid to consume the major portion of the zinc in 5 minutes,
was carefully considered, but the difficulties were so discouraging,
that the work was not undertaken.

The lightest motors of 1 horse-power capacity of which any trace
could be found weighed 25 pounds, and a prominent electrician stated
that he would not attempt to construct one of that weight.

In trials with a 1/2 horse-power motor driving an 80 cm. propeller
of 1.00 pitch-ratio, I apparently obtained a development of 0.56
indicated horse-power at 1265 revolutions; but at lower speeds when
tried with the Prony brake, the brake horse-power fell to 0.10 at 546
revolutions, and even at 1650 revolutions [p028] it was but 0.262
indicated, with a brake horse-power of 0.144, or 55 per cent of that
indicated.

With these results both of theoretical calculation and practical
experiment, all thought of propelling the proposed aerodrome by
electricity was necessarily abandoned.

CARBONIC-ACID GAS

At the first inception of the idea, it seemed that carbonic-acid gas
would be the motive power best adapted for short flights. It can
be obtained in the liquid form, is compact, gives off the gas at a
uniform pressure dependent upon the temperature, and can be used in
the ordinary steam engine without any essential modifications. The
only provision that it seemed, in advance, necessary to make, was
that of some sort of a heater between the reservoir of liquid and the
engine, in order to prevent freezing, unless the liquid itself could
be heated previous to launching.

The engines in which it was first intended to use carbonic acid were
the little oscillating cylinder engines belonging to Aerodrome No.
1. The capacity of each cylinder was 21.2 cu. cm., so that 84.8 cu.
cm. of gas would be required to turn the propellers one revolution
when admitted for the full stroke, and 101,760 cubic cm. for 1200
revolutions. The density of the liquid at a temperature of 24° C. was
taken as .72, and as 1 volume of liquid gives 180 volumes of gas at a
pressure of 2-1/2 atmospheres, we have 101,760/180 = 565 cu. cm. of
liquid, or 407 grammes required for 1200 revolutions of the engines.

Thus, a theoretical calculation seemed to indicate that a kilogramme
of liquid carbonic acid would be an ample supply for a run of two
minutes. The experiments were, at first, somewhat encouraging. The
speed and apparent power of the engines were sufficient for the
purpose, but the length of time during which power could be obtained
was limited.

In 1892, 415 grammes of carbonic acid drove the engines of Aerodrome
No. 3 700 revolutions in 60 seconds, 900 in 75, and 1000 in 85
seconds, at the end of which time the gas was entirely expended. The
diameter of these cylinders was 2.4 cm., the stroke of the pistons 7
cm., and the work done, that of driving a pair of 50 cm. propellers,
when taken in comparison with the propeller tests detailed elsewhere,
amounted to an effective horse-power of about 0.10 for the output of
the engine.

The difficulties, however, that were experienced were those partially
foreseen. The expansion of the gas made such serious inroads upon the
latent heat of the liquid, that lumps of solid acid were formed in
the reservoir, and could be heard rattling against the sides when the
latter was shaken, while the expansion of the exhaust caused such a
lowering of temperature at that point, that the [p029] pipes were
soon covered with a thick layer of ice, and the free exit of the
escaping gas was prevented.

Such difficulties are to be expected with this material, but here
they were enhanced by the small scale of the construction and the
constant demand for lightness. And it was found to be very hard
to fill the small reservoirs intended to carry the supply for the
engines. When they were screwed to the large case in which the liquid
was received and the whole inverted, the small reservoir would be
filled from one-third to one-half full, and nothing that could be
done would force any more liquid to enter.

In view of these difficulties, and the objections to using a heater
of any sort for the gas, as well as the absolute lack of success
attendant upon the experiments of others who were attempting to use
liquid CO_2 as a motive power on a large scale elsewhere, experiments
were at first temporarily and afterwards permanently abandoned.

The above experiments extended over nearly a year in time, chiefly
during 1892, and involved the construction and use of the small
aerodromes Nos. 1, 2, and 3, presently described.

[p030]

CHAPTER IV
EARLY STEAM MOTORS AND OTHER MODELS

In dealing with the development of the aerodrome, subsequent to the
early rubber-driven models, the very considerable work done and
the failures incurred with other types of motors than steam, have
been briefly dealt with in the preceding chapter, but are scarcely
mentioned here, as no attempts at long flights were ever successful
with any other motor than steam, and no information was gained from
any of the experiments made with compressed air, gas, carbonic acid,
or electricity, that was of much value in the development of the
successful steam machines.

In November, 1891, after the long and unsatisfactory experiments with
rubber-driven models already referred to, and before most of the
experiments with other available motors than steam had been made,
I commenced the construction of the engines and the design of the
hull of a steam-driven aerodrome, which was intended to supplement
the experiments given in “Aerodynamics” by others made under the
conditions of actual flight.

In designing this first aerodrome, here called No. 0, there was no
precedent or example, and except for the purely theoretical conditions
ascertained by the experiments described in “Aerodynamics,” everything
was unknown. Next to nothing was known as to the size or form, as to
the requisite strength, or as to the way of attaching the sustaining
surfaces; almost nothing was known as to the weight permissible,
and nothing as to the proper scale on which to build the aerodrome,
even if the design had been obtained, while everything which related
to the actual construction of boiler and engines working under such
unprecedented conditions was yet to be determined by experiment.

The scale of the actual construction was adopted under the belief
that it must be large enough to carry certain automatic steering
apparatus which I had designed, and which possessed considerable
weight. I decided that a flying machine if not large enough to carry
a manager, should in the absence of a human directing intelligence,
have some sort of automatic substitute for it, and be large enough to
have the means of maintaining a long and steady flight, during which
the problems (which the rubber-driven models so imperfectly answered)
could be effectually solved.

When, in 1891, it was decided to attempt to build this steam
aerodrome, the only engine that had been made up to that time
with any claim to the lightness and power I was seeking, was the
Stringfellow engine, exhibited at the Crystal Palace in London, in
1868, which it was then announced developed 1 horse-power [p031] for
a total weight (boiler and engines) of 13 pounds. The original engine
came into the possession of the Institution in 1889 as an historical
curiosity, but on examination, it was at once evident that it never
had developed, and never could develop the power that had been
attributed to it, and probably not one-tenth so much.

With the results obtained on the whirling-table at Allegheny as a
basis, a theoretical computation of the weight which 1 horse-power
would cause to soar showed that, with a plane whose efficiency
should be equal to that of a 30×4.8 inch plane set at an angle of
5° and moving at a speed of 34 miles an hour, 1 horse-power would
support 120 pounds.[19] With a smaller angle even better results
could be obtained, but as the difficulties of guidance increase as
the angle diminishes, I did not venture to aim at less than this.
In this computation, no allowance was made for the fact that these
results were obtained by a mechanism which ‹forcibly maintained› the
supporting surface in the ideal condition of the best attainable
angle of attack as if in perfect equilibrium, and above all in the
equally ideal condition of perfectly horizontal flight.

Besides this, I had to consider in actual flight the air resistance
due to the guy wires and hull, but after making an allowance of as
much as three-quarters for these differences between the conditions
of experiment and those of free flight, I hoped that 1 horse-power
would serve to carry 30 pounds through the air if a supporting
surface as large as 3 feet to the pound could be provided, and this
was the basis of the construction which I will now describe.

The general form of this Aerodrome No. 0, without wings or
propellers, is shown in the accompanying photograph in Plate 10. Its
dimensions and its weights, as first designed, and as finally found
necessary, are as follows:

COMPARISON OF ESTIMATED AND ACTUAL WEIGHTS OF PARTS OF
AERODROME “0”--IN POUNDS AND OUNCES.

Estimated Actual
lbs. oz. lbs. oz.
Engines 4 0 4 1
Boilers and Burners 8 11 13 14
Pumps and Attachments 0 0 1 10
Steering Apparatus 0 6 0 0
Frame of Hull and Braces, including bowsprit
and tail tube 7 7 8 11
Oil tank covering and pipes 0 0 0 13
Shafts, ball bearings (2:1) and wooden
propellers (1:7) 1 14 3 8
Wings (5:4) and guys (0:9) 4 0 5 13
Tail 1 5 2 2
Jacket at prow 0 0 4 0
--------- ---------
Total without oil or water 27 11 44 8

(The weights attained in the actual making were, as is seen, nearly
double those first estimated, and this constant increase of weight
under the exigencies of construction was a feature which could never
be wholly eliminated.) [p032]

After studying various forms for the hull or body of the prospective
aerodrome, I was led to adopt the lines which Nature has used in the
mackerel as most advantageous so far as the resistance of the air was
concerned, but it proved to be difficult in construction to make the
lines of the bow materially different from those of the stern, and in
this first model the figure was symmetrical throughout.

As I wish that my experience may be of benefit to the reader, even
in its failures, I will add that I made the not unnatural mistake
of building on the plan on which the hull of an ordinary ship is
constructed; that is, making the hull support the projecting bowsprit
and other parts. In the aerodrome, what corresponds to the bowsprit
must project far in advance of the hull to sustain the front wings,
and a like piece must project behind it to sustain the rear wings and
the tail, or the supporting surfaces of whatever kind. The mistake
of the construction lay in disjoining these two and connecting them
indirectly by the insufficiently strong hull which supported them.
This hull was formed of longitudinal U-shaped ribs of thin steel,
which rested on rings made of an alloy of aluminum, which possessed
the lightness of the latter metal with very considerable toughness,
but which was finally unsatisfactory. I may say parenthetically that
in none of the subsequent constructions has the lightness of aluminum
been found to compensate for its very many disadvantages. The two
rods, which were each 1 metre in length, were with difficulty kept
rigorously in line, owing to the yielding of the constructionally
weak hull. It would have been better, in fact, to have carried the
rod straight through at any inconvenience to the disposition of the
boilers and the engine.

[Illustration: PL. 10

STEEL FRAMES OF AERODROMES NOS. 0, 1, 2, 3, 1891 AND 1892]

I may add that the sustaining surfaces, which were to be nearly flat
wings, composed of silk stretched from a steel tube with wooden
attachments, were to [p033] have been carried on the front rod,
but, as subsequent experience has shown, these wings would have been
inadequate to the work, both from their insufficient size and their
lack of rigidity.

The propellers, which were to be 80 cm. in diameter, 1.25
pitch-ratio, and which were expected to make from five to six hundred
revolutions a minute, were carried on the end of long tubular shafts,
not parallel, but making with each other an angle of 25 degrees, and
united by gears near the bow of the vessel in the manner shown in
Plate 10.

The first engines were of the oscillating type, with the piston-rod
connected directly to the crank; were very light, and were unprovided
with many of the usual fittings belonging to a steam engine, such as
rod or piston packing; and their construction was crude in comparison
with their successors. They were tested with the Prony brake and
found to be deficient in power, for with a steam pressure of 80
pounds to the square inch, they ran at the rate of 1170 revolutions
per minute, and developed only .363 horse-power. It soon became
evident that they were too light for the work that it was intended
that they should do, and steps were taken, even before the completion
of these tests, for the construction of a pair of more powerful
cylinders, which should also be provided with a special boiler for
the generation of the steam. Acting upon the supposition, in a saving
of steam, it was decided to work with compounded cylinders. As two
propellers were to be used, they were each fitted with a distinct
pair of cylinders working directly upon the shaft, but so connected
by gearing that they were compelled to turn at the same rate of speed.

The cylinders were of the inverted oscillating type, like the first
pair of engines, but, unlike them, they were single-acting. The
dimensions were: diameter of high-pressure cylinder 1.25 inches; low
pressure, 1.94 inches, with a common stroke of 2 inches, and with
cranks set opposite to each other so that one cylinder was always at
work. The cylinders were held at their upper ends by a strap passing
around a hollow conical trunk, which served the double purpose of
a support for the cylinders and an intermediate receiver between
them. This receiver had a mean inside diameter of 1.25 inches, with
a length of 4.75 inches, so that it had about twice the cubical
capacity of the high-pressure cylinder, while the displacement of
the low-pressure cylinder was about 2.5 times that of the high;
ratios that would have given satisfactory results, perhaps, had
the steam pressure and other conditions been favorable to the use
of the compound principle in this place. There were no valves for
the admission of the steam, for, inasmuch as the engines were
single-acting, it was possible to make ports in the cylinder-head
act as the admission and exhaust ports as the cylinder oscillated,
and thus avoid the complication and weight of eccentric and valves.
[p034]

These cylinders were set in a light frame at an angle of 25° with
each other, or 12.5° with the median line of the aerodrome, and drove
the long propeller shafts as shown in Plate 10, No. 0. At the extreme
forward end of the crank-shafts there was a pair of intermeshing
bevel gears which served to maintain the rate of revolution of the
two propellers the same.

[Illustration: FIG. 3. Boilers in use in 1891–1892.]

The boiler built for this work was a beehive-shaped arrangement
of coils of pipe. It consisted at first, as shown in Fig. 3, of
three double coils of 3/8-inch copper pipe coiled up in the shape
of a truncated cone, carrying in the central portion a pear-shaped
receiver into the upper portion of which the water circulating
through the coils discharged. Each of these receivers was connected
at the top with the bottom of a long cylindrical drum, with
hemispherical ends, which formed a steam space from which supply for
the engines was drawn. The lower ends of the coils were connected
with an injection pipe supplying the water. Each “beehive” had 23
turns of tubing, and had a base of 7.5 inches and a top diameter of
6 inches, the steam drum being 2.5 inches in diameter. I may here
say that in the selection of the general type of boiler for the work
to be done, there was never any hesitation regarding the use of
the water-tube variety. Their superiority for the quick generation
of large volumes of steam had been so pronounced that nothing else
seemed capable of competing with [p035] them in this respect,
regardless of the absolute economy of fuel that might or might not be
exhibited. Hence, to the end of my experiments nothing else was used.

Even before the “beehive” boiler was completed, I was anxious to
ascertain what could be done with a coil of pipe with a stream of
water circulating through it, as well as with various forms of
burners, for I realized that the success of the apparatus depended
not only upon getting an exceedingly effective heating surface, but
also an equally effective flame to do the heating.

For fuel I naturally turned to the liquids as being more compact
and readily regulated. Whether to use some of the more volatile
hydrocarbons or alcohol, was still an unsolved problem, but my
opinion at the time was that, on the limited scale of the model,
better results could probably be obtained with alcohol.

In the experiments made with a coil preliminary to the trial of the
“beehive” boiler, I tried a simple horizontal coil of 3/8-inch copper
pipe into which two forked burners working on the Bunsen principle
and using city illuminating gas, were thrust. The jets were about 1/2
inch apart. The arrangement primed so badly that the engines could
not get rid of the entrained water, and would only make a few turns.

I then tried the same coil with two 1.25-inch drums in the inside
and with five longitudinal water tubes at the bottom, beneath which
were the same two forked burners used in the previous experiment. The
coils were covered with a sheet of asbestos, and two round burners
were added. This boiler would hold a steam pressure of about 15
pounds and run the engine slowly; but if the pressure were allowed
to rise to 60 pounds, the engine would drive a 2-foot propeller of
18-inch pitch at the rate of about 650 turns per minute for from 80
to 90 seconds, while the steam ran down to 10 pounds, showing that
this boiler, at least, was too small. This was further shown in a
trial of the plain coil made in October, 1891; 6 pounds of water were
evaporated in 32 minutes under a pressure of 60 pounds. This was at
the rate of 11.25 pounds per hour, or, taking the U. S. Centennial
standard of 30 pounds of evaporation per horse-power, gave an
available output of less than 1/3 horse-power.

With these results before me, I decided to make a trial of the
“beehive” principle upon a smaller scale than in the boiler designed
for Aerodrome No. 0. I used a small boiler of which the inner coil
consisted of 8 turns of 3/8-inch copper tube about 28 gauge thick,
and the outer coil of 11 turns of 1/4-inch copper pipe. This gave 12
feet of 3/8-inch, and 16 feet of 1/4-inch tubing. The drum was of No.
27 gauge, hard planished copper. With this boiler consuming 6 oz. of
fuel, 80.3 oz. of water were evaporated in 28 minutes, or at the rate
of about 10.75 pounds per hour. As these coils contained but 2.22
square feet of heating surface, and as the three to be built would
contain 3.7 square feet each, it was estimated the [p036] 10 square
feet afforded by them could safely be depended upon to provide steam
for a 1 horse-power engine. As far as fuel consumption was concerned,
the rate of evaporation was about 15.6 pounds of water per pound of
gasoline, all of which was satisfactory.

The burner originally designed for use in connection with the
“beehive” boilers, consisted of a small tank in which a quantity of
gasoline was placed, the space above being filled with compressed
air. Rising from the bottom of this tank was a small pipe coiling
back and down and ending in an upturned jet from which the gas
generated in the coil would issue. The burner thus served to generate
its own gas and act as a heater for the boilers at the same time.

In the construction of Aerodrome No. 0, four of the “beehive” coils
were placed in a line fore and aft. The fuel tank was located
immediately back of the rear coil and consisted of a copper
cylinder 11 cm. in diameter and 9 cm. long. The engines were placed
immediately in front of the coils, all the apparatus being enclosed
in a light framing, as shown in the photograph (Plate 10).

Extending front and back from the hull were the tubes for supporting
the wings and tail, each one metre in length. The cross-framing for
carrying the propeller shafts was built of tubing 1.5 cm. diameter,
and the shafts themselves were of the same size. The ribs of the hull
were rings made of angle-irons measuring 1.50×1.75 cm., which were
held in place longitudinally by five 0.7 cm. channel bars.

As it had been learned in the preliminary experiments with the model
“beehive” boiler that the heated water would not of itself cause a
sufficiently rapid circulation to be maintained through the tubes to
prevent them from becoming red-hot, two circulating pumps were added
for forcing the water through the coils of the two forward and two
rear boilers respectively, the water being taken from the lower side
of the drum and delivered into the bottom of the coils, which were
united at that point for the purpose. A worm was placed upon each of
the propeller shafts, just back of the engines, meshing in with a
gear on a crank-shaft from which the pumps were driven. This shaft
rotated at the rate of 1 to 24, so that for 1200 revolutions of the
engine, it would make but 50, driving a single-acting plunger 1.2 cm.
in diameter and 2 cm. stroke.

Apparently all was going well until I began to try the apparatus.
First, there was a difficulty with the burner, which could not be
made to give forth the relative amount of heat that had been obtained
from the smaller model, and steam could not be maintained. With one
“beehive” connected with the compound engine, and a 70 cm. propeller
on the shaft, there were about 250 turns per minute for a space
of about 50 seconds, in which time the steam would fall from 90
pounds to 25 pounds, and the engine would stop. Then, as we had no
air-chamber on the pumps at the time, they would not drive the water
through the coils. Subsequent experiments, however, showed that the
boilers could be [p037] depended upon to supply the steam that the
compound engines would require; but after the whole was completed,
the weight, if nothing else, was prohibitory.

I had gone on from one thing to another, adding a little here and a
little there, strengthening this part and that, until when the hull
was finally completed with the engines and boilers in place, ready
for the application of the wings, the weight of the whole was found
(allowing 7 pounds for the weight of the wings and tail) to be almost
exactly 45 pounds, and nearly 52 pounds with fuel and water. To this
excessive weight would have to be added that of the propellers, and
as the wings would necessarily have to be made very large in order to
carry the machine, and as the difficulties of launching had still to
be met, nothing was attempted in the way of field trials, and with
great disappointment the decision was made in May, 1892 (wisely, as
it subsequently appeared) to proceed no further with this special
apparatus.

However, inasmuch as this aerodrome with its engines and boilers had
been completed at considerable expense, it was decided to use the
apparatus as far as it might be practicable, in order to learn what
must be done to secure a greater amount of success in the future. The
fundamental trouble was to get ‹heat›. In the first place there was
trouble with the burners, for it seemed to be impossible to get one
that would vaporize the gasoline in sufficient quantity to do the
work, and various forms were successively tried.

All of the early part of 1892 was passed in trying to get the boilers
to work at a steam pressure of 100 pounds per square inch. On account
of the defects in the tubes and elsewhere this required much patient
labor. The writer, even thus early, devised a plan of using a sort
of aeolipile, which should actuate its own blast, but this had to
be abandoned on account of the fact that the pear-shaped receivers
would not stand the heat. This necessitated a number of experiments
in the distillation of gas, in the course of which there was trouble
with the pumps, and a continual series of breakages and leakages,
so that the middle of April came before I had secured any further
satisfaction than to demonstrate that ‹possibly› the boilers might
have a capacity sufficient for the work laid out for them to do; but
subsequent experiments showed that even in this I was mistaken, for
it was only after additional jets had been put in between the coils
that I succeeded in getting an effective horse-power of 0.43 out of
the combination.

Finally, on the 14th of April, after having reduced the capacity
of the pumps to the dimensions given above (for the stroke was
originally 1.25 inch) I obtained the development of 1 full
horse-power by the engine for 41 seconds, with a steam pressure of
100 pounds per square inch, and a rate of revolution of 720 per
minute. But at the end of this brief period, the shafts sprung and
the worm was thrown out of gear. [p038]

I pass over numerous other experiments, for their only result was to
make it clear that the aerodrome, as it had been constructed, could
not be made to work efficiently, even if its great weight had not
served as a bar to its flight. It was, therefore, decided to proceed
with the construction of another.

After the failure of the first steam-driven model No. 0, which has
just been described, subsequent light models were constructed. These,
three in number, made with a view to the employment of carbonic acid
or compressed air, but also to the possible use of steam, are shown
in Plate 10, Nos. 1, 2, 3; on the same scale as the larger model
which had preceded them. In describing these, it will be well to
mention constructive features which were experimented on in them, as
well as to describe the engines used.

In No. 1, which was intended to be on about 2/5 the linear scale
of No. 0, the constructive fault of the latter, that of making the
support depend on a too flexible hull, was avoided, and the straight
steel tube (“midrod” it will hereafter be called) was carried
through from end to end, though at the cost of inconvenience in the
placing of the machinery, in what may be called the hull, which
now became simply a protective case built around this midrod. The
mistaken device of the long shafts meeting at an angle, was, however,
retained, and the engines first tried were a pair of very light ones
of crude construction.

These were later replaced by a pair of oscillating engines, each 3
cm. diameter by 3 cm. stroke, with a combined capacity of 42 cubic
cm. and without cut-off. The midrod was made of light steel tubing
2 cm. outside diameter. The framing for the hull was formed by a
single ring of U section, 8 cm. across and 18 cm. in depth, stayed
by five ribs of wood measuring 0.7×0.3 cm. The inclined propeller
shafts, which were connected by a pair of bevel gears as in No. 0,
were made of tubing 0.5 cm. outside diameter, and were intended
to turn propellers of from 40 to 45 cm. in diameter. The weight,
without engine or reservoir for gas, was 1161 grammes. With a weight
equivalent to that of the intended reservoir and engines plus that of
the proposed supporting surfaces, the whole weight, independent of
fuel or water, was 2.2 kilogrammes.

The engines, which were not strong enough to sustain a pressure of
over 2 atmospheres, at an actual pressure of 20 pounds drove the 45
cm. propellers through the long V shafts and lifted only about 1/7 of
the flying weight of the machine. The power developed at the Prony
brake was collectively only about .04 horse-power, giving 1200 turns
a minute to two 40 cm. propellers. This was the best result obtained.

This aerodrome was completed in June, 1892, but changes in the
engines and other attempted improvements kept it under experiment
until November of that year, when it appeared to be inexpedient to do
anything more with it.

Aerodrome No. 2 (see Plate 10), was a still smaller and still lighter
construction, in which, however, the midrod was bent (not clearly
shown in the [p039] photograph), so as to afford more room in
the hull. This introduced a constructional weakness which was not
compensated by the added convenience, but the principal improvement
was the abandonment of the inclined propeller shafts, which was done
at the suggestion of Mr. J. E. Watkins, so that the propellers were
carried on parallel shafts as in marine practice. These parallel
shafts were driven by two very small engines with cylinders 2.3 cm.
in diameter by 4 cm. stroke, with a collective capacity of 33 cu. cm.
and without cut-off, which were mounted on a cross-frame attached to
the midrod at right angles near the rear end of the hull.

These engines, driven either by steam or by carbonic-acid gas
developed 0.035 horse-power at the Prony brake, giving 750
revolutions of the 45 cm. propellers, and lifting about 1/5 of the
total weight which it was necessary to provide for in actual flight.
A higher rate of revolution and a better lift were occasionally
obtained, but there was little more hope with this than with the
preceding models of obtaining power enough to support the actual
weight in flight, although such sacrifices had been made for
lightness that every portion of the little model had been reduced to
what seemed the limit of possible frailty consistent with anything
like safety. Thus the midrod was lighter than that of No. 1, being
only 1 cm. in outside diameter. The frame was made of thin wooden
strips 5 mm.×3.5 mm., united by light steel rings. The cross framing
carrying the engines was also of wood, and was formed of four strips,
each 7 mm.×3 mm. The shafts were but 4 mm. in diameter.

As these engines did not give results that were satisfactory, when
using carbonic-acid gas, experiments were commenced to secure a
boiler that would furnish the requisite steam. As the “beehive”
boiler had proved to be too heavy, and as the steam obtained from it
had been inadequate to the requirements, something else had to be
devised. A few of the boilers used in 1892 are shown in Fig. 3. The
one marked ‹A› is one of the “beehives,” while an element of another
form tried is that marked ‹B›. It consisted of 3/8-inch copper tubes
joined to a drum of 10-oz. copper. This was made in May, 1892, and
was tested to a pressure of 50 atmospheres, when it burst without any
tearing of the metal.

In July another boiler like that shown at ‹C› in Fig. 3 was made.
This was formed of tubes 3 cm. in diameter, and weighed 348 grammes.
It carried about 300 grammes of water and stood a steam pressure of
125 pounds per square inch, but failed to maintain sufficient steam
pressure.

Accordingly, in the same month, a third boiler like that shown at
‹D› was built. It consisted of a tube 12 inches long to which were
attached fifteen 1/4-inch tubes each 7 inches long, in the manner
shown. The heating surface of this boiler, including the tubes and
the lower half of the drum, amounted to 750 square cm., and it was
thought that this would be sufficient to supply steam for a flight of
a [p040] minute and a half. But when a test was made, it also was
found to be deficient in steaming power even after changes were made
in it which occupied much time.

By the first of October, 1892, there had been built one large
aerodrome that could not possibly fly, a smaller one, No. 1, on 2/5
the linear scale of No. 0, with a pair of engines but no means of
driving them, and the still smaller No. 2 with a boiler that was yet
untried.

Aerodrome No. 3 (Plate 10) was an attempt to obtain better conditions
than had existed in the preceding model without any radical change
except that of moving the cross frame, which carried the engines
and propellers, nearer the front of the machine. Instead of the
oscillatory engines used up to this time, two stationary cylinder
engines, each 2.4 cm. in diameter and 4 cm. stroke, having a combined
capacity of 36 cu. cm. without cut-off were employed for driving
the propellers. The engines, though occasionally run in trials with
steam from a stationary boiler, were intended to be actuated either
by compressed air or carbonic-acid gas contained in a reservoir which
was not actually constructed, but whose weight was provisionally
estimated at 1 kilogramme. The weight of the aerodrome without this
reservoir was but 1050 grammes, including the estimated weight of the
sustaining surfaces, which consisted principally of two wings, each
about 1 metre in length by 30 cm. in breadth and which were in fact
so slight in their construction, that it is now certain that they
could not have retained their shape in actual flight.

The only trials made with this aerodrome, then, were in the shop,
of which it is sufficient to cite those of November 22, 1892, when
under a pressure of 30 pounds, the maximum which the engines would
bear, two 50 cm. propellers were driven at 900 revolutions per
minute, with an estimated horse-power of 0.07, about 35 per cent of
the weight of the whole machine being lifted. This was a much more
encouraging result than any which had preceded, and indicated that
it was possible to make an actual flight with the aerodrome if the
boilers could be ignored, the best result having been obtained only
with carbonic acid supplied without limit from a neighboring ample
reservoir.

This aerodrome was also tested while mounted upon a whirling-arm and
allowed to operate during its advance through the air. The conclusion
reached with it at the close of 1892, after a large part of the year
passed in experiments with carbonic-acid gas and compressed air,
was that it was necessary to revert to steam, and that whatever
difficulties lay in the way, some means must be found of getting
sufficient power without the weight which had proved prohibitory in
No. 0.

With this chapter, then, and with the end of the year 1892, I close
this very brief account of between one and two years of fruitless
experiment in the construction of models supplied with various
motors, subsequent to and on a larger scale indeed than the toy-like
ones of india rubber, but not even so efficient as those had been,
since they had never procured a single actual flight.

[p041]

CHAPTER V
ON SUSTAINING SURFACES

The following general considerations may conveniently precede the
particular description of the balancing of the aerodrome.

In “Experiments in Aerodynamics,” I have given the result of trials,
showing that the pressure (or total resistance) of a wind on a
surface 1 foot square, moving normally at the velocity of 1 foot per
second, is 0.00166 pounds, and that this pressure increases directly
as the surface of the plane, and (within our experimental condition)
as the square of the velocity,[20] results in general accordance with
those of earlier observers.

I have further shown by independent investigations that while the
shape of the plane is of secondary importance if its movement be
normal, the shape and “aspect” greatly affect the resultant pressure
when the plane is inclined at a small angle, and propelled by such
a force that its flight is horizontal, that is, under the actual
conditions of soaring flight.

I have given on page 60 of “Aerodynamics,” the primary equations,

‹P›_α = ‹P›_{90}‹F›(α) = ‹k›‹A›‹V›^2‹F›(α),
‹W› = ‹P›_α cos α = ‹k›‹A›‹V›^2‹F›(α) cos α,
‹R› = ‹P›_α sin α = ‹k›‹A››V›^2‹F›(α) sin α,

where ‹W› is the weight of the plane under examination (sometimes
called the “lift”); ‹R› the horizontal component of pressure
(sometimes called the “drift”); ‹k› is the constant already given;
‹A› the area in square feet; ‹V› the velocity in feet per second; ‹F›
a function of α (to be determined by experiment); α the angle which,
under these conditions, gives horizontal flight.

I have also given on page 66 of the same work the following table
showing the actual values obtained by experiment on a plane, 30×4.8
inches (= 1 sq. ft.), weighing 500 grammes (1.1 pounds):

Weight with planes
Angle Soaring speed Horizontal Work expended of like form that
with ‹V›. pressure per minute 1 horse-power will
horizon ‹R›. 60 ‹RV›. drive through the
α. air at velocity ‹V›.
------- ------------- ---------- ----------------- --------------------
Metres Feet Grammes. Kilogram- Foot- Kilo- Pounds.
per per metres. pounds. grammes.
sec. sec.
======= ======= ===== ========== ========= ======= ======== =======
45° 11.2 36.7 500 336 2,434 6.8 15
30 10.6 34.8 275 175 1,268 13.0 29
15 11.2 36.7 128 86 623 26.5 58
10 12.4 40.7 88 65 474 34.8 77
5 15.2 49.8 45 41 297 55.5 122
2 20.0 65.6 20 24 174 95.0 209

It cannot be too clearly kept in mind that these values refer to
‹horizontal› flight, and that for this the weight, the work, the
area, the angle and the velocity are inseparably connected by the
formulæ already given.

It is to be constantly remembered also, that they apply to results
obtained under almost perfect theoretical conditions as regards not
only the maintenance of equilibrium and horizontality, but also the
rigid maintenance of the angle α and the comparative absence of
friction, and that these conditions are especially “theoretical”
in their exclusion of the internal work of the wind observable in
experiments made in the open wind.

EXPERIMENTS IN THE OPEN WIND

I have pointed out[21] that an indefinite source of power for the
maintenance of mechanical flight, lies in what I have called the
“internal work” of the wind. It is easy to see that the actual effect
of the free wind, which is filled with almost infinitely numerous and
incessant changes of velocity and direction, must differ widely from
that of a uniform wind such as mathematicians and physicists have
almost invariably contemplated in their discussions.

Now the artificial wind produced by the whirling-table differs from
the real wind not only in being caused by the advancing object,
whose direction is not strictly linear, and in other comparatively
negligible particulars, but especially in this, that in spite of
little artificial currents the movement on the whole is regular and
uniform to a degree strikingly in contrast with that of the open wind
in nature.

In a note to the French edition of my work, I have called the
attention of the reader to the fact that the figures given in the
Smithsonian publication can show only a small part of the virtual
work of the wind, while the plane, which is used for simplicity of
exposition, is not the most advantageous form for flight; so that,
as I go on to state, the realization of the actually successful
aerodrome must take account of the more complex conditions actually
existing in nature, which were only alluded to in the memoir, whose
object was to bring to attention the little considered importance of
the then almost unobserved and unstudied minute fluctuations which
constitute the internal work of the wind. I added that I might later
publish some experimental investigations on the superior efficiency
of the real wind over that artificially created. The experiments
which were thus alluded to in 1893, were sufficient to indicate the
importance of the subject, but the data have not been preserved.

What immediately follows refers, it will be observed, more
particularly to the work of the whirling-table. [p043]

RELATION OF AREA TO WEIGHT AND POWER

In order to get a more precise idea of the character of the
alteration introduced into these theoretical conditions by the
variation of any of them, let us, still confining ourselves to the
use of the whirling-table, suppose that the plane in question while
possessing the same weight, shape, and angle of inclination, were to
have its area increased, and to fix our ideas, we will suppose that
it became 4 square feet instead of 1 as before. Then, from what has
already been said, ‹V›, the velocity, must vary inversely as the
square root of the area; that is, it must, under the given condition,
become one-half of what it had been, for if ‹V› did not alter, the
impelling force continuing the same, the plane would rise and its
flight no longer be horizontal, unless the weight, now supposed to be
constant, were itself increased so as to restore horizontality.

I have repeated Table XIII under the condition that the area be
quadrupled, while all the other conditions remain constant, except
the soaring speed, which must vary.

+--------+-----------+-----------------+----------------------+
| | Soaring | Work. | Weight. |
| | speed +-----------------+----------------------+
| α |(feet per | Work expended | Weight of like |
| | second) | per minute. | planes which |
| | ‹V′›. |‹A› = 4 sq. ft. | 1 H.P. will drive |
| | |‹W› = 500 gr. | through the air |
| | | = 1.1 lbs. | with velocity ‹V′›. |
+--------+-----------+-----------------+----------------------+
| | | ‹Foot-pounds.› | ‹Pounds.› |
| 45° | 18.4 | 1,217 | 30 |
| 30 | 17.4 | 634 | 57 |
| 15 | 18.4 | 312 | 116 |
| 10 | 20.4 | 237 | 154 |
| 5 | 24.9 | 148 | 244 |
| 2 | 32.8 | 87 | 418 |
+--------+-----------+-----------------+----------------------+

‹W› is the weight of the single plane; ‹A› is the area; ‹R› is the
horizontal “drift.” ‹Wt› is the weight of like planes which 1 H. P.
will drive at velocity ‹V›. Work is ‹RV›.

I. If Work is constant, ‹R› varies as ∛‹A›. II. If ‹R› is constant,
Work varies as 1/(∛‹A›). III. If ‹W› is constant while ‹A› varies,
the weight which 1 H. P. will support varies as √‹A›.

The reader is reminded that these are simply deductions from the
equations given in “Aerodynamics,” and that these deductions have
not been verified by direct trial, such as would show that no new
conditions have in fact been introduced in this new application.
While, however, these deductions cannot convey any confidence
beyond what is warranted by the original experiments, in their
general trustworthiness as working formulæ at this stage of the
investigations, we may, I think, feel confidence.

I may, in view of its importance, repeat my remark that the relation
of area and weight which obtain in practice, will depend upon yet
other than these theoretical considerations, for, as the flight
of the free aerodrome cannot be expected to be exactly horizontal
nor maintained at any constant small angle, the [p044] data of
“Aerodynamics” (obtained in constrained horizontal flight with the
whirling-table) are here insufficient. They are insufficient also
because these values are obtained with small rigid planes, while the
surfaces we are now to use cannot be made rigid under the necessary
requirements of weight, without the use of guy wires and other
adjuncts which introduce head resistance.

Against all these unfavorable conditions we have the favoring one
that, other things being equal, somewhat more efficiency can be
obtained with suitable curved surfaces than with planes.[22]

I have made numerous experiments with curves of various forms upon
the whirling-table, and constructed many such supporting surfaces,
some of which have been tested in actual flight. It might be expected
that fuller results from these experiments should be given than those
now presented here, but I am not yet prepared to offer any more
detailed evidence at present for the performance of curved surfaces
than will be found in Part III.[23] I do not question that curves are
in some degree more efficient, but the extreme increase of efficiency
in curves over planes understood to be asserted by Lilienthal and by
Wellner, appears to have been associated either with some imperfect
enunciation of conditions which gave little more than an apparent
advantage, or with conditions nearly impossible for us to obtain in
actual flight.

All these circumstances considered, we may anticipate that the
power required (or the proportion of supporting area to weight)
will be very much greater in actual than in theoretical (that is,
in constrained horizontal) flight, and the early experiments with
rubber-driven models were in fact successful only when there were
from three to four feet of sustaining surface to a pound of weight.
When such a relatively large area is sought in a large aerodrome,
the construction of light, yet rigid, supporting surfaces becomes
a nearly insuperable difficulty, and this must be remembered as
consequently affecting the question of the construction of boiler,
engines and hulls, whose weight cannot be increased without
increasing the wing area.

[p045]

CHAPTER VI
BALANCING THE AERODROME

By “balancing” I mean such an adjustment of the mean center of
pressure of the supporting surfaces with reference to the center
of gravity and to the line of thrust, that for a given speed the
aerodrome will be in equilibrium, and will maintain steady horizontal
flight. “Balance” and “equilibrium” as here used are nearly
convertible terms.

LATERAL STABILITY

Equilibrium may be considered with reference to lateral or
longitudinal stability. The lateral part is approximately secured
with comparative ease, by imitating Nature’s plan, and setting the
wings at a diedral angle, which I have usually made 150°. Stability
in this sense cannot be secured in what at first seems an obvious
way—by putting a considerable weight in the central plane and
far below the center of gravity of the aerodrome proper, for this
introduces rolling. Thence ensues the necessity of carrying the
center of gravity more nearly up to the center of pressure than
would otherwise be necessary, and so far introducing conditions
which tend to instability, but which seem to be imposed upon us by
the circumstances of actual flight. With these brief considerations
concerning lateral stability, I pass on to the far more difficult
subject of longitudinal stability.

LONGITUDINAL STABILITY

My most primitive observation with small gliding models was of the
fact that greater stability was obtained with two pairs of wings,
one behind the other, than with one pair (greater, that is, in the
absence of any instinctive power of adjustment).

This is connected with the fact that the upward pressure of the air
upon both pairs may be resolved into a single point which I will call
the “center of pressure,” and which, in stable flight, should (apart
from the disturbance by the propeller thrust) be over the center
of gravity. The center of pressure in an advancing inclined plane
in soaring flight is, as I have shown in “Aerodynamics,” and as is
otherwise well known, always in advance of the center of figure, and
moves forward as the angle of inclination of the sustaining surfaces
diminishes, and, to a less extent, as horizontal flight increases
in velocity. These facts furnish the elementary ideas necessary in
discussing this problem of equilibrium, whose solution is of the most
vital importance in successful flight. [p046]

The solution would be comparatively simple if the position of the
‹CP› could be accurately known beforehand, but how difficult the
solution is may be realized from a consideration of one of the facts
just stated, namely, that the position of the center of pressure in
horizontal flight shifts with the velocity of the flight itself,
much as though in marine navigation the trim of a steamboat’s hull
were to be completely altered at every change of speed. It may be
remarked here that the center of pressure, from the symmetry of the
aerodrome, necessarily lies in the vertical medial plane, but it may
be considered with reference to its position either in the plane
‹XY› (‹cp›_1) or in the plane ‹YZ› (‹cp›_2). The latter center of
pressure, as referred to in the plane ‹YZ›, is here approximately
calculated on the assumption that it lies in the intersection of this
vertical plane by a horizontal one passing through the wings half way
from root to tip.

Experiments made in Washington, later than those given in
“Aerodynamics,” show that the center of pressure, (‹cp›_1) on a plane
at slight angles of inclination, may be at least as far forward as
one-sixth the width from the front edge. From these later experiments
it appears probable also that the center of pressure moves forward
for an increased speed even when there has been no perceptible
diminution of the angle of the plane with the horizon, but these
considerations are of little value as applied to curved wings such
as are here used. Some observations of a very general nature may,
however, be made with regard to the position of the wings and tail.

In the case where there are two pairs of wings, one following the
other, the rear pair is less efficient in an indefinite degree than
the front, but the action of the wings is greatly modified by their
position with reference to the propellers, and from so many other
causes, that, as a result of a great deal of experiment, it seems
almost impossible at this time to lay down any absolute rule with
regard to the center of pressure of any pair of curved wings used in
practice.

Later experiments conducted under my direction by Mr. E. C. Huffaker,
some of which will appear in Part III, indicate that upon the curved
surfaces I employed, the center of pressure moves forward with an
increase in the (small) angle of elevation, and backward with a
decrease, so that it may lie even behind the center of the surface.
Since for some surfaces the center of pressure moves backward, and
for others forward, it would seem that there might be some other
surface for which it will be fixed. Such a surface in fact appears to
exist in the wing of the soaring bird. These experiments have been
chiefly with rigid surfaces, and though some have been made with
elastic rear surfaces, these have not been carried far enough to give
positive results.

The curved wings used on the aerodromes in late years have a rise of
one in twelve, or in some cases of one in eighteen,[24] and for these
latter the following empirical local rule has been adopted: [p047]

The center of pressure on each wing with a horizontal motion of 2000
feet per minute, is two-fifths of the distance from front to rear.
Where there are two pairs of wings of equal size, one following the
other, and placed at such a distance apart and with such a relation
to the propellers as here used, the following wing is assumed to
have two-thirds of the efficiency of the leader per unit of surface.
If it is half the size of the leader, the efficiency is assumed to
be one-half per unit of surface. If it is half as large again as
the leader, its efficiency is assumed to be eight-tenths per unit
of surface. For intermediate sizes of following wing, intermediate
values of the efficiency may be assumed.

These rules are purely empirical and only approximate. As
approximations, they are useful in giving a preliminary balance, but
the exact position of the center of pressure is rarely determinable
in either the horizontal or vertical plane, except by experiment in
actual flight. The position of the center of gravity is found with
all needed precision by suspending the aerodrome by a plumb-line in
two positions, and noting the point of intersection of the traces of
the line, and this method is so superior to that by calculation, that
it will probably continue in use even for much larger constructions
than the present.

The principal factor in the adjustment is the position of the wings
with reference to the center of gravity, but the aerodrome is moved
forward by the thrust of its propellers, and we must next recall the
fact of experiment that as it is for constructional reasons difficult
to bring the thrust line in the plane of the center of pressure of
the wings, it is in practice sufficiently below them to tend to tip
the front of the aerodrome upward, so that it may be that equilibrium
will be attained only when ‹CP›_1 is ‹not› over ‹CG›_1.

In the discussion of the equilibrium, then, we must consider also the
effect of thrust, and usually assume that this thrust-line is at some
appreciable distance below the center of pressure.

We may conveniently consider two cases:

1. That the center of pressure is not directly over the center of
gravity; that is, ‹CG›_1−‹CP›_1 = ‹a›, and estimate what the value of
a should be in order that, during horizontal flight, the aerodrome
itself shall be horizontal; or, [p048]

2. Consider that the center of pressure is directly over the center
of gravity (‹CP›_1−‹CG›_1 = 0), and in this case inquire what angle
the aerodrome itself may take during horizontal flight.

First case. The diagram (Fig. 4) represents the resultants of
the separate system of forces acting on the aerodrome, and these
resultants will lie in a vertical medial plane from the symmetry of
their disposition.

Let ‹af› represent the resultant of the vertical components of the
pressure on the wings; the horizontal component will lie in the line
‹ae›.

[Illustration: FIG. 4. Diagram showing relation under certain
conditions of thrust, C. P. and C. G.]

Let the center of gravity be in the line ‹bd›, and the resultant
thrust of the propellers be represented by ‹cd›.

Let ‹W› = weight of aerodrome.

Let ‹T› = thrust of propellers.

Then if we neglect the horizontal hull resistance, which is small
in comparison with the weight, equilibrium obtains when ‹W›×‹ab› =
‹T›×‹bd›.

Second case. The diagram (Fig. 5) represents the same system of
forces as Fig. 4, but in this case the point of support is directly
over the center of gravity ‹g›, when the axis of the aerodrome is
horizontal.

Let ‹W› = weight of aerodrome.

Let ‹T› = thrust of propellers.

Let ‹R› = distance of ‹CG›_2 below ‹CP›_2 = ‹ag›.

Let ‹S› = distance of thrust-line below ‹CP›_2 = ‹ad›.

If now the aerodrome under the action of the propellers be supposed
to turn about the ‹CP›_2 (or, ‹a›) through an angle α, so that ‹g›
takes the position ‹g′›, we [p049] obtain by the decomposition of
the force of gravity an element ‹g′k› = ‹W› sin α which acts in a
direction parallel to the thrust-line.

If we again neglect the horizontal hull resistance, equilibrium will
be obtained when

‹kg′›×‹ag′› = ‹T›×‹ad′›
or ‹WR› sin α = ‹TS›
∴ α = sin^{−1}×(TS/WR)

[Illustration: Fig. 5. Diagram showing relation under certain
conditions of thrust, C. P. and C. G.]

The practical application of these rules is greatly limited by the
uncertainty that attaches to the actual position of the center of
pressure, and this fact and also the numerical values involved may be
illustrated by examples.

CONDITION OF AERODROME NO. 6, NOVEMBER 28, 1896

The weight was 12.5 kilos. On November 28, the steam pressure was
less than 100 pounds, and the thrust may be taken at 4.5 kilos. The
distance ‹bd› was 25 cm.

Hence 12.5×‹ab› = 4.5x25 cm.
‹ab› = 9 cm.

This appears to give the position of ‹CP›_1, but ‹CP›_1 is a
resultant of the pressure on both wings, and its position is
determined by the empirical rule just cited. We [p050] cannot
tell in fact, then, with exactness how to adjust the wings so that
‹CG›_1−‹CP›_1 may be 9 cm., and equilibrium was in fact obtained in
flight when (the empirically determined) ‹CG›_1−‹CP›_1 = 3 cm.

Again, let it be supposed that ‹CP›_1 was really over ‹CG›_1 . . . .
The distance of the center of gravity below the center of pressure is
43 cm. = ‹R›.

Then α = sin^{−1} {(4.5×25)/(12.5×43)} = 12° nearly.

The doubt as to the actual position of the resultant center of
pressure, then, renders the application of the rule uncertain. In
practice, we are compelled (unfortunately) after first calculating
the balance, by such rules as the above, and after it has been thus
found with approximate correctness, to try a preliminary flight.
Having witnessed the actual conditions of flight, we must then
readjust the position of the wings with reference to the center of
gravity, arbitrarily, within the range which is necessary. This
readjustment should be small.

[Illustration: FIG. 6. Diagram showing effect of Pénaud tail.]

In the preceding discussion it has been assumed that, if there is a
flat tail or horizontal rudder, it supports no portion of the weight.
This is not an indispensable condition but it is very convenient,
and we shall assume it. In this case the action of the so-called
Pénaud rudder becomes easily intelligible. This is a device, already
referred to in Chapter II, made by Alphonse Pénaud for the automatic
regulation of horizontal flight, and it is as beautiful as it is
simple.

Let ‹AB› (Fig. 6) be a schematic representation of an aerodrome whose
supporting surface is ‹Bb›, and let it be inclined to the horizon at
such an angle α that its course at a given speed may be horizontal.
So far it does not appear that, if the aerodrome be disturbed from
this horizontal course, there is any self-regulating power which
could restore it to its original course; but now let there be added
a flat tail ‹AC› set at an angle −α with the wing. This tail serves
simply for direction, and not for the support of the aerodrome,
which, as already stated, is balanced so that the ‹CG› comes under
the ‹CP› of the wing ‹Bb›.

It will be seen on a simple inspection that the tail under the given
conditions is horizontal, and that, presenting its edge to the wind
of advance, it offers no resistance to it, so that if the front rises
and the angle α increases, the wind will strike on the under side of
the tail and thereby tend to raise the rear and depress [p051] the
front again. If the angle α diminish, so that the front drops, the
wind will strike the upper surface of the tail, and equally restore
the angle α to the amount which is requisite to give horizontal
flight. If the angle α is not chosen originally with reference to the
speed so as to give horizontal flight, the device will still tend to
continue the flight in the straight line which the conditions impose,
whether that be horizontal or not.

From this description of its action, it will be seen that the Pénaud
tail has the disadvantage of giving an undulatory flight, if the tail
is made rigid. This objection, however, can be easily overcome by
giving to it a certain amount of elasticity. It does not appear that
Pénaud gave much attention to this feature, but stress is laid upon
it in the article “Flight,” in the ninth edition of the Encyclopædia
Britannica, and I have introduced a simple device for securing it.

The complete success of the device implies a strictly uniform
velocity and other conditions which cannot well he fulfilled in
practice. Nevertheless, it is as efficient a contrivance for its
object as has yet been obtained.

More elaborate devices have been proposed, and a number of them,
depending for their efficiency upon the action of a variety of
forces, have been constructed by the writer, one of which will be
described later. This has the advantage that it tends to secure
absolutely horizontal flight, but it is much inferior in simplicity
to the Pénaud tail.

Apart from considerations about the thrust, the ‹CP› is in practice
always almost directly over the ‹CG›, and this relationship is,
according to what has been suggested, obtained by moving the
supporting surfaces relatively to the ‹CG›, or ‹vice versa›,
remembering, however, that, as these surfaces have weight, any
movement of them alters the ‹CG› of the whole, so that successive
readjustments may be needed. The adjustment is further complicated
by another important consideration, namely, that those parts which
‹change› their weight during flight (like the water and the fuel)
must be kept very near the ‹CG›. As the water and fuel tanks are
fixed, it appears, then, that the center of gravity of the whole is
practically fixed also, and this consideration makes the adjustment a
much more difficult problem than it would be otherwise.[25]

[Illustration: PL. 11

STEEL FRAMES OF AERODROMES NOS. 4, 5, 6. 1893, 1895 AND 1896]

[p053]

CHAPTER VII
HISTORY OF CONSTRUCTION OF FRAME AND ENGINES OF AERODROMES

During the years 1892 and 1893, it will be recalled, four aerodromes,
known as Nos. 0, 1, 2, and 3, had been built, which were of two
general types of construction. First, that represented by No. 0, in
which a radically weak hull was made to support rods at the front and
rear, to which the wings and tail were attached. This aerodrome was
abandoned on account of the inability to provide it with sufficient
power, as well as because of its constructional weakness. Second,
that type represented by Nos. 1, 2, and 3, in which a midrod was
carried through from front to rear, around which the hull supporting
the machinery was built. These models were much lighter than No. 0,
but were all abandoned because it was found impossible to propel even
the lightest of them. While all these machines were in the strictest
sense failures, inasmuch as none of them was ever equipped with
supporting surfaces, yet the experience gained in the construction
of them was of the very greatest value in determining the points at
which strength was needed, and in indicating the mode of construction
by which strength and rigidity could be obtained.[26]

1893

Another aerodrome, known as No. 4 (shown in Plate 11), was designed
in the latter part of 1892, and by the end of March, 1893, its
construction was well under way. It was of the second type, in that
the midrod was continuous, but it differed from the preceding forms
in having the machinery (boilers, burners, and tanks) attached
directly to the midrod, the hull now taking the form of a mere
protective sheathing. As in Nos. 2 and 3, two engines were used,
which were mounted on a cross-frame of light tubing attached to the
midrod at right angles. It had, as at first constructed, no provision
for the generation of steam, but only for carrying a reservoir of
carbonic acid to supply gas for the engines.

The whole, including wings, tail, and engines, but without the
carbonic acid reservoir, weighed 1898 grammes (4.18 lbs.). A
cylindrical reservoir, weighing 521 grammes (1.14 lbs.) and capable
of holding 1506 cu. cm. (92 cu. in.) was constructed for this
purpose, and tested for 30 minutes with a pressure of 100 [p054]
atmospheres. If the weight of the cylinder, with its contents and
adjuncts, be taken as 800 grammes (1.76 lbs.), the total weight
of the aerodrome was 2698 grammes (5.95 lbs.). The wings were
plane surfaces of silk, stretched over a very light frame, with no
intermediate ribs to prevent the wing from being completely distorted
by the upward pressure of the air. Even if they had been sufficiently
strong and stiff, the total surface of both wings and tail was but
2601 sq. cm. (2.8 sq. ft.) or approximately 0.5 sq. ft. of supporting
surface to the pound, much less than was found adequate, even under
the most favorable circumstances. The weight was much more than had
been contemplated when the wings were designed, yet, if all the other
features of the aerodrome had been satisfactory, and sufficient
power had been secured, the work of providing suitable supporting
surfaces would have been attempted. But as it was found that the
engines when supplied with carbonic-acid gas were unable to develop
anything like the power necessary to propel the aerodrome, and that
the construction could be greatly improved in many other ways, this
aerodrome was entirely rebuilt. The work of the engines with carbonic
acid had been so completely unsatisfactory that the idea was entirely
abandoned, and no further attempts to develop an efficient motor
other than steam were made.

It now became realized more completely than ever before that the
primary requisite was to secure sufficient power, and that this could
be obtained only by the use of steam. This involved a number of
problems, all of which would have to be solved before any hope of a
successful machine could be entertained. In the first place, engines
of sufficient power and strength, but of the lightest possible
construction, must be built. Second, a boiler must be constructed of
the least possible weight, which would develop quickly and maintain
steadily steam at a high enough pressure to drive the engines. This
demanded some form of heating apparatus, which could work under
the adverse condition of enclosure in a narrow hull, and steadily
supply enough heat to develop the relatively large quantity of steam
required by the engines.

The first of these problems, that of procuring suitable engines, was
at least temporarily solved by the construction of two engines with
brass cylinders, which had a diameter of 2.4 cm. (0.95 in.), and a
piston stroke of 5 cm. (1.97 in.). The valve was a simple slide-valve
of the piston type, arranged to cut off steam at one-half stroke. No
packing was used for the piston or the valve, which were turned to
an accurate fit to the cylinder and the steam-chest respectively.
In the engines built up to this time, the parts had frequently been
soldered together, and a great deal of trouble and delay had arisen
from this cause. In these new engines, however, as strong and careful
a construction was made as was possible within the very narrow
limits of weight, with the result that the engines, though by no
means as efficient as those constructed later, were used in all the
experiments of 1893 and also during the first part of 1894. [p055]

As soon as these engines were completed, in February, 1893, a test
was made of one of the cylinders, steam being supplied from the
boiler of the shop-engine. The experiments were made with the Prony
brake, and showed that at a speed of 1000 revolutions per minute, the
power developed from a single cylinder was 0.208 H. P., with a mean
effective pressure in the cylinder of only about 21 pounds per square
inch of piston area, allowing a loss of 25 per cent for the internal
resistance of the engine. This pressure was so much less than should
have been obtained with the steam pressure used, that it now seems
evident that the steam passages and ports were too small to admit and
exhaust the steam with sufficient rapidity to do the work with the
same efficiency that is obtained in common practice. This, however,
was not immediately recognized. The piston speed at 1000 R. P. M.
was 328 feet per minute, at which speed the steam at a pressure of
80 pounds should have been able to follow up the piston and maintain
almost, if not quite, full boiler pressure to the point of cut-off,
but it did not do so.

The problem of generating steam was much more difficult and required
a long and tedious series of experiments, which consumed the greater
part of the year before any considerable degree of success had
been attained. In the course of these experiments many unexpected
difficulties were encountered, which necessitated the construction
of special forms of apparatus, which will be described at the
proper point. Numerous features of construction, which seemed to
be of value when first conceived, but which proved useless when
rigorously tested, will be noted here, whenever a knowledge of their
valuelessness may seem to be of advantage to the reader.

The boiler was necessarily developed simultaneously with the
development of the heating apparatus, and in the following pages, as
far as possible, they will be treated together; but often for the
sake of clearness and to avoid repetition, separate treatment will be
necessary.

At the beginning of these experiments, there was much doubt as to
whether alcohol or gasoline would be found most suitable for the
immediate purpose. An alcohol burner had been used in connection with
the earliest aerodrome, No. 0, but from the results obtained with it
at that time, there seemed to be little reason to hope for success
with it. It is to be premised that the problem, which at first seemed
insoluble, was no less than to produce steam for something like 1
H. P. by a fire-grate, which should occupy only a few cubic inches
(about the size of a clenched hand) and weigh but a few ounces.
It had to be attacked, however, and as alcohol offered the great
advantage of high calorific properties with freedom from all danger
of explosion, it was at first used.

Early in 1893, it occurred to me to modify the burner so as to make
it essentially an aeolipile, and in April of that year the first
experimental aeolipile model shown at ‹A› (Plate 12) was made. It was
very small and intended for the [p056] demonstration of a principle
rather than for actual service, but the construction of this small
aeolipile was an epoch in the history of the aerodrome. It furnished
immensely more heat than anything that had preceded it, and weighed
so little and worked so well that in May the aeolipile marked ‹B› was
made. In this design two pipes were led from the upper portion of
the cylinder, one to a large Bunsen burner which heated the boiler,
the other to a small burner placed under the tank to vaporize the
alcohol. This was followed by the one shown at ‹C›, wherein the
heating burner was smaller and the gas pipe, leading to the main
burner, larger.

Figures ‹D›, ‹E›, ‹F›, and ‹G› (Plate 12) were really continuations
and improvements of the same idea. In ‹C› there was simply a tube or
flue through the tank; in ‹F›, however, this tube discharged into a
smoke-stack fastened to the end of the cylinder, while in ‹G› the
flue turned upward within the tank itself and discharged into the
short stack on top. The object of these changes was to increase the
draft and heating power of the small flame, so that the gas would be
more rapidly generated and a greater quantity be thus made available
for use under the boiler in a unit of time. They were, however,
though improvements in a construction which was itself a great
advance, still inadequate to give out a sufficient amount of heat to
meet the excessive demands of the required quantity of steam. The
boilers in connection with which these aeolipiles were used must now
be considered.

The first boiler ‹E› (Plate 13) made during this year was a
double-coil boiler of the Serpollet type, formed of 19 feet of copper
tubing having an internal diameter of about 1/8 inch. Attached to the
boiler was a small vertical drum, from the top of which steam was
led to the engine, a pipe from the bottom leading to the pump. This
boiler was tested in April with an alcohol heater, the pump in this
trial being worked by hand. This apparatus developed a steam pressure
varying from 25 to 75 pounds, which caused the engines to drive a 60
cm. propeller of 1.25 pitch-ratio 565 revolutions per minute. The
greatest difficulty was experienced in securing a sufficient and
uniform circulation in the boiler coils. The action in the present
case was extremely irregular, as the pressure sometimes rose to 150
pounds, driving the engines at a dangerous speed and bending the
eccentric rod, while at other times it would fall so low that the
engines stopped completely.

As the pump used in this trial had proved so unsatisfactory and
unreliable, it was replaced by a reservoir of water having an
air-chamber charged to 10 atmospheres, the flow from which could
apparently be regulated with the greatest nicety by a needle valve
at the point of egress; but for some reason its performance was
unsatisfactory and remained so after weeks of experiment.

[Illustration: PL. 12

BURNERS, AEOLIPILES, AND SEPARATORS]

[Illustration: PL. 13

BOILERS OF AERODROMES]

There was used in connection with this device the double-coil boiler
shown at ‹F› (Plate 13) which was made of tubes flattened so as to
be nearly capillary. The idea of this was to obtain a larger heating
surface and a smaller volume of [p057] water, so that by proper
regulation at the needle valve, just that quantity would be delivered
which could be converted into steam in its passage through the coils,
and be ready for use in the engines as it left the boiler at the
farther extremity. The results obtained from this were an improvement
over those from the original coil, and a third set of coils (‹G›, in
Plate 13) was made. This boiler consisted of three flattened tubes
superposed one over another.

These two boilers were tried by placing them in a charcoal fire and
turning on an alcohol blast, while water from a reservoir under
constant air pressure was forced through them past a pin valve. The
result was that the two-stranded coil supplied steam at from 10 to
40 pounds pressure to run the engines at about 400 revolutions per
minute. The pressure rose steadily for about 40 seconds and then
suddenly fell away, though the coils were red-hot, and neither the
water nor the alcohol was exhausted--apparently because of the
irregularity of the supply of water, due to the time taken by it
after passing the valve to fill the considerable space intervening
between that point and the boiler.

An attempt was made to overcome this difficulty by putting a
stop-cock directly in front of the boiler so that the water, while
still under the control of the needle valve, could be turned in at
once; the alcohol blast was also arranged to be turned on or off at
pleasure, and provision was made, by taking out the end of the flue
inclosing the boiler, to provide for an increased air supply. With
this arrangement a flame eight or nine inches long was obtained,
but a test showed that not more than 25 grammes of water per minute
passed through the tubes, which was not enough.

Further tests with these boilers were so far satisfactory as to
show that with the flattened-tube Serpollet boiler, comprising from
60 to 80 feet of tubing, from 80 to 100 pounds pressure of steam
could be maintained, but not steadily. As there were difficulties
in flattening the tubes to make a boiler of this sort, a compromise
was effected in the construction of the one shown at ‹H› (Plate
13), which was made of light copper tubes 5 mm. in diameter, laid
up in three lengths of 6 metres each. The ends of these coils were
so attached to each other that the water entering at one end of
the smallest coil would pass through it and then enter the middle
coil, whence it passed through the third or outer coil. Two sets of
these coils were made and placed in the thin sheathings shown in the
photograph. Repeated experiments with these boilers demonstrated
that the pressure did not rise high enough in proportion to the heat
applied, and that even the pressures obtained were irregular and
untrustworthy. The principal difficulty still lay in maintaining
an active and uniform circulation through the coils, and for this
purpose the water reservoir under constant air pressure had proved
itself inadequate. This pointed to a return to the use of the force
pump, the construction of which had hitherto presented so many
special difficulties that it had been temporarily abandoned. [p058]

A further difficulty experienced in the use of these boilers had been
that of obtaining ‹dry› steam for the engines, as during the early
experiments the steam had been delivered directly into the engines
from the boiler coils. But in August the writer devised a chamber,
known as the “separator,” where it had an opportunity to separate
from the water and issue as dry steam, or at least approximately
dry steam. This was an arrangement familiar in principle to steam
engineers under another form, but it was one of the many things
which, in the ignorance of steam engineering the writer has already
freely admitted, he had to reinvent for himself.

At about the same time, a new pump was designed to drive the water
from the bottom of the separator, which served the double purpose of
steam drum and reservoir, into the coils. This pump had a diameter of
4.8 cm., and was run at 180 strokes per minute.

The result of the first experiments with these improvements
demonstrated that, within certain limits, the amount of water
evaporated is proportional to the circulation, and in this boiler
the circulation was still the thing that was at fault. Finally, the
results of the experiments with the two-stranded, triple-coil boiler
may be summed up in the statement that it was possible to maintain a
pressure of 80 pounds, and that with it the engines could be made to
develop from 0.3 to 0.4 H. P. at best. It weighed 650 grammes (1.43
pounds) without the asbestos jacket.

About this time the writer had the good fortune to secure the
temporary services of Dr. Carl Barus, an accomplished physicist, with
whose aid a great variety of boilers were experimented on.

The next form of boiler tested was that shown at ‹N› (Plate 13), made
on a system of coils in parallel, of which there were twenty complete
turns. In the first test it generated but 20 pounds of steam, because
the flame refused to work in the colder coils. The work of this
boiler was very unsatisfactory, and it was only with the greatest
difficulty that more than ten pounds pressure could be maintained.
There was trouble, too, with the circulation, in that when the flame
was in full play the pump seemed to meet an almost solid resistance,
so that it could not be made to do its work.

A new boiler was accordingly made, consisting of three coils of four
strands each. With this the pump worked easily, but whereas it was
expected to get 120 pounds pressure, the best that could be obtained
was 70 pounds. The outer coil was then stripped off, and a trial made
in which everything ran smoothly and the pressure mounted momentarily
to 90 pounds. After some adjustment, a mean pressure of 80 pounds was
obtained, giving 730 revolutions of the engine per minute, with an
indicated horse-power of 0.32.

It was shown in this work that, within certain limits, steam is
generated most rapidly when it is used most rapidly, so that two
engines could be used [p059] almost as well as one, the reason
apparently being that the rapid circulation increased the steam
generating power of the boiler, and that the engines worked best at
about 80 pounds. It was also found that a larger tubing was better
than the small, weight for weight, this fact being due to the greater
ease with which circulation could be maintained, since fewer coils
were necessary in order to obtain the same external heating surface.
The pressure in the coils and the separator was also much more nearly
equalized. The result was that the boiler temporarily approved was
one made of tubing 6.35 mm. (0.25 inch) in diameter, bent into a
two-coil, two-stranded boiler, having sixteen complete turns for each
strand in each coil. The total weight was 560 grammes (1.23 pounds)
with a total heating surface of 1300 sq. cm. (1.4 sq. ft.).

The separator used in the experiments made during August and
September was of a form in which the water was forced below a series
of partitions that prevented it from following the steam over into
the cylinders of the engines. It weighed 410 grammes (0.9 pound) and
was most conveniently worked with 700 grammes (1.54 pounds) of water.
The boiler and separator together weighed 970 grammes (2.1 pounds).

A new separator was, however, designed, which was horizontal instead
of vertical, as it was intended that it should be placed just below
the midrod. Another form, devised for constructional reasons,
consisted of a cylinder in which a pump was imbedded. Heretofore the
pump used had been single-acting, but it was now proposed to make a
double-acting pump. Upon testing this apparatus, it was found that
when using an aeolipile, it took 150 grammes of alcohol to evaporate
600 grammes of water. It was evident that the latter was used very
wastefully, so that the thermal efficiency of the engine was not
over one per cent; but it was also evident that, under the necessity
of sacrificing everything to lightness, this waste was largely
inevitable.

About the middle of October, another boiler (O, Plate 13) was
made, which consisted of two coils wound in right and left hand
screw-threads, one fitting loosely over the other, so as to make a
cylindrical lattice-work 32 cm. (12.6 in.) long. Each coil contained
two strands of copper tube 0.3 mm. thick, and weighing 54 grammes to
the metre (0.036 pound to the foot). The inner coil had a diameter
of 5.63 cm. (2.22 in.), with nine turns of tube to the strand, the
two strands making a length of 319 cm. (10.5 feet) for the coil. The
outer coil had a mean diameter of 6.88 cm. (2.71 in.) and a length of
388 cm. (12.7 feet) for the two strands. The total length of the two
coils was, therefore, 707 cm. (23.2 feet), with a heating surface of
about 1415 sq. cm. (1.52 sq. ft.) and a total weight of 382 grammes
(0.84 pound).

The results obtained with this boiler were so far satisfactory as to
show that, under the most favorable conditions, when air was supplied
in unlimited quantities and there were no disturbing currents to
put out or interfere with the work [p060] of the burners, steam
could be supplied at a sufficient pressure to run the engines. It
was realized, however, that the conditions in flight would be very
different, and that in order to protect the apparatus from the wind,
some sort of protecting covering would have to be devised, which
would of itself introduce new difficulties in providing the burners
with a proper and uniform draft.

[Illustration: FIG. 10. Diagram of pendulum.]

The hull, as at first constructed, consisted of a cylindrical
sheathing open in front, through the rear end of which the boiler
and aeolipile projected inward, so that the air taken in at the
front would be drawn through the boiler and hearth to the exclusion
of lateral currents. In the first tests, however, after the hull
had been applied, it was impossible to secure a proper rate of
combustion, nearly the whole hull being filled with a bluish flame,
while only a very small portion of the gases of combustion passed
into the coils of the boiler. The remedy for this lay in obtaining
an increased draft, and a small stack was, therefore, arranged to
carry off the products of combustion. This proved inadequate, and
it was only after several weeks of experiment with various types of
smoke-stack, and constant alteration of the aeolipile, that it was
possible to make the apparatus work [p061] efficiently when it was
inside the hull. Finally such a degree of success was attained that
the burners could be kept lighted even when the aerodrome was placed
in a considerable artificial breeze, created by a blower in the shop.

In connection with these tests of the engines and boilers, some
method was desired, in addition to the Prony brake tests, by which
the thrust of the propellers when driven by the engines at various
speeds could be measured accurately and in terms which would be
readily available in judging whether the aerodromes were ready to be
given an actual trial in free flight. Such a method was found in the
use of an apparatus known as the “pendulum,” which was introduced
near the end of 1892, but was not generally used until the end of
1893. After this time, however, this test was made a condition
prerequisite to taking any of the aerodromes into the field, and
proved of the greatest assistance in estimating the probable outcome
of the trials.

The apparatus used, which is diagrammatically shown in Fig. 10, was
extremely simple both in theory and operation. It consisted primarily
of a horizontal arm ‹AC› carrying the knife-edge ‹B› by which it
is pivoted on each side on supporting beams not shown. Depending
from ‹AC› is the light vertical arm ‹DE›, rigidly joined to it and
carrying the lower horizontal arm ‹FG›, all of which are braced
together so as to maintain the arm ‹DE› constantly perpendicular
to ‹AC›. To this arm ‹FG› the model was rigidly attached with its
center of gravity in line with the vertical arm ‹DE› and its weight
increased by the addition of properly disposed flat weights, in
order to make the angle of lift for a given thrust of the propellers
smaller and less likely to interfere with the working of the boiler
and separator.

Before the actual test of the “lift” could be made, it was necessary
to know the exact distance of the vertical center of gravity of
the model and the extra weights from the knife-edge ‹B›. This was
determined by the following method: A known weight was suspended
from the arm ‹AB› at some arbitrarily selected distance from the
point ‹B›. This weight caused the perpendicular arms ‹AB› and ‹DE›
to rotate through an angle, θ, which was measured on the scale ‹KL›.
Knowing, then, the weight on the arm ‹AB›, its point of application,
the weight of the aerodrome suspended on the arm ‹DE›, and the angle
of rotation, it is easy, by a simple application of trigonometric
functions, to determine the distance of the center of gravity of the
model from the point ‹B›.

In a test of Aerodrome No. 6 made on September 23, 1898, the weight
suspended from ‹AB› was 10,000 grammes, its point of application
50 cm., the model was weighted to 20,450 grammes, and the angle of
rotation, θ, was 7° 2′. Letting y equal the distance of the ‹CG› from
‹B›, we may equate the balanced forces thus:

10,000×50 cos 7° 2′ = 20,450×‹y› sin 7° 2′
10,000×50 cot 7° 2′ = 20,450‹y›
‹y› = 198.2 cm.

Having determined this distance, the weight on ‹AB› was removed and
the aerodrome was allowed to regain its former position. The distance
of the center of thrust from ‹B› was then measured. The engine was
next started and the number of revolutions of the propellers counted
by a tachometer. The thrust of the propellers, acting perpendicularly
to the arm ‹BD›, produced rotation around the point ‹B›, the angle of
which was measured as above.

In the power test of No. 6, the following data were obtained:

‹W› = weight of aerodrome = 20,450 grammes.
θ = angle of lift = 19° 30′.
Distance of ‹CG› from center of rotation = 198.2 cm.
Distance of center of thrust from center of rotation = 186.3 cm.

As the propeller thrust and the weight of the model are forces acting
in opposite directions at known distances from a center of rotation,
letting ‹L› equal the “dead lift,” we may express the equation thus:

‹W› sin θ×198.2 = ‹L›×186.3,
‹L› = (198.2/186.3)×sin 19° 30′×20,450,
‹L› = 7,263 grammes “dead lift.”

The flying weight of Aerodrome No. 6 was 12,064 grammes, and the per
cent of this weight lifted was, therefore,

7,263/12,064 = 60.3.

This was much more than was necessary for flight, but in order to
insure successful flights and avoid delay, the rule was made in
1895 that no aerodrome was to be launched until it had previously
demonstrated its ability to generate enough power to maintain for at
least two minutes a lift of 50 per cent of the total flying weight.
At the same time other important data were obtained, such as the
steam-pressure, the time required to raise sufficient steam, the
total time of the run, and the general working of the boilers and
engines.

As will easily be seen, these tests afforded a most satisfactory
basis of judging what the aerodromes might be expected to do in
actual flight if the balancing were correct.

At this time, October, 1893, the aerodrome (Old No. 4) was
practically complete, and the most anxious thought was given to
lightening it in every way consistent with the ever-present demand
for more power, which necessitated an increase in the weight of both
burners and boilers to supply the requisite steam.

On November 14, when the aerodrome was prepared to be shipped
to Quantico for trial, its condition was about as follows. The
steam-generating apparatus--the parts of which were of substantially
the forms last described, although some slight improvements had
been introduced—had been developed to [p063] such a point that a
pressure of from 70 to 80 pounds of steam could be maintained for 70
seconds, when it was tested in the shop. What it would do under the
unfavorable conditions imposed by flight was to be learned only by
trial.

At this pressure, the engines, the efficiency of which had been
increased by an improvement in packing, would develop approximately
0.4 indicated H. P., while at 105 pounds pressure they at times
developed as much as 0.8 H. P. When the aerodrome was tested on the
pendulum, these engines, when making less than 700 revolutions per
minute, lifted over 40 per cent of the total flying weight.

The propellers used at this time were accurate helices, having a
diameter of 60 cm., a width of blade of approximately 36 degrees, and
a pitch-ratio of 1.25. They were formed of wood, and were bushed with
brass where they were attached to the shafts.

AERODROME OLD NO. 4 AS PREPARED FOR FLIGHT BEFORE BEING SHIPPED FOR
TRIAL ON NOVEMBER 14, 1893

------------------------+-------+------+------+-----+
Part. |Copper.|Steel.|Brass.|Iron.
| | | |
| | | |
------------------------+-------+------+------+-----+
| gms. | gms. | gms. | gms.
Aeolipile | 200 | .. | 92 | ..
Boiler | 350 | .. | 37 | ..
Separator and pumps | 300 | 30 | 100 | 20
Engine and frame | .. | 350 | 570 | ..
Midrod (200 cm. long) | .. | 220 | .. | ..
Two smoke-stacks | 70 | .. | .. | ..
Asbestos jacketing | .. | .. | .. | ..
Air chamber | .. | .. | .. | 82
Spider between boiler | | | |
and burner | 32 | .. | .. | ..
Intake valve | .. | .. | 15 | ..
|-------|------|------|-----+
Total | 952 | 600 | 814 | 102
|-------|------|------|-----+
Hull | 50 | .. | 50 | ..
Pins for starter | .. | 15 | .. | ..
Two large wings and tail| .. | .. | .. | ..
Buffer and steerer | .. | .. | .. | ..
Propellers | .. | .. | .. | ..
|-------|------|------|-----+
Total | 50 | 15 | 50 | ..
|-------|------|------|-----+
Grand total | 1002 | 615 | 864 | 102
|=======|======|======|=====+
Density | 8.9 | 7.8 | 8.5 | 7.5
Volume (cu. cms.) | 113 | 79 | 102 | 136
Alcohol | .. | .. | .. | ..
Water | .. | .. | .. | ..
|-------|------|------|-----+
Total | .. | .. | .. | ..
Density | .. | .. | .. | ..
| | | |
Volume (cu. cm.) | .. | .. | .. | ..
------------------------+-------+------+------+-----+

------------------------+------+---------+------+---------------------
Part. | Wood |Mica and |Fluid.| Total and mean
| and |asbestos.| | weights.
| silk.| | |
------------------------+------+---------+------+---------------------
| gms.| gms. | gms. | gms.
Aeolipile | .. | .. | .. | 292
Boiler | .. | .. | .. | 387
Separator and pumps | .. | .. | .. | 450
Engine and frame | .. | .. | .. | 920
Midrod (200 cm. long) | .. | .. | .. | 220
Two smoke-stacks | .. | .. | .. | 70
Asbestos jacketing | .. | 50 | .. | 50
Air chamber | .. | .. | .. | 82
Spider between boiler | | | |
and burner | .. | .. | .. | 32
Intake valve | .. | .. | .. | 15
|------|---------|------|-----
Total | .. | 50 | .. | 2518 = 5.54 lbs.
|------|---------|------|-----
Hull | .. | 25 | .. | 125
Pins for starter | .. | .. | .. | 15
Two large wings and tail| 571 | .. | .. | 571
Buffer and steerer | 53 | .. | .. | 53
Propellers | 250 | .. | .. | 250
|------|---------|------|-----
Total | 874 | 25 | .. | 1014 = 2.33 lbs.
|------|---------|------|----- ----
Grand total | 874 | 75 | .. | 3532 = ┐ 7.77 lbs.
|======|=========|======|===== │
Density | 0.8 | 3.0 | .. | 2.48 │ I.
Volume (cu. cms.) | 1092 | 25 | .. | 1425 = ┘ 87 cu. ins.
Alcohol | .. | .. | 100 | 100
Water | .. | .. | 500 | 500
|------|---------|------|-----
Total | .. | .. | .. | 4132 = ┐ 9.1 lbs.
Density | .. | .. |┌125┐ | │
| | |└500┘ | 2.01 │ II.
Volume (cu. cm.) | .. | .. | .. | 2050 ┘
------------------------+------+---------+------+---------------------

Permanent air spaces:

in midrod, vol. = 355 cc.┐
in engine frame, vol. = 100 cc.│ ┐
volume as per II. 2050 cc.│ Density = 4132/2505 = 1.65│ III.
--------│ ┘
2505 cc.┘

The total flying weight of Old No. 4, including fuel and water,
was 4132 grammes (9.1 lbs.), a much larger weight than had been
contemplated when the original designs were made. A detailed
statement of the weights of the various parts of the aerodrome,
together with some data as to its density, is given on the preceding
page. There were provided in the wings and tail approximately 2 sq.
ft. of supporting surface to the pound of weight, which would have
been barely sufficient to sustain the aerodrome, even if it had been
successfully launched and the wings had been built much stronger than
the flimsy construction in use at this time.

An air chamber, which served the double purpose of floating the
aerodrome and of providing a moveable weight by which the center of
gravity could be shifted to the proper position relatively to the
center of pressure, was constructed of the thinnest sheet-iron and
attached to the midrod.

This aerodrome, the fifth in actual construction, and the first,
after years of experiment, to be carried into the field, was
transported to Quantico, where the first trial with it was made on
November 20, under the conditions described in Chapter IX.

1894

The aerodrome, No. 4, which has just been described, had not been
put to the test of an actual flight, for reasons connected with the
difficulties of launching, which are more fully described elsewhere;
but, when the completed machine was more fully studied in connection
with the unfavorable conditions which it was seen would be imposed
on it in trials in the open air, many possibilities for improvement
presented themselves. It was seen, for instance, that a better
design might be made, in which the engines, boiler and aeolipile
might be placed so that the center of gravity of each would lie in
the same vertical plane as the central line of the aerodrome. In
order to do this the construction of a single midrod, which was the
distinguishing feature of Old No. 4, had to be essentially departed
from, the midrod of this new one, No. 5, being opened out into two
rods, so to speak, which were bent out so that the open space between
them furnished a sufficiently large hull space to hold the entire
power generating apparatus. In arranging the machinery within this
hull, it was provided that, as the water and fuel were expended, the
center of gravity of the aerodrome would shift little, and, if at
all, backward relatively to the center of pressure.

Instead of the two small engines, which it will be remembered were
mounted on the cross-frame in No. 4, a single engine with a larger
cylinder, having a diameter of 3.3 cm. (1.3 in.) and a stroke of 7
cm. (2.76 in.), capable of developing about 1 H. P. was used. This
engine was mounted within the hull near the forward end and drove the
propellers by suitable gearing. [p065]

In addition to these radical changes many important improvements were
made in the different parts. Internal compartments were built in the
separator, so that even if the water was displaced by the pitching
of the aerodrome, it could still perform its functions properly.
The pump was provided with a ratchet, so that it could be worked by
hand after the burners were lighted, and before enough steam had
been raised to enable the engine to run it. An active circulation
was thus maintained in the coils of the boiler as soon as the burner
was lighted and before the engine was started, which prevented the
tubing from being burnt out, as had frequently happened previously.
The wing construction was also improved and many other changes were
introduced, which will be treated separately.

In the meantime, No. 4, which had been damaged in the attempted
launching in November, 1893, was strengthened and prepared for
another trial which took place in January, 1894.

By the end of the first week in February, the engine of No. 5 was
ready for trial, and with a boiler pressure of about 80 pounds per
square inch, apparently developed 0.56 H. P. on the Prony brake, when
making 800 revolutions per minute. To accomplish this called for such
good distribution of steam in the cylinder, that it is doubtful if
the power could be exceeded at that speed and pressure.

It was, however, apparent that it was desirable to have a boiler
capable of supplying steam for at least one horse-power, and that in
order to do this, there must be an improvement in the aeolipiles.
The problem consisted in arranging to evaporate more than 500 cu.
cm., and in fact as nearly as possible 1000 cu. cm. (61 cu. in.)
of water per minute, and, since from 200 to 300 cu. cm. per minute
had already been evaporated, this was not regarded as impossible of
accomplishment. The theoretical advantages of gasoline had for a
long time been recognized, as well as the very practical advantage
possessed by it of keeping lighted in a breeze, and several attempts
had been made during the latter part of the previous year to
construct a suitable burner for use with it. These had not been
very successful; but in view of the increasing demand for a flame
of greater efficiency than that of the alcohol aeolipiles, it was
decided to resume the experiments with it.

Accordingly, a gasoline evaporator was tried, consisting in the first
experiment of a gasoline tank with nine flues, through which steam
was passed. A flow of steam gave a rapid evaporation of gasoline
when the pressure did not exceed 5 pounds. The chief difficulty with
the burner employed was that the supply of gasoline gas would rise
and fall as the steam rose and fell, conditions just the opposite
of what was really desired. On the other hand, it was thought that
this gasoline tank would form a real condenser for the steam, so
that a [p066] portion of the exhaust steam would be condensed and
be available for use in the boiler again. The gasoline vapor had
many advantages over the alcohol; but it was at first possible to
evaporate only 120 cu. cm. of gasoline in a minute.

In the experiments that were made at this time (March 9) with
gasoline, the main object in view was to obtain a smooth blue flame
at 10 pounds pressure. There had been failures to accomplish this,
owing to the high boiling point of the liquid, and while the work
was in progress it was still evident that the problem of the boiler
and the flame which was to heat it had not been solved. A Prony
brake test gave, at 130 pounds pressure, 1.1 H. P. with about 1000
revolutions of the propellers; but this was with steam supplied from
the boiler of the stationary shop engine.

On April 1, 1894, the following record was made of the condition of
Aerodrome No. 5:

“The wings, the tail, and the two 80 cm. propellers, as well as the
two smaller propellers, are ready. The cylinders, gear, pump, and
every essential of the running gear, are in place. The boilers,
separators, and adjuncts are still under experiment, but may be
hoped to be ready in a few days. At present, the boilers give from
450 to 600 grammes of mixed steam and water per minute. With 130
pounds of steam, the engine has actually developed at the brake,
without cut-off, considerably more than 1 H. P., so that it may be
confidently considered that at 150 pounds, with cut-off, it will
give at least 0.8 H. P., if it works proportionately well.”

The delays incident to the accomplishment of the work in hand were
always greater than anticipated, as is instanced by the fact that
it was the latter part of September before the work was actually
completed. The greater part of this delay was due to the necessity
for a constant series of experiments during the spring and summer to
determine the power that it was possible to obtain with the various
styles of boilers, aeolipiles, and gasoline burners.

While No. 5 was thus under construction, new and somewhat larger
engines had been built for No. 4, the work on them having been
begun in January. The cylinders of these engines, which are more
fully described in connection with Aerodrome No. 6, were 2.8 cm. in
diameter, with a 5 cm. stroke, each cylinder thus having a capacity
of 30.8 cu. cm., which was an increase of 36 per cent over that of
the old brass cylinder engines, which had previously been used on
No. 4. On April 28, under a pressure of 70 pounds, these engines
drove the two 60 cm. propellers at a rate of 900 R. P. M., and
lifted on the pendulum nearly 40 per cent of the total flying weight
of Aerodrome No. 4, which was now approximately 5 kilos. A trial
was made at Quantico in the latter part of May, which is described
in Chapter IX. It is only necessary to mention in this connection
that there was a great deal of trouble experienced with the alcohol
aeolipile, the flame being extinguished in the moderate wind to which
the [p067] aerodrome was subjected while preparations for the launch
were being made. Moreover the flame was so nearly invisible in the
sunlight that it was uncertain whether it was burning in the critical
instants just before the launch, when doubt might be fatal. These
conditions resulted in a final decision in favor of gasoline, on
account of its greater inflammability, and in the provision of such
hull covering that the fires could be lighted and maintained in a
breeze.

In June, I tried a modification of the burner, in which the gasoline
was delivered under the pressure of air to the evaporating coil. In
the first trial steam was raised to a final pressure of about 70
pounds, and a run of 45 seconds was secured under a pressure of 40
pounds in the gasoline tank, which was thought to be altogether too
high; for, at the end of the run, the whole apparatus was enveloped
in flames, because of the gasoline that was projected through the
burner-tips.

Continual experiments with different forms of burner, illustrated
in Plate 12, occupied the time, with delays and imperfect results,
which were trying to the investigator, but are omitted as of little
interest to the reader. They had, however, the incidental result
of proving the practical superiority of gasoline over alcohol, and
culminated in the evolution of the burner that was finally used
successfully. It consisted of a tank for the gasoline, from which
compressed air delivered the liquid to a small coil surrounded by
asbestos, in which it was vaporized. At the rear end of this coil
three pipes were led off, one of which was a small “bleeder,” which
fed the burner for heating the gasoline, the other two leading to the
main burners. After the generation of gas in the small coil had been
started, the heat from the small burner was expected to continue the
vaporization, so that nothing but gas would be able to reach the main
burners. A device was also introduced, which had greatly increased
the amount and uniformity of the draft and consequently made the
burners and boilers more efficient than before. This consisted simply
in passing the exhaust steam from the engines into the smoke-stack,
and it is remarkable that it was not thought of earlier.

By the middle of September, 1894, both aerodromes were completed and
ready for another test. On September 27 the condition of Aerodrome
No. 4 was as follows: The general type of construction, namely, that
of a single midrod, to which all the steam generating apparatus was
attached, and which supported also the cross-frame and the wings, was
the same as in the construction of 1893. On account of the increased
weight of the model, and the substitution of an inferior piece of
tubing in place of the former midrod, it was found necessary to
stiffen it by the use of temporary trusses. Permanent bearing points
for holding the aerodrome securely to the newly devised launching
apparatus were also attached to this midrod. [p068]

The engines in use at this time were the small steel cylinders
described above, which were mounted on the cross-frame, and drove the
propellers directly. These engines were capable of delivering to the
propellers, as had been proved by repeated tests, at least 0.66 brake
horse-power.

The boiler consisted of two inner coils and an enveloping outer coil,
loosely wound and connected in series. The inner coils, each of which
had about 17 turns of 8 mm. diameter, 0.2 mm. thick tubing, developed
about 80 per cent of the steam; the outer coil of 8 turns, while not
exactly useless as a steam generator, afforded an efficient means of
fastening the smoke-stack and cover of the boiler, and for attaching
the latter to the midrod. This boiler was externally 30 cm. long, 16
cm. wide, and 10 cm. deep, weighing with its cover approximately 650
grammes. The stack for the burnt gases, into which exhaust steam was
led from a central jet, was about 1 foot long. At best this boiler
was capable of developing slightly over 100 pounds of steam.

The separator was of the form last described, except that the steam
dome had been moved toward the front, to prevent the jerk of the
launching car in starting from causing water to be pitched over
into the engines. It was constructed of sheet aluminum-bronze, and
weighed, together with its pump, 580 grammes. The pump, which was
double-acting and fitted with ball valves, was capable of discharging
4.5 grammes of cold water per stroke, its efficiency being only about
one-half as great with hot water.

The gasoline burner, which had been finally adopted in place of the
alcohol aeolipiles, had now been perfected to the form in which
it was finally used. Two Bunsen burners of special construction
were provided with gasoline gas by the heat of an intermediate
accessory burner, which played upon a coil to which all three
burners were connected. Gasoline was furnished from a tank made
of aluminum-bronze, under an air pressure of about 20 pounds, the
fluid being under the control of a screw stop-cock. This tank, which
was capable of holding 100 to 150 cu. cm. of gasoline, weighed 180
grammes, and the burners with an outer sheathing weighed 302 grammes.

It was calculated that about 3300 cu. cm. (201 cu. in.) of air
space would be required to float the aerodrome in water, and this
was supplied by an air chamber, having a capacity of 2700 cu. cm.
(165 cu. in.), which could be shifted to adjust the longitudinal
equilibrium of the aerodrome, and about 900 cu. cm. (55 cu. in.) of
space in the gasoline tank and the midrod. The reel and float, which
served to indicate the location of the aerodrome, if for any reason
it should be submerged, were in one piece, and so moored that there
was no danger of fouling the propellers.

The total weight of the aerodrome was about 6 kilogrammes (13.2
lbs.), or, with a maximum quantity of fuel (850 cu. cm. of water,
150 cu. cm. of gasoline), [p069] less than 7 kilogrammes. From 60
to 90 pounds of steam could be maintained by the boilers for about
2 minutes, at which pressure the engines developed about 0.66 brake
horse-power, driving the 70 cm., 1.25 pitch-ratio propellers at 700
R. P. M., and giving a lift of from 2.6 to 3.0 kilos (5.7 to 6.6
pounds), or about 40 per cent of the flying weight.

The wings and tail had a total surface of 2.62 sq. m. (28.2 sq. ft.),
giving a ratio of 2.7 kilos to 1 sq. m. of wing surface (1.8 sq. ft.
per pound). If the hull resistance be neglected, the soaring speed of
this aerodrome was about 5.9 metres (19 feet) per second, or 13 miles
per hour.

Turning now to the completed No. 5, its frame was of the “double
midrod” type described above, the two tubes which formed the
frame being prolonged at the front and rear to afford points of
attachment for the wings and tail. The range through which the wings
could be shifted to adjust the position of the center of pressure
was, however, very small. The hull, which, it will be remembered,
contained all the power generating apparatus, was much stronger
and heavier than that of No. 4, and resembled somewhat the hull of
a ship. It had a frame-work of steel tubing brazed to the midrod,
to which an outer sheathing of sheet aluminum 0.3 mm. thick was
attached. It was, however, excessively heavy, weighing nearly 800
grammes.

The engine, which was mounted near the front of the hull, was the
single cylinder, one horse-power engine, described above, which drove
the two propellers by suitable gearing. The remaining parts of the
power plant were identical with those already described in connection
with No. 4, but the more advantageous location of them in No. 5
rendered them somewhat more efficient.

It had been planned to use 80 cm. propellers of 1.25 pitch-ratio on
No. 5, but it was found in the shop tests of the aerodrome that the
cross-frame was not strong enough to withstand the strains, and that
the engine could be made to work much more steadily with a smaller
propeller. Accordingly, propellers of 70 cm. diameter and 1.25
pitch-ratio, similar to those used on No. 4, were finally substituted.

For floating the aerodrome, when it descended into the water, an
air-chamber similar to that of No. 4, but of a larger capacity was
provided. With this in place on the aerodrome, it was calculated
that, if all the parts except this float and the gasoline tank
were filled with water, there would still be a buoyancy of over 2
kilogrammes.

The total weight of No. 5 was 8200 grammes, or with its full supply
of fuel and water 9200 grammes. In this aerodrome the same boilers
used in No. 4 were capable of maintaining for at least a minute 115
pounds of steam, so that the engine now gave the maximum of one
brake horse-power for which it was designed, and, driving the 70
cm. propellers, lifted repeatedly nearly 45 per cent of the flying
weight. [p070]

The wings and tail constructed for No. 5 were identical with those
of No. 4, being slightly curved and containing 2.62 sq. m. (28.2 sq.
ft.), equivalent to 1.4 sq. ft. to the pound, which with the flimsy
construction of the wings gave an entirely inadequate support to the
aerodrome.

During the summer a launching apparatus of a new and improved type,
which is described in Chapter X, had been perfected, and with it
repeated tests were made of both aerodromes in October, November,
and December, with the unsatisfactory results recorded in Chapter
IX. In the course of these experiments, many slight modifications
of the burners and boilers were made, but no important changes were
introduced except that the cross-frame of No. 5 was enlarged and
strengthened so as to admit of its carrying one metre propellers
safely. The results, however, which were obtained, did not compensate
for the increased weight of the larger frame.

Viewing the work of this year from the standpoint of results obtained
in the numerous attempts at flight, it would seem that very little
progress had been made, and that there was small reason to expect
to achieve final success. However, if the work be examined more
particularly, it will be seen that two of the most difficult problems
had been solved, one completely as far as the models were concerned,
and the other to a very satisfactory degree. First, a launching
apparatus, with which it was possible to give the aerodrome any
desired initial velocity, had been devised, and so far perfected
that no trouble was ever experienced with it in testing the models.
Second, as a result of the extended and systematic series of
experiments, which had been conducted under the direction of Dr.
Barus, a steam pressure of 115 pounds could be maintained steadily
in the boilers for at least a minute, and the burners could be kept
lighted even in a considerable breeze.

A summary of these experiments, together with some account of the
difficulties encountered and the results finally obtained with the
apparatus in use at the end of the year, is given in the following
report, which was prepared by Dr. Barus in December, 1894.

“If water be sprayed upon a surface kept in a permanent state of
ignition, any quantity of steam might be generated per time unit.
Similarly advantageous conditions would be given if threads of
water could be passed through a flame. In practice this method
would encounter two serious difficulties, the importance of which
is accentuated when the boiler apparatus is to be kept within the
degree of lightness essential in aerodromics. These difficulties are
(1) the danger of chilling the flame below the point of ignition
or of combustion of the gases, and (2) the practical impossibility
of maintaining threads of water in the flame. For it is clear
that the threads must be joined in multiple arc, so as to allow a
large bulk of water to circulate through the boiler, whereas even
when there are but two independent passages for the water through
the furnace, it is hard to keep both supplied with liquid without
unduly straining the pump. If the water be even slightly deficient,
circumstances will arise in which one of [p071] the passages
is better than the other. This conduit will then generate more
steam and drive the water under force through the other passage,
increasing the temperature discrepancy between them. Eventually
the hot passage reaches ignition and either bursts or melts. This
is what sooner or later takes place in boilers adapted for flying
machines and consisting of tubes joined in multiple arc, when a
single moderately strong circulating pump supplies the system.

“To avoid these annoyances, ‹i. e.›, to increase the length of life
of the boiler, the boiler tubes are joined in series to the effect
that a single current of water may flow successively through all of
them. It is needful therefore to select wide tubes, such as will
admit of an easy circulation in consideration of the length of
tubing employed without straining the pump and at the same time to
allow sufficient room for the efflux of steam. Other considerations
enter here, the bearing of which will be seen presently: if the
tube be too wide the difficulty of coiling it on a mandrel of
small diameter is increased, while at the same time the tube loses
strength (‹cæt. par.›) in virtue of the increased width.

[Illustration: FIG. 11.

Diagram 1. Diagram 2.]

“It is from considerations such as these that, in the course of many
experiments, copper tubing about 8 mm. in diameter has been adopted.
Copper is selected because of its freedom from internal corrosion,
easy coiling, and because of its availability in the market. The
thinnest tube to be had (walls only 0.1 mm. thick) will withstand
more pressure than can be entrusted to the larger steam receivers
in circuit with the boiler. The boiler weight is thus a negligible
factor, and it is quite feasible to reduce the thickness of boiler
tubing, by the superficial application of moderately strong nitric
acid, to 200–400 grammes per horse-power of steam supplied. External
corrosion due to flames occurs only in case of deficient water, and
if the boiler be made of tubing with the walls 0.2 mm. thick, it is
in view of the possibility of such accidents. Boilers may then be
tested to 25 atm. without endangering the metal.

“Boilers are wound or coiled with regard to the two points above
suggested, viz.: to avoid chilling the flame the successive turns
are spaced on all sides, and to bring the water as nearly into the
flame as possible, the diameter of the coils is chosen as small
as expedient. Further reasons for this will presently be adduced.
The type of boiler eventually adopted is shown in the accompanying
diagrams, 1 and 2, Fig. 11.

“Diagram 1, is a perspective diagram showing the plan of winding
and Diagram 2, an end view. The circulation is indicated. There are
two inner coils [p072] each containing about 17 turns, wound on a
mandrel 5 cm. in diameter. The turns are spaced so as to allow about
1 cm. clear between successive turns. The outer coil envelopes both,
and in this there are about 3 cm. between successive turns, and 8
turns in all. Length, say, 30 cm., breadth 16 cm., thickness 10 cm.,
give the external dimensions of the boiler. The shell space between
outer and inner layers of tubing must nowhere be less than 1 cm.
When so wound, the inner coils (here as in other boiler forms) raise
about 80 per cent or more of the steam; the outer or enveloping
coil, while not quite useless, make the most effective frame work
for the boiler jacket which has been devised. The coils are brazed
together by blind tubes, as shown in Diagram 2, to keep the whole in
shape. Weight with couplings and cover when complete 535 grammes.

“The cover is preferably of mica, through which the flame within
the boiler may be seen, and in which lightness, nonconduction, and
resistance to the disintegrating effects of high temperature are
met with in a pronounced degree. This jacket is held down by copper
bands and the end band is continuous with the long smoke-stack, as
will be presently shown.

“The wide form of boiler with two coils within the envelope is not
absolutely essential. The same amount of steam can be generated from
one coil in an envelope in other respects equal to Diagram 1 if a
sufficiently hot flame be passed axially through the coils. Such a
flame, however, is unstable, and for this reason two milder flames
with a good air access are to be preferred on practical grounds even
if the weight is thereby increased.

“To further understand the boiler construction it is advisable
to consider the action of the flame. Inasmuch as wide tubes must
be used, the problem of evaporating water as fast as possible
is equivalent to getting heat into the current (water and steam
circulating through the coils) as fast as possible from without.
If, therefore, ‹t› is the mean temperature of the fluids within the
coils, and ‹T› the effective temperature surrounding the tube, then
the rate at which heat will flow into the tubes is proportional to
‹T›−‹t›. Now ‹t› the temperature of the steam is nearly constant
(100°–150°) whereas ‹T› the effective flame temperature may vary
from 800° to, say, 1600°. It is for this reason that the heat
sponged up by the boiler depends almost directly on the flame
temperature.

“What conditions, therefore, will make the flame effectively hot?

“(1) The coils must obviously be brought as nearly into the flame as
feasible: for this purpose the cylindrical helix is better than any
other form. But

“(2) The turns and coils must not be so crowded together as to chill
the flame into imperfect combustion in various parts of its extent.
Hence the loose form of winding. Again

“(3) There must be oxygen enough to allow complete combustion, and

“(4) The flame itself must be hot and the radiation checked by good
jacketing.

“To take up the last points: the effective heat of the flame depends
not only on the combustion heat of the fuel used; it depends also,
among other things, on the speed with which this combustion takes
place. A flame burning from a low pressure of alcohol gas will be at
low temperature as compared with a flame burning from high pressures
of the gas. If the flame be burnt from a Bunsen burner in the usual
way it is an interesting question to know how flame temperature
will vary with gas pressure. At present we know it merely in steam
pressures incidently produced in a given engine (No. 4) as for
instance:

Flame pressure, 10 lbs., 20 lbs., 30 lbs. ┐
Steam pressure, 40 lbs., 80 lbs., 120 lbs. ┘ in the running engine.

“Unfortunately there is a limit set to this process of increasing
the steam supply, quite aside from conditions inherent in the
method. This is due to the fact that a certain speed of efflux
cannot be exceeded without putting the flame out. Suppose, for
instance, in Fig. 12, that a gas generated from a liquid is ignited
at the end of the Bunsen burner ‹F›; then if the velocity of efflux
of mixed gas and air in the direction ‹AB› from the mouth of ‹F›
exceeds the velocity of combustion in the direction ‹BA›, the flame
will obviously be carried away from the mouth of the tube and
dissipated. This state of things is actually realized at pressures
exceeding about 15 lbs., depending on the degree of mixture of
the combustible gases used, and therefore on apparently haphazard
conditions connected with the jet, the air holes, the air supply,
etc.

[Illustration: FIG. 12.]

[Illustration: FIG. 13.]

“If, however, the velocity of the jet at the point of efflux be
checked by an obstruction like a cylinder ‹C›, Fig. 13, placed
co-axially with the burner tube ‹F›, the speed of combustion will no
longer be exceeded (supposing ‹C› properly chosen) and flames will
then burn from high-pressure gas. In this way flames were maintained
generated from alcohol gas at even 40 lbs. and above.

[Illustration: FIG. 14.]

“The gas escaping from the Bunsen burner is never sufficiently
aërated to burn completely. Otherwise there would (in general) be
explosions in the tube ‹F›. A part of this air is supplied at the
mouth of the boiler ‹B›, Fig. 14, and the amount available here will
depend on the velocity of the jet ‹F›. Hence it does not follow
that a high-pressure burner like that in Fig. 11 will supply a
proportionate amount of heat, since its jet suction is not intense
and the combustion within the boiler is incomplete. This difficulty
may be remedied by placing [p074] air holes in the jacket of the
boiler, provided the boiler be wrapped loosely enough not to chill
the flame below ignition. It is with reference to this effect that
the boilers, Fig. 11, were wound. A number of rifts ‹aaa›, Fig. 15,
are then left in the jacket through which air may enter in virtue of
the burner flame acting as a jet at the mouth of the boiler.

“When so constructed the flame at first enters the inner coil only;
but after a little while it suddenly spreads out throughout the
whole interior space and envelops the coils. This sudden expansion
is due, probably, to the assumption of the spheroidal state by the
water within the coils, the current now flaring on an enveloping
cushion of steam. The pump must work well, for deficient water means
a hot tube and deficient steam, or eventually a rupture of the tube.

“Thus far the dependence for draft has been on the burner jet and
the suction of the smoke-stack in virtue of the inertia of the
moving gases. But even with this ventilated boiler, this method is
limited to certain dimensions of the boiler. Thus a boiler 80 cm.
long yielded about the same quantity of steam as a boiler half as
long and otherwise similar. Only the initial parts of the boiler
are, therefore, relatively efficient, and the reason of this seems
to be that, apart from shape, etc., the flame as a heat-producing
agent is practically defunct, when a certain amount of heat has
been taken out of it: in other words, even with fair ventilation
the flame is eventually chilled off by the voluminous products
of combustion continually accumulating in the boiler. The same
choking action accompanies the presence of unburnt gases. If, for
instance, the flame be burnt in the air, it is slender and much
smaller in volume than in the boiler. The flame is also of small
volume and burns completely in a wide boiler, but the steam is
always deficient, because of the distance between flame and coils
(see above). With the above apparatus about 1/2 lb. of dry steam per
minute per square foot of heating surface was attained.

[Illustration: FIG. 15.]

“This introduces the final condition for rapid steam generation.
There must be artificial suction at the smoke-stack. By passing the
exhaust steam in the form of a central jet through the smoke-stack
the yield of steam was increased 20 to 30 per cent. In fact as the
supply of gas from the burner is given, the artificial suction in
question means more air in the boiler for the same amount of gas
and it means also a more rapid removal of the exhaust gases. The
experiments with steam suction are yet to be completed, and with
them the boiler question is to be finally laid at rest. The chief
points at issue are these:

“1. Seeing that the jet suction increases with the length of the
smoke-stack, up to a certain length at least, how long and how wide
must the efficient smoke-stack be made? Thus a smoke-stack 10 cm.
long is all but useless. Good results are obtained when the stack
measures 30 cm. in length beyond the end of the steam jet. [p075]

“2. What is the relative efficiency of the initial and final halves
of the length of the boiler? This will show in how far it is
useful to increase the length of the boiler for a given burner and
steam jet. It will also show what advantage is to be gained from
triplicate boilers with three burners, as compared with duplicate
boilers with two burners, or single boilers with one burner, ‹when
the same weight› of tubing is used throughout.

“3. What is the effect of pressure on the aeolipile tank, or in
how far does the steam generated depend on what may be called the
pressure of the flame? This is also an important point which remains
for quantitative solution. It can be approached in two ways: either
by finding the steam evaporated in terms of the tank pressure, or by
finding the temperature of the flame pyrometrically.

“4. What speed of water circulation best conduces to steam
generation? A good pump is now installed by which the circulation
can be varied. If water can be put into the boiler just fast enough
to come out dry steam at the other end, the efficiency ought to be
a maximum, but it does not follow that it will be so, for one can
imagine a wet circulation sponging up more heat than one which is
just dry at the end.”

1895

During January and February, 1895, the experiments with boilers and
burners were continued and even better and more uniform results than
those given above were obtained. The boilers of Aerodrome No. 5 were
finally brought to such a state of efficiency, that under favorable
conditions a lift of nearly sixty per cent of the flying weight was
secured. This was much more than was required for flight, but it was
decided to postpone the trials until No. 4 could also be made ready
for a test and the frame of No. 5 could itself be strengthened in
many weak places.

Upon examining No. 4, which had been put aside since the trials in
December, it was found to have rusted so badly throughout and to be
so unfit in every way for trial, that a complete reconstruction of
the whole would be necessary. So many advantages had been gained in
No. 5 by the double midrod type of construction that it was decided
to rebuild No. 4 on a modification of the same plan, as shown in
Plate 11, retaining, however, the same engines which had been used
before.

In this a very guarded return was made to the type which had proved
so unsatisfactory in No. 0, that is, making the hull support rods at
the front and rear for attaching the wings and tail. In this case,
however, the hull was constructed very rigidly, and the tubes at the
front and rear were firmly attached and braced so that they could
withstand a considerable strain without undue distortion. The work on
this frame was completed in March, but the other parts were not in
entirely efficient condition even in May, when the aerodromes were
taken to Quantico for trial. Moreover, it was found that the weight
of this aerodrome had increased far beyond the original estimates.
[p076]

In view of the disasters from trials in the field, due to inability
to obtain automatic equilibrium in flight and to the flexure of the
large wings rather than to defects of the engines, the conditions at
this time, after three years of failure, seemed so nearly hopeless,
that without abandoning the work on these steam aerodromes, I again
had recourse to the early plan of constructing smaller models driven
by India rubber, in which the small wings employed could be made
of the requisite stiffness. Instead of employing twisted rubber,
however, the defects of which had been amply proved in previous
trials, these new constructions were meant to employ rubber directly
stretched and pulling. In this condition the rubber exercises nearly
six times the power in proportion to weight that it does when
twisted, but on the other hand it requires a very strong frame and
subordinate parts.

I spent an inordinate amount of time and labor during this year in
attempting to employ this latter form of construction and finally got
a few useful results from it, but none in proportion to the labor
expended.

During March, Aerodrome No. 5, the frame of which had proved on
test to be radically weak, was completely refinished except for
the wings. The propellers had hitherto been made of wood, but in
May, I commenced a new construction of steel, wood and cloth, on a
plan giving a figure which, though not rigorously helicoidal, was
practically near enough to the theoretical form and was also both
lighter and more elastic than the wooden construction.

On May 8 and June 7 Aerodrome No. 5 was again tried at Quantico, and
although the tests were unsuccessful, in that the aerodrome failed
to fly, partly because of the fact that so much time was spent in
raising steam that practically the entire supply of fuel and water
was exhausted before the aerodrome was actually launched, yet it had
come so much nearer flying than any machine had previously done,
that it was felt that if either the power could be increased or the
weight decreased even a slight amount, the aerodrome would probably
fly. In view of the great care that had been exercised in keeping
down the weight, it seemed almost hopeless to attempt to reduce it,
and it also seemed equally hopeless to attempt to get more power
without increasing the weight. However, something had to be done to
increase the ratio of power to weight, and as it was seen that this
would involve extensive changes in No. 5, it was decided to entirely
rebuild No. 4 with this idea in view, though it was evident that it
involved a plan of construction even lighter than the dangerously
light plan on which No. 4 had already been constructed.

During Mr. Langley’s absence in Europe in the summer, Aerodrome
No. 4 was entirely reconstructed and made to embody many new
characteristics, the changes introduced being so radical that
this model was henceforth designated as “New No. 4.” The new
characteristics of this model were its unprecedentedly [p077] light
frame and the elevation of the transverse frame 12 centimeters
above the midrod, whereby the position of the line of thrust was
raised so that it was 20 centimetres from the center of pressure,
which from theory seemed to be very nearly its correct position.
The total flying weight was but 6400 grammes (14 pounds), with a
total supporting surface of fifty-four square feet, equivalent to
very nearly four square feet per pound. It was hoped that with
this extremely light construction the “dead lift” would amount to
a large percentage of the flying weight, and as much as sixty per
cent was actually lifted on the pendulum. As, however, the aerodrome
approached completion it became more and more evident that the
construction was hopelessly fragile, the frame being scarcely able
to support itself in the shop. By November this conclusion became
certain, and this aerodrome (New No. 4) was never put to an actual
test in the field. The very expensive set of wings covered with gold
beater’s skin, which were also constructed at this time for this
model, proved so weak under test that they were entirely abandoned.

When Mr. Langley returned to Washington in the fall, many important
points, which had been under special consideration during the past
year, particularly those relating to the disposition of sustaining
surfaces, and the provision of automatic equilibrium, were still
not definitely determined. It was not yet decided whether two sets
of wings of equal area should be used for the aerodrome, or what
the efficiency per unit of area of the following surfaces was in
comparison with the leading surfaces. To aid in determining these and
other important points concerning the relative position of the center
of gravity and the center of pressure in the horizontal planes, he
had several small gliding models made, which could be used with
either one or two pairs of wings, and afforded an opportunity for
testing and comparing several types of curved surfaces.

These models were built so that the center of gravity could be
adjusted to any desired point, and had in addition, as a means of
assisting in preserving equilibrium, a small tail-rudder, shaped
somewhat like a child’s dart, which was intended to support no part
of the weight.

The tests with these models were very satisfactory and aided greatly
in the final development of what is known as the “Langley type.”
Indeed, in the single month of November all the points, which had
hitherto been more or less indefinite, were finally decided upon, and
the tests of the following spring proved these decisions correct.

Two sets of wings of equal area were hereafter provided for every
aerodrome, which not only greatly increased the stability, but also
overcame the difficulty hitherto experienced in bringing the ‹CP›
over the ‹CG›. The tail-rudder, formed of planes intersecting at
right angles, was adopted as the means of control. In use on the
aerodromes it was set at a negative angle, and given a certain [p078]
degree of elasticity, which was at first provided in the frame of
the rudder, but was later given by a flat wooden spring, by which it
was attached to the aerodrome. The tail in this form now became the
sole means of controlling the equilibrium, and the results obtained
with it were so very satisfactory that no further attention was given
either to the gyroscopic control built during the previous summer, or
to any of the electrical forms of control constructed prior to that
time, all of which involved more or less delicate apparatus.

The definite form into which these ideas crystallized is perhaps best
exemplified in the letter of instructions issued by Mr. Langley on
November 30, 1895 to the men employed on the work. The text of this
letter is given in the Appendix, and the forms referred to in it for
recording the weights and adjustments of the aerodromes are those
used in the data sheets after this time.

In October work was resumed on Aerodrome No. 5, on which nothing had
been done since its test on June 7. The reconstruction of “Old No.
4” into “New No. 4” which had occupied the entire summer, and the
final result of which was the production of a machine so radically
weak as to be useless, had been so discouraging that it seemed vain
to attempt in any way to decrease the weight of No. 5. The addition
of the rear wings in place of the tail had, however, so greatly
increased the supporting surface that it seemed possible that No. 5
might now be able to fly with no greater engine power than it had on
June 7. Some weak places in its frame were, therefore, strengthened
and the midrod at the front was raised five centimetres in order to
raise the center of pressure farther above the center of gravity
and give the front wings a greater range of adjustment. Some slight
changes were also made in the gearing which drove the pump, so as
to make it work faster, and new burners, boilers and a gasoline
tank were constructed during November. Later the midrod, which had
formerly consisted of two separate pieces attached at the front
and rear respectively of the main frame, was made continuous, and
in order to avoid passing it through the smoke-stack, the stack
was made to fork at this point. These changes are clearly shown in
Plates 14 and 15, which are photographs taken on December 3. This
plan was, however, soon changed so that the midrod passed through the
smoke-stack and was rigidly attached to the frame at several points,
and a new pump and new boilers were substituted for those which had
been worn out. Aside from these changes, which although small, added
very materially to the general strength of the frame, no important
changes were made in No. 5 prior to its remarkable flight of May 6,
1896.

[Illustration: PL. 14

AERODROME NO. 5, DECEMBER 3, 1895. PLAN VIEW. RUDDER REMOVED]

[Illustration: PL. 15

AERODROME NO. 5, DECEMBER 3, 1895. SIDE VIEW]

While these changes were being made in No. 5, similar ones were
also being carried out in New No. 4, and the addition of the rear
wings to No. 4, together with other slight changes, made it such a
distinctively different machine from what it had been, that it was
now designated as No. 6. After making extensive [p079] repairs
to the extremely light frame of No. 6 (formerly New No. 4) it was
thought to be in suitable condition for flight and was accordingly
boxed preparatory to sending it to Quantico.

The year, therefore, closed with No. 6 apparently in condition for
test, but it was decided not to take it to Quantico until No. 5,
which was still undergoing repairs, could also be got ready.

1896

A few days after the beginning of the new year, while the repairs on
No. 5 were being completed, it was decided that the frame of No. 6
which had been boxed ready to be carried into the field for trial,
was so weak that before putting it to an actual test in flight it
would be best to make some tests on the strength of its frame. While
testing the frame for torsional strength, it broke under the moderate
test of a weight of 500 grammes placed at the tips of the wings, the
angle of deflection just prior to its breaking being 35°, while the
frame of Old No. 4 in March, 1895, had shown a deflection of only
10.5° under a similar test. This breaking of the frame showed very
plainly that the worst fears in regard to it had been realized and
that by some means or other the frame must be strengthened. This was
finally accomplished by making the midrod continuous through the
smoke-stack as had already been done in No. 5, and at the same time
an additional improvement was made in the means of attaching the
Pénaud tail, whereby it was lowered in order to give it a greater
clearance in passing under the launching car in actual test. Later
the boilers proved defective and new ones were substituted, but
except for some minute details no further changes were made in
Aerodrome No. 6 prior to its test in May.

On May 6, No. 6 was unsuccessfully tried at Quantico just prior to
the very successful test of No. 5. In this test no serious damage
was done to the frame, but before going to Europe in the summer, Mr.
Langley ordered that both aerodromes be completely overhauled and put
in condition for further experiments in the fall. In this remodelling
practically no changes were introduced in the frame of either No. 5
or No. 6, but the engines of No. 6 were refitted and a new boiler was
substituted, which, with slight improvements in the burner, resulted
in a somewhat increased power in the engines.

A complete description, giving all essential details of both
Aerodromes Nos. 5 and 6, will be found in Chapter X.

[p080]

CHAPTER VIII
HISTORY OF CONSTRUCTION OF SUSTAINING AND GUIDING SURFACES
OF AERODROMES 4, 5 AND 6

INTRODUCTION

In some early experiments in 1887 with the small models without motor
power, which have not been particularly described, two pairs of
wings, in the same plane, were employed for reasons connected with
stability. Afterward, in many of the rubber-driven motor models,
which have been described in Chapter II, two large front wings
were employed and the following pair were diminished into what may
properly be called a tail. This plan was a retrogression in design,
and it was pursued by the writer with a pertinacity which was not
justified by the results obtained, being used even on the early
rubber-driven models.

In this construction, it will be observed that the flat tail was
in fact not only a guiding but a sustaining surface, since it bore
its own share of the weight. It was not until a much later date
(November, 1895) that the writer returned to his earlier construction
of two pairs of wings in the same plane bearing the whole weight of
the aerodrome, to which was now added a flat tail, whose function
was not to support, but wholly to guide. This was developed into the
final construction by the addition of a vertical rudder or rudders.

The present chapter is not concerned with the history of the earlier
attempts with small models, or of those numerous constructions of
sustaining surfaces which were never put to actual trial; nor does it
give any description of the experiments which were made in placing
one set of surfaces over the other, according to a method suggested
in “Experiments in Aerodynamics.”[27]

The experiments in “Aerodynamics,” and the theoretical considerations
given in Chapter V on sustaining surfaces, would never alone have led
to the construction which was finally reached, which was largely due
to the hard lessons taught by incessant accident and failure in the
field. The present chapter, therefore, should be read in connection
not only with the pages of “Aerodynamics,” but with Chapters V and IX
of this book.

[Illustration: PL. 16

EARLY TYPES OF WINGS AND SYSTEMS OF GUYING]

It is to be remembered that, while the center of gravity of the
aerodrome could be determined readily and exactly, the center of
pressure could be determined only approximately in advance of trial
in actual flight. The positions [p081] of the supporting surfaces
given in this chapter are, then, approximations made from rules for
“balancing,” ‹i. e.›, for obtaining equilibrium in actual flight,
rules which are in fact tentative, since they are founded on ‹a
priori› considerations with partial correction from the empirical
knowledge gained by previous field trials. For these rules see
Chapter VI.

1893

With reference to the supporting and guiding surfaces of Aerodromes
Nos. 4, 5, and 6, Aerodrome No. 4, in its earliest condition
mentioned in the preceding chapter, was taken into the field, but
never brought to trial in the air. It is sufficient to say that in
the largest of the three sets of wings constructed, each wing was
17×51 inches, and therefore contained about six square feet, so that
with the tail (which was at this time a supporting surface), whose
area was one-half that of the two wings, the total supporting surface
was 18 square feet, or since the flying weight was 9.1 pounds, the
proportion of surface to weight was somewhat less than 2 square feet
to the pound. The wings were at this time ribless, it being expected
that the silk cover which was purposely left loose would take its
curve from the air filling it, which subsequent experience has
shown would have led to certain disaster if the aerodrome had been
launched. It may be added that there was a vertical rudder of what is
now seen to have been a wholly inadequate size. These remarks may be
applied with little modification to the attempted flight with No. 4
on May 25, except that the vertical rudder had been made larger, but
was still much too small.

1894

From the account of the field trials to be given in Chapter IX, it
will be seen that in numerous attempts at flight prior to October
6, 1894, the cause of failure can in every instance be traced to
imperfections more fundamental than those of the sustaining surfaces,
either the launching device or some other part failing to work
satisfactorily. I therefore commence a description of the sustaining
surfaces with those of Nos. 4 and 5 as used on that day.

The construction of the wings of No. 4 and No. 5, which were nearly
identical, is shown in Fig. ‹A› Plate 16. A rod of hickory, tapering
from 1/2 inch in diameter at the larger end to 1/4 inch at the
smaller, was steamed and bent, as shown in the drawing, to form the
main front rib of the wing. This was firmly clamped to the midrod,
and to the rib in turn were attached a number of cross-ribs of
hickory, slightly curved, the inner one of which was fastened to the
hull at its inner extremity, while the whole was covered with silk.
The length of each wing was 162 cm. (63.75 inches), and the width
54 cm. (21.25 inches). The tail was plane and equal in area to one
of the wings, so that the joint area of the wings and tail was 2.62
square metres (28.2 sq. ft.). [p082]

Each wing was attached to the midrod by a single clamp, different
forms of which are shown at ‹F›, ‹G›, ‹H›, ‹I› (Fig. 16). The clamp
consisted of two short split tubes, into which the main front ribs
were securely clamped by means of screws. They were set at an angle
and united to a grooved frame, by which the wings could be readily
attached to a second piece clamped about the midrod. The tail clamp,
like the wing clamp, was composed of two pieces, sliding one upon
the other, but as the tail formed a single surface, one part was
permanently attached to it. Clamps ‹F›, ‹G› were fitted to aerodrome
No. 4, and ‹H›, ‹I› to No. 5. The wings were set at a diedral angle
of about 150°, but as they were not guyed in any way, this angle in
flight and under the upward pressure of the air probably became much
less. The tail was plane but ribbed like the wings.

[Illustration: FIG. 16. Wing clamps, 1892–1896.]

In preparing the machine for flight, the wings and tail of No. 4 were
set at a very small root angle with the midrod, perhaps not exceeding
3°, but while this angle might be maintained at the firmly held root
of the wing, it was later seen to be probable that the extremity
of the wing was flexed by the upward pressure of the air after
launching, though the full extent and evil effect of this flexure
was not recognized at the time. In the approximative calculations
for “balance,” made at this time, the tail was treated as bearing
1/3 of the weight of the aerodrome, as it was 1/3 of the supporting
area, for though it was recognized that its position in the “lee” of
the wings rendered it less efficient, the degree of this diminution
of efficiency was not realized. A vertical rudder 20 cm.×70 cm. (8
in.×28 in.), with an area of 0.14 metres (1.5 sq. ft.) was used.
[p083]

The particulars of the launch will be found in Chapter IX. In the
present connection, it is sufficient to say that though launched with
the requisite velocity and without accident, it fell into the water
at a distance of about 15 metres (49 feet) with the midrod nearly
horizontal, the combined effect of engines and initial impulse having
in fact kept it in the air for less than two seconds. The true cause
of this failure not then being recognized, it was attributed to the
angle of the wings with the midrod having been too small.

The launch of No. 5 followed almost immediately, but taking warning
by the supposed cause of failure of No. 4, its wings were set at
a root angle of 20°, and a hurried adjustment was made to secure
greater rigidity, the tip being partly secured against twisting by
a light cross-piece, and guyed so that the wing as a whole was not
only at a greater angle, but stiffer than in the case of No. 4.
These changes it was hoped would cause the aerodrome to advance at a
considerable initial angle with the horizontal, and it did so, for
instantly after the launch, as the aerodrome escaped from its bonds
into free air, the inclination of the midrod increased until it stood
at about 60°, when the machine, after struggling a moment to maintain
itself, slid ‹backward› into the water (with its engines working at
full speed) after advancing about 12 metres (39 feet), and remaining
in the air about 3 seconds.

On the whole, the result of the first actual trial of an aerodrome
in the field was disconcerting, for unless the result was due to the
wings being placed in a position wholly unfavorable to support, there
seemed to be no doubt that either the engine power or the supporting
surface was insufficient. Now this engine power was by computation
between three and four times what was necessary to support the
aerodrome in horizontal flight at an angle of 20°, and after making
every allowance for slip, there should have been still an excess of
power for the first flight of No. 4, whereas actual trial indicated
that it was insufficient. But on the other hand, the experiment with
No. 5, which momentarily held its position in the air at an angle of
60°, seemed to indicate that the engine power was abundant, and that
the failure must be traced to some other cause.

As a result of these experiments it was concluded, “that it is
an all-important thing that the angle of the front wing shall be
correct, and that this cannot be calculated unless it is known how
much the tip will turn up under pressure of the weight.” I felt,
then, that I had learned something from the failures as to the
need of greater rigidity of the wings, though how to obtain this
without adding to their weight was a trying problem. It was thus
at an early stage suspected that the evil to be guarded against in
wing construction was the distortion of the form of the wing under
pressure, chiefly by torsion, which is specially hard to provide
against without a construction which is [p084] necessarily heavy.
This suspicion was a correct one, though the full extent of the evil
was not yet surmised.

In the light of subsequent experiment it may now be confidently
stated that the trouble was with the wings, which at the moment
after launching were flexed wholly out of the shape which they were
designed to have, and which they retained up to that critical moment.

After returning to Washington, one of the wings was inverted, and a
quantity of sand, equal in weight to the pressure upon the wing in
flight, was added, under which the yielding at the tip amounted to
65°, or from +20° to −45°, showing that the wings were entirely too
weak to sustain the aerodrome.

In speaking of the efforts to strengthen the wings, it must be
constantly remembered that this could hardly be done in any way which
did not involve increased weight; that is, it could hardly be done at
all, since increased weight was forbidden.

The first attempt at systematic guying was made on October 27. As
shown in Fig. ‹B›, Plate 16, two guy-posts extending beneath the
midrod were connected by guy-wires with the outer extremities of
the wing, by means of which it was sought to hold the wing in place
and prevent its extremity from twisting upward, while a third wire
connecting with the bowsprit prevented its moving backward. In
addition, two aluminum wires, stretched across above from wing to
wing, kept the lower guys tight.

On October 27, Aerodrome No. 5, equipped with large new wings and
tail, having a combined area of 3.7 square metres (40 sq. ft.), the
wings being each 64 cm.×192 cm. (25.25 in.×75.75 in.), turned sharply
and completely round, apparently through some internal current of
the main wind against which it was advancing. Owing to this almost
instantaneous turn, it lost headway and came down. This led to the
subsequent construction and use of a much larger vertical rudder,
intended to prevent in future any such sudden pivoting and consequent
loss of momentum. The wings showed a tendency to “pocket”[28] and
bag, which indicated some serious fault in their construction.

As a result of these experiments, it was decided on October 29 to
attempt to make the wings stiffer (though their weight was almost
prohibitory), by inserting more cross-pieces, cross-pinning and
guying them so as to make them more rigid as a whole, and less liable
to pocket.

At this time an automatic device in the form of a sliding tail was
designed, which it was thought would cause the center of pressure to
move backward when the aerodrome reared, and forward when it plunged
downward, but the device, though afterward constructed, was never
brought to trial in the field.

Aerodrome No. 5, equipped with a new set of wings similar to those
used [p085] on October 27, and guyed as in the previous experiment,
was again launched on November 21, with the results recorded in
Chapter IX. The failure was attributed to the twisting of the wings
under pressure to such an extent that not only was their effective
area greatly reduced, but the outer portions were upturned so as to
catch the air upon the upper surfaces, the result being in part a
downward pressure.

On the following day a pair of the wings was inverted and a weight
of sand equal to the air pressure to which they were subjected in
flight, was distributed over their surfaces. Under the action of
this, the twisting of the wing was seen to increase from the root,
which was held with comparative rigidity, up to the tip, where in
spite of the cross-ribs it amounted to 45°. The resistance to torsion
lay chiefly in the front rib, which, in addition, could be bent
easily, allowing the surface to become distorted with great loss of
lifting power.

The experiments of 1894 had demonstrated the urgent necessity
for greater rigidity in the sustaining surfaces, which might, as
it seemed, be obtained either by increasing the strength of the
framing (which meant additional weight) or by resorting to some new
and untried construction, or by a proper system of guying. Guying
seemingly offered the most feasible solution of the problem; but
although the system of wire guying was thoroughly tried, the result
was very unsatisfactory, as the wings continued to twist and bag in a
way that was extremely discouraging.

1895

I accordingly had recourse in 1895 to the system of wooden guy-sticks
shown in Fig. ‹D›, Plate 16, which necessarily added greatly to
the weight of the sustaining surfaces. Each wing was separately
strengthened by means of a light rod of spruce, in cross-section
about the size of the main front rib, extending across the upper
surface of the wing, at a distance of about one-third the width of
the wing behind the front rib. It was tied to each of the cross-ribs
and to the outer bent portion of the front rib, and at its root was
fastened to the frame of the aerodrome.

This effectually prevented the bending of the front rib and the
consequent bagging of the cover, and to that extent marked a decided
advance in wing construction. But it was faulty, in that, not being
supplemented by wire guying, it offered little resistance to the
twisting of the wing about the main front rib, the rear tip of the
wing being free to turn up under pressure, as it had done on former
occasions. A similar guy-stick was stretched across the tail. To
guard against torsion, rods extending diagonally across the wings and
tail were used, which, with the aid of the guy-sticks just described,
prevented the surfaces from twisting greatly. In addition, a rod
joining the front ribs and stretching across from wing to wing tended
to maintain a fixed diedral angle. [p086]

The wings as thus guyed were rigid enough, and in the field-trials of
No. 5 on May 8 and June 6, did not yield noticeably under pressure,
and there seemed to be no serious default in their lifting power, but
the guy-sticks were heavy and the system was not again employed. The
wings used in these trials, shown in Fig. ‹C›, Plate 16, had a frame
of hickory, consisting of a front rib and nine cross-ribs, over which
the silk was tightly stretched. The curvature of the wings, which is
shown in the cross-sectional drawing, had a rise of about one-twelfth
the width, the highest point of curvature occurring about one-fourth
the distance from front to rear. Each wing was 64 cm.×192 cm. (25.25
in.×75.75 in.), the two with the tail, in surface equal to a single
wing, having an area of 3.7 square metres (40 sq. ft.). The combined
weight of the wings was 1150 grammes (2.53 pounds), and of the tail,
583 grammes (1.28 pounds).

The evolution of a vertical rudder had meanwhile been going steadily
forward. Those first used had been small, rectangular, stiff, and
heavy, but in the experiments of May 8 a much lighter and larger
construction, consisting of a frame 92 cm.×76 cm. (36 in.×30 in.)
covered with paper, was used, and on June 7 this was replaced by a
long, diamond-shaped rudder, having a spruce frame covered with silk,
very light and seemingly more effective than any hitherto used.

I had in the meantime designed a “tail-rudder,” consisting of a
horizontal tail and vertical rudder combined, each having an area of
about 0.6 square metres (6.5 sq. ft.) which, however, was not used
until 1896.

In August was begun the construction of a deeply curved and arched
pair of wings for No. 4, which consisted of a light framing of
spruce elaborately guyed and covered with gold-beater’s skin drawn
tight as a drum-head with pyroxelene varnish. In their construction
a new feature, foreshadowed in the method of guying the separate
wings used in the field-trials of May and June, was introduced,
which was adopted in all subsequent constructions--the guy-stick,
previously described as stretching lengthwise across the wing being
now made a part of the wing itself, which was thus provided with
two longitudinal ribs instead of one. The additional rib occupied a
central position, and like the front rib was attached to the midrod
by means of a strong wing clamp. Its outer end was united to the
front rib, which was here bent into a quadrant of a circle. This pair
of wings had an expanse of 435 cm. (14.3 feet), an area of 2.5 square
metres (26.8 sq. ft.), a weight of 660 grammes (1.45 pounds), and a
depth of curvature equal to one-tenth their width.

This construction offered a two-fold advantage in its resistance
to both torsion and bagging, for as the pressures upon the wing
were nearly balanced about the middle rib, the tendency to twist
was reduced to a minimum, while the bagging, which results from the
bending of the framework, as distinct from [p087] its twisting, was
greatly reduced by the manner in which the frame was put together,
the whole construction permitting a return to the system of wire
guying at first adopted, which had been found inapplicable to a wing
having but a single longitudinal rib forming its front margin. When
completed, the wings were strongly guyed with piano wire, both above
and below, to guy-posts attached to the midrod, and each cross-rib
was separately guyed with wire chords. Although these wings had cost
much in time and labor, and contained many points of improvement,
they were eventually found to be too weak to support the aerodrome,
and were therefore abandoned without a trial in the field.

For the plane horizontal tail hitherto used a pair of curved wings
was substituted, similar in all respects to those just described, but
having only half their area, and these were later replaced by a pair
equal in size and in every way the counterpart of the front wings.
The tail as hitherto used accordingly disappeared, and gave place
to another having a wholly different function to perform; for while
the old tail, like the rear pair of wings which superseded it, was
intended to bear a definite part of the weight of the aerodrome, the
new tail which was now added behind the rear pair of wings was not
supposed to bear any part whatever of the weight, but to act solely
as a guide, and this new feature, first introduced in October, 1895,
was continued to the end.

This arrangement of the surfaces is quite different from that adopted
by Pénaud in 1872, in which the tail became automatic in its action
through its small angle of elevation as compared with that of the
wings, while still acting as a supporting surface, whereas in the
present arrangement the function of the tail was solely one of
guidance. This, I believe, was one of the important changes which
perhaps as much as any other led to final success.

During the fall of 1895 a large number of experiments were made both
in free flight with gliding models, and in constrained flight with
the whirling-table, to determine the relative lifting power of the
front and rear wings per unit of area, and from these the following
new rules were deduced for finding the center of pressure:

If a following wing is the size of the leader, assume that its
efficiency is 66 per cent per unit of surface.

If it is half the size of the leader, assume that its efficiency is
50 per cent per unit of surface.

If it is half as large again as the leader, assume that its
efficiency is 80 per cent per unit of surface.

For intermediate sizes of surface, proportionate values per unit of
surface may be assumed.

If we consider the area of the front wing to be unity, and that of
the rear wing to be ‹n›, and if ‹m› be the efficiency of the rear
wing per unit of surface, [p088] the above is expressed in the
following formulæ, which it will be remembered take account only of
wings following each other in the same or nearly the same plane,
and are not applicable where one wing is either above or below the
plane of the other. In the formulæ, ‹CP› is the resultant center
of pressure upon both wings expressed in the notation described in
Chapter II, ‹CP›_{fw} is the center of pressure of the front wings,
and ‹CP›_{rw} the center of pressure of the rear wings.

If the value of ‹n› lie between one-half and unity,

‹n› + 1
‹m› = -------;
3

while if the value of ‹n› lie between unity and 1-1/2,

6 + 4‹n›
‹m› = --------- .
15.

In either case

‹CP›_{fw} + ‹mn›‹CP›_{rw}
‹CP› = ---------------------- ;
1 + ‹mn›

where the leading and following wings are equal

3‹CP›_{fw} + 2‹CP›_{rw}
‹n› = 1, ‹m› = 2/3 and ‹CP› = ----------------------- .
5

The steady flight of one of the gliding models referred to led to
the construction of a new set of wings for No. 5, patterned after
those used on the gliding model. These wings, shown in Plate 17, were
rectangular in outline, 200 cm.×80 cm. (6.56 ft.×2.62 ft.), each
wing having an area of 1.6 square metres (17.1 sq. ft.) They were
constructed with spruce framing covered with China silk, and were
strongly guyed with piano wire in much the same manner as the light,
skin-covered wings already described, which had preceded them. The
combined weight of the two pair was 1950 grammes (4.3 pounds).

The long central rib was now much the larger of the two which, as
in the preceding wing, formed the foundation of the structure. It
occupied a position two-fifths the distance from front to rear, and
presumably coincided at all points with the center of pressure of
fore and aft sections of the wings, so that the pressure in front of
the rib was at all points balanced by the pressure in the rear, and
there was consequently little tendency in the wing to twist under
pressure of the wind. The two main ribs were rigidly connected by
cross-ribs of spruce, 20 cm. (8 inches) apart, steamed and bent to
the desired form. The curvature of these ribs was the same for all,
and in depth was one-twelfth the width of the wing, while the highest
point of curvature was one-sixth of the distance from front to rear,
these ratios having been chosen as approximating those found in the
wing of the soaring bird. These wings were subsequently used in the
first successful flights of the following year.

[Illustration: PL. 17

AERODROME NO. 5. PLAN OF WINGS AND SYSTEM OF GUYING]

[p089]

During the year 1895 but two field-trials were made with the steam
aerodromes, and neither of these was successful; but a great step
forward had been taken in the construction, guying and arrangement
of the sustaining surfaces. The wings had been made stronger with
no increase in weight per unit of area. On the contrary, the ratio
of weight of sustaining surfaces to area had been actually reduced
from 43 to 28 grammes per square foot, so that the surfaces were both
lighter and stronger.

Two longitudinal ribs had taken the place of the single one before
used, a second wing clamp had been added to correspond to the midrib,
the difficult problem of torsion had been effectually solved, the
system of guying greatly improved, and it appeared that in the next
trial the wings might be expected to bear the weight of the aerodrome
without serious distortion.

1896

In January, 1896, two new pairs of wings were designed for No. 6,
and in order to give a greater efficiency to the rear wings, they
were made larger than the front ones, the area of the latter being 22
square feet, and of the former 27 square feet, and whereas the width
of each wing had formerly been one-third of its length, it was now
increased to two-fifths to correspond to those of No. 5.

The progress made in construction and guying is shown by the fact
that when on January 28 one pair of the wings of No. 5 was inverted
and sanded, the yielding at the tip was less than 5° greater than at
the root, whereas at one time it had been 65°. A similar test applied
to a pair of wings of No. 6 on March 4 gave even better results, as
the yield at the root was but 1° 45′, and at the tip 2° 30′.

The successive stages of the development of the wing clamps are shown
in Fig. 16. In its final form the front wing clamp, or that which
held the main front rib, shown at ‹AB› (1896), had adjustable sliding
pieces, by means of which the wings could be set at any desired angle
of elevation, the wing as a whole revolving about the rear wing
clamp, shown at ‹CD› (1896).

The general system of guying the wings, as shown in Plate 17, had
been greatly improved. In the present form a bowsprit and guy-posts
firmly attached to the midrod furnished points of attachment for
the piano wires with which the wings were guyed and held rigidly in
place, other wires being stretched across from wing to wing so as to
maintain them at a constant diedral angle of about 150°. The clamps
by which the guy-posts were attached to the midrod, are shown at ‹EF›
(Fig. 16).

In the successful flights of No. 5 on May 6, the completed wings
already described weighed together 1950 grammes (4.29 pounds), and
had a total sustaining area of 6.4 square metres (68.8 square feet),
the flying weight of the [p090] aerodrome was 11,775 grammes (26
pounds), and the sustaining surfaces therefore amounted to 2.6 square
feet to the pound, which, as the event proved, was amply sufficient.

The “tail-rudder,” shown in Plate 17, comprised a vertical and
horizontal surface of silk intersecting in a central rod or axis,
having a length of 115 cm. (3.8 feet). The framing was of spruce and
consisted of two sets of four arms, each radiating from the central
rod, the hexagonal outline of the surfaces being formed of piano
wire, over which the silk was drawn and sewed. The area of each
surface was about 0.6 square metres (6.45 square feet), and the total
weight was 371 grammes (0.8 pounds).

A flat steel spring inserted in the forward end between the rudder
and the midrod gave it a certain desirable degree of elasticity in
a vertical direction. The rudder was held in place by a pin passing
through the midrod, and was so set as to coincide with the line of
direct flight, its purpose, as already explained, being to guide the
aerodrome, but to take no part in its sustention.

In balancing Aerodrome No. 5 on May 6, the wings were so adjusted
that in accordance with the notation given above, p. 15:

‹CP›_{fw} = 1575

‹CP›_{rw} = 1415.5;

and as the wings were of equal size, from what has preceded in the
present

3‹CP›_{fw} + 2‹CP›_{rw}
‹CP›_1 = ------------------------------ = 1501.2.
5

The center of gravity was located at 1497, so that there should have
been a very slight tendency on the part of the aerodrome to rise, as
was actually the case. The formula was perhaps not quite so accurate
as the prolonged flight of the aerodrome would seem to indicate, as
it takes no account of the thrust of the propellers, which in action
tended to elevate the aerodrome in front while their resistance
would tend to depress it when they had ceased to revolve, which
consideration accounts for the action of the aerodrome on May 6, as
described in Chapter IX. The formula may, however, be regarded as
approximately correct.

In the final successful trial with No. 6 on November 28, 1896, the
wings used were similar in general construction and manner of guying
to those of No. 5 on May 6, but, as shown in the photograph (Plate
29A, Chapter X), the front rib at its outer extremity was bent to a
quadrant to connect with the midrib, this construction being somewhat
stronger than that adopted in the wings of No. 5. The curvature was
but one-eighteenth of the width of the wing instead of one-twelfth as
in No. 5. The front and rear pairs were similar and equal and had a
combined area of 5 square metres (54 sq. ft.), and a weight of 2154
grammes [p091] (4.74 lbs.). The flying weight of the aerodrome was
12,120 grammes (26.7 lbs.), the sustaining surface thus amounting to
slightly more than 2 square feet to the pound.

The position of the wings, in accordance with the notation adopted,
was

‹CP›_{fw} = 1563.2,

‹CP›_{rw} = 1374.

Since the wings were equal in size,

3‹CP›_{fw} + 2‹CP›_{rw}
‹CP›_1 = ----------------------------- = 1487.5.
5

The center of gravity was located at 1484, which was 3.5 cm. in
the rear of the center of pressure. The flight was approximately
horizontal, and the setting seems to have been as accurate as could
be desired. The angle of elevation of the wings at the root was 10°
30′, and so well were they guyed that there was no visible yielding
at any point during the flight. As the midrod during flight was
approximately horizontal the angle of elevation of the wings may be
taken as 10° 30′; the efficiency of the rear wings was two-thirds
that of the front wings, and the effective area was therefore
27+27×2/3 = 45 square feet.

The wings being very nearly plane we have therefore the data for
determining the soaring speed from the formula of “Aerodynamics”
(Chapter VI, p. 60).

‹W› = ‹P›_α cos α = ‹k›‹A›‹V›^2‹F›(α) cos α,

in which ‹W› = 26.7 pounds; A = 45 sq. ft.; ‹k› = 0.00166; α = 10°
30′; ‹F› (α) cos α = 0.353. By substituting these values in the
formula we obtain ‹V› = 32 feet per second.

The speed actually attained, however, was about 30 miles an hour,
or 44 feet per second, which seems to indicate that the angle of
elevation under pressure was reduced to much less than 10° 30′. For a
velocity of 44 feet per second, the theoretical value of α would be
but 6°. In this calculation, however, the hull resistance and that of
the system of guy-wires, which must have been comparatively large,
has been omitted. It would appear, therefore, that the actual results
obtainable in flight are much more favorable than calculations based
on experimental data would presuppose.

[p092]

CHAPTER IX
HISTORY OF LAUNCHING APPARATUS AND FIELD-TRIALS OF
AERODROMES 4, 5 AND 6

LAUNCHING APPARATUS

I have elsewhere mentioned that the difficulties of launching even
a very small model aerodrome are considerable. Early experiments
were tried with an apparatus something like a gigantic cross-bow,
and in later years with various forms of pendulum, all of which
latter brought out the inherent theoretical defect of the movement of
rotation of the aerodrome, and were otherwise practically inefficient.

A device, consisting of two pendulums, one behind the other,
connected by a rigid rod, from which the aerodrome could be
suspended and cast off without rotation, was at one time considered,
but abandoned. Experiments were also made with several forms of
railroad, upon which the aerodrome was to run up to the moment of
release, before the form of launching apparatus, which finally proved
successful, was adopted.

All these had failed chiefly for two reasons; first, it was difficult
to cause the aerodrome to be released just at the moment it attained
sufficient speed to soar; second, the extensive surface presented to
the wind by the wings of the aerodrome, made it necessary to provide
means for holding the machine securely at several points up to the
moment of release without danger of interfering in any way with
the aerodrome when it was cast into the air. This proved a serious
problem, which can be appreciated only by one who has seen such a
machine in the open air, where its wings are subject to movement
and distortion by the slightest breeze. The steps by which these
difficulties were removed and the final type of launching apparatus
perfected are recorded in the following pages in connection with the
field-trials of the model aerodromes.

1892

As the end of the year 1892 approached and with it the completion of
an aerodrome of large size which had to be started upon its flight in
some way, the method and place of launching it pressed for decision.
One thing at least seemed clear. In the present stage of experiment,
it was desirable that the aerodrome should-—if it must fall-—fall
into water where it would suffer little injury and be readily
recovered, rather than anywhere on land, where it would almost
certainly be badly damaged. [p093]

The shores of the Potomac on both banks were scrutinized for this
purpose, from a point about two miles above Washington to below
Chopawamsic Island, some thirty miles below the city. Several lofty
and secluded positions were found, but in all these there was the
danger that the aerodrome might be wrecked before reaching the
water, or, turning in its course, fly inland; but more than this, it
could be launched only on the rare occasions when the exact wind was
blowing which the local conditions demanded.

Finally, the idea, which seems obvious enough when stated, presented
itself of building a kind of house-boat, not to get up initial motion
by the boat’s own velocity, but to furnish an elevated platform,
which could be placed in the midst of a considerable expanse of
water, if desired, under conditions which admitted of turning in the
direction of the wind, as it need hardly be repeated that it was
indispensable to the machine, as it is to the bird, to rise in the
face of a wind, if there be any wind at all.

The house-boat in question was nothing more than a scow about 30 feet
long by 12 feet wide, upon which a small house was erected, to be
used for the occasional storing of the aerodromes. On account of the
accidents which were certain to occur in the first attempts, it was
fitted up with the means of making small repairs. On the roof of the
house there was a platform upon which the operator stood when making
a launch, and upon which were mounted the launching devices hereafter
described.

This boat, shown in Plate 18, was completed in November, 1892.

1893

By the kindness of the Superintendent of the Coast Survey, the
house-boat was towed in May, 1893, down to Chopawamsic Island, a
small island near the western bank of the Potomac River, not far from
the Quantico station of the Washington and Richmond Railroad Company.
A map of the island and the adjacent land and water is shown in Plate
19.

The house-boat was at all times moored somewhere on the west side of
the island, in the stretch of quiet water between that and the west
shore of the river. The waters shown here are, with the exception of
a narrow channel, very shallow, and, indeed, partly dry at low tide,
so that there was no danger of an aerodrome being lost, unless its
flight carried it a long distance away and over the land.

FIELD TRIALS[29]

Aerodrome No. 4, as shown in Plate 11, had a single midrod, a flying
weight of 9 pounds,[30] and supporting surface, consisting of wings
and tail, of 18 square feet. [p094] Its engines, with about 100
pounds pressure, developed an aggregate of 0.4 H. P., and lifted 50
per cent of the flying weight. The propellers were 60 cm. (2 feet) in
diameter and 1-1/4 pitch ratio.

The aerodrome was intended to be launched by a contrivance called the
“starter,” which was an inclined rod, hinged at the bottom, on the
top of which the aerodrome was supported on a rod which was thrown
down at the instant of flight, giving the aerodrome a slight forward
impulse, with the expectation that it would get up sufficient initial
speed to soar from the action of its propellers.

On November 18 the writer (L), with Dr. Barus (B) and the two
mechanics (R and M), went to Quantico by an early train, and
superintended with interested expectation the arrangements for this
first trial in the open air of the mechanism which had now been over
two years in preparation.

We met with an unexpected difficulty—that of launching the aerodrome
at all, for though the wind was only a very gentle breeze, it was
only by holding it down with the hands that it was possible to keep
the aerodrome in position for the launch, during the few minutes
which passed from the time it was placed upon the apparatus to the
time of releasing it. Whether the launching device itself might be
effective or not could not be ascertained, since it was found that
nothing which could even be called an attempt to launch could be made
except in an absolute calm; a condition of things very difficult for
any one to understand who has not passed through the experience. The
writer returned to Washington at the close of the day without having
done anything, but having learned a great deal.

November 20. L, with B and M, came down again, and waited until 4.20,
when, the breeze having fallen to almost a calm, the aerodrome was
maintained in place on the launching apparatus with great difficulty,
while it was repeatedly set on fire by the scattering liquid fuel.
Finally it was let go, and fell close to the house-boat, the tail
striking the edge of the platform. The immediate cause of failure was
the defective launching apparatus, for the design of which the writer
felt himself responsible.

November 24. L, with B, M, and R came down again to Quantico, but the
very moderate wind proved completely prohibitory to any attempt at
launching, and all returned again to Washington.

November 27. L, with B and M, came down to try a new launching
apparatus, not different in principle from the preceding one, but
of better construction. The morning was exceptionally calm, but the
engines were found to be out of order, and precious time was spent
in slight repairs which should have been made in the shop. At 3.30
p. m., when the engines were at last ready, the exceptional calm
gave place to a very gentle and almost imperceptible breeze, [p095]
which, nevertheless, again proved prohibitory to the launching, and
with extreme disappointment the party returned to Washington, it
being at last fully recognized that unless some ways were found of
holding down all the extended supporting surfaces upon the launching
piece, and at the same time of firmly clamping the body of the
aerodrome until it could be dropped, as well as of releasing all
this simultaneously at the critical instant, no attempt at launching
was likely to succeed except in such an entire and perfect calm as
rarely occurs. Independent of this launching difficulty, some way of
protecting the fires from the wind had to be found, which was by no
means easy, since an efficient protection meant an enclosure of them
and a diminished influx of air, of which it was essential that there
should be an unlimited supply.

December 1. L, with B, R, and M proceeded to Quantico. The same
conditions presented themselves and the party returned, without
effecting anything.

December 7. L, B, R, and M present; day overcast but perfectly calm.
Taught by experience, we had everything ready, and a little after one
o’clock the launch was made. The aerodrome fell directly into the
boat, the rod of the starter having broken. It was little damaged,
but in view of the injury and the rising wind, all other attempts
were abandoned for the day.

December 11. Present, L, with B, R, and M. A new “starter” had been
devised and brought down, but was not yet quite ready for use, and
an attempt was made to employ the old one with the improvements
suggested by experience, but, after two attempts to launch, the work
was abandoned for the day, owing this time not to the launching
apparatus, but to troubles in the engines and pumps, due probably to
injuries received in the fall of the 7th, which were not detected
until the time of the actual trial.

December 20. L, with B, M, and G, present; engine and aerodrome
in order and everything apparently favorable. What seemed to be
an almost entire calm came toward evening, yet once more the all
but imperceptible breeze which prevailed was found to defeat all
arrangements for holding the aerodrome to the launching ways before
it was let go.

Trips to Quantico were also made on November 24, and December 1
and 21, of which no account is given as the very moderate wind
which prevailed in each case precluded any attempt at launching the
aerodrome.

It will be seen that eight trips were made to Quantico, and that, far
from any flight having been made, not once even was the aerodrome
launched at all. The principal cause for this lay in the unrecognized
amount of difficulty introduced by the very smallest wind,
irrespective of the unfitness of the launching apparatus to give the
desired initial speed and direction.

In all these trials, the aerodrome rested on the launching apparatus,
by which it was projected forward by means of a spring in such a way
as not to interfere with the propellers. [p096]

Previous tests with the rubber-driven models had demonstrated the
futility of all simple pendulum types of “cast off,” and likewise all
the trials hitherto of a railroad form of launching apparatus, in
which the aerodrome was mounted on a car, which had itself to get out
of the way, were equally failures, so that when the device referred
to above proved to be worthless, it seemed that almost every plan had
been exhausted. There were, moreover, other difficulties, some of
which have been indicated above, such as that of making the burners
work properly in even a moderate wind during the very short time
required for attaching the wings and so adjusting the aerodrome on
the launching apparatus.

These difficulties, which, now that they have been overcome, seem
difficulties no longer, but which then seemed insuperable, were all
connected with the ever-present problem of weight. It would have
been easy to make rigid sustaining surfaces which would not bend in
the wind; to make fires which would not go out; and easy to overcome
all the impediments which seem so trivial in description and were
so formidable in practice, were it not that the mandate of absolute
necessity forbade this being done by any contrivance which would add
to the weight of an already phenomenally light construction. The
difficulties of the flight as they were seen in the workshop were
multiplied, then, beyond measure by the actual experiments in the
field, and the year closed with a most discouraging outlook.

1894

The new year began without any essential improvement in the means
already described, though a new launching apparatus had been devised
by the writer, which was scarcely so much an apparatus for launching,
in the ordinary sense of the word, as one of holding the aerodrome
out over the water, and simply letting it drop from a height of
about 25 feet, during which fall it was hoped (exact data being
unobtainable in advance of experiment) that there would be time for
the propellers to give the aerodrome the necessary soaring speed
before reaching the water. This device consisted of an inverted
tripod, which held the aerodrome comparatively steady by three
bearing points, while a cross-bar of wood was added to prevent the
wings from swaying before the launch. Previously, the supporting
surfaces, wings and tail, had been put on only at the last minute.
Now it became possible to keep them on in a gentle breeze for an
indefinite time before launching.

January 9. The previous day having been spent in practicing the
steps preliminary to launching, so as to avoid delay in assembling
and mounting the aerodrome, the writer, with Dr. Graham Bell, went
to Quantico. The day was calm, and every condition seemed favorable.
The aerodrome was dropped fairly, under full steam, and it fell in
a nearly horizontal position, but touched the water at a distance
of only 50 or 60 feet, evidently before the necessary initial speed
[p097] could be impressed on it by its engines. The conclusion
should have been that by this method nothing but a practically
unsuitable height would suffice to start the aerodrome in a calm,
though it might perhaps be done in the face of a considerable breeze.

May 25. After a considerable interval of delay, due to the river
being closed by ice and other causes, Aerodrome No. 4 was again
dropped from the starter under nearly the same conditions as in
the trial of January 9, and with a quite similar result, the final
conclusion being that this method must be abandoned. It may be added
that a vertical rudder was tried on this day.

June 12. No. 4, with an improved blast, was tried at Quantico, Mr.
Goode being present. The day ended in failure from another cause, the
improved blast, which worked well in the shelter of the shop, but
proved useless in the field, being extinguished by the feeblest wind.
At this time (in June and July) I designed a horizontal railroad
with launching springs and track, underneath which ran a car which
held the aerodrome firmly until the moment of automatic release.
This apparatus finally proved to be the successful solution of the
launching problem. The description given later, with the drawing in
Plate 18, shows the after-improvements, but no specific change from
that in use from the first.

About this time I also arranged for certain changes in the boilers
and burners, having decided that I would not go into the field
without some ground for confidence not only that the aerodrome could
be launched successfully, but that a steady flame could be maintained
under the boilers.

October 6. No. 4, as remodelled, having a flying weight of about 14.5
pounds, a supporting surface of about 28 square feet, with a total
engine power of about 0.5 H. P., and having lifted 40 per cent of
its weight on the pendulum, was taken down the river for trial with
the new railroad launching apparatus, and several days were spent in
erecting the launching apparatus on the house-boat, and in launching
“dummy” aerodromes from it for practice.

Aerodrome No. 4 then being fitted under conditions which apparently
insured a good start (the center of pressure being nearly over the
center of gravity, the root angle of the wing being zero, the midrod
nearly horizontal, the engine working well, and with apparently ample
sustaining surface) was finally successfully launched, but the hopes
which were reasonably entertained proved to be unfounded. The result
of this first actual trial of a “flying machine” in free air was most
disconcerting, for the aerodrome, which had ‹in theory› many times
the power required for horizontal flight, plunged into the water with
its engines working at full speed, after a course hardly longer than
that performed by the dummy. This result was at first inexplicable.

No. 4, then, did not fly at all, from some at first inscrutable
cause, and it was decided to make a trial of No. 5, though it was
hard to put the result of so much [p098] time, painstaking and cost
to the hazard of destruction. With the experience just acquired from
the trial of No. 4, the wing of No. 5 was set at an angle of about
20° with the midrod, and the tip was secured by a light cross-piece,
so guyed that the wing as a whole, while set at this considerably
greater angle with the rod, was stiffer than before. In addition to
this, the air chamber was moved back so that the center of gravity
was from 6 to 10 cm. behind the (calculated) center of pressure.
These changes were made in order to insure that the front should at
any rate keep up, and it did.

The aerodrome was launched successfully with the engines working
under a pressure of 110 pounds of steam. The head rose continually
until the mid-rod stood up at an angle of about 60°, checking all
further advance. It remained in the air in a stationary position for
nearly a second, and then slid ‹backward› into the water, striking on
the end of the rudder and bending it. The distance flown was about 12
metres, and the time of flight 3 seconds. One of the propellers was
broken short off, and the shaft was bent.

It thus became clearly evident that some cause prevented the proper
balancing of the machine, which was necessary to secure even
approximately the theoretically simple condition of horizontal
flight. It was all-important that the angle of the front wing should
be correct, but its position could not be accurately known in advance
of experiment, and this experiment could only be made with the
machine itself, and involved the risk of wrecking it.

These trials gave a very vivid object lesson of what had already
been anticipated,[31] that the difficulties of actual flight would
probably lie even more in obtaining exact balance than in the first
and more obvious difficulty of obtaining the mere engine power to
sustain a machine in the air. The immediate problem was to account
for the totally different behavior of the two aerodromes in the two
flights, under not very different conditions.

Observations of the movement of the two aerodromes through the air,
as seen by the writer from the shore, seemed to show, however, that
the wings did not remain in their original form, but that at the
moment of launching there was a sudden flexure and distortion due to
the upward pressure of the air. The time of flight was too short,
and the speed too great, to be sure of just what did occur, but it
seemed probable that the wings flexed under the initial pressure
of the weight which came upon them at the moment of launching, and
that they were in fact, while in the air, a wholly different thing
from what they were an instant before, so that a very slight initial
difference in the angle at which they first met the air might cause
the air to strike in the one case on the top of the wings and throw
the head down, and in the other case so as to throw the head up.
To ascertain the extent and character of this flexure, caused, it
will be observed, by [p099] the ‹weight› of the aerodrome suddenly
thrown on the wings, I inverted the aerodrome and distributed a
weight of dry sand equal to that of the whole machine evenly over the
supporting surfaces. It was found that under the weight of the sand
the extremity of the wings bent to an angle of 45° downwards (and
consequently must have bent to an angle of 45° upwards in the air),
a condition of affairs worse than anything that had been suspected,
and seeming to demand the entire reconstruction of the wings with
a strength and consequent weight for which there was no means of
providing.

There had been some injuries to the machines in the trials of the 5th
and 6th, and these were repaired. A new float had been made for No.
4, and a new set of larger wings for No. 5. Each of these wings had
a length of 76 inches and a breadth of 25 inches, making the total
surface of the two 26.4 sq. ft., while that of the tail was 13.2 sq.
ft., or about 40 sq. ft. in all.

October 22. When No. 5 was finally prepared for another trial, its
condition was as follows:

Flying weight 22 pounds
Area of supporting surfaces (wings and tail) 40 sq. ft.
Sq. ft. of surface per pound of weight 1.8[32]
Engine power with 115 lbs. steam pressure 1.0 H. P.[33]
Power necessary to soar 0.35 H. P.
Theoretical soaring speed (plane wings at 20°) 24 ft. per sec.
Previous lift on pendulum 40 per cent of
flying weight

October 25. The aerodromes having been taken to Quantico on October
23, and satisfactory experiments made with dummies in order to
test the launching apparatus, the house-boat was carried out into
midstream and moored.

Aerodrome No. 4 was launched in the face of a wind of about 1100
feet per minute. The midrod was at a very small inclination with
the horizontal, about 3°. The angle (α) of the chord of the curved
wing measured at the rod, where it was rigidly held, was 15°. The
adjustment was such as to bring the ‹CG› immediately under the ‹CP›,
without any allowance for the fact that the line of propeller thrust
was below the ‹CP›.[34] The aerodrome under these conditions was
launched with the head high. It made a real, though brief, flight of
about 130 feet in 4-1/2 seconds, when it swung abruptly round through
90°, and, losing headway, sank continuously, finally falling backward
into the water.

October 27. Aerodrome No. 4, having been repaired and guyed with
wires from the wings to vertical guy-posts beneath, was launched
again, but one of the [p100] guy-wires caught on the launching car,
and threw the aerodrome immediately into the water with but little
damage.

On the same day No. 5 was launched. The theoretical ‹CP›−‹CG› was
nominally 0, but, for the reasons stated in the footnote on p. 99,
was really something positive, that is to say, the ‹CP› was really
somewhat in advance of the ‹CG›; inclination of midrod less than α
(=20°). The aerodrome under these circumstances, while keeping its
head up, at first fell rapidly, yet seemed about to rise just as it
struck the water, conveying the idea that if the launching had been
made with a greater initial velocity it would have risen and cleared
the water. The wings visibly pocketed, however, and it was clear that
some better disposition must still be made for them. The flight was
3-1/2 seconds.

No. 5 was tried again on the same day with larger wings, whose area
was 40 square feet. These wings, though stiffer, pocketed a little,
α=20° as before. It flew rapidly, and at first horizontally, to a
distance of 100 feet or more against a five-mile breeze. It then
turned abruptly round through 180°, at first falling (from loss of
headway), then distinctly rising, and at the same time throwing its
head up until it reached an angle of nearly 60° with the vertical,
when it fell backward after a flight of between 6 and 7 seconds. The
wings were evidently not yet strong enough to resist flexure.

November 21. No. 5, in nearly the same condition as before. Two extra
springs had been placed on the launching car, in order to give the
aerodrome a greater initial velocity than before. Everything appeared
favorable, but as it left the launching track a piece flew out of the
port propeller, in spite of which the aerodrome, after dropping 5
feet, rose bodily at an angle of 45° and fell backward into the water
(time, 5 seconds).

Another trial was made the same day with the same aerodrome, under
similar conditions, except that the angle of inclination (α) was
reduced to 7°. It now, with all the other circumstances of launching
like those immediately before, behaved entirely differently, plunging
head downward into the water at a distance of 30 feet. Once more it
was shown beyond dispute that the wings must somehow be made even
stiffer.

December 8. Another trial was undertaken with No. 5, the ‹CG› being
10 cm. in front of the ‹CP› at rest. The root angle of the wings was
18°, tip angle 27°, elevation of midrod 1 in 24. The other changes
made since the previous trial consisted chiefly in the increased
weight due to the longer and stronger frames and shafts that were
made to carry 100 cm. propellers. The flight obtained was so short
that it was as unsatisfactory as before.

The aerodrome rose in the air after leaving the launching apparatus,
and then slid back into the water in the plane of its own wings. On
the first trial, it struck the boat, and was slightly injured; on
the second, with root angle of [p101] wings 10°, tip angle 20°, the
flight partook of the same character, but the machine struck the
water clear of the boat.

The fact that with the ‹CG› 10 cm. in advance of the calculated ‹CP›
the aerodrome steadily rose in front, seems to indicate that the rule
used at that time for calculating the ‹CP› (see Chapter II) was not
very accurate. This rule was based upon the assumption that the tail,
having an area equal to one-third the entire sustaining surface,
supported one-third the total weight (expressed by the formula ‹CP› =
(2‹CP›_{wm} + ‹CP›_{tm})/3, where ‹CP›_{wm} and ‹CP›_{tm} represent
respectively the ‹CP› of the wings and tail in motion), and that the
‹CP› of each surface was one-fifth its width in front of the center
of figure.

December 12. Four days later, the tail had been moved back 21 cm.,
thus carrying the ‹CG› back 7 cm., but the vertical rudder (weighing
105 grammes), for which there was now no room, was taken off, which
in a measure counteracted this change.

A trial was then made with the wings set at an initial angle of 8°
at the root and 20° at the tip. The aerodrome was released with the
engines working under a steam pressure of 90 pounds, and soared off
horizontally for some distance, when suddenly it swerved to the right
as though something on that side had given out, and turning quite
through 180° headed toward the boat, striking the water about 76 feet
away. The time of the flight was 4 seconds.

It was found upon the recovery of the machine that one of the
propellers had been twisted through 90°, so that the two were no
longer symmetrical. The turning may have been due to this twist or to
unequal influence of the wind upon the two wings; for when I applied
the sand test to the wings after returning them to Washington, it
was found that they deflected so much that the grains would not lie
upon them, which, to a great extent, explains the failure to secure a
better flight.

Thus the end of another year had been reached, and what might be
called a real flight had not yet been secured. The only progress
that seemed to have been made was that the aerodromes were not quite
so unmanageable and erratic in their flights as at the beginning
of the year, and that it had been demonstrated, at least to the
writer’s satisfaction, that the power was sufficient for the work to
be done. The launching device had been so perfected that it worked
satisfactorily, but the problem of balancing seemed as far from
solution as before.

1895

While, for convenience in narrating the progress of the work with the
aerodromes, each year has been treated as a unit, it is, of course,
understood that the work itself shows no especial difference between
the closing of one year and the beginning of another. Changes which
had important effects were introduced [p102] at various times,
but were, of course, made as they suggested themselves without any
reference to time or season. But while it was customary to make,
from time to time, a résumé of the progress of the work, yet at
the closing of the calendar year it was the custom to make a more
complete digest of just what had been accomplished during the year.

Upon thus reviewing the progress of the work during 1894, it was
felt that the results which had been accomplished for such a large
expenditure of time seemed small, since no real flight had been
made by any of the aerodromes, and no definite assurance that a
successful flight would be obtained within the immediate future
seemed warranted by what had already been accomplished. But now that
the principal difficulties connected with the launching apparatus
had been overcome, thus permitting the aerodromes themselves to be
given a fair trial, the belief was encouraged that the continuance of
the actual tests of the machines, with slight changes which previous
tests had shown advisable, would finally result in a successful
flight.

The early weeks of 1895 were spent in a series of pendulum tests on
No. 5, and in making such slight changes as these tests indicated
would be advisable. As a result of small improvements introduced in
the boilers, No. 5 had by the middle of March shown a repeated lift
of considerably over 50 per cent, and in some tests as much as 62
per cent of its flying weight. Certain radical changes previously
described in Chapter VII were also made in Aerodrome No. 4, and in
the pendulum tests of it a lift of 44 per cent of its flying weight
had been obtained.

Encouraged by the better results which the aerodromes had shown in
the above tests, it was decided to test them again in free flight,
and they were accordingly sent down to Quantico in charge of the two
mechanics, R and M, Mr. Langley, accompanied by Dr. Graham Bell,
whom he had invited to witness the tests, following on May 8. On the
evening of May 8 No. 5 was mounted on the launching apparatus in
order to drill the mechanics so that when favorable weather presented
itself the aerodrome could be got ready for launching with the
minimum delay.

On May 9 Mr. Langley and Dr. Bell reached the house-boat at 5 a. m.,
but even with the drill of the previous evening the mechanics were
not able to have No. 5 ready for trial until 6.15 a. m. The principal
conditions of No. 5 at this time were:

Total weight 11,200 grammes (24.6 pounds), including 800 grammes of
fuel and water. Previous lift on the pendulum 54 per cent, with a
steam pressure of 150 pounds. With this steam pressure the engine
made about 600 R. P. M. when driving the 95 cm. propellers, which
through their reduction gearing made about 500 R. P. M. [p103]

When the aerodrome was balanced for flight so as to bring the
theoretical “center of pressure in motion” over the center of
gravity, it was found that it was not possible to carry the center of
gravity in front of this point, although it was known by experience
to be necessary. Accordingly in the first trial the outer ends of the
tail were pressed down by the guys so that the wind of advance tended
to lift the tail and throw the head down more than if the tail had
been flat. Furthermore, the float, weighing 200 grammes, instead of
being placed in its normal position near the base of the bowsprit,
was carried out to its extremity, this change in the position of the
float alone being sufficient to carry the center of gravity forward
three or four centimetres. The curved wings were set at an angle of
nine degrees at the root and eleven degrees at the tip. They were
well guyed, and in flight appeared to be not materially twisted or
altered.

It was anticipated that the pressing down of the outer ends of the
tail and the shifting of the center of gravity would cause the
aerodrome to point downward in flight, and this anticipation was
verified in the test. At 6.15 a. m. the aerodrome was launched at a
steam pressure of 120 pounds. A perfect calm prevailed at the time
and the machine started straight ahead. There was no perceptible drop
at the moment it was released from the launching car, but a smooth
and steady descent until it struck the water, nose down, at a point
approximately 200 feet from the boat. Dr. Bell noted that the length
of time the aerodrome was in the air was 2.8 seconds. One of the
propellers was broken and the other one was found to have twisted its
shaft one-fourth of a turn.

At 9.45 a. m., the wings having been dried, No. 5 was again tried.
The float was moved back to its normal position at the base of the
bowsprit, and the guys, by which the outer ends of the tail had been
depressed in the previous trial, were so adjusted that the tail was
flat. The machine was, therefore, in the condition of theoretical
equilibrium for rapid motion with a plane wing. All the other
conditions were precisely as in the previous trial, except that
the round-end 100-centimetre propellers were substituted for the
95-centimetre ones which had been broken, and a new paper-covered
tail was used. The mechanic in charge was directed to let the steam
reach its highest pressure consistent with a flight of one-half a
minute, before launching the machine, but he seemed to have lost all
sense of the length of time the fuel and water would last, as he let
the engines run until almost the whole charge was exhausted before
launching it. The aerodrome went off almost horizontally, then turned
up into the wind and rose to an angle of about twenty degrees; then
(while moving forward) slowly sank as though the engine power had
given out, as in fact it doubtless had. The actual distance travelled
was 123 feet and the length of time 7.2 seconds. While the exhaustion
of the fuel and water prior to launching the machine had prevented
what apparently would otherwise have been an [p104] exceedingly good
flight, yet the fact that the aerodrome rose immediately after being
launched, and continued to do so until the power gave out, was in
itself very encouraging.

At 1.40 p. m. No. 5 was again ready for trial (the third one for
the day), and this time Mr. Langley and Dr. Bell witnessed it from
a greater distance in hopes of being able more clearly to study its
behavior when actually in the air.

The previous trial having missed success through the fuel and water
having been consumed before the machine was launched, special
instructions were given to avoid the recurrence of this mistake. But
the machine was held for probably two minutes after the burners were
lighted, with very much the same result as before. The conditions of
the aerodrome were the same as in the previous trial, except that the
tail was a little flatter, so as to tend to make the head slightly
lower in flight. It was launched at an angle of about thirty degrees
with the very gentle wind that was blowing, and, apparently under
the direction of the rudder, turned into the wind, the midrod rising
to an angle of about twenty degrees and (as noted in Mr. Langley’s
record book) “The whole machine absolutely rising during five or
six seconds--a fine spectacle! Then the power visibly gave out, the
propellers revolving slower. It settled forward and lost nearly all
of its forward motion at the end of about seven seconds, but did not
finally touch the water until ten and a quarter seconds.”

While the length of time that the aerodrome had been sustained in
the air was so short that no actual flight had really been achieved,
yet the results encouraged the belief that with the aerodrome more
accurately balanced, it could reasonably be hoped that a somewhat
longer flight would be obtained. It was, however, very evident that,
although the correct balancing which would insure equilibrium for
a few minutes might soon be attained, the machine, lacking a human
intelligence to control it, must be provided with some mechanism
which would tend to restore the equilibrium, the conditions of which
must necessarily change in a machine depending on the air for its
support. In order to see what could be done in this direction, it
was, therefore, decided to return immediately to Washington with
the machines and make some minor changes in them before attempting
further flights.

By the end of May, Nos. 4 and 5 were again in readiness for a trial,
and the mechanics were accordingly sent to Quantico to complete
preparations for the tests. During May Mr. A. M. Herring, who had
been experimenting with model machines for several years, was engaged
for a few months as an assistant, and he was immediately put in
charge of the field trials of Nos. 4 and 5, which were now about to
be made. On June 6 Mr. Langley, accompanied by Mr. Herring, went to
Quantico, and on June 7, at 5 a. m., Aerodrome No. 5 was ready for
trial, but the wind was so high that nothing could be done. The wind
later diminished in intensity, but the house-boat had become stuck
on the beach [p105] and it was impossible to make the launching
apparatus point directly into the wind, which was blowing from the
rear of the boat. An attempt was made to launch the aerodrome even
with the wind blowing at its rear, but it was found impossible to
make the fires burn and the test was accordingly postponed. Later
in the afternoon the house-boat was floated and the preparations
for a test were immediately completed. At 5.42 p. m. the fires were
lighted, but the burners did not work properly and the proper steam
pressure could not be obtained. At 6.20 p. m. the fires were again
lighted, and at 6.22 the aerodrome was launched, its midrod having
an upward angle of 25 degrees, or more, with the launching track.
The aerodrome moved off nearly horizontally, but seemed to be very
sluggish in its movement and fell in the water about seventy feet
from the boat, after having been in the air only 4.8 seconds. The
damage consisted of a broken propeller and a slight strain in the
main frame, the extent of which, however, was not immediately seen.

The steam pressure at the time of launching was 110 pounds, which was
obviously insufficient. The aerodrome had lifted fifty per cent of
its weight on the pendulum, and its sluggishness of movement seemed,
therefore, unaccountable even for this pressure. It seemed probable,
however, that the pressure ran down immediately after the machine was
launched, on account either of the use of the light-weight burners in
place of the larger and heavier ones, or of the diminution of the air
pressure in the gas tank.

At 7.55 the aerodrome was again launched, and this time made a still
shorter flight than before, being in the air only three seconds. A
serious leak in the engine cylinder was, however, discovered just as
the machine was launched, and this probably accounted for the lack of
power.

Not only had the tests which have just been described indicated that
there was a lack of power during flight, although previous pendulum
tests had repeatedly shown lifts greater than fifty per cent, but,
furthermore, the wings themselves, while appearing perfectly capable
of supporting the aerodrome when viewed with the machine stationary,
were seen to flex to such an extent in flight that it seemed probable
that much of the power was consumed in merely overcoming the head
resistance of a large portion of the wings which had lost all lifting
effect.

During the fall and winter, as recorded in Chapters VII and VIII,
Aerodrome “New No. 4,” which had been reconstructed during the
summer, and which upon test was found radically weak, was almost
entirely rebuilt and afterwards known as No. 6. Important changes
were also made in No. 5, which greatly increased its strength and
power. The improvements, however, which contributed more than
anything else to the marked success achieved in the next trial of
the aerodromes, were those which had to do with the nature and
disposition of the sustaining surfaces and the means for securing
equilibrium. [p106]

It will be recalled that in the more recent trials the apparent
causes of failure had been the inability to provide sufficiently
rigid wings, the great difficulty of properly adjusting the relative
positions of the centers of pressure and gravity, and the lack of any
means of regaining equilibrium when the balance of the aerodrome had
in any way been disturbed. In the fall of 1895, accordingly, it was
finally decided to employ a second pair of wings equal in size to the
first or leading pair. This not only added greatly to the stability
of the aerodrome, but also made it possible, without any alteration
in the plan of the frame, to bring the center of pressure into the
proper position relative to the center of gravity. In addition the
plan of constructing the wings was modified by the introduction of
a second main rib, which, placed at approximately the center of
pressure of the wings, made them much stiffer, both against bending
and torsion. The two pairs of wings now became the sole means of
support, and the tail which had hitherto been made to bear part of
the weight of the aerodrome, as well as assist in preserving the
longitudinal equilibrium, was now intended to perform only the latter
function. It was placed in the rear of the wings and was combined
with the vertical rudder. Further, in adjusting it on the aerodrome,
it was set at a small negative angle and given a certain degree of
elasticity, as described above. This device proved to be a most
efficient means of maintaining and restoring the equilibrium, when it
was disturbed, and its value was apparent in all future tests of the
models.

1896

The important changes in the steam-driven models which had been
begun in the previous fall, and which in the case of No. 4 had been
so extensive as to convert it into a new aerodrome, No. 6, were
continued during the early spring, and it was not until the last of
April that the models Nos. 5 and 6 were ready for actual test in free
flight.

[Illustration: PL. 18

HOUSE-BOAT WITH OVERHEAD LAUNCHING APPARATUS, 1896]

The condition of No. 5, which made the first successful flight, is
given in the data sheet for May 6, 1896, and its general form at this
time may be seen in the photograph of May 11, Plate 27A. Although the
changes described above, as well as the modifications in the boilers
and burners of both aerodromes had undoubtedly effected a great
improvement in every detail of the machines, the disappointments
experienced in the preceding years prevented any great feeling
of confidence that the trials which were now to be made would be
entirely successful. On May 4, however, the two mechanics, Mr. Reed
and Mr. Maltby, were sent down to Quantico with Aerodromes Nos. 5
and 6, and Mr. Langley, accompanied by Dr. Graham Bell, who had been
invited to witness the tests, followed on the afternoon of the 5th.
On May 6 the wind was so very high all the morning that a test was
found impracticable. During the forenoon, however, the wind gradually
died down, and by 1 p. m. was blowing from six to ten miles an
hour [p107] from the northeast. At 1.10 p. m. Aerodrome No. 6 was
launched, but the guy-wire uniting the wings having apparently caught
on one of the fixed wooden strips which held the wings down, the left
wing was broken before the aerodrome was really launched, and the
result was that the machine slowly settled down in the water by the
boat, breaking the propellers and slightly injuring the Pénaud tail.

After removing No. 6 from the water, No. 5 was placed on the
launching car and immediately prepared for a test. At 3.05 p. m.
it was launched at a steam pressure of 150 pounds and started
directly ahead into the gentle breeze which was then blowing. The
height of the launching track above the water was about twenty feet.
Immediately after leaving the launching track, the aerodrome slowly
descended three or four feet, but immediately began to rise, its
midrod pointing upward at an increasing angle until it made about ten
degrees with the horizon and then remained remarkably constant at
this angle through the flight. Shortly after leaving the launching
track the aerodrome began to circle to the right and moved around
with great steadiness, traversing a spiral path, as shown in the
diagram (Plate 19). From an inspection of the diagram it will be
noticed that the aerodrome made two complete turns and started on the
third one. During the first two turns the machine was constantly and
steadily ascending, and at the end of the second turn it had reached
a height variously estimated by the different observers at from 70
to 100 feet. When at this height, and after the lapse of one minute
and twenty seconds, the propellers were seen to be moving perceptibly
slower and the machine began to descend slowly, at the same time
moving forward and changing the angle of inclination of the midrod
until the bow pointed slightly downward. It finally touched the water
to the south of the house-boat at the position shown, the time the
machine was in the air having been one minute and thirty seconds
from the moment of launching. The distance actually traversed, as
estimated by plotting its curved path on the coast-survey chart and
then measuring this path, was approximately 3300 feet, which is the
mean of three independent estimates. This estimate of the distance
was checked by noting the number of revolutions of the propellers
as recorded by the revolution counter, which was set in motion at
the moment the machine was launched. On the assumption that the
slip of the propellers was not greater than fifty per cent, the
1166 revolutions as shown by the counter would indicate a distance
travelled of 2430 feet. As it was felt very certain that the slip
of the propellers could not have amounted to as much as fifty per
cent, it seemed a conservative estimate to place the length of flight
at 3000 feet, which would mean a rate of travel of between 20 and
25 miles an hour. The circular path traversed by the aerodrome was
accounted for by the fact that the guy-wires on one of the wings had
not been tightened up properly, thus causing a difference in the
lifting effect of the two sides. [p108]

The aerodrome was immediately recovered from the water and
preparations made for a second test, the machine being launched again
at 5.10 p. m. at a steam pressure of 160 pounds. The conditions were
the same as at the first trial, except that the wind had changed
from north to south and was perhaps of less velocity than before.
The path traversed by the aerodrome in this second trial was almost
a duplicate of the previous one, except that on account of the
change in the direction of the wind the machine was launched in the
opposite direction. In tightening up the guy-wires, which had not
been properly adjusted in the previous test, they were probably
tightened somewhat too much, since in this second test the aerodrome
circled towards the left, whereas in the first flight it had circled
towards the right. The aerodrome made three complete turns, rising to
a height of approximately sixty feet with its midrod inclined to the
horizon at a slightly greater angle than before. The propellers again
ceased turning while the machine was high in the air and it glided
forward and downward and finally settled on the water after having
been in the air one minute and thirty-one seconds. The distance
travelled was estimated as before, by plotting the path on the
coast-survey chart, and was found to be 2300 feet.

During these flights several photographs were secured of the machine
while it was actually in the air, some of the pictures being taken
by Dr. Bell and others by Mr. F. E. Fowle. The clearest of these are
shown in Plates 20, 21, and 22.

Just what these flights meant to Mr. Langley can be readily
understood. They meant success! For the first time in the history of
the world a device produced by man had actually flown through the
air, and had preserved its equilibrium without the aid of a guiding
human intelligence. Not only had this device flown, but it had been
given a second trial and had again flown and had demonstrated that
the result obtained in the first test was no mere accident.

Shortly after returning to Washington, Mr. Langley left for Europe,
but before doing so he gave instructions to the workmen to remedy the
small weaknesses and defects which had been found in Aerodrome No. 6,
and to have both aerodromes ready for trial before his return in the
fall.

[Illustration: PL. 19

PATH OF AERODROME FLIGHTS, MAY 6 AND NOVEMBER 28, 1896, NEAR
QUANTICO, VA., ON THE POTOMAC RIVER]

[Illustration: PL. 20

INSTANTANEOUS PHOTOGRAPH OF THE AERODROME AT THE MOMENT AFTER
LAUNCHING IN ITS FLIGHT AT QUANTICO ON THE POTOMAC RIVER, MAY 6,
1896. ENLARGED TEN TIMES]

[Illustration: PL. 21

INSTANTANEOUS PHOTOGRAPH OF THE AERODROME AT A DISTANCE IN THE AIR
DURING ITS FLIGHT AT QUANTICO ON THE POTOMAC RIVER, MAY 6, 1896.
ENLARGED TEN TIMES]

[Illustration: PL. 22

INSTANTANEOUS PHOTOGRAPH OF THE AERODROME AT A DISTANCE IN THE AIR
DURING ITS FLIGHT AT QUANTICO ON THE POTOMAC RIVER, MAY 6, 1896.
ENLARGED TEN TIMES]

[Illustration: PL. 23

OVERHEAD LAUNCHING APPARATUS]

[Illustration: PL. 24

OVERHEAD LAUNCHING APPARATUS]

After returning in the fall, Mr. Langley again had Aerodromes Nos.
5 and 6 taken down to Quantico for trial, and this time had as his
invited guest Mr. Frank G. Carpenter. On November 27 a test was
made of Aerodrome No. 6, the general disposition of which at this
time may be learned from the description in Chapter X, and the
photographs in Plates 29A, 29B. The model was launched at 4.25 p.
m. with a steam pressure of 125 pounds. The aerodrome went nearly
horizontally against the wind, and descended into the water in six
and a quarter seconds at a distance of perhaps 100 yards. After
the machine had been recovered from the water, it was found that
a pin had broken in the synchronizing rod which connects the two
propeller shafts together, and that the counter, which showed 495
revolutions of the propellers, had been caused to register [p109]
inaccurately on this account. The balancing of Aerodrome
No. 6 had been made the same as that of No. 5, but in No. 6 the line
of thrust was twelve centimetres higher, and this fact, which had not
been taken into account in determining the proper balancing for No.
6, seemed to be sufficient cause for the aerodrome coming down into
the water so soon after being launched. Darkness had descended before
the aerodrome could be recovered and prepared for a second trial. On
the next day, November 28, a high wind prevailed in the morning, but
in the afternoon it became comparatively calm, and No. 6 was launched
at 4.20 p. m. under the same conditions as on the preceding day,
except that the float, which weighed 275 grammes, was moved back from
the bowsprit eighty centimetres in order to make the machine lighter
in front. The aerodrome was launched at a steam pressure of not much
over 100 pounds, the air draft for the burners being temporarily
bad. The midrod made an angle of approximately three degrees with
the horizontal. On account of a slight rain, which had occurred just
before the machine was launched, the wings were wet and the weight
of the entire aerodrome was doubtless as much as twelve kilos.
Immediately on being launched the aerodrome started directly ahead in
a gentle south wind, moving horizontally and slowly turning to the
right and appearing to approach dangerously near to some thick woods
on the west shore. However, it fortunately continued turning until
it pointed directly up the beach with the wind in the rear. It then
moved more rapidly forward, dipped and rose but once, and this very
slightly, and continued its remarkable horizontal flight, varying not
more than two yards out of a horizontal course, and this only for a
moment, until it finally descended into the bay at a point nearly in
a line between the house-boat and the railroad station at Quantico.
Upon being recovered, it was found to be absolutely uninjured, and
another flight would have been made with it immediately but darkness
had descended. The time of flight, as determined independently by
two stop-watches, was one minute and forty-five seconds. The number
of revolutions of the propellers was 2801, or at the rate of 1600
R. P. M., which, with an allowance of fifty per cent slip, should
have carried the aerodrome a distance of 4600 feet in one and
three-quarter minutes. While the distance from the house-boat in a
straight line to the point at which the aerodrome descended was only
about 1600 feet, yet it was estimated by those present that this
straight-line distance was certainly not greater than one-third the
total length of the path traversed, which would mean a distance of
something like 4800 feet. The length of the course, as plotted on
the coast-survey map and afterwards measured, was 4200 feet, and it,
therefore, seemed safe to say that the total distance travelled was
about three-quarters of a mile, and the speed was, therefore, about
thirty miles an hour.

[p110]

CHAPTER X
DESCRIPTION OF THE LAUNCHING APPARATUS AND OF
AERODROMES Nos. 5 AND 6

Reference has already been made to the development of the “cast-off”
apparatus that was used at Quantico for launching the aerodrome. An
initial velocity is indispensable, and after long experiment with
other forms which proved failures, an apparatus was designed by me,
which gave a sufficient linear velocity in any direction. It had,
moreover, been found that, when the aerodrome was attached to any
apparatus upon the roof of the house-boat, such slight changes in
the direction and intensity of the wind as would ordinarily pass
unperceived, would tend to distort or loosen it from its support,
so that only the most rigid of fastenings at three independent
bearing points were of any use in holding it, while the wings must
be separately fastened down, lest they should be torn from their
sockets. It was, then, necessary to be able to fasten the aerodrome
very firmly to the cast-off apparatus, to start it upon its journey
in any direction with an initial linear velocity that should equal
its soaring speed, and to release it simultaneously at all points at
the very same instant, while at the same time the points of contact
of the launching device, to which it had just been fastened, were
themselves drawn up out of the way of the passing propellers and guys.

All these requirements and others were met by the apparatus finally
adopted, which is shown in Plates 23 and 24. It consists of a strong
timber frame-work, carrying a track, consisting of two flat iron
rails set on edge, upon which runs the launching car, suspended from
two small wheels on each side. At the front end of the frame there
are two cylindrical air buffers to receive the buffing pistons and
thus stop the car after the aerodrome has been released. The car is
drawn to the rear end of the track and held by the bell-crank lever
‹A› (Plate 23). The contact points ‹BB› and ‹C› are turned down and
the clutch-hook ‹D› set over the clutch-post ‹K›. The aerodrome
is thus held firmly up against the three points ‹BB› and ‹C› by
the clutch ‹D›, and a distortion from its proper position rendered
impossible. All these points are thrown up out of the way of the
projecting portions of the aerodrome at the instant of release. This
result is accomplished as follows: when the car has reached the
proper point in its forward course, the cam ‹E›, which is hinged at
1, is depressed by a roller fixed to the framework of the device. In
this motion it pushes down the adjustable connections ‹FF›, which
are attached at their lower ends to the bell-crank arms ‹GG›, which
turn about a central pivot at 2. Thus the downward movement of the
connections ‹FF› opens the jaws of the [p111] clutch ‹D›. While the
clutch ‹D› is rigidly attached to ‹G› to prevent transverse movement,
it is hinged to the latter at 3 so that it can fold in a longitudinal
direction. Screwed to the clutch ‹D› is a narrow plate 4, which,
when the clutch is closed, is behind the lug 5, thus preventing any
turning about the hinge 3.

But when the arms of ‹G› and the jaws of the clamp are thrown out by
the depression of ‹F›, the plate 4 is moved out from behind the lug
5 and the clamp is free to fold to the front. The strut, hinged at
6, is under a constant tension from the spring 7 to fold up, and is
prevented from doing so only by the connections 8, by which it is
held down until the release of the plate 4 from behind the lug 5,
when the spring snaps them instantly up and out of the way.

As the struts ‹BB› have no fixed connection with the aerodrome,
they are released by the relaxation in the rigidity of the other
connections and are thrown up by their spring 9 and held in that
position by the clip 10 catching beneath the upper cross-piece.

The power for the propulsion of the car is obtained by means of from
one to nine helical springs working under tension, and multiplying
their own motion four times by means of a movable two-sheave pulley,
as shown in the drawing.

DESCRIPTION OF AERODROME NO. 5

When the details of the aerodrome, whose description is to follow,
are considered from the standpoint of the engineer accustomed to
make every provision against breakage and accident and to allow an
ample factor of safety in every part, they will be found far too
weak to stand the stresses that were put upon them. But it must be
remembered that in designing this machine, all precedent had to be
laid aside and new rules, adapted to the new conditions, applied.
It was absolutely necessary, in order to insure success, that the
weight should be cut down to the lowest possible point, and when
this was reached it was found that the factor of safety had been
almost entirely done away with, and that the stresses applied and the
strength of material were almost equal.

The same observation holds true of the boilers, aeolipile, and
engines, when regarded from the point of view of the economical
generation and use of steam. It was fully recognized that the waste
of heat in the coil boilers was excessive, but as it was necessary
that there should be an exceedingly rapid generation of steam with a
small heating surface, this was regarded as inevitable.

In the engine the three points aimed at in the design were lightness,
strength and power, but lightness above all, and necessarily in a
degree which long seemed incompatible with strength. No attempt was
made to secure the requirements of modern steam-engine construction,
either in the distribution of the steam or the protection of the
cylinder against the radiation of heat by a suitable jacketing.
The very narrow limits of weight permissible required that the
[p112] barrel of the cylinder should be as thin as possible, that
no protective jacketing should be used, and that the valve motion
should be of the simplest description. To obtaining the greatest
lightness consistent with indispensable power, everything else was
subordinated; and hence, all expectation of ordinary economical
efficiency had to be abandoned at the outset.

It was only after long trials in other directions that Mr. Langley
introduced the aeolipile device, which for the first time provided
sufficient heat. Even in the aeolipile, however, is was apparent that
nothing short of the most complete combustion accompanied by the
highest possible temperature of the flame would be sufficient for
the extreme demand. To secure this result under all conditions of
wind and weather, with the aerodrome at rest and in motion, required
the long series of experiments that are given in another chapter. In
respect to the generation of heat, then, it is probable that it would
be difficult to exceed the performance of the final type of burner in
practical work, but in the utilization of this heat in the boiler, as
well as in the utilization of the steam there generated, the waste
was so great as to be prohibitive under ordinary conditions. But this
was not ordinary work, and the simplest protection against radiation
from boiler, separator, and engine could not well be used.

The framework of the aerodrome is made of thin steel tubes, the main
or midrod extending the whole length of the machine and carrying the
attachments to which the wings are fastened. Suspended from this
midrod by rigid connections is a skeleton hull of steel tubing,
shaped somewhat like the framework of a boat, from which, directly
abeam of the engines, arms are run out like the outriggers of a
rowboat for carrying the propellers. Within this central hull are
placed the aeolipile, the boiler, and the engine, which with their
auxiliary parts, the pump and the separator, constitute the entire
power-generating apparatus.

The aeolipile consists of four essential parts: the spherical air
chamber containing the supply of compressed air by which the gasoline
in the reservoir tank is forced into the burner; the reservoir
tank containing the gasoline that is to be used as a fuel; the gas
generator wherein the liquid gasoline is heated and converted into
gas; and the burners where it is finally utilized to heat the boilers.

The air chamber ‹D›, Plate 25, is a spherical vessel 120 mm. in
diameter, located at the extreme front end of the hull. It is made
of copper 0.25 mm. thick and has two openings. The front opening
has a copper pipe 1 cm. outside diameter, to which the air pump for
charging the chamber is connected. From the back a copper pipe 5 mm.
outside diameter extends to the top of the gasoline reservoir.

[Illustration: PL. 25

SIDEVIEW OF STEEL FRAME OF AERODROME NO. 5 SUSPENDED FROM
LAUNCHING-CAR, OCTOBER 24, 1896]

This reservoir, shown at ‹I›, Plate 25, is also a light, hollow
sphere 120 mm. in diameter; both this and the air chamber being
made by soldering hemispheres [p113] of copper together at their
circumferences. There are three openings in the reservoir tank; two
at the top and one at the bottom. One of those at the top serves for
the admission of the 5-mm. pipe bringing compressed air from the
air chamber; the other is connected with a pipe 1 cm. in diameter,
through which gasoline is supplied to the tank, and which is closed
by a simple plug at the top. The hole in the bottom serves as the
outlet for the gasoline to the burners. Close to the bottom of the
tank there is placed a small needle valve, which serves to regulate
the flow of oil, for, were the pipe left open, the compressed air
would force the oil out with such rapidity that the burners would be
flooded and the intensity of the flame impaired. The construction
of this valve is clearly shown in Plate 26A. It consists of a brass
shell having one end (‹a›) soldered to the bottom of the tank. The
needle enters through a stuffing box whose gland is held by two small
screws. The stem of the needle is threaded and engages in a thread
cut in the body of the casting and is operated by a fine wire on the
outside. It will readily be seen that this device affords a means of
making a very accurate adjustment of the flow of the liquid to the
burners.

After leaving the needle valve the gasoline flows along the pipe
‹S›, Plate 25, until it reaches the evaporating coil, ‹N›. In order
to subject the oil to as large a heating surface as possible, in
comparison with the sectional area through which it is flowing, the
pipe, which left the needle valve with a diameter of 6 mm. soon
contracted to 5 mm., is here flattened to a width of 7 mm. and a
thickness of 2 mm. There are seven complete turns of this flattened
tubing coiled to an outside diameter of 30 mm. At the end of the
seventh coil the pipe is enlarged to a diameter of 1 cm. and two
coils of this size are added, the inside diameter being the same as
that of the flattened coil. This enlarged portion serves as a sort
of expansion chamber for the complete gasification of the gasoline,
which is then led back through a turn of the enlarged pipe, beneath
the coils and to the front. At the front end of the coil a small
branch is led off, forming a “bleeder,” which takes sufficient gas to
supply the burner by which the coil is heated, the products of whose
combustion pass into and between the coils of the boiler like those
of the regular heating burners. The gas pipe rises in front of the
coil and by a ‹T› connection branches to the two burners that are
placed in front of the coils of the boiler. These burner pipes are 5
mm. in diameter and enter sheet-iron hoods forming regular burners of
the Bunsen type, which are fully shown in all their details in the
accompanying engraving, Plate 26. The pipe is plugged at the end, and
a hole 0.9 mm. in diameter drilled for the nipple of the burner in
front of the coil where the water first enters from the separator,
and 0.85 mm. for the one in front of the return coil. The face of the
burner shell stands exactly central with and 41 mm. in front of the
coils.[35] [p114]

This constitutes the heat-generating portion of the machine, and
with it it is probable that a flame of as high a temperature is
produced as can be reached, with the fuel used, by any practical
device.

The boiler or steam-generating apparatus may be said to consist of
three parts: the separator, the circulating pumps, and the generating
coils.

The separator (‹M› in Plate 25) is a device which has attained its
present form after a long course of development. As at present
constructed, it is formed of a hollow sphere 190 mm. in diameter and
is located as nearly as possible over the center of gravity of the
whole apparatus. It serves the double purpose of water reservoir and
steam drum, and is called a “separator” on account of the function
which it performs of separating the water from the steam as it enters
from the coils. There is a straight vertical pipe 10 mm. in diameter
rising from the top of the sphere and fastened to the right-hand side
of the midrod. This is used for filling the separator with water.
Upon the other side of the midrod there is a small steam dome 42 mm.
in diameter with a semi-spherical top rising to a height of 70 mm.
above the top of the sphere. From this dome two steam pipes are led
off, one to the engine and the other to the steam gauge.

As already stated elsewhere, it was found in the experiments with
the coil boiler that an artificial forcing of the circulation of
the water was a necessity, as the natural circulation was too slow
to be of any service. Accordingly, but only after numerous devices
involving less weight had failed, a pump driven from the engine
shaft was designed and used. In the early experiments various types
of pumps were tried in which the valves were opened and closed
automatically by the pressure of the water. It was found, however,
that with the mixture of steam and water to be handled, the valves
could not be depended upon to open and close properly at the high
speeds at which is was necessary to run the engine. In Aerodrome
No. 5, therefore, a double-acting pump with a mechanically operated
valve was used. The pump, shown in detail in Plate 26A, is driven
from a shaft connected with the main engine shaft by a spur gear
and pinion, which rotates at half the speed of the engine shaft.
The pump itself consists of two barrels, the main barrel having a
diameter of 23 mm. with a piston stroke of 20 mm. The outer shell of
the barrel is made of aluminum bronze and is lined with a cast-iron
bushing 1.25 mm. in thickness. The piston has a length of 14 mm. and
is formed of an aluminum disc and center, having a follower plate
of the same material with two cast-iron split rings sprung in. The
water is received into and delivered from the valve cylinder, which
is 18 mm. in diameter and also lined with a cast-iron bushing 1.25
mm. thick. The aluminum bronze shells of both cylinders are 0.75 mm.
in thickness. The valve is a simple piston valve 35 mm. long with
bearing faces 4 mm. long at each end. The water is taken from the
bottom of the separator and led to the center of the valve chest of
the pump by a copper pipe 1 cm. outside diameter. The ports [p115]
leading from the valve to the main cylinder are 3 mm. wide and 34
mm. apart over their openings. It will thus be seen that when the
valve is in its central position, as it should be at the beginning
of the piston stroke, both ports are covered with a lap of 0.5 mm.
inside and out, so that the valve has to move 0.5 mm. before suction
or discharge can take place. As the valve is moving most rapidly at
this point, it opens and both functions begin before the piston has
advanced perceptibly. The delivery is made at the ends of the valve
cylinder through two copper pipes of 1 cm. diameter that unite into
a single pipe before reaching the boiler. The throw of the valve is
14 mm. so that the ports are uncovered and held wide open for the
greater portion of the stroke of the piston, and begin to close only
when the latter approaches the end of its stroke. In this way perfect
freedom is given to the flow of the water and all choking is avoided.
As the engine has been run at a speed of more than 688 revolutions
per minute, the pump must have made at least 344 strokes in the same
time, thus displacing 166.2 cc. of water. The diameter of the piston
rod and valve stem is 3 mm. and they pass through stuffing boxes with
glands of the ordinary type for packing. This pump served its purpose
admirably, and with it it was possible to maintain a continuous
circulation of water through the two coils of the boiler.

The third element in the steam-generating system is the boiler
proper[36] (Plates 25 and 26A), which consists of two coils of copper
pipe, having an outside diameter of 10 mm., each coil being formed of
21 turns each 75 mm. in diameter upon the outside and spaced 7.5 mm.
apart, so that the total axial length of each coil is 36 cm.

The water is delivered to the front end of the right-hand coil, and,
first passing through this, crosses over at the rear of the boiler to
the left-hand coil, returning through it to the front whence it is
led to and delivered into the top of the separator. Here the steam
and water are separated, the former going through the separator and
thence to the engine, while the unevaporated water falls to the
bottom to be again taken into the pumps and sent through the coils.

In order that the draft of the burner and the gases of combustion
might not be dissipated, it was necessary to sheathe the boiler. The
method of doing this is shown in Plate 25. It will be seen that the
front half of the boiler is wrapped in a sheet of mica through which
the coils can be faintly seen. This, in turn, is held at the extreme
front end by a strip of thin sheet-iron, ‹O›. Over the back end the
stack ‹Q›, made of very thin sheet-iron, is slipped. This has an
oblong cross-section at the lower end where it goes over the boiler;
it is provided with a hole through which the midrod passes, and
terminates in a circular opening of about 10 cm. diameter. [p116]

The engine, which is clearly shown in the dimensional drawing, Plate
26B, is of the plain slide-valve type, using a piston valve and solid
piston, without packing rings. The cylinder is formed of a piece of
steel tubing 35 mm. outside diameter, with flanges 47 mm. in diameter
and 2.25 mm. thick brazed to each end, to which the cylinder heads
are attached by small machine screws. Inside this cylinder is a thin
cast-iron bushing in order to obtain a better rubbing surface for the
piston. The cross-head is a small piece of aluminum bronze, running
on round guides that also serve as cylinder braces. There are also
four hollow braces, 5 mm. in diameter, running from the back cylinder
head to a corrugated steel bed-plate, that stands vertically and
reaches from one side rod of the frame of the hull to the other, and
to which are bolted the bearings of the main shaft. The connecting
rod has the cross-section of a four-rayed star and drives a crank
in the center of the shaft. The following are some of the principal
dimensions of the engine:

millimetres.
Inside diameter of cylinder 33
Stroke of piston 70
Length of cylinder inside 88
Length of piston 11
Clearance at each end 0.5
Diameter of piston rod 5
Length of cross-head 17.5
Diameter of guides 4.5
Distance from center to center of guides 26
Length of guides 110
Length of wrist-pin bearing 8.5
Length of connecting rod 150
Ratio of connecting rod to stroke 2-1/7 to 1
Length of crank pin 10
Diameter of main shaft 8
Length of main bearings 25
Distance from center of cylinder to center of valve stem 35
Length of valve 72
Width of ports 2
Outside lap of valve 4
Inside lap of valve 3
Lead of valve 0
Travel of valve 13
Cut-off from beginning of stroke 57
Exhaust opens End of stroke
Exhaust closes on return stroke 48
Diameter of valve stem 4.5
Diameter of eccentric 36
Width of eccentric 4
Width of crank arm 4

The weights were nearly as follows:

grammes.
Engine 464
Pump and pump shafts 231
Gasoline tank and valves 178
Burners 360
Boilers, frames holding boilers, and mica covers over boilers 651
Separator, steam gauge and pipe for engine 540
Exhaust pipe 143
Smoke stack 342
In all, 2909 grammes, or 6.4 pounds.

[Illustration: PL. 26A

DIMENSIONED DRAWING OF BOILER COILS, BURNERS, PUMP, NEEDLE VALVE AND
THRUST BEARING]

[Illustration: PL. 26B

DIMENSIONED DRAWING OF ENGINE NO. 5]

[Illustration: PL. 27A

SIDE AND END ELEVATIONS OF AERODROME NO. 5, MAY 11, 1896]

[Illustration: PL. 27B

AERODROME NO. 5 PLAN VIEW. OCTOBER 24, 1896]

[p117]

These weights are those determined in December, 1896, when some
slight changes had been made from the conditions existing at the time
of the flight by this aerodrome on May 6. Previous to that time, with
a pressure of 130 pounds, between 1.1 and 1.25 horse-power was given
on the Prony brake. At the actual time of flight the pressure was
about 115 pounds, and the actual power very near 1 horse-power.

The valve stem was pivoted to the center of the valve partly because
this was the lightest connection that could be made, and partly to
allow the valve perfect freedom of adjustment upon the seat. Many
parts, such as guides, braces, crank-pins, wrist-pin and shafts are
hollow. The steam is taken in at the front end of the steam chest,
and the exhaust taken out of the center, whence it is led back to
the stack and by means of a forked exhaust pipe discharged in such
a way as to assist the draught of each coil of the boilers. Like
the cylinder the steam chest is made of a piece of steel tubing, 20
mm. diameter on the outside, with an inside diameter of 19 mm., and
is fitted with a cast-iron bushing 0.5 mm. thick, making the inside
diameter of the steam chest 18 mm. It, too, has flanges brazed to the
ends, to which the heads are held by small machine screws.

The shaft for conveying the power to the propeller shafts extends
across the machine from side to side; it is hollow, being 8 mm.
outside diameter, with a hole 5 mm. diameter through the center.

It is formed of five sections: the middle section, containing the
crank, has a length of 110 mm. and is connected at either end,
by flanged couplings, to lengths 320 mm. long, which are in turn
extended by the end sections having a length of 230 mm. In addition
to the four main bearings that are bolted to the pressed-steel
bed-plate already mentioned, there are two bearings on the outer
framework on each side. At the outer end of each shaft there is keyed
thereto a bevel gear with an outside diameter of 27 mm. and having 28
teeth. This gear meshes with one of 35 teeth upon a shaft at right
angles to the main shaft and parallel to the axis of the aerodrome.
These two shafts, one on either arm, serve to carry and transmit the
power to the propellers. They are 192 mm. long, 8 mm. in diameter,
and are provided with three bearings that are brazed to a corrugated
steel plate forming the end of the outrigger portion of the frame.
These shafts are also hollow, having an axial hole 4 mm. in diameter
drilled through them. The propeller seat has a length of 43 mm. and
the propeller is held in position by a collar 25 mm. in diameter at
the front end, from which there project two dowel-pins that fit into
corresponding holes in the hubs of the propellers, which are held up
against the collar by a smaller one screwed into the back end of the
shaft. The thrust of the collar is taken up by a pin screwed into
the end of the forward box and acting as a step against which the
shaft bears, the arrangement being clearly shown by the accompanying
drawing, Plate 26A. [p118]

This, then, comprises the motive power equipment of the aerodrome,
and, to recapitulate, it includes the storage, automatic feeding and
regulation of the fuel; the storage, circulation and evaporation of
the water; the engine to convert the expansive power of the steam
into mechanical work; and the shafting for the transmission of the
energy developed by the engine to the propellers.

The propellers were made with the greatest care. Those used in the
successful trials were 1 metre in diameter, with an actual axial
pitch of 1.25 metres. They were made of white pine, glued together in
strips 7 mm. thick. The hub had a length of 45 mm. and a thickness
or diameter of 25 mm. At the outer edge the blade had a width of 315
mm. and a thickness of 2 mm. These propellers were most accurately
balanced and tested in every particular; each propeller blade was
balanced in weight with its mate and the pitch measured at every
point along the radius to insure its constancy; finally the two
propellers of the pair to be used together were balanced with each
other so that there would be no disturbance in the equilibrium of
the machine. As will be noted from the foregoing description of the
machinery, the propellers ran in opposite directions, as they were
made right- and left-hand screws. The weight of each propeller was
362 grammes.

We now turn again to take up the details of the construction of the
framework by which this propelling machinery is carried. The whole
aerodrome, as clearly shown in the photographs, Plates 27A and 27B,
is built about and dependent from one main backbone or midrod, which
extends well forward of all of the machinery and aft beyond all other
parts. This rod, as well as all other portions of the framework,
is of steel tubing. The midrod, being largest, is 20 mm outside
diameter, with a thickness of 0.5 mm. It is to this midrod that the
wings are directly attached, and from it the hull containing the
machinery is suspended.

The plan outline of the hull skeleton is similar to that of the
deck of a vessel. The steel tubing, 0.5 mm. thick, of which it is
formed, has an outside diameter of 15 mm. from the front end to
the cross-framing used to carry the propellers, back of which the
diameter is decreased to 10 mm.

The midrod makes a slight angle with this frame, the vertical
distance between the centers of the tubing being 73 mm. at the front
and 67 mm. at the back. The tube, corresponding to the keel of a
vessel, is braced to the upper tubes by light U-shaped ribs and by
two 8-mm. tubes forming a V brace on a line with the back end of the
guides of the engine. At the extreme front and back there is a direct
vertical connection to the midrod.

The propeller shafts are 1.23 m. from center to center, and are
carried on a special cross-framing, partaking, as already stated, of
the character of an outrigger on a row-boat. (See Plate 27B.) The
rear rods, which are of 10 mm. steel tubing, start from the front end
of the rear bearings of the propeller shaft and [p119] extend across
from side to side. The top rod is brazed to the side pieces of the
hull and the bottom rod to the keel. They are connected by a vertical
strut of 8-mm. tubing at a distance of 265 mm. inside of each
propeller shaft. At the front end of the propeller shaft two more
rods run across the frame. The lower is similar and parallel to the
back rod already described, while the upper is bowed to the front,
as shown in the plan view of the frame (Plate 30). In order to take
the forward thrust of the propeller a second cross-brace is inserted,
which runs from the rear bearing of the propeller shaft to a point
just in advance of the front head of the cylinder, and is brazed to
the two upper tubes of the cross-frame as well as to the upper tubes
of the main framing of the hull. The outer ends of the tubes of the
cross-framing are brazed to a thin, stamped steel plate which firmly
binds them together, while at the same time it forms a base for
attaching the bearings of the propeller shaft. This end plate has a
thickness of one millimetre.

In addition to the framing proper there are two guy-posts which fit
into the sockets ‹CC›, and over which truss wires are drawn, as shown
in the side view in Plate 27A. These posts have a length of 730 mm.
from the lower edge of the socket, and are capped at their lower
extremity by a light steel ferrule whose outside diameter is 10 mm.

From the drawing of the wings of No. 5, shown in Plate 17, it will
be seen that they are formed of two pine rods 15 mm. in diameter at
the inner ends, tapering to a half circle of the same diameter at
the tips. These rods are connected by eleven spruce ribs measuring
8 mm.×3 mm., and curved, as shown in the side elevation, these, in
turn, being covered by a light white silk drawn so tightly as to
present a smooth, even surface. The total length of the wing is 2
metres, and the width over all is 805 mm. Vertical stiffness is
obtained in the wings by a series of guy-wires, which pass over light
struts resting upon the main rods. These main rods are inserted and
held in the wing clamps ‹A› and ‹B›, Fig. 16, and make an angle of
150° with each other. As is the case with all other essential details
of the aerodrome, a great deal of time and attention was given to the
designing of the wing clamps before a satisfactory arrangement was
secured.

To enable it to control the aerodrome in both directions, the
tail-rudder, Plate 27A, has both a horizontal and a vertical surface,
the approximate dimensions of which are, length 115 cm. (3.8 feet),
maximum width 64 cm. (2.1 feet), giving each quarter section an area
of about 0.64 sq. m. (6.9 sq. ft.). It is given the proper angle and
degree of elasticity in a vertical direction by the flat hickory
spring, which fits into the clamp ‹N›, and attaches the rudder to the
frame.

The only other attachments of the aerodrome are the reel, float,
and counter. They have nothing whatever to do with the flying of
the machine, and are [p120] merely safety appliances to insure its
recovery from the water. The reel consists of a light spool on which
a fine cord is wound, one end of which is attached to a light float
that detaches itself and lies upon the surface of the water when the
machine sinks, while the other end is fastened to the spool that goes
down with the aerodrome. The “float” is a light copper vessel with
conical ends which is firmly fastened to the midrod, and which is
intended to so lower the specific gravity of the whole machine that
it will not sink. The cylindrical portion of this float has a length
of 250 mm. and a diameter of 170 mm., one cone having a length of 65
mm. and the other and front one a length of 140 mm., which makes the
total length of the float 375 mm. It is made of very thin copper, and
served in the successful trials not only as a float to sustain the
machine on the surface of the water, but also as a weight by which
the center of gravity was so adjusted that flight was possible.

The counter records the number of revolutions of the propellers
after launching. It is a small dial counter, reading to 10,000, with
a special attachment which prevents any record being made of the
revolutions of the propellers, until the actual moment of launching,
when a piece on the launching apparatus throws the counter in gear at
the instant that the aerodrome leaps into the air.

DESCRIPTION OF AERODROME NO. 6

Aerodrome No. 6, it will be remembered, was the outgrowth of a number
of changes made in No. 4 during the fall of 1895 and the early part
of 1896. In this reconstruction the aim was to lighten the whole
machine on account of the smaller engines in either No. 4 or No. 5.
The modifications from No. 4 were so radical and the differences that
exist between Nos. 5 and 6 are so considerable as to demand careful
attention.

As regards general appearance the frame of Aerodrome No. 6 resembles
that of No. 5 in consisting of a single continuous midrod of steel
tubing, 20 mm. in diameter, 0.5 mm. thick, immediately beneath which
the hull containing the machinery is situated. In reconstructing
the framework after the tests in January, 1896, had shown it to be
dangerously weak, especially against torsion, it was decided to make
the hull only strong enough to carry its contents and to attach it to
the stronger midrod in such a way that all torsional strains would
be taken up by it, whereas in No. 5 the hull structure must bear a
large proportion of such strains. It was therefore built throughout
of 8-mm. tubing, 0.3 mm. thick, and was rigidly attached to the
midrod by braces at the front and rear, and also at the cross-frame.
The hull was also made narrower (except at the rear, where it was
widened to contain the boiler) and shorter than the hull of No. 5--an
advantageous change made possible by the fact that the engines were
not contained in the hull, but mounted on the transverse frame.

[Illustration: PL. 28

STEEL FRAME OF AERODROME NO. 6, ON LAUNCHING CAR]

[p121]

In No. 5, as described above, a single engine mounted at the
front end of the hull communicated its power through transmission
shafts and gearing to the propellers, which were necessarily in
the same plane. This brought the line of thrust very nearly in the
same plane as the center of gravity of the aerodrome, a condition
tending to promote instability of longitudinal equilibrium. In No.
6, however, the use of two engines situated on the transverse frame
and communicating their power directly to the propellers, made it
possible to raise the transverse frame 12 cm. above the hull, and
thus raise the line of thrust to a position intermediate between the
center of pressure and the center of gravity, without materially
affecting the latter. As a result of this change Aerodrome No. 6
was rendered much more stable and made steadier flights with fewer
undulations than No. 5.

The engines in use on No. 6 were the small engines described above
in connection with No. 4. The cylinders were of steel tubing 2.8
cm. in diameter, with a 5-cm. stroke, each cylinder thus having a
capacity of 30.8 cc. They were lined with a thin cast-iron bushing
and cast-iron rings were sprung in the piston head so as to give as
smooth a rubbing surface and as perfect action as possible. As in the
engine of No. 5 a plain sliding valve of the piston type was used,
cut-off being approximately at one-half, though the ports were so
small that it was difficult to determine it with any great accuracy.
No packing was used, but the parts were carefully ground so as to
give a perfect fit.

These engines, as is most clearly shown in Plate 30, were mounted
symmetrically on either side of the cross-frame and were connected
directly to the propeller shafts. In order to insure that the
propellers would run at the same rate, there was provided a
synchronizing shaft, ‹T›, in Plate 30, having on each end a bevel
gear, which intermeshed with similar gears on the propeller shafts.
Steam for the cylinders was conveyed from the separator through the
pipes ‹LL›.

The steam-generating apparatus for No. 6 was exactly like that
already described in connection with No. 5, the only difference being
in the more compact arrangement in the case of No. 6. The relative
location of the apparatus in the two models is clearly shown in
Plates 28, 29B, and 30, the corresponding parts being similarly
labeled, so that a separate description for No. 6 is superfluous.

The wings used on No. 6 were somewhat smaller than those of No. 5,
and differed from them in having the front mainrib bent to a quadrant
at its outer extremity and continued as the outer rib of the wing.
The degree of curvature of the wings was also somewhat less, being
one-eighteenth for No. 6 and one-twelfth for No. 5. The four wings
were of the same size and had a total area of 54 sq. ft. On account
of the shortened hull of No. 6 they were allowed a much greater range
of adjustment, which rendered it much easier to bring the ‹CP› into
the proper relative position to the ‹CG› than was the ease with No.
5. [p122]

The Pénaud rudder for No. 6 was similar to that for No. 5, the two in
fact being interchangeable, and was similarly attached to the frame.
The reel, float, counter, and all other accessories were identical
for the two machines.

To sum up the comparative features of these two successful
steam-driven models: Aerodrome No. 6 was both lighter and frailer
than No. 5, and required much more delicate adjustment, but when the
correct adjustments had been made its flying qualities were superior,
as regards both speed and stability.

[Illustration: PL. 29A

PLAN VIEW OF AERODROME NO. 6. OCTOBER 23, 1896]

[Illustration: PL. 29B

SIDE ELEVATION OF AERODROME NO. 6. OCTOBER 23, 1896.]

[Illustration: PL. 30

PLAN VIEW OF STEEL FRAMES AND POWER PLANTS OF AERODROMES NOS. 5, 6]

[Illustration: PL. 31

DETAILS OF AERODROME NO. 5]

FOOTNOTES.

[2] “Experiments in Aerodynamics,” ‹Smithsonian Contributions to
Knowledge›, Vol. 27, 1891.

[3] This chapter was written almost entirely by Mr. Langley in 1897.

[4] 1897.

[5] In this statement, of course, no account is taken of the
“internal work of the wind.”

[6] Ten years prior to 1897.

[7] Communication to the French Academy. Extract from the Comptes
Rendus of the Sessions of the Academy of Sciences, Vol. 122, Session
of May 26, 1896.

(Translation.)

A Description of Mechanical Flight. By S. P. Langley.

In a communication which I addressed to the Academy in
July, 1891, I remarked that the results of experimental
investigation had shown the possibility of constructing
machines which could give such a horizontal velocity to
bodies resembling in shape inclined planes, and more than
a thousand times heavier than air, that these could be
sustained on this element.

While I have elsewhere remarked that surfaces other than
planes might give better results, and that absolutely
horizontal flight, which is so desirable in theory, is
hardly realizable in practice, so far as I know there
has never been constructed, up to the present time, any
heavy aerodrome, or so-called flying-machine, which can
keep itself freely in the air by its own force more than
a few seconds, the difficulties encountered in absolutely
free flight being, for many reasons, immeasurably greater
than those experienced when the flight is controlled
by the body’s pressing upward against a horizontal
track, or whirling-arm. No one is unaware that many
experimenters have been engaged in trying to execute free
mechanical flight, and although the demonstration which I
furnished in 1891 [“Experiments in Aerodynamics,” 1891]
of its theoretical possibility with means then at our
disposition, seemed conclusive, so long a time has elapsed
without practical results, that it might be doubted
whether these theoretical conditions are to be realized.
I have thought it well, then, to occupy myself with the
construction of an aerodrome with which I might put my
previous conclusions to the test of experiment.

The Academy will, perhaps, find it interesting to read the
narrative given here by an eye-witness, who is well known
to it. I am led to present it not only by the request
with which he honors me, but by the apprehension that my
administrative duties may put a stop to these researches,
so that it seems to me advisable to announce the degree in
which I have already succeeded, although this success be
not as complete as I should like to make it.

The experiments took place on a bay of the Potomac River,
some distance below Washington. The aerodrome was built
chiefly of steel, though lighter material entered into the
construction, so that its density as a whole was a little
below unity. No gas whatever entered into the construction
of the machine, and the absolute weight, independent
of fuel and water, was about 11 kilos (24 pounds). The
width of the supporting surfaces was about 4 metres (13
feet), and the power was furnished by an extremely light
engine of approximately one horse-power. There was no
one to direct it on board, and the means for keeping it
automatically in horizontal flight were not complete. It
is important to remark that the small dimensions of the
machine did not allow it to include any apparatus for
condensing the steam, so that it could only carry water
enough for a very brief course--a drawback which would not
be encountered in one of a larger construction.

It is also to be noted that the speed estimated by
Mr. Bell was that obtained in a continuous ascending
flight, and much less than would have been attained in a
horizontal course.

On Mechanical Flight. Letter of Mr. Alexander Graham Bell
to Mr. Langley.

Washington, May 6, 1896.

I am quite aware that you are not desirous of publication
until you have attained more complete success in obtaining
horizontal flight under an automatic direction, but it
seems that what I have been privileged to see to-day marks
such a great progress on everything ever before done in
this way, that the news of it should be made public, and
I am happy to give my own testimony on the results of two
trials which I have witnessed to-day by your invitation,
hoping that you will kindly consent to making it known.

For the first trial, the apparatus, chiefly constructed
of steel and driven by a steam engine, was launched from
a boat at a height of about 20 feet from the water. Under
the impulse of its engines alone, it advanced against the
wind and while drifting little, and slowly ascending with
a remarkably uniform motion, it described curves of about
100 metres in diameter; till at a height in the air which
I estimate at about 25 metres (82 feet), the revolutions
of the screws ceased for want of steam, as I understood,
and the apparatus descended gently and sank into the
water, which it reached in a minute and a half from the
start. It was not damaged, and was immediately ready for
another flight.

In the second trial it repeated in nearly every respect
the action of the first, and with an identical result.
It rose smoothly in great curves until it approached a
prominent wooded promontory, which it crossed at a height
of 8 to 10 metres above the tops of the highest trees,
upon the exhaustion of the steam descending slowly into
the bay, where it settled in a minute and thirty-one
seconds from the start. You have an instantaneous
photograph of it, which I took just after the launch. [See
plates 20, 21, and 22 of present work.]

From the extent of the curves which it described, which
I estimated with other persons, from measurements which
I took, and from the number of revolutions of the
propellers, as recorded by the automatic counter which I
consulted, I estimate the absolute length of each course
to be over half an English mile, or, more exactly a little
over 900 metres (2953 feet).

The duration of flight during the second trial was one
minute and thirty-one seconds, and the average velocity
between twenty and twenty-five miles an hour, or, let us
say 10 metres a second, in a course which was constantly
ascending. I was extremely impressed by the easy regular
course of each trial, and by the fact that the apparatus
descended each time with such smoothness and gentleness as
to render any jar or danger out of the question.

It seemed to me that no one could have witnessed these
experiments without being convinced that the possibility
of mechanical flight had been demonstrated.

[8] It is desirable that the reader should be acquainted with the
contents of this treatise, and of another by me, entitled “The
Internal Work of the Wind,” both published by the Smithsonian
Institution. A knowledge of these works is not absolutely necessary,
but of advantage in connection with what follows.

[9] “Experiments in Aerodynamics,” p. 107.

[10] Chapter VIII.

[11] His device for obtaining automatic equilibrium is found in
connection with the description of his “Aeroplane Auto Moteur,” in
“L’Aeronaute” for January, 1872.

[12] I have never obtained so good a result as this with any rubber
motor. S. P. Langley.

[13] One pound of twisted rubber appears, from my experiments, to be
capable of momentarily yielding nearly 600 foot-pounds of energy, but
this effect is attained only by twisting it too far. It will be safer
to take at most 300 foot-pounds, and as the strain must be taken up
by a tube or frame weighing at least as much as the rubber, we have
approximately 0.0091 as the horse-power for one minute, or 0.091
horse-power for six seconds as the maximum effect, in continuous
work, of a pound of ‹twisted› rubber strands. The longitudinal pull
of the rubber is much greater, but it is difficult to employ it in
this way for models, owing to the great relative weight of the tube
or frame needed to bear the bending strain. In either form, rubber is
far more effective for the weight than any steel spring (see later
chapter on Available Motors).

[14] The aerodrome is sustained by the upward pressure of the
air, which must be replaceable by the resultant pressure at some
particular point, designated by ‹CP›.

[15] See Century Magazine, October, 1891.

[16] Subsequent observations indicate that the maximum velocity of
horizontal flight must have been about 10 metres per second.

[17] Observers following de Lucy have long since called attention to
the fact that as the scale of Nature’s flying things increases, the
size of the sustaining surfaces diminishes relatively to the weight
sustained. M. Harting (Aeronautical Society, 1870) has shown that the
relation √area/∛weight is surprisingly constant when bats varying
in weight as much as 250 times are the subject of the experiment,
and later observations by Marey have not materially affected the
statement. As to the muscular power which Nature has imparted with
the greater or lesser weight, this varies, decreasing very rapidly
as the weight increases. The same remark may be made apparently with
at least approximate truth, with regard to the soaring bird, and the
important inference is that if there be any analogy between the bird
and the aerodrome, as the scale of the construction of the latter
increases, it may be reasonably anticipated that the size of the
sustaining surfaces will relatively diminish rather than increase.
We may conveniently use M. Harting’s formula in the form ‹a› =
‹n›^2‹w›^{2/3} = ‹l›^2/‹m›^2 where ‹a› = area in sq. cm., ‹w› the
weight in grammes, ‹l› the length of the wing in cm., ‹n› and ‹m›
constants derived from observation.

[18] A singular fact connected with the stretching of rubber is
that the extension is not only not directly proportional to the
power producing it, but that up to a certain limit it increases more
rapidly than the power, and after this the relation becomes for a
time more nearly constant, and after this again the extension becomes
less and less in proportion.

In other words, if a curve be constructed whose abscissae represent
extensions, and ordinates the corresponding weights, it will show
a reverse curvature, one portion being concave toward the axis of
abscissae, the other convex.

[19] The following table taken from “Experiments in Aerodynamics,”
p. 107, gives the data for soaring of 30×4.8 inch planes, weight 500
grammes.

-------+-----------------------+-----------------+--------------------+
| | | Weight with planes |
| Soaring speed | Work expended | of like form that |
Angle | ‹V›. | per minute. | 1 horse-power will |
with | | |drive through the |
horizon| | |air at velocity ‹V›.|
α. +-----------+-----------+---------+-------+----------+---------+
| Metres | Feet |Kilogram-| Foot- | Kilo- | Pounds. |
|per second.|per second.| metres. |pounds.| grammes. | |
-------+-----------+-----------+---------+-------+----------+---------+
45° | 11.2 | 36.7 | 336 | 2,434 | 6.8 | 15 |
30 | 10.6 | 34.8 | 175 | 1,268 | 13.0 | 29 |
15 | 11.2 | 36.7 | 86 | 623 | 26.5 | 58 |
10 | 12.4 | 40.7 | 65 | 474 | 34.8 | 77 |
5 | 15.2 | 49.8 | 41 | 297 | 55.5 | 122 |
2 | 20.0 | 65.6 | 24 | 174 | 95.0 | 209 |
-------+-----------+-----------+---------+-------+----------+---------+

The relations shown in the above table hold true only in case of
planes supporting about 1.1 pounds to each square foot of sustaining
area. For a different proportion of area to weight, other conditions
would obtain.

[20] This pressure per unit of area varies with the area itself, but
in a degree which is negligible for our immediate purpose.

[21] See “Internal Work of the Wind”; also Revue de L’Aeronautique,
3^e Livraison, 1893.

[22] More recent experiments under my direction by Mr. Huffaker give
similar results, but confirm my earlier and cruder observations that
the curve, used alone, for small angles, is much more unstable than
the plane.

[23] As stated in the Preface, Part III has not yet been prepared for
publication.

[24] According to Wellner (“Zeitschrift für Luftschiffahrt,”
Beilage, 1893), in a curved surface with 1/12 rise, if the angle of
inclination of the chord of the surface be α, and the angle between
the direction of resultant air pressure and the normal to the
direction of motion be β, then β<α and the soaring speed is

‹V› = √(‹P›/‹K›×(1/(‹F›(α)×cos β)))

while the efficiency is

‹W›/‹R› = Weight/Resistance = tan β

The following were derived from experiments in the wind:

α = −3° 0° +3° 6° 9° 12°
‹F›(α) = 0.20 0.80 0.75 0.90 1.00 1.05
Tan β = 0.01 0.02 0.03 0.04 0.10 0.17

so that according to him, a curved surface shows finite soaring
speeds when the angle of inclination is 0° or even slightly negative.

[25] The following formulæ proposed by Mr. Chas. M. Manly show how
the center of pressure may be moved any desired distance either
forward or backward without in any way affecting the center of
gravity, and by merely moving the front and rear wings the same
amounts but in opposite directions, the total movement of each wing
being in either case five times the amount that is desired to move
the mean ‹CP›_1, and the direction of movement of the front wing
determining the direction of movement of ‹CP›_1.

In Figure 7, ‹CP›_{fw} and ‹CP›_{rw} are the centers of pressure of
the front and rear wings respectively; the weights of the wings,
which are assumed to be equal and concentrated at their centers of
figure, are represented by ‹w›, ‹w›, and ‹a› is the distance of the
center of pressure in either wing from its center of figure. The
original mean center of pressure of the aerodrome is ‹CP›_1, ‹W› is
the weight of the aerodrome, supposed to be concentrated at ‹CG›_1,
while ‹m› is the distance from ‹CP›_{rw} to ‹CG›_1.

Now, if we have assumed that the rear wing, being of the same size
as the front one, has a lifting effect of only 0.66, and on this
assumption is calculated the proper relative positions of the front
and rear wings to cause the ‹CP›_1 to come directly over the ‹CG›_1,
and upon testing the aerodrome find that it is too heavy in front
and, therefore, wish to move the center of pressure forward an
amount, say ‹b›, without affecting the center of gravity, we can
calculate the proper relative positions of the front and rear wings
in the following manner. While the aerodrome as a whole is balanced
at the point ‹CG›_1, the weight of the wings is not balanced around
this point, for the rear wing, owing to its decreased lifting effect,
is proportionately farther from ‹CP›_1 than the front wing. In order,
therefore, to avoid moving the center of gravity of the machine as
a whole, any movement of the wings must be made in such a way as to
cause the difference between the weight of the rear wing multiplied
by its distance from ‹CG›_1 and the weight of the front multiplied by
its distance from ‹CG›_1 to equal a constant: that is,

‹w›(‹m› + ‹a›)−‹w›(0.66‹m›−‹a›) = constant,

and

0.33‹w›‹m› + 2‹w›‹a› = constant.

[Illustration: FIG. 7.]

[Illustration: FIG. 8.]

[Illustration: FIG. 9.

FIGS. 7–9. Diagrams Illustrating formulæ for moving C. P. without
disturbing C. G.]

If now the wings be moved so that ‹CP›_1 is moved forward a distance
‹b›, we may indicate the distance from ‹CG›_1 to the new ‹CP›_{rw}
by ‹z›, and equating the difference between the weight of the rear
wing multiplied by its new distance from ‹CG›_1 and the weight of the
front wing multiplied by its new distance from ‹CG›_1 and making this
difference equal to the constant difference, we can calculate ‹z› in
terms of ‹m› and ‹b›, as follows:

Fig. 8,

‹w›(‹a› + ‹z›)−‹w›(0.66(‹z› + ‹b›) + ‹b›−‹a›) =
0.33‹w›‹m› + 2‹w›‹a›,

∴ ‹z› = ‹m› + 5‹b›.

Knowing ‹z›, we readily find that the new distance from ‹CP›_{fw} to
‹CG›_1 equals:

0.66(‹z› + ‹b›) + ‹b› = 0.66‹m› + 5‹b›.

In a similar manner we may calculate the proper relative positions of
the front and rear wings when we wish to move the center of pressure
backward a distance, ‹b›, from the original ‹CP›_1 without changing
the position of ‹CG›_1. From Fig. 7, we have as before:

‹w›(‹m› + ‹a›)−‹w›(0.66‹m›−‹a›) = constant,
0.33‹w›‹m› + 2‹w›‹a› = constant.

Fig. 9,

‹w›(‹z›_1 + ‹a›)−‹w›(0.66(‹z›_1−‹b›)−‹b›−‹a›) =
0.33‹w›‹m› + 2‹w›‹a›.

∴ ‹z›_1 = ‹m›−5‹b›.

Similarly we have for the new distance from ‹CP›_{fw} to ‹CG›_1:

0.66(‹z›_1−‹b›)−‹b› = 0.66‹m›−5‹b›.

[26] It is to be remembered that these aerodromes were under
incessant modifications, No. 4 for instance, presenting successive
changes which made of it in reality a number of different machines,
one merging by constant alterations into the other, though it still
went under the same name. After 1895 the type of the models remained
relatively constant, but during the first five years of the work,
constructions equal to the original building of at least eight or ten
independent aerodromes were made.

[27] Chapter V.

[28] “Pocketing” is a form of distortion in which the canvas or silk
bags locally in numerous places between the cross-ribs.

[29] The site of these experiments, which was 30 miles below
Washington, has been described. The writer is designated by the
initial “L”; Dr. Barus, who several times assisted, by the letter
“B”; Mr Reed, carpenter, by “R”; Mr Maltby, machinist, by “M”; and
Mr. Gaertner, instrument maker, by “G.”

[30] Weights and dimensions are here given in approximate pounds and
feet.

[31] “Experiments in Aerodynamics.”

[32] On the data of “Aerodynamics,” a plane having 1.8 sq. ft. of
surface per pound, and advancing at an angle of 20°, would soar at a
speed of 24.1 ft. per second.

[33] It will be remembered that the purely theoretical conclusions
just cited apply to the power delivered in direct thrust, but that of
the above actual H. P. an indefinite amount was lost in friction and
slip of propellers.

[34] It may be observed that at this time the position of the ‹CP›
was calculated on the assumption that the pressure for flight
surfaces was proportional to the areas, without also allowing for
the fact that the following surfaces, like the tail, were under the
“lee” of the wind and so far less efficient. It follows, then, that
the value ‹CP›−‹CG› was not really 0, as was assumed, but something
considerable.

[35] Very exact accuracy in these minute details is indispensable to
the efficient working of the engines.

[36] The reader who may care to note the evolution of this boiler,
by trial and error, will find a portion of the many discarded types
shown in Plate 13.

[p123]

PART II. 1897 TO 1903
BY CHARLES M. MANLY
Assistant in Charge of Experiments

CHAPTER I
INTRODUCTORY

Although in 1896 Mr. Langley had made the firm resolution not to
undertake the construction of a large man-carrying machine, as he
realized that his multitudinous administrative duties left him
practically no time available for original research, yet the longing
to take the final great step of actually transporting a human being
through the air, which the successful flights of the models had now
for the first time in the history of the world actually proved to be
possible, soon became irresistible.

Ten years of almost disheartening difficulties, a full appreciation
of which can hardly be gained from the preceding description,
had already been spent in demonstrating that mechanical flight
was practicable, and Mr. Langley thoroughly realized that the
construction of a large aerodrome would involve as great, if not
even greater difficulties. Nevertheless, his indomitable will,
which balked at no obstacle, however great it might seem, prevailed
against the advice of his close friends and associates, and even
that of his physician, who had counselled him that a resumption of
concentrated thought and vigorous endeavor would materially shorten
his life, which had already passed three score years. Only a few were
privileged to come into close contact with him in his daily work,
and thereby catch the inspiration of his unwavering persistence, his
ceaseless perseverance, his plain inability to submit to defeat; but
no one who has read the record of his astronomical expedition to Mt.
Whitney, or the story of his development of the Bolometer, or the
preceding chapters of this history of his years of patient work in
the development of the flying machine, can have failed to obtain some
appreciation of this most striking feature of his character. Having
once determined on the accomplishment of a definite object, no amount
of difficulty that might arise deterred him from pushing on until in
some way and by some means he had succeeded; and no one appreciated
better than he that if the thin edge of the right wedge can be
inserted under an obstacle, that obstacle can be removed, no matter
how formidable it may seem.

The undertaking of the construction of a large aerodrome was very
largely influenced by President McKinley, who had become impressed
with the great [p124] possibilities of a flying machine as an engine
of war. When he found that Mr. Langley was willing to devote his
own time to the development of a machine, provided the Government
would furnish the funds for the actual construction and tests of it,
he appointed a joint board, consisting of Army and Navy officers,
to investigate and report on the plans with which Mr. Langley had
achieved success with the models. The report of this joint board of
Army and Navy officers being favorable, the Board of Ordnance and
Fortification of the War Department, at the direction of President
McKinley, requested Mr. Langley to undertake the construction and
test of a machine, which, while not expected to be a practical war
machine, might finally lead to the development of such an engine of
war. In this connection it is interesting to read a letter which Mr.
Langley addressed to the Board of Ordnance and Fortification at the
time he undertook this work.

SMITHSONIAN INSTITUTION, December 12, 1898.

‹The Board of Ordnance and Fortification, War Department›.

GENTLEMEN: In response to your invitation, I repeat what I had the
honor to say to the Board--that I am willing, with the consent of
the Regents of this Institution, to undertake for the Government the
further investigation of the subject of the construction of a flying
machine on a scale capable of carrying a man, the investigation to
include the construction, development and test of such a machine
under conditions left as far as practicable in my discretion, it
being understood that my services are given to the Government in
such time as may not be occupied by the business of the Institution,
and without charge.

I have reason to believe that the cost of the construction will come
within the sum of $50,000.00, and that not more than one-half of
that will be called for in the coming year.

I entirely agree with what I understand to be the wish of the Board
that privacy be observed with regard to the work, and only when it
reaches a successful completion shall I wish to make public the fact
of its success.

I attach to this a memorandum of my understanding of some points of
detail in order to be sure that it is also the understanding of the
Board, and I am, gentlemen,

With much respect,
Your obedient servant,
S. P. LANGLEY.

MEMORANDUM

ATTACHED TO MY LETTER OF THIS DATE TO THE BOARD OF ORDNANCE AND
FORTIFICATION

While stating that I have, so far as I know, an exclusive right of
property in the results of the experiments in aerodromics which
I have conducted heretofore and am now conducting, and while
understanding that this property and all rights connected with it,
whether patentable or otherwise, will remain mine unqualifiedly, I
am glad to place these results, without charge, at the service of
the Board of Ordnance and Fortification for the special construction
at present proposed, which seems to me to be of National utility.
[p125]

I assume that no public statement will be made by the permission
of the Board until the work is terminated, but that I may publish
ultimately at my discretion a statement of any scientific work done
in this connection.

I understand that the exercise of this discretion includes the
ordering and purchase of all material by contract or in open market,
and the employment of any necessary help, without restriction, and
that, while I desire that no money shall pass through my hands,
itemized bills for each expenditure, made in proper form and
approved by me, will be paid by the Chief Signal Officer.

Much has already been spent at the Smithsonian Institution for the
purpose in question, in special apparatus, tools and experiments,
and in recent constructions now actually going on, which have
involved still more time than money, and which are essential for
experimental use in building the proposed machine; and since to
re-create all this independently would greatly defer progress, I
assume that my discretion includes the decision as to how far this
shall be used and paid for at the cost of this allotment (it being
understood that I have no personal property in any of the material
which might be transferred for the purpose of the work); and I also
assume that my discretion includes the decision as to where the work
shall be conducted--that is, whether in shops already constructed,
or in others to be elsewhere erected or rented, with the necessary
adjuncts, whether on land or water, and generally whatever is
necessary to the earliest attainment of the object desired by the
Board.

S. P. LANGLEY.
SMITHSONIAN INSTITUTION, WASHINGTON, D. C.,
December 12, 1898.

As is always the case in experimental work, especially in a field so
very new as was the field of aerodromics at the time that this larger
construction was undertaken, the “plant,” or shops and laboratories
required for the constructional and testing work, grew to a size
far beyond what seemed even remotely possible at the beginning of
the work; and even the mere administration involved in the carrying
on of this work proved to be no inconsiderable matter before it had
progressed very far.

The years of experiment with the models had demonstrated clearly that
the greatest difficulty in the development of the aerodrome was the
construction of a suitable power generator, which should combine the
elements of extreme lightness and unusual power with a fair degree
of durability. Although remarkably good results had been secured in
the case of the models through the use of steam, it was realized
from the first that not only would the development of a steam-power
plant for a large man-carrying aerodrome present difficulties of a
constructional nature, but that such a steam plant would necessarily
be so fragile and delicate as to make it a constant menace to the
machine which it was to propel. The solution of the difficulty, it
was believed, was to be found in the use of an internal combustion
engine; but Mr. Langley had had very little experience with such
engines, and was averse therefore to undertaking the construction of
a large aerodrome until he had assurance that a suitable gasoline
engine could be secured. Before making an agreement to attempt the
work for the War [p126] Department, he had, therefore, made a search
for a reliable builder who would undertake to construct a gasoline
engine of not less than 12 horse-power to weigh not exceeding 100
pounds, and what then seemed a safe contract had been entered into
with such a builder to supply one engine which would meet these
requirements.

Almost immediately before the Board of Ordnance and Fortification
had officially placed the work in Mr. Langley’s hands and had made
an allotment of fifty thousand dollars to meet the expenses thereof,
it was found that the engine builder could not be depended on, and
that it would, therefore, be necessary to find one who was more
reliable and more experienced in the construction of light engines.
After a most extended search for the best builder to undertake this
work, a contract was entered into on December 12, 1898, with Mr. S.
M. Balzer, an engine builder in New York City. He was to furnish a
twelve-horse-power engine to weigh not more then 100 pounds, and
delivery of it was to be made on or before February 28, 1899. With
this great problem of the engine apparently provided for, every
facility of the Institution shops was pressed to the utmost limit in
order to have the frame, supporting surfaces, launching apparatus,
and other accessories ready as soon as possible after the delivery of
the engine. It was expected from the first that more power would be
necessary than this one engine would furnish, and provision had been
made in the contract that a duplicate engine should be constructed
immediately after the completion of this first one. From past
experience, however, it was not likely that the correct balancing of
the aerodrome could be determined from ‹a priori› calculation based
on the results obtained with the models, and it was, therefore,
expected that the aerodrome would have to be launched several times
before a successful flight could be obtained. In view of this it was
planned to make a test of the machine as soon as the first engine
was ready, with the expectation that, while the aerodrome would not
have sufficient power to fly, yet the test would furnish definite
data on the all-important question of balancing, and also determine
whether or not the launching apparatus would require modification. In
fact, Mr. Langley felt so apprehensive that the first, and possibly
the second test, would be unsuccessful that, in order to avoid the
possibility of a fatal accident, it was planned that a dummy should
be used to represent the weight of the man in these preliminary tests.

This plan, however, was not carried out. In 1903, when the large
aerodrome was finally completed, so much time had been lost that the
writer proposed to assume the risks of such an accident and to guide
the machine in its first test, in the hope of avoiding a disaster,
with the consequent delay of months for repairs, which the presence
of a controlling hand capable of correcting any inaccuracies of
balancing rendered far less likely to occur. To this proposal Mr.
Langley assented with great reluctance, as he fully realized the
danger involved. [p127]

Particular attention is called to the above facts, which clearly show
that while a certain degree of success in the initial tests was later
hoped for, yet from the beginning it had been felt rather certain
that several tests would have to be made before final success would
be achieved.

To those experienced in scientific experiments this realization of
the probability of several tests being necessary before success could
reasonably be expected does not seem strange, for the record of past
experience contains very few examples of epoch-making inventions
springing full fledged from the hand of their maker and proving a
success on the first test.

The two experiments made in the fall of 1903, in which the aerodrome
was each time so damaged in the process of launching that its ability
to fly was never really tested, should therefore be considered merely
as the first of a series which it had been expected would need to
be made before success would be achieved. Further tests were made
impossible at the time on account of the lack of funds, the expense
of such work being unusually heavy.

While the lack of funds, therefore, was the real cause of the
temporary suspension of the work, yet an influence which does not
often enter into scientific work—the unjust criticism of a hostile
press—was directly responsible for the lack of funds. It seems very
certain that had it not been for this criticism of the press the
funds would have been readily forthcoming for continuing the work to
the point of success.

[p128]

CHAPTER II
GENERAL CONSIDERATIONS

In the development of man-carrying flying machines two well-defined
paths are open. First: Starting with gliding machines, in which
gravity furnishes the motive power, the operator may by practice
acquire sufficient skill in controlling them to warrant the addition
of propelling mechanism, and individual skill in control may be
gradually replaced by automatic controlling mechanism. Second: From
self-propelled models, possessing automatic-equilibrium controlling
mechanism, and of a sufficient size to furnish determinative data,
one may, by proper modification in size and construction, progress
to an automatically controlled man-carrying machine in which, for
ideal conditions, no especial skill on the part of the operator is
required. Each method has its advantages.

After concluding his earlier and purely physical researches, the
results of which were embodied in “Experiments in Aerodynamics,” Mr.
Langley was so firmly convinced of the practicability of mechanical
flight that he undertook the construction of the model aerodromes
in order to demonstrate it. It is very doubtful if at any time,
prior to the successful flights of the models in 1896, he seriously
contemplated the construction of man-carrying machines. His object
in developing the models was not, therefore, to furnish a prototype
for a large machine, but merely to demonstrate the feasibility of
mechanical flight; and this he did. This is shown very clearly by the
closing remark of the article he published in 1897, describing the
flights of the models. “I have now brought to a close the portion of
the work which seemed to be specially mine—the demonstration of the
practicability of mechanical flight-—and for the next stage, which is
the commercial and practical development of the idea, it is probable
that the world may look to others.”[37] When he later undertook
the construction of the large machine for the War Department it
was natural that, with the inspiring sight of the models in flight
still fresh in his mind, he determined to use as a prototype these
successful machines, which were the only things of human construction
that had ever really flown for any considerable distance.

Not being an engineer, and realizing that to pass from the
construction of models to that of man-carrying machines involved the
solution of many engineering problems, Mr. Langley, in the spring of
1898, sought the advice of Dr. R. H. Thurston, who had from the first
manifested the deepest interest in his [p129] work in aerodromics.
On the recommendation of Dr. Thurston he engaged the services of the
writer, who assumed charge of the work in June, 1898.

While the method of “cut and try” had brought success in the models,
and was perhaps the only method by which they could have been
successfully developed, it was thought that, with these models as a
basis of design, much time would be saved by making an analytical
study of them as engineering structures, and from the data thus
obtained the proper proportions for the parts of the larger machine
could be calculated.

Such an analytical study, however, revealed very little from which to
make calculations as to the strength necessary for the various parts
of the large machine, but it did show very clearly that most of the
parts were working under stresses generally far above the elastic
limit of the materials, and in many cases the ultimate breaking
strength was closely approached. Such a condition was the natural
outcome of the method by which these models had been developed—all
the various parts having been built at first of the least possible
weight and, when they proved too weak, strengthened until they would
withstand the stresses imposed on them. It is extremely doubtful if
previous calculations as to the strength necessary would have been
of any assistance, in fact it is probable that it would have been a
distinct disadvantage and would have resulted in the machines being
entirely too heavy for flight.

The exact strength which had been incorporated in the frames of
the models was as unknown as was the exact amount of the stresses
which they has been made to withstand. Their static strength was
easily determined by calculation, but the stresses due to the live
loads were incapable of exact determination from the available
data, for stresses produce strains, which in turn generally cause
distortions accompanied by greatly increased stresses. While exact
data were, therefore, lacking as to stresses and strengths in many
of the important parts, yet the models furnished most important
illustrations of unusual strength for minimum weight, and a careful
study of them showed many ways in which increased strength could be
obtained with decreased weight which could hardly have been devised
without these concrete examples.

It was, however, by no means possible to build the large aerodrome
within the permissible limits of weight by simply increasing the
various parts of the models according to some predetermined function
of the size of the whole.

The fundamental difficulty is that inevitably, by the laws of
geometry, which are mere expressions of the properties of space,
if a solid of any form is magnified, the weight increases as the
cube, while the surface increases only as the square, of the linear
dimensions. Successive generations of physicists and mathematicians
pointed out that while this “law of the cube” is of advantage in
the construction of balloons, yet it is a stumbling block that will
prevent man [p130] from ever building a dynamic flying machine
sufficiently large to carry even one human being.[38]

However, since strength is a function of material and form rather
than weight, it is possible by selecting proper materials and
adopting suitable structural forms to evade to a certain extent
this “law of the cube.” The whole history of structural science has
therefore been a series of attempts to find stronger and lighter
material and to discover methods of so modifying form as to dispense
with all parts of a structure that do not contribute to its strength.
So in aerodromics the structural problem has been that of finding
materials and forms best suited to the purpose for which they are
required, for it does not always follow that either the form or
the material best suited for one scale of construction is the most
advantageous to employ on a different scale. Nor is even the form
or material which gives the greatest strength for the least weight
necessarily the best to employ. For the structural problem must
necessarily be co-ordinated with those of balancing, propelling, and
transporting, and each must, therefore, have its proper attention in
the design of the whole machine.

Many of the general considerations of the design of an aerodrome
sufficiently large to transport a man were determined during the
spring and summer of 1898, when the first actual drawings (Plate
32, Figs. 1, 2 and 3) of the proposed machine were made. Starting
with the assumption that the Models Nos. 5 and 6 were capable of
transporting a load of approximately ten pounds more than their
weight, it was seen that, since the supporting surface of any
aerodrome would increase approximately as the square of the linear
dimensions, in order to carry a man the aerodrome would need to be
approximately four times the linear dimensions of these models.
Calculations based on the results accomplished in the construction
of the models indicated that such an aerodrome would need to be
equipped with engines developing 24 horse-power. The best that could
reasonably be hoped for was that these engines would not weigh over
200 pounds, and, therefore, allowing 40 pounds for fuel and fuel
tanks, it became necessary to bring the weight of frame, supporting
surfaces, tail, rudder, propellers and every other accessory within
250 pounds, if the total weight of the machine, including 150 pounds
for the aeronaut, was not to exceed 640 pounds, or 16 times the
combined weight of the model and its load of 10 pounds. Although the
problem of constructing the frame, wings and all other parts within
the limit of 250 pounds seemed indeed formidable, it was believed
that the greatest obstacle in the production of such a machine would
be that of securing a sufficiently light and powerful engine to
propel it.

[Illustration: PL. 32

DRAWINGS OF PROPOSED MAN-CARRYING AERODROME, 1898]

[p131]

A brief account has already been given of the attempts made by Mr.
Langley to secure a suitable gasoline engine for the large aerodrome,
but the difficulties encountered in the search have not perhaps been
sufficiently emphasized. At this time (1898) the automobile industry,
through which has come the development of the gasoline engine, was
in its infancy, and there were few builders either in the United
States or Europe who were attempting anything but rough and heavy
construction. Many of them were enthusiastic over the possibilities
of the internal combustion engine, and were ready to talk of devising
such an engine as the aerodrome would require, but few were willing
to guarantee any such definite results as were demanded. However,
the prospects of securing a suitable gasoline engine from a reliable
builder within a reasonable time seemed so strong that it was decided
early in 1898 to begin the construction of the frame on the general
plan which would probably be best adapted for use with a gasoline
engine, and in case it finally proved impossible to secure such an
engine, to construct later a steam plant which could be adapted to
this particular frame.

Some tentative work on the construction of the frame was accordingly
begun in the summer of 1898, some months before an engine builder was
found who seemed likely to be successful in furnishing the engines.
An extensive series of tests on propellers was also made at this time
for the immediate purpose of determining what form and size would
be best, since the dimensions of the transverse frame could not be
definitely settled until it was known how large the propellers would
need to be.

Preliminary designs were also begun for the wings, rudders, and
launching apparatus, but when the point was reached of actually
making the working drawings for these, it was seen that the change
in the scale of the work required many important modifications in
constructional details. As the models had flown successfully only
three times, and in each case under practically the same conditions,
it was felt that it would be unwise to make changes in important
details without first making a series of tests of the models in
flight to determine the effect of such changes. It was therefore
decided to completely overhaul Models Nos. 5 and 6, strengthening
them in many important parts and “tuning up” their power plants,
which had slightly deteriorated since they were last used in
November, 1896. When the work of preparing these models for further
experiments was begun it was thought that it would require at most
only a few weeks, but as it progressed it was found that certain
parts of the mechanical work on the engines had been so poorly
executed originally that it would be necessary to practically rebuild
the engines. The final result was that the power plants of both
aerodromes were entirely rebuilt, and they were not ready for actual
test in flight until the spring of 1899. [p132]

Much of the preliminary work necessary for the determination of
actual working plans was therefore completed in the summer and fall
of 1898, and when on December 12 a seemingly satisfactory contract
for the engines for the large aerodrome had been made it was thought
that rapid progress could be made on the constructional work after
January 1, 1899, when the allotment from the War Department would
become available.

[p133]

CHAPTER III
EXPERIMENTS WITH MODELS

Immediately after the contract for the engine had been placed and the
actual work had been begun, attention was given to the problem of
providing means for properly launching the aerodrome. On the theory
that the plan of launching the small aerodromes, which had finally
been adopted after many years of painstaking experiment, would be
the best to employ for the large aerodrome, Mr. Langley decided to
have constructed a large house-boat with the launching track arranged
on it in a way similar to that used for the small machines. While
the general plans for this boat had been under consideration for
some time, the actual working drawings were completed in January,
1899, and so great seemed the need for expediting its construction,
in order to have it ready at the time when the engine was expected,
that the contract which was made for its construction specifically
provided for its being completed promptly, there being a large
forfeit to cover any delay on the part of the contractor.

While the boat itself was being constructed, the working drawings
were completed for the house to be built on it, and a contract was
made for the construction of this house within a given period, there
being also a time forfeit in this contract.

When the end of February arrived, it was found that, although the
engine builder had succeeded in constructing an engine which weighed
one hundred pounds, and which theoretically should have given
something over twelve horse-power, yet he was unable to make it work
properly. And then began a protracted period of most exasperating
delays, the engine builder promising from week to week that certainly
within the succeeding ten days he would be able to make delivery of
the engine developing the full horse-power for which the contract
called. After this delay on the engine had continued for some
months—a delay which necessitated the cessation of the work on the
main steel frame of the aerodrome, as it was deemed best to make
certain tests of the engine running while supported by a portion of
the frame to determine whether or not it was strong enough before
completing the rest of it-—Mr. Langley decided to employ part of
the time in the construction of a model of one-eighth the linear
dimensions of the large aerodrome, which was to be used in testing
a model of the newly designed launching apparatus described later,
and which might also be flown as a kite in making check measurements
on the proper balancing which should be employed for the large
aerodrome. [p134]

The perfected launching apparatus which had been used for the
steam-driven models Nos. 5 and 6 (described in Part I, Chapter X) had
proved most satisfactory and reliable, but when the designs were made
for a launching apparatus for the large machine it was found that
an exact duplication of the plan of the small one involved serious
difficulties in connection with the construction of the house-boat,
owing to the very considerable weight and size of the turn-table
necessary to permit the aerodrome to be launched in any desired
direction, regardless of the direction in which the houseboat might
be pointing under the influence of the wind and tide. A new design
was accordingly made for a launching apparatus in which the launching
car was to run on a track mounted directly on the turn-table, the
launching car supporting the aerodrome from underneath, instead of
being mounted in an inverted position on an overhead track with the
aerodrome depending from it.

From the previous description of the launching apparatus, it will be
recalled that, in order to provide that the aerodrome should drop
slightly at the moment of its release from the car, and thereby avoid
all danger of entanglement, the speed of the launching car at the
point at which the aerodrome was released was purposely made ‹less›
than the “soaring speed” of the aerodrome. Having this feature in
mind, when designing the “underneath” launching apparatus, it was
recognized that the danger of the aerodrome becoming entangled with
this form of apparatus could be avoided by making the launching
speed ‹greater› than the velocity which it would be necessary for
the aerodrome to have in order to soar, ‹provided the balancing was
correct and the aerodrome did soar›. Nevertheless, it was deemed
unwise to put too much dependence on the empirical calculations from
which the balancing of the large aerodrome would necessarily be
determined, and, therefore, some means seemed necessary for causing
the launching car to drop out of the way immediately upon releasing
the aerodrome. In the new design, more completely described below,
in Chapter IV, this was accomplished by so arranging a portion of
the front end of the track that, at the moment the launching car
released the aerodrome, it dropped like a disappearing gun carriage,
leaving the aerodrome free in the air with no possibility of becoming
entangled, provided the aerodrome itself did not drop more rapidly
than an angle of 15 degrees.

A small working model of this launching apparatus, one-eighth the
linear dimensions of that which would be necessary for the large
aerodrome, was first designed and constructed in the shop, the small
one-eighth-size model of the large aerodrome being launched from it
into a sheet stretched in front of it to act as a buffer. When it was
found to work very satisfactorily, a large one, twice this size, was
immediately built for use with the steam-driven models Nos. 5 and 6.
[p135]

These models, Nos. 5 and 6, which had flown so successfully in 1896,
had, during the preceding twelve months, been completely overhauled
and thoroughly tested in preparing them for trials in actual flight.
Many pendulum tests were made on both aerodromes, and it was found
after repeated trial that each could be depended on to show a lift of
sixty per cent of its flying weight.

This was more than sufficient for flight, but in order to insure
successful trials and avoid delay no aerodrome was launched until it
had shown previously its ability to generate enough power to maintain
for at least two minutes a lift of at least fifty per cent of the
total flying weight.

Models Nos. 5 and 6, having thus proved their readiness for trial
in flight, were accordingly, in April, 1899, taken to Chopawamsic
Island, together with the old “overhead” launching apparatus and the
new one above described, and placed on a small house-boat similar to
the one which had been used in 1896. Two men were detailed for this
special work, and were first employed in mounting the old launching
apparatus for a few preliminary tests with it, in order to make sure
that the aerodromes were in proper working order before trying them
on the new “underneath” one. After considerable delay, due to various
causes, this apparatus and the aerodromes were got into proper
working condition, and during June, July and August the following
flights were made with these machines, the record being condensed
from the reports made by the writer to Mr. Langley while he was
abroad.

CONDENSED RECORD OF FLIGHTS OF AERODROMES NOS. 5 AND 6
FROM JUNE 7 TO AUGUST 3, 1899

JUNE 7--AERODROME NO. 6

After making a preliminary test of the engines and boiler, with the
aerodrome mounted on benches inside the house-boat, to insure that
everything connected with the power plant was in proper working
order, the aerodrome was mounted on the launching apparatus on top of
the house, the various parts were assembled and everything made ready
for a flight. As it was calculated that this aerodrome would require
a soaring speed of something like twenty-five feet a second, the
springs which furnished the motive power for the initial acceleration
of the car were adjusted to the proper tension to cause it to reach
a speed of approximately twenty-three feet a second at the moment of
launching. Everything being in readiness the burners were lighted
but worked somewhat sluggishly at first, so that two minutes were
consumed in raising a steam pressure of 110 pounds. Although this
pressure should have been reached within one minute after lighting
the burners, and the extra minute which had been consumed had made
a drain on the supply of fuel and water which should have [p136]
been left for consumption during flight, yet it was thought best to
launch the aerodrome, so at 12.37 p. m. the car was released and the
aerodrome launched. The launching apparatus worked perfectly; the
aerodrome started off smoothly, and immediately after being released
from the car it dropped slightly and began to turn to the right. It
had been impossible to move the house-boat out into the stream so
as to point the launching apparatus directly into the wind, as one
end had settled slightly on the muddy beach in consequence of the
existing low tide. For this reason it was necessary to launch the
aerodrome due south, while the wind, which was very light, was from
the north-northeast, and, therefore, blowing on its port quarter. The
effect of the aerodrome turning to the right immediately after being
launched was that it caused the wind to strike it to an increasing
extent on the port side until, finally, it was going directly with
the wind. It did not, however, continue in this direction, but kept
turning to the right in a circle until it headed directly into the
wind, which, now striking the under instead of the upper surface of
the wings, immediately caused the aerodrome to rise. It continued
circling, making three complete circles of approximately 200 feet
diameter, dropping slightly when moving with the wind, but rising
when moving against it, until, at the completion of the third circle,
it had altered its path to such an extent that the left front wing
touched a tree and caused the front of the machine to dip a little.
It, however, kept up its flight, but the contact with the tree had so
lowered its bow, and apparently also caused the wings to be twisted
to such an extent, that it seemed unable to rise again, and after
making another quarter circle it descended. Although the propellers
were still turning when it struck the water, they had very greatly
decreased their speed, making it apparent that the power had been
very greatly reduced through the exhaustion of the fuel and water
supply. The aerodrome did not sink, but slowly drifted with the
current of the creek and was recovered in about five minutes and
brought to the house-boat, where the wings were dismounted and
dried, and the metal parts were carefully wiped off to prevent them
from rusting. The path of this flight is plotted on a portion of a
coast-survey chart and is shown in Plate 33.

[Illustration: PL. 33

PATHS OF FLIGHT OF AERODROME NO. 6, JUNE 7, 1899]

This erratic circling at first seemed unaccountable, but on
closer examination, after the aerodrome had been brought into
the house-boat, it was found that the pin which connects the
synchronizing gear to the port propeller shaft had been sheared off.
This had evidently happened while the aerodrome was still on the
launching apparatus. The effect of this was to throw the total work
of the water-circulating pump on the starboard engine, thus giving
the port engine less work to do, and consequently making the port
propeller run much faster than the starboard one, and thereby causing
the peculiar and erratic circling of the aerodrome. It is evident
that the undulatory motion of the [p137] aerodrome was due to the
fact that, when it was moving against the wind, the speed relative to
the air was greater than when it circled so as to go with the wind,
and that this greater relative velocity increased the lifting power
of the aerodrome.

The total time of the flight was 57 seconds, and the distance covered
was between 2000 and 2500 feet, thus giving a speed of a little less
than 30 miles an hour. Comparing this flight with that of November
28, 1896, made by the same machine, it will be noted that in the
earlier flight the velocity was practically the same, but that the
time of flight and the distance traversed then were nearly twice as
great as in the present case.

A complete record of the details, not only of weight, but also of the
position of the wings, the center of gravity, etc., which show the
exact condition of the aerodrome when it made this flight, will be
found in the appendix (Data Sheet, No. 3).

JUNE 13--AERODROME NO. 6

In the flight of June 7 there was a slight trembling of the aerodrome
while it was in the air, and although this was probably due to the
fact that the synchronizing gear was out of operation on account of
the shearing off of one of the pins which held it, allowing the port
engine to run faster than the starboard one, it was thought possible
that some of the trembling might be due to the “wind-vane” rudder,
which had been added to represent the equivalent of a steering device
by which the operator would control the direction of the large
machine. It was decided, therefore, to omit the “wind-vane” rudder in
the present test, but to test the aerodrome with the same equipment
of single-tier wings and Pénaud tail that had been used in the
previous flight, the reel and float being moved to bring the ‹CG› the
same as on June 7.

Everything being in readiness, with the launching track pointed
south, and the wind blowing only about 5-1/2 miles an hour from the
southwest, the burners were lighted and 63 seconds were consumed
before the steam pressure rose to 100 pounds. Although the valve
which controlled the burner was open to its full extent the pressure
showed no tendency to rise above 100 pounds, which was not considered
quite high enough to furnish sufficient power for a successful
flight, but as it was desired to determine at once at how low a
steam pressure the aerodrome would fly successfully, it was decided
to launch it even at this pressure. The launching apparatus was
accordingly released and the aerodrome started off, gliding down
about three feet immediately after being released, and then rising
again, turning slightly to the right and then heading directly for
the Virginia shore, where it seemed that it would smash itself in the
heavy growth of timber, but when it was about 250 feet from the shore
it turned towards the right and started back towards the island.
The wind, however, which was blowing from its rear, evidently got
down the smoke-stack and put out the fire, [p138] for the aerodrome
commenced to descend as soon as it turned its back to the wind, and
came down in the channel of the creek. The path of this flight is
shown by the solid line in Plate 34.

The total distance covered, as measured by plotting the course of its
flight on the coast-survey chart, was about 1800 feet, and the length
of time of flight was 40 seconds. The aerodrome was immediately
recovered and brought into the house-boat, where it was found that
there were still about 1000 grammes of water and 100 grammes of fuel
unused in it, showing conclusively that the fire had been put out by
the wind.

Upon inspection it was found that the aerodrome was uninjured, and
although the burner had not worked at all satisfactorily, yet as the
weather was exceedingly favorable it was decided to make another
trial with it immediately, using the superposed wings.[39]

Everything being in readiness the burners were lighted, and 70
seconds were consumed before the pressure rose to 90 pounds, beyond
which it was impossible to make it rise. Although it was felt certain
that 90 pounds was not sufficient pressure to furnish the power
necessary, yet as a storm was approaching in the distance, it was
decided to launch the aerodrome, as it could at least be determined
whether it was properly balanced for the superposed wings. When a
total of 75 seconds had been consumed the car was released and the
aerodrome was launched. The wooden arrangement for pressing down on
the top of the wings to keep the aerodrome from being injured by the
wind while it was on the car had been raised to the proper height for
the superposed wings, but it had not been noticed that the sticks
which support this arrangement had been elevated so much that they
would come in contact with the beam extending across the boat, and
from which the launching track was supported. Just as these sticks
reached the cross-beam, however, it was noticed that they projected
about three inches above the lower side of it; but the next moment
they struck it, and although the force with which the car was running
broke all four of them, the blow was sufficient to slow down the car,
and thereby cause the aerodrome to be launched at a very greatly
reduced speed; not over one-fifth of what it should have been. The
shock of breaking these sticks evidently jarred the burners so that
the fire was extinguished, for the aerodrome shot forward for about
25 feet and settled with everything intact, and with its midrod
perfectly horizontal. The aerodrome itself sustained absolutely no
injury, coming down as easily as though it had been lowered by a
rope, and would have been given another trial immediately but for the
fact that it was very late in the afternoon and darkness was rapidly
approaching. The data on setting of wings, tail, etc., are shown on
Data Sheet No. 4 (Appendix). [p139]

JUNE 22--AERODROME NO. 6

After several days’ delay, due to numerous small but exceedingly
annoying troubles,—such as the leaking of boilers because of
defects in the copper tubing, and the bursting of the air tank, due
to its being pumped up to an excessive pressure, which a defective
pressure gauge had failed to indicate,-—Aerodrome No. 6 was made
ready for another trial, and it was decided to test it again with the
superposed wings which had been used in the second experiment of June
13. The aerodrome was mounted on the “overhead” launching apparatus,
which it will be remembered had been used in all the previous tests,
and after 90 seconds had been consumed in raising a steam pressure
of 110 pounds, it was launched directly into the wind, which was due
south. After leaving the launching car, the aerodrome flew straight
ahead for about 75 feet, when it suddenly turned its bow up into the
air at an angle of about 15 degrees, and it seemed that the machine
would be blown back onto the house-boat. However, when the rear end
of the tail was within about 10 feet of the boat, and only about 10
feet above the water, it suddenly regained its equilibrium and went
straight ahead again in the face of the wind with the guy-posts only
about 4 feet above the surface of the water, flying almost exactly
horizontally for a distance of about 100 feet, when the bow again
suddenly became elevated. As the aerodrome was so close to the water,
the wind forced it down until the burners were extinguished by coming
in contact with the water. This brought the aerodrome to a standstill
absolutely uninjured, the propellers being several inches above the
water when they quit turning. The aerodrome was brought into the
house-boat and thoroughly dried out, and another trial would have
been made with it immediately but the wind which had been steadily
increasing was now blowing something more than 12 miles an hour,
and it was considered best not to attempt experiments in so strong
and gusty a wind, for fear of the wings being broken by the wind
suddenly veering and striking them on the side or rear while the
aerodrome was still on the launching apparatus. The peculiar action
of the aerodrome in the air appeared to be due to the fact that
the propellers interfered more with the lifting power of the rear
superposed wings, as they were then constructed, than they did with
the “single-tier” ones. The data on the setting of the wings, tail,
etc., are shown on Data Sheet No. 5 (Appendix).

It was also found after the experiment that one of the workmen, in
assembling the machine on the launching car, had secretly increased
the stiffness of the spring which controls the elasticity of the
Pénaud tail. The effect of this increase in the stiffness of the
Pénaud tail might at first thought appear to be similar to that
of moving the center of pressure forward. Upon a closer analysis,
however, it will be seen that the effect is very much greater, as
excessive stiffness of the Pénaud tail not only causes the aerodrome
to elevate its bow, [p140] but requires the overcoming of a strong
downward force at the rear, even more serious than would be caused by
placing an extra load at the rear of the machine without regard to
its effect on the balancing. In experiments of this kind, however,
the workmen get certain ideas of their own as to how the work should
be conducted, and it is almost impossible in assembling the aerodrome
to prevent them from making adjustments which are quite different
from those which they have been directed to make, and which have been
definitely planned with a view to determining the effect of slight
changes which it is desired shall not be masked by changes of any
kind in other details.

JUNE 23--AERODROME NO. 6

The wind, which had been blowing half a gale all day, gradually
quieted down towards sunset and at five o’clock was very light,
blowing only two miles an hour from the east-southeast. As one of
the rear superposed wings had been injured on the previous day in
carrying the aerodrome into the house-boat after its short and
erratic flight, it was decided to use the “single-tier” wings in
this experiment, and also to continue using the “overhead” launching
apparatus for a few more flights. Everything being in readiness,
the burners were lighted and 70 seconds were consumed in raising a
steam pressure of 120 pounds, at which pressure the aerodrome was
launched. It started straight ahead, dropping not more than a foot,
and flying on an absolutely even keel for about 800 feet, when it
suddenly turned to the left and made a short half circle of about
100 feet diameter, heading for a point about 150 feet east of the
house-boat. When it was about 200 feet from the shore, a sudden gust
of wind caught under the Pénaud tail, raising the rear portion of the
aerodrome and causing the bow to point down at an angle of about 30
degrees. The aerodrome kept this angle and struck the shallow water
only about 20 feet from the shore. The aerodrome was comparatively
uninjured, and another flight would have been made immediately
but for the fact that by the time the aerodrome had been properly
inspected it was quite late, and entirely too dark, and there would
have been danger of losing it in the adjacent marshes, which are
difficult to traverse even under the best conditions of tide and
light. The path of this flight is shown by the dotted line in Plate
34.

JUNE 27--AERODROME NO. 5

While the preceding tests had been going on with Aerodrome No. 6,
such time as could be spared for it was spent in getting Aerodrome
No. 5 into proper condition. The copper tubing from which the boilers
for both aerodromes were made was greatly inferior to that which had
been used in previous years, and as this tubing could be procured
only by having it specially drawn to order in France, and as it
required several months after placing an order before the [p141]
tubing could be delivered, it was necessary to make the best of
what was already on hand. The copper tubing for the boilers which
had been used in 1896, after being carefully annealed and filled
with fine sand, could be wound into a perfectly smooth helix, free
from all wrinkles, indentations, and so forth, on the inner side of
the coil. But no amount of care, both in annealing and in winding
this present lot of tubing, would produce a smooth helix, the tubing
being badly wrinkled on the inner side of the coil in spite of every
precaution. These wrinkles, however, were not so much the cause of
serious trouble as was the fact that the tubing was not uniform in
quality, each length of it having numerous rotten spots which did not
always show up in the winding, but which gave way after the boiler
had been completed and one or two preliminary runs in the shop had
been made with it. While the effect of such small things cannot be
appreciated from merely reading about them, yet they were the cause
of the most exasperating annoyance and delay, as no sooner had the
aerodrome been gotten into what appeared to be perfect working order
than the boiler would break at one or more points, thus causing a
delay which at the moment would seem to involve not more than a few
hours, but before everything was again in working order would amount
to several days.

[Illustration: PL. 34

PATHS OF FLIGHT OF AERODROME NO. 6, JUNE 13 AND 23, 1899]

However, after much perseverance, Aerodrome No. 5 was put in
satisfactory working condition, and on June 27 was launched with
its “single-tier” wings and Pénaud tail. The data on settings of
wings, tail, etc., are given on Data Sheet No. 6. After lighting the
burners, 70 seconds were consumed in raising a steam pressure of 120
pounds. Immediately upon leaving the launching car the aerodrome
started to rise with its bow elevated to an angle of about 15
degrees. It flew straight ahead about 80 feet, when it came backward
and downward and touched the water about 40 feet from the boat. The
failure of the aerodrome to fly properly was evidently due to its not
being in proper balance. The cause of this lack of proper balance
was not immediately apparent, but was very soon detected and will be
discussed later on.

JUNE 30--AERODROME NO. 5

After several days of incessant rain and strong winds, which
prevented an experiment, the weather became brighter and the wind
quieted down and the afternoon of June 30 was almost ideal for an
experiment. At five o’clock Aerodrome No. 5, with “single-tier” wings
and Pénaud tail, was placed on the launching apparatus, a few minutes
later the burners were lighted, and just as the propellers started to
turn a racking noise was heard. Upon investigation it was found that
the circulating pump had broken. The break was a very small matter
and could have been repaired in an hour, but it was then too late to
repair the damage and get a flight before dark, so the aerodrome was
reluctantly dismounted and the men put to work repairing the broken
pump. [p142]

JULY 1 TO JULY 8

The great disadvantage of conducting the experiments at a point forty
miles from the city and the shops was felt at all times. Workmen,
even of the very best class, cannot be kept contentedly at work at a
point so far removed from their homes, even by bringing them to the
city on Saturday afternoon and carrying them back to the experimental
grounds the following Monday. Moreover, it is worse than useless to
try to get even as much as one-third the ordinary amount of work
done if there is the slightest excuse for tightening anchor ropes,
watching passing boats, or wasting time on any of the multitudinous
small variations from their usual routine of life.

On July 7, Aerodrome No. 5, equipped with “single-tier” wings and
Pénaud tail, was made ready for a flight in the afternoon. The
settings of the wings, tail, etc., are given on Data Sheet 6. Using
the “overhead” launching apparatus, the aerodrome was launched with a
steam pressure of 115 pounds. Immediately upon being launched its bow
rose to an angle of about fifteen degrees or more, and the aerodrome
came backward and downward and touched the water about three or four
feet from the house-boat.

It may be well to recall from what has been said in Part I, Chapter
IX, that Aerodrome No. 5 is the one with the very low thrust line,
and in 1896 had its “separator” several centimetres in front of its
center of gravity. When this aerodrome was overhauled just previous
to these experiments, the separator was moved back to the same
relative position as that in Aerodrome No. 6, so that the gradual
depletion of the water supply during flight would not cause it to
become light in front of the center of gravity.

In the launching of Aerodrome No. 5, above described, it showed
no tendency to drop immediately upon leaving the launching ways,
but on the contrary its bow in every case rose almost immediately
until it was at an angle of about fifteen degrees or more. From
the photograph (Plate 35) it will be noticed that the wings of the
aerodrome are held down by the longitudinal strips, ‹A›, fastened to
cross-beams attached to the launching car. If, now, the launching
speed is too great and the aerodrome tries to rise immediately upon
being released, the front end, which passes from under the launching
car before the rear does, and is thus free to rise, will immediately
rise, while the rear cannot rise until it has passed entirely in
front of the car, which being a distance of several feet requires
an appreciable fraction of a second, during which time the bow of
the machine has been able to rise to quite a steep angle. This has
the effect of slowing down the aerodrome so that it does not get
quite the proper chance to start on its flight with a minimum head
resistance.

In view of the above facts, it was decided to decrease the speed of
the launching car slightly when using Aerodrome No. 5, so that this
matter could be thoroughly tested out.

[Illustration: PL. 35

AERODROME NO. 5 ON LAUNCHING-WAYS]

[p143]

JULY 11 TO JULY 14--AERODROME NO. 5

The very early morning preceding actual sunrise on July 11 was
undoubtedly as calm as it is possible to find; there was absolutely
no breeze stirring and the water in the river was as smooth as glass
as far as one could see. The anemometer cups were stationary, the
wind vane stood absolutely parallel to the launching apparatus and
everything promised a most successful experiment. After mounting
the aerodrome on the “overhead” launching apparatus the burner was
lighted, and while the steam pressure was still rising and the
propellers were revolving faster and faster all the time, there
was a snap and they ceased to turn. The fire, which was burning
fiercely, ran the pressure immediately to 150 pounds. An attempt
was at once made to start the propellers again by giving them an
initial turn by hand, it being thought possible that a sudden gush
of water had taken place and, accumulating in one end of the engine
cylinder, had blocked the engine. However, as the engine refused
to keep the propellers going after they were started, and as the
pressure was still rising very rapidly, the burner was shut off and
an investigation made. Upon removing the hull covering, it was found
that the connecting rod bearing had broken off short near the crank
pin of the engine, and that it would be necessary to take the part to
Washington in order to repair it, as there were no machine tools on
the house-boat.

After several days of exceedingly bad weather, the conditions grew
more favorable. Late in the afternoon of July 14, Aerodrome No. 5 was
again placed on the “overhead” launching apparatus and prepared for a
trial. After lighting the burners, 95 seconds were required to raise
a steam pressure of 120 pounds. Upon leaving the launching apparatus
the aerodrome went directly ahead for a few feet, but immediately
commenced to rise, elevating its bow to an angle of 20 degrees by the
time it had travelled 40 feet. With its bow in this position, it was
blown back towards the house-boat and a little to the right of it,
and, when within about 5 feet of the water, suddenly righted itself
and started ahead again, rising all the time and reaching a height of
about 20 feet by the time it had travelled 100 feet. In the meantime
the bow had again become elevated to an angle of about 15 degrees and
the aerodrome was blown backwards and downwards again. Just before
reaching the water it started to right itself, but it had descended
so that the front guy-post was in the water, thus destroying its
equilibrium and causing it to settle into the water. The path of this
flight is shown by the peculiar S-shaped line in Plate 34.

In the adjustments preliminary to the above trial the Pénaud tail
was elevated to an angle of 7-1/2 degrees when the aerodrome was
stationary in the shop. This excessive elevation, coupled with the
fact that the center of gravity was also probably a little too
far forward, no doubt accounts for the erratic flight. The data
on setting of wings, tail, etc., are given on Data Sheet No. 7
(Appendix). [p144]

JULY 19--AERODROME NO. 5

After several days of exceedingly bad weather the conditions were
more favorable on July 19. Since the last experiment on July 14 the
coefficient of elasticity of the Pénaud tail had been decreased, the
rear wings moved back 5 centimetres, and the “float” so placed that
the center of gravity of the machine was brought to the same position
it had had on that day, that is, 2 centimetres back of the line of
thrust. With this arrangement, assuming that the ‹CP› is over the
‹CG›, we should have an apparent efficiency of the rear wings of 63.6
per cent, since the distance between ‹CP›_{fw}, and ‹CG› is 79.7
centimetres, and the distance between ‹CP›_{rw} and ‹CG› is 125.3
centimetres. With the adjustment of July 14, the distance between
‹CP›_{fw} and ‹CG› was 79.7 centimetres, and the distance between
‹CP›_{rw} and ‹CG› was 118.3 centimetres, thus allowing for an
apparent efficiency of 67.37 per cent for the rear wings. It will be
recalled that in the unsuccessful flight of July 14 the midrod of the
aerodrome was inclined at an angle of about 20 degrees during most of
the time that it was in the air, thus indicating that the front wings
were lifting proportionately more than they should. On July 14 the
Pénaud tail had a negative elevation of 7° 30′, and it required 1240
grammes placed at its center to bring it to the horizontal. On July
19 the elevation of the tail was changed to 5° and a weaker spring
for controlling the elasticity was substituted, so that it required
only 200 grammes placed at the center of the tail to bring it to the
horizontal. A rubber band, of about one-half the strength of the
upper spring, was attached by means of a cord to the lower guy-post
and the lower vertical ribs of the tail, so that the tail would be
elastic both ways. This rubber band was in place and acting to help
draw the tail down when the above measurement of the coefficient of
elasticity was made. A rubber band connected to the lower side of the
tail was also used in the flight of July 14, but it was so very weak,
compared to the upper spring, that its effect was negligible.

The effect of this change in the balancing of the aerodrome, and also
the more considerable effect which the coefficient of elasticity of
the tail has on the balancing, will be immediately noticed from the
description of the next flight. The data on setting of wings, tail,
etc. are given on Data Sheet No. 8.

At 3 p. m., the wind having died down, Aerodrome No. 5, equipped with
its “single-tier” wings and Pénaud tail adjusted as above, was placed
on the “overhead” launching apparatus. After lighting the burners,
one minute and thirty seconds were required to raise a steam pressure
of 120 pounds. Immediately upon leaving the launching apparatus, the
aerodrome started straight ahead, dropping about 3 feet by the time
it had gone 100 feet; it then rose with its midrod at an angle of
about 6 or 8 degrees, regaining its level very quickly, however, and
making three of these undulations by the time it had gone [p145] 300
feet. It continued straight ahead for another 300 feet and began to
circle to the left, the diameter of the first circle being about 200
feet. As soon as it started to circle, it rose with its midrod at
an angle of about 15 degrees, and by the time it had made its first
half turn it started to descend, coming down to within 15 feet of
the water. As soon, however, as it had completed this first turn, it
again rose, making another half circle, then, upon the completion of
this half turn of the second circle, descended, this time to within
10 feet of the water, rising again for the third half turn, but again
descending to within 2 feet of the water at the completion of this
third circle, and then rising and completing the first half turn of
the fourth circle. By this time, however, it had sunk so near to
the water that the guy-posts caught in the tall grass while it was
descending just before the completion of the fourth circle, thus
pulling the aerodrome down into the water with the propellers still
running. The total time the aerodrome was in the air was 46 seconds.
The total number of revolutions of the propellers was 488, or at the
mean rate of 637 R. P. M. Upon examining the aerodrome, after it was
recovered, it was found that there were 925 grammes of water left in
the separator, the fire having been put out by the aerodrome coming
down into the water.

When the aerodrome first commenced to circle during its flight, it
was noticed that the front wing clamps had twisted on the midrod, the
left wing being dipped downwards, and the right one, of course, being
elevated, and the peculiar circling of the aerodrome was undoubtedly
due to this fact. The cause of the wing clamp twisting on the midrod
was that one of the workmen forgot to tighten one of the screws of
the wing clamp when the wings were being adjusted on the aerodrome.
But for this unfortunate twisting of the wings, it is probable that
the flight would have been perfectly straight and the distance
covered would have been considerably greater than it was, the total
path traversed being about 2600 to 2800 feet, found by plotting the
path on the coast-survey chart and measuring it.

JULY 27--AERODROME NO. 6

As the proper balancing of both Aerodrome No. 5 and No. 6 had now
been determined with reasonable accuracy, and as much more time had
already been given to the experiments than had been intended, it was
decided to dismount the “overhead” launching apparatus at once and
substitute the “underneath” one, so that it could be immediately
determined whether this newer plan for launching the aerodrome by
a car supporting it from underneath would be suitable for use with
the large machine. After a considerable period of exceedingly bad
weather, during which time the change was made in the launching
apparatus, the weather conditions became more favorable on July 27.
Aerodrome No. 6, equipped with “single-tier” wings and Pénaud tail,
was mounted on the [p146] “underneath” launching apparatus, and
everything was got ready for a flight. On lighting the burners, they
failed to work properly, and, upon investigation, it was found that
the air valve controlling the air pressure on the gasoline tank,
was out of order. While this was being repaired, the wind rapidly
increased in velocity and became very gusty, thus endangering the
aerodrome, as the wings were very liable to be broken by the wind
suddenly veering more rapidly than the house-boat could turn or the
turn-table could be moved, and thus striking the wings from the side
and putting an enormous upward pressure on them, owing to the fact
that the diedral angle between them gave to each wing an elevation
of 7-1/2 degrees from the horizontal. The aerodrome was accordingly
dismounted and everything kept in readiness for a trial, with the
hope that the wind would die down, or at least become steady, but it
did not do so until after dark.

JULY 28--AERODROME NO. 6

Aerodrome No. 6, equipped with “single-tier” wings and Pénaud tail,
was launched from the “underneath” launching apparatus. There was a
dead calm, the river not showing a ripple; the wind vane pointed to
the northeast, but as the tide was low and the boat was aground, the
launching track was pointing due south. At 7 a. m. the burners were
lighted, and 80 seconds were consumed in raising a steam pressure of
120 pounds. Everything worked perfectly; the uprights on the car,
which initially support the aerodrome and upon its being released
are instantaneously pulled down by rubber springs, as well as the
disappearing part of the track, acted without the slightest hitch.
Immediately upon leaving the launching apparatus, the aerodrome
depressed its bow to an angle of between 3 and 4 degrees and made
a direct line for the water. At this angle it struck just on the
opposite side of the channel, about 300 feet from the house-boat, and
while several minor parts, such as guy-posts, were injured no damage
of importance was done. Owing to the difficulty of getting through
the marsh and recovering Aerodrome No. 6, it was found impossible
to make another trial with No. 5 before the wind had increased to a
prohibitive velocity. The path of this flight is shown by the dotted
line in Plate 36. The data on setting of wings, tail, etc., are given
on Data Sheet No. 9.

The last previous trial of Aerodrome No. 6 was made on June 23, and
the balancing at that time was evidently correct for the settings of
the tail which were then used. The Pénaud tail then had an elevation
of 7-1/2 degrees, and the coefficient of elasticity was such that
1240 grammes were required at the center of the tail to deflect it
to the horizontal. In the trial above recorded, on July 28, the
adjustments of the wings were practically what they were on June 23,
the ‹CG› being moved forward 1 centimetre, but the Pénaud tail had
an elevation of something less than 5 degrees, and the coefficient
of elasticity was such that [p147] 200 grammes placed at the
center were required to deflect the tail to a horizontal. It was
not intended that the angle of the tail should have been less than
5 degrees, but it was found that one of the workmen had improperly
attached the fastening wire, and had considerably decreased the
angle. This last adjustment of the Pénaud tail should have been the
same as that used on Aerodrome No. 5 in its flight of July 19. The
‹CG› had purposely been moved forward slightly, but the effect of
moving the ‹CG› forward and at the same time decreasing the stiffness
and angle of the tail was shown by this flight.

The above trial not only very clearly emphasizes the importance of
carefully determining what the elasticity of the Pénaud tail should
be, but also emphasizes the fact that even the best workmen, who have
had several years of experience, cannot be relied on in anything
which requires that everything be done ‹exactly right› and not
‹nearly right›.

JULY 29--AERODROME NO. 5

The aerodrome equipped with “single-tier” wings and Pénaud tail was
launched from the “underneath” launching apparatus at 9 a. m., 1
minute and 30 seconds having been required to raise 120 pounds steam
pressure. The wind was from the southeast, with a velocity of 3 miles
an hour, and the launching track was pointed directly into it.

The launching apparatus, with the disappearing track, worked
perfectly, and the aerodrome started straight ahead, dropping
slightly at first, but immediately regaining its level and going
ahead, gradually raising its bow to an angle of about 8 or 10
degrees, and slightly slacking up its speed by the time it had gone
about 300 feet. It then made a circle to the left of a radius of
about 75 feet and started back. As soon as it had made this turn it
regained its level and directly regained its speed. But as soon as it
had speeded up again it elevated its bow, which slackened its speed
as before. It then again righted itself, still going in the same
direction and crossing the sand-bar on the point of the island at
a height of about 40 feet. As soon as it had crossed the sand-bar,
it again made a circle to the left with a radius of about 75 feet,
heading directly for the house-boat, but when it had got back above
the sand-bar it again circled to the left, passing directly between
two tall trees, and barely missing them, and still circling to the
left, when it again reached the opposite side of the sand-bar. It,
however, kept on circling to the left and once more started back
towards the house-boat, this time passing to the left of the trees
and again barely missing them, and completing this, its second,
circle over the sand-bar. It then started due north, heading directly
for Quantico, but by this time something had evidently happened to
the burners as the fire went out, and the propellers gradually slowed
up. However, it kept on towards Quantico, gradually descending on
an even keel, and came down in the water at a point about 500 feet
[p148] from the sand-bar and about 1000 feet from the house-boat.
The propellers had almost ceased turning when the aerodrome came down
into the water, and it settled almost as quietly as though it had
been picked up and placed there, so that no damage was done to it.

The total time that the aerodrome was in the air was 63 seconds, and
the total length of flight was about 2500 feet. The path of this
flight is shown by the dotted line with the double circle in Plate
36. The data on settings of wings, tail, etc., are given on Data
Sheet No. 10.

As soon as the workmen had had their breakfast, Aerodrome No. 5 was
again placed on the launching apparatus, equipped this time with
the superposed wings and Pénaud tail. Upon lighting the burners, it
was found that they did not work properly, a small piece of soot
having clogged up the tip of the vaporizing coil. While this trouble
with the burners was being remedied, the wind increased to such an
extent that it was found necessary to remove the aerodrome from the
launching apparatus to prevent its being injured by side gusts. As
it was Saturday and the wind showed no signs of quieting down, the
experiments were discontinued until the next week.

AUGUST 1--AERODROME NO. 5

After placing the aerodrome on the launching apparatus and getting
everything in readiness for a flight, upon lighting the burners a
sudden sheet of flame shot out of the smoke-stack and so seriously
charred three panels of each of the rear wings that they had to be
removed for repairs. The silk covering of the wings had been coated
with a special fire-proofing preparation, but the intensely hot
flame, of course, charred all the silk that it came in contact with.

By the time that the wings had been repaired, and the defect in the
burner which caused the accident had been remedied, a severe storm
had arisen, making it necessary to remove everything to the interior
of the boat. While waiting for the weather to become more suitable,
a test of the engine of Aerodrome No. 5 was made inside of the
house-boat. In this test a steam pressure of 140 pounds was obtained,
giving 650 R. P. M. of the round-end, 100-centimetre propellers,
which previous tests had shown to mean a thrust of 7480 grammes. As
the flying weight of the aerodrome was now 14,104 grammes, the thrust
obtained would correspond to a lift of 53 per cent of the flying
weight, which was maintained in this test for 90 seconds.

As the ‹CG› of Aerodrome No. 5 seemed to be a little too far forward
in the flight of July 28, it was decided to change it slightly, and
it was moved back 4 millimetres.

[Illustration: PL. 36

PATHS OF FLIGHT OF AERODROME NO. 5, JULY 29, 1899]

A trial run in the house-boat was also made on Aerodrome No. 6, while
waiting for the weather to become more suitable, but, unfortunately,
the result of this test was disastrous. The aerodrome had been placed
on trestles and [p149] held down to the floor by wires fastened to
the cross-frame. In the midst of the test one of the wires slipped,
allowing the aerodrome to push forward and thus permitting the
propellers to come in contact with the wires which held it to the
floor. Both propellers were entirely demolished and the cross-frame
was broken off short just at the right-hand engine. The disaster was
entirely due to the carelessness of one of the workmen in tightening
one of these wires, a further example of the extreme heedlessness of
workmen, even in the most important details, which concern the very
existence of the machine.

AUGUST 3--AERODROME NO. 5

After the very satisfactory trial of Aerodrome No. 5 in the shop
two days previous, it was hoped, now that the weather had become
suitable, that a good flight with the superposed wings would be
obtained. The aerodrome, equipped with these wings, was accordingly
placed on the launching apparatus and the burners were lighted, but
they refused to work properly, a steam pressure of only 80 pounds
being obtained. After much delay the burners were finally got to
work properly, but the wind had increased in velocity to such an
extent that it was necessary to remove the aerodrome to the interior
of the house-boat. As the wind continued to increase in velocity it
was decided to make another trial of the aerodrome inside of the
house-boat. Upon doing this it was very soon found that there was a
small leak in the front turn of one of the coils of the boiler, and
the steam from this played directly against the burner, causing it
to work intermittently. A new coil was substituted, and after some
adjustment a very excellent run was obtained, the steam pressure
reaching 130 pounds and the propellers making 654 R. P. M.

In the afternoon the wind quieted down and the aerodrome, equipped
with superposed wings, was again placed on the launching apparatus.
The burners were lighted but again refused to work properly, the
vaporizing tip being stopped up with soot. This caused the burner to
“flood,” which sent a sheet of flame through the stack and burned the
rear right wing.

A new wing was substituted, the burner tip was cleaned out and
everything was again put in readiness for a flight. Upon lighting
the burners, 1 minute and 58 seconds were required to raise 120
pounds steam pressure. The underneath launching apparatus, with
the disappearing track, worked perfectly, the aerodrome dropping
slightly, but going straight ahead. It, however, continued to descend
for a distance of about 100 feet, the bow being elevated about
5 degrees. The bow then became horizontal, the aerodrome rising
slightly at the same time, but going only about 50 feet farther, when
it again started to descend slightly, and finally settled gently on
the water between 300 and 500 feet from the house-boat, with its bow
elevated about 3 degrees. There was a hiss as the hull touched the
water, showing that the fire was still burning and making it [p150]
improbable that the failure of the flight was due to lack of power.
The data on settings of wings, tail, etc., are given on Data Sheet
No. 11.

The speed of the launching car, one foot in front of the point at
which the aerodrome was released, was twenty feet a second, as shown
by the carbon record sheet carried by the launching car and moved in
front of a tuning fork which had been set in vibration.

The aerodrome, being uninjured in the previous flight, was again
placed on the “underneath” launching apparatus, and before attaching
the wings a short run was made in order to see that everything was in
proper working condition. As everything seemed to be all right, the
wings and tail were immediately adjusted for another trial. As the
bow was slightly elevated in the previous trial, it was thought best
to bring the ‹CG› a little farther forward, and this was accordingly
done. As the aerodrome also seemed to drop slightly in leaving the
launching car in the above trial, the tension of the launching
springs was slightly increased so as to increase the velocity at the
moment of release.

Just as the sun was setting the aerodrome was again launched, 1
minute and 30 seconds having been required to raise 120 pounds steam
pressure, but the pressure was rising very rapidly at the moment
of launching. There was an absolutely dead calm prevailing, the
river being as smooth as glass. The launching apparatus, with the
disappearing track, worked perfectly. Immediately upon being released
the aerodrome went straight ahead, with its midrod horizontal, but
gradually glided downward as though the wings had very little lifting
power, and settled in the water about 200 feet from the house-boat.
The velocity of the launching car, 1 foot before the aerodrome was
released, was 22 feet a second, as shown by the carbon record sheet.

In the above trials of the superposed wings, the conditions of the
wind and of the aerodrome were certainly as favorable as could be
expected. There was as much power being furnished by the engine as
had been furnished in the previous flights with the “single-tier”
wings, and the balancing of the aerodrome was exceedingly good.
The superposed wings, unquestionably, had a fair trial and proved
inferior to the “single-tier” ones, for they had a supporting surface
of 2.75 square feet to the pound, whereas with the “single-tier”
wings there was approximately 2 square feet to the pound. The
decreased lifting power of the superposed wings seems to be another
confirmation of the results of the Allegheny experiments with the
“plane-dropper.”[40]

As more time had already been given to these tests than it seemed
well to [p151] spend on them at that time, owing to the pressure of
the work of construction for the large machine, it was deemed best
to discontinue them for the time being, and as soon as time could be
found for it, to construct a set of wings with superposed surfaces,
using only two surfaces and making their distance apart at least
equal to or greater than their width.

It will be remembered that the prime object in making these tests was
to obtain data for use in the balancing of the large aerodrome and in
constructing a launching apparatus for it. The chief deductions drawn
from them were: First: That it would be best to construct the first
set of wings for the large machine on the “single-tier” plan, and
later to make a set of superposed ones, should further experiments
with new designs develop a type of superposed surfaces which gave
as good lifting power as the “single-tier” ones. Second: That the
proportioning of the coefficient of elasticity of the Pénaud tail
should be given as careful attention as the setting of the wings.
Third: That the “underneath” launching apparatus was equally as good
as the “overhead” one, and that both worked as well as could be
desired; and, fourth, that while short periods of calm weather might
be expected during some part of the day on a portion of the days of
each month, yet the most favorable conditions were more apt to be met
with between the first break of day and the actual rising of the sun,
or from an hour preceding sunset until darkness actually came.

It will be noted that while considerable delay was experienced in
making these tests, nearly all of it was due to the very delicate
adjustments required in the power-generating apparatus of the
aerodrome, but it should also be noted that when these adjustments
were accurately made the models operated exceedingly well, and could
be depended upon to give good flights of sufficient duration to
permit a careful study of their action while in the air.

In the experiments of June 27 and July 7, above described, the
aerodrome immediately after leaving the launching apparatus began
to rise with its midrod pointed upward at an angle of about 15
degrees. From Data Sheet No. 6, which gives in detail the important
data as to the settings of the wings, the elasticity of the Pénaud
tail,[41] etc., we note that the tail had a negative angle of 7-1/2
degrees, and that the spring which held it at this angle was of
such a stiffness that it required 1240 grammes placed at its center
of figure to depress it to the horizontal. It will also be noticed
that the position of the front and rear [p152] wings relative to
the center of gravity of the machine was not the same as that which
existed at the time of the very successful flights of 1896, as shown
by Data Sheet No. 1 of No. 5, May 6, 1896. When the elasticity of the
tail was adjusted before making this test it was thought that it was
made the same as in the experiments of 1896, though accurate data as
to the exact amount of this elasticity had, unfortunately, not been
kept.

A slight change had also been made in the method employed of
attaching the Pénaud tail to the machine. In 1896 the tail was
attached to the machine by means of a flat piece of wood (hickory)
which had been steamed and bent to the proper extent to cause the
rudder to have a negative angle of about 5 degrees, but no accurate
note was made of its angle or stiffness, so that in 1899 no data were
available as to exactly what the angle had been or how stiff the
spring was. Owing to the fact that wood not only warps and twists,
but also that any piece which has been steamed and bent gradually
loses a certain amount of its curvature, it was decided in 1898 to
change this method of attaching the tail, the wooden spring being
replaced by a coiled steel spring attached to an upper guy-post and
connected to the tail by a bridle wire fastened to the center of
figure of the tail.

After the experiment of July 7, 1899, a lower spring, consisting of
small rubber bands, was connected by a wire to the lower part of the
rudder and fastened to the guy-post, thereby more nearly reproducing
the conditions obtained when using a wooden spring, which, of
course, tends to return the rudder to its normal position when it
is displaced in either direction. After attaching this lower spring
to the rudder, the experiment of July 14 was made, and it was found
that the aerodrome still flew with its midrod pointed upward at a
very steep angle. It was, therefore, felt certain that the upper
spring on the rudder was too stiff, and that it should not require so
much as 1240 grammes to bring it to the horizontal. This spring was,
therefore, replaced by a weaker one, and the angle of the rudder was
also decreased until it had a negative angle of only 5 degrees and
required only 200 grammes placed at its center of figure to bring it
to the horizontal. From the description of the flight of July 19, it
will be seen that these changes immediately corrected the tendency of
the aerodrome to point its nose upward at such a sharp angle, and it
will be later seen that after a further slight adjustment the flight
of July 29 was made, in which the proper balancing was obtained and
the aerodrome made a good horizontal flight.

After these preliminary tests with the “overhead” launching
apparatus, it was dismounted and the “underneath” one substituted and
the experiments of July 28, 29 and August 3 were made. Everything
connected with this “underneath” launching apparatus worked perfectly
from the start and four flights of the aerodromes were made using it.

[Illustration: PL. 37

EXPERIMENTAL FORMS OF SUPERPOSED SURFACES, 1898, 1899 (SEE ALSO
PLATES 64 AND 65)]

[p153]

It will be recalled that in “Experiments in Aerodynamics” Mr. Langley
made tests of the soaring speed, etc., of surfaces when superposed.
In many of his experiments with rubber-driven models, he also
employed superposed surfaces. During the summer of 1898 several forms
of superposed surfaces, of a proper size for use on the steam-driven
models Nos. 5 and 6, were constructed and were tested under as
nearly as possible the same conditions as would exist when used on
the aerodrome, by mounting the surfaces on the whirling-table and
measuring their soaring speed, lift, drift, etc., to determine just
what arrangement of surfaces gave the greatest lifting effect with
the least resistance. Two of the forms which were tested are shown
in Plate 37, Figs. 1 and 2, and Plates 64 and 65. At the conclusion
of these tests, it was decided to construct a set of surfaces on
the plan shown in Plates 64 and 65, and to have them ready for use
on either of the models Nos. 5 and 6. These surfaces were taken to
Chopawamsic Island in April, 1899, when all of the other aerodromic
material was first carried there. It was planned to make some tests
with them to determine whether or not it would be best to use
superposed surfaces on the large aerodrome or to follow the plan of
“single-tier” ones, which had the great advantage of having already
proved their worth in the successful flights of the models. On
August 3, Aerodrome No. 5, equipped with these superposed surfaces,
was launched. It will be noted from Data Sheet No. 11 that the
superficial area of the superposed surfaces was considerably greater
than that provided by the “single-tier” ones, and on the assumption
of the same efficiency per unit of surface in both cases, the
aerodrome should have soared at a less speed and required less power
when using the superposed surfaces. The results obtained, however,
were just the reverse, the aerodrome being unable to sustain itself
when using the superposed surfaces, whereas with the “single-tier”
ones it was evident that a slight excess weight might easily have
been carried without preventing the aerodrome from soaring properly.
While it was felt that these tests were not entirely conclusive as
to the superior lifting power of the “single-tier” surfaces, yet as
the engine builder was constantly promising, each time with increased
emphasis, that he would within less than a fortnight deliver the
engine for the large aerodrome, and that it would develop even more
power than the specifications called for, it was deemed best to cease
the experiments with the models and concentrate all effort on the
completion of the large aerodrome frame and the construction of a
set of “single-tier” supporting surfaces for it. It was recognized
from the first that the “single-tier” supporting surfaces lacked the
rigidity which could be secured by the truss construction afforded by
the superposed plan, yet these models, which were the only machines
in the history of the world that had ever flown successfully, had
been equipped with “single-tier” surfaces; and the experience so
dearly bought during the long [p154] years of development of these
models had taught the very valuable lesson that in work of this
kind where we have no margin on anything, but everything has to be
calculated on the “knife-edge” basis, it is an exceedingly unwise
thing to introduce any modification from what has been proved to be
satisfactory, unless such modification is absolutely necessary.

The principal object in building the one-eighth size model of the
large aerodrome, as mentioned in the first part of this chapter,
was to determine by actual experiment whether the new form of
“underneath” launching apparatus, which had just been designed, was
likely to prove as satisfactory as the original “overhead” type,
which had been used in the successful flights of the models in 1896.
Yet after it was completed this aerodrome was found so very strong
and stiff, even though roughly constructed by merely tying the joints
of the tubing together with wires and soldering over the joints,
that it was decided to equip it with power, if a suitable form of
power could be found which could be easily applied. Just at this time
liquid air as a motive power was attracting considerable attention
all over the country, and attempts were made to procure a small power
plant for operation by liquid air. After devoting considerable time
to the matter it was found impossible to do anything with it just at
that time, as the liquified air could not be obtained in Washington,
and one of the chief experimenters in New York, who had been given a
commission to make certain experiments at his plant, so continuously
delayed beginning them that it was found necessary to give up the
idea.

However, after the completion of the tests of the launching apparatus
some experiments were made in flying the model as a kite. For this
purpose a mast twenty feet high was constructed and so arranged
that it could be mounted at the center of a small power launch. The
model aerodrome was flown by a cord connected to it by a bridle, the
cord passing over a swivel pulley on top of the mast and down into
the boat, whence it could be played out or hauled in as occasion
required. By heading the launch into the wind it was possible to
secure sufficient relative velocity to cause the model to support
itself and a number of tests were made in this way. It was found that
when the bridle was attached at the point at which the propellers
would deliver their thrust, had they been in use and driven by power,
the model flew exceedingly well, maintaining its equilibrium even
during very strong gusts. Owing to the rolling produced by waves
from the large boats which were continually passing in the part of
the river where these tests were made, the power launch was often in
danger of being upset by its tall mast; and finally, when the tests
were just reaching the point where accurate information was being
obtained on the balancing of the model, a sudden rolling of the boat
caused the mast to snap off while the model was in the air. Before it
could be picked up from the water a passing boat had swamped it and
it was lost in the river. [p155]

Although the model was, as has been said, rudely constructed and,
therefore, did not represent a serious loss, yet the pressure of the
more important construction work for the large machine prohibited
the construction of another rough model for continuing these kite
experiments, which it was felt could not at best be more than
approximate indications of the general stability of the machine under
practical conditions.

[p156]

CHAPTER IV
HOUSE-BOAT AND LAUNCHING APPARATUS

The use of a house-boat seemed to Mr. Langley so indispensable in
former years in making open-air tests of the models that he decided
from the outset, though advised by the writer against doing so, to
use the same plan on a much larger scale in connection with the
large aerodrome. Aside from its supposed utility as a convenient
and apparently safe place from which to launch the aerodrome, the
house-boat was valuable as a portable workshop for making necessary
repairs and as a temporary storehouse for the apparatus, thereby
saving much packing and unpacking. It also provided sleeping quarters
for the workmen.

It was early seen that this plan would require a boat at least 60
by 40 feet, which could be built only at a large initial cost. But
as the experience with models had so firmly convinced Mr. Langley
that it was necessary not only that the aerodrome be launched over
the water, but also at a considerable height above it, and from a
station that commanded all points of the compass, he decided to adopt
this plan for the large aerodrome, and designs for such a boat were
accordingly made in the latter part of 1898.

In order to insure the completion of this house-boat by the time the
aerodrome was expected to be ready for trial, it was built under
contract. Immediately after its delivery in May, 1899, work was
begun on the superstructure which carried the launching track. This
superstructure was a considerable undertaking, involving a turn-table
weighing about 15 tons, supported on a double circular track, and
this track in turn was supported entirely from the side walls of
the house to avoid having columns in the middle of the floor. From
the photographs, Plate 38, Figs. 1, 2 and 3, it will be seen that
the entire superstructure was supported by three trussed girders
extending across the boat above the roof and carried by vertical
posts built into the side walls of the house. The turn-table was 48
feet square and the launching track carried by it was 5 feet gauge by
80 feet long.

[Illustration: PL. 38

FIG. 1.

FIG. 2.

FIG. 3.

HOUSE-BOAT AND LAUNCHING APPARATUS, 1899]

In making tests of the models, it had been the practice to carry
the main body of the aerodrome up a ladder to the upper works of
the boat, the wings being also carried up in the same manner. As
the large aerodrome was expected to weigh at least 640 pounds, of
which 350 pounds would be the steel frame with its undetachable
parts, such as the engine and its appurtenances, it was seen that
something more effective than a ladder would need to be provided for
getting the aerodrome from the interior of the boat to the launching
track [p157] above. It was therefore decided to place the upper
works of the boat rather nearer the rear end than the front, thus
leaving a space over the front end of the house through which a large
trap-door might be cut in the roof, and it was thought that in this
way the aerodrome might be passed up to the launching track by the
use of suitable ropes and pulleys. The upper works were so arranged,
and a sliding trap-door was provided in the roof, but more intimate
knowledge of the difficulties of handling so large and heavy a frame
made it certain, even before the aerodrome was ever placed upon the
house-boat, that it would be impossible to transport it to the upper
works by passing it through the trap-door. A different plan was then
resorted to. A very large door was constructed at the rear end of the
house, through which the completely assembled frame could be carried
in a level position and placed upon a large raft, consisting of a
lattice flooring over pontoons, moored at the rear end of the boat,
as clearly seen in Plate 38. In order to raise the aerodrome frame
from the raft to the upper works, a large, but light, mast and boom,
with suitable stays were provided. As the wings, when mounted in
their proper position on the aerodrome, would be interfered with by
such a mast, the mast and boom were so devised as to be capable of
rapid erection and dismounting, only five minutes being necessary for
either operation. In Plate 38 the mast and boom are seen in position
in Fig. 3, while in Figs. 1 and 2 they have been dismounted.

The construction of the launching track and car was begun in
November, 1899, but their completion was long delayed, as they were
frequently put aside for the more immediately important parts of
the work. Moreover, the arrangement of the struts and clutch of
the launching car depended entirely on the form and dimensions of
the frame of the aerodrome, which could not be entirely decided
until a proper engine had been secured and tested in the frame to
determine what modifications of it were necessary. In the spring of
1902, however, the launching car was entirely finished and a number
of tests of the large engine were made in the shop with the frame
mounted in position on the car.

From the description of the “overhead” launching apparatus (Part
I, Chapter X) which had proved so successful in the tests of the
models, both in 1896 and in the later experiments of 1899, it will be
recalled that the essential features of it were a track and a light
car with three hinged struts which extended below the body of the
car, and against which suitable co-acting bearing points attached to
the frame of the aerodrome were tightly drawn by means of a clutch
which gripped a special fitting fastened to the aerodrome frame near
the central point of its length. After the engine of the aerodrome
had been started and got to running at full speed, the car was
released and moved forward along its track by the combined force of
the thrust of the propellers and the pull of the coiled launching
springs. Just before the car reached the forward end of the track, a
cam at this point caused the clutch to open and release [p158] the
aerodrome, which immediately dropped slightly, as it had purposely
not quite reached a speed sufficient to cause it to soar. This slight
drop of the aerodrome, even if it were only a fraction of an inch,
made it possible for the hinged struts, against which it had been
held by the clutch, to be folded up by their special springs against
the floor of the car, thus leaving the aerodrome free in the air
without danger of entanglement.

The struts referred to above were three in number, two being placed
near the rear and one at the center of the front of the car. The use
of three points of support had the advantage of furnishing a rather
rigid foundation against which the frame could be tightly drawn by
means of the clutch-hook without risk of straining it. In designing
the “underneath” launching apparatus, which was very thoroughly
tested in the experiments with the models in the summer of 1899, the
plan of having three struts with the aerodrome drawn tightly against
them by means of a central clutch-hook was continued with most
satisfactory results.

When the position of the struts on this launching apparatus had been
changed so as to permit it to be used for the quarter-size model,
it was found, in making shop tests of the engine with the aerodrome
mounted on the launching car, that, owing to the greater vibration
produced by the gasoline engine, the three points of suspension
did not hold the model in a sufficiently rigid manner. It became
necessary, therefore, to use four struts, the two rear ones being
left as before, and the single one in front being replaced by two
interconnected ones arranged similarly to those in the rear. After
making this change no difficulty was found in holding the aerodrome
rigidly against the struts, and this modification was therefore
immediately introduced in the designs for the large launching car
which was already under construction.

[Illustration: PL. 39

METHOD OF ATTACHING GUY-WIRES TO GUY-POSTS TO RELIEVE TORSIONAL
STRAIN]

Experience, both with models 5 and 6, and with the quarter-size
model, had also demonstrated the necessity of providing some means
whereby the aerodrome frame would be relieved of the torsional
strains produced upon it by a side wind striking the under surface of
the wings when the aerodrome was mounted on the car preparatory to a
test. The means for preventing these torsional strains in the case of
the models, when “overhead” type of launching car was used, has been
described in Chapter X of Part I. However, with the “underneath” type
of launching car, a different means was necessary. A plan, in which
outriggers projected from the body of the car and wires running from
these outriggers up to the main ribs of the wings, with means for
releasing the wires just before the car reached the end of the track,
was used with the “underneath” car in the tests of models 5 and 6 in
the summer of 1899, but the outriggers were frequently deranged by
the sudden stopping of the car at the end of the run and they were
replaced by a simpler arrangement. In this plan the torsional strains
were relieved by providing, at the forward and rear ends [p159] of
the car, smaller hinged uprights furnished in their upper part with a
small slot into which a pin projected from the bottom of the forward
and rear guy-posts, respectively. The guy-wires from wings being
connected to the lower ends of the guy-posts the torsional strain
produced by a side wind was immediately transmitted from the wings
through the guy-wires to the guy-post, whence it was transmitted to
the car itself, and thus prevented from acting on the metal frame of
the aerodrome, as shown in Plate 39. These additional short struts
for taking up the torsional strain were first added to the small
launching car in 1901, and in the succeeding tests made with the
quarter-size model no trouble of any kind was indicated as likely to
be caused by them. As it was these extra struts which were directly
responsible for the accident in the launching of the large aerodrome
October 7, 1903, at the time of its first trial, and possibly also
for that on December 8, 1903, at the time of the second trial,
special attention is here called to them.

The length of travel which could be provided for the launching
car in the case of the large aerodrome, as well as in that of the
models was necessarily very limited, owing to the fact that the
track had to be constructed on the top of the house of the boat. It
was therefore necessary, in order that the aerodrome might attain
a speed sufficient for soaring before being launched, to keep the
weight of the launching car as small as possible, a given spring
tension being capable of accelerating a given mass a definite amount
in a given length of travel. With a heavier launching car the spring
tension would have to be increased. Moreover, since the blow which
would be struck when the car was suddenly stopped at the end of the
track, would depend on its mass as well as its velocity, there was an
additional reason for trying to keep the weight of the car as small
as possible.

While it was found perfectly feasible to keep the weight of the
launching car for the model low enough for practical purposes, in
designing the launching car for the large aerodrome it was only by
eliminating all flooring of the car and providing merely a box frame
with necessary cross-braces, that its weight was kept within what
appeared reasonable limits. Even then the blow which it would strike
when it reached the end of the track was found by calculation to be
exceedingly formidable.

Referring to the drawings of Plate 40, Figs. 1, 2 and 3, it will
be seen that the large launching car consisted essentially of two
parallel longitudinal side members 6 inches deep by 1.5 inches thick
by 19 feet long, connected by three main sets of cross-members:
one set near the rear, at the point at which the rear struts for
supporting the aerodrome were mounted; a second rather heavier set
about the middle of its length, at the point where the strut which
carried the clutch-hook was mounted; and a third near the front,
at the point where the front struts were mounted. Projecting from
the forward end of each of the [p160] longitudinal side members
were piston rods, on which were mounted leather-cup pistons, which
co-acted with buffer cylinders fixed at the extreme front of the
track to absorb the blow when the car reached them at the end of its
travel. The car was supported on each side by means of four hangers
(Figs. 4 and 5) which carried grooved wheels having ball-bearings
and running on a steel track consisting of flat plates fastened on
the side of the timbers of the launching track. On the extreme lower
point of these hangers were small guide pulleys, so placed as to be
just below and out of contact with a guard rail on the side of the
launching track, thus preventing any possibility of the launching car
being raised from the track either during its forward motion or by a
side wind striking underneath the wings.

[Illustration: PL. 40

‹Aerodrome “A.”›
‹General Plan & Details of Launching Car›.
(‹Details 1/3 Full Size›)

GENERAL PLAN AND DETAILS OF LAUNCHING-CAR]

[Illustration: PL. 41

FIG. 1.

FIG. 2.

FIG. 3.

AERODROME ON LAUNCHING-CAR]

[Illustration: PL. 42

‹Aerodrome “A”›
‹Details of Clutch Post for Launching Car›.
‹Scale 1/3 Full Size›

DETAILS OF CLUTCH POST FOR LAUNCHING-CAR]

[Illustration: PL. 43

FRONT END OF TRACK JUST PREPARATORY TO LAUNCHING AERODROME]

On the large launching car the arrangement of the struts against which
the bearing points of the frame were tightly drawn by the clutch was
similar in all respects to that used on the model car, there being only
slight differences in details. The details of the uprights on which the
bearing points of the aerodrome frame rested are clearly shown in Figs.
6, 7, 8, and 9 of Plate 40. From the photographs (Plate 41, Figs. 1,
2, and 3) which show the large frame mounted on the launching car, the
general arrangement of the struts and the clutch-hook can be readily
seen; and from Plate 42, Figs. 1, 2, and 3, which show in detail most
of the important features of the clutch-post and its clutch, a very
good idea of the size of the different parts may be had by observing
that the distance from the fulcrum of each half of the hook to the pin
by which it was connected through the universal joint to the vertical
rods is five inches. As previously stated, this clutch-hook gripped the
lower pyramid and pulled the bearing points of the frame firmly against
the forward and rear struts of the launching car, and in launching the
aerodrome the triggers arranged on the bottom of the car, which at the
proper time pull on the vertical rods and thereby force the two halves
of the clutch-hook apart, are so arranged that they strike a cross-beam
at the front end of the track one inch before the triggers, which keep
the struts from being pulled down by their springs, which tend to
fold them up and force them down against the car. The triggers, which
prevent the struts from being folded down, strike a cross-beam in the
track one foot before the buffer pistons on the end of the car begin to
enter the buffer cylinders at the end of the track, and, consequently,
one foot before the folding prop, which supports the front end of the
track, is knocked out by the car striking a special trigger which
allows this folding prop to swing forward when the front end of the
track folds down to insure that the aerodrome will not become entangled
with the car, even though the aerodrome be not quite up to soaring
speed at the moment of launching. The manner in which this front end
of the track folds down can be very readily seen by comparing Plate 43
with Plate 95 of Chapter XII, the former showing the front end of the
track in horizontal position, with [p161] the aerodrome at the
extreme rear end just preparatory to launching, and the latter showing
the front end of the track folded down with the hinged prop standing
outward in its downward path and the aerodrome just launched. These
photographs will be more particularly referred to later, but attention
is here called to them so that the description immediately following
may be more easily understood.

Although this method of launching the aerodrome seemed to Mr.
Langley, both theoretically and from the experience with the models,
to be a satisfactory and feasible plan, there were two very important
respects in which it seemed from the very first open to objection.
In the first place, it was necessary that the aerodrome should be
launched as nearly at its soaring speed as possible, because either
an excess or deficiency of speed interfered to some extent with the
equilibrium of the machine. So many factors were involved in the
determination of what this final velocity should be that it seemed
almost impossible to be sure of the results until at least one test
of the aerodrome had been made. In the second place it was not known
whether the rapid acceleration of the car would seriously interfere
with the equilibrium of the aviator.

In reference to the first question it was, of course, known that
a freely falling body acquires a speed of 32 feet per second at
the end of the first second after having fallen a distance of 16
feet. It was proposed to launch the aerodrome at approximately 35
feet per second; and, since the distance over which the car would
pass in acquiring this speed was approximately 60 feet, the rate of
acceleration would, of course, be less than that for a freely falling
body. The conditions in the two cases, however, are quite different.
In the case of the freely falling body there is the constant force of
gravity which causes the acceleration. In the case of the aerodrome
the car is initially standing still but ready to be acted upon by
the combined force of the thrust of the propellers and the tension
of the springs. The propeller thrust is approximately 450 pounds
at the moment of releasing the car, while the spring tension adds
approximately 400 pounds more pull, giving a total pull of 850
pounds acting on the car at the start. The weight of the aerodrome
including the aeronaut being approximately 850 pounds, and the
weight of the car being approximately 450 pounds, the total weight
to be accelerated is 1300 pounds. The resistance of the car and the
aerodrome is zero at the moment the car is released, and increases
approximately as the square of the velocity until it reaches
approximately 300 pounds at the soaring speed of the aerodrome;
while on the other hand the spring tension decreases uniformly from
400 pounds at the start to approximately 76 pounds at the end of
the track, and the thrust due to the propellers decreases from 450
pounds at the start to approximately 250 pounds at the moment of
launching. Consequently, it is in a general way clear that the rate
of acceleration of the aerodrome and car decrease, probably in a
geometric ratio, the rate of acceleration [p162] at the moment of
launching the aerodrome being much less than that of a freely falling
body. Since so many factors enter into the problem no confidence was
felt in calculations as to what the rate of acceleration would be. It
was, therefore, decided to determine it experimentally at the same
time that tests were made on the car to determine what spring tension
would be necessary to enable the aerodrome and car to acquire soaring
speed by the time they reached the end of the track.

It was obviously impossible to make this initial test with the
aerodrome mounted on the launching car, as the aerodrome would
certainly wreck both itself and the car were it allowed to remain
fastened when the car was stopped at the end of the track. It was,
therefore, decided to make the tests by mounting on the car boards
which would have a head resistance equal to that of the aerodrome.
In order to minimize as much as possible the blow due to the car
striking the buffers at the end of the track, the car had been made
as light as possible. On this account it was felt to be unwise to
risk adding to it a weight of 850 pounds to represent the aerodrome,
and supplying an additional spring tension to represent the thrust of
the propellers, as the total effect of the added weight and the added
pull would certainly completely demolish the car. By calculation it
was found that the omission of the 850 pounds weight of the aerodrome
and the spring tension to represent the thrust of the propellers
would practically counterbalance each other; and that if sufficient
spring tension were provided to cause the car, with the light boards
representing the head resistance of the aerodrome, to reach the
soaring speed by the time it arrived at the end of the track, it
would be safe to assume that this spring tension would be sufficient
for use in launching the aerodrome.

The method of measuring the final speed of the launching car for
the models consisted in fastening a strip of smoked paper to the
launching car in such a position that it was drawn past a stylus
fastened to the end of a vibrating tuning fork placed at the end
of the track. This had proved perfectly successful, but it gave a
record merely of the final speed attained by the car at the moment
of launching the aerodrome. In the case of the large aerodrome it
was desirable to have a record of the speed of the car during the
first few feet, and also at several other points in its travel down
the launching track, and the more numerous these points the better.
Short strips of copper were accordingly placed every twelve inches
along the length of the track, and these were connected by a wire
to one terminal of a small electric battery. Mounted on the car, in
such a way that it would be drawn across these contact strips, was a
copper brush arranged to make continuous contact with another wire
stretched along the track, this second wire being connected to the
other terminal of the electric battery and having in its circuit
the magnet which actuated a pen on a chronograph. Since the rate of
revolution of the chronograph barrel was known, the [p163] distance
between the marks which the magnet would cause the pen to make when
its circuit was closed by the brush on the car passing across the
contact strips on the track would give correct measures of the time
consumed by the car in passing over each twelve inches of its travel.
Upon test, however, it was found impossible to get the chronograph
magnets to work rapidly enough to respond to the very rapid opening
and closing of the circuit after the car had passed over the first
one-quarter of its length of travel. As a large part of the slowness
of action seemed to be due to the weight of the fountain pens, they
were replaced by small glass tubes drawn out to a fine point and
containing a small amount of ink. These seemed, however, to be still
too heavy to respond to the rapid closing of the circuit unless
the contacts were made unduly long. The contacts were finally made
three inches long and placed only every three feet along the track,
but just as these contacts were completed and placed in position
the clock-work of the chronograph itself became deranged. Before it
could be repaired, the tests were discontinued, as everything was in
readiness for the boat to proceed down the river where the actual
tests in free flight were to be made. Tests of the final speed of the
car were, however, made by the tuning-fork method, and the springs
were adjusted until their tension was sufficient to cause the car to
attain a speed of thirty-five feet a second at a point three inches
in front of the point at which the aerodrome would be released from
the car.

[p164]

CHAPTER V
CONSTRUCTION OF FRAME OF LARGE AERODROME

The general plan for the large aerodrome was never a matter of
uncertainty. At the time when the first general designs were made
there had been in the history of mankind only one type of machine,
that of the steam-driven Langley models, which had proved capable
of flight for any considerable distance. Furthermore, the selection
of this type had been the result not of sudden fancy or of purely
theoretical consideration, but of years of the most careful
experimentation, in the course of which nearly every conceivable
style of machine had been tested with some form of power. It would
have been worse than folly, therefore, if the one clear path had been
left to seek some unknown way.

It was fully realized from the first, however, that the increase in
size alone would make necessary in the design for the large aerodrome
a great many modifications from the designs of the steam-driven
models. It was not possible here, as in nearly every other kind of
structure, simply to magnify uniformly the parts and proportions of
the small machine in order to obtain a successful large one. This is
particularly true in the case of the aerodrome, because the rapid
increase of weight in the larger structure is out of all proportion
to the increase in strength, while it is very desirable that the
more expensive machine which is designed to carry a human being
shall be relatively even stronger than the easily replaced model.
This problem of increasing size without sacrificing strength and
stability, it was known from the beginning, would be encountered in
a particularly difficult form in designing the frame of the large
machine, and was to be solved not by the discovery of some new and
wonderfully strong material, but by improvements both in the general
plan and the details of the machine. Here, as is often the case, it
was not the large changes in the design but the improvements in small
and sometimes seemingly unimportant details which demanded the most
careful consideration and, as a whole, contributed most to the final
result. For this reason, as well as because the large changes, when
pointed out, are usually easily understood, the present chapter is
for the most part a description of the improvement of details.

From the experience gained in the construction of the frames of the
several steam-driven models, it was decided that the frame for the
large aerodrome must consist essentially of two principal parts.
First, a rigid backbone was required, extending from the point of
attachment of the front wings to the point of attachment of the rear
wings; and this backbone, for convenience designated [p165] the
“main frame,” must support the second principal part, the “transverse
frame,” which formed a cross with the main frame, and at the ends
of which the propellers were mounted. While it was necessary that
this transverse frame should have considerable rigidity and strength
in a vertical direction, yet its main strength and stiffness was
required in the horizontal plane for withstanding the thrust of the
propellers. It had been possible to construct the frames of the later
steam-driven models stiff enough, and at the same time light enough,
by the use of properly proportioned steel tubing, but calculation
very soon showed that in order to secure sufficient rigidity for the
frame of the large aerodrome and at the same time keep the weight
within the permissible limit, it would be necessary to depend very
largely on guy-wires and to use tubing only for forming the struts
against which the guy-wires should act. But this obviously introduced
a new series of problems. The extensive system of guy-wires necessary
would add materially to the head resistance of the aerodrome, and
this might conceivably be so great as to require more propulsive
power than would be required for a frame heavier but unincumbered by
the head resistance of the wires. It became necessary to consider
these problems, but no data were accessible from which the head
resistance could be computed with any confidence. The coefficient
of resistance for a cylindrical body moving through the air in a
direction perpendicular to its length may in general be taken as
one-half that of a flat body of the same cross-section; but it was
thought very certain that, owing to the fact that tightly stretched
wires are in constant vibration when the aerodrome is in the air,
the resistance of the wires must be considerably greater than would
be calculated from treating them as cylinders having a coefficient
of 0.5. Unfortunately, no data on the resistance of vibrating wires
were at hand. Before proceeding with the designs for the guying
of the frame, therefore, the following brief series of tests was
made in November, 1898, on the whirling table, in order to learn
approximately the resistance that the proposed system of guy-wires
for the large aerodrome would offer:

MEASUREMENTS OF THE RESISTANCE OF GUY-WIRES, USING FRAME ATTACHED TO
“BALANCE.”

RESISTANCE OF FRAME WITHOUT WIRES.

Frame consists of: 4 tubes, 1 cm. diameter, 14.5 cm long; 2 tubes, 1
cm. diameter, 41 cm. long; 2 tubes, 1 cm. diameter, 101 cm. long.

Revolutions of Velocity of Resistance. Calculated resistance
turn-table per frame. Feet Grammes. of frame.
minute. per minute. ‹r.› Grammes.
6.75 608 11.5 14.2
9.75 877 34.0 29.6
12.0 1080 51.8 44.8
16.35 1475 97.0 83.8
19.75 1775 134.0 121.3
22.7 2045 168.0 161.2
25.5 2290 205.0 202.0

RESISTANCE OF FRAME WITH 1ST SET OF WIRES.

First set of wires: 16 wires, 0.6 mm. diameter, 102 cm. long; 6
wires, 0.6 mm. diameter, 42 cm. long.

Revolutions Velocity of Resistance Resistance Calculated
of turn-table wires. Feet of frame of wires. resistance
per minute. per minute. and wires. R_1−r=r_1. of wires.
Grammes. Grammes.
R_1.
9.75 877 47.5 13.5 8.88
12.0 1080 73.5 21.7 13.47
13.75 1237 93.5 25.5 17.65
17.25 1550 144.0 37.0 27.7
20.25 1822 187.0 45.5 38.4
22.50 2025 216.0 47.5 47.4
22.875 2060 225.0 52.0 49.0
24.56 2215 250.0 56.5 56.7

RESISTANCE OF FRAME WITH 2D SET OF WIRES.

Second set of wires: 15 wires, 1.2 mm. diameter, 102 cm. long; 2
wires, 1.2 mm. diameter, 42 cm. long.

Revolutions Velocity of Resistance Resistance Calculated
of turn-table wires. Feet of frame of wires. resistance
per minute. per minute. and wires. R_2−r=r_2. of wires.
Grammes. Grammes.
R_2.
9.25 833 54.0 26.5 15.35
9.35 841 55.0 27.0 15.4
11.3 1018 82.0 36.75 22.65
11.5 1035 82.0 35.25 23.4
13.0 1170 104.5 43.0 29.9
13.15 1185 105.0 42.5 30.60
16.7 1505 160.0 59.0 49.5
16.75 1510 160.0 58.0 49.9
19.5 1755 196.0 64.0 67.4
19.7 1770 203.0 69.5 68.5
21.60 1945 236.0 77.0 82.6
21.65 1950 237.0 77.75 83.2
21.75 1957 235.0 75.5 83.7

RESISTANCE OF FRAME WITH 3D SET OF WIRES.

Third set of wires: 15 wires, 2 mm. diameter, 102 cm. long; 2 wires,
2 mm. diameter, 42 cm. long.

Revolutions Velocity of Resistance Resistance Calculated
of turn-table wires. Feet of frame of wires. resistance
per minute. per minute. and wires. R_3−r=r_3. of wires.
Grammes. Grammes.
R_3.

9.25 833 65 37.5 25.2
11.55 1040 91 43.5 39.35
11.55 1040 101 53.5 39.35
15.25 1375 160 75.0 68.7
18.1 1630 203 86.5 96.6
19.25 1735 221 92.0 109.5
19.25 1735 216 87.0 109.5
20.63 1860 237 90.5 125.8

The last column of these tables is calculated for a coefficient of
form equal to 0.5, which has been found to be approximately correct
for a rigid cylindrical body.

These tables are not sufficiently extensive to determine accurately
the exact resistance that wires of various sizes will offer at given
velocities, or to serve as the basis for the deduction of formulæ,
and were not made for that purpose. However, from the above data, and
the curves plotted in Plate 44, it will be seen that some unexpected
results were obtained.

[Illustration: PL. 44

RESISTANCE OF WIRES AT GIVEN VELOCITIES]

[p167]

These results are fairly well summarized in the following general
statements: First, that the coefficient of resistance increases to
some degree as the size of the wire is decreased; second, that in
the case of wires of the size which it was expected to use, and at
approximately the soaring speed of the aerodrome, the resistance
is certainly not greater than 75 per cent, and more probably less
than 50 per cent of the resistance encountered by a flat surface of
the same projected area; third, that the coefficient of resistance
did not seem to be increased by the vibration of the wires. On
the contrary, it was noted during the experiments that when they
reached a speed which just caused them to “sing,” there was a marked
diminution in the resistance. This statement is made, however, with
some reserve, for it is probable that the singing of the wires was
due to vibration in the horizontal plane, and it is not definitely
known what the effect would be of vibration in the vertical plane.

To make the very extensive experiments necessary to determine these
propositions conclusively would have required much more time than
could at this period be spared from the actual constructional work
on the aerodrome. Nevertheless, the data did seem to indicate that
it was at least not unwise to employ the extensive system of guying
which had been planned in order to give the necessary strength to
the frame of the large aerodrome. This plan of construction was,
therefore, definitely adopted, and as a result of later experience
the system of guying was still further extended.

As the transverse frame had to be made comparatively rigid in order
to prevent undue binding of the bearings of the transmission and
propeller shafts, it was necessary to make it intrinsically stronger
and, therefore, heavier in proportion to its size than the main
frame. The main frame, although requiring great strength to enable
it to withstand the strains, both torsional and direct, which were
imposed upon it by the weights which it supported, did not need
excessive rigidity, and could, indeed, be distorted an appreciable
amount without danger of any serious effect on the action of the
wings or rudder; but even a small amount of distortion in the
transverse frame might easily cause such friction at the bearings of
the shafts as to absorb fifty per cent or more of the engine power.

In the photographs, Plates 45 to 48, which show the actual condition
of the frame on January 31 and February 1, 1900, the letters ‹A›,
‹B›, ‹C›, ‹D›, ‹E›, ‹F›, ‹G›, ‹H› and ‹I› designate parts of the main
frame, ‹A› and ‹H› being the rear and front midrods, respectively,
to which the wings were to be attached. ‹B› and ‹I› are curved
extensions of the starboard main tube, the port main tube being
exactly similar, and ‹C›, ‹D›, ‹E›, ‹F› and ‹G› are cross-tubes which
connect the midrods to the port and starboard tubes. ‹R› is the
front main tube of the transverse frame, the rear main tube being
exactly similar, and both being connected to the main tubes of the
main frame where they cross them. The ends of the main tubes of the
[p168] transverse frame are joined together by the “bed plates” ‹L›,
which are of I-beam section, and have mounted on their outer faces
the bearings which support the propeller shafts. At ‹V› are bevel
gears mounted on the propeller shafts, which are driven by co-acting
bevel gears, ‹M›, mounted on the outer ends of the transmission
shafts, ‹O›, the latter being at this point firmly supported in
bearings mounted on the inner faces of the bed plates and steadied
by the intermediate bearings, ‹N›. The two transmission shafts are
seen to be not in line, the rotary cylinder engine that was then
under construction requiring this arrangement. The bed plates, ‹L›,
are further stiffened by the brace tubes, ‹K›, and the transverse
frame is braced against the thrust of the propellers by the tubes
‹J›. The four tubes, ‹P›, unite at their upper ends to form what
was designated as the upper “pyramid,” and the wires, ‹S› and ‹T›,
radiate from its apex to the rear and front, respectively, of the
main frame. The lower “pyramid,” on the under side of the frame, also
has similar wires running fore and aft. The main portions of both
frames are further strengthened by their sub-frames, which merge
together, and the main tubes of the main frame are individually
stiffened in the vertical plane by a minor system of guying. The
scales shown in the photographs are calibrated in metres.

It is to be particularly noted that the midrod, which had heretofore
formed the backbone of the main frame, was now made to act merely as
a means of attaching the wings to the frame, the main strength of
the frame being furnished by the two parallel fifty millimetre tubes
which extended the entire length of the frame and which, reinforced
by the guy-wires, formed a truss not only more rigid transversely,
but also many times stronger in its ability to resist torsional
strains than could be secured by a single tube of equal weight. In
this plan of constructing the main frame, the pyramids constituted
a very important element, for with the guy-wires arranged as they
were it was impossible for any portion of the frame to experience
a stress which was not transmitted in some way to the pyramids. In
the frame, as here shown, these pyramids were formed of tubes 15 mm.
in diameter, 0.5 mm. thick, stiffened against buckling under the
end pressure by means of the cross-braces, which united them near
their midpoints. While the sole function of the upper pyramid was
to serve in the system of guying the frame, the lower pyramid not
only served a similar purpose, but also provided a means for holding
the aerodrome to the launching car in the process of launching
it, the clutch-hooks gripping around the short horizontal tube at
the apex of the pyramid and thus drawing the “bearing points” of
the machine firmly against the uprights on the car. In fact, the
particular arrangement of these pyramids was largely determined by
this necessity for providing means for holding the aerodrome to the
launching car, and the form which seemed best suited to the purpose
was duplicated on the upper side of the frame.

[Illustration: PL. 45

FRAME OF AERODROME A, JANUARY 31, 1900]

[Illustration: PL. 46

FRAME OF AERODROME A, JANUARY 31, 1900]

[Illustration: PL. 47

FRAME OF AERODROME A, FEBRUARY 1, 1900]

[Illustration: PL. 48

FRAME OF AERODROME A, FEBRUARY 1, 1900]

[p169]

The “bearing points” were not attached to the frame at the time these
photographs were taken, but are seen leaning against the scales in
the foreground of Plate 46. Their position on the frame will be more
clearly seen in later photographs, where it will be noted that they
were made use of in the more elaborate system of guying which was
adopted.

While, in general, the frame at this time seemed to be reasonably
stiff and strong, yet it was subjected to a very thorough test by
supporting it at different points and suspending from it weights to
represent the various parts, such as engine, aviator, wings, rudder
and so forth, the deflections which were produced by these weights
being carefully noted. It was further tested by subjecting it to
vibratory strains, such as it would be likely to meet in actual use.
After this the whole frame was tested against torsional strains, such
as would be caused by the wind twisting one set of wings more than
the other. As a result of these tests it was decided that the frame
should be strengthened as far as it was possible to do so without
greatly increasing the weight, which even now was found to be rapidly
increasing beyond what had been calculated as permissible. The main
guy-wires were replaced by heavier and stronger ones, and while
these were found to add somewhat to the stiffness of the frame, yet
something more seemed necessary to insure safety.

The delay in securing the engine, which had been contracted for
with a guarantee that it would be delivered in February, 1899, had
become so serious and had delayed the completion of the frame to
such an extent that the question of building an exact duplicate of
the large machine, but of one-quarter its linear dimensions was
being carefully considered at this time, and it was decided to make
no further changes in the guying of the large frame until after the
small one was built. On account of its smaller size changes could be
more readily and cheaply made on it, and the advantages of different
methods of guying could be just as well studied. Later, when this was
completed, it was found that, with the same system of guying that
had been used in the larger frame, the model was so very stiff that
it did not require any further strengthening, the smaller scale,
of course, accounting for the difference. What was thought to be
the best system to follow in strengthening the frame of the large
machine was, however, first tried on the smaller one, and it was
found that for a very slight increase in weight a very great increase
in strength could be obtained. This change in the system of guying
consisted essentially of building a “trestle” of tubing at a point on
the upper side, midway between the pyramid and the rear end of the
frame. One of the former sets of guy-wires which passed to the rear
of the frame was then replaced by a set which started at the foot of
the rear tubes of the upper pyramid, passed over and was fastened to
the trestle, and from there passed to the rear end of the frame at
the points where the longer guy-wires from the pyramid had formerly
been attached. The [p170] guy-wires on the lower side of the frame,
at the rear, were correspondingly changed so that the upper and lower
systems should be similar, the wires which started from the main
tubes at the foot of the pyramid passing to the bearing points, and
from there to the rear end of the frame.

In order to keep the main frame of the large aerodrome as short as
possible, it had originally been planned to make the distance between
the center of pressure of the front wings and the center of pressure
of the rear equal to five metres. When these same proportions were
followed in the quarter-size model, it was found that it brought the
rear wings so close to the propellers that their lifting effect was
certain to be interfered with by the blast of air created by the
slip of the propellers. It was therefore decided that all things
considered it would be best to increase this distance between the
wings, even though this involved an increase in weight, partly on
account of the increased amount of tubing, and still more on account
of the guy-wires which it would be necessary to add in order to make
up for the weakness due to increased length. The large aerodrome
frame was accordingly lengthened 2.5 feet (76.2 cm.), and the
guy-wire system was changed to that clearly shown by the photographs
of July 10, 1902, Plates 49, 50 and 51, the black cross-lines on the
background being 50 centimetres apart. From an inspection of these
photographs it will be seen that two sets of guy-wires were carried
from the upper and lower pyramids, respectively, towards the rear
of the frame, the first set being carried to the main tubes at the
foot of the “trestle” and the bearing points, and the second set to
these same main tubes at the second cross-tube. The sets of wires
which started from the feet of the pyramids were carried over the
“trestle” on the upper side and the bearing points on the lower side,
and both joined to the main tubes at the rear cross-tube. Additional
cross-guy-wires for stiffening the frame sideways were added in each
of the squares formed by the junction of the cross-tubes with the
main tubes. A secondary system of truss guy-wires running over short
guy-posts attached to the tubes of the main frame also contributed to
the strength and rigidity of the whole.

Although the pyramids had shown no signs of weakness, nevertheless,
because of increased strains due to the lengthening of the main
frame, it was thought advisable to make them stronger. Instead of the
15-mm. tubing, which had formerly been used, 25-mm. tubing of the
same thickness was therefore substituted, and additional cross-braces
were added, as will be seen from the photographs, and from the scale
drawings in Plates 52, 53 and 54, which show the aerodrome as it was
when completed. The numerals attached to these drawings refer to the
detail drawings shown in later plates.

[Illustration: PL. 49

GUY-WIRE SYSTEM, JULY 10, 1902]

[Illustration: PL. 50

GUY-WIRE SYSTEM, JULY 10, 1902]

[Illustration: PL. 51

GUY-WIRE SYSTEM, JULY 10, 1902]

[Illustration: PL. 52

SCALE DRAWING OF AERODROME A, END ELEVATION]

[Illustration: PL. 53

SCALE DRAWING OF AERODROME A, SIDE ELEVATION]

[Illustration: PL. 54

SCALE DRAWING OF AERODROME A, PLAN]

In order to secure the proper adjustment of the guy-wires, not only
of the frame but of many other parts, notably the wings, propellers
and rudder, it was necessary to use a large number of turn-buckles.
As almost every wire [p171] required at least one, and in some
cases two turn-buckles, the weight represented by this single item
rapidly became so formidable as to require serious attention. In
the construction of the models, it had been necessary to employ
some special turn-buckles in connecting the guy-wires of the wings
to their guy-posts in order to secure the minute adjustment of the
wires necessary to prevent the wings from being warped and distorted
by unequal and improper adjustment. These turn-buckles had been made
in the Institution shops, as the very lightest ones which could
be secured in the market were from ten to twenty times as heavy
as it was necessary for them to be to provide ample strength. In
the construction of the large aerodrome, however, the large number
required, and the desire to complete the machine at the earliest
moment, made it advisable to procure the turn-buckles, if possible,
from outside sources, and a very careful search was accordingly made
among the various dealers. After much delay some bronze turn-buckles
were secured which were very much stronger for their weight than any
others on the market, but upon testing them it was found that while
they weighed 45 grammes, their average breaking strength was only
593 pounds. Previous experience had shown that turn-buckles which
would not break under a less load than 750 pounds could certainly
be made to weigh not more than 18 grammes. As even at this time it
was realized that at least 100 turn-buckles would be necessary for
the entire machine, the excess weight which the heavy turn-buckles
would add was felt to be absolutely prohibitory, and the construction
of steel turn-buckles was immediately begun in the Institution
shops. These turn-buckles were at first made in several sizes, and
while some few were at first made “double ended,” most of them
were threaded at only one end, the other end being provided with
a swivel-hook, or eye. They were at first made of mild steel, the
swivel-hooks, in fact, being made of wire nails in order to utilize
the head of the nail as a shoulder without the expense of machining
rod steel of a size large enough to form the shoulder. It was found,
however, that the weak point of this type of turn-buckle was the
swivel end, and most of those which were then on hand were made
double ended by removing the hook, tapping a left-hand thread into
this end of the shank, and fitting a threaded eye-socket in it. The
guy-wires themselves were attached to the eyes of the turn-buckles
and to the fittings on the frame by twisting loops at the ends of the
wires, and although the very greatest difference in the strength of
a completed guy-wire may result from the way in which the loops are
twisted, yet, after much training, the workmen were taught to twist
these very uniformly, following the plan which can be best understood
by an inspection of the drawings in Plate 55 which show the loops
more clearly than they can be described. After the loops had been
properly twisted, soft solder was run all through the twist in order
to unite firmly the twists of the wire. Although special grades of
wire were found which showed very high tensile strength when the wire
was [p172] tested without having loops formed in its ends, yet it
appeared that the twisting of these high-grade wires so seriously
affected them that in the case of guy-wires with loops at the ends,
better final results could be obtained by using softer grades of
steel. The wire which was actually found best, after much experiment,
was a good grade of Bessemer steel of a medium hardness, which had
been “coppered” to prevent rusting. However, even with the softer
grades of steel wire, it was found that there were sometimes hard
spots in the wire which revealed themselves only upon test, and that
when a hard spot occurred in the twisted portion where the loop was
formed, the final strength of the completed guy-wire was sometimes
only twenty-five per cent of what it should be. The precaution was
then taken to subject each of the completed guys to a test strain at
least twenty-five per cent greater than it was calculated the wire
would have to stand in actual use, so that no accident from defective
wires would be likely to occur.

Later on, however, much trouble was caused by the loops in the
ends of some of the guy-wires slipping, owing to the giving way
of the solder which had been run through the joint, the amount of
slipping, while small, being sufficient to alter completely the
relative stresses on the various wires, thus causing distortion of
the framework itself. In order to avoid this difficulty a new method
was devised of attaching the guy-wires to the turn-buckles and to
the fittings by which they were carried to the frame. This method
consisted in threading the ends of the guy-wires so that they could
be inserted directly in the threaded ends of the turn-buckles.
The wires when connected in this way to the turn-buckles showed
absolutely no slip, and the entire system gained greatly in strength
thereby. The only disadvantage which was found in this new method of
attaching the guy-wires to their fittings, was that if the wire was
bent very close to the fitting, it would break in the screw thread
very easily. But since most of the guy-wires when once attached to
the machine are always tight, and in fact, under more or less strain,
there was in most cases no likelihood of the wires being endangered
by being bent close to the fittings. Since the screw threads,
which it was necessary to adopt in this new plan of connecting the
guy-wires, had to be very much finer than the threads which had been
used in the turn-buckles previously constructed, it was necessary to
make new turn-buckles, the others being too thin to permit of their
being bored out, bushed and re-threaded. The new turn-buckles were
made of a much higher grade of steel, and probably represent very
nearly the maximum of strength for the minimum of weight possible
without the use of some of the very much higher-grade steels which
have recently come on the market, but which are exceedingly expensive
to work. By means of this improved plan of attaching the wires,[42]
it [p173] was found possible to gain practically fifty per cent in
the strength of the entire system of guy-wires used on the frame.

Many small changes were from time to time made in the various small
fittings by which the guy-wires were attached to the frame, nearly
all of these fittings having been originally made of a very mild
grade of steel owing to the fact that it was so very much easier to
work. At the time these fittings were made it was constantly expected
that a trial of the aerodrome would be possible very soon, and it
seemed necessary to expedite the work as much as possible and avoid
the delay involved in using grades of steel that would have been
materially harder to work. As is always the case in work of this
kind, retrospect shows many instances where what was supposed to be
a short cut to results actually proved to be the longest path, but
the work as a whole was remarkably free from imperfect parts which
necessitated reconstruction.

In the construction of the frames of the models it had been customary
to fit the tubing accurately at the joints and to join it permanently
together by brazing, as this was not only the lightest form of joint
that could be made, but also the most expeditious method consistent
with securing a strength of the joint comparable with that of the
tubing itself. The construction of the frame by this method of
brazing the joints together permanently, offered, however, several
serious drawbacks: among them, that when a tube got injured it was
a considerable task to replace it, while the brazing of the new
tube in place required extreme care to prevent the frame from being
warped when completed, as the tube became longer while very hot and
contracted after the joint had set. Furthermore, the great heat
required destroyed to a considerable degree the desirable qualities
due to the tube being “cold drawn,” a reduction of strength of
something like 25 per cent being almost inevitable, even when the
brazing was most carefully done. It was, therefore, decided that in
the construction of the large machine all of the main joints should
be made by a system of “thimbles,” and it was planned at first to
make these thimbles by brazing short pieces of steel tubing into the
proper shapes and angles so that they would accurately fit the tubes
which were to be joined. The construction of the thimbles in this
manner, however, seemed to involve an excessive amount of work; and,
as it was found that very thin castings of aluminum-bronze could be
obtained, which would show a tensile strength very nearly as great as
steel, it was decided to make up patterns for the thimbles and cast
them of aluminum-bronze.

The aluminum-bronze castings were obtained and properly machined
to fit the tubes, but when it was attempted to “tin” the interior
walls of the thimbles it was found that the solder could not be made
to stick to the bronze. As a considerable amount of work had been
expended on the machine work of these thimbles much time and effort
was spent in attempting to devise “fluxes” [p174] and solders which
could be made to work with the aluminum-bronze, but the final result
was that the aluminum-bronze thimbles had to be abandoned. They were
replaced by similar castings of gun-metal of a slightly heavier
section, which at the time were thought to be very suitable for the
purpose.

But, in finally assembling the frame after the changes described
above had been made, steel thimbles, built up of short pieces of
tubing, as had originally been planned, were substituted for the
gun-metal thimbles. This change was made not only because of the
great increase in strength, but more particularly because many of the
gun-metal fittings had been imperfectly constructed, so that it was
extremely difficult to align the frame. The steel thimbles, which
were made in the Institution shops proved thoroughly satisfactory and
gave no trouble of any kind. Many of these thimbles and the method of
attaching the guy-wire fittings to them are shown in Plates 56 and
57, as well as in Plate 55.

TRANSVERSE FRAME

It will be recalled from the description of the models Nos. 5 and
6, in Part I, that the position of the line of thrust, with respect
to the positions of the center of pressure and center of gravity in
the vertical plane was, theoretically, very much better in No. 6
than in No. 5. In designing the large aerodrome, it was desired to
reproduce as nearly as possible the relative position of the line of
thrust with reference to the center of pressure and center of gravity
which existed in No. 6, but for constructional reasons it was found
impossible to do so. In fact it appeared that without seriously
complicating the construction of the frame it was impossible to
raise the line of thrust with respect to the center of gravity
materially higher than it was in No. 5. In No. 6 the line of thrust
was 12 centimetres above the midrod, this being effected by placing
the engines some distance from the boiler, and at the extreme ends
of the transverse frame where they were connected directly to the
propellers. In the case of the steam engine the weight of the engine
proper is a relatively small portion of the entire weight of the
power plant, and it is, therefore, possible to put the engine almost
anywhere without materially affecting the center of gravity. But
where a gas engine is used the engine itself constitutes the greater
part of the weight of the power plant, and any raising of the engine,
therefore, materially raises the center of gravity of the whole
machine. The line of thrust in the large aerodrome was, therefore,
practically in the plane of the main frame, and consequently very
little higher than the center of gravity.

[Illustration: PL. 55

FRAME FITTINGS AND GUY-WIRE ATTACHMENTS, ETC.]

[Illustration: PL. 56

FRAME FITTINGS AND GUY-WIRE ATTACHMENTS, ETC.]

[Illustration: PL. 57

FRAME FITTINGS AND GUY-WIRE ATTACHMENTS, ETC.]

The use of one engine to drive two propellers mounted at opposite
ends of the transverse frame, and in a direction perpendicular to
the crank shaft of the engine, necessitates the use of a pair of
bevel gears between each of the propeller shafts and the shafts by
which the power is conveyed to them from [p175] the engine
shaft. Since the efficient transmission of power through bevel gears
requires that they be very accurately placed with reference to each
other, and maintained very accurately in this position while they
are at work, it was necessary to make the transverse frame very
rigid, especially at its extreme ends. This was accomplished by
the use of what were called “propeller-shaft bed plates.” They are
designated by the numeral 27 in Plate 54, and are shown in detail
in Plate 58 as of a very deep I-beam section, having very narrow
flanges top and bottom, the web of the I-beam furnishing the strength
in a vertical direction, while sufficient stiffness laterally was
obtained from the flanges, assisted by the brace tubes, which acted
as struts between the bed plates and the main tubes of the transverse
frame. These struts, while very light, added enormously not only to
the lateral stiffness of the propeller bed plates, but furnished
for a minimum weight a maximum prevention against twisting of the
plates. The propeller-shaft bed plates were originally planned to
be made of sheet metal with the flanges brazed to the web. But at
the time that they were constructed the pressure of the work was so
great in the Institution shops that it was found necessary to have
some of the work done outside, and the parties who undertook the
construction of these bed plates were unwilling to attempt to braze
them up, and accordingly worked them from steel forgings made for
the purpose. The expense of this plan of construction proved large
and unnecessary, as both previous and later experience proved that
it was not only practicable to braze up bed plates more complicated
in their design than these, but that equal strength for equal
weight could thus be obtained for less than one-quarter the cost of
constructing them from solid forgings. Furthermore, where such parts
are made from the solid, changes which later tests prove advisable
can frequently not be carried out without very serious cost and
delay, while with the bed plates formed by brazing less hesitancy is
felt in removing parts which are brazed thereto and substituting new
parts, or even discarding the bed plates altogether and substituting
new ones. Particular emphasis is laid on this point for the reason
that much expense and delay would have been avoided had these very
expensive propeller-shaft bed plates been discarded as early as 1901
and replaced by others which would have permitted a considerable
strengthening of the ball-bearings, which, while strong enough to
stand even more power than they were originally designed for, were
far too weak to be safe when working under the greatly increased
stress due to the very much higher engine power which was later used.
Instead of discarding these bed plates then for new ones, they were
strengthened by brazing to them crescent-shaped pieces, as shown in
the drawings and photographs. This strengthening was made necessary
by the larger hole cut in the bed plates for the larger bevel gears.
The bed plates for the engine, which are later described, besides
other bed plates which were made for other purposes, were all
[p176] formed by the use of sheet metal and tubing properly brazed
together, and none of them ever gave any trouble.

In the early photographs of the aerodrome frame, especially that
of January 31, 1900, Plate 45, it will be noted that the two
transmission shafts, which extend from the propeller-shaft bed plates
towards the center, are not in line, the port transmission shaft
being at the center of the transverse frame, while the starboard
shaft is three inches to one side. This arrangement was necessary in
order to connect the shafts to the rotary cylinder engine which was
being constructed under contract, and which was almost momentarily
expected for more than a year after its original promise of delivery
on February 28, 1899. Later, when this engine was finally found to be
a failure, and the writer constructed the engine in the Institution
shops, the starboard transmission shaft was moved over to the center
line and the crank shaft of the engine, which was carried through on
the center line of the transverse frame, was then connected directly
to the inner ends of the transmission shafts.

These shafts, as well as the propeller shafts, were originally
constructed of steel tubing 1.5 inches in diameter and 1/16 of an
inch thick, but on account of the increased power of the large engine
it was found necessary to increase the thickness of the shafts to 1/8
of an inch. Difficulty was also found with the tubing of which the
shafts were made. This, though not exactly straight when received
from the factory, could be pretty accurately straightened in the
lathe by exercising proper care, but the moment any real strain was
put upon it in the transmission of power, it again went out of shape
and caused serious damage to the bearings by whirling, buckling, and
so forth. As the skin of the tubing is really the strongest part,
owing to the cold-drawing process to which it has been subjected,
great care was taken to secure shafts which were sufficiently
straight for use without machining, but it was finally found
impossible to rely on the unmachined shafts, and all the later shafts
for the aerodrome were made by getting tubing a sixty-fourth of an
inch thicker than was calculated to be necessary and turning off this
extra metal in a lathe.

[Illustration: PL. 58

BEDPLATE, GEARS, ETC.]

Suitable flanges and collars were brazed to the propeller shafts;
but, for convenience in assembling, the flanges by which the main
transmission shafts were connected to the crank shaft of the engine
were at first fastened to the shafts by screw-threads, the threads
being in the proper direction to cause the flanges to jam against
the shoulders of the shafts when the engine turned in its normal
direction. This method of fastening, however, caused serious trouble,
owing to the flanges jamming so tight that it became impossible to
unscrew them after they had once been used in driving the propellers.
The usual provisions of keys and key-ways adopted in general
engineering practice, where solid shafts are employed, were, of
course, out of the question, since the shaft would have to be greatly
increased in thickness throughout its entire length [p177] merely
to provide the extra metal at the small place in which the key-ways
were formed. Taper pins either sheared off or very soon stretched
the holes so badly as to leave the parts loose, and were otherwise
very unsatisfactory. The method finally adopted, which proved very
successful, was that of forming integral with the couplings shallow
internal tongues and grooves which fitted corresponding tongues and
grooves either in the exterior surface of the shafts or in collars
brazed to them at the proper point. The form of flange coupling, in
which bolts draw the two flanges tightly together, was also a source
of considerable trouble and delay, which was finally overcome by
forming shallow tongues and grooves in the faces of the flanges, the
tongues taking up the torsion and relieving the bolts which held the
flanges together of all strain except one of slight tension. The same
difficulties experienced in mounting the couplings on the shafts were
met with in connection with the gears, both on the propeller and
transmission shafts, and were finally obviated in a manner similar to
that described above.

The bevel gears originally constructed for transmitting the power
from the transmission shafts to the propeller shafts, were made of
case-hardened steel and were eight-pitch, twenty-five teeth, with
three-quarter inch width of face. The gears were very accurately
planed to give as perfect a form of tooth as possible, in order to
avoid loss of power in transmission, and although the manufacturer
who cut the teeth on them asserted at the time they were made
that they would not be capable of transmitting more than five
horse-power, yet they actually did transmit considerably more than
twelve horse-power on each set; but they were not strong enough
to transmit the full power of the large engine which was finally
used. The gears that were finally used were similarly constructed
of mild steel which was case hardened 1/64 of an inch deep after
they were finished, there being thirty-one teeth in the gear on the
transmission shaft and forty teeth in the one on the propeller shaft,
the teeth being eight-pitch, three-quarters of an inch face. These
light gears proved amply strong, and several times stood the strain
which they accidentally received when one of the propellers broke
while the engine was under full power, and thus threw the entire
fifty horse-power over on the other propeller, which was consequently
driven at a greatly increased speed.

Plain bronze bearings had been used throughout on the model
aerodromes, but in the construction of the large aerodrome
ball-bearings were used on all of the propeller and transmission
shafts, not only on account of the decreased loss through friction,
but also because ball-bearings can be built much lighter than solid
bronze ones, and, furthermore, do not present such great difficulties
in lubrication. However, owing to the limited size which it was
possible to secure for these bearings, because of their having been
originally designed for only twenty-four horse-power, and without any
margin for a later increase of the [p178] space in which they had
to be applied, they were never really large enough for the work they
had to do when transmitting the full power of the large engine. They
gave continual trouble, and were the source of delay which, while it
cannot be accurately measured, since there were often other causes,
yet might be conservatively estimated at not less than three or four
months. Such a delay, when reckoned in retrospect, can easily be seen
to have caused an expense which would have sufficed for almost any
change in the bearings, bed plates, etc., had the change been made
immediately after the bearings were found to give trouble. With the
better steel which it is now possible to obtain for the races of the
bearings, and with the high-grade balls now obtainable, the bearings
could be readily replaced without changing any other parts and still
be amply strong for the work.

PROPELLERS

Both the tests on the whirling-table and the actual results with the
models had shown that propellers which were true helices formed out
of wood were rather more efficient than those constructed by the use
of a hub in which were inserted wooden arms, forming a framing over
which cloth was tightly drawn. But the very great difference in the
cost of construction and the facility with which the latter type
could be repaired in case of damage—the wooden ones were practically
of no use if once they were much injured-—made it seem advisable to
construct all the propellers for the large aerodrome in the manner
just explained. Several pair of small propellers had been built on
this plan, some as early as 1895, and one very important advantage
had been found to be possessed by this type besides cheapness and
facility of repair. Wooden propellers of even so small a diameter as
one metre had been found to suffer a quite appreciable bending of the
blades, due to the thrust produced by them, even though the blades
had been made of considerable thickness. In planning a propeller 2.5
metres in diameter for the large aerodrome it was seen that in order
to make the blade sufficiently strong to withstand its own thrust it
would be necessary to make it inordinately thick, which, of course,
would mean a considerable increase in weight. In fact, it was seen
that the weight of the larger propellers would increase practically
as the cube of the diameter; which, for the 2.5-metre propeller,
would involve a weight of something over fifteen times the weight of
those one metre in diameter. The other type, which for convenience
we will call “canvas covered,” permitted the bending moment produced
on the blade by the thrust to be taken up by guy-wires running from
the corners of the blades to a central post projecting from the hub
of the propeller, and it was found that in this way a considerable
saving in weight could be effected. [p179]

In November, 1897, in order to obtain by actual test some data on
propellers, such as it was planned to use on the large aerodrome in
case it was later built, it was decided to construct one propeller
2.5 metres in diameter and 1.25-pitch ratio with two blades, each
covering the sector of 36 degrees on the projected circle. About
this same time an engine builder, who some years before had made
some experimental model engines in the Institution shops, proposed
to construct a gasoline engine for the proposed large aerodrome. As
past experience, not only with such engines but with all other forms
of explosive motors, had not been very reassuring it was thought
best to make brake tests of one of the heavier engines which he was
at this time building, and at the same time make tests with one of
these large propellers. A first series of tests was made at several
different speeds, and then a second series was made with the engine
driving the propeller at the same speeds. The engine varied so much,
however, in the power developed at any speed that the data obtained
were of little value. As it was also desired to learn just how much
thrust could be obtained from these propellers, when driven by a
given horse-power, a special hand car was fitted up to carry the
engine, which was connected to a shaft on which the propeller was
mounted. The propeller was raised above the floor of the car and
projected over the rear end of it so as to be as little disturbed
as possible by the deflection of the air currents caused by the
car. This car, with the engine and propeller, was tested on a track
near Mount Holly, N. J., in November, 1897, but the results were
very unsatisfactory. In the first place, the car with the engine
mounted on it was so very heavy and offered such a strong tractive
resistance that very little speed of propulsion could be obtained.
In the second place, the engine, which was said to have furnished
over six horse-power on Prony-brake tests, evidently did not furnish
anything like this amount of power at this time. And in the third
place, the propeller was evidently far too large to permit the engine
to run at the speed at which it would develop a reasonable amount of
power unless some reduction gearing were interposed between it and
the propeller. As the tests, for various reasons, had to be made at
a great distance from Washington, and the supervision of them had to
be entrusted by Mr. Langley to others, who either did not understand
or appreciate the value of obtaining accurate data, it was found
impracticable to continue them.

The large propeller used in these tests was built without special
regard to weight, since it was expected that it would be subjected
to rather rough usage under the very sudden strains produced by
the irregular working of the gas engine. Its hub was made of brass
tubing, the horns being brazed to rings which were slid over a
central tube, the rings being finally soldered to the tube after
the arms had been adjusted to the positions which would give the
blade the correct shape and dimensions. The wooden arms were 1.5
inches in [p180] diameter at the hub end, tapering to 1.25 inches
at the end of the blade. The blade was exceedingly stiff as regards
pressure produced by thrust, but it was found to be considerably
strengthened and made very much safer when guy-wires were added, in
the manner explained above. This general type of construction was
adhered to in all the future propellers for the aerodrome, though
slight modifications, both as to the size of the arms and the number
and position of the cross-pieces which formed the framing of the
blade, were adopted from time to time. A pair of heavy propellers,
2.5 metre, 1.25-pitch ratio, 36-degree blade, the hubs of which were
formed of brass castings, was, however, constructed for experimental
purposes, where weight was not an important factor.

When these propellers were designed, the calculations as to their
size and the horse-power which would be required to drive them at a
certain speed were based on the very incomplete data obtained from
the various propeller tests conducted during the preceding years.
When later calculations were made for them, on the data obtained in
the more accurate tests made in the summer of 1898, it was found
that the power of the engines with which it was proposed to equip
the aerodrome would not be sufficient to drive the propellers at
anything like the speed which the former calculations had shown would
be possible; and that, therefore, either the ratio of the gearing
between the propellers and the engine would have to be changed so
as to permit the engine to run at a very much higher speed than the
propellers, or that propellers, having either less pitch or a smaller
diameter, and possibly both, would have to be substituted for these
larger ones.

Since it was easier to change the propellers then to change the
gearing, a new set of propellers was designed which were of 2 metres
diameter, with a pitch ratio of unity, and with a width of blade of
only 30 degrees. It was calculated that 20 horse-power would drive
these two propellers at a speed of 640 R. P. M., when the aerodrome
was flying at a speed of 35 feet per second and the propellers were
slipping about 50 per cent, this being found to be about the speed
at which the engines might be expected to develop their maximum
power. As the larger propellers having the brass hubs were thought
to be excessively heavy, the hubs weighing 10.25 pounds each, and
as any change either in size, pitch, or width of blade necessitated
a new set of patterns in case the hubs were cast, it was decided
to construct the new hubs of steel tubing. The weight was further
reduced by decreasing the size of the wooden arms to 1-1/4 inch in
diameter at the hub, tapering to 1 inch at the end of the blade.

After the engine builder in New York had been unable to fulfil his
contract on the engine, and it had been condemned, propeller tests
were made with the experimental engine built in the Institution
shops. These tests showed: First, that the results which might be
expected from larger propellers could be very safely predicted by
extrapolation from the results of the propeller tests of 1898; [p181]
and, second, that in order to get a thrust which would equal fifty
per cent of the flying weight of the aerodrome it would be necessary
to use propellers larger than two metres in diameter unless a very
large surplus of power were provided. It was accordingly decided
to make a set of propellers intermediate between the two-metre,
unit-pitch ratio, thirty-degree blade ones, and the original ones
which were two and one-half metres, one and one-quarter-pitch ratio,
thirty-six-degree blade. A set was, therefore, designed two and
one-half metres in diameter, unit-pitch ratio, and thirty-degree
width of blade, the hubs being made of steel tubing brazed up in the
same manner as the two-metre ones, and the wooden arms of the blades
being one and three-eighths inches in diameter at the hub end, and
tapering to one inch at the end of the blade.

Later, when the larger engine was actually tested in the frame, the
inability of the original transmission and propeller shafts to stand
the extra strain caused by the engine starting up very suddenly at
times, together with the unsatisfactoriness of the screw-thread
method of fastening the gears and couplings to the shafts made it
necessary to provide new shafts, gears, couplings, etc. It was then
decided to change the ratio of gearing between the engine and the
propellers, which had been one to one, so that the engine might run
faster and, therefore, permit the use of larger propellers. For
constructional reasons the ratio chosen was thirty-one to forty,
thus making the engine run approximately one-third faster than the
propellers.

In the various tests made of the engine working in the frame there
were two or three instances in which the propellers were damaged
either by the sudden starting of the engine or by their not being
able to stand the strain to which they were subjected by the power
absorbed, but in every case such breakages were found to be due to
imperfections of the brazing in the joints. While, therefore, it
would have been desirable to make the propellers somewhat heavier,
yet since the total weight of the aerodrome had been growing so
very rapidly, it was felt that this need not be done, as a pair of
propellers which had stood quite severe service in shop tests might
reasonably be expected to stand the strain of actually propelling the
aerodrome through the air.

Nevertheless, when in the summer of 1903 the actual trials of the
large aerodrome were started, it was found that the very important
difference between a propeller working in a closed room and one
working in the open air had not been given due consideration.
Several sets of propellers, 2.5 metres in diameter, unit-pitch
ratio, 30-degree blade had been constructed and were on hand, in
order that no delays might be caused through a lack of such extra
parts. On September 9, 1903, when the aerodrome frame without the
wings was mounted on the launching car on top of the boat for some
trial runs with the engine to make sure that everything was again
in readiness, before the engine had made 500 revolutions, the
port propeller broke; and a few minutes [p182] later, when a new
propeller had been substituted for this and the engine was again
started up, the starboard propeller also broke. When, upon further
trials and replacements of propellers, all had been so thoroughly
demolished that there was not a complete set remaining, it was seen
very clearly that the strains produced on a propeller working in the
open air are very much greater than those produced in shop tests,
where the air is necessarily quiet. These open-air tests of the
propellers had demonstrated that their weakest point was where the
steel tubes which received the wooden arms of the blade terminated,
and that another, though not so serious, point of weakness was where
the steel arms were brazed to the central hub, the thin metal tending
to tear loose even before the brazed joint would give way. It was,
therefore, decided to construct immediately a new set of propellers
in which the steel arms should be made of much heavier tubing, that
is, a sixteenth of an inch thick at the end where it was brazed to
the central hub, and tapering in thickness to one-thirty-second of
an inch at the other end. These arms were further made twelve inches
long in place of being only three inches long as before. This added
length carried the steel out beyond the point where the first section
brace joined the three arms together, and where they were further
strengthened by having the cloth covering tightly stretched around
them. In order to utilize such of the hubs of the former propellers
as had not been seriously damaged when the propellers broke, it was
also decided to try the effect of merely adding an extra length
of tube to the short arms by means of a thimble slipped over and
brazed to the two parts, which would make these arms twelve inches
long. The construction of these propellers was pushed as rapidly as
possible; and after their completion no further trouble was at any
later time caused by insufficient strength of the propellers. Even
in the test of October 7, 1903, when the aerodrome came down in
the water at a speed of something like fifty miles an hour, and at
an angle of approximately forty-five degrees, no break occurred in
either propeller until, when the aerodrome was plunging through the
water, a blade of one propeller was broken by the terrific blow which
it received when it struck the water under the impulse of the engine
driving it at full speed. The severity of this blow is attested by
the fact that the shaft, which was of steel tubing one-eighth inch
thick, was twisted about ninety degrees.

This experience with propellers very strongly emphasizes the fact
that on any flying machine the strains which are apt to be met with
in the open air must be allowed for in the proportioning of the parts
of the machine. But since an indiscriminate increase of strength
in all the various parts of the machine would entail a prohibitory
weight, very careful judgment, based on experience, will have to be
exercised in deciding just where added strength must be employed, and
also where the “live strains” are not apt to exceed very appreciably
the calculation for statical conditions.

[Illustration: PL. 59

WING CLAMPS]

[p183]

Owing to Mr. Langley’s belief that the tests of the man-carrying
aerodrome must not only be made over the water, but that it was
necessary that the machine be launched from a car running on a
track at a considerable elevation in order to permit the machine
to drop a short distance after being launched in case it was not
quite up to soaring speed when launched, it was necessary that the
aerodrome be so constructed that it could be readily transported
to the launching track from the interior of the house-boat where
it was stored. This plan of storing the main body of the machine
in the interior of the boat and hoisting it to the launching track
just before attempting a flight (some of the difficulties of which
may be more clearly appreciated by an inspection of Plate 60), made
it necessary that the wings, tail and guy-posts be so constructed
as to be readily attachable to and detachable from the main frame,
and since the weather conditions are seldom suitable for a test
for more than a couple of hours at a time, it was necessary that
the mechanism employed for attaching these parts be so arranged
that the proper settings of the different parts could be quickly
obtained, and without requiring the exercise of judgment which past
experience had shown did not often manifest itself during the hurry
of the preparations for a test. While the wings, therefore, were
made removable, yet all of the sockets, guy-wires, etc., which were
loosened in removing them, were made with positive stops on them so
that each fitting that was to be tightened up in assembling could be
adjusted to its definitely determined position.

As all of the models had been constructed with these same parts
removable in order to permit them to be readily shipped back and
forth in the many trips which had been made with them from Washington
to Chopawamsic Island, the same details of arrangement were used
for attaching these parts on the large aerodrome, though the actual
fittings by which the parts were attached in the latter case became
more elaborate.

In the drawings, Plates 52, 53 and 54, the method of attaching the
wings to the frame is clearly shown. Each of the two main ribs of
each wing was secured to the midrod of the frame by a wing clamp,
shown in detail in Figs. 1, 2, 5, 6 and 7 of Plate 59. Figs. 1 and
2 show the clamp for the middle main rib of each pair of wings, and
Figs. 5 and 6 show the clamp for the main front rib, the latter being
so constructed that the wings could be rocked on the midrib clamp as
a pivot and secured at any angle of lift desired from 6-1/2 degrees
to 15 degrees. The horns on each clamp merely acted as receiving
sockets for the ends of the ribs, and were not in any way intended
to do anything more than merely hold the ends of the ribs in their
correct positions. The wings were fastened to the frame by the
guy-wires which ran from two points on each main rib to an upper and
a lower guy-post mounted on the midrod. The system of guy-wires for
the wings is clearly shown in Plates 52, 53 and 54, and [p184] in
Plate 61, which shows the aerodrome mounted on its launching car at
the rear end of the track, and with the front pair of wings in place
and all the guy-wires adjusted. The details of the guy-posts are
shown in Plate 62, where it will be noted that the lower guy-post was
of wood, with metal fittings, and was 2 metres long from the center
of the midrod to the bottom, while the upper guy-post was a steel
tube 109 centimetres long from the center of the midrod to its top.
The guy-wires from the middle rib of each of the pair of wings were
fastened to the fittings at the bottom of the lower guy-post, while
the wires from the front main rib were fastened to the fittings which
were brazed and riveted to the slidable collar, which was mounted
on the steel tube forming the cap on this guy-post. This collar was
made slidable to permit the angle of lift of the wings to be readily
changed without affecting the length of the guy-wires. This collar,
when once set for any particular angle of the wing, was prevented
from sliding by a taper pin (not shown) which passed through it and
the guy-post. In order to secure the wings more rigidly to the main
frame and thereby throw on it all torsional strains from the wings,
which it was specially designed to take, each of the middle main
ribs was secured to one of the main tubes of the main frame by an
auxiliary clamp at the point where this rib crossed the main tube.
These auxiliary clamps are clearly shown in Figs. 3 and 4 of Plate 59.

Projecting from the lower end of each of the lower guy-posts was a
five-sixteenth-inch steel rod about one inch long, as clearly seen
in Plate 62. Brazed to the side of this rod, in such a position that
it would project towards the rear of the aerodrome when the guy-post
was in position, was a small arm or bracket. When the guy-post was
in place with the aerodrome on the launching car, this pin was in a
slot formed in a metal cap on the top of the small folding upright
at the front or rear of the car, as seen in Fig. 1, Plate 63, while
Fig. 2 of Plate 63 shows the pin just being inserted into this slot
as the guy-wires of the guy-post are being fastened. This small arm
or bracket on this rod projected under the cap to prevent the rod
of the guy-post from being lifted out of the slot in the folding
upright, when the wind acting under the wings tended to lift the
aerodrome from the car. Particular attention is here called to this
apparently insignificant detail, for it was this arm or bracket on
this small rod of the front guy-post which, hanging in the cap on
top of the folding upright, caused the accident in the launching of
the aerodrome on October 7, 1903. Certain it is that but for the
accident due to this apparently insignificant detail, success would
have crowned the efforts of Mr. Langley, who above all men deserved
success in this field of work, which his labors had so greatly
enriched.

[Illustration: PL. 60

FIG. 1

FIG. 2

FIG. 3

HOISTING AERODROME TO LAUNCHING-TRACK]

[Illustration: PL. 61

AERODROME ON LAUNCHING-CAR; FRONT WINGS IN PLACE, GUY-WIRES ADJUSTED]

[Illustration: PL. 62

DETAILS OF GUY-POSTS]

[Illustration: PL. 63

FIG. 1.

FIG. 2.

GUY-POST AND PIN ON LAUNCHING CAR]

[p185]

AVIATOR’S CAR

In determining on a suitable car for the aviator various designs were
made, differing all the way from that in which the aviator occupied
a sitting position facing directly ahead and with practically no
freedom of movement, but was even strapped to the machine to avoid
the possibility of being thrown out, to the one finally adopted, in
which he was provided with the greatest freedom of movement, could
either stand or sit, as the occasion seemed to demand, and could
face in any direction for giving proper attention to any of the
multitudinous things which might at any time require his attention,
and could, if agile, even climb from the extreme front of the machine
to the rear. The wisdom of giving the aviator complete freedom
without hampering him in any way by provisions for preventing his
being thrown out of the machine was amply justified, as will later be
seen in the description of the tests of the machine, where freedom of
movement and agility prevented a fatal accident.

The aviator’s car was therefore designed to occupy the entire
available space between the engine and the front bearing points, and
between the two main tubes of the main frame, thus allowing him a
space of something like three feet by five feet. The car itself was
shaped like a flat-bottomed boat, the bottom being approximately
level with the bottom of the lower pyramid. It had a guard rail
of steel tubing eighteen inches above the floor, with a cloth
covering drawn over the frame to decrease the head resistance of the
appurtenances of the engine which were placed at the rear end of the
car. The car was supported by vertical wires passing from its bottom
up to the main frame, and was prevented from longitudinal or side
motion by being fastened at the front to the cross-rod connecting the
front bearing points, and at the rear to the lower pyramid. A light
wooden seat extended fore and aft of the car at a height of about two
feet from the floor, this seat resting on blocks of sponge rubber to
absorb some of the tremor which existed in the whole aerodrome when
the engine and propellers were working at high speed. The aviator
was thus free to stand, to sit sidewise or to straddle the seat,
and while the network of wires surrounding him prevented any great
possibility of his being thrown out, yet there was a comparatively
large opening between the guy-wires passing overhead which permitted
him to climb out of the machine.

In order to enable the aviator to know exactly how the engine was
operating, a tachometer, giving instantaneous readings of the number
of revolutions, was connected by a suitable gear to one of the
transmission shafts and placed where it could readily be seen.

During 1898 and 1899 considerable time and attention had been given
to designing an instrument to be carried by the aerodrome which would
automatically record the number of revolutions of the engine, the
velocity and direction [p186] of the wind relative to the machine,
the height of the aerodrome as shown by a specially sensitive aneroid
barometer, and the angle of the machine with the horizontal plane
of the earth. The construction of this instrument was undertaken by
a noted firm of instrument makers, but after many months of delay,
during which it was several times delivered as being complete,
only to be returned for further work, it was finally condemned as
unsatisfactory, and it was decided not to encumber the machine with
such a delicate apparatus, which, even if perfectly made, could not
be depended on to work properly when mounted on the aerodrome frame,
in which there was a constant, though minute, tremor due to the high
speed and power of the engine.

The completed frame, which is perhaps best shown in Plates 49, 50
and 51, and Plate 60, Figs. 1, 2 and 3, in spite of its size gave an
appearance of grace and strength which is inadequately represented
in the photographs. In making the designs for the large aerodrome no
data were available for use in calculating the strains that would
come on the different parts of the frame while in the air, and the
size and thickness of the tubes and the strength of the guy-wires
were consequently determined almost entirely by “rule of thumb,”
backed by experience with the models. Although the dimensions, shape,
and arrangement of most of the auxiliary parts of the machine were
considerably changed during the course of construction in accordance
with the indications of the exhaustive series of shop tests, the
fundamental features of the construction were practically unaltered,
but the changes in the guy-wire system and in the fittings by which
they were attached, made the frame as a whole several times as strong
as it was originally, and it was felt that the direction of further
improvements in it would be shown only by actual test of it in flight
where any weaknesses would be certain to manifest themselves.

It may be well to remark here that even with the data which were
later obtained, judgment based on experience proved after all to
be the safest guide for proportioning the strength of the various
parts. It can be assumed that a live stress will produce a strain
ten times as great as that due to a static stress on the part when
the machine is stationary. For greater safety, it would be still
better to assume a strain twenty times as great. If one is building
bridges, houses, and similar structures, where weight is not a prime
consideration, it would be criminal negligence to fail to provide a
sufficient “factor of safety,” or what in many instances may be more
properly termed a “factor of ignorance,” while at the present time
the insistence on large factors of safety in machines intended to
fly would so enormously increase the weight that, before one-half
the necessary parts were provided, the weight would be many times
what could possibly be supported in the air. Later, no doubt, as
experience is gained in properly handling the machine in the air,
increased strength entailing [p187] increased weight may be added
in proportion to the skill acquired; and there is no doubt that man
will acquire this skill with marvelous rapidity, approaching, if not
equaling, that exhibited by him in the use of the bicycle, which,
when first ridden, requires not only all of the rider’s skill but
that of a couple of assistants, but when once mastered requires
hardly more thought for its proper manipulation than even the act of
walking involves, the balancing and guiding being done intuitively
merely by the motion of the body and with practically no exertion.

[p188]

CHAPTER VI
CONSTRUCTION OF SUPPORTING SURFACES

An examination of the wings of birds, whether those of soarers or
of any other type, impresses one not only with the general strength
of the wing, but also with the fact that, while it possesses
considerable stiffness, there is also a graduated pliability, not
only of the whole wing, including the bones, but more especially
in the feathers, the rear tips being exceedingly pliable so that,
when the wing is held in a stiff breeze, they are seen to be easily
deflected in a gentle curve towards the rear and upper side. This
lack of rigidity has several advantages, among the more notable of
which is the lessening of the strains on the wing caused by sudden
wind gusts. Of great importance is the further fact that a supporting
surface having a graduated pliability, such as is possessed by a
bird’s wing, does not experience a shifting of the center of pressure
to the same extent as a rigid surface of similar form. Furthermore,
since any bird, even the best soarer, must use its wings not only
for soaring, but, when starting to fly from a state of rest, for
flapping, a rigid surface would not furnish anything like the same
universally available sustaining and propelling means that the bird’s
wing does.

In an inspection of the various wings or supporting surfaces which
Mr. Langley built, from the very earliest rubber-pull models up
to the successful steam machines Nos. 5 and 6, the point which is
most impressed upon the observer is the increasing strength and
rigidity embodied in these wings. While the success with the later
models was due to many things, including the development of a
strong frame and a suitable power plant giving sufficient power for
the permissible weight, besides the very important development of
effective equilibrium mechanism, yet it is safe to say that even with
the development of all these other things to the state to which they
had been brought in 1896, success would not have been achieved had
not the wings themselves been simultaneously changed from the very
flimsy construction which was at first used to the later type, using
a very strong and rigid wooden frame over which the cloth covering
was tightly stretched, and which possessed only a small amount of
pliability at the extreme rear ends of the cross-ribs.

The development of this successful type of wing for the models, it
will be remembered, had been achieved only after an extensive series
of experiments; and it was realized that the construction of suitable
wings for the large aerodrome, even with the knowledge gained in the
early work, would be still more [p189] difficult. The problem was
that of constructing for a very little greater weight per square
foot, wings containing approximately sixteen times the area of the
model wings.

It will be recalled from the previous description of model Aerodrome
No. 5, that its four wings had a combined area of 68 square feet and
weighed approximately 2500 grammes, or 37 grammes per square foot. It
was not expected that the large wings would be of so light a weight
per square foot, which would have meant only about 35,500 grammes
(approximately 78 pounds) weight for the 960 square feet originally
planned. It was hoped, however, that the increase in weight per
square foot for the large wings would be less than the square root of
the increased linear dimensions. In this case, the increase in linear
dimensions being approximately four, it was, therefore, hoped that
the larger wings would not have quite twice the weight per square
foot of the smaller ones; the computed weight permissible for the
large wings was therefore placed at 120 pounds.

To obtain the required area within the permissible limits of weight
two well-defined paths of procedure were open: First, it was possible
to so modify the structural form of the wing as to obtain the
advantage of the increased strength of trussed structures, that is,
by superposing the wings. Or, second, the “single-tier” type of wing,
the efficiency of which had been fairly well determined, could be
retained, and strength gained without increase of weight by improving
the method of constructing the wooden framework and by extending the
system of guy-wires.

Some knowledge of the superposed type of supporting surfaces had
already been gained by the experiments at Allegheny and the tests of
the rubber-driven models, in which superposed wings had frequently
been used; but it was felt that this knowledge was altogether
inadequate to aid in determining either whether the superposed type
of construction possessed in practice the advantages which theory
would indicate, or how and at what distance apart the surfaces
should be superposed to obtain the best results. In order to obtain
the desired information, a series of tests on the whirling-table
of complete wings suitable for use on the models was made. These
experiments were supplemented by the practical tests with the models,
which have already been described in Chapter III, in order to give
the wings a trial under the conditions of flight, where they would be
subjected to the action of the propellers and the uneven character of
the wind.

In addition to determining what type of construction and what form
of surface would give the greatest “lift” with the smallest “drift,”
these whirling-table tests supplied data as to how much greater
the actual resistance of the wing with its necessary guy-posts and
guy-wires was than the theoretical resistance, found by extrapolation
from the results obtained in the tests of rigid [p190] curved
surfaces formed of wood. The first of this series of tests, the
results of which are given below, was made November 30, 1898, on the
superposed wing shown in Plate 37, Figs. 1 and 2. It should be noted,
however, that when this test was made the wing was not provided with
the stiffening strips or the vertical partitions.

Weight of wing = 1000 grammes; weight of guy-posts, etc., = 475
grammes; distance of mean center of gravity of guy-posts, etc., from
pivots of balance arm = one-half distance of CP of wing from pivots
of balance arm; the wing, therefore, had a lever arm of two to one
with reference to weight of guy-posts, etc., so that the equivalent
weight of guy-posts, etc., = 237 grammes. This gives 1237 grammes
of equivalent load on the wing = 2.73 pounds. Area of wing = 21.85
square feet. Therefore load on wing = 0.125 pounds per square foot.

Angle Revolutions Velocity of Velocity Drift
of of turn- center of (ft. per (grammes).
chord. table. wing (ft. second).
per min.)
2.0° 10.75 1086 18.1 255
3.0° 10.0 1010 16.85 255
5.0° 9.5 960 16.0 255
10.0° 7.75 783 13.0 255

Angle Drift Foot-pounds Calculated
of (pounds). per sec. soaring speed
chord. RV. carrying 0.5
pounds per sq. ft.
(ft. per sec.).
2.0° 0.561 10.15 36.2
3.0° 0.561 9.47 33.7
5.0° 0.561 8.98 32.0
10.0° 0.561 7.3 26.0

The very interesting phenomenon was noted in this test that the
“drift” or resistance of the wing seemed to remain unchanged at
soaring speed at different angles of elevation. It is hardly probable
that this result is accurate, for the “balance arm” undoubtedly
twisted under the action of the wing, and this caused it to strain on
its pivots, and thus, to a certain extent, falsify the record as to
drift.

A test of a single-tier wing at different angles of elevation was
made on December 6, 1898. This wing was nearly the same as those used
in actual flights of Aerodromes Nos. 5 and 6 in May and November,
1896, the wing being of the same width fore and aft, but somewhat
shorter. The actual wing was a little too long to permit its being
used on the whirling-table in the limited space of the shop.

Weight of wing = 420 grammes; weight of guy-posts, etc., = 320
grammes; equivalent weight of guy-posts, etc., = 150 grammes applied
on the wing. Therefore, total load on wing = 570 grammes. Area of
wing = 11.2 square feet; equivalent load on wing = 0.112 pounds per
square foot.

Angle Revolutions Velocity of Velocity Drift
of of turn- center (ft. per (grammes).
chord. table. of wing second).
(ft. per min.)
2.0° 11.6 1195 19.9 210
3.0° 9.75 1005 16.7 157
5.0° 8.25 850 14.2 133
10.0° 6.75 695 11.6 129
12.5° 6.0 618 10.3 129

Angle Drift Foot-pounds Calculated
of (pounds). per sec. soaring speed
chord. RV. carrying 0.5
pounds per sq. ft.
(ft. per sec.).
2.0° 0.462 9.2 42.1
3.0° 0.345 5.77 35.3
5.0° 0.293 4.16 30.0
10.0° 0.284 3.29 24.5
12.5° 0.284 2.92 21.8

In this test it is to be noted that the “drift,” or resistance,
while considerably greater at soaring speed for 2 degrees than for 5
degrees, remains practically the same between 5 degrees and 12-1/2
degrees. Comparing it with the preceding test with the superposed
wing, it is seen that at soaring speed at an angle of 10 degrees, the
single-tier wing having a load of 0.112 pounds per [p191] square
foot, has only 129 grammes drift, while the superposed one, while
supporting 0.125 pounds per square foot, has 255 grammes drift.
Moreover, the soaring speed of the single-tier wing is only 11.6 feet
per second, while the superposed one requires a speed of 13 feet per
second.

As the superposed wing tested on November 30 was so weak structurally
that it could not be made to keep its proper shape without adding an
excessive number of guy-wires, it was decided that it was not adapted
for use on the aerodrome, but before abandoning it the partitions and
strips were added and it was again tested on the whirling-table on
March 1, 1899, with the following results:

Weight of wing = 905 grammes; weight of guy-posts, etc., = 320
grammes; equivalent weight of guy-posts, etc., = 150 grammes applied
at ‹CP› of the wing; equivalent load on the wing = 1055 grammes =
2.321 pounds; area of wing = 21.85 square feet; equivalent load on
wing = 0.1062 pounds per square foot.

Angle Revolutions Velocity of Velocity Drift
of of turn- center (ft. per (grammes).
chord. table. of wing second).
(ft. per min.)
5.0° 10.875 1100 18.35 250
5.0° 10.75 1085 18.07 250
5.0° 10.75 1085 18.07 250
10.0° 8.0 808 13.47 250
10.0° 8.0 808 13.47 250
10.5° 7.875 797 13.3 250
10.5° 7.875 797 13.3 250
13.0° 7.0 707 11.78 250

Angle Drift Foot-pounds Calculated
of (pounds). per sec. soaring speed
chord. RV. carrying 0.5
pounds per sq. ft.
(ft. per sec.).
5.0° 0.55 10.1 39.81
5.0° 0.55 9.94 39.19
5.0° 0.55 9.94 39.19
10.0° 0.55 7.4 29.226
10.0° 0.55 7.4 29.226
10.5° 0.55 7.32 28.86
10.5° 0.55 7.32 28.86
13.0° 0.55 6.48 25.553

An examination of the data obtained in this test shows the wing to
be of slightly less efficiency than when first tested. While it was
considerably stronger it was still too weak for use on the aerodromes.

A second type of superposed wing, Plates 64 and 65, was therefore
constructed and tested on the whirling-table on March 2, 1899, with
the following results:

Weight of wing = 1025 grammes; weight of guy-posts, etc., = 320
grammes; equivalent weight of guy-posts, etc., = 150 grammes applied
at ‹CP› of the wing; equivalent load on the wing = 1175 grammes =
2.585 pounds; area of wing = 21.85 square feet; equivalent load on
wing = .1183 pounds per square foot.

Angle Revolutions Velocity of Velocity Drift
of of turn- center (ft. per (grammes).
chord. table. of wing second).
(ft. per min.)
5.0° 11.625 1170 19.5 250
5.0° 11.625 1170 19.5 250
8.0° 10.5 1060 17.7 250
10.0° 9.125 919 15.3 250
10.0° 9.125 919 15.3 250

Angle Drift Foot-pounds Calculated
of (pounds). per sec. soaring speed
chord. RV. carrying 0.5
pounds per sq. ft.
(ft. per sec.).
5.0° 0.55 10.72 40.087
5.0° 0.55 10.72 40.087
8.0° 0.55 9.75 36.37
10.0° 0.55 8.43 31.4
10.0° 0.55 8.43 31.4

During the tests on the whirling-table this type of construction
seemed to be exceedingly strong and stiff, and to be easily
maintained in whatever position it was placed. It was therefore
thought that it would prove strong enough for the aerodrome, and
it was accordingly inverted and given a “sanding test” [p192] by
sprinkling sand uniformly over it to such a thickness as to cause
it to have a load of 0.75 pounds per square foot. As it showed no
serious deflection or change of form under the sanding test, it was
decided that it was strong enough for use in tests of the model
aerodromes in actual flight.

Upon the completion of these whirling-table tests, the cloth
covering of this wing was painted with collodion varnish, which
increased the weight of the wing only 50 grammes. In order to make
the results of its tests more easily comparable with those obtained
before varnishing, the cross guy-wires on the wing were changed to
a slightly smaller size in order to make the weight of the wing the
same as before. It was tested on March 3, and the following results
were obtained:

Weight of wing = 1025 grammes; weight of guy posts, etc., = 320
grammes; equivalent weight of guy-posts, etc., = 150 grammes applied
at ‹CP› of the wing; equivalent load on wing = 1175 grammes = 2.585
pounds; area of wing = 21.85 square feet; equivalent load on wing =
.1183 pounds per square foot.

Angle Revolutions Velocity of Velocity Drift
of of turn- center (ft. per (grammes).
chord. table. of wing second).
(ft. per min.)
5.0° 10.5 1060 17.7 250
5.0° 10.5 1060 17.7 250
10.0° 8.5 859 14.3 250
10.0° 8.5 859 14.3 250

Angle Drift Foot-pounds Calculated
of (pounds). per sec. soaring speed
chord. RV. carrying 0.5
pounds per sq. ft.
(ft. per sec.).
5.0° 0.55 9.75 36.37
5.0° 0.55 9.75 36.37
10.0° 0.55 7.88 29.4
10.0° 0.55 7.88 29.4

Although the varnishing of the wing seemed to have no effect on the
“drift,” the soaring speed was slightly decreased.

As a result of these tests it was decided to construct three more
wings like this second type, the four forming a complete set for use
on the steam-driven models Nos. 5 and 6. Although the tests on the
whirling-table indicated a superior efficiency for the “single-tier”
wings, and it was not expected that in actual use on the aerodrome
the result would be different, yet it was felt that as the conditions
of actual use are so very different from those of a whirling-table
experiment it would not be safe to decide too definitely against
the superposed wings without first giving them a test under actual
conditions. Aside from the decreased lifting effect shown by the
superposed wing when compared with the “single-tier” one, it was also
thought that under the actual conditions of use on the machine the
superposed wing would show up still worse. The deflection of the air
by the front wings diminishes the lift of the rear ones even for the
“single-tier” type, and this, it seemed certain, would be greatly
aggravated in the case of the superposed type.

In order to emphasize more fully the results of these tests the
following table is added, which gives the data for the “single-tier”
wing and this second type of superposed one, when each was tested at
ten degrees angle of elevation:

[Illustration: PL. 64

EXPERIMENTAL TYPE OF SUPERPOSED WINGS, MARCH 2, 1899]

[Illustration: PL. 65

EXPERIMENTAL TYPE OF SUPERPOSED WINGS, MARCH 2, 1899]

[p193]

Wing
“Single-tier” Superposed.
Type No. 2
Length (feet). 4.27 4.27
Area (sq. ft.). 11.2 21.9
Weight (pounds). 1.26 2.59
Angle of chord. (°) 10 10
Soaringspeed, (ft. per
sec.). 11.6 14.3
Weight (lbs. per sq.
ft.). .112 .118
Drift (lbs. per sq.
ft.). .025 .026
Calculated soaring
speed, carrying 0.5
lbs. per sq. ft.
(ft. per sec.). 24.5 29.4

The “single-tier” wings actually used on Aerodrome No. 6 were 5.33
feet long, while the wing tested above was only 4.27 feet long. In
order to bring out more fully what might be expected of Aerodrome No.
6, when using the two different types of wings, the following table,
calculated from the preceding one, is given. This shows the results
which might be expected from the aerodrome when the resistance of the
machine itself was included:

Aerodrome No. 6 without wings weighs 22 pounds.

“Single-tier” “Single-tier” Superposed.
(short) (full-length) Type No. 2
Length (feet). 4.27 5.30 4.27
Area of two pair of
wings (sq. feet). 44.8 54.0 87.6
Weight of two pair of
wings (pounds). 5.04 5.5 10.36
Weight of aerodrome with
two pair of wings (lbs.). 27.04 27.5 32.36
Total weight to be
supported (lbs. per sq.
ft.). 0.603 0.51 0.369
Drift of wings (lbs.). 6.06 6.13 6.9
Assumed drift of
aerodrome body (lbs.). 1.0 1.0 1.0
Total drift (pounds). 7.06 7.13 7.9
Soaring speed (ft. per
sec.). 27.0 24.7 25.3
Thrust horse-power
expended. 0.35 0.32 0.364
Brake horse-power
expended. 0.70 0.64 0.73

The first line shows the calculations for the aerodrome when equipped
with the short “single-tier” wings; the second line, when equipped
with the “single-tier” wings of the full length used in the flights
of 1896; and the third line, when equipped with superposed wings,
Type No. 2.

It will be seen that, on the whole, the result of the comparison
of the full-length “single-tier” wing and the superposed one is
less in favor of the latter than was to be expected, as, aside from
its greater structural strength, it seems to have no real point of
superiority, except that it is shorter; and, as already pointed out,
one point of presumable inferiority, though not exhibited in the
table, is the fact that the rear set of wings would suffer relatively
more from being in the lee of the front ones, in the case of the
superposed wings, than in the case of the “single-tier” ones.

Besides these “conventional” forms of wings, various other types
were tested on the whirling-table. The data of these tests are not
given, as in the rough preliminary tests the results were so entirely
negative in character that accurate quantitative tests were never
made. However, since in work of this kind the greatest delay is
experienced in learning what not to do, and in ridding one’s self of
freak notions which are continually suggesting themselves, it may
be well here to describe sufficiently at least one of these types
of wing to enable others to avoid any loss of time in experiments
with it. Since the principal disadvantages of a wing possessing
considerable width in the fore and aft direction are due to the great
extent through which the center of pressure [p194] shifts when the
velocity of advance or angle of incidence is changed, and to the
further fact that a wide surface does not support proportionately as
much per square foot as a long and narrow one, it was thought that
some advantage might be gained by making the covering of the wing
in the form of strips, the edges of which would be perpendicular
to the direction of motion, or by making this covering in more or
less slat-like form, which would permit the air which had already
been acted upon by the leading slat to slip through between the rear
edge of the first slat and the leading edge of the succeeding one.
In the tests on the whirling-table, however, it was found that this
type of construction not only did not possess any advantages, but
was even less effective than a similar one in which the covering was
continuous. The difference was probably due to the fact that the air
which passed between the slats reduced the suction on the upper side
of the following slat, and also to the fact that the distance between
the slats was not sufficient to gain the effect of having each slat
act on air which had not already been partially deflected by the
preceding one.

In view of the results of these tests on various types of wings,
it was decided that in constructing the first set of wings for the
large aerodrome it would be best to employ the “single-tier” type,
which had proved successful with the models, and that after getting
a successful flight with these the superposed wings would be tried
in order to get, if possible, the advantage which they possessed
of being structurally stronger and more compact. It was therefore
clear that any gain in the strength and rigidity of the first set
of wings, as a whole, would have to be obtained by improvements in
the construction of its integral parts, that is, in the main and
cross-ribs which made up its framework.

Before attempting to proportion the parts of the necessary wooden
wing frame, which it was expected would probably undergo many changes
before a final design was secured which would embody maximum strength
for minimum weight, various tests were made to determine just how
light a cloth covering could be obtained which would be strong enough
and sufficiently impervious to the air. In the construction of the
wings for the models a good grade of China silk had been employed,
but on account of the greatly increased quantity of cloth required
for the large wings, it was hoped that something approximately as
good as the silk could be secured at a much less cost, and various
grades of percaline were therefore tested. The weight of the various
grades of percaline ranged from three grammes to ten grammes per
square foot, the lighter samples being of a rather coarse mesh,
while the heaviest ones were not only close mesh but some specimens
contained a large amount of “sizing.” The particular grade which was
finally adopted weighed seven grammes per square foot. This material
was practically impervious to air at a pressure of one pound per
square foot, which, of course, was considerably [p195] more than
it would be subjected to in flight. This grade of percaline weighed
approximately one and a half times as much as a grade of silk, which
on test was found to have a slightly greater tensile strength than
the percaline, though the latter did not “flute” or “pocket” nearly
as much as the silk. Moreover, the cost of the percaline was only
about one-third that of the silk, and it was chiefly for this reason
that percaline was adopted in place of silk. Allowing for necessary
seams and extra material to be turned over at the front and rear
edges of the wings, the percaline covering, which under the original
plans comprised approximately 1000 square feet, was therefore
calculated to weigh approximately 7000 grammes, exclusive of the
necessary cords for lacing the coverings to the wooden frames of the
wings.

As the one hundred and twenty pounds allowed for the four wings
permitted only thirty pounds per wing, and as the cloth covering,
lacing cords, etc., were found to weigh something over four pounds,
there remained only about 25 pounds as the permissible weight of
the wooden framing, including the necessary metal clips, secondary
guy-wires, etc., for each wing. With the relative proportions of the
various parts of the wooden framing of the wings of the models as a
basis, it was decided to make the main ribs of the large wings 1.5
inches in diameter for one-half their length, and have them taper
from this size to one inch in diameter at the extreme point. After
making allowance for the weight of these ribs, it was found that, if
the cross-ribs were to be spaced no farther than ten inches apart,
and the two end ones were to be made at least as wide as 1.5 inches
in order to resist the end strain due to the stress of the cloth, the
twenty-six intermediate cross-ribs could be only seven-sixteenths of
an inch in diameter at the point where they crossed the main rib, and
that they must be tapered to three-eighths of an inch in diameter at
the front end and to one-fourth of an inch in diameter at the rear
tip.

A trial wing, whose total weight was 30 pounds 2 ounces, was made up
with the various parts of its frame of the above dimensions. Even
upon inspection it appeared to be too flimsy to withstand the sudden
gusts of wind which were certain to be met in actual practice. In
order, however, to get some definite data as a guide, the wing was
inverted and guyed in the same way that it was proposed to guy it on
the aerodrome, and a uniform thickness of sand was then sprinkled
over it to such a depth as to give it a load of 0.7 pounds per
square foot. Even before one-quarter of the sand was sprinkled over
it, it was seen that the wing was rapidly going out of shape, and
it was feared that the full amount of sand would not only seriously
distort it, but would even break it. The full quantity of sand,
however, did not break it, but distorted it to such an extent
that, had the pressure been due to its being propelled through the
air, its serious change in form would have rendered it worse than
useless. [p196] While the main ribs had shown a certain amount of
deflection under the sanding test, the more serious distortion had
been in the cross-ribs, the small guy-wires, which had been fastened
to each cross-rib, becoming loose instead of tight, as had been
expected, since the rib tended to increase its curvature instead of
straightening out. This increase in the curvature of the cross-ribs
was partly overcome by tying the guy-wire flat against the cross-rib
for a distance of about 2 feet from the rear tip. But while this
caused the guy-wire to tighten the general contour of the wing showed
very little improvement, as the ribs now assumed a curve more or less
like the letter S, the rear tip now being bent downward to form the
tail of the elongated S.

From this sanding test it was seen that the cross-ribs must be
materially stiffer, and a new set was accordingly made one-sixteenth
of an inch larger in diameter at the various points of measurement.
Upon giving the wing, equipped with these larger ribs, a sanding
test it was found that, while there had been some improvement, it
was entirely too flimsy, even when it been double-guyed by running
a second wire on each cross-rib from the middle of the portion
in front of the mid-rib to the middle of the portion behind the
mid-rib. As the weight of the wing with these larger solid cross-ribs
had now increased to more than 33 pounds, and the wing had proved
itself altogether too weak for use on the aerodrome, it was evident
that some other plan of constructing the ribs which would give
greater strength for the same weight must be found. At first sight
it might appear that the obvious way of increasing the stiffness
of the cross-ribs was to employ a cross-section other than a round
one, since material added to the depth of the rib is very much
more effective than if added to the width. It must, however, be
remembered that these cross-ribs were 11 feet long, and that, as the
main mid-rib was 6 feet in front of the rear tips of the cross-ribs,
with no intermediate bracing, except the light threads by which the
cloth cover was attached, it was inevitable that, should the depth
be made materially greater than the width, the rib would buckle
sideways. Test ribs of I-beam form, which are later described, were
constructed, but, although they proved exceedingly stiff, had to be
discarded.

In view of these facts the obvious remedy appeared to be to make
the rib hollow, and one cross-rib, 3/4 of an inch in diameter at
the point where it crossed the main rib, tapering to 5/8 of an inch
at the front and 3/8 of an inch at the rear tip, was accordingly
constructed. Tests showed that this form of rib, which was about
10 grammes lighter than the 1/2-inch solid ribs, was much stiffer
than anything yet constructed. But when a wing, with cross-ribs of
this size placed 20 inches apart, was sanded it was found that,
although a great advance in construction had been made, still further
improvement was necessary before a suitable wing for the large
aerodrome could be procured. [p197]

Before proceeding with the construction of any more complete wings,
an extended series of experiments was made in order to secure ribs
of proper lightness and strength. Various forms of metal tubes were
tested; but, although aluminum seemed at one time to promise good
results, it was found that hollow ribs could be constructed of spruce
which were much stronger than aluminum tubes of the same weight. In
order to determine more accurately what mode of construction would
give the greatest stiffness and strength for a minimum weight, it was
decided to make up some test pieces of different forms before making
up complete ribs. For convenience in construction, these test pieces
were made straight and shorter than the large cross-ribs. Each piece
was tested by fastening it in the testing clamp with 1 metre of its
length projecting horizontally, and attaching at its end a weight of
1 kilogramme. The deflection from the horizontal gave an index of the
stiffness of the piece under examination.

The first test piece was a hollow square, 17 mm. length of side on
the exterior, and 11 mm. length of side on the interior, the walls
thus being 3 mm. thick. This weighed 73 grammes per metre and had
small internal stiffening pieces, like the partitions in bamboo,
glued into it 4 inches apart. A weight of 1 kilogramme at the
distance of 1 metre gave a deflection of 56 mm. The second test piece
was a duplicate of the first one, except that it had no internal
stiffening pieces, and the weight per metre was made the same, 73
grammes, as formerly, by leaving the walls a fraction thicker. The
deflection in this case was, as would be expected, exactly the same
as in the first one. The first test piece, however, was superior to
the second one in that it was stiffer against being crushed in by
accident. The third test piece was a hollow cylinder, 22 mm. outside
diameter and 17 mm. inside diameter, the walls thus being 2.5 mm.
thick. The weight per metre was 91 grammes, and the deflection was
46 mm. The fourth test was made by taking two of the original solid
cross-ribs, 12 mm. in diameter, and fastening them in the clamp side
by side, with a length of 1 metre projecting. The weight per metre
for the two ribs was 105 grammes, and the deflection produced on the
two by 1 kilogramme at 1 metre distance was 115 mm. The fifth test
piece was an I-beam of spruce, having a depth of 25 mm., with the
flanges 12.5 mm. wide and the web 3 mm. thick. The weight per metre
was 65 grammes, and the deflection was 26 mm. All of these test
pieces were made of carefully selected straight-grained spruce.

It is readily seen that the test piece having the I-beam section
weighed less than the hollow square in the first and second tests,
and had a deflection of less than half. This I-beam section, however,
did not show up so well when a longer piece was tested, for as soon
as the length was made appreciably greater than a metre it began
to twist, the twisting becoming more and more serious the [p198]
greater the length, until with a piece 11 feet long, the full length
of a cross-rib, the twisting was so serious as to make the rib
practically useless. It was at first thought that this twisting might
be overcome by making the webs slightly wider, and it would to a
certain extent, but in looking ahead and planning how the cross-ribs
were to be fastened to the main ribs, the I-beam section was seen to
present so many difficulties that it was thought hardly worth while
to spend time on further experiments with it. This decision was made
all the more imperative by foreseeing the difficulty of bending the
I-beam section to the curve which the cross-ribs were to have. In
fact it had been found by experience that while many different forms
of ribs could be bent to the proper curve by steaming and clamping
them over a form and then drying them out while still clamped to the
form, yet the grain of the wood varied so in different ribs, that of
a dozen steamed and bent over the same form it was seldom that as
many as three would have approximately the same amount of curvature
when removed from the form after drying. If, however, the curve was
formed in the ribs by making them in two parts, which were glued
together and clamped up on the form while the glue dried, practically
any number could be made which would have the same curvature when
thinned down to the proper thickness of wall.

It was recognized at all times that the gluing together of the
ribs not only entailed extra work, but introduced an element of
uncertainty unless some kind of a varnish for the ribs could be found
which would prevent any possibility of the glue becoming soft from
moisture in the atmosphere or from the wings actually coming down
into the water when the aerodrome was tried in flight. A search was
therefore made for a varnish that was water-proof. A large number
of different varnishes were tried, and one was finally found which,
after repeated tests, seemed to be thoroughly good. Several test
ribs were given three coats of this varnish, and were then kept
immersed in water for 24 hours without the glue showing any signs
of softening. It was therefore decided to follow the plan of gluing
the ribs together and protecting them with three coats of this
varnish, which seemed to possess the remarkable properties of being
not only impervious to water, but also unaffected by the application
of concentrated ammonia or of gasoline, either of which produces
immediate softening when applied to ordinary varnishes.

Following the indication of these tests that the hollow, round
section, 22 mm. outside diameter by 17 mm. inside diameter, would
probably give the best cross-rib for the weight that it seemed
possible to allow, a set of cross-ribs of this form was constructed
and put in place in the large experimental wing, in which the former
solid ribs had been tested. The wing was inverted and fastened into
two posts at the angle it would have in flight, the guy-wires from
the [p199] lower guy-posts of the aerodrome being represented by
wires stretched from the posts. In actual use on the aerodrome it was
proposed to have three main guy-wires running from each of the main
cross-ribs to the lower guy-post, but in the test, which is now to be
described, the wires which would have come nearest the body of the
machine were left off to see what effect their removal would have on
the wing.

The weight and dimensions of the wing, as set up, were as follows:
Length of the main ribs, 24 feet; length of the cloth covering, 22
feet; width of the cloth covering, 11 feet; total weight, 29 pounds.
The two main ribs (front rib and mid-rib) were solid, 3.5 cm. in
diameter at butt, 2.5 cm. in diameter at tip, and tapering from the
middle to the tip. There were twelve regular cross-ribs set 50.8 cm.
(20 inches) apart, each rib being as above described, 11 feet long,
22 mm. outside diameter by 17 mm. inside diameter at the butt, and
tapering from where they were attached to the mid-rib to the tip,
and each weighing 300 grammes. There were two extra cross-ribs,
one at the inner end next to the body of the machine and the other
at the outer end. These were solid strips of wood 3.8 cm. wide by
1.2 cm. thick, made extra wide and stiff in order to withstand the
strain of stretching the cloth covering. There was also a thin, flat
strip at the rear edge, which connected together all the tips of the
cross-ribs, holding them a uniform distance apart, and also serving
to fasten the cloth. The main mid-rib was stiffened in a vertical
direction by a system of small guy-wires drawn over short guy-posts
about 6 inches high. With the wing inverted and fastened in the way
above described, a weight of 2 kilogrammes placed at the inner rear
corner produced a deflection of 26.7 cm. When the inner rear corner
was pulled up by a spring balance until the balance registered 2
kilogrammes, there was an upward deflection of 41.3 cm. When the main
mid-rib was held at the inner end, the pull of 2 kilogrammes, applied
to the inner corner as before, caused an upward deflection of 25.4
cm. instead of 41.3 cm. This wing was afterwards given a sanding test
under a weight of 0.7 pound per square foot. With fine guy-wires
fastened from the front of the cross-ribs to the tip and drawn just
taut, the ribs showed an average deflection of 9 inches at the tip
under the above weight. When a small wooden guy-post was added under
each of these small guy-wires, the same weight produced an average
deflection of 5 inches at the tip of each rib under the same load. In
a previous test of the wing, using hollow cross-ribs 16 mm. outside
diameter by 10 mm. inside diameter at the butt, and only half as
far apart as the later ones, a load of 1 pound per square foot on
the wing produced an average deflection of 9 inches at the tip of
each rib when the cross guy-wires on each rib were held up by short
guy-posts, but when these short guy-posts were removed, the same load
produced a deflection of nearly 25 inches at the tip of each rib.
[p200]

Although this wing was a great improvement in every way over any of
the previous constructions, it was felt that it was too weak for the
large aerodrome. Further experiments were therefore made in order to
secure a form of cross-rib which would meet the rigorous requirements
imposed. An inordinate amount of time was spent in the construction
and tests of various forms of rib, but as a result a satisfactory
cross-rib was at last constructed of the form shown in Plate 66,
Figs. 4–8, the dimensions at the three principal points, viz., first,
where the cross-ribs join the front rib; second, where they cross
the mid-rib; and third, at the rear tip, being given both for the
intermediate cross-ribs and the end cross-ribs.

Following the plan employed by Nature in the construction of the
bamboo pole, small partitions, approximately one millimetre thick,
were placed every three inches in the thin, hollow rib to keep it
from being crushed. The partitions were glued in place when the
hollow rib was glued together on the form around which it was bent
and clamped until the glue dried. Longer blocks were also inserted in
each of the intermediate ribs at the point where it crossed the main
rib and also at the front end where it was attached to the front rib.
In the end ribs blocks were also inserted at the points where the
cross-braces were fastened to them for resisting the end stress due
to the cloth covering.

Upon making up one of these ribs and testing it, it was found to
possess remarkable stiffness, so much so that it was thought probable
that it was as stiff in proportion to its size as the best thing that
Nature had produced in the bird’s wing. A large quill from the wing
of a harpy eagle was therefore stripped and the large end clamped
in a special holder, and measurements were made of the deflection
produced by weights at various distances from the clamp. As the main
mid-rib of the wing of the aerodrome is placed approximately at the
point of the center of pressure, the bending action on the cross-ribs
may be assumed to act on a lever arm from the mid-rib towards the
front, and from the mid-rib towards the rear in the cases of the
pressure on the front and rear portions of the wing, respectively. In
testing these cross-ribs, therefore, against the quill, the rib was
clamped at the point where it crosses the mid-rib of the wing, and
measurements were made of the deflection produced by weights placed
at various distances from the point of clamping both front and rear.

[Illustration: PL. 66

DETAILS OF RIBS AND FITTINGS FOR WINGS]

[Illustration: PL. 67

CROSS SECTION OF RIBS]

The quill on which the measurements were made was 19.5 inches long
and had a gradual curve, the highest point of the curve being about
the center of the length of the quill, and the depth of curvature
being about 2 inches. When the butt of this quill was placed in the
clamp the tip stood 17 cm. above the horizontal. The hollow spruce
rib, when clamped at a point 5 feet from the tip (the point from
which it tapers in both directions) had its tip 2.2 cm. above the
horizontal, there being very little curve in that portion of the
rib. The quill weighed 4 grammes when stripped and 18 inches of
it projected from the [p201] clamp which held it during the
tests. The rear portion of the spruce rib projected 5 feet from the
clamp, being thus 3.3 times as long as the quill, and it weighed 120
grammes, the weight for the larger size having, therefore, increased
slightly less than the cube of the length.

The results of the tests of both the quill and the rib are given in
the following table. The approximate cross-section of the quill at
the point of clamping, the middle and the tip are shown in diagrams
‹A›, ‹B› and ‹C›, respectively, of Plate 67. The cross-sections of
the rib at the corresponding points are shown in diagrams ‹D›, ‹E›
and ‹F›. The cross-sections of the quill, enlarged five times, are
shown in diagrams ‹A′›, ‹B′›, and ‹C′›.

QUILL FROM THE REMIGES OF HARPY EAGLE.

Weight, 4 grammes; length, 45 cm.; tip, 17 cm. above butt when the
latter is horizontal.

Point of Weight
application Absolute in terms Deflection
of weight weight in of in terms
in terms of grammes. greatest of length.
length. weight.
0.39 1050 1.0 .38
0.445 605 0.58 .38
0.56 405 0.39 .38
0.75 210 0.20 .38
0.95 77 0.075 .38

HOLLOW SPRUCE RIB.

Weight, 120 grammes; length 153 cm.; section, rectangular; tip, 17
cm. above butt.

Point of Weight
application Absolute in terms Deflection
of weight weight in of in terms
in terms of grammes. greatest of length.
length. weight.
0.39 15,000 1.0 .11
0.445 11,400 0.76 .11
0.56 7,900 0.53 .11
0.75 4,000 0.27 .11
0.95 2,000 0.135 .11

In each case the unit of length was the portion extending beyond the
clamp; the unit of weight, the greatest weight employed to produce
the deflection. It should be noted, however, that the relative
deflection was quite different in the two comparisons. In the case of
the quill the deflection was 17 cm. in 45 cm., or 38 per cent; in the
case of the rib it was 17 cm. in 153 cm., or 11 per cent. In the case
of the rib at the point 0.39 the absolute weight was 15,000 grammes,
the relative weight unity and the deflection in terms of length 0.11.
While no rigorous comparison can be instituted, since the rib was
not deflected nearly as much proportionately as the quill, yet the
general inference is that while the rib was not intended to be, and
was not as elastic proportionately as the quill, it was probably at
least as strong in proportion to its weight. Briefly summarizing
these results it will be noted that the spruce rib was about 3.3
times the length and 30 times as heavy, while it was 15 times as
stiff near the butt and 26 times as stiff at the tip, as the quill.

As this test on the rib for the large wings had apparently shown
that the plan of constructing the ribs in the form of a hollow
square secured maximum strength for minimum weight, it was decided
to construct a few sample ribs after the same plan for the wings of
the new quarter-size model of the large aerodrome, and to test, these
ribs in a similar manner. The following table shows the results of
the test on one of these ribs:

Total length of rib = 80 cm. Curve = 1 in 18. Highest point of
curvature = 0.25 from front. Section of rib = 10 mm × 14 mm. at the
point of attachment to mid-rib, tapering to 8 mm. × 12 mm. at the
front point and to 7 mm. × 2 mm. at the tip. The rib was clamped
with the tip projecting [p202] 46 cm. and was weighted at different
percentages of its length to such an extent that it was deflected
11 per cent of its length, or 5 cm. The weight of the 46 cm. length
of rib which projected from the clamp was 11 grammes, the whole rib
weighing 22 grammes and balancing on a knife edge placed at the
point where it was clamped.

Point of Absolute Weight in Deflection
application weight terms of in terms
of weight in greatest of
in terms of grammes. weight. length.
length.

0.39 7680 1.0 0.11
0.445 5980 0.78 0.11
0.56 3680 0.48 0.11
0.75 2300 0.30 0.11
0.95 1100 0.143 0.11
1.00 930 0.121 0.11

A lighter rib than the above, which was constructed at the same time,
was also tested with the results shown in the following table. This
rib was also 80 cm. long, but was only one-half the linear dimensions
in section of the rib previously tested. The rear portion of it
projected 46 cm. from the clamp. The total weight of the rib was 11
grammes, or 5.5 grammes for the 46 cm. on which the measurements were
made.

Point of Absolute Weight in Deflection
application weight in terms of in terms
of weight grammes. greatest of
in terms of weight. length.
length.

0.39 1400 1.0 0.11
0.445 1100 0.785 0.11
0.56 700 0.50 0.11
0.75 400 0.275 0.11
0.95 250 0.178 0.11
1.00 220 0.157 0.11

A still lighter rib of the same length, weighing 9 grammes, suitable
for use in the wings of the quarter-size model, was constructed and
a set of tests was made on it with the following results. As in the
above test, 46 cm. of the rear portion of it projected from the clamp
which held it.

Point of Absolute Weight in Deflection
application weight in terms of in terms
of weight grammes. greatest of
in terms of weight. length.
length.

0.39 1450 1.0 0.11
0.445 1150 0.795 0.11
0.56 740 0.51 0.11
0.75 380 0.262 0.11
0.95 210 0.145 0.11
1.00 180 0.124 0.11

Among quite a number of different forms of cross-ribs which were
constructed of a size suitable for use in the model aerodrome,
but made primarily for use in tests to determine the best form to
employ, may be mentioned the following, in which both ribs were
seven-sixteenths of an inch outside diameter and five-sixteenths of
an inch inside diameter. One was filled with elder pith, formed up
into a round rod that just fit the interior of the hollow rib, and
was glued into it when the rib was glued up. The other rib was left
hollow. Upon testing these by suspending weights at different points,
the rib without [p203] the pith showed a slightly less deflection
than the one with it, it happening probably that the wood in one case
was a little stiffer than in the other, although they were carefully
selected to be as nearly alike as possible. The rib with the pith
in it weighed 34 grammes and the one without it weighed 30 grammes.
It was inferred from this test that the placing of a light pithy
material in the interior of the ribs would have no good effect, and
would not only add weight, but also complicate the construction. The
reason for making this test with pith in one of the ribs was that it
was thought probable that the rib flattened out somewhat when it was
deflected under a load, and that the pith stiffened with the glue
with which it was fastened in, might lessen this.

As the cross-rib described above, which was tested on October 23,
1899, seemed in every way suited for use in the wings of the large
aerodrome, a complete wing equipped with similar ribs but of slightly
changed dimensions, as shown in Plate 66, Fig. 5, was immediately
constructed. As previous tests had shown that the wing covering did
not “flute” or “pocket” to any considerable extent even when the ribs
were as much as thirty inches apart, only ten cross-ribs were used
in this wing. The eight intermediate cross-ribs were of the form
described above, but the ribs at either end of the wing were made of
a larger cross-section and otherwise stiffened in order to resist the
strain of the tightly stretched cloth covering.

On April 13, 1900, a final sanding test was made on this wing, guyed
in a manner similar to that used in the aerodrome, in which the
following results were obtained:

SANDING TEST OF LARGE WING.

Area, 260 sq. ft.; weight of wing, 29 pounds; weight of sand on
wing, 231 pounds; total weight supported by wing, 260 pounds, or one
pound per square foot.

Deflection of cross-rib, numbering from inner edge to extreme outer
edge of wing--

Number of rib. Deflection.
Inches.
1 (Heavy end rib) 5.5
2 9.5
3 11.75
4 12.25
5 12.5
6 12.75
7 12.9
8 13.0
9 12.0
10 (Heavy end rib) 9.75

The weight of sand put on the wing in this test was 1.5 times as
great as the pressure which at this time it was expected would be
imposed upon it in flight, and was in fact 1.2 times as great as the
normal pressure when supporting the aerodrome as finally constructed.
Even under this weight the greatest deflection noted in terms of the
total length of the rib was less than 0.10, showing that the elastic
limit of the rib was far from being reached. [p204]

As this test seemed to indicate that the wings constructed in
this manner were certainly strong and rigid enough for use on the
aerodrome, and that immediate further improvement could hardly be
made, three similar wings were at once constructed to complete the
set. Somewhat later two additional wings were provided, so that when
the large aerodrome was taken to Widewater on the Potomac in 1903 one
and a half complete sets of wings were on hand, which seemed to be
ample to provide for any emergencies that might arise.

Each of these wings had, as is clearly shown in the drawings,
Plates 53 and 54, two main ribs, which formed the main strength
of the framework and gave the wing longitudinal rigidity. To the
main front rib were attached the cross-ribs and the pieces for the
curved extension later described. The mid-rib extended across the
cross-ribs, parallel to and about 5 feet behind the front rib, this
being approximately the line in which lay the center of pressure of
the wing. It was upon this rib, therefore, that the greatest strain
would fall.

The mid-rib, Plate 66, Fig. 2, was 731.5 cm. (24 ft.) long, having at
the butt an outer diameter of 38 mm. (1.5 in.) and an inner diameter
of 25 mm. (1 in.), the walls being, therefore, approximately 6.5 mm.
(0.25 in.) thick. From the butt to the middle point the section was
uniform, but from this point it had a taper of one-twenty-fourth of
an inch to the foot, so that at the tip it had an outer diameter of
25 mm. (1 in.), the thickness of the wall being unchanged. At the
butt end a wooden block 8 inches long was glued inside the rib, and
at uniform distances of 75 mm. (30 in.) 10 smaller blocks were glued
in where the cross-ribs were attached. The main front rib was of the
same form and size, except that it was some 2 inches shorter and had
no blocks, except the long one at the butt, glued in it.

To these main ribs were attached, in the manner later described,
the 10 cross-ribs, to which the cloth cover was attached. The 8
intermediate cross-ribs have already been described in connection
with the tests. The cross-ribs at the end of the wings, upon which
greater lateral strains would come from the stretching of the cloth,
were made of the larger cross-section shown in Fig. 8 of Plate 66.
Additional longitudinal stiffness was provided by gluing a strip
2 mm. thick between the upper and lower halves, as shown in the
section. These end ribs, as well as those next to the ends, had
small blocks glued into them where they were crossed by the diagonal
braces, in addition to the small partitions 1 mm. thick, which were
glued into the ribs every 3 inches to prevent crushing, and the
blocks 2.5 and 3 inches long respectively, where they were attached
to the front rib and to the mid-rib. At the extreme rear edge of the
wing the cross-ribs were attached to the small “D”-rib, which served
to hold the ribs at equal distances and to keep the cloth cover
stretched tight. This “D”-rib, as shown in Plate 66, Fig. 3, had
semi-circular walls 4 mm. thick, 21 mm. in diameter, to the edge of
which was glued a flat strip 3 mm. thick. [p205]

As originally designed the wings had a curve of only 1 in 18, the
main front rib forming the leading edge of the wing. Later, however,
it seemed desirable to “quicken” the curve and at the same time give
the wing a sharper leading edge. This was accomplished by attaching
to the front rib, at the points where the cross-ribs joined it,
properly curved wooden pieces of the form shown in Plate 66, Fig. 10,
over which the cloth cover of the wing was stretched. The curve of
the wing after the addition of this extension is shown in Plate 66,
Fig. 4, and was a curve having a rise of approximately 1 in 12, with
the highest point .25 from the front end.

On account of the large size of these wings and the consequent
difficulty in handling them it was necessary to construct them in
such a manner that they could be easily taken apart, rolled up,
transported to the house-boat or any other point where they might
need to be used, and then quickly reassembled. After much experiment
as to the best means of constructing them, the following plan was
devised. The cloth covering was permanently fastened to the front
rib, to which were attached the front extension pieces by means of
small metal clips secured by small wood screws. On the rear edge
of the front main rib, at a uniform distance of 30 inches apart,
10 small metal horns of 1-mm. tubing, 5 cm. long, each brazed to
an independent clamping thimble, as shown in Fig. 9 of Plate 66,
were fastened. The front end of each of the cross-ribs was slightly
rounded out to fit the front main rib, and in the wooden block which
was glued in this end of the cross-rib a hole was bored to fit
these horns. Each of the cross-ribs was then pushed over its proper
horn and against the front main rib, and the cloth covering then
drawn back toward the rear tips of the cross-ribs. In the extreme
rear edge of the cloth covering a seam was made, and in this was
inserted the “D”-rib already described. The cloth was then tightly
stretched and a wood screw forced through the “D”-rib and into and
through the metal ferrule at the tip of the cross-rib. Near the
inner and outer edges of the cloth covering eyelets were placed
about 6 inches apart, through which small cords were then inserted
and tied to the end cross-ribs. The main or mid-rib was then placed
on top of the cross-ribs and fastened to them with wood screws,
and the cross-braces were then fastened on the top of the wing, as
shown in Plate 54. The frame of the wing was stiffened horizontally
by cross guy-wires which passed from each cross-rib, at the point
where the mid-rib crossed it, to the adjoining cross-rib, at the
point where it was connected to the front rib. Each of the main ribs
was individually guyed, in the manner clearly shown in Plate 52, in
order to stiffen it in the vertical direction, the fittings for these
guy-wires being shown in detail in Figs. 11–15 of Plate 66. Finally,
small guy-wires were run from the front end of the cross-ribs over
a guy-post 12 inches high at the point where the cross-rib crossed
the mid-rib to the rear tip of the cross-rib. These cross guy-wires
were regulated in [p206] tightness by raising and lowering a screw
in the slot of the head of which they rested, and which was threaded
in the end of the small guy-post. Upper and lower guy-wires, running
from the main ribs to the guy-posts on the aerodrome, as already
described, and as is clearly shown in the drawings, Plates 52 and 54,
completed the guy-wire system for the wings, except for the “drift
wires,” which for the front wings were run from the lower side of the
mid-rib to the bowsprit at the front of the machine, and for the rear
wings to the main frame.

Each wing when completely assembled weighed approximately 29 pounds,
and had a rectangular surface 22.5 by 11.5 feet (measured on the
chord of the curve), or 260 square feet, making the weight per square
foot equal about 50 grammes, rather less than 1.5 times as much per
square foot as the wings for the steam-driven models. The total
supporting surface of the aerodrome was 1040 square feet, and as the
aerodrome when equipped for flight weighed, including the aviator,
850 pounds this gave 1.22 square feet to the pound, or 0.82 pound to
the square foot. Although this was a somewhat larger proportion of
weight to supporting surface than it had originally been expected to
have, there is every reason to believe that it was sufficient, for
the quarter-size model, when weighted so that it had 1.22 square feet
to the pound, flew well, as will later appear.

[p207]

CHAPTER VII
EQUILIBRIUM AND CONTROL

In an aerodrome it is essential not only that its component parts
shall be so disposed that the initial equilibrium is correct and
highly stable, but also that some efficient means be provided for
quickly and accurately restoring the equilibrium, if for any reason
it is disturbed. If the aerodrome is of sufficient size and power to
carry a human being it is, of course, possible merely to supply an
efficient means of controlling the lateral and horizontal equilibrium
of the machine and depend upon the intelligence and skill of the
operator, as developed by practice and experience, to maintain the
proper equilibrium of the machine while in the air. This method,
however, is open to the objection that no matter how skilled the
aviator may be there remains the probability of a serious if not
fatal accident as the result of any momentary lapse or diversion
of attention until the “sense of equilibrium” has been developed.
One of the chief problems, therefore, which had impressed itself
from the beginning of the work, was to devise some means by which
the equilibrium of the aerodrome would be automatically maintained
under the varying conditions of flight, so as to leave the aviator
free, as far as possible, to control the direction of flight and
to devote his attention to other important matters connected with
the proper functioning of the various parts of the aerodrome. In
the development of the models it had been absolutely necessary to
develop some efficient automatic control, as they were far too small
to carry an aviator, and the conditions of flight in the open air,
even on the calmest day, were such that constant readjustments of the
equilibrium were necessary. The success attained in the automatic
control of the equilibrium of the models had been so great, and so
much time would have been required for an aviator to acquire skill
sufficient to control a machine without such automatic equilibrium,
that it was considered both expedient and safe to embody in the large
aerodrome the plans which had proved so successful in the models.
It was necessary, however, to provide in addition in the large
machine means whereby the aviator could quickly and accurately either
modify the action of the automatic devices or, if desired, entirely
supersede the automatic control by purely manual control. Three
distinct problems were, therefore, encountered in connection with the
equilibrium and control of the large aerodrome. In the first place,
the machine as a whole had to be so designed, and its component parts
so disposed as to secure a highly stable initial equilibrium; second,
automatic means had to be provided for [p208] maintaining this
equilibrium under the varying conditions of flight and for restoring
it if for any reason it was disturbed, and, finally, provision had
to be made for the quick and accurate control of the flight by the
aviator. These problems, while intimately related, had to be met one
by one and solved separately.

The general type of machine adopted was that which had been developed
in the years of experiment with the steam-driven models. From
the very first consideration of the large aerodrome, it seemed
advisable to follow this type, which not only had shown itself to
be distinguished by remarkable longitudinal and lateral stability
in the tests, but was actually the only type in the world which had
at that time shown any possibility of successful flight. There was,
of course, a question whether single surface or superposed wings
would be used, and in spite of the negative results obtained in the
tests of the models with the superposed wings, it was felt that
a considerable field for development was open in this direction.
However, in spite of the advantages which theoretical considerations
showed might be obtained through the introduction of this and various
other modifications of the original type, the whole teaching of past
experience in the construction of the model aerodromes had been that
success was more certain to be achieved by following the course in
which genuine practical results had been achieved. It was decided,
therefore, that in the construction of the large aerodrome the design
should follow as closely as constructional conditions would permit
the lines of the successful model Aerodromes Nos. 5 and 6, which have
already been fully described.

The longitudinal stability of an aerodrome is largely dependent
upon the relation of three chief factors; the center of pressure,
the center of gravity and the line of thrust. For an aerodrome of
the “Langley” type, the relative positions of these which give the
greatest degree of stability had been determined as far as possible
through the years of experiment with the models. However, while it
is the usual experience in designing machinery, or even scientific
apparatus, that what appears theoretically to be the best plan has
to be considerably modified for constructional reasons, yet in the
design of an aerodrome this is particularly true, for not only must
all the various parts function properly, both separately and as
a whole, but this result must be secured for the very minimum of
weight. Experience alone can enable one to appreciate thoroughly how
seriously this consideration of weight complicates the problem.

In making the original designs for the large aerodrome it had been
recognized that the relative positions of the line of thrust, center
of pressure, and center of gravity were much better in model No. 6
than in model No. 5. From Data Sheet No. 1, for Aerodrome No. 5 when
it made its flight on May 6, 1896, it will be noted that the line
of thrust being assumed to be at the point 1500,[43] [p209] the
center of gravity was at the point 1497, and that, assuming the rear
wings to have two-thirds of the lifting effect of the front ones,
the center of pressure was calculated to be at the point 1498, or
one centimetre in front of the center of gravity, measured in the
horizontal plane. In the vertical plane the center of pressure was
calculated to be at the point 2536, and the center of gravity was
found by test to be at the point 2501, when the line of thrust was
assumed to be at the point 2500, the center of gravity being actually
one centimetre above the line of thrust.

From the data sheet of Aerodrome No. 6, for its flight of November
28, 1896, it will be noted that the line of thrust being at the point
1500 the center of pressure was at the point 1487, and the center
of gravity at the point 1484; that is, the center of pressure was
three centimeters in front of the center of gravity, measured in the
horizontal plane. In the vertical plane, taking the line of thrust at
the point 2500, the center of pressure was at the point 2525, and the
center of gravity at the point 2486, the center of gravity being 14
centimetres ‹below› the line of thrust and 39 centimetres below the
center of pressure, the distance from the center of pressure to the
line of thrust being, therefore, 64 per cent of the distance between
the center of pressure and the center of gravity.

As has been explained in Part I, while it is not desirable that the
center of gravity be a great distance below the center of pressure,
as such a relation tends to produce a special kind of rolling and
pitching in varying currents of air, it is highly desirable that the
center of gravity should lie some distance below the line of thrust
in order that the three forces may be balanced. In a machine like
model No. 5, where the center of gravity was actually, though very
slightly above the line of thrust, there is a constant tendency to
produce rotation of the aerodrome, if for any reason its equilibrium
is disturbed, which is corrected in practice by the action of the
Pénaud tail. In model No. 6, on the other hand, the disposition of
the three factors was such that they tended to maintain, rather than
to destroy, the initial equilibrium of the machine.

These desirable relative positions had been made possible in model
No. 6 by the fact that the center of gravity and line of thrust could
be located at practically any desired point, since with the use of
steam the power plant consists of two separable parts, the boiler,
with its fuel and water tanks, and the engine. These parts can,
therefore, be placed in any part of the aerodrome that constructional
or theoretical reasons demand. Furthermore, the engine constitutes
such a relatively small portion of the weight of the entire machine
that, if for any reason it is desirable to place the engine in the
same plane as the line of thrust, its weight is not sufficient to
alter materially the position of the center of gravity, since the
boiler, water and fuel tanks can be placed as low as desirable and
connected with the engine by suitable pipes. [p210]

With a gasoline engine, however, the conditions are very greatly
altered. Here the engine constitutes practically the entire weight
of the power plant, only such accessories as the ignition coil,
batteries, and carburetor being available for lowering the center of
gravity, unless the fuel, cooling water tanks and radiator be placed
below the engine and the liquids forced up by means of a pump. In
making the first designs for the large aerodrome, therefore, it was
found that it would be practically impossible to make the relative
positions of the center of gravity and line of thrust the same as had
existed in model No. 6, however desirable it might be. The center of
gravity could be brought appreciably lower than the line of thrust
only by placing the gasoline engine in a plane considerably below
that of the propellers, and this necessitated the addition of at
least two more sets of gears with heavy bearings and braces. Besides
this almost prohibitive factor of weight, it was also foreseen that
great difficulty would be experienced in keeping even the two sets
of bevel gears already necessary aligned and in proper condition for
efficiently transmitting the power to the propellers unless the frame
and other parts were made prohibitively heavy. It was, therefore,
found necessary to bring the center of gravity practically in the
same plane with the line of thrust, which made its general features
as regards equilibrium more nearly resemble those of model No. 5 than
of No. 6.

The weight of the aviator, it is true, constituted an appreciable
part of the flying weight of the large machine, and it at first
seemed possible to lower the center of gravity by placing him at a
considerable distance below the line of thrust. But it was recognized
from the beginning that the aviator would probably have to give a
great deal of attention to any form of engine in order to insure its
working properly, and his position must, therefore, be selected with
a view to the proper supervision of the engine and without regard to
its effect on the center of gravity.

Although the repeated successful flights of model No. 5 under varying
conditions of wind and power inspired the belief that the minor
adjustments, as well as the general plan of the large aerodrome,
were such as to give highly stable equilibrium, nevertheless, more
direct corroboration of this opinion was desired, and it was largely
for this reason that the quarter-size model was constructed. In it
every detail of the larger machine which in any way affected its
equilibrium was exactly reproduced to scale, and the greatest care
was taken that the same relative positions of the center of pressure,
the center of gravity and the line of thrust which it was proposed
to employ for the large aerodrome should be used on the model in
its flight of August 8, 1903, which is later described. The entire
success of this flight, so far as the balancing was concerned, in
spite of the fact that the engine worked erratically and that the
launching speed was much less than it should have been, removed every
doubt [p211] that the equilibrium of the large aerodrome would be
satisfactory under normal conditions.

The second problem encountered in connection with the balancing and
control of the large aerodrome was that of providing an efficient
means for maintaining the equilibrium under varying atmospheric
conditions. Although much had been done toward the solution of
this problem in the development of the models, the whole question
was reopened and thoroughly reconsidered in designing the large
aerodrome. The Pénaud tail, when made elastic or when more or less
rigid, but attached to the frame through an elastic connection,
and normally set at a negative angle, furnishes a means of
automatically controlling the equilibrium, which is sufficiently
sensitive and accurate to enable a machine to fly for a considerable
distance, at least in moderately calm weather, as is evidenced by
the various flights of the model aerodromes, where there was no
human intelligence to control them. But owing to the principle of
action of the Pénaud tail, the flight of an aerodrome controlled
by it must of necessity be more or less undulatory in its course.
Furthermore, the tests with the models had indicated that, while the
Pénaud tail served remarkably well as a means of controlling the
equilibrium of the machine, provided the balancing had been rather
accurately determined, and, further, provided nothing happened to
affect seriously the equilibrium of the machine, it was limited in
its effectiveness by its narrow range of action. It was thought
that a control mechanism which should be more sensitive and at the
same time should act more powerfully to prevent the upsetting of
the equilibrium when the machine was subjected to rather strong
disturbing forces was desirable for any machine which was to
transport a human being and, therefore, involved the risk of a fatal
accident.

In the earlier period of the work and before the correct application
of the Pénaud tail to the model aerodromes had been found, Mr.
Langley had planned a large number of different forms of automatic
control for preserving the equilibrium of the machines. The more
frequently recurring of these were devices for changing the angle of
the wings or tail, and others for shifting the wings or tail bodily
so as to shift the position of the center of pressure with respect
to the center of gravity, the motive power for operating the devices
being in some cases that derived from a gyroscope or a pendulum, and
in others small electric motor apparatus controlled by a pendulum
or a gyroscope. Most of these, however, never reached the stage
of development where they were actually tried on the machines in
flight, as the tests of some of them in the shop showed that they
were unreliable, while others were abandoned either when partly
built or when only the drawings for them had been made. Among the
better-preserved models of devices for this purpose which were in
existence when the writer became associated with the work are those
shown in Plate 68, [p212] where the piece at the top is a pendulum
(inverted or direct) which controls the movement of the horizontal
tail by means of the cords and apparatus shown, actuating these
through the small electro magnets and apparatus attached. Just below
the rod, which represents a piece of the midrod, are three parts,
the first of which is a group of six little batteries clustered in a
circle, while next to it is a system of needles hung in gymbals, with
electro-steering apparatus in cups which itself turns on a graduated
base, these electric connections, together with the battery,
controlling the vertical rudder. On the right of this is another
piece of apparatus for actuating windlass cylinders which turn one
way or the other as the contact is made by one side or the other of
the pendulum or the needle. At the bottom, on the two rods, is a
tail-piece which automatically throws the center of pressure forward
or backward according as the aerodrome departs one way or the other
from the horizontal.

In spite of the fact that all the early attempts of Mr. Langley
to devise such a mechanical control had been very unsatisfactory,
the idea that something of this kind was necessary had never
really been abandoned by him. Here was to be seen one of his chief
characteristics, which was never to abandon any idea that seemed
valuable until it was brought to a successful issue or some very
strong proof was developed that the idea was impracticable. While
on a trip abroad during the summer of 1899, and especially while
resting at Vallombrosa, Italy, Mr. Langley’s mind again turned to
this problem, and he wrote a number of very interesting letters
emphasizing the importance of devising such a mechanism which should
be controlled by gravity. When he returned to the Institution in the
fall he insisted upon the same idea.

[Illustration: PL. 68

AUTOMATIC EQUILIBRIUM DEVICES]

[Illustration: PL. 69

FIG. 1

FIG. 2

MECHANISM OF CONTROL]

A mechanism which had been devised by the writer for another, but
somewhat similar, purpose seemed to be well adapted to this end,
and it was accordingly decided to construct a small model of such a
size as would be suitable for use on one of the steam-driven models.
The plan of control which it was proposed to follow was to have
some mechanism which would control the angle of the tail through
the action of gravity on a pendulum bob. Since it would require an
exceedingly heavy pendulum should the deflections of it be directly
utilized to produce corresponding movements of the tail, the most
feasible plan seemed to be to have a light pendulum, which, while
free to move under the action of gravity, would nevertheless by
its movement cause some outside force to produce corresponding and
simultaneous movements of the tail. The general scheme of arrangement
is shown in Plate 69, Figs. 1 and 2. This device consists essentially
of a cylinder (1) in which is mounted a piston with the piston rod
(3) passing through the cylinder head and connected to the cord (5)
which passes over the pulley (6), fastened to the tube (2), which is
slidably mounted on the midrod (7), whence it is carried over the
pulley (8) on the guy-post (9). From here it is connected to the
spring (10) which is fastened by the [p213] bridle (11) to the
upper side of the Pénaud tail (12). The other end of the piston rod
(3) passes through the head in the other end of the cylinder, and
has connected to it a cord (14) which passes over the pulley (15)
fastened to the tube (2), whence it is continued over the pulley (16)
and is joined to the spring (17), which is connected by the bridle
(18) to the lower side of the tail. Mounted on top of the cylinder
(1) is a valve chamber (20) having ports leading to the two ends
of the cylinder. Mounted in the valve chamber is a rocking valve
surrounded by a bushing having ports in it, and to which is fastened
a rod (25) which passes through the said valve and the head of the
valve chamber. Fastened to the rod (25) of the bushing is a lever
(26), which by means of the link (27) is connected to the piston rod
(3). Fastened to the rocking valve is a rod (28) which telescopes
over the rod (25) and also passes through the same head of the valve
chamber, and carries at its outer end a pendulum (29) on the lower
end of which is the bob (30).

If steam or any other fluid under pressure is furnished to the valve
chamber through the pipe (31), none will be admitted to the cylinder
so long as the pendulum is vertical or at right angles to the axis
of the cylinder; and the tail will be in its normal position, which
we will suppose to be an upward inclination of five degrees. If,
now, the front of the machine be depressed, thereby causing the
pendulum to move to the right, such movement of the pendulum will
cause the valve to open, admitting fluid to the left-hand end of
the cylinder. This, acting on the piston, will force it towards
the right, which, by means of the cord, will cause the angle of
the tail to be increased, thereby causing the rear of the machine
to be depressed and the front to be raised. But as soon as the
piston begins to move under the action of the fluid pressure it
simultaneously moves the bushing which surrounds the valve by means
of the connecting links and levers, so that as soon as the piston
has moved a distance proportional to the amount that the valve has
been opened by the pendulum, it causes the bushing to shut off the
port and thus prevents further fluid entering the cylinder. As soon
as the aerodrome responds to the action of the tail the pendulum
will, of course, begin to move back to its normal position of
perpendicularity to the cylinder, and will then open the valve to
the other port, thereby causing fluid to pass into the opposite end
of the cylinder. This fluid acting on the piston will move it in the
opposite direction and thereby cause the tail to be drawn back to its
normal position at the same time that the pendulum gradually reaches
its normal position, owing to the return of the aerodrome to its
normal position. In the explanation given above it was assumed that
the slidable tube (2) was in a fixed position. It was planned to have
the equilibrium normally maintained automatically and at the same
time permit the operator to modify the automatic control and even to
assume full manual control. To secure this, the slidable tube (2) was
connected at each end to an [p214] endless cord (20) which after
passing over suitable pulleys was connected to the control wheel (51)
at the aviator’s car.

A model of this device was constructed in the spring of 1900 and was
tested with steam pressure in the shop. The test showed that the
device acted immediately and with precision, the piston performing
movements simultaneously and in exact accordance with the pendulum.
The device, however, was never tried in a flight of any of the
aerodromes owing to the lack of time necessary to properly install
it on the machine. Furthermore, it was thought probable that the
rapid acceleration of the aerodrome at the moment of launching would
so disturb the pendulum as to cause it to be in a very different
position from that of vertical, and also that the motion of the
aerodrome through the air would itself be a somewhat disturbing
factor.

Because of the difficulties involved in this or any other mechanical
device for controlling the equilibrium, it was in every way advisable
to retain in the large machine the Pénaud system, which, though
itself imperfect in many ways, had been thoroughly tested in actual
flight. In the models, it will be remembered, the combined Pénaud
tail and rudder controlled the longitudinal equilibrium by movement
in the vertical plane under the combined influence of its initial
negative angle and the elasticity of its connection with the frame,
the flight being kept as nearly as possible in a straight line by the
vertical surfaces of the tail. Although it was necessary that the
large aerodrome should be capable of being steered in a horizontal
direction, it was felt to be unwise to give the combined Pénaud
tail and rudder motion in the horizontal plane in order to attain
this end, since the use of it for such a double function might
very seriously interfere with its proper action in preserving the
longitudinal stability. It was, therefore, at first thought best to
dissociate the rudder and tail so that the rudder might be used for
horizontal steering without in any way interfering with the proper
functioning of the tail. But, as the main desideratum was to obtain
a flight of the large machine as soon as possible, and perfection
of steering control seemed secondary, it was decided, after further
consideration, in order not to risk the unpredictable effects that
might result from small changes, to duplicate on the large machine
the combined Pénaud tail and rudder of the model, and to add
another rudder for steering in the horizontal plane. Constructional
requirements determined as the only available position for this
rudder a rather disadvantageous one. As will be seen from Plate 53,
its efficiency was diminished by its being only about half as far
from the center of gravity as the combined Pénaud tail and rudder,
and by being located in the lee of a considerable portion of the
frame, where it would be subject to the cross-currents of air created
by the forward motion of the frame. [p215]

For the preservation of the equilibrium of the aerodrome, though the
aviator might assist by such slight movements as he was able to make
in the limited space of the aviator’s car, the main reliance was upon
the Pénaud tail. But, in the absence of any data for determining
the effect produced in passing from the model to the large machine,
it could not be certain that calculations based upon the balancing
of the model would accurately determine the proper balancing of the
large machine. It was therefore decided to provide such attachment
for the Pénaud tail that, while it would always have elastic
connection with the main frame, yet its angle could be appreciably
changed without affecting in any way the degree of elasticity of this
connection. After many changes in plans for securing this result,
it was finally decided to arrange it in the manner shown in the
drawings. Referring to the general plans in Plates 53 and 54, and to
the details in Fig. 1 of Plate 56, the main stem of the Pénaud tail
is seen to be connected by a pin to the horn (17), which is brazed
to the clamping thimble, by which it is mounted on the vertical tube
(16), suitably connected and braced to the rear end of the midrod,
the horn (17) being larger than the stem of the tail and set at an
angle to the vertical tube (16), the pin connection permitting the
tail to swing up and down. The bridle (40), connected to the center
of the tail on its upper side, passes upward where it is connected
to the spring (41), the other end of which is connected to a single
wire rope (42), which passes over the pulley mounted on the top of
the post (43), which is guyed to the upper guy-post by the wire (44).
The wire rope (42), after passing over the pulley, is connected to
the spring (45), around the two ends of which it forms a loop, and
from there it passes down to the plane of the main frame and through
suitable pulley blocks to the aviator’s control wheel (50), which is
mounted on the starboard side of the main frame, convenient to the
aviator’s right hand when he is facing forward. From this point the
wire rope passes through the various pulley blocks towards the rear
of the machine, and through the pulley block (46) mounted on the side
and near the bottom of the rear lower guy-post. At a short distance
beyond this pulley it is connected to a weaker spring (47), the other
end of which is connected by a second bridle (48) to the under side
of the Pénaud tail at its center. In order to prevent the springs
(41), (45) and (47), which furnish the elasticity for the Pénaud-tail
connection, from being strained beyond their elastic limit, either
by a sudden gust of wind or by the aviator attempting to move so
large an area of surface too suddenly, the wire rope (42) was made
continuous around the springs, the portion between the points where
it was joined to the two ends of the springs being made of such a
length as to take the entire strain should the strain on the cord
become greater than sufficient to stretch the springs 50 per cent of
their original length. [p216]

In the construction of the equilibrium control wheel it was decided
that some arrangement must be secured whereby the wheel would
normally be inactive and maintain whatever position it had been set
to, and at the same time could be moved by the aviator with one
hand, the mere act of grasping it rendering it free to be moved, and
whereby it must automatically lock itself in any position in which it
might be when the aviator removed his hand from it. The multiplicity
of things requiring the attention of the aviator made it desirable
that his attention to any one of the important details, whether the
engine, the equilibrium, or the steering, should never require more
than one hand, thus leaving the other hand free either to hold on to
the machine or to control some other detail at the same time. While
an irreversible wheel, such as would be secured by the use of a worm
and worm-wheel, at first seemed likely to answer the purpose, yet the
movement of a worm-wheel by means of a worm is necessarily very slow
if it is irreversible, and it here seemed desirable to so arrange the
wheel that in case of emergency, of for rising or descending, the
aviator could swing the Pénaud tail from its extreme upper position
to its extreme lower one by a small motion of his hand, and thus
small or large adjustments of the Pénaud tail could be intuitively
felt to have been produced without the aviator having to remember how
many turns he had made of the wheel.

The control of the steering rudder was effected by a steering wheel
(51) similar in construction to the equilibrium control wheel (50), a
continuous cord (52) passing from the steering wheel through suitable
pulleys to either side of the steering rudder (‹r›), springs being
interposed in loops in the cord on either side of the steering rudder
to give some elasticity to the control apparatus in order to prevent
possible danger from the aviator attempting to move the rudder too
suddenly. This steering rope passed directly through the steering
rudder at the points where it was joined to it; so that, should one
side of the cord in any way become entangled with the frame or with
its pulleys, the strain produced by the aviator in attempting to
move it in the opposite direction would be taken up by the cord and
thereby avoid the possibility of destroying the rudder. For even
should the cord become entangled on one side, the rudder could be
given a slight amount of adjustment through the elasticity of the
coiled springs.

The design of the combined Pénaud tail and rudder followed very
closely that which had been used for the models, and its area
of ninety-five square feet on the horizontal surface with a
corresponding area of vertical surface bore the same relation to the
area of the tail and rudder of the models that the area of the wings
of the large machine bore to that of the wings of its prototype.

While the provisions for automatic equilibrium and manual control
were not entirely ideal, even for the quiet atmospheric conditions
under which it [p217] was proposed to make the first tests,
nevertheless it was and still is believed that the provisions for
such conditions were sufficient to enable a successful flight of a
few miles to be obtained. It was thought to be very certain that,
once a successful flight could be made, the funds for the further
prosecution of the work would be readily forthcoming, and that when
these funds were obtained the many problems of control, rising and
alighting, could be undertaken.

[p218]

CHAPTER VIII
THE EXPERIMENTAL ENGINE

It will be recalled that the contract for the engine for the large
aerodrome, which had been entered into on December 12, 1898, called
for its completion on February 28, 1899. Between the time when the
engine should have been completed and May, 1900, the engine builder
had been engaged in a continuous series of changes on it, all
connected with what might be briefly called its proper functioning.
The actual mechanical construction of the more important parts had
been admirably executed, and this main portion of the constructional
work had been completed within the time called for by the contract.
The trouble was that the engine, which was of the rotary cylinder
type, would not furnish anything like the power which had been
expected of it, and which the size and number of its cylinders
indicated that it should furnish. No one who has not had practical
experience in the development of gasoline engines, can understand or
appreciate how fourteen months could be spent in changes in the minor
details of the engine with the expectation that each contemplated
change would bring success; and to anyone who has had experience in
the matter, an attempt to explain the delays would merely seem like
a history of his own experiences. It is, therefore, sufficient to
say that the delay on the engine had now reached a point where it
was necessary to bring it to a successful completion immediately or
to abandon it definitely, and either find a competent builder who
had already built engines which, while not necessarily light, were
successful, and who would undertake to construct a light one on the
same principles, or, as a last resort, to turn to steam; and even the
contemplation of this was appalling.

On May 6, 1900, the writer went to New York to see what could be done
towards assisting the engine builder to complete the large engine
and also, if possible, the small one which had been ordered for the
quarter-size model later described. He immediately made brake tests
of the engine to determine accurately just what effects were being
produced by the different changes the engine builder was making. Upon
the first test the engine was found to develop only 2.83 horse-power,
and this could not be maintained for more than a few minutes, when
without any apparent cause and without any signs of overheating the
engine would altogether cease to develop any power. After remaining
in New York for several weeks, during which time many changes were
made in the engine, he finally got it to the point where it would
develop four horse-power continuously; but, as it seemed impossible
to get any better results [p219] without an indefinite amount of
experiment, it was decided that all hope of making this engine an
immediate success would have to be abandoned.

Interest in the development of the automobile was increasing at a
rapid rate all over the world, and while the builders in this country
had not reached the stage of development which had been attained
in Europe, especially in France, yet some American builders had
succeeded in constructing cars propelled by gasoline engines which
could be depended upon to run at least a short distance, and it
was, therefore, hoped that some one of the more competent of these
builders might be found who would undertake to construct a suitable
engine. After making a most extensive but fruitless search for such
a builder in this country, it was decided that it would be best to
see what could be done in Europe, and as other administrative matters
made it necessary for Mr. Langley to go to Europe about the middle of
June, the writer accompanied him to see what could be done towards
having a suitable engine built there. Some six weeks were spent in
visiting all the important builders of gasoline engines in Europe,
and the results were very discouraging. Everywhere the builders said
that they did not care to undertake the work, and that they did
not consider it possible to construct an engine of 12 horse-power
weighing less than 100 to 150 kilograms (220 to 330 lbs.), or that,
if they had thought it possible, they would already have built it,
as they had had numerous inquiries for such engines, and also wanted
them for their own use. The last hope of securing a suitable gasoline
engine seemed to have vanished.

But, discouraging as was the refusal of the engine builders of Europe
to undertake to build the engine, and still more so their opinion
that such an engine was an impossibility, inspection of the engines
exhibited at the Paris Exposition had so strengthened the writer’s
conviction of the possibility of the undertaking that, before parting
with Mr. Langley on August 3 to return to America, he personally
assumed the responsibility of building an engine which would meet the
requirements.

Upon returning from Europe on August 13, and finding that the engine
builder in New York had made no progress whatever towards improving
the engine during his absence, the writer condemned both the large
engine and the small one. The engine builder had practically
bankrupted himself in his attempts to construct these two engines,
having spent something like $8000 or $10,000 in actual wages over
and above the contract prices for the engines, to say nothing of
remuneration for his own time or such expenses as shop rent and
power. As all of the money for the large machine and practically all
for the small one had been advanced to him at various times to assist
him over financial stringencies--such advances, however, having been
secured by suitable bonds--it was decided to take the various parts
of the two engines in [p220] payment for the money which had been
advanced, as it was hoped that some of the parts of the engines might
prove of use in experimental work.

Immediately after the writer’s return to Washington he began work
on the development of an engine. Taking some of the parts of the
engine which had been condemned and constructing others, he was able
by September 18 to have an experimental engine at work which, while
not water-jacketed, but provisionally cooled by wrapping wet cloths
around the cylinders, developed 18-1/2 horse-power on the Prony brake
at 715 R. P. M., the engine, including these wet cloths, weighing
108 pounds. Of course these wet cloths sufficed to keep the engine
cool for only a short time--three to four minutes being the maximum.
This was only a temporary expedient for enabling the engine to run
for a sufficient time to make brake tests and determine the power it
developed, but the results obtained were so very encouraging that it
was decided to make water jackets for the cylinders of this engine
and see what power it would then develop for more extended periods.

This experimental engine, which was merely a “patched-up” affair,
was first equipped with a sparking arrangement built on the
wiping-contact principle. With this sparking arrangement several
important difficulties presented themselves, among which may be
particularly mentioned the great difficulty of so adjusting the
sparking arrangements that the explosion in each cylinder occurred
at exactly the same point in its cycle that the explosions occurred
in all the other cylinders, it being necessary to secure this result
to a reasonably accurate degree in order to cause the engine to run
smoothly enough to be used in the aerodrome. Where an engine has a
large and heavy fly-wheel running at a high rate of speed, the nicety
of adjustment of the sparking arrangement is not so essential, for
the fly-wheel acts as a reservoir of energy and tends to smooth out
the rough and jerky impulses which would be otherwise introduced by
slight variations in the force of the explosions in the cylinders.
In constructing an engine for an aerodrome, however, the permissible
weight of the engine is so very small that the use of a fly-wheel
having sufficient weight to act as an energy reservoir is practically
prohibited. Another serious difficulty which was encountered with
the wiping-contact type of sparking arrangement was that of keeping
the stuffing boxes around the rotating contact rods tight enough
to prevent leakage, without at the same time binding and causing
excessive friction. Although it seemed probable that the difficulties
which have been mentioned, and other minor ones which were apparent,
could be remedied by further experiment, yet the high tension or
“jump-spark” type of sparking apparatus seemed to offer much greater
advantages. Since it had fewer moving parts, and furthermore since
the wiping-contact sparking arrangement would have to be considerably
modified in order to permit the construction of water jackets around
the cylinders, it was decided to construct a [p221] new sparking
arrangement for the engine on the jump-spark principle. After
introducing this change in the engine it was found to run very much
more smoothly and to require a minimum amount of care in adjusting it.

At the time that this engine was being developed it was practically
impossible to obtain any outside information regarding the proper way
of constructing it. The little that was then known had been learned
through laborious experience and at great cost by the experimenters
who were attempting to build automobiles, and was zealously guarded
in the hope of preventing their rivals from utilizing the results
of their labors. It was the known custom, however, of all engine
builders at this time to use a separate spark coil and a separate
contact maker for each cylinder of an engine, no matter how many
cylinders there were. This multiplication of the spark coils, which
at that time were very heavy, not only added greatly to the weight
but also had the same defect that the wipe-spark type of sparking
arrangement had of being exceedingly difficult to so adjust that
all of the contact makers would perform their functions at exactly
the same point in the cycle for each cylinder. To obviate these
difficulties, both of adjustment and of excessive weight, the writer
devised what is supposed to have been at that time a new and valuable
multiple-sparking arrangement whereby only one battery, one coil
and one contact maker were utilized for causing the spark in all
five cylinders, a small commutating arrangement in the high-tension
circuit distributing the sparks to the proper cylinders at the
proper time. This form of sparking arrangement was found upon test
to work so satisfactorily that it was afterwards adopted for the
small engine of the quarter-size model, and also for the new and
larger engine which was afterwards built and which will be described
further on. It is needless to describe in detail the many and
perplexing difficulties which were experienced in procuring suitable
spark coils, spark plugs and other appurtenances of the sparking
apparatus, all of which at this time were in a very crude state of
development, there being only a few different makes on the market,
and most of these being very unsatisfactory. One important minor
improvement connected with the spark plugs may be described, as the
beneficial effect produced by it was so very great that its use was
continued in all future spark plugs for all of the engines. This
improvement, however, is now incorporated in many of the plugs which
are on the market, and in some cases patents, covering the particular
form in which the improvement is incorporated, are exploited by
the manufacturer. Considerable difficulty was at first experienced
with the spark plugs from a coating of soot (resulting from the
incomplete combustion of the gas and oil in the cylinder at the time
of explosion) which formed on the porcelain and thereby caused a
short-circuit, preventing the plug from working properly. This was
overcome by extending the metal portion of the plug for some distance
into the cylinder, and for something like three-quarters of an
[p222] inch beyond the end of the porcelain insulator. The terminal
which passed through the insulator was also extended for something
like half an inch beyond the porcelain and bent to a proper extent
to co-act with a piece of platinum wire inserted in the interior
wall of the plug which formed the other terminal. After making this
improvement in the plugs practically no difficulty was experienced
from short-circuits caused by the soot.

In making the tests of this experimental engine it was found
practically impossible to absorb the power by a Prony brake in a
sufficiently uniform manner on account of the fact that the engine
was being run without a fly wheel. The consequent variation in
the torque and speed during each revolution caused such great
fluctuations in the reading of the scales which measured the pull of
the Prony brake that no confidence could be felt in the accuracy of
the readings and, therefore, no confidence could be placed in the
determinations of the effect which different changes in the engine
produced. A water-absorption dynamometer consisting of a number
of flat, circular discs fastened to a shaft and rotating between
other parallel flat discs arranged in a circular drum which was
filled to any desired extent with water was immediately planned,
and the construction of two of them was begun so that power could
be taken from both ends of the engine shaft, which, on account of
its necessary lightness, was apt to be injured by being twisted
when all the power was taken from one end of the shaft. In order to
continue the tests on the engine while this dynamometer was being
made it was decided to employ one of the propellers as a dynamometer.
Although no accurate tests had been made to determine just how much
power was required to drive these propellers at various speeds, yet
the fundamental law was known that under the same conditions the
power required to drive any propeller would vary as the cube of the
number of revolutions, and since the Prony-brake tests had given an
approximation as to the amount of power which the engine developed at
certain speeds, the law of the propeller, and extrapolations from the
data obtained in the tests of the smaller propellers in 1898, enabled
further approximations to be made as to the amount of extra power
which the engine developed when certain changes enabled it to drive
the propeller at increased speeds. This method had also the great
advantage that, since the power required varies as the cube of the
number of revolutions, it is practically impossible for the engine to
“run away” with the propeller and cause serious damage through the
possible excessive strains introduced by high speed. This feature is
also possessed by water-absorption dynamometers of the type which
were built and used in the later tests.

The construction of water jackets for this engine proved an
exceedingly formidable task, it being impossible to braze the jackets
directly to the walls of the cylinders without risk of ruining
them. It therefore became necessary to attach them by means of
stuffing boxes, which, on account of their large size [p223] and
the necessity for keeping the weight a minimum, was a most difficult
piece of work. The work was rendered still more difficult by the fact
that the water jackets had to be made in halves which were brazed
together after they had been fitted over the head of the cylinder.
Even when the work was done in the most careful way this method of
construction gave a great deal of trouble from the leaking of the
stuffing boxes or the jackets themselves. However, after much delay,
the water jackets were finally completed, and upon test the engine
was found to develop 21.5 horse-power at 825 R. P. M., the engine
itself weighing 120 pounds.

Further changes were made in this engine, especially in the pistons,
a new set of which were constructed which weighed 15 pounds less than
the original set. On account of the difficulty with the leakage of
the water around the stuffing boxes of the water jackets, and also
from imperfections in the brazed joints of the jackets themselves,
it was found impossible to rely on the power that the engine would
develop at any particular time, as the water leaking from the jackets
and running down on the spark plugs of the lower cylinders caused
these cylinders to work erratically, and this not only materially
reduced the power but also caused jerky impulses in the absence of
fly wheels.

It seemed so desirable to obtain as soon as possible a first test in
actual flight of the large machine that the writer offered to put
this engine in the aerodrome frame and make a test with it if the
machine were launched over the water, but with the launching track
mounted directly on the river bank. However, Mr. Langley felt it so
necessary to make the initial test from the top of the house-boat and
at an elevation of 30 feet or more that he would not consent to this,
and as the engine at its best did not develop quite 24 horse-power,
which had been calculated as the minimum which should be provided,
it was thought unwise to attempt to make the first test from the top
of the house-boat until the aerodrome had been provided with engines
that could be depended on to develop continuously not less than 24
horse-power.

It then became necessary either to build a duplicate engine and use
both of them in the aerodrome, the original plan as already explained
having been to have two engines developing the 24 horse-power
together; or, second, to construct an entirely new engine large
enough to furnish a minimum of 24 horse-power and use this single
engine.

As the construction and tests of this experimental engine had shown
many places in which the weight might be safely reduced, the writer
decided to construct an entirely new and larger single engine, and
thereby avoid the extra weight and difficulties which would be
introduced by having to use synchronizing gears where two engines
were used, it being impossible, of course, to run the two propellers
from the two engines independently without risk of serious disaster.
[p224]

It will be recalled that when the aerodrome was originally planned
in 1898 it was proposed to have two engines of 12 horse-power each,
and the contract for the single engine of 12 horse-power provided
that a duplicate was to be supplied, if desired, immediately upon
the completion and delivery of the first one. The calculations,
both from the whirling-table tests and from the results with the
steam-driven models in actual flight, indicated that 24 horse-power
would be ample for the aerodrome, which it was then expected would
not exceed 640 pounds in weight, with a supporting surface of 960
square feet. But it was found that the total weight of the machine
was rapidly increasing on account of slight increases in the various
details, which when added together made a considerable increase in
weight. Furthermore, as it had been found difficult to keep all five
of the cylinders of the experimental engine working uniformly, it was
thought best to build this new engine sufficiently large to provide
not only the extra power necessary because of the increased weight of
the aerodrome, but also to provide for further inevitable increases
in weight, and over and above all this, to provide also that the
engine would furnish all the power necessary, even though one of its
cylinders should absolutely fail to work and act as a dead load on
the others. The writer accordingly designed this new engine to give
40 horse-power when all five of the cylinders were working, and 28
horse-power even though one cylinder should act as a dead load on the
others.

The various materials for the construction of this engine were
ordered early in December, 1900, with the promise of delivery not
later than January, 1901. Owing to various causes, however, the major
portion of the materials could not be obtained until late in the
spring, and, in fact, a portion of them were not obtained until the
summer of 1901. During this period of delay, however, the engine for
the quarter-size model was completely reconstructed and further tests
were made with the experimental engine in developing accessories,
such as carburetors and spark coils.

The float-feed type of carburetor which was then coming into
prominence in automobile work proved at that stage of its development
to be totally unsuitable, as the slight but constant tremor of the
aerodrome frame, when the engine was working at high speeds under
a heavy load, caused the float to act as a pump and periodically
flood the carburetor. This resulted in an irregularity of action of
the engine which at times injured not only the transmission shafts,
gears, and frame, but the engine itself by the serious pounding
which occurred. A form was next tried in which the gasoline was fed
in through the valve seat of a lightly loaded valve which raised
whenever there was suction in the inlet pipe, the amount of gasoline
fed being regulated by a pin valve. Later there were built several
shapes and sizes of tanks filled with absorbent material, which was
saturated with gasoline and the surplus drawn off before starting
the engine. Some of these tanks were provided with a jacket through
which [p225] a portion of the exhaust gases was passed in order to
compensate for the cooling of the tank caused by the evaporation of
the gasoline. As a result of these tests it was found that a type
consisting essentially of a tank filled with small lumps of a porous
cellular wood (tupelo wood) which was initially saturated with
gasoline, and into which the gasoline was fed through a distributing
pipe as rapidly as it was taken up by the air, which was sucked
through it by the engine, gave the best results. Instead of jacketing
this tank, the cooling effect due to evaporation was compensated by
drawing the somewhat heated air from around the engine cylinders
up through the loosely packed lumps of wood. When tested in the
shop this type was found to give such a very uniform mixture that
the engine ran as smoothly and regularly as an electric motor, the
vibration in no way interfering with it, and even when the sudden
change from a state of rest to one of rapid motion through the air
was imitated by suddenly turning on the carburetor the blast of
several large electric fans from various angles, it was found to have
no appreciable effect on the running of the engine, thus indicating
that the trouble which was experienced with the model aerodrome in
the trials of 1901 was not likely to be repeated with the large
aerodrome. Somewhat more than a dozen carburetors of various forms
were constructed before this last type was devised, but this proved
so satisfactory that there were never thereafter any carburetor
troubles. In fact, as will later appear, a carburetor of this type
kept the engine on the large aerodrome running at full power not only
when the aerodrome was in a vertical position in the air, but also
after it had turned completely over on its back.

[p226]

CHAPTER IX
THE QUARTER-SIZE MODEL AERODROME

Owing to the very considerable changes which constructional reasons
necessitated in the relative positions of the center of pressure,
center of gravity, and line of thrust from those which theoretical
considerations pointed to as being best, it was decided in January,
1900, to build a one-quarter-size model of the large aerodrome, if
a suitable engine capable of furnishing something like one and a
half horse-power could be procured without delay. It was hoped that
it might be possible to construct this model immediately without
seriously interfering with the progress of the work on the large
machine, and that some tests in free flight could then be made with
it, which would give very much more reliable data from which to
determine the balancing of the large aerodrome than had been obtained
from the tests of the steam-driven models Nos. 5 and 6. A factor of
uncertainty would still remain, due to the difference in size between
the large machine and the model, which could be determined only by
actual trial of the large machine itself; but by making the model
an exact duplicate, on a smaller scale of the large machine, very
valuable results could be obtained. Tests of it in free flight would
involve, even with the probable attendant breakages, a comparatively
small expenditure of time and money. A search was immediately begun
for an engine builder who would undertake to furnish a suitable
engine for this model. The specifications called for an engine
developing one and a half horse-power on the Prony brake for five
minutes without diminution in power caused by over heating. While
it was desired if possible to get an engine which would come within
the given weight and develop the required power for a longer time
than five minutes, it was foreseen that the construction of a
multiple-cylinder engine of so small a power made it necessary to
resort to the air-cooled type, and that such an engine would be
doing exceedingly well to develop its maximum power continuously
for as much as five minutes. The only engine builder who could be
found willing to undertake the construction of such an engine was
the one already engaged in the construction of the larger engine.
As this builder was already twelve months behind in the delivery of
the large engine, it was felt that it would be unwise to give it
to him, both because the work on it might still further delay him
in the completion of the large one, and also because he was still
having troubles with the large one, which it was not certain he would
ever be able to overcome. After further consideration of the matter,
however, it seemed so important to have a model which was an exact
duplicate of the large machine for the [p227] making of tests, which
might prevent not only serious damage but possibly fatal accidents,
that upon the assurance of the engine builder that the undertaking
of the small engine would in no way interfere with the completion
of the large one, a contract was entered into on February 23, 1900,
which specified that the engine should be delivered by April 1, with
a penalty for any delay beyond that date.

The frame for this quarter-size model was immediately begun and
extra workmen were employed for work on it in order that its
construction should in no way delay the completion of the large
machine. The decision to construct this quarter-size model of the
large aerodrome had been made on the assumption that, since it was
to be one-sixteenth the weight of the large machine, and therefore
much heavier in comparison to its size than the steam models Nos. 5
and 6, it would, therefore, not need to be so carefully constructed
in order to obtain sufficient strength. But when construction was
actually begun it was found not only that the simpler and less
expensive methods which it had been proposed to use in joining its
frame together resulted in a weak construction, but also that the
time consumed in tinkering up the imperfections in the joints more
than counterbalanced the extra time which would have been required to
make the joints in the best manner from the beginning. Before going
very far it was therefore decided to make the joints by following
the same process which had been developed in the construction of
the previous models. The frame was accordingly built in the most
substantial manner, and when guyed by a system of guy-wires similar
to that employed for the large machine it was found to be exceedingly
stiff, in fact very much stronger and stiffer than the frame of any
of the preceding models.

In originally planning the model the intention was to make all its
linear dimensions exactly one-fourth those of the large aerodrome.
Before the designs were completed, however, it was seen from the
previous experience with the steam-driven models that instead of the
62.5-cm. propellers, which a strict adherence to the quarter-size
plan would demand, it would be necessary to use propellers which were
at least one metre in diameter. Moreover, as the small engine would
be more than one-fourth the size of the engine under construction
for the large aerodrome, a departure from the scale in the case of
the transverse frame would be necessary. The designs were therefore
altered so as to admit of using the larger propellers, and the tubes
which formed the front of the transverse frame were bent, as shown in
the plan photograph, Plate 70, in order to give a large enough space
for properly mounting the engine.

The frame with these modifications was completed in June, 1900, but
no engine was ready for it, as the builder had failed to fulfill
his contract for either the large or the small engine, although
several trips to New York had been made to expedite their successful
completion. [p228]

Soon after this it became certain that the engines for both
aerodromes would have to be constructed in the shops of the
Institution, and owing to the greater importance of the experimental
engine for the large aerodrome, all the facilities of the shops were
devoted to the early completion of it. In November, 1900, however,
it was seen that the experimental engine alone would not furnish
sufficient power for the large aerodrome, and that a duplicate
of it would have to be built or a new and larger engine designed
and constructed, and that therefore it would be impossible to get
the first tests of the large aerodrome in free flight before the
following summer. It was therefore decided that it would be best
to suspend work temporarily on the large aerodrome and its engine,
and put all the workmen who could possibly be employed on the
construction of the small engine, so that it would be ready in time
to permit some tests of the quarter-size model to be made during the
following spring.

In order to expedite its construction as much as possible, the
attempt was made to utilize all the available parts from the small
engine which had been undertaken by the engine builder in New York.
The cylinders, which it had been expected would be kept cool by
their rotation around the crank pin, were not well adapted for use
as stationary cylinders, since they were not provided with radiating
ribs, but it was hoped that by using them an engine could be very
quickly constructed which would keep cool long enough to enable some
short flights to be made with the model.

The work on this small engine was pushed forward very rapidly, so
that within a short time it was sufficiently complete to allow some
power tests to be made with it. In the first of these tests the
attempt was made to measure the power by means of the Prony brake,
but as the engine had no fly wheel the fluctuations in speed during
each revolution were so great as to make it impossible to obtain
readings of any value. When it was attempted to remedy this by
putting a fly wheel on either side of the crank shaft of the engine,
it was found that the sudden starting of the engine caused such
severe strains in the crank shaft, which had been built strong enough
for driving the propellers but not for suddenly starting fly wheels
having considerable inertia, as to make it unsafe to continue the use
of fly wheels. As without them the Prony brake could not be used, it
was decided to build a small water-absorption dynamometer on the same
principle as the larger ones which were under construction for the
large engine. As this larger dynamometer has already been described,
it is only necessary to add that the small one consisted of twelve
rotating plates and twelve stator plates twelve inches in diameter.
In order to avoid the construction of a special and elaborate testing
frame for mounting the engine and the dynamometer exactly in line
with each other, it was attempted to connect them by means of a
universal joint. This “short cut” also proved the “long way around.”
The strains set up in the universal joint by the sudden starting of
[p229] the engine caused so much trouble on account of the inertia
of the rotating plates of the dynamometer that the time lost in
keeping the universal joint in working order during the tests more
than counterbalanced the extra time which would have been required to
construct a special wooden frame on which the dynamometer and engine
could have been mounted in line with each other so that the crank
shaft of the engine could have been directly connected to the shaft
of the dynamometer.

Much time was also lost in the effort to construct an apparatus
by which a record could be obtained of the power actually used in
propelling the aerodrome. Various methods were in use by which
the thrust of the propellers could be more or less satisfactorily
measured while the aerodrome was at rest, but it was desired to
know just how much power the aerodrome consumed while in actual
free flight. Such a record it was hoped to obtain from a device
incorporated in the propeller shafts. This thrust-measuring device
consisted essentially of a propeller shaft made in two sections, one
section telescoping the other for a short distance. On the section
of the shaft to which the propeller was attached there was mounted
a drum, having in its circumference two long slots diametrically
opposite. To the other section of the shaft a disc was fastened with
two diametrically opposite rollers mounted on its periphery, which
fitted the slots in the drum of the other section. A compression
spring was interposed between the disc and the drum, and the outside
of the drum was so arranged that a strip of paper could be wound
around and fastened to it which would serve as a chronograph sheet. A
pencil was fastened to the frame, and, since the drum was connected
to the section of the shaft to which the propeller was attached and
which therefore moved to and from the frame under the action of the
propeller thrust, a record of the actual thrust of the propeller at
any particular moment could be obtained by simply pressing the pencil
up against the paper on the drum and calculating the thrust from
the calibration of the compression spring. Since the thrust would
naturally be greater when the propellers were revolving in a moored
condition, during the few moments after the engine was started up and
before the aerodrome was launched, it was necessary to provide means
for having the pencil point held away from the chronograph sheet
until the aerodrome was launched, and then have the point come to
bear on the sheet. This was accomplished by having the point held off
by a small trigger arrangement which was to be released just at the
moment that the aerodrome left the launching car. A set of propeller
shafts embodying this thrust-recording device was constructed, but
when they were actually tested on the aerodrome many difficulties
were encountered which had not been anticipated. In the first place
the gasoline engine for the model was started up (or “cranked over”)
by turning the propellers by hand. A gasoline engine never starts
slowly, and on account of this suddenness of starting causes a very
great strain in any [p230] shafting by which it is connected to any
driven mechanism. The inertia of the driven mechanism, even though it
be apparently small, becomes a most serious matter when an attempt is
made to start up very suddenly. This effect is very much intensified
if the driven mechanism is connected to the engine through even one
pair of gears, for there is always a certain amount of back-lash
between the teeth of the gears, and the effect of this back-lash
is still further intensified when the driven mechanism is turned
over by hand in order to start the engine, as this takes up the
back-lash on one side of the gears, and the moment the engine starts
permits a free movement until it suddenly takes up the back-lash and
strikes the other side of the gear teeth with a blow. The effect
of this sudden starting of the engine proved most disastrous to
the thrust-recording devices, and, although they were considerably
strengthened, it was found after a short time that in order to make
them strong enough to withstand the shock of the sudden starting of
the engine it would be necessary to make them inordinately heavy.
It was therefore decided to abandon all attempts to incorporate the
thrust-recording device on this quarter-size model, but it was hoped
to install it later on one of the steam-driven models, where the
engine starts so slowly that there would be no need for excessive
strength in it.

The engine for the quarter model when reconstructed with stationary
instead of rotating cylinders was found in the shop tests referred
to above to develop when working at its best between 1-1/2 and 2
horse-power, as measured by the absorption dynamometers. However,
it was impossible to maintain this power steadily for more than
30 seconds. In the first place, the same difficulties (heretofore
described) that were met with in securing a suitable carburetor for
the experimental engine were experienced at the same time in the
development of the small engine. In the second place, as the engine
had no cooling apparatus of any kind, it was found that it could not
be tested in the shop for more than 30 seconds owing to premature
explosions. It was hoped, however, that by having everything ready
for a flight before starting the engine, it might be possible to
launch the aerodrome before the cylinders began to heat seriously,
and that the greatly increased cooling effect due to the motion of
the aerodrome through the air would permit the engine to develop
sufficient power to secure a flight that would show whether or not
the balancing was correct, as the final disposition of some of the
accessories on the large aerodrome could not be so well settled until
it was known just how the calculated balancing of this new model
corresponded with the actual balancing necessary for flight.

On account of Mr. Langley’s reliance on the generally sound theory
that where a successful method of conducting an experiment has been
found only after a long series of failures it is best not to change
to some unknown and untried plan, it was impossible, especially
where failure in the test might involve a fatal accident, to get him
to deviate from his original plan of [p231] launching the large
aerodrome from the top of the house-boat. He apparently realized as
well as anyone, that in many respects the making of the test from the
top of the house-boat had many serious drawbacks, but he emphasized
and impressed on the writer the importance of following as far as
possible in the construction and test of the large machine, the
plans which had brought success with the models. Believing, however,
that there was probably a better method of launching the aerodrome
than from the top of the house-boat, and that it would be well to
prepare before hand as far as possible for following some other
plan of launching immediately after a first successful test had
been obtained from the top of the boat, Mr. Langley had constructed
some floats which were arranged to be attached to the launching car
of the quarter-size model so that the car could be converted into
a catamaran raft. It was not believed that this crude arrangement
would suffice for a complete launching apparatus, since the power of
the aerodrome propellers would not be great enough to force the raft
through the water at a sufficiently high speed; still it was thought
that by having the launching car arranged in this way the model might
be allowed to drive the raft rapidly through the water and thus give
some idea as to what would be necessary, in a more complete launching
apparatus, to obviate the danger of the drag of the raft causing the
model to plunge over headlong into the water. The launching car with
these floats attached to it, and with the quarter-size model mounted
on the car, is clearly shown in Plates 73 and 74.

While the results obtained with superposed wings in the tests
of models Nos. 5 and 6 in the summer of 1899 indicated that the
“single-tier” surfaces were much more efficient, still, as has been
already stated, the great advantages of the superposed surfaces, so
far as strength of construction is concerned, was fully realized
at all times. As a result of these tests it was decided to use the
“single-tier” surfaces in the first test of the large machine in
order to insure as far as possible the best conditions. However,
it was from the beginning planned to construct superposed surfaces
for use in the later tests of the large machine; and, in order to
obtain more reliable data on such surfaces than had been obtained in
the tests of the models in the summer of 1899, a set of superposed
surfaces for the quarter-size model were constructed during the
winter of 1900–1901. The quarter-size model, equipped with these
surfaces, is shown in Plates 75 and 76, where the model is seen
mounted on its launching car, which is attached to the floats
heretofore referred to. It was originally planned not to employ
guy-posts when using the superposed surfaces, but after the latter
had been constructed and attached to the frame, it was found that
they would have to be made with rigid joints instead of hinged joints
if the guy-posts were omitted. As the hinged joints, however, were
already made, and permitted the surfaces to be folded up so as to
occupy a much smaller [p232] space in shipping them, it was decided
to retain the hinged form of construction and use the guy-posts as
shown in the above plates.

[Illustration: PL. 70

PLAN VIEW OF QUARTER-SIZE MODEL AERODROME, JUNE 1, 1900]

[Illustration: PL. 71

PLAN VIEW OF QUARTER-SIZE MODEL AERODROME]

[Illustration: PL. 72

END, SIDE, AND THREE-QUARTER ELEVATION OF QUARTER-SIZE MODEL
AERODROME]

[Illustration: PL. 73

LAUNCHING-CAR WITH FLOATS]

[Illustration: PL. 74

LAUNCHING-CAR WITH FLOATS]

[Illustration: PL. 75

QUARTER-SIZE MODEL AERODROME EQUIPPED WITH SUPERPOSED SURFACES, JUNE
11, 1901, SIDE VIEW]

[Illustration: PL. 76

QUARTER-SIZE MODEL AERODROME EQUIPPED WITH SUPERPOSED SURFACES, JUNE
11, 1901. END VIEW]

[Illustration: PL. 77

CYLINDERS OF ENGINE OF QUARTER-SIZE MODEL AERODROME]

After much delay, due to various causes, the quarter-size model,
as shown in plan, end elevation, side elevation and three-quarter
elevation in Plates 71 and 72, respectively, was taken down the river
in June, 1901, in order to make some tests with it from the small
house-boat, which had been previously moved to the middle of the river
opposite Widewater, Va. A test of it in free flight was made on June
18, its condition at this time being shown by Data Sheet No. 12 in
Appendix. The launching apparatus worked perfectly and the aerodrome
started off on an absolutely even keel, dropping only a few inches
immediately upon leaving the launching apparatus, and continuing
straight ahead directly into the light wind of something less than
2 miles an hour. After it had gone only about 100 feet, however, it
began to descend slowly, but still maintained a perfectly even balance,
and finally touched the water about 150 feet from the house-boat,
having been in the air between 4 and 5 seconds. It was immediately
recovered, and as soon as the wings could be dried out another test
was made, as it was thought probable that the wind had interfered with
the carburetor to such an extent that the engine had not received the
proper mixture of gas. Upon this second test the launching apparatus
again worked perfectly and the aerodrome again flew straight ahead on
a perfectly even keel, and at a uniform height from the water until
it had gone about 300 feet, when it again began to descend slowly
and finally touched the water about 350 feet from the house-boat,
having been in the air about 10 seconds. While the tests were very
disappointing, owing to the extreme brevity of the flights, yet they
showed conclusively that the balancing of the aerodrome was correct,
at least as far as motion in a straight line and in a quiet atmosphere
was concerned. As one and a half horse-power, which was felt to be
the very minimum which would successfully propel the aerodrome, was
furnished by the engine only when working at its very best, and as the
change in conditions from a quiet state to a velocity of something
like 40 feet per second evidently caused a considerable drop in the
power because of the change in the gaseous mixture which the carburetor
furnished to the engine, it was decided not to make any further test
of the aerodrome until the engine cylinders could be reconstructed
so as to provide more effective means for cooling it, and thereby a
reasonable margin of power above that actually necessary. The aerodrome
was accordingly returned to Washington for the purpose of making new
cylinders for the engine. In constructing these new cylinders the
old cylinder heads from the previous cylinders were used in order to
expedite their completion. This proved in the end to be a very great
mistake, though at the time it seemed probable that the use of them
would save much delay and considerable expense. The new cylinders were
constructed of steel tubing originally one-half inch thick, which
[p233] was machined to the form clearly shown in the photograph,
Plate 77, where it will be seen that thin radiating ribs spaced
one-quarter inch apart were formed integral with the cylinder, the
combustion chambers or heads being screwed on and brazed to the
cylinders. After much delay the new cylinders were completed, and upon
test it was found that while the radiating ribs assisted very greatly
in keeping the engine cool, yet the valves were so small that the gas
was not able to get in and out of the cylinders rapidly enough to
permit the engine to furnish its full power. Even at this stage it
would have been better either to have made new cylinder heads with
larger valves or to have made entirely new cylinders and cylinder
heads, but in the effort to economize time and money it seemed best to
try to overcome part of the defect by adding an auxiliary inlet valve.
This was constructed, and upon test it was found that, although the
engine developed 3.2 horse-power on the Prony brake at 1800 R. P. M.,
and even maintained 5.1 horse-power on the brake for a few seconds when
running at 3000 R. P. M., the ports leading from the valve chamber to
the cylinders were so small that they became heated after the engine
had run for 2 minutes and premature ignition occurred, which, of
course, immediately and very greatly reduced the power developed.

It was decided, however, in view of the tests in which the engine had
developed 3.2 horse-power at 1800 R. P. M., that there was sufficient
margin of power to enable it to propel the quarter-size model, even
if it was not working at its best. After concluding the Prony-brake
tests on the engine, it was mounted in its proper position in the
aerodrome frame and connected to the propeller shafts. Some pendulum
tests were then made, showing an average lift of approximately 57
per cent of the total flying weight. But it was found that the
propeller and transmission shafts and their bearings would not stand
the strain due to the increased power of the engine. Newer and
stronger shafts and bearings were, therefore, constructed and further
pendulum tests were made. It was then found that the transverse frame
which supported the shafts and bearings was too weak, and this was
strengthened by substituting newer and thicker tubing where it seemed
necessary.

These changes and repairs were all completed by October, 1901, and
the quarter-size model was at last, after months of delay, felt to be
in a condition which justified the expectation that its next flight
would be entirely successful. In view of the much more important
work on the large aerodrome which demanded immediate attention the
quarter-size model in this completed condition was put aside. Nothing
more was done with it until April, 1903, when some shop tests were
made preliminary to taking it to Quantico, where, on August 8, it
made a successful flight, which is described in Chapter XII.

[p234]

CHAPTER X
CONSTRUCTION AND TESTS OF THE LARGE ENGINE

The main requirement in an engine for an aerodrome--aside from
reliability and smoothness of operation, which are necessary in an
engine for any kind of locomotion—is that it shall develop the
greatest amount of power for the least weight. It is, therefore,
desirable to reduce the weight and number of parts of the engine to
the very minimum, so far as this can be done without sacrificing
reliability and smoothness of running. Furthermore, since the
strongest metal for its weight is steel, and since the greatest
strength of steel is utilized when the stress acting on it is one
of tension, it is advisable to design the engine so that the parts
which sustain the greatest strains shall be of steel and, as far as
possible, meet with strains which are purely tensional ones.

In designing the new engine for the large aerodrome it was,
therefore, planned to make it entirely of steel, as far as this was
possible. The only parts which were not of steel were the bronze
bushings for the bearings, the cast-iron pistons, and cast-iron
liners of the cylinders. Previous experience had shown that, while
it is possible to use a cast-iron piston in a steel cylinder or
even a steel piston in a steel cylinder, provided the lubrication
be kept exactly adjusted, yet the proper lubrication of the piston
and cylinder of a gas engine is difficult even under the most
favorable conditions, owing to the fact that excessive lubrication
causes trouble from the surplus oil interfering with the sparking
apparatus. It was, therefore, determined not to risk serious trouble
by attempting to have the pistons bear directly on the steel walls of
the cylinders.

While visiting the French engine builders in the summer of 1900 in
the attempt to find one willing to undertake the construction of a
suitable engine for the aerodrome, it was pointed out to them that
the great amount of weight which they claimed to be necessary for the
cylinders, and which they stated made it impossible for them to build
an engine which would meet the requirements as to power and weight,
could be very greatly reduced by making the cylinders in the form of
thin steel shells having cast-iron linings. All, however, to whom
this suggestion was made declared that it was impossible to build
satisfactory cylinders in this way; some of them even stated that
they had tried it and found it impossible to keep the thin liners
tight in the steel shells. The difficulty which they had encountered
is due to the difference in expansion of the steel and the iron when
raised to a rather high temperature by the heat of the explosions,
if the cylinders are not well jacketed with water; and if the steel
[p235] shells are water jacketed they then do not expand as much
as the cast-iron liners, and this causes the latter to become “out
of round” because of the compression strains produced in them when
trying to expand more than the steel shells. As past experience had
shown, however, that it was possible to keep the liners tight in
small cylinders, it was believed that by taking proper care in the
construction there would be no difficulty in this respect with the
cylinders of this larger engine.

In carrying out these plans, however, of making the cylinders of
steel, numerous constructional difficulties were encountered which
could not be foreseen when the design was made. Had they been
foreseen, provision for obviating them could easily have been made.
As will be seen from the drawing, Plate 78, the engine cylinders
consisted primarily of a main outer shell of steel one-sixteenth
of an inch thick, near the bottom end of which was screwed and
brazed a suitable flange, by which it was bolted to the supporting
drum or crank chamber. These shells, which were seamless, with the
heads formed integral, were designed to be of sufficient strength
to withstand the force of the explosion in them, and, in order to
provide a suitable wearing surface for the piston, a cast-iron
liner one-sixteenth of an inch thick was carefully shrunk into
them. Entering the side of the cylinder near the top, was the
combustion chamber, machined out of a solid steel forging, which
also formed the port which entered the cylinder and was fastened to
it by brazing. The water jackets, which were formed of sheet steel
.020 inch thick, were also fastened to the cylinder by brazing,
and it was in connection with the brazing of these water jackets
that the first serious difficulty was met in the construction of
the engine. In the first place, as the jackets were of an irregular
shape and of a different thickness of metal from the walls of the
cylinder to which they were joined, the expansion and contraction
due to the extreme heat necessary for properly brazing the joints
caused such serious strains in various and unexpected directions
that it was only by exercising the very greatest care and patience
that a completely tight joint at all points of the jacket could be
secured. In the second place, the size of the cylinders and the
consequently large extent of water-jacket surface, complicated the
problem. The maintenance over this large surface of the extreme
heat necessary for brazing involved discomfort and, indeed, actual
suffering to the person engaged in the work, and much care and skill
were demanded in so distributing the heat that the temperature
of the surface of the jackets would be uniform enough to prevent
serious strains from expansion and contraction. As no workman could
be found either competent to do the work or willing to undergo the
personal discomfort, the writer was obliged to do all this brazing
work himself. Besides the difficulties due to the expansion and
contraction of the jackets while they were being brazed, the greatest
care had to be exercised to avoid heating the cylinders so hot as to
weaken the [p236] joint where the explosion chambers were joined to
the cylinders, which, of course, had been brazed before the jackets
were fitted to them preparatory to brazing them.

Another great difficulty was that the ring which encircled the
cylinder near the middle of its length, and which formed the bottom
part of the water jacket, expanded very much more than the cylinder
itself, so that, if it was brazed to the cylinder before the jacket
was brazed to it, the heat of brazing the jacket to the ring would
cause the ring to break loose from the cylinder; while if the ring
was not previously brazed to the cylinder, but was brazed after the
jacket had been brazed to it, the very much greater heat required
for brazing the ring to the cylinder caused the spelter to burn
out of the joint between the jacket and the ring. Furthermore, it
was found very difficult to braze the two joints at the same time,
since in brazing the ring to the cylinder it was best to have the
cylinder in an inverted vertical position, so that the spelter could
be made to flow evenly around the ring and form a fillet against the
wall of the cylinder, while in brazing the jackets to the ring it
was best to have the cylinder in the reverse vertical position or
lying on its side so that the spelter could properly flow into this
joint. Finally, however, after what proved to be most exasperating
and tedious work, the five cylinders necessary for the engine were
completed and a series of tests was immediately made. During the
course of these tests the water circulation became obstructed in
several instances, and the consequent high temperature to which
the cylinders and jackets were raised caused severe strains in the
jackets which, in turn, produced breaks in the brazed joints. These
breaks had to be rebrazed, and in brazing them it was necessary
in almost every case to remove the cast-iron liners and rebraze
the entire jackets from start to finish, as the application of the
intense heat necessary for brazing at any one point produced such
severe strains that before the break which was being repaired could
be completed other breaks developed at various points of the jacket.
It was, therefore, necessary to get the whole jacket up to a fairly
uniform heat and complete the brazing while it was in this condition,
and then keep the whole cylinder at a uniform but gradually
decreasing temperature until it had sufficiently cooled off.

On account of these troubles with the water jackets and the cylinders,
it was decided to build some extra cylinders, not only because past
experience had suggested improvements in detail in the construction of
the jackets, which would prevent to a large extent the great troubles
which had been met with in the brazed joints, but also to insure
having sufficient cylinders to enable the engine to be always in
working condition, even though several of the cylinders might be out of
commission from slight imperfections in the jackets or at other points.
While the construction of these new cylinders involved a repetition
of the arduous task of brazing, yet the minor improvements which
were introduced [p237] proved eminently successful in providing
against future troubles from leaky jackets.

[Illustration: PL. 78

ENGINE OF AERODROME A. SECTION THROUGH CYLINDER AND DRUM]

[Illustration: PL. 79

ENGINE OF AERODROME A. END ELEVATION, PORT SIDE]

[Illustration: PL. 80

ENGINE OF AERODROME A. TOP PLAN]

[Illustration: PL. 81

ENGINE OF AERODROME A. ELEVATION STARBOARD BED PLATE, SPARKING
MECHANISM]

The general form of construction of the engine with the improved
cylinders will be readily understood from the drawings, Plates 78–81,
in which Plate 78 is a detail sectional view, previously referred to,
through one of the cylinders; Plate 79 is an end elevation of the
port side, Plate 80 is a plan view, and Plate 81 is an elevation of
the starboard bed plate which supports that side of the engine, and
by which it was fastened to the aerodrome frame, this view showing
particularly the sparking apparatus which was mounted on the bed
plate. The engine consists primarily of a single crank shaft provided
with a single crank pin, the shaft having bearings in a drum which
consists essentially of two heads. Arranged around the crank shaft
and attached at equidistant points of the drum are five cylinders.
Mounted on the port side of the crank shaft and close to the crank
arm is a small gear, which through suitable gears mounted on the port
head of the drum drives a double-pointed cam which has a bearing on
the exterior of the hub of the drum. The ratio of these gears is such
that the cam is driven at one-quarter the speed of the crank shaft,
and in the reverse direction. Mounted on the exterior side of the
port head of the drum are five punch rods, the upper ends of which
are within a sixty-fourth of an inch of being in contact with the
exhaust-valve stems of the cylinders, and on the lower end of these
rods are hardened-steel rollers which rest on the double-pointed
cam--this one cam thus serving to operate the exhaust valves of all
five of the cylinders. The port head of the drum is connected to
the port bed plate, by which it is supported, by means of a flanged
bushing in which are formed tongues and grooves which fit into
corresponding grooves and tongues formed in the hub of the drum, it
being necessary to have a certain amount of space between this bed
plate and the head of the drum to provide room for the exhaust-valve
cam and its co-acting punch rods. The starboard bed plate is fastened
to the starboard head of the drum by bolts which draw the web of the
bed plate against the face of the drum. The sparking gears are driven
by means of a gear formed on a sleeve which telescopes over the hub
of the starboard drum, and has a bearing thereon, the end of the
sleeve terminating in a ring which is fastened to the crank shaft.

Since the five connecting rods must center on the one crank pin, the
bronze shoes in which they terminate can occupy only a portion of the
circumference of the pin, and with the relative proportions which
here existed between the length of stroke of crank and the length of
the connecting rod, the circumferential width of the connecting-rod
shoes was slightly less than sixty degrees, thus leaving uncovered
a crank space of about one-sixth of the circumference, which it was
necessary to have in order to provide room for the change in relative
position of the shoes due to the angularity of the connecting rods.
In [p238] the experimental engine the connecting-rod shoes were
all given their bearing directly on the crank pin, as heretofore
described, being held in contact therewith by means of cone nuts,
which were screw-threaded to the crank pin, the taper of the cones
permitting adjustment for wear. This method of connecting these
parts to the crank pin is the usual plan of connecting three or
more connecting rods to one crank pin. So much trouble had been
experienced with the water jackets and with minor defects in the
experimental engine that no long runs had been possible with it,
and consequently no trouble had been experienced because of the
small amount of bearing area provided by this method of joining the
connecting rods to the crank pin. When, however, the new engine
was completed it was found that after working at high power for a
few minutes the connecting-rod shoes heated so rapidly that it was
impossible to run the engine for more than ten or twelve minutes, the
excessive heating of the shoes causing a great diminution in power
besides the danger of serious damage if the tests were continued
longer. At first this defect seemed almost fatal, as there appeared
to be no way of providing sufficient bearing area for the five
connecting rods on one crank pin. Happily, however, the writer was
able to overcome this defect by an improved design which enables all
five connecting rods to operate on the one crank pin, and at the
same time provides each with the full amount of bearing area which
it would have were it the only connecting rod operating on the crank
pin. This arrangement consists essentially of a main connecting rod
formed of a steel forging terminating in a sleeve which encircles
the crank pin and is provided with a bronze lining for giving a
proper bearing surface between the connecting rod and the crank pin,
both the steel sleeve and the bronze lining being split, but at
right angles to each other, to permit assembling them on the crank
pin. This steel sleeve, the upper half of which is formed integral
with the main connecting rod is rounded off to a true circle on its
exterior circumference, except at the point where the rod joins it.
The other four connecting rods terminating in bronze shoes are then
caused to bear on the exterior of this sleeve, being held in contact
therewith, and permitted to have a sliding motion thereon sufficient
to take care of the variation in angularity of the connecting rods,
by means of the cone nuts which are screw-threaded to the sleeve and
locked thereto by means of the jam nuts, as shown in the drawings.
The main connecting rod, of course, acts in the same way as in the
ordinary case where each cylinder has its separate crank pin. The
other four connecting rods deliver their effort to the crank pin
through the sleeve in which the first connecting rod terminates, and
they, therefore, do not receive any of the rubbing effect due to
the rotation of the crank pin, except that of slipping a very short
distance over the circumference of the sleeve during each revolution,
the amount of slipping depending on the angularity of the connecting
rod. This improved type of bearing was successful from the time of
its first trial, and even in later [p239] tests in which the engine
was run for ten consecutive hours at full power it showed no signs
whatever of overheating. As this new form of connecting-rod bearing
for the crank pin had never been tried before, the precaution was
taken to leave the threads on the crank pin for the cone nuts, so
that if this new bearing should not prove successful the old plan of
having the connecting-rod shoes bear directly on the crank pin could
be reverted to. These threads are clearly seen in Plate 78 and were
never removed from the crank pin, though their removal would have
added considerably to the area of the bearing surface of the main
connecting rod, had more bearing surface seemed necessary.

The lubrication of the main crank-shaft bearing and of the crank
pin was effected by means of a small oil cup, fastened to the port
bed plate, which fed oil through a hole in the hub of the drum to a
circular groove formed in the bronze bushing in the hub. The crank
shaft being hollow, a hole was drilled through it in line with the
groove in the bushing, and the oil was then led from the interior
of the crank shaft through a pipe connected to the plug in the end
thereof, and through a hole drilled in the crank arm to the hollow
crank pin. Small holes through the crank pin permitted oil to pass to
the exterior thereof and thus oil the bearing of the main connecting
rod. Small holes through the sleeve and bushing of the main
connecting rod fed oil under the shoes of the other four connecting
rods, the small holes being placed in oil grooves formed in the
interior of the bronze bushing. The lubrication of the pistons was
effected by means of small crescent-shaped oil cups fastened to the
outer wall of the cylinders, which distributed the oil equidistantly
around the circumference of the pistons, through small tubes which
projected through corresponding holes drilled in the cylinder wall.
These oil cups for the cylinders were, while small, of sufficient
size to furnish a supply for approximately one hour, and were so
positioned on each cylinder as to have a gravity feed. It may be
mentioned here that while there were many parts of the engine which
were of unprecedented lightness there was nothing which excelled
these oil cups in this respect, as they were made of sheet steel .003
of an inch thick, riveted and soldered up. The crank-shaft bearing in
the starboard drum was oiled from an oil cup mounted on the outside
of the bed plate and connected by a pipe to a hole in the inner wall
of the drum, which was connected to the oil grooves in the bronze
bushing in the hub of the drum.

The first set of pistons for this engine were similar in design to
those shown in the assembled drawings, except that they had side
walls and heads which were twice as thick as those shown. These
lighter pistons were constructed later, and were just as good as
the earlier and heavier ones. It will be noted that the pistons
have two deep but thin ribs reinforcing the head. The pistons were
slightly tapered from the middle, where they were .005 inch smaller
than the cylinder bore, toward the outer end, where they were .0075
inch smaller [p240] than the bore. The outer piston ring was .0035
inch narrower than its groove, the second one .003 inch, the third
.0025 inch, and the inner one .002 inch narrower than its groove.
The rings were bored one-sixteenth inch off center with the exterior
surface, and had one-eighth inch diameter of spring. They were of
the lap-joint type, with the sides of the laps carefully fitted and
only one-sixty-fourth-inch clearance at the ends of the laps to allow
for thermal expansion. As no grinding facilities were obtainable in
Washington, the cylinders were carefully bored smooth and free from
taper, and the pistons were worn in to a perfect fit by running them
in by a belt for twenty-four hours, with copious oil supply.

The main connecting rod was 7/8-inch diameter and solid, while
the other four were of the same diameter but with a 5/8-inch hole
in them. The gudgeon pins in the pistons were hollow steel tubes
7/8-inch diameter and case-hardened, and were oiled entirely by the
oil thrown off by centrifugal force from the crank-pin bearing, the
oil running along the connecting rods and through suitable holes at
the heads into oil grooves in the bronze bushings in these heads.

Since on an engine for an aerodrome the best plan for releasing
the exhaust gases from the engine is to get rid of them as soon
as possible, so long as they are released behind the aviator and
do not interfere with his view in the direction of motion, it was
decided to have the gases exhaust immediately from the combustion
chambers; but in order to prevent their playing on and heating the
main bearing of the crank shaft in the port drum the combustion
chambers were each provided with a chamber below the exhaust-valve
seat, with a side outlet therefrom. The manifold pipe through which
the gaseous mixture was supplied to the inlet valves of the engine
consisted of a tube bent to a circle and having five branch tubes,
each leading to one of the automatic inlet valves, which fitted
removable cast-iron seats fastened by a nut in the upper part of
each combustion chamber. The very small amount of clearance between
the engine and the frame necessitated that this pipe be cut in
three places and joined by flanges in order to properly assemble
it on the engine when the latter was mounted in the frame. The
carburetor, which was placed near the rear of the aviator’s car,
was connected through suitable pipes to this circular inlet pipe,
at a point horizontally in line with the center of the shaft. The
auxiliary air valve consisted of a sleeve rotatably mounted on the
vertical pipe leading from the carburetor to the manifold, holes in
the sleeve being brought to coincide more or less with holes in the
vertical pipe, by the operator, when more or less air was required
or when he wished to vary the speed of the engine. The cooling water
for the jackets of the cylinders was led to them through a circular
manifold pipe on the starboard side connected by a vertical pipe
with the centrifugal pump situated at the lower point of the lower
pyramid of the aerodrome frame. The heated water was led from the
jackets through another [p241] circular manifold pipe on the port
side, through two connections to the radiating tubes at the front and
rear, respectively, of the cross-frame. These radiating tubes, which
were provided with thin radiating ribs soldered to them, finally led
the cooled water to the tank situated in the extreme rear of the
aviator’s car, a suitable pipe from the bottom of this tank being
connected to the inlet side of the centrifugal pump. The centrifugal
pump was driven by means of a vertical shaft connected to the crank
shaft through a set of bevel gears which drove it at three times the
speed of the engine. The bearings through which these gears were
connected were mounted on the port bed plate, and in order to allow
for a certain amount of vibration between the engine and the pump
this vertical connecting shaft had a telescoping section connected
through suitable splines.

The sparking apparatus comprised, first, a primary sparker similar
to the simplest form of such devices which have since come into
common use, where a cam driven by the engine co-acts with a pawl
on the end of a spring, but in this case, as this sparker was used
for all five cylinders, the cam was driven at a speed of two and
one-half times that of the engine shaft, thus making and breaking the
primary circuit five times in each two revolutions of the engine.
Second, a spark coil, the primary terminals of which were connected
to the primary sparker and to a set of dry batteries. Third, a
secondary distributor consisting of a disc carrying a contact brush
and driven at a speed one-half that of the engine, this brush being
constantly connected through a contact ring to one of the terminals
of the high-tension side of the spark coil and running over the
face of a five-section commutator, each of the sections of which
was connected to a spark plug, the other high-tension terminal of
the spark coil being, of course, grounded on the engine frame. This
sparking apparatus was first constructed by using blocks of red
fibre for insulation. After the engine was completed and was being
tested difficulties were met with in the sparking apparatus which
at that time appeared inexplicable. After a great deal of annoyance
and loss of time it was finally discovered that the red fibre was
not as good an insulating medium as it was supposed to be, owing
to the zinc oxide used in making it. In damp weather the sparking
apparatus absolutely refused to work, and it was found that the
moisture in the air caused the zinc oxide in the fibre to nullify its
insulating qualities. This trouble, after being located, was cured by
substituting hard rubber for the red fibre.

At the time when this engine was built, as well as earlier when the
experimental engine was built, it was impossible to procure any wire
which had been properly insulated to withstand the high voltages
necessary for the connections between the high-tension side of the
spark coil and the secondary distributor, and from the secondary
distributor to the spark plugs in the cylinders. While at this time
this appears a very simple matter, yet the trouble experienced and
[p242] the delays caused by the lack of such small accessories
which are now so easily procurable were very exasperating, and it
was finally necessary to insulate these wires by covering them with
several thicknesses of ordinary rubber tube of different diameters
telescoped over each other.

In the early tests of this new engine, which were made with it
mounted on a special testing frame and delivering its power to the
water-absorption dynamometers, the engine was operated without any
fly wheels, and, so far as its smoothness of operation was concerned
and its ability to generate its maximum power, it did not require any.

After the completion of the tests on the testing frame the engine
was assembled in the aerodrome frame, which was first mounted on the
floor of the launching car. The car itself was mounted on a short
track in the shop, which arrangement provided a smoothly rolling
carriage which could be utilized for measuring the thrust of the
propellers by merely attaching a spring balance between the rear of
the car and a proper holding strap on the track. In the first tests
of the engine under these conditions, it was found that while the
engine itself did not require any fly wheels, yet the lack of them
caused trouble with the transmission and propeller shafts, which,
while it had never been anticipated, was easily understood when it
was encountered. This difficulty was caused by the “reverse torque,”
which fluctuated from a maximum to a minimum five times during
each double revolution of the engine, and which set up fluctuating
torsional strains of such magnitude in the transmission and propeller
shafts that the shafts themselves became exceedingly hot after a few
minutes operation of the engine, and under more prolonged periods
of operation these fluctuating torsional strains caused a permanent
twisting and bending of the shafts. The transmission and propeller
shafts were at first made of tubing one-sixteenth of an inch thick,
but these were abandoned both on account of the necessity of
abandoning the screw-thread method of attaching the flange couplings
and gears, and also because these shafts had been designed when it
was expected to transmit only twelve horse-power to each propeller,
while the increase of power in the large engine necessarily required
much stronger shafts. The first shafts which were actually tested
in the frame were, therefore, one and one-half inches in diameter
by three-thirty-seconds of an inch thick, the tubing having been
one-thirty-second of an inch larger originally and turned down to
this size to insure a straight shaft. When these shafts twisted under
the action of the reverse torque of the engine, a very much heavier
set, practically twice as thick, were constructed. When used in the
tests these heavier shafts, while much stronger, still showed a large
amount of heating due to the fluctuating torsional strains.

Upon calculation it was found that by providing specially light fly
wheels the major portion of this reverse torque could be eliminated
for a less increase [p243] in weight than would be occasioned
by sufficiently increasing the thickness of the transmission and
propeller shafts to safely stand it. Since it was desired to
concentrate as much as possible of the weight of the fly wheels
in the rims, the idea at once suggested itself of building them
up like a bicycle wheel by means of tangent spokes. Two steel
automobile-wheel rims were therefore procured thirty-three inches in
diameter, and these were provided with tangent spokes connected to
special steel hubs fitted to the crank shaft of the engine. The rims
themselves not being quite heavy enough, and constructional reasons
necessitating their being at different distances from the center of
length of the crank pin, the extra weight which it was desired to
give to these rims was provided by means of steel wire wound tightly
around and fastened to the rims, the weight of each rim being made
inversely proportional to its distance from the center of the crank
pin. The first spokes which were used for these wheels were standard
bicycle spokes three-thirty-seconds of an inch in diameter, but these
were soon found to be entirely too weak to withstand the sudden
strains due to the rapid starting of the engine. They were therefore
replaced by standard spokes one-eighth of an inch in diameter, but
these also proved too weak and were later replaced with special
spokes made in the shop out of No. 10 coppered-steel wire, which by
test was found to have a tensional strength of 2192 pounds. As these
steel rims were only one-sixteenth of an inch thick and had not been
made exactly true, but had been straightened before being used, it
was found that they very quickly went out of shape under the strain
due to the centrifugal force at high speeds, and also when the engine
was suddenly accelerated. As long as they did stay true, however, it
was found that they were sufficiently heavy to provide all of the
fly-wheel effect it was necessary to have in order to eliminate all
trouble from the reverse torque.

After further consideration, it was decided that the only means of
constructing a fly wheel which would have a stiff rim and at the
same time would not be heavier than the steel ones, which had been
found adequate, was by perpetrating what would at first sight appear
to be an absurdity. A new set of rims for the fly wheels was made
by constructing them of an aluminum casting, the section of the rim
being U-shaped. After machining these rims and assembling the fly
wheels with them, it was found that they were many times stiffer
than the previous steel ones of the same weight, and after this
change no further trouble was experienced in keeping the fly wheels
perfectly true, even under the most severe strains. In fact, on one
occasion when the engine broke loose from the propellers, it ran to a
speed, which, while not exactly known, yet reached the limit of the
tachometer, which was 2000 R. P. M., without injury to the fly wheels.

It will be recalled that in starting up the engine on the
quarter-size model, the initial “cranking” necessary with a gasoline
engine was accomplished by [p244] having two of the mechanics turn
the propellers. While this same plan might have been followed in the
case of the large aerodrome, yet it would have involved some danger
to the mechanics and would also have left the aviator without any
means of restarting the engine should it for any reason stop while
in the air. Believing it to be very important to provide means for
enabling the aviator to restart the engine in case it stopped in the
air, the writer devised the starting mechanism shown in the drawings,
Plates 78 to 80. Fastened by tongues and grooves to the port side
of the engine crank shaft, just outside of the bed plate, is a worm
wheel, on the hub of which is mounted the bevel gear which drives
the water-circulation pump through the bevel pinion, as already
described. Mounted on the web of the bed plate are two brackets,
in which the shaft for the starting crank is journaled, this shaft
passing forward and downward through the front of the cross-frame
of the aerodrome, where it is journaled in a bracket secured to the
brace tubes thereof. At the front or lower end of the shaft a crank
handle is connected thereto by a ratchet mechanism. The upper end
of the starting shaft, between the bearings of the two supporting
brackets, is tongued and grooved, and slidably mounted thereon with
co-acting grooves and tongues is a worm screw which, in the position
shown in Plates 79 and 80, is in gear with the worm wheel just
described. However, when the worm screw is slid along on the shaft
until it is against the upper bracket it is out of gear with the
worm wheel. Mounted in the interior of the tubular starting shaft is
a spring-pressed pawl plug, not shown, but which projects through
one of the tongues on the shaft near the upper bracket. If the worm
screw is slid up against this upper bracket, this pawl catches in a
radial hole in the worm screw and holds it in this position out of
gear with the worm wheel. Connected to this pawl plug and passing
longitudinally through the center of the shaft is a wire which
terminates in a button just at the end thereof. By pulling on this
button the operator may release the worm and thus permit it to slide
downward so that when the starting crank is turned in a clockwise
direction the worm will screw itself into gear with the worm wheel,
and any further turning of the starting crank will cause the worm to
force the worm wheel, and, consequently, the engine shaft, around in
a clockwise direction. As soon as the engine gets an explosion the
worm wheel slides the worm along against the upper bracket, where the
spring pawl catches and holds it till it is again released by the
operator as before.

This starting mechanism was a success from the first, and the engine
was never started up in any other way. With an aerodrome having the
qualities of automatic equilibrium, which the Langley machines have,
it was felt very certain that by this mechanism the engine could
be easily restarted while in the air, in case it was inadvertently
stopped. [p245]

The reason for building the engine with five cylinders instead of
some other number, and for arranging them radially on a central drum
using only one crank pin may not appear quite obvious. The advantages
gained by such a construction, however, are very great, and may be
briefly summed up as follows:

First, since in a gas engine of the four-cycle type there is only one
explosion in each cylinder every two revolutions, and the crank shaft
and crank pin therefore are loaded only one-quarter of the time for
each cylinder, it is obvious that by having four cylinders arranged
radially around a central drum the load on the bearings of a single
crank shaft and crank pin may be kept very uniform. However, with
four cylinders thus arranged it is impossible to have the cylinders
explode and exert their effort on the crank at uniform intervals
in the cycle, it being necessary to have the cylinders explode in
the order of 1, 3, 4, 2, 1, etc., thus giving intervals between
explosions of 180 degrees, 90 degrees, 180 degrees, 270 degrees,
etc., or to have them explode in the order of 1, 3, 2, 4, 1, etc.,
thus giving intervals of 180 degrees, 270 degrees, 180 degrees, 90
degrees, etc. On the other hand, with any odd number of cylinders the
explosions will occur at equal intervals in the cycle. With three
cylinders they will explode in the order of 1, 3, 2, 1, etc., or at
equal intervals of 240 degrees, while with five cylinders they will
explode in the order of 1, 3, 5, 2, 4, 1, etc., or at equal intervals
of 144 degrees. It is therefore seen that there is a great advantage
in smoothness of operation and uniformity of torque of the engine
through having an odd number of cylinders instead of an even number.

Second, it is readily apparent that the greater the number of
cylinders, provided the number is an odd one, the more uniform the
torque will be, and it would seem at first that seven cylinders
would therefore be better than five, since the uniform intervals
between explosions with seven cylinders would be only 103
degrees (approximately). The advantage gained, however, through
seven cylinders instead of five is largely, if not completely,
counterbalanced by the added number of parts and the difficulty of
providing sufficient circumferencial width for the connecting-rod
shoes on the crank-pin bearing, even with the improved construction
of this bearing already described. There is considerable fluctuation
of the torque in each revolution of the engine with five cylinders,
but this fluctuation of torque is more easily smoothed out by the use
of very light fly wheels than by increasing the number of cylinders,
and thus adding to the complication of the engine.

Third, the strongest point in favor of the radially arranged
cylinders is the reduction in weight and complication which it
permits. The crank shaft is reduced to the very minimum, there being
only one crank pin with two main bearings which can, without any
difficulty whatever, be kept absolutely in line with each other
and thus prevent binding and loss of power. Again, the use of a
single-throw crank not only reduces the cost and weight of the crank
[p246] itself, but makes it very much less liable to damage; long
crank shafts with several crank pins being frequently twisted by
improper explosions in the cylinders. The supporting drum or crank
chamber is likewise reduced to the very minimum, both in weight
and simplicity, the drums being perfectly symmetrical with no lost
space either inside of them or on their exteriors. The cam mechanism
for operating the valves is reduced to a simple ring carrying (for
a five-cylinder engine) a double-pointed cam and journaled on the
exterior of the hub of one of the drums, the cam being driven by a
train of gears journaled on studs mounted on the drum, and co-acting
with a gear fastened to the crank shaft against the crank arm.

The radial arrangement of the cylinders is thus seen to give not
only an engine with the smallest number of parts, each of which is
as far as possible worked to a uniform amount during each complete
revolution of the crank shaft, but it also gives a very compact and
readily accessible mechanism with its center of gravity coincident
with its center of figure, and with the liability of damage to it,
in case of a smash of the vehicle on which it is used, reduced to
the minimum from the fact that the greatest weight is located at the
strongest part.

Fourth, and of almost as great importance as the reduction in
weight which the five-cylinder radial arrangement permits, is its
unusual qualities as regards vibration. Since these five-cylinder
engines were built by the writer a very thorough treatment of their
properties as regards balancing has been given in a treatise on
the balancing of engines,[44] so no discussion of the mathematical
formulæ involved in a study of the question of the inherent balancing
properties of these engines will be here given. It is sufficient to
call attention to the fact that in an engine having five cylinders
arranged radially, all of the reciprocating parts are balanced for
all forces of the first, second and third orders. As it is only the
reciprocating parts which give any trouble in balancing any engine,
the unbalanced rotating parts being readily balanced by placing an
equal weight at an equal distance from the center of rotation, and
on the opposite side thereof, it is readily seen that the properties
of balancing which are inherent in this type of engine are unusual.
A six-cylinder engine having a six-throw crank shaft is not nearly
so thoroughly balanced as this type having its five cylinders
radially arranged, for in the latter case all the moving parts are
in one plane, while in the former case the moving parts are in six
separate and parallel planes, and there is consequently considerable
longitudinal vibration which can never be overcome. While this is
true as regards the vibration due to moving masses, it is still more
impressively true as regards vibration due to reaction arising from
the force of the explosions in the engine cylinders, especially when
the engine is running slowly and having heavy explosions.

The usual practice in balancing the rotating parts of an engine is to
attach [p247] balance weights to the crank arms which are prolonged
beyond the center of the crank shaft and on the opposite side from
the crank pin; the radius of rotation of these balance weights being
made approximately equal to the radius of the crank pin. But aside
from the constructional difficulties which would be introduced, it
was seen that if this plan was followed in this engine it would
require a very large additional weight. Since the amount of this
weight could be diminished in exact proportion to the increase of the
radius of rotation of the balance weights, it was at first decided
to attach the weights to the rims of the fly wheels, the relative
amount of weight attached to each wheel being inversely proportional
to its actual longitudinal distance from the crank-pin center. It
was very soon found that the attachment of these balance weights to
the fly wheel caused excessive strains on the rims of the wheels,
thereby causing them to go out of line. In order, therefore, to keep
the amount of balance weight small by carrying it at a considerable
distance from the center of the shaft, the weights were finally
arranged as clearly shown in the drawings, Plates 78 to 80. There
it is seen that the main portion of each of the balance weights
consists of a flat arm bolted between the flanges which couple the
transmission shafts to the engine shafts. The flat arm terminates in
a lozenge-shaped lug, additional weight being provided by a plate
fastened to one end of a tube, the other end of which terminates in a
collar fastened around the transmission shaft. The tube is inclined
at an angle of about thirty degrees with the flat balance arm, thus
acting as a brace to prevent the balance arm from wobbling, the plate
on the bracing tube being fastened to the lozenge-shaped lug by means
of small bolts.

The tabulated statement of the weight of this large engine is given
below. From this it will be readily seen that the net weight of
the engine proper is 124.17 pounds. The fly wheels were in no way
necessary to the engine itself, but were used solely for the purpose
of smoothing out the torque of the engine so that the transmission
shafts and propeller shafts might be kept down to the very minimum in
weight. Including the two fly wheels, the weight is 140 pounds.

Including the 20 pounds of cooling water the total weight of the
power plant is 207.47 pounds. Without flywheels the total weight is
191.64 pounds.

The construction of this large engine was completed in December,
1901, and the first tests of it were made in January, 1902. As
already stated, these first tests were made with the engine
mounted on a special testing frame and delivering its power to two
water-absorption dynamometers, no fly wheels being used, as none were
required. Later, when it became necessary either to use fly wheels
or to greatly increase the weight of the transmission and propeller
shafts, in order to overcome the reverse torque, the two light fly
wheels were added, and another series of tests was made of the engine
on its testing frame. The arrangement of the engine, dynamometers,
and accessory [p248] apparatus is clearly shown in Plates 82, 83
and 84. The engine ran in a clockwise direction, as viewed in Plate
82. ‹AA› are the fly wheels; ‹BB› the balance weights; ‹CC› the
dynamometer shafts, on which are fastened the rotor plates which
revolve inside of the dynamometer drums, ‹DD›, between stator plates
fastened therein. The drums have a hub on either side, by which
they are supported, these hubs being journaled on ball-bearings in
the pedestals resting on the wooden framework. The rotor plates do
not touch the stator plates in the dynamometers, but drag on the
water with which the drums are partially filled, and thus tend to
cause the drums to revolve around with them. The torque on each
drum is measured by means of a rope, not shown, fastened into the
hook at the top of the drum, the rope being given a partial coil
around the drum and passing off tangent thereto at the horizontal
diameter is fastened to a pair of spring scales hung from the ceiling
vertically above the point of tangency. The scales and ropes were
unfortunately not in position when these photographs were taken, but
the arrangement of them should be readily understood. As the friction
of the rotor plates on the water heats it in exact proportion to the
amount of power absorbed, the small amount of water in the drums
would be soon converted into steam unless continually renewed or
cooled. When the rotor plates are revolving the centrifugal force
keeps the water pressed toward the circumference of the drum, and the
friction at any speed is dependent on the area of the rotor plates
in contact with the water. The horse-power required to revolve the
plates at any definite speed can therefore be controlled by having an
outlet for the water at the proper radial distance from the shaft.
The water from the water mains is led through the upper vertical pipe
and allowed to flow into the funnel, and thence into the drum near
the center where the centrifugal force throws it to the circumference
of the drum. The lower vertical pipe is connected to the drum at a
suitable radial distance from the center, and the heated water thus
passes through this pipe and into the lower funnel connected to
the sewer. By the use of the funnels the drums are allowed to rock
sufficiently to exert their pull on the spring scales without being
affected by the supply and exhaust of water.

[Illustration: PL. 82

DYNAMOMETER TESTS OF LARGE ENGINE]

[Illustration: PL. 83

DYNAMOMETER TESTS OF LARGE ENGINE]

[Illustration: PL. 84

DYNAMOMETER TESTS OF LARGE ENGINE]

The water for cooling the cylinders is led from the bottom of the
tank ‹E› to the circulating pump ‹F›, supported in a discarded lower
pyramid of the aerodrome frame, the pump being driven by the small
vertical shaft, as already described. The water, after passing
through the pump and the engine cylinders, is led back to the upper
part of the tank. By suitable connections to the water mains and
sewer, the water in the tank is kept at any desired temperature. The
gasoline supply tank is seen on the left-hand side of the testing
frame, as viewed in Plate 82, the carburetor being placed below it
and the gas supply pipe from the carburetor passing through the
gasoline tank. Instead of jacketing the carburetor, a grid formed
of thin copper tubes is supported just above the multitude of small
air pipes leading into the carburetor, and some of [p249] the
hot water from the engine is by-passed through this grid and thus
warms the air as it passes into the carburetor. The small pipe that
by-passes this water through the grid is seen connected to the outlet
water pipe just above the cylinders, a small butterfly valve in the
outlet pipe enabling the amount of heated water passing through
the grid to be controlled. The return from the grid is by means
of the small pipe leading to the top of the large water tank. The
tachometer, which gives instantaneous readings of the speed of the
engine, is seen at ‹G›, where it is at all times in full view of the
operator.

These dynamometers proved to be excellently suited for the testing
work, and far ahead of anything else the writer has ever found for
engine testing. Since the power required to rotate the rotor plates,
with a uniform amount of water in the drums, varies as the cube of
the speed, it is readily seen that it is impossible for the engine to
race or injure itself by running away, as frequently happens where
there is no engine governor and Prony brakes are used to measure the
power.

In the early tests the engine was never allowed to develop more than
40 horse-power, as it was feared that by letting it develop more,
which it was clearly seen to be capable of, it might be injured and
cause a delay in the tests of the aerodrome. In the second series of
tests it was allowed to develop 51 horse-power at 935 R. P. M., but
it was not thought to be advisable to let it run at maximum power
for more than an hour, for the same reason as before. In the summer
of 1904, after it was seen that there was no immediate possibility
of securing funds for continuing the tests of the aerodrome, it
was planned to enter the engine in the competitive tests at the
St. Louis Exposition, where a prize of $2500 was offered for the
lightest engine for its power. As the conditions specified in this
competition required that the engine run at its maximum power for one
hour, and that this be followed by a durability test of ten hours’
continuous running, it was decided to make some durability tests of
the engine before taking it to St. Louis. In these tests, the engine
was run on three separate trials for a period of ten hours[45] with
a constant load of 52.4 horse-power at 950 R. P. M. Even in these
long durability tests the engine and the dynamometers both worked
so smoothly and evenly that the engine did not vary its speed more
than ten revolutions per minute, and the pull on the spring scales
varied less than ten pounds in the entire ten hours. Considerable
correspondence was had with the officials of the St. Louis Exposition
regarding the entrance of the engine in the competition, in order
to make sure that suitable facilities for conducting the tests had
been provided. After receiving assurance that everything necessary
had been provided, the engine and its testing dynamometers were
boxed for shipment to St. Louis and arrangements were just being
completed for their transportation when the following telegram was
[p250] received from the director in charge of the aeronautical
department of the Exposition: “On account of lack of competition
engine tests abandoned.” As the main object of entering the engine
in the competition was to insure for it an unquestioned record of
its performance it was decided to reassemble it in the testing frame
in Washington and invite some engineers of prominence to witness and
certify to its performance, but on account of the lack of funds for
meeting the expenses incident to such a series of tests as it was
planned to make this was never done.

In the tests which were witnessed on April 26, 1902, by Captain I.
N. Lewis, Recorder of the Board of Ordnance and Fortification, the
engine was held down to a pull of 200 pounds on a 13-inch lever, when
running at 1000 revolutions per minute. In the later tests in May,
1903, which were witnessed by Captain Gibson, who was then Recorder
of the Board of Ordnance and Fortification, and Mr. G. H. Powell, the
Secretary of the Board, the engine was allowed to work at a pull of
265 pounds on the 13-inch lever arm at a speed of 950 revolutions per
minute. In the tests made in August, 1904, the engine was run for ten
consecutive hours[46] at a pull which varied from 263 to 271 pounds,
or an average of 267 pounds, on a 13-inch lever, with the speed
varying from 945 to 955 revolutions per minute, thus showing 52.4
horse-power at the average speed of 950 R. P. M.

DETAILED WEIGHT OF NEW LARGE ENGINE.

Name of Weight in
part. grammes.

Crank shaft 5,225
Connecting rods (total) 5,005
Pistons--
No. 1 1,652
No. 2 1,647
No. 3 1,655
No. 4 1,660
No. 5 1,646

Cylinders--
No. 1 (including exhaust and inlet valves, oil
cups, etc.) 4,768
No. 2 (including exhaust and inlet valves, oil
cups, etc.) 4,685
No. 3 (including exhaust and inlet valves, oil
cups, etc.) 4,638
No. 4 (including exhaust and inlet valves, oil
cups, etc.) 4,637
No. 5 (including exhaust and inlet valves, oil
cups, etc.) 4,796

Port crank chamber drum, including cam, cam
gears, punch rods, etc. 5,225
Starboard crank chamber drum 3,440
Spark plugs (5) 450
Outlet water pipe 450
Inlet water pipe 360
Inlet gas manifold 1,700
Primary and secondary sparkers and wires 512
Balance arm with braces for same--starboard 1,040
Balance arm with braces for same--port 1,067
------
Total 56,323 = 124.17 lbs.
Starboard fly wheel 3,946
Port fly wheel 3,234
------
Total weight of engine and fly wheels 63,503 = 140.00 lbs.
Spark coil and batteries 6,800
Carburetor 3,751
Inlet gas pipe from carburetor to manifold 756
Gasoline tank 1,004
Water tank 717
Water circulating pump and shaft 807
Radiator 7,700
------
Total weight of power plant 85,038 = 187.47 lbs.

[p251]

CHAPTER XI
SHOP TESTS OF THE AERODROME

In June, 1902, after the proper adjustments of the carburetor and
other accessories of the engine had been accurately determined in the
tests on the testing frame, the engine was assembled in its proper
position in the aerodrome frame and connected to the propellers.
The aerodrome frame was then mounted directly on the floor of the
launching car, which was placed on a short track laid on the floor of
the shop, as previously described. A large spring balance, which had
been previously calibrated, was then connected between the car and an
upright fastened to the track, and tests were made to determine the
thrust developed when the engine drove the propellers at different
speeds. Upon finding that there was comparatively little vibration
when the engine was driving the propellers even at its maximum speed,
it was felt safe to raise the aerodrome from the floor of the car
and place it upon the uprights on which it would be supported in
launching it. Quite an extended series of tests was then made, and
although the uprights raised the aerodrome frame until the midrod
was practically 9 feet from the floor of the car, and in the tests
at maximum power the propellers developed an average thrust of 450
pounds, yet it was found that the clutch hook held the bearing
points of the frame so securely on the uprights of the car that all
fear that the aerodrome might break loose from the car during the
launching process was removed.

Upon the completion of these tests, which had proved most
satisfactory, the aerodrome frame was supported from the ceiling
of the shop by means of four short coil springs which reproduced
as nearly as possible the elastic or flexible suspension which the
aerodrome would have when supported by its wings in the air. These
springs were attached at the same points on the main frame of the
aerodrome at which the wings would be attached, thus permitting a
careful study of the amount of flexure and vibration which it would
undergo in actual flight. The most remarkable difference in the
nature of the vibration induced in the frame was found when the
aerodrome was thus supported by springs. When it was supported on
the rather unyielding launching car, the general tremor set up in
the frame by the engine and propellers was, while small, yet harsh,
the effect on a person standing in the aviator’s car being rather
unpleasant in the joints of the knees when experienced for several
minutes. When the frame was suspended by the springs it was found
that all this harshness of tremor disappeared, it being replaced by
a slight general and rapid tremor of the whole frame, which was not
at all unpleasant, and which [p252] had no tiring effect on one
standing in the aviator’s car. In fact, the vibration in the first
case resembled rather closely that of a motor vehicle supported on
wheels having metal tires, and in the second case a motor vehicle
supported on wheels having pneumatic tires.

As in these tests in the shop it was impossible to keep the engine
cool by circulating its cooling water through the radiator, since
there was no air current blowing across the latter to carry away
the heat, it was necessary to connect an extra water tank in the
cooling-water circuit. A tank holding about ten gallons was used, and
this sufficed for about ten minutes before the water was raised to
the boiling point.

During one of these tests when the frame was supported from the
springs, and while the engine was developing about fifty horse-power,
without any warning whatever, both propellers suddenly twisted off
from the flanges by which they were connected to the propeller
shafts, thus leaving the engine entirely unloaded. The propellers
both dropped quietly to the floor, making only about one or two turns
in falling the distance of approximately 10 feet, and the engine,
which had been running at about 850 R. P. M., immediately speeded up
to an exceedingly high speed, which, while not exactly known, since
the tachometer only read to 2000 R. P. M., yet from the deflection
produced on the tachometer needle must have been considerably higher
than this. Although the fly wheels, which were 33 inches in diameter,
with the aluminum rims and wire spokes, had been exceedingly well
made, yet it was not considered safe to run them at this speed, and
the engine was immediately shut down. At the moment, however, that
the engine had broken loose from its propellers and also momentarily
jumped to this exceedingly high speed there was absolutely no
vibration that could be noticed, the unloaded engine running as
smoothly as an electric motor. This showed very clearly that the
running balance of the engine was as near perfect as it would be
possible to get it, except with a seven-cylinder engine, which is
theoretically capable of more perfect balance. It was evident that
what small vibration there was in the frame while the engine was
developing its power was due almost entirely to the reverse torque,
and, of course, could never be entirely eliminated.

In the tests of the engine working in the frame, both while mounted
on the car and also when suspended from the springs, a great
amount of delay was caused from the fact that the ball-bearings on
the transmission and propeller shafts frequently went to pieces.
There were two reasons for this: In the first place, although
carefully selected balls were used, defective ones were continually
encountered. Even a slight defect in a single ball resulted in its
breaking under the rather severe test to which they were subjected,
and, as is well known, the breaking of one ball in a ball-bearing
usually results in the destruction of the whole bearing, especially
if the races are light. The second cause was that [p253] the whole
aerodrome had been originally designed with the expectation of using
a maximum of 24 horse-power, and as no margin had been left to
provide for possible increases in the size of the bearings, there
was no room to permit them to be increased without almost completely
reconstructing portions of the transverse frame. While in the end
it would have been cheaper to have reconstructed these portions
in order to put in larger bearings, yet, as is always the case in
experimental work of this kind, small changes which seem to hold out
hope of overcoming difficulties are usually followed, rather than
reconstructions which can be seen to involve considerable expense
and delay. After a number of minor changes had been made in the
bearings, they were finally able to stand up fairly well under the
severe strain to which they were subjected when the engine developed
its full power, and no further changes were made in them; a defective
race being, however, replaced by a new one as occasion demanded.

These tests demonstrated very clearly that at speeds of approximately
1000 revolutions per minute ball-bearings which are subjected to
considerable loads should be calculated with a considerable margin
of safety, as the yielding of the frame, which must necessarily be
far from rigid, causes more or less error in the alignment of the
shafts and bearings, and this introduces considerably increased
strains on the bearings. In the early tests before the bearings were
strengthened, the balls in some of the races were on a few occasions
ground to a very fine powder before it was discovered that they had
failed. Such a result, it will be understood, could and did occur in
the course of a very minute length of time.

In imitating as nearly as possible the conditions to which the
carburetor of the engine would be subjected during the period of
launching, numerous tests were made in which the engine was brought
to its maximum speed and, without changing the adjustment of the
mixture-controlling devices of the carburetor, sudden blasts of air
were turned on it from various directions, and these were continued
until the mixture-control devices were perfected to such a point
that gusts of thirty miles an hour suddenly directed from any point
against any portion of the apparatus would in no way effect the
speed and power of the engine. These tests were considered necessary
in view of the very sudden changes in conditions to which the
aerodrome would be subjected during its brief run down the launching
track, the conditions changing in approximately three seconds from
absolute quiescence of the aerodrome to a plunge through space at
thirty-five feet per second. An aviator would be more than occupied
with maintaining control of himself and of the aerodrome, which at
the moment of leaving the track might require considerable change
in the adjustment of the Pénaud tail, and he would, therefore, not
be able to make any adjustments of the engine-control devices.
This supposition was entirely confirmed in the actual tests of the
aerodrome which are to be later described, the rush down the track
being [p254] so very brief that the engine could not have been given
any attention by the aviator had it needed it, which fortunately it
did not.

It is hardly necessary to recount at any length the great
difficulties which was experienced in these tests of the engine in
the aerodrome frame before the shafts, bearings, propellers, and,
in fact, the frame itself were all properly co-ordinated so that
confidence could be felt that all of the parts would stand the
strains which were likely to come on them when the aerodrome was in
flight. These tests were really not tests of the engine itself, but
of the frame, shafts, and bearings. Suffice it to say that nearly a
year was consumed by the various breakages of the shafts, bearings,
and propellers before it was felt that all of these parts could
be depended on, and even then the weakness of the bearings above
referred to was fully recognized. Had some of the better-grade balls
and steels for the bearings, which have since that time come on the
market, been obtainable then, there would have been no difficulty
with these bearings. However, this same remark might be made with
reference to nearly all of the details of the aerodrome, for it was
the accessories, such as bearings for the transmission and propeller
shafts, spark plugs, coils, batteries, and a suitable carburetor for
the engine, that caused the chief delay after the main difficulty of
getting a suitable engine had been overcome.

[p255]

CHAPTER XII
FIELD-TRIALS IN 1903

The extended series of shop tests which had occupied a considerable
portion of the late winter and early spring of 1903 had demonstrated
the following facts: First, with the aerodrome mounted on the
launching car, a propeller thrust of from 450 to 475 pounds could
be maintained indefinitely by the engine, and even when the engine
was delivering its full power to the propellers, the vibration was
so small as to cause no apprehension that the wings and rudder would
be made to vibrate sufficiently to produce undue strains in them.
Second, with the aerodrome suspended from the ceiling by springs
at the points at which the wings would be attached, the vibration
produced by the engine developing it’s full power was even less than
when the machine was mounted on the launching car and there was,
consequently, even less cause for concern that the wings and rudder
might be set in vibration when the machine was free in the air.
Third, the engine could be depended upon to deliver something over
52 horse-power when the five cylinders were working properly, and
even with one cylinder not working, but acting as a dead load against
the others, approximately 35 horse-power could be developed, while
with two cylinders not working at all, the three which were working
would deliver about 25 horse-power. Therefore, even assuming that two
of the five cylinders might become deranged during a flight, there
should still be sufficient power to propel the machine. These tests,
some of which had been witnessed by members of the Board of Ordnance
and Fortification, clearly demonstrated that the time had arrived
when it was safe to give the aerodrome a test in free flight. The
machine itself together with all its appurtenances and much extra
material for repairs in case of breakages, which previous experience
had shown to be almost certain, was accordingly taken from the shop
and placed on the house-boat preparatory to taking it down the river
to the point opposite Widewater, Va., which had already been selected
as the “experimental ground.”

Owing to the limited size of the shops it had been impossible to
place the wings and rudder in their proper positions on the aerodrome
and determine its balancing in a way similar to that practiced with
the models. The approximate settings for the wings and rudder had,
however, been determined by calculation from the data obtained in the
test of the quarter-size model, so that it remained only to place the
wings and a weight to represent the rudder actually on the machine
in the large space of the house-boat (which, however, was not large
enough to permit the rudder to be assembled along with the wings),
and thus check the balancing previously determined by calculation.
There were very [p256] few appurtenances which could be shifted in
balancing the aerodrome, but the proper disposition of weight had
been so accurately determined by calculation that the floats, which,
as will be seen from the various photographs, were merely cylindrical
tanks with pointed ends, and of a sufficient capacity to cause a
displacement great enough to float the aerodrome when it came down
into the water, proved sufficient ballast for shifting the center of
gravity to its proper point. The flying weight of the aerodrome was
830 pounds,[47] including the weight of the writer, which was 125
pounds. The total area of the wings or supporting surfaces was 1040
square feet, or the ratio of supporting surface to weight was 1.25
square feet per pound, which is the same as .8 pound per square foot.

After the balancing of the large aerodrome had been completed on the
house-boat, and everything else got in readiness as far as could be
done before actually arriving at the point at which the test was to
be made, the house-boat was towed down the river on July 14, 1903,
and fastened to its mooring buoy, which had been placed in the middle
of the river at a point practically opposite Widewater, Va., and
approximately forty miles from Washington. See Coast-Survey Chart,
Plate 85.

Sleeping quarters for the force of eight workmen and the regular
soldier from the United States Army, who had been detailed as a
special guard, had been provided on the boat, but owing to the lack
of space it had been found impracticable to arrange proper cooking
facilities on the boat, and it had been found necessary to arrange
to transport the workmen to Chopawamsic Island, near Quantico, Va.,
for their meals. It had been planned to use the twenty-five-foot
power launch for this purpose, but owing to the heavy storms which
became quite frequent soon after the house-boat was taken down the
river, it was found that the small launch was not sufficient, and
it was necessary to employ a tug-boat and keep it stationed there
at all times. This added very considerably to the expense of the
experiments, as the hire of this one tug-boat very nearly equalled
the pay-roll of the workmen, and while it was not expected that the
stay down the river would be so greatly prolonged as afterwards
proved the case it was felt certain that minor delays were sure to
occur and the experiments would at the very least require several
weeks.

[Illustration: PL. 85

LOCATION OF HOUSE BOAT IN CENTER OF POTOMAC RIVER, JULY 14, 1903

FROM SHEET NO. 3, U. S. COAST AND GEODETIC SURVEY CHART OF POTOMAC
RIVER, ISSUE OF 1882 SCALE 1 1-16 INCH TO STATUTE MILE]

Had it been possible to foresee the great delay which finally
occurred before the large aerodrome was actually launched, and the
great expense arising from the necessity of maintaining one or
more expensive tug-boats constantly, it is very certain that an
experimental station nearer Washington would have been selected,
even though the nearer places on the river which were available
were much less suitable, both on account of the river being much
narrower and the traffic very much heavier. In fact, at the time
that the house-boat was taken down the river on July 14, with the
expectation that the experiments with the [p257] large aerodrome
would certainly be concluded within four weeks, the expenses of the
work, which had been met from the Hodgkins Fund of the Smithsonian
Institution since the original allotment from the Board of Ordnance
and Fortification was exhausted more than a year previously, had
already made such heavy drafts on this fund that Mr. Langley was most
reluctant to draw further on it, even to the extent which seemed
necessary to meet the expenses of a month of “field-work.”

Before making the tests of the large aerodrome, it was intended to
give the quarter-size model a preliminary trial to test the balancing
which it was proposed to use on the large machine. For this test it
was planned to employ the small launching apparatus mounted on top
of the small house-boat, which had been used in the experiments with
the steam-driven models Nos. 5 and 6 in 1899, and later with the
quarter-size model in 1901. However, after arriving down the river,
it was found that the small house-boat which had been anchored at
Chopawamsic Island since the experiments in 1901 had deteriorated
to such an extent that it was unsafe to take it out into the river.
The launching apparatus for the model was, therefore, removed from
it and placed on the turn-table of the large house-boat, alongside
the launching track for the large machine. After completing this
transfer of the model-launching apparatus everything was thought to
be in readiness for a test of the quarter-size model, but upon making
a shop test of the model to make sure that its engine was working
properly, it was found impossible to get it to work at all. A few
explosions could be obtained once in a while, but very irregularly.
After spending considerable time in trying to locate the difficulty,
it was found that the commutator which distributes the high-tension
sparking current to the proper cylinder at the proper time was
short-circuited. This commutator had been made of “insulating fibre”
and had never caused any previous trouble. It was now found, however,
that the very damp atmosphere which had been experienced during the
preceding two weeks, when the fog for a large portion of the time
was so heavy that objects at a short distance across the water could
not be seen, had caused the moisture to penetrate the fibre and thus
destroy its insulating qualities. After much trouble some vulcanite
and mica were secured and a new commutator made to replace the fibre
one, and, then, after some minor difficulties had been remedied, the
engine for the model was got into good condition again. After getting
satisfactory shop tests on the model aerodrome, and having everything
in readiness for a flight, it was necessary to wait many days before
the weather was calm enough for a test. However, on August 8 the
weather quieted down and the model was launched at 9.30 a. m. into a
wind blowing about 12 miles per hour from E. SE.

Referring to Plate 86, which shows the quarter-size model mounted on
its launching car on top of the large house-boat, and which was taken
only a few [p258] minutes before the model was actually launched,
it will be noted that a board (‹A›) projects from the front of the
launching car. This board, which is mounted in a false floor of the
launching car, is so arranged that when it strikes the two blocks
(‹B›) at the end of the track it is driven backward in the car
against the triggers which prevent the uprights (‹D›), supporting
the aerodrome, from being folded down against the floor. When this
board strikes the triggers it releases them and the springs (‹C›),
which in this case were rubber bands, immediately fold the vertical
posts or uprights (‹D›) against the brace posts (‹E›), which are
immediately folded down flat against the floor of the car through
the action of the spring hinges, by which they are connected to it.
These uprights (‹D›), which support the aerodrome at the front and
rear, respectively, are not released until a fraction of a second
after the release of the clutch hook (‹F›), which is attached to
the middle upright (‹G›), and which, grasping the lower pyramid,
holds the machine down firmly against the uprights (‹D›) previously
referred to. In order to prevent the possibility of the aerodrome
being released prematurely while the car is held at the extreme
rear end of the track by the hook (‹H›), a steel pin (‹J›), which
can just be seen in the photograph, is pushed through a hole in the
board (‹A›), and into a hole in a cross-member on the bottom of the
car, thus holding the board in its proper position. After the engine
is started up one of the mechanics who has assisted in starting it
is under orders to remove the pin at the word “Ready,” and at the
word “Go” the other mechanic who has assisted in starting the engine
is under orders to release the hook (‹H›), and thus allow the car
to dash down the track. In the experiment on August 8 the mechanic
failed to remove the pin (‹J›) at the proper time, and it was only
after the machine had been released and started down the track that
it was seen that the pin had not been removed. It was then, however,
too late to stop it, so the car dashed down the track. Although the
striking of the board against the blocks caused the pin to split
the board to pieces, the launching apparatus worked perfectly and
the aerodrome started off on a perfectly even keel, the propellers
revolving at an exceedingly high rate of speed. The aerodrome flew
straight ahead for a distance of 350 feet, when it began to circle
towards the right, descending slightly as it circled. Upon completing
a quarter circle it again began to rise, flying straight ahead until
it had gone a similar distance, when it again lost headway, but
before it reached the water the engine increased its speed and the
aerodrome again rose. When the engine slowed down for the third time,
however, the aerodrome was not many feet above the river, so that
before the engine regained its normal speed the aerodrome touched the
water with its propellers still revolving, but very slowly. While
the total distance covered was only about 1000 feet, and the time
that it was actually in the air 27 seconds, yet in this brief time
it had served the main purpose for which it had been built, which
was to find out if the balancing of [p259] the large aerodrome,
which had been determined by calculation from the results obtained
with the steam-driven models, was correct. For it was assumed that
if the quarter-size model, which was an exact counterpart of the
large machine, should fly successfully with the same balancing as
that calculated for the large one, the large one could reasonably
be expected to act similarly. It was at first thought best to make
another test with the model immediately after recovering it from the
water, but by the time it could be brought into the house-boat and
the water which had got into the engine cylinders could be removed
and the engine made to work properly quite a strong wind had sprung
up and rendered further tests of the model on this day impossible.
If the launching track for the small machine could have remained
on the top of the boat without interfering with the completion of
the preparations for testing the large machine, it would have been
left there and other tests made with the model when the weather was
suitable, but as this could not be done without interfering with the
work on the large machine, and the delays with the model had already
been so great, the small track was immediately removed and the model
stored away in the house-boat for possible later tests.

At the first it was impossible to account for the engine on the
model running so irregularly and slowing down so soon after it was
launched, as it was felt very certain that the cylinders could not in
so short a time, and with the aerodrome actually moving through the
air, have heated up sufficiently to cause it. After a while, however,
one of the workmen volunteered the information that in his zeal to
fill the fuel tank completely so as to insure a long flight, he had
caused the tank to overflow so that some of the gasoline had run into
the intake pipe, and that he had noticed gasoline dripping from the
intake pipe as the machine went down the track. This excess gasoline
in the intake pipe had caused the mixing valve which controls the
quality of the explosive mixture to be improperly set, so that it
would not furnish the proper mixture when the fuel was supplied in
the proper way by the carburetor, and consequently when this excess
gasoline had evaporated, the mixture furnished to the engine was
not proper, and it consequently slowed down, there being no human
intelligence on board to correct the adjustment of the mixing valve.

A series of seven photographs of this flight of the quarter-size
model is given in Plates 87 to 93. Plate 87, taken with a kodak from
the tug-boat stationed several hundred yards directly ahead of the
house-boat, shows the machine in full flight heading directly for
the tug-boat. Although the aerodrome was about fifteen or twenty
feet higher above the level of the water than the camera, still, at
the considerable distance from which the photograph was taken, this
view would not show so much of the under side unless the machine had
been pointing upward. The photograph also proves very clearly that
at the time it was taken the machine had certainly not dropped at
all below the level [p260] at which was launched. In Plate 88 the
camera was unfortunately not well aimed, and only the front guy-post,
bearing points, float and bowsprit are visible, besides the blur of
the propellers, which, it will be noted, were moving very rapidly.
The camera with which this and the succeeding plates were taken was
one of the two special telephoto cameras belonging to the Zoological
Park, but built in the course of the aerodromic work and used where
especially rapid shutters were needed. As the shutters on these
cameras give an exposure of only 1/500 of a second, and consequently
are sufficiently rapid to show the individual feathers in a rapidly
moving bird’s wing, any distortion of the machine in flight would
certainly have been shown, but, as will be seen from the later
photographs, no distortion of any kind occurred, both the surfaces
and the framework remaining in a perfectly straight condition. Near
the bottom of Plate 88 is the tug from which Plate 87 was taken,
and a careful inspection of Plate 87 shows two persons standing on
the roof of the house-boat, below the upper works, the gentleman on
the left being Mr. Thomas W. Smillie, the official photographer of
the Smithsonian Institution, who took all of the photographs except
Plate 87, and, as stated above, used therefor the special telephoto
cameras with the rapid shutters. Plate 89 is an exceedingly good
view, and shows the propellers revolving very rapidly while Plates
90, 91 and 92 show very clearly that the speed of the propellers had
greatly decreased between the successive photographs. Plate 93 shows
the aerodrome shortly after it touched the water and had been almost
completely submerged, in spite of its floats, by the very strong tide
which was running. Though these plates show all that photographs
can, they give no adequate idea of the wonder and beauty of the
machine when actually in flight. For while the graceful lines of the
machine make it very attractive to the eye even when stationary,
yet when it is actually in flight it seems veritably endowed with
life and intelligence, and the spectacle holds the observer awed and
breathless until the flight is ended. It seems hardly probable that
anyone, no matter how skeptical beforehand, could witness a flight
of one of the models and note the almost bird-like intelligence with
which the automatic adjustments respond to varying conditions of the
air without feeling that, in order to traverse at will the great
aerial highway man no longer needs to wrest from nature some strange,
mysterious secret, but only, by diligent practice with machines of
this very type, to acquire an expertness in the management of the
aerodrome not different in kind from that acquired by every expert
bicyclist in the control of his bicycle.

[Illustration: PL. 86

QUARTER-SIZE MODEL AERODROME MOUNTED ON LAUNCHING-CAR]

[Illustration: PL. 87

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903]

[Illustration: PL. 88

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903]

[Illustration: PL. 89

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903]

[Illustration: PL. 90

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903]

[Illustration: PL. 91

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903]

[Illustration: PL. 92

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903]

[Illustration: PL. 93

QUARTER-SIZE MODEL AERODROME AT END OF FLIGHT, AUGUST 8, 1903]

In describing this flight immediately after it was made, Professor
John M. Manly, who took the photograph shown in Plate 87, said: “The
flight of the small aerodrome was an event which all who saw it will
remember for the rest of their lives. We were, of course, in a state
of considerable nervous excitement and tension, for, after weeks
of delay from high winds, rains, and [p261] other uncontrollable
causes, at last we had a day ideally suited to the test. This was,
to be sure, not the great test, the final test, the test of the
man-carrying flyer, but it was felt by all to be of almost equal
importance, for if the balancing of the small aerodrome was correct,
the large one would maintain its equilibrium, and the problem of
human flight would be solved practically as well as theoretically.
That the weather was now favorable for the test filled us with
excitement. Again and again the favorable moment had seemed to
come, and had gone again before we could make ready for it. The
aerodrome was rapidly carried to the upper works of the house-boat
and the observers and helpers went hastily to their positions. The
large tug-boat was stationed directly ahead, almost in the line of
flight, and about a mile from the house-boat. Signals of readiness
were exchanged, and with every sense astrain we awaited the supreme
moment. The rocket gave the starting signal, and instantly there
rushed towards us, moving smoothly, without a quiver of its wings,
with no visible means of motion and no apparent effort, but with
tremendous speed, the strange new inhabitant of the air. Onward it
moved, looking like a huge white moth, but seeming no creature of
this world, not only on account of its size, its ease of movement and
its wonderful speed, but also because of its strange, uncanny beauty.
It seemed visibly and gloriously alive as it advanced, growing
rapidly larger and more impressive. Straight at us it came, and for
a moment there was a wild fear that it would come right on and crush
itself against the ponderous tug-boat. There was a half impulse to
move the tug-boat out of its way, but the aerodrome seemed to realize
its danger and rapidly, though not abruptly or violently, as if it
had intelligence and power of self-direction, it checked its speed
and circled to the right, descending slightly. Soon it quickened
its speed again and went straight ahead for about ten seconds, when
it again checked its flight and descended, circling once more. Once
again it attempted to increase its speed and rise, but it was too
near the water, and in a few moments the waves had wet its propellers
and wings, and it sank, a poor, bedraggled creature. But the vision
of its beauty and power and seeming intelligence and life will long
remain with those who saw its flight.”

After removing the model-launching track so that the final
arrangements could be completed for testing the large machine, many
weeks of delay were experienced, almost entirely due to the unusually
bad weather conditions which prevailed, and which were unprecedented
for the time of the year. However, on September 3 the weather became
more suitable, and the aerodrome being in readiness the metal frame
of the large machine was hoisted to the top of the boat and placed
on the launching car, and the wings, rudder, etc., were then hoisted
up and properly assembled and everything made ready for a flight.
The parties with the telephoto cameras were sent to their stations
on the shore, where definite base lines had been marked out so
that with the data as to [p262] altitude and azimuth, which these
cameras automatically recorded, the speed, height, etc., of the
machine in flight could be accurately computed. After stationing the
tug-boats at proper points, so as to render assistance should the
aerodrome come down into the water at a considerable distance from
the house-boat, it was found, upon attempting to start the engine,
that for some reason it would not operate. The sparking battery which
had been placed at the extreme rear of the aerodrome was found to
be giving such a weak spark that it would not ignite the mixture
in the cylinders. Upon removing the connection which grounded the
terminal of the battery to the framework and replacing it by a large
copper wire leading up to the engine so as to decrease the resistance
of the circuit it was found that the battery still would not give
sufficient spark. A large quantity of dry cells, such as were used
for the engine, had been procured to insure against delay from
lack of batteries, but upon attempting to get a new set from this
reserve supply it was found that they, as well as the set that was
on the machine, had so deteriorated that instead of giving eighteen
amperes on short circuit they would give only three, which was not
a sufficient current to enable the engine to operate. No shop tests
on the large engine had been made since the large aerodrome had been
brought down the river, as no provision had been made for properly
supporting the aerodrome in the house-boat in such a way as to permit
the large propellers to whirl around without causing damage, and,
therefore, the batteries which had hitherto proved to be suitable had
not had any special test since they had been brought down the river.
As no batteries suitable for use were on hand, and as none could be
procured from a point nearer than Washington, the test had to be
abandoned for the day and the aerodrome removed to the interior of
the boat.

It was at first impossible to account for the rapid deterioration of
so large a number of dry cells, but it was later found that the damp,
penetrating fogs which had been experienced for nearly two months
were responsible for it, and that in order to preserve the batteries
in such a climate it was necessary to place them in metallic boxes
which could be nearly, if not quite, hermetically sealed. New
batteries were immediately procured from Washington, and before again
mounting the aerodrome on the launching track provision was made for
testing the engine inside the house-boat.

[Illustration: PL. 94

HOISTING WING OF FULL-SIZE AERODROME]

Up to this time the wings had been stored inside the house-boat by
suspending them from the ceiling, but the time required to hoist
them to the upper works on top of the boat, after the main body of
the aerodrome had been placed on the launching car preparatory to
making a flight, had added so greatly to the delay, and consequently
to the difficulty of getting the machine entirely ready for a flight
while the weather conditions remained suitable for a test, that it
was decided to build some framework on the upper works and cover it
with canvas so as to provide some boxes in which the wings could be
[p263] stored whenever it seemed probable that a flight would
soon be possible. Some of the difficulties experienced in hoisting
these wings from the interior of the boat to the upper works may be
appreciated by an inspection of Plate 94, where one of them is seen
just ready to be hoisted from the raft. Only one wing at a time could
be handled on the raft, even when there was no appreciable wind or
roughness of the water, so that in order to hoist all four wings the
raft had to be hauled around from the door at the end of the boat to
the side where the wing was hoisted, and back again four times every
time the machine was assembled preparatory to a flight. The necessity
for making occasional tests of the engine in order to make sure that
no trouble would be again experienced in having proper batteries,
etc., for the engine when the machine was again on the point of
being launched also made it imperative to remove the wings from the
interior of the house-boat, as the tremendous blasts of air from the
propellers would certainly have wrecked the wings had they remained
in the boat while the engine was being tested.

After the wings had been stored in the “wing boxes,” thorough tests
of the engine were made, and before there came another day which was
at all suitable for a trial, it was accidentally discovered that the
glued joints in the cross-ribs of the large wings had been softened
by the moisture of the fogs which had penetrated everything, and
that the joints had all opened up and left the ribs in a practically
useless condition.

It will be recalled from the description of these cross-ribs, Chapter
VI, that the rib is composed of two channel-shaped strips, the edges
of which are glued together while the strips are bent over a form
which causes the ribs to maintain the curved form desired after
the glue has hardened. Recalling these facts, it will be readily
understood that there is at all times a considerable strain on the
glued joints due to the two strips of wood trying to straighten
out, and, therefore, if the glue should at any time become softened
sufficiently to allow one strip to slide along on the other, the
joint would open up and the rib would consequently become straight.
When the construction of the hollow ribs was first contemplated it
was realized that although the hollow construction would enable the
ribs to be strong, and at the same time exceedingly light, yet it
would make it imperative that the ribs be covered with a water-proof
varnish in order to prevent the glue from being softened when the
aerodrome came down into the water, as it was expected from the first
that it would do at the end of its flight. Considerable time and
attention had, therefore, been given to this very problem of securing
a suitable water-proof varnish, and ribs coated with the varnish
which was finally used had been submerged in water for more than 24
hours in testing this very point, and no softening of the glue could
be detected after this long submergence. It had, therefore, been
felt that the ribs had been given a test which was much more severe
than any conditions which [p264] were likely to be met with, since
the aerodrome would, in no case which could be anticipated, be in
the water for so long a period as 24 hours, and no trouble from this
source need be anticipated.

In the present case, however, the moisture of the atmosphere, which
had been heavily laden with fog for several weeks, had penetrated
the varnish and softened the glue, even though the submergence of 24
hours in water had shown no effect. To construct new ribs for the
wings would have required several weeks, and the delays which had
already been experienced had by this time prolonged the stay down
the river so greatly that even under the very best conditions it
seemed hardly possible to complete the tests before the coming of
the equinoxial storms, which would make it necessary to remove the
boat from the middle of the river and place it in a safe harbor.
Something, therefore, had to be done, and that very quickly, so
that an immediate test could be made, or else the tests would have
to be delayed until the following season, or possibly postponed
indefinitely on account of the lack of funds.

Owing to the varnish with which the ribs were covered, it was
impossible in repairing them to carry out the first plan which
suggested itself of binding the ribs with a strip of cloth
impregnated with glue and wound spirally from end to end. As the wood
was so very thin, it was impossible to bind the two parts together
with wire, and even thin bands of metal driven up on the tapered
portion of the rib were not likely to draw the two strips together
without crushing the wood. What was finally done was to scrape the
edges of the two strips where the joint had opened, thereby removing
all the old glue, and after putting fresh glue on all these edges the
two strips were drawn together and bound with surgeons’ tape, which
was found to adhere very firmly even to the varnished surface.

After repairing the ribs in this manner and readjusting the guy-wires
of their framework so as to make the wing assume the correct
form, which had been slightly altered by the warping and twisting
consequent on the opening up of the ribs, everything was again in
readiness for a test in free flight, numerous tests of the engine
having meanwhile been made both with the aerodrome frame inside of
the house-boat and also when mounted on the launching track above.
The weather, which had been unprecedentedly bad all summer, now
became even worse, and although short periods of calm lasting an
hour or less occasionally occurred, there were for several weeks no
calm periods long enough for completing the necessary preparations
and making a test, although the time required for assembling the
aerodrome had been greatly shortened by building the “wing boxes”
on the superstructure, and in other ways previously described. On
several occasions when an attempt was made to utilize what appeared
to be a relative calm, the aerodrome was assembled on the launching
apparatus and everything got in readiness except the actual fastening
of the [p265] wings and rudder to it, but in every instance, before
the wings could be actually applied and a flight made, the wind
became so strong as to absolutely prohibit a test. On two occasions
when the wings were actually attached, heavy rain storms suddenly
came up and drenched the machine before the wings could be removed,
and on several occasions it was necessary to leave the entire metal
frame and engine of the aerodrome mounted on top of the boat all
night, because the heavy sea which was running made it impossible to
utilize the large raft in returning the frame to the interior of the
boat.

Finally, however, after it seemed almost useless to hope for calm
weather, what appeared to be a most propitious day arrived on October
7. The wind which had been quite high in the early morning gradually
quieted until at 10 a. m. it was blowing only about twelve miles
per hour and the indications were that it would quiet down still
more. Every energy was concentrated in getting the aerodrome ready
at the earliest possible moment, as previous experience had shown
too clearly that the conditions might be completely reversed in less
than an hour. As the tide and wind caused the boat to swing up the
river from its buoy, and thus made the launching track point down
the river, the steam tug-boat was sent down the river for a distance
of a mile or more so that, should the aerodrome come down into the
water without being able to make a return trip to the house-boat,
the tug-boat would be able to reach it quickly and render assistance
to both the writer and the machine should they need it. At 12.20 p.
m. everything was in readiness and what appeared to be the decisive
moment had arrived, when the writer, after starting up the engine
and gradually raising its speed to the maximum, and after taking the
last survey of the whole machine to insure that everything was as it
should be, finally gave the orders to release it.

Although the writer did not have the privilege of seeing it glide
down the track, as his attention was too thoroughly engaged in
insuring that he was in the proper position for reaching immediately
any of the control apparatus, either of the aerodrome or of the
engine, yet those who did witness the actual passage of the machine
down the track have said that the sight was most impressive and
majestic. No sign of jar was apparent when the machine was first
released, but with lightning-like rapidity it gathered its speed as
it rushed down the sixty feet of track, the end of which it reached
in three seconds, at which time it had attained a speed of something
over thirty-two feet per second. Just as the machine reached the end
of the track the writer felt a sudden shock, immediately followed
by an indescribable sensation of being free in the air, which had
hardly been realized before the important fact was intuitively felt
that the machine was plunging downward at a very sharp angle, and he
instinctively grasped the wheel which controls the Pénaud tail and
threw it to its uppermost extent in an attempt to depress the rear of
the machine and [p266] thereby overcome the sharp angle of descent.
Finding that the machine made no response to this extreme movement
of the tail, he immediately realized that a crash into the water was
unavoidable and braced himself for the shock. The tremendous crash of
the front wings being completely demolished as they struck the water
had hardly become apparent before he found himself and the machine
plunging downward through the water. By some instinct he grasped
the main guy-wires which were above his head, and pulling himself
through the narrow space between them freed himself from the machine
and swam upward as rapidly as possible. A few moments after reaching
the surface of the water the uppermost point of the pyramid of the
machine was seen to project from the water and he swam over and sat
down on it until a row-boat could be sent to it from the nearby
power-boat.

The first thing that the writer saw after looking around him was a
newspaper reporter, his boatman expending the utmost limit of his
power in pushing his boat ahead to be the first one to arrive.

After giving directions to the workmen regarding the recovery of
the machine, the writer returned to the house-boat to obtain dry
clothing, and although his first inclination was not to make any
statement until a complete examination could be made to determine
both the cause of the lack of success and also the extent of the
damage which had been sustained by the machine, yet owing to the very
great pressure brought to bear by the press representatives who said
that unless some statement was given out they would write their own
conclusions as to the cause of the mishap, he finally gave out the
following statement:

STATEMENT MADE BY MR. MANLY TO ASSOCIATED PRESS

“It must be understood that the test to-day was entirely an
experiment, and the first of its kind ever made. The experiment
was unsuccessful. The balancing, upon which depends the success of
a flight, was based upon the tests of the models and proved to be
incorrect, but only an actual trial of the full-size machine itself
could determine this. My confidence in the future success of the work
is unchanged. I can give you no further information. I shall make a
formal report to Secretary Langley.”

[Illustration: PL. 95

FLIGHT OF LARGE AERODROME, OCTOBER 7, 1903]

[Illustration: PL. 96

FLIGHT OF LARGE AERODROME, OCTOBER 7, 1903

PHOTOGRAPH BY T. W. SMILLIE]

After recovering the machine the foreman of the workmen (Mr. Reed)
[who together with Mr. McDonald were the only ones on top of the
boat when the launching actually took place], busied himself to
discover what had caused the jerk to the machine at the moment it was
released, which had been immediately followed by the great depression
of the front end. After some little time he discovered that the
upright guide at the extreme front of the launching car (which, as
heretofore stated, was slotted to receive a metal lug projecting from
the end of the guy-post, and thus prevent the front end of the [p267]
framework from being twisted by a side wind striking the machine
while it was still on the launching car) had been distorted, the
metal cap on it being stretched out of shape in a way which indicated
that the pin of the front guy-post had hung in the cap, and that the
guy-post was not therefore free from this part of the car when the
end of the launching track dropped. The shock which the writer felt
at the moment of launching and which had also been seen by others to
occur was thus conclusively shown to have been due to the falling
track, dragging the front end of the machine down with it. As the
machine was travelling forward and the car had been almost instantly
brought to a standstill by its buffer pistons co-acting with the
buffer cylinders at the foot of the track, this front guy-post had
been pulled backwards, and thus not only pulled the main guy-wires
of the wings backwards and thereby depressed the front edge of
the front wings so that they had no angle of inclination, but had
also bent the front end of the metal framework downward,--effects
which were discovered from the later examination of the frame and
the guy-post itself. From the instantaneous photographs which were
obtained, indisputable evidence was obtained that this was what
actually occurred. Referring to the photograph, Plate 95, which was
taken by Mr. G. H. Powell, Secretary of the Board of Ordnance and
Fortification, and which shows the machine just a few feet in front
of the point where it was actually launched, it will at once be
seen that the front end of the frame is bent downward and that the
front guy-post instead of being parallel with the rear one has been
deflected backward at the lower end through an angle of 30 degrees.
Referring further to the photograph, Plate 96, which was taken at
the same instant as the one just described, it will be seen that
even this one, which is a view of the machine as it passed almost
directly over Mr. Smillie’s head, most clearly shows the extreme
extent to which the front wings had been distorted, the rear edges of
the wings near the frame having been twisted up until they struck the
cross-frame, and the outer ends being free to twist had been forced
up very much higher.

After completing the recovery of the machine and the examination
as to the extent of the injuries it had sustained, and finding
unquestionable evidence that the accident had been caused by the
front guy-post hanging in its guide block on the launching car, the
workmen were set to work straightening out and arranging the various
parts, fittings and accessories, and cleaning up the engine which
fortunately had sustained no injury whatever. After a consultation
in Washington with Mr. Langley, who had been unable to be present at
the experiment, both concerning what had already occurred and also
what should be done regarding the future of the work, and in view
of the fact that the statement which the writer had given to the
press representatives, immediately after the accident, had been made
before there had been time to make an examination of the machine
itself, it was decided that it would be best to give to the press
[p268] a short statement to correct the earlier one, and Mr. Langley
accordingly made public the following note:

“Mr. Langley states that he was not an eye witness of the experiment
at Widewater yesterday, having been detained in Washington by
business, but that on the report of Mr. Manly, immediately in
charge, he is able to say that the latter’s first impression that
there had been defective balancing was corrected by a minuter
examination, when the clutch, which held the aerodrome on the
launching ways and which should have released it at the instant of
the fall, was found to be injured.

“The machinery was working perfectly and giving every reason to
anticipate a successful flight, when this accident (due wholly to
the launching mechanism) drew the aerodrome abruptly downward at the
moment of release and cast it into the water near the house-boat.
The statement that the machine failed for lack of power to fly was
wholly a mistaken one.

“The engine, the frame and all the more important parts were
practically uninjured. The engine is actually in good working order.
The damage done was confined to the slighter portions, like the
canvas wings and propellers, and these can be readily replaced.

“The belief of those charged with the experiment in the ultimate
successful working of the machine is in no way affected by this
accident, which is one of the large chapter of accidents that beset
the initial stages of experiments so novel as the present ones.
It is chiefly unfortunate in coming at the end of the season when
outdoor work of this sort is impossible.

“Whether the experiments will be continued this year or not has not
yet been determined.”

In view of the many inaccurate accounts published in the daily press
at the time of this experiment, special attention is directed to the
fact that even under the enormous strain to which the aerodrome was
subjected, due to its striking the water at an angle of approximately
forty-five degrees and at a speed certainly not less than forty miles
an hour, no bending or distortion of any kind was found in the frame
after it was recovered, except that a slight depression at the front
had been produced by the lower guy-post catching on the launching
car, as previously described. This is very clearly seen in Plate 97,
Fig. 1, which shows the aerodrome being hoisted from the water, and
in Plate 97, Fig. 2, which shows it just afterwards resting on the
raft, the wings, tail and rudder having been completely demolished by
towing it through the water to the house-boat from the place where it
struck the water. This single distortion, therefore, was in no way a
result of the strains experienced by the frame either while it was
in the air or when it struck the water. Some of the press reports,
and, in fact, some of the accounts published in the scientific press,
stated that the aerodrome frame had proved so weak that it broke
while the machine was in the air, and that this was the cause of the
accident. Nothing could be farther from the actual facts than this,
for though there were many things connected with the machine which
could not be properly tested until it was actually in the air, yet
the strength of the frame had been most thoroughly [p269] tested in
the shops prior to the trial, and it had been found that with the
frame supported only at the extreme front and rear, no appreciable
deflection was produced upon it by the concentrated weight of four
men at the center, even when they simultaneously jumped up and
down on it. That the aerodrome frame was amply strong was further
evidenced by the fact that in the later trial, hereafter described,
no injury was sustained by the frame even when the machine turned
over in mid-air and struck the water flat on its back. In fact, no
point regarding the aerodrome is more certain than that the frame was
more than strong enough for its purpose.

Plates 98 to 100 show the aerodrome in the water from the moment
after it arose and the writer, who had extricated himself while it
was plunging down through the water and beat it to the surface,
had swum over to it and sat down on the upper pyramid to await a
row-boat, until the machine was taken in tow by the tug-boat.

As the weather conditions were continually growing worse, owing
to the lateness of the season, it was decided that it would be
absolutely impossible to undertake to keep the house-boat down the
river until the aerodrome could be repaired and another test made,
and the writer accordingly returned to Quantico on the following
day, expecting to take the tug-boat from there to the house-boat
and complete arrangements for bringing everything to Washington.
On reaching Quantico, however, it was found that a most violent
storm was raging on the river, and had, in fact, been increasing
in violence since the evening of October 7, immediately following
the trial. On account of the storm it was impossible to reach the
house-boat or to get into communication with the workmen, who had
sought refuge at the hotel at Clifton Beach, as the tug-boat itself
was not at the point at which it was expected to be found, and, in
fact, it had not been seen by any of the river people since the
morning of October 8, when it was seen taking the workmen from the
boat to Clifton Beach. Two days later, or October 11, when the storm
had subsided and the tug-boat, which had been blown many miles
down the river, was able to return the workmen to the house-boat,
it was found that the storm had made a complete wreck of all the
row-boats, the power-launch, and the large raft. The row-boats had
been completely demolished on the beaches, the launch had been broken
from its moorings to the house-boat and driven ashore some four miles
down the river, where it was found with the deck torn completely
off, a large hole stove in it amidships, and the engine seriously
damaged, while the raft had been very seriously damaged on the beach
many miles down the river. After making temporary repairs to the raft
and getting it launched, it was used as a floating dock for making
temporary repairs on the power-launch; both were then returned to
their moorings at the house-boat and everything got in readiness
for towing the house-boat to Washington, and this was finally
accomplished on October 12. [p270] Even while the boat was en route
some of the workmen were busily engaged in the repair of the damaged
parts, the others having been sent ahead to Washington to begin work
on the construction of new wings, so that another trial could be had
at the earliest moment that the weather would permit.

One extra pair of wings was on hand, but these had been stored in the
house-boat while it was down the river, and the damp weather, which
had caused such serious damage to the cross-ribs of the wings which
were actually used, had also so seriously affected the ribs of these
extra wings that it was necessary to discard some of them and repair
the others. An extra Pénaud tail was on hand, as well as a steering
rudder, and it was estimated that unless some unforeseen delay
occurred the aerodrome would be ready for flight in three weeks.

After making a careful examination of the places on the river which
seemed most available for an experiment, it was finally decided to
make the next test just off the Potomac Flats, at the junction of
the main body of the river and the Eastern Branch, the traffic on
this part of the river, which would have been more dangerous and
troublesome during the summer, being quite light at this time of the
year. By making the experiment at this point it was possible to leave
the house-boat at its dock until the weather seemed suitable and then
have a tug-boat tow it to the exact point, which would be determined
by the state of the wind and the tide.

After more completely examining the condition of the framework of
the machine, and discussing and maturely deliberating on the causes
which had led to the accident of October 7, the writer advised Mr.
Langley not to make any changes either in the machine itself or in
the launching apparatus, except to remove the small lug from the
metal rod which projected from the end of the guy-post, and which
by catching in its guide on the launching car had been the sole
cause of the accident. The aerodrome was accordingly repaired so
as to reproduce exactly the conditions which obtained at the time
of the previous experiment, except for this slight change, and it
was again ready for trial by the middle of November. The weather,
however, at this time was very variable, there being at times
comparatively quiet periods which lasted for only an hour or less,
which was not sufficient time for procuring a tug-boat and towing
the boat to the proper point, and then assembling the aerodrome and
making a trial. However, after many days waiting, what appeared
to be an exceptionally quiet day occurred on December 8, the wind
quieting down by noon to such an extent that practically a dead calm
prevailed. Vigorous search was immediately instituted for a tug-boat
to tow the house-boat to the point selected, but it was very late in
the afternoon before one could be procured, and by the time the boat
arrived at the proper place darkness was descending and a strong
[p271] and exceedingly gusty wind had sprung up, and it seemed
almost disastrous to attempt an experiment.

[Illustration: PL. 97

AERODROME BEING RECOVERED, OCTOBER 7, 1903]

[Illustration: PL. 98

AERODROME IN WATER, OCTOBER 7, 1903]

[Illustration: PL. 99

AERODROME IN WATER, OCTOBER 7, 1903]

[Illustration: PL. 100

AERODROME IN WATER, OCTOBER 7, 1903]

However, the funds which had been appropriated by the Board of
Ordnance and Fortification had been exhausted nearly two years
before, and all the expense since that time had been met from a
special fund of the Smithsonian Institution. But, owing to the
heavy drains which the work had made upon this fund, Mr. Langley
felt unwilling to draw further upon it, and since there were no
other funds available from which to meet the expenses which would
be incurred by postponing the experiments until spring, it was
decided that it was practically a case of “now or never,” and
although the river was full of large blocks of floating ice several
inches thick, which added enormously to the danger involved in the
experiment, the writer decided to make the test immediately so that
the long-hoped-for success, which seemed so certain, could be finally
achieved.

After considerable delay, due to the great difficulty of properly
assembling the huge wings in the strong and gusty wind, into which
the boat could not be kept directly pointed, owing both to the
strong tide which was running and to the fact that the wind itself
was rapidly varying through as great a range as ninety degrees, and
after many minor delays, due to causes too numerous to mention, the
aerodrome was finally ready for test.

The wind was exceedingly gusty, varying in velocity from twelve to
eighteen miles per hour and shifting its direction most abruptly and
disconcertingly, so that the aerodrome was at one moment pointed
directly into it and at the next moment side gusts striking under the
port or starboard wings would wrench the frame severely, thus tending
to twist the whole machine from its fastenings on the launching car.
After starting up the engine and bringing it to full speed, the
writer gave the signal for the machine to be released, and it started
quietly, but at a rapidly accelerated pace, down the launching track.
Exactly what happened, either just before or just as the aerodrome
reached the end of the track, it has been impossible to determine,
as all the workmen and visitors had gone to their stations on the
various auxiliary boats, except the two workmen (Mr. Reed and Mr.
McDonald) who had been retained on top of the boat to assist in the
launching. It had grown so dark that the cameras of Mr. Smillie, the
official photographer, were unable to get any impression when he used
them, owing to the extreme rapidity of the shutters with which they
were equipped. Fortunately, one photograph of the machine while still
in the air was secured, which shows the result of what had occurred
in the launching and before any further damage had been caused by its
coming down into the water, but the all-important question as to just
what caused the accident which did occur remains to a certain extent
a mystery. [p272]

Mr. Reed, the foreman, who was qualified to observe accurately, not
only through his having worked continuously for many years on the
machines, but also from his having witnessed the numerous tests of
the models, states that from his position near the rear end of the
launching track he noticed that at a point about ten feet before
the machine reached the end of the track the Pénaud tail seemed to
have dropped at the rear end in some inexplicable way so that it
was dragging against the cross-pieces of the track, and that at the
next instant, when the car reached the end of the track, he saw the
machine continue onward, but the rudder and whole rear portion of the
frame and the wings seemed to be dragging on the launching car. Mr.
McDonald, the head machinist, states that he had his attention so
concentrated on the engine, which he noticed was working perfectly
and driving the propellers at a higher rate of speed than he had ever
before seen it do, that he did not see anything happen until he saw
the machine shoot upward in the air, gradually attaining a vertical
position with its bow upward, where it was sustained for a few
moments by the upward thrust of the propellers. After a few moments,
however, the strong wind, which was blowing from twelve to eighteen
miles an hour directly ahead and acting against the wings which were
now vertical, drove the machine backwards towards the house-boat,
and he saw it come down into the water on its back, with the writer
gradually righting himself in accordance with the turning of the
machine until he was finally hidden from view by the machine coming
down on top of him. The witnesses on the tug-boats seem not to have
been able to perceive exactly what occurred. All unite in stating
that something seemed to happen to the machine just a few feet before
the launching car reached the end of the track, but what it was they
could not say. Everyone who saw the accident and who was sufficiently
familiar with the construction of the machine to be able intuitively
to form an idea as to just what was taking place was so very close
to the machine that when the accident happened everything seemed to
merge into one vision, which was that of the whole rear of the wings
and rudder being completely destroyed as the machine shot upward at
a rapidly increasing angle until it reached the vertical position
previously mentioned.

The writer can only say that from his position in the front end of
the machine, where he was facing forward and where his main attention
was directed towards insuring that the engine was performing at its
best, he was unable to see anything that occurred at the rear of
the machine, but that just before the machine was freed from the
launching car he felt an extreme swaying motion immediately followed
by a tremendous jerk which caused the machine to quiver all over,
and almost instantly he found the machine dashing ahead with its
bow rising at a very rapid rate, and that he, therefore, swung the
wheel which controls the Pénaud tail to its extreme downward limit
of motion. Finding that [p273] this had absolutely no effect, and
that by this time the machine had passed its vertical position and
was beginning to fall backwards, he swung himself around on his arms,
from which he supported himself, so that in striking the water with
the machine on top of him he would strike feet foremost. The next few
moments were for him most intense, for he found himself under the
water with the machine on top of him, and with his cork-lined canvas
jacket so caught in the fittings of the framework that he could
not dive downward, while the floor of the aviator’s car, which was
pressing against his head, prevented him from coming upward. His one
thought was that if he was to get out alive he would have to do so
immediately, as the pressure of the water on his lungs was beginning
to make itself seriously felt. Exerting all of the strength he could
muster, he succeeded in ripping the jacket entirely in two and thus
freeing himself from the fastenings which had accidentally held him,
he dived under the machine and swam under the water for some distance
until he thought he was out from under the machine. Upon rising to
the surface his head came in contact with a block of ice, which
necessitated another dive to get free of the ice. Upon coming to the
surface of the water he noticed Mr. Hewitt, one of the workmen, just
about to plunge in; before he could call out to indicate he was safe,
Mr. Hewitt had heroically plunged in with the expectation of diving
under the machine where he believed the writer to be entangled.
Finding the house-boat was being rapidly shoved upon him, imperilling
the life of both himself and Mr. Hewitt, besides the safety of the
aerodrome, the writer gave orders that the tug-boat reverse and tow
the house-boat away. Then, with the assistance of a row-boat, he
reached the house-boat, where willing hands drew him on board and
assisted him into dryer and warmer clothing.

Meanwhile, it had become quite dark, and when the writer went outside
to see about the aerodrome he found that the men on the tug-boat, in
their zeal to render assistance, had fastened a rope to the rear end
of the machine, at the same time pulling it in the direction in which
the front end was pointed, and through their ignorance had forced it
down into the muddy bottom of the river and broken the main framework
completely in two, thus rendering it absolutely impossible with the
facilities at hand to remove it from the water to the interior of
the boat. It was finally necessary to tie the wrecked machine to the
stern of the house-boat and have the boat towed to its dock where the
mast and boom were assembled and the wrecked machine hoisted from
the water. This was finally accomplished about midnight, when the
workmen, who had been working at a fever heat all day, were glad to
close up the work for the day, which had proved so unfortunate.

[Illustration: PL. 101

ATTEMPTED LAUNCHING OF AERODROME, DECEMBER 8, 1903

ENLARGEMENT OF PHOTOGRAPH BY THE WASHINGTON STAR]

As has already been remarked, darkness had descended to such an
extent that the light was not strong enough to give photographs
with the very rapid shutters with which Mr. Smillie had his cameras
equipped, and that, therefore, [p274] incontrovertible evidence,
which the instantaneous photographs had given as to just what
had occurred to the machine in the accident of October 7, was in
this case unfortunately lacking. It was at first thought that no
photographs had been obtained while the machine was actually in
the air, but it was later found that by some rare fortune the
photographer for ‹The Washington Star› had secured a photograph,
which, while small, showed very distinctly some decidedly interesting
facts. An enlargement of this photograph is shown in Plate 101, by
the kind permission of ‹The Washington Star›. Referring to this
photograph, it will be seen that at the moment it was taken the
machine was practically vertical in the air, and it confirms the
testimony of the eye witnesses, and also the writer’s impression
that the machine was maintained in a vertical position for several
moments by the upward thrust of the propellers. It will also be seen
that the Pénaud tail has been completely demolished and is hanging as
a limp roll of cloth, which the strong wind has deflected backwards
towards the house-boat, the port rear wing has broken its main ribs,
both where they are attached to the main frame and also about midway
the length of the wing, the outer end being partially folded towards
the frame. The starboard rear wing has also broken both of its main
ribs at the point where they are joined to the frame, and they have
also broken at a point about one-third their length from the frame,
the outer end being likewise folded towards the frame. By a still
more careful inspection, it will also be seen that the port front
wing is apparently uninjured, while the starboard front wing has
broken the middle main rib at a point between the sixth and seventh
cross-ribs, and while it cannot be distinctly seen at first that
the front main rib has also broken at the same point very careful
inspection will show that this is the case, as the sixth and seventh
ribs, showing as faintly darker lines in the photograph, are seen to
be displaced, so that they are together and actually crossing each
other. It will furthermore be seen that both front wings have been
pressed upward by the wind until their tips near the inner ends are
in contact with the cross-frame. This could not have happened unless
the front guy-post had given away either by bending or breaking. The
fact that it has given way is further evidenced by a more careful
examination of the extreme front end of the machine, where it will be
seen that the bowsprit and the curved tubes which form the extreme
end of the steel frame have been bent from a straight line with
reference to the main frame. This bending of the bowsprit and the
curved tubes could be produced only by the front guy-post coming in
contact with some obstruction on the launching car as the machine
left it. It is known very certainly that the rear end of the machine
came in contact with the launching car, as the car itself shows a
very deep gash in the wooden cross-piece at its center, which was
produced by the port-bearing point at the rear striking it. As this
bearing point was elevated five feet above the cross-piece of the
launching car, and was also six feet six inches to [p275] the rear
of the point where the wood is torn, this rear-bearing point must
have travelled downward at an angle of approximately thirty-eight
degrees in order for the bearing point to strike the car at this
point. As the lower end of the rear guy-post was only eighteen inches
above the cross-piece of the launching car, it, of course, would be
broken before the bearing point could descend so much. As has been
previously stated, Mr. Reed, who was at the rear of the launching
track, states very positively that the rudder was dragging on the
track at least ten feet before the launching car reached the front
end of the track where the machine was actually launched. There
are several ways in which the rudder could have gotten down on the
track, but positive information is lacking. If it was dragging on
the track, as Mr. Reed states (and from his extended experience and
rather acute powers of observation I should place great credence in
his report), the subsequent demolition of the guy-posts succeeded by
the destruction of the rear wings and serious injury of the front
ones is easily explained. If the dropping of the rudder on the track
occurred from the breaking of the upper rudder post, over which the
upper control wire passed, the lower vertical surface would first
come in contact with the track, and the destruction of this part
would certainly occasion subsequent destruction of the horizontal and
upper vertical surfaces of the rudder, leaving the central rib of
the rudder still attached to the frame, and upon the machine being
released from the car a few moments later this destroyed rudder would
easily catch in the launching car and pull the aerodrome down on it,
and thus cause the destruction of the guy-posts, wings, and so forth.
If the dropping of the rudder was caused primarily by its main rib
breaking loose from its connection with the frame, the rudder would
still be dragged along behind the machine by the wire cords through
which it was operated, and the subsequent launching of the machine
would still give the rudder every chance to catch in the launching
car and drag the machine down on it.

It can therefore be said that, while positive information is lacking,
there is very strong evidence that the accident in the launching
was due to the rudder becoming entangled with the launching track
owing to the breakage of some part of the mechanism by which it was
connected to the main frame.

It is of importance to note that the photograph furnishes
incontrovertible evidence that the main frame of the machine was in
no way injured, except for the slight bending of the forward curved
extension, and that, therefore, the accident was in no way due to
the weakness of the frame. The main frame was not even injured by
the machine coming down in the water on its back, and the later
damage was entirely caused by the combination of the ignorance of the
tug-boatmen and the darkness in which they were working, when they
attempted to tow it to the rear of the house-boat so that it could be
removed from the water. [p276]

On the day following the trial a very careful inspection was made
in the hope of obtaining some more definite information as to just
what caused the accident, but the serious injury to the machine
caused by the tug-boatmen breaking it in the water had so greatly
tangled things up that it was impossible to tell anything about
it. The workmen were immediately put to work removing fittings
from the broken wings, rudder, etc., and dismounting the engine,
which was immediately reassembled on its testing frame and found to
be absolutely uninjured. The transverse frame of the machine was
comparatively uninjured, the damage done by the men on the tug-boat
being the breaking of the machine in two at a point just back of the
cross-frame, together with the consequent destruction of the bearing
points, “trestle,” and certain fittings by which the main guy-wires
were attached to the main tubes and pyramids.

The situation which now existed was most distressing and
disheartening. Mr. Langley felt that he could not approve of further
expenditures from any Smithsonian fund, and the Board of Ordnance and
Fortification of the War Department having been severely criticised
on the floors of Congress for its original allotment for the work,
deemed it inexpedient to incur a possible curtailment of the funds
annually placed at its disposal for general experimental work through
a manifestation of continued interest in the flying machine.

As has already been stated, representatives from the Board of
Ordnance and Fortification of the War Department were present at
both tests of the large aerodrome; on October 7 Major Montgomery
M. Macomb and Mr. G. H. Powell, and on December 7 General W. F.
Randolph accompanied by Major Macomb and Mr. Powell, represented the
War Department, and Dr. F. S. Nash, at that time Contract Surgeon,
U. S. A., was officially present at both trials to render medical
assistance should it be needed.

By permission of the War Department, the official report of the tests
submitted by Major Macomb to the Board of Ordnance and Fortification
is here made public:

Enc. 1st to 3d end’t, BOF 6191.

REPORT

Experiments with working models which were concluded August 8 last
having proved the principles and calculations on which the design
of the Langley aerodrome was based to be correct, the next step
was to apply these principles to the construction of a machine of
sufficient size and power to permit the carrying of a man, who could
control the motive power and guide its flight, thus pointing the
way to attaining the final goal of producing a machine capable of
such extensive and precise aerial flight, under normal atmospheric
conditions, as to prove of military or commercial utility.

Mr. C. M. Manly, working under Prof. Langley, had, by the summer of
1903, succeeded in completing an engine-driven machine which under
favorable [p277] atmospheric conditions was expected to carry a man
for any time up to half an hour, and to be capable of having its
flight directed and controlled by him.

The supporting surface of the wings was ample, and experiment showed
the engine capable of supplying more than the necessary motive power.

Owing to the necessity of lightness, the weight of the various
elements had to be kept at a minimum, and the factor of safety in
construction was therefore exceedingly small, so that the machine
as a whole was delicate and frail and incapable of sustaining any
unusual strain. This defect was to be corrected in later models
by utilizing data gathered in future experiments under varied
conditions.

One of the most remarkable results attained was the production of a
gasoline engine furnishing over fifty continuous horse-power for a
weight of one hundred and twenty pounds.

The aerodrome, as completed and prepared for test, is briefly
described by Prof. Langley as “built of steel, weighing complete
about seven hundred and thirty pounds, supported by one thousand and
forty feet of sustaining surface, having two propellers driven by a
gas engine developing continuously over fifty brake horse-power.”

The appearance of the machine prepared for flight was exceedingly
light and graceful, giving an impression to all observers of being
capable of successful flight.

On October 7 last everything was in readiness, and I witnessed the
attempted trial on that day at Widewater, Va., on the Potomac. The
engine worked well and the machine was launched at about 12.15 p. m.
The trial was unsuccessful because the front guy-post caught in its
support on the launching car and was not released in time to give
free flight, as was intended, but on the contrary, caused the front
of the machine to be dragged downward, bending the guy-post and
making the machine plunge into the water about 50 yards in front of
the house-boat. The machine was subsequently recovered and brought
back to the house-boat. The engine was uninjured and the frame only
slightly damaged, but the four wings and rudder were practically
destroyed by the first plunge and subsequent towing back to the
house-boat. This accident necessitated the removal of the house-boat
to Washington for the more convenient repair of damages.

On December 8 last, between 4 and 5 p. m., another attempt at a
trial was made, this time at the junction of the Anacostia with the
Potomac, just below Washington Barracks.

On this occasion General Randolph and myself represented the Board
of Ordnance and Fortification. The launching car was released at
4.45 p. m., being pointed up the Anacostia towards the Navy Yard.
My position was on the tug Bartholdi about 150 feet from and at
right angles to the direction of proposed flight. The car was set
in motion and the propellers revolved rapidly, the engine working
perfectly, but there was something wrong with the launching. The
rear guy-post seemed to drag, bringing the rudder down on the
launching ways, and a crashing, rending sound, followed by the
collapse of the rear wings, showed that the machine had been wrecked
in the launching, just how, it was impossible for me to see. The
fact remains that the rear wings and rudder were wrecked before the
machine was free of the ways. Their collapse deprived the machine
of its support in the rear, and it consequently reared up in front
under the action of the motor, assumed a vertical position, and then
toppled over to the rear, falling into the water a few feet in front
of the boat. [p278]

Mr. Manly was pulled out of the wreck uninjured and the wrecked
machine was subsequently placed upon the house-boat, and the whole
brought back to Washington.

From what has been said it will be seen that these unfortunate
accidents have prevented any test of the apparatus in free flight,
and the claim that an engine-driven, man-carrying aerodrome has been
constructed lacks the proof which actual flight alone can give.

Having reached the present stage of advancement in its development,
it would seem highly desirable, before laying down the
investigation, to obtain conclusive proof of the possibility of free
flight, not only because there are excellent reasons to hope for
success, but because it marks the end of a definite step toward the
attainment of the final goal.

Just what further procedure is necessary to secure successful flight
with the large aerodrome has not yet been decided upon. Professor
Langley is understood to have this subject under advisement, and
will doubtless inform the Board of his final conclusions as soon as
practicable.

In the meantime, to avoid any possible misunderstanding, it should
be stated that even after a successful test of the present great
aerodrome, designed to carry a man, we are still far from the
ultimate goal, and it would seem as if years of constant work and
study by experts, together with the expenditure of thousands of
dollars, would still be necessary before we can hope to produce an
apparatus of practical utility on these lines.

M. M. MACOMB,
Major Artillery Corps.

WASHINGTON, January 6, 1904.

The attitude of the Board of Ordnance and Fortification, with
reference to rendering further financial assistance to the work, is
clearly shown by the following extract from the official report of
the Board on October 6, 1904, to the Secretary of War:

THE LANGLEY AERODROME

Early in the year 1898 a board composed of officers of the Army
and Navy was appointed to examine the models and principles of the
aerodrome devised by Dr. S. P. Langley, Secretary of the Smithsonian
Institution, and to report whether or not, in its opinion, a large
machine of this design could be built, and, if so, whether it would
be of practical value.

The report of this board was referred to the Board of Ordnance and
Fortification for action, and Doctor Langley was invited to appear
before the Board and further explain the proposed construction.

In view of the great utility of such a device, if a practical
success, the Board, on November 9, 1898, made an allotment of
$25,000 for the construction, development, and test of an aerodrome
to be made under the direction of Doctor Langley, with the
understanding that an additional allotment of the same amount would
be made later. On December 18, 1899, the additional allotment of
$25,000 was made.

The construction of the machine was delayed by Doctor Langley’s
inability to procure a suitable motor, which he was finally obliged
to design. The aerodrome was completed about July 15, 1903, and
preparations for its test were made at a point in the Potomac River
about 40 miles below Washington. [p279]

Preliminary arrangements having been completed and tests made of
a quarter-size model, the first attempt at actual flight with the
man-carrying aerodrome was made on October 7, 1903.

On this occasion there were present on behalf of the Board, Major M.
M. Macomb, Artillery Corps, and Mr. G. H. Powell, clerk of the Board.

Major Macomb in his report to the Board stated that--

“The trial was unsuccessful because the front guy-post caught in its
support on the launching car and was not released in time to give
free flight, as was intended, but on the contrary, caused the front
of the machine to be dragged downward, bending the guy-post and
making the machine plunge into the water about 50 yards in front of
the house-boat.”

This accident necessitated the removal of the house-boat to
Washington for the more convenient repair of damages. The repairs
having been completed, on December 8, 1903, another attempt at a
trial was made, this time at the junction of the Anacostia and the
Potomac Rivers. General W. F. Randolph and Major Macomb, members of
the Board, and Mr. Powell, were present. Major Macomb reported as
follows:

“The launching car was released at 4.45 p. m. . . . The car was set
in motion and the propellers revolved rapidly, the engine working
perfectly, but there was something wrong with the launching. The
rear guy-post seemed to drag, bringing the rudder down on the
launching ways, and a crashing, rending sound, followed by the
collapse of the rear wings, showed that the machine had been wrecked
in the launching, just how, it was impossible for me to see.”

March 3, 1904, the Board stated that it was not “prepared to make an
additional allotment at this time for continuing the work,” whereupon
Doctor Langley requested that arrangements be made for a distribution
of the aerodrome material procured jointly from funds allotted by
the Board and by the Smithsonian Institution. Doctor Langley was
informed that all of the material would be left in his possession and
available for any future work that he might be able to carry on in
connection with the problem of mechanical flight.

That this refusal of the Board of Ordnance and Fortification to
render further assistance to the work was due to the fear that such
action would result in a curtailment of their appropriation by
Congress is clearly shown by the following extract from the official
report of the Board on November 14, 1908, to the Secretary of War:

AERIAL NAVIGATION

For a number of years the Board has been interested in the subject
of aerial navigation, and as long ago as 1898 made allotments to
carry on experiments with a machine of the heavier-than-air type,
under the direction of the late Dr. S. P. Langley, Secretary of
the Smithsonian Institution, who had made exhaustive experiments
in aerodynamics,[48] and who had demonstrated the practicability
of mechanical flight by the successful operation of engine-driven
models.

The many problems and mechanical difficulties met with in the
development of the full-size machine have been set forth in the
various published statements[49] [p280] of Doctor Langley, and the
unsuccessful outcome of the experiments is too well known to require
reiteration. It may be said, however, that at the time of the trials
the Board was of the opinion that the failure of the aerodrome to
successfully operate was in no manner due to the machine itself, but
solely to accidents in the launching apparatus, which caused the
wreck of the aerodrome before it was in free flight.

Doctor Langley considered it desirable to continue the experiments,
but the Board deemed it advisable, largely in view of the adverse
opinions expressed in Congress and elsewhere, to suspend operations
in this direction.

These adverse opinions expressed in Congress were wholly due to the
bitter criticism by the newspapers, whose hostility was engendered
by Mr. Langley’s refusal to admit their representatives to the
shops and house-boat where the work was in progress. Mr. Langley
had at all times tried to make his position in the matter clear to
the newspapers, but, on August 19, 1903, at the time of one of his
visits to the experimental station near Widewater, Va., he found the
newspaper representatives so persistent in their misrepresentations
of his reasons for excluding them that he gave out the following
statement, which was published at that time:

SMITHSONIAN INSTITUTION, WASHINGTON, D. C.,
August 19, 1903.

TO THE PRESS: The present experiments being made in mechanical
flight have been carried on partly with funds provided by the Board
of Ordnance and Fortification and partly from private sources,
and from a special endowment of the Smithsonian Institution. The
experiments are carried on with the approval of the Board of Regents
of the Smithsonian Institution.

The public’s interest in them may lead to an unfounded expectation
as to their immediate results, without an explanation which is here
briefly given.

These trials, with some already conducted with steam-driven flying
machines, are believed to be the first in the history of invention
where bodies, far heavier than the air itself, have been sustained
in the air for more than a few seconds by purely mechanical means.

In my previous trials, success has only been reached after initial
failures, which alone have taught the way to it, and I know no
reason why the prospective trials should be an exception.

It is possible, rather than probable, that it may be otherwise now,
but judging them from the light of past experience, it is to be
regretted that the enforced publicity which has been given to these
initial experiments, which are essentially experiments and nothing
else, may lead to quite unfounded expectations.

It is the practice of all scientific men, indeed of all prudent men,
not to make public the results of their work till these are certain.
This consideration, and not any desire to withhold from the public
matters in which the public is interested, has dictated the policy
thus far pursued here. The fullest publicity, consistent with the
national interest (since these recent experiments have for their
object the development of a machine for war purposes), will be given
to this work when it reaches a stage which warrants publication.

(Signed.) S. P. LANGLEY.

Although it was impossible to immediately find funds for actively
continuing the work, the writer finally, after some delay, persuaded
Mr. Langley to allot a small sum from a limited fund which personal
friends had some time previously placed at his disposal for use in
any experiments he might wish to make. This small sum was used to
meet the expense of the workmen who were kept employed long enough to
completely repair the main frame so that, should further experiments
be possible at a later time, there would be no danger of important
parts and fittings having been lost in the meantime, and even if no
further experiments were made the frame would be in such condition
that others could profit from an examination of it, the frame itself
embodying the solution of many important problems which had cost much
time and money.

In the spring of 1904, after the repairs to the main frame were
well under way, the writer on his own initiative undertook to see
what could be done towards securing for Mr. Langley’s disposal the
small financial assistance necessary to continue the work; but he
found that while a number of men of means were willing to assist
in the development of the aerodrome, provided arrangements were
made for later commercialization, yet none were ready to render the
assistance from a desire to assist in the prosecution of scientific
work. Many years prior to this Mr. Langley had had some very tempting
propositions made to him by certain business men with a view to
carrying on the work in a way that would lead to later commercial
development. He had never patented anything previously in his life,
and although many friends had urged that it was only proper that he
should patent whatever of value had been developed in connection with
the aerodromes, he steadfastly refused to do so. He had given his
time and his best labors to the world without hope of remuneration,
and he could not bring himself at his stage of life to consent to
capitalize his scientific work. Success seemed only a step away, and
his age was such that any delay in achieving success increased the
probability of his not living to see it, but he maintained positively
and resolutely that, if neither the War Department nor others felt
sufficient interest in the work to provide the small amount of funds
necessary to continue the experiments, and they therefore could
be continued only by his giving in and permitting his work to be
capitalized, he would have to deny himself the hope of living to see
the machine achieve success.

The result is well known to all.

PRESENT STATUS OF THE WORK

The completely repaired frame of the large machine is now stored
in one of the workshops at the Smithsonian Institution. The large
engine, the steam-driven models Nos. 5 and 6, and the quarter-size
model, driven by the three [p282] horse-power gasoline engine, are
on exhibition at the U. S. National Museum. The launching-car and
a small amount of materials have also been stored away. The large
house-boat, the construction and maintenance of which proved such a
serious drain on the finances, and the preservation of which would
have entailed the continuance of heavy fixed charges, has been turned
over to the War Department and sold, as has also the power-launch and
other paraphernalia which it seemed useless to preserve.

The writer is firmly convinced that the aerodrome is not only correct
in principle but that it possesses no inherent faults or weaknesses,
and that the success which the work deserves has been frustrated by
two most unfortunate accidents in the launching of the machine. Other
plans of launching, several of which were studied out during the
early stages of the work on the large machine, would have avoided the
accident which did occur, but, of course, might have produced others
possibly even more disastrous, but which could be determined only by
actual trial. But even recognizing certain fundamental weaknesses
of the launching mechanism as used, he believes that there is no
inherent reason why the machine should not have been successfully
launched, and that the accidents which proved so disastrous in the
two experiments were not such as should cause a lack of confidence in
the final success of the aerodrome.

It might be of interest to add that the writer is now preparing to
resume the work at the earliest opportunity, and that the machine
will be used in practically the form in which it existed at the two
previous experiments, though a slight change will be made permitting
experiments over the land rather than the water. The only thing that
prevents an immediate resumption is the pressure of private business
matters.

Before closing this record the writer wishes to acknowledge the very
valuable assistance in the work rendered by Mr. Richard Rathbun,
Assistant Secretary of the Smithsonian Institution, through his
moral support and interest in it at all times, and especially during
the trying days of the summer of 1903; by Captain I. N. Lewis, who,
while Recorder of the Board of Ordnance and Fortification from 1898
to 1902, manifested keen interest in the work and gave it his moral
support before the Board; by Professor John M. Manly, who devoted
the whole of the summer of 1903 to it; and by Professor W. G. Manly,
who devoted a large part of the summer of 1903 to assistance in the
preparation for the actual field-trials of the aerodrome.

Mention must also be made of the very loyal and valuable services
rendered by Mr. R. L. Reed, the very efficient foreman of the work
during the last ten years of its progress, to whom much credit is due
for his perseverance and skill in overcoming many of the difficulties
which presented themselves, as well as to Mr. G. D. McDonald, Mr.
C. H. Darcey, Mr. F. Hewitt, Mr. R. S. Newham [p283] and the other
employees who labored faithfully for the several years they were
engaged on it.

BLÉRIOT MACHINE OF
1907 ON LANGLEY TYPE

Since completing the preparation of this Memoir, the writer’s
attention has been called to some very interesting tests made at
Issy by M. Louis Blériot with a machine of the Langley type. These
tests confirm in such a practical manner the conviction that the
large aerodrome would have flown successfully had it not been wrecked
in launching that it has seemed well to here quote an interesting
description of them published in the “Bollettino della Società
Aeronautica Italiana, August, 1907,” under the title “Il nuovo
aeroplano Blériot,” a translation of which is as follows:

THE NEW BLÉRIOT AEROPLANE

The Blériot IV in the form of a bird, of which we spoke at length
in No. 4 of the Bulletin of this year, does not appear to give good
results, perhaps on account of its lack of stability, and Blériot
instead of trying some modifications which might remedy such a
grave fault, laid it aside and at once began the construction of
a new type, No. V, adopting purely and simply the arrangement of
the American, Langley, which offers a good stability (see Bulletin
11–12, November to December, 1905, pages 187 and 188).

The experiments, which were commenced a month ago, were first
completely negative, because the 24 HP. motor would not turn the
propeller, which was 1.80 m. in diameter and 1.40 m. pitch.

By advice of Captain Ferber, Blériot reduced the pitch of his
propeller to 0.90 m., so that the motor could give all its force.

This modification was an important one for his aeroplane. From
that moment every trial marked an advance. On July 12, he made a
flight of 30 m., and the aviator was able to show that the lateral
stability was perfect. On July 15, the trial was made against a wind
of 6 miles an hour, but gave good results. He made a flight of 80
m., showing, however, that the hind part of the aeroplane was too
heavy. In this flight he arose as high as a second story, and on
landing the wheels and one propeller were somewhat damaged.

On July 24, repairs having been completed, a new trial was made.
This time, in order to remedy the defect in the balance, Blériot
had moved his seat forward about 80 cm. The correction was too
great, for on that day the aeroplane, although the hind part arose,
was not able to leave the ground. On July 27, after having mounted
the seat on wheels as skiffs, Blériot resumed the trials and made
a flight of 120 m., at first moving his seat back and then, after
getting started, bringing it forward. Blériot had not provided this
aeroplane with an elevating rudder, but, following the example
of Lilienthal, changed the center of gravity of the apparatus by
moving his own person, and after having established the proper angle
remained immovable on his seat. In order to arise or descend, the
aviator made use of the spark lever, thus varying the number of
turns of the propeller.

During a second trial on the same day, having accidently reached
the limit of the aviation field, Blériot, without allowing himself
to be surprised and obliged to descend, decided to attempt a turn
by maneuvering the steering rudder [p284] and to return again to
the center of the field. With marvelous precision, the aeroplane
began to describe a circle of about 200 m. radius, inclining as if
on a banked track. Having finished the flight, he quickly regained
his balance still in the direction of the wind, but on account of a
slight movement of the aviator, the aeroplane fell to such an extent
that he was obliged to land. He landed gently and without shock,
rolling on his wheels.

On August 1, he made another flight of 100 m. in 6-1/2 seconds; and
on the 6th, one of 265 m. with one interruption. While the attention
of the pilot was distracted for a moment, the aeroplane, which was
flying at a height of 2 or 3 m. above the ground, touched the soil
with its sustaining wheels at the end of 122 m. and then immediately
arising, covered the remaining 143 m. at a height of 12 m. Blériot,
moving forward too quickly, caused the aeroplane to descend swiftly
to the ground, and the shock broke the axle and the blades of the
propeller were bent. In order to confirm this account, we reproduce
what was said in the “Auto” of August 7, 1907.

“M. Blériot, continuing the trials of his aeroplane yesterday,
surpassed the superb results which he had already obtained. The
trial took place at 2 o’clock in the afternoon on the aviation field
of Issy. After a sustained flight of about 122 m. at a height of 2
m., the aeroplane touched the ground, without stopping, however, and
set out again almost immediately at a height of 12 m. and traversed
about 143 m. M. Blériot, who for the time had no other means of
balancing but by moving his body, then moved a little forward to
stop the ascent. The aeroplane plunged forward, and in the fall the
propeller was damaged and the axle broken.

“M. Blériot, whose courage as a sportsman equals his learning
as an engineer, was fortunately uninjured. An inspection of the
apparatus showed that one blade of the propeller was bent, which
was sufficient to prevent the maneuver made by the aviator having
its desired effect and contributed to the fall. The engine will be
repaired without difficulty and the trials will be resumed Friday.”

On August 10, he made a flight of 80 m., but the motor was not in
perfect order, so Blériot did not make other trials. He decided,
however, to substitute definitely a 50 HP. motor for the 24 HP.
motor with which he made all the experiments above reported, which
were of a character to encourage the most sanguine expectations.

Ferber advised Blériot to adopt an elevating rudder also, because
the effect produced by changing the position of the center of
gravity, although efficacious is very difficult and delicate to
control.

The conclusion of an article by Ferber in “Nature” of August 10, is
worthy of note. He says: “Let us remark, in conclusion, how fruitful
is the method of personal trial which we have always advised in
preference to any calculation. This year, with his fourth apparatus,
Blériot has not met with any damage to his aeroplane. He made the
trials himself and they quickly led to results, because each trial
gave him an exact idea of what was to be corrected. That is the
condition of success.”

[p285]

APPENDIX
STUDY OF THE AMERICAN BUZZARD AND THE “JOHN CROW”

In the preparation of this Memoir, the writer has deemed it best to
generally omit any mention of plans and ideas which were brought
forth in the work, unless constructions or tests in accordance with
them were carried to a sufficient extent to admit of some definite
conclusion regarding them. However, owing to the important part
played by the warping of the supporting surfaces, or the variation
in the angle of auxiliary surfaces, in the methods of preserving the
equilibrium of practically all flying machines of the present day, it
may be of interest to here add a short mention of the direction in
which plans along this line were originally proposed in this work.
Mention has already been made of the importance which Mr. Langley
attached to the study of the works of the great master-builder,
Nature, though recognizing at the same time that owing both to the
difference in the forces and methods of construction possible to man,
it was not in general possible for him to produce the best results by
attempting to too closely imitate the methods or plans of Nature.

Mr. Langley considered it not practicable or best to attempt to
imitate the details of construction of the flying mechanism of
birds. At the same time, he strongly believed that much was to be
learned from them about the practical side of the art of balancing,
and he therefore spent a great deal of time both in analyzing the
methods practiced by the birds in preserving their equilibrium and
in criticizing his own plans in this direction in the light of what
Nature would seem likely to do if she had to construct a flying
creature on such a large scale. In carrying on his investigations in
the art as practiced by the birds, he made a trip to Jamaica during
the early weeks of 1900, in order to study the species of buzzard
which are so numerous and tame there and are known locally as the
“John Crow.” After his return from this trip he wrote the following
very interesting letter to Mr. Robert Ridgway, requesting certain
data regarding the American buzzard, which he wished to compare with
some data on the “John Crow” which he had obtained on this trip:

MARCH 29, 1900.
DEAR MR. RIDGWAY:

I have just returned from Jamaica, where among other occupations,
I have been studying the evolutions of the buzzard locally called
the “John Crow,” a soaring bird which is almost as much superior in
skill to our buzzard as that is to a barn-yard fowl in its power of
keeping itself in the air without flapping its wings, in what is
very nearly a calm.

I have observed particularly the following points with the Jamaica
specimen (which I can only give, however, approximately), and I
should like to have you give corresponding ones for our Washington
buzzard if you can oblige me. [p286]

I note here that the measurements were made on a live bird and that
it was impracticable to get the separate weight of the wings except
by estimate, but the two wings may be estimated collectively as
1-1/4 lbs., the whole weight being 2-3/4 lbs. to 3 lbs.

Approximate values:

Weight of the bird complete, 3 pounds.
Length of bird, 23 inches.
Spread of wings from tip to tip, 5 ft. 5 in.

Complete curtate area of both wings (that is, the area of the shadow
of the bird’s wings when these are fully extended under a vertical
sun) is 600 square inches, or nearly 4 sq. ft., consequently each
square foot of the bird’s sustaining surface carries 3/4 lbs.
Diedral angle nearly 150°.

When the bird is soaring in a nearly calm atmosphere, which it
inexplicably does,--soaring I mean nearly in line of the observer’s
eyes and coming directly to of going directly away from him,--it
presents nearly the following appearance:

[Illustration: FIG. 1--Jamaica, Mch. 22, 1900. “John Crow.” Sketch
soaring horizontally, by W. H. Holmes. Weight 3 lbs. Total wings
area = 546 in. Perpendicular distance ‹c› below ‹a› ‹b› = 3.3 in. =

√(546)/7 = ‹CP›_2−‹CG›_2.]

[Illustration: FIG. 2--Another.

‹CP›_2−‹CG›_2 = 3.3 in. = √(546)/7.]

FIGS. 1 and 2.--Type sketches of wings by Holmes from a mean of
positions taken from his own sketches and photographs, and also from
sketches and photographs by Langley.

[Illustration: FIG. 3.--Type sketch of same birds, average type,
position of wings.--S. P. Langley

‹CP›_2−‹CG›_2−3.6 in. = √(546)/6.5.]

[Illustration: FIG. 4.--Average typical position of wings in soaring
gull. From memory by S. P. Langley. (The scale here may be taken
‹approximately› at 1/13).]

[p287]

I must preface what follows by a little statement of the things
which particularly interest me here and which are not a naturalist’s
ordinary concern.

First, I want to know the ‹CG› of the bird when in flight. You will
understand that though there is but one center of gravity (here
symbolized as ‹CG›), it may be considered (1) with reference to its
position on the horizontal plan of the bird with wings extended,
when it will always be found somewhere in the medial vertical plane,
passing through the body, and usually nearly at a certain point with
reference to length, the position thus considered being called ‹CG›,
or (2) the position of the same ‹CG› with reference to a vertical
plane passing transversely through the medial line, the position
thus considered being called ‹CG›_2. In the latter case you will
understand that the ‹CG› which is that of the whole body, wings and
all, will be carried more or less upward when the wings are thrown
high up, and will be carried temporarily downward when the wings are
at their lowest point of the stroke. It would have a certain position
when the bird was at rest and another position when it was soaring
and the wings were above the body.

The soaring bird is chiefly held upward by the pressure of the air
under each wing, and just as the common center of gravity is a
point where all the efforts of gravity are supposed to be centered,
so there is a common center of pressure, or one point where all
the efforts of the upper pressure of the air may be supposed to be
centered, and it will be clear, on very little consideration that
this latter point must be always nearly in a vertical line through
the ‹CG›, and usually above it. Call it ‹CP›.

‹CG›_1 and ‹CP›_1 are then, the symbols of ‹CG› and ‹CP› as referred
to the horizontal plane. ‹CG›_2 and ‹CP›_2 are the symbols for the
corresponding ones when referred to their position in the vertical
plane.

I shall be glad to explain to you, if you are not familiar with it,
the simple method of finding the ‹CG›_1 and ‹CG›_2. It consists in
bending the wings into just the position that they would ordinarily
occupy above the body in plain soaring flight, keeping them there by
a very light bent stick or wire, then hanging the bird up by a line
attached to the tip of one wing, and see where this line would pass
through the body of the bird, for the ‹CG› will be somewhere in this
line. After marking then, on the body of the bird its position, hang
it up a second time by the head or tail and note again where the new
vertical line runs in the new position. There is but one ‹CG› and but
one point in which two straight lines can cross, and that will be
the ‹CG› necessarily. Note with all care just where this is above or
below the center of the body of the bird.

As for the ‹CP› for either wing, that may be nearly found by tracing
the wing on a flat piece of thick paper or cardboard strong enough
not to bend much--cutting out the tracing and balancing it well on
the point of a pencil--the point about which it balances is very near
‹CP›_2 or the center of pressure in the vertical plane. There is such
a point of course in each wing, and when they are thrown up in the
actual position that they have in calm soaring flight, we may suppose
a horizontal line drawn between them, and it is the distance from
this horizontal line to ‹CG›_2 compared with the area of the wings or
with the distance between their extended tips which we want to know,
which gives the vertical distance which the ‹CG› is below the ‹CP›,
the thing we want to know.

It will be very convenient also to have a wing dissected from the
body and the wing itself held in about the soaring curve by a bit of
light stick balanced on a pencil point, which will give the ‹CG› of
the wing as distinct from that of the body. However, the three things
I principally want, beside a sketch or [p288] photograph of the bird
from about its own level coming directly toward or going directly
away in soaring flight, are these:

Approximate weight of the bird,--and approximate tracing of its
extended wing with the area, so that we can tell the area of the
supporting surface relative to the weight, and finally, the distance
between ‹CP›_2, and ‹CG›_2, which is obtainable by the process which
I have explained.

I am afraid that what I have just been describing at such length
may have a certain obscurity to you, but if you will give me an
opportunity, I shall be pleased to illustrate it with the actual
experiment when the bird is hung up by a string, and you will see
that it is in reality simple.

Referring to the sketches on page 3 of this communication, ‹a› and
‹b› correspond to the centers of pressure on either wing where the
upward pressure of the air distributed over each wing may be supposed
to be gathered in a single point. This, as I have said, is called
the center of pressure with reference to the vertical flight, and
its symbol is ‹CP›_2, while the horizontal dotted line between them
represents the level of ‹CP›_2, from the best estimate that I could
make when the wings are in their natural position of soaring. It is
evident that this line passed far above the body of the vulture, and
if (the corresponding symbol for the height of the center of gravity
being ‹CG›_2), the ‹CG›_2, of the entire bird be taken, it will be
found to lie nearly in the point ‹c›. Where ‹c› is in the present
case, I could not determine exactly in my hasty examinations in the
live bird, but I assume that it is about 1/2 way between the central
horizontal axial line of the bird’s body and the upper portion. I
repeat that it is important to me to know what the vertical distance
is between ‹CP›_2 and ‹CG›_2 in each specimen of soaring bird. I may
observe in illustration that in the common sea-gull, it is nearly as
shown in the faint sketch; that is to say, that the corresponding
line ‹a› ‹b› in the soaring gull passes distinctly through the upper
part of the body, and the distance down to the ‹CG›_2 of the whole in
the gull is almost nil, while in the buzzard it is very considerable
as shown by the corresponding distance in the “John Crow.”

Now, what I want to get from you is the corresponding figures for
an average specimen of our Washington buzzard. If you will kindly
have one killed and weighed while fresh, and before the rigor-mortis
has set in, first noting the position of its wings when soaring in
a calm, and (if possible) when coming toward you or going away in
about a horizontal plane with your eye, in which position the wings
will be elevated and bent somewhat as in the case of the above sketch
of the “John Crow”; if you will kindly do this, so as to give me
corresponding facts with reference to the buzzard, namely weight,
area of extended wing surface, distance between tips as bent up in
ordinary flight, distance between ‹extended› tips, ‹the quantity›
‹CP›_2−‹CG›_2, and also will make such a tracing of the buzzard’s
wing as Mr. Manly will show you of the “John Crow’s,” I shall be
obliged.

My impression is that the buzzard is a considerably heavier bird
than the “John Crow,” without, however, very much greater spread of
wing. I may observe that when the wings of the Jamaica bird were
spread out, they were spread quite to their utmost extent, and the
distance between the tips of the terminal feathers was much greater
than when in flight. I wish you would kindly also add the scientific
name of the “John Crow,” with any particulars that you would think of
interest.

If there be any special expenses incurred in the preparation of this
memorandum, including the time of a photographer, I will direct them
to be paid from the Smithsonian fund. [p289]

If you could get Mr. Holmes (who made most of the sketches and all
of the photographs of the “John Crow”), to try and do something like
this for your buzzard, especially getting such a photograph of it ‹in
flight›, as will give the position of its center of gravity relative
to the center of pressure on the wings, it would add very greatly to
the value of your memoranda, and I think Mr. Holmes takes so full and
intelligent an interest in the subject, that he might be pleased to
give his help.

Very truly yours,
S. P. LANGLEY,
‹Secretary›.

MR. ROBERT RIDGWAY,
Smithsonian Institution,
Curator, Division of Ornithology, U. S. National Museum, Washington,
D. C.

In response to this request, Mr. Ridgway submitted the following very
interesting information:

SMITHSONIAN INSTITUTION,
UNITED STATES NATIONAL MUSEUM

WASHINGTON, D. C., October 16, 1900.

PROF. S. P. LANGLEY,
Secretary, Smithsonian Institution.

SIR:

I have the honor of submitting herewith the data obtained by Mr.
Rolla P. Currie concerning measurements, etc., of the common Turkey
Buzzard (‹Cathartes aura›) of the United States, as requested by you
in your letter of March 29, last.

The difficulties in the way of securing these data, already
explained by me in previous communications, are responsible for the
delay in submitting them.

Hoping that this material may prove of use to you, I am,

Very respectfully,
R. RIDGWAY,
‹Curator, Division of Birds›.

MEMORANDA IN REGARD TO THE TURKEY BUZZARD (SECOND SPECIMEN)

1. ‹Weight›.--1850 grammes.

2. ‹Area of outstretched wings›.--641 square inches. (Computed from
three sheets of tracings, ‹A›_1 and ‹A›_2 comprising the entire area
of both wings; ‹B›, a single wing.)

‹Note›.--As the bird was in process of moult, one of the large wing
quills, as shown by the tracings and compo-board patterns, is but
partially developed, thus slightly modifying the results obtained.
Its length, if full grown, would be nearly the same as that of the
quill just above it.

3. ‹Distance between the tips of these wings›.--5 feet, 8.7 inches.

4. ‹Distance between the tips of the same wings when the bird is in
horizontal soaring flight›.--Estimating the dihedral angle of the
wings to be 150°, and elevating the wings so as to make this angle,
the distance between their tips [p290] measures 5 feet, 5.7 inches,
or 3 inches less than when fully extended in the horizontal plane.

5. ‹The position of the center of pressure of the wing›.--This is
indicated on two compo-board patterns, ‹C› and ‹D›. ‹C› was made
from a fully extended wing, while ‹D› was made from the wing in the
soaring position. The centers of pressure of the wings are about
2 feet, 0.5 inches apart, or 1 foot, 0.25 inches from the central
point of the bird’s body.

6. ‹The position of the center of gravity of the soaring
bird›.--(Length of buzzard, 26 inches.) The center of gravity of
the soaring buzzard in the horizontal plane, CG_1, was found to lie
9-1/2 inches behind the tip of the beak and 16-1/2 inches in front
of the tip of the tail.

The center of gravity of the soaring bird in the vertical plane,
‹CG›_2, was found to lie 2.8 inches above the ventral point of the
body and 1.6 inches below the dorsal point, the depth of the bird’s
body at ‹CG›_1, being 4.4 inches.

In determining the center of gravity, the bird was frozen in the
soaring position, its wings making a dihedral angle of 150°. It
was then hung up, first horizontally and then vertically, and
balanced till the line from which it was suspended coincided with a
plumb-line placed in front of it; the measurements were then made.

The bird was afterwards, and while still frozen, hung up in the same
way in Mr. Smillie’s photographic room, and exposures made by him
in both positions. These photographs, ‹E›_1 and ‹F›_1 were enlarged
to natural size, and measurements made on the enlargements yielded,
as nearly as could be determined, the same results as when taken
directly upon the bird.

As determined by measurements upon the buzzard in soaring position,
the center of gravity was found to be 2.65 inches below the center
of pressure (estimating the center of pressure to be at the bend of
the wing); or, employing the compo-board pattern in a corresponding
position, the distance was seen to be a small fraction of an inch
less.

7. ‹The position of the root of the wing›.--This is indicated on the
tracing A_1.

‹a.› (Depth of the body on a vertical line with root, 3.5 inches.)
The root lies 1.6 inches below dorsal line, 1.9 inches above ventral
line.

‹b.› (Length of body, 26 inches.) The root lies 7.6 inches behind
tip of beak, 18.4 inches in front of tip of tail.

8. ‹The dihedral angle between the wings›.--The photographs taken
previously were not sufficiently large or distinct to enable us to
determine this with exactness. It was estimated, however, as 150°,
and experiments were made on this basis.

9. ‹The center of gravity of the dissected wing›.--This was found,
‹first›, for the wing having all the muscles, up to the ball and
socket joint, intact. One of the wings was frozen in the soaring
position and its center of gravity found by balancing on a point.
Its position was marked by a wire thrust through the wing at this
place, and the wing (‹H›) is preserved in formalin. This position
is also marked on a special tracing, ‹I›. It lies 6 inches from the
base of the humerus bone (root of wing). ‹Secondly›, it was found
for the wing denuded of all muscle. Its position was marked on
the other wing of the bird, which is preserved dry, spread in the
soaring position. It lies 9-3/4 inches from the base of the humerus.
[p291]

10. ‹The weight of the dissected wing›.--

‹a.› With all muscle up to the ball and socket joint intact, 325
grammes.

‹b.› With all muscle removed, 190 grammes.

Weight of muscle, therefore, 135 grammes.

‹The position of the root of the tail›.--

‹a.› In the horizontal plane, 11.8 inches in front of the tip of the
longest tail feather; 14.2 inches behind tip of beak.

‹b.› In the vertical plane: (depth of body from ventral point below
root of tail to a point directly above, which is on a level with the
highest point of the back, 2.5 inches.) 1.5 inches above ventral
point, 1 inch below dorsal point.

‹Weight of tail›.--With muscle, 40 grammes; ‹without› muscle, 30
grammes. Weight of muscle, therefore, 10 grammes.

EXHIBITS ACCOMPANYING THESE MEMORANDA

[Illustration: EXHIBIT E_1.--Turkey Buzzard suspended in soaring
position. (R. P. Currie.)]

‹A›_1 and ‹A›_2. Two sheets, comprising a tracing of the entire
turkey buzzard with fully outstretched wings. From these the area
of the wings and the distance between their tips was obtained. The
position of the root of the wing and the root of the tail is also
marked on one of these sheets.

‹B.› One sheet, comprising a tracing of a single wing, and from
which the area was also computed. This area, multiplied by 2,
gives the same result as the sum of both wings on A_1 and A_2. The
compo-board pattern ‹C› was made from this tracing.

‹C.› Compo-board pattern of fully extended wing, on which the center
of pressure is indicated.

‹D.› Compo-board pattern of wing in soaring position, on which the
center of pressure is shown. [p292]

‹E›_1. Photograph of bird in soaring position, suspended
horizontally.

‹E›_2. Same, enlarged to natural size.

‹F›_1. Photograph of bird in soaring position, suspended vertically.

‹F›_2. Same, enlarged to natural size.

‹G.› Tracing of wing in soaring position, from which the compo-board
pattern ‹D› was made.

[Illustration: EXHIBIT F_1.--Turkey Buzzard suspended vertically in
soaring position. (R. P. Currie.)]

‹H.› Wing preserved in formalin, on which the center of gravity is
recorded.

‹I.› Tracing of wing ‹H› when frozen in soaring position, on which
the center of gravity is marked.

‹J.› Wing with muscle removed, on which the center of gravity is
shown.

Several persons connected with the Smithsonian Institution and U.
S. National Museum have contributed towards securing the results
herewith submitted. Among them, I desire especially to mention Mr.
W. H. Holmes, Mr. [p293] F. A. Lucas, Mr. N. R. Wood, and Mr. R.
L. Reed. Mr. Holmes superintended the experiments in connection
with ‹No. 6› (finding the bird’s center of gravity), and by his
suggestions and criticisms helped me in many other particulars. The
photographs and enlargements were made by Mr. T. W. Smillie.

Respectfully submitted,
ROLLA P. CURRIE,
‹Aid, Division of Insects, acting in the Division of Birds›.

OCTOBER 16, 1900.

The feats of airmanship performed by the “John Crow” seemed to
greatly impress Mr. Langley and shortly after this trip he wrote the
following letter to the writer:

SMITHSONIAN INSTITUTION
WASHINGTON, D. C., April 16, 1900.

DEAR MR. MANLY:

I am reminded of the consequence that I have, in connection with
Mr. Chanute and perhaps Mr. Huffaker, attached in the past to the
possibility of directing the bird, and consequently the flying
machine, by the mere inflection of the wing, that is, by changing
its angle; and you recall to me that Mr. Huffaker at one time
proposed to arrange a wing, with some provision of a spring, which
should enable it to change its angle automatically. . . . .

I have been noting this ability to guide by the slight inflection
of the wing, in my studies of the Jamaica buzzard, and am ready
to say that I think, while the quarter-sized working model of the
great aerodrome is building, it will be worth while to make some
arrangement of the frame or wing-holder which will make it possible
to test this idea. I will endeavor to work out something of the
kind more in detail myself, but whatever it is, it will apparently
involve the ability of the wing to rotate about a line passing
nearly through it lengthwise, and an allowance for this; if not in
the wing itself, then in the wing-holder; will need to be made while
the present model is under construction.

I will request you to especially look out for this, as far as you
can on these indications.

Very respectfully yours,
S. P. LANGLEY,
‹Secretary›.

The instructions and suggestions contained in this letter and in many
conferences on the subject were never carried out by the writer, on
account of the extreme pressure of the work already on him which
had for its object, not the production of a flying machine which
would embody all of the control which we wished it to have, but
which would be burdened only with such devices and arrangements as
would enable it to transport a human being, and thus demonstrate the
practicability of human flight.

[p294]

SECRETARY LANGLEY’S INSTRUCTIONS TO ASSISTANTS

SMITHSONIAN INSTITUTION, WASHINGTON, D. C., November 30, 1895.

DEAR SIR:

The following instructions are to replace those of May 13, 1895:

1. The ‹minimum› fraction of its own “flying weight” (that is,
weight complete with initial water and fuel), which the aerodrome
shall lift on the pendulum, is 50 percent,[50] under such engine
power as can certainly be gotten up in the field and maintained
during forty seconds from the time the aerodrome is let go.

The blast, the pumps, and all other essential parts must, in other
words, be in such a condition that steam enough for this lifting
over 50 per cent of weight can be gotten up readily and surely
in the field and in a time which will still leave at least forty
seconds’ supply.

2. The ‹minimum› relation of supporting area to weight in any
aerodrome constructed hereafter, is to be two feet to the pound,[50]
and the minimum of power at the rate of one steadily-maintained
horse power[50] at the brake under ordinary conditions, to not over
twenty-two pounds (ten kilos) of flying weight. In absence of a
brake determination horse power may be taken--

H. P. = (revs. per min. at rest × pitch ×
diameter (in ft.) × thrust (in lbs.)) / 33,000.

These rules do not apply to No. 5, but they do to No. 6, which is to
be built over, if necessary, to meet them.

3. In balancing an aerodrome, unless otherwise instructed, set wings
at a root angle of either 10°, 7°, or 5°, after being certain from
previous inversion and sanding, that the tip angle in motion will
not differ from this root angle as much as 5°.

The object in balancing any aerodrome with a single pair of wings
is to be able to bring the ‹c g›_2 under their ‹c p›_2 without any
reference to the tail, which supports nothing, unless specially
ordered. But as this condition cannot now be obtained in Nos. 5
and 6, these at any rate, and perhaps future aerodromes, are to
carry a second pair of wings. When this second pair of wings is of
nearly equal size with the first it is to be assumed in preliminary
adjustments for weight and center of pressure, that the second pair
has two-thirds the lifting efficiency per unit area of the first.

Calling the whole distance from the mean center of pressure of
the wings to the center of gravity ‹M›. ‹M› is to have a definite
relation to the breadth of [p295] wings from tip to tip (‹b›) and
total fore and aft length (1), which is provisionally fixed at M =
√(bl)/8, and the line of thrust is to be not over one-fourth the way
from ‹c p›_2 to ‹c g›_2.

Generally speaking the front pair of wings will be fixed in position
and the adjustment for balancing made by moving the rear pair.

The individual weights of all parts checked by lump weighing are
to be given by the caretaker (Mr. Huffaker), under the general
scheme shown in the note. The work on the aerodromes being divided
into two classes, viz.: metal work and all which is not metal, the
two in charge of this work (Mr. Reed and Mr. Maltby) are severally
responsible for knowing the weight in grammes of any of the parts
they have put into their work, giving these weights to Mr. Huffaker,
together with any data for filling out the annexed tables,[51] on
his request.

Until further orders, Mr. Huffaker is charged with the
responsibility of seeing that these conditions are met before
any aerodrome is boxed, and will keep the record of weights of
the aerodromes and their principal parts as already completed,
in a book, to be preserved in your keeping, which will also be
arranged to show with signed ‹photographs› and descriptions, and
with sketches where needed, the condition and weight (as far as
constructed) of every aerodrome, and of any new construction of any
part, on the first of each month.

Particular attention is directed to the preceding paragraph, and to
the need that evidence of a definite character is to be obtained and
preserved of everything already done, and being done.

Without special orders to the contrary, you will not authorize the
boxing of any aerodrome which does not, to your knowledge, meet
these conditions.

Each aerodrome is to have the following parts in duplicate or in
triplicate:

2 pairs wings;
2 pairs tails;
2 pairs light silk covered rudders;
3 pairs wheels;

with any other parts in duplicate or triplicate, which experience
has shown to be necessary.

Mr. Reed will not box any aerodrome till a certificate from Mr.
Huffaker can be put on the inside cover, with the list of contents,
showing what the conditions are as to weight, wing area, power,
etc., and the person in the field charged with the duty of launching
the aerodrome (at present Mr. Reed), is authorized not to let it go
unless he is satisfied that it has a full forty seconds’ supply of
steam. [p296]

I am satisfied that a great deal of time is lost in putting
the aerodrome together for flight, owing to the absence of any
preliminary drill in doing this. Before it goes into the field the
whole is to be completely boxed, and then taken out from the box
and set up on the clutch, and steam gotten up for flight. All this
is to be done in the shop before the final boxing, and provision is
to be made so that no wiring or adjusting of parts is to be done in
the field which can possibly be avoided by forethought in the shop.
The tail-piece, for instance, is to be bushed with brass, so that it
will always come into the same place, and make a tight fit, in spite
of wetting or shrinking, in the steel tube, where it is to go into a
guide-way with a bayonet spring, or a like contrivance for setting
it at once securely into position.

The mean positions of the wings and tail are to be laid out
in some way permanently on the mid-rod, but every guy-rod or
adjustable piece is to be arranged so as to fit at once securely and
permanently in its position without wiring or like slow process.

Very truly yours,
S. P. LANGLEY,
‹Secretary›.

W. C. WINLOCK, Esq.,
Assistant in Charge,
Smithsonian Institution.

A copy to be communicated to:—
Mr. Huffaker,
Mr. Reed,
Mr. Maltby.

FOOTNOTES.

[37] “The Flying Machine” ‹McClure’s Magazine›, June, 1897.

[38] One noted astronomer and mathematician re-affirmed this opinion
as late as 1900 and even stated that man could not hope to construct
a flying machine capable of sustaining a weight as great as our
largest birds, knowing that even at that time the model Aerodromes
Nos. 5 and 6 had already done more than this.

[39] These wings are described in Chapter VI, pp. 191.

[40] See “Experiments in Aerodynamics.” It will be recalled that in
the experiments with the “plane-dropper” there was a greatly reduced
lifting power with superposed planes when their distance apart was
one-half the width the planes, unless a speed of about 42.5 feet a
second was obtained. In the above tests with the superposed wings,
the speed was only from twenty to twenty-two feet a second at the
time of launching, and as the distance between the surfaces was only
one-half as great as their width, it is not surprising that the
lifting power should not be as great as with the “single-tier” wings.

[41] In fact the setting of the tail at a negative angle and
fastening it to the frame by an elastic or spring connection was only
begun in 1896, and while it proved to be the key to the solution
of the problem of automatic longitudinal stability, yet it was not
at that time so recognized, although the first real test of the
aerodromes after the elastic connection and negative angle of the
tail were adopted resulted in the epoch-making flight of No. 5 on May
6. By comparing the angle of the tail on No. 5 in Plate 27A, Part I,
with the angle of the tail on No. 6 in Plate 27B, Part I, it will be
seen that while the first had an angle of much less than 5 degrees,
the latter had an angle of about 15 degrees. But the wooden springs
changed so that it was not accurately known what the angle really was
at the time at either flight in 1896.

[42] The drawings, Plate 55, which illustrate many of the fittings
used on the frame, show the guy-wires as attached by means of loops
twisted in their ends, these drawings having been made before the
final plan of attaching the wires had been devised.

[43] See explanation of system of locating points in Part I, Chap.
II, p. 15.

[44] See Balancing of Engines, by Archibald Sharpe.

[45] Except for a ten minute stop to renew the supply of lubricating
oil and change the sparking batteries.

[46] See foot-note, page 249.

[47] The weight was afterwards increased to 850 pounds due to
repairing the wings and adding more sparking batteries.

[48] See Experiments in Aerodynamics, Smithsonian Contributions to
Knowledge, Vol. 27, Washington 1891.

[49] Researches and Experiments in Aerial Navigation, Smithsonian
Publication No. 1809, Washington, 1908.

[50] All these minimum permissible conditions are connected by the
tacit assumption that the supporting area is not greatly over 2 ft.
to the pound of weight. If for instance the weight were increased by
larger wings or more wings, furnishing a much greater supporting area
per pound, these conditions would not necessarily apply.

[51] These tables were later designated as “Data Sheets.” Several
copies, with the data duly entered on them, are given in this
appendix, and the form which Mr. Langley included in this letter is
therefore not repeated here.--EDITOR.

[p297]

DATA SHEETS.

DATA SHEET No. 1.

Weight of Aerodrome No. 5, as photographed on May 11, 1896.
Certified to by R. L. Reed, May 6, 1896.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for clutch, etc. | | | 2443| |
| | | | |
2 Engine, gears, shafts, etc. | | | 1110| |
| | | | |
3 Pump, pump shaft | | | 231| |
| | | | |
4 Hull covering | | | 350| |
| | | | |
5 Gasoline tanks, valves | | | 178| |
| | | | |
6 Smokestack | | | 342| |
| | | | |
7 Float | | | 275| |
| | | | |
8 Reel | | | 77| |
| | | | |
9 Wing clamps, 235; clamp for | | | | |
guy-posts, 29 | | | 264| |
| | | | |
10 Other things, counter | | | 75| |
| | | | |
11 Burners | | | 360| |
| | | | |
12 Boilers | | | 651| |
| | | | |
13 Separators, steam gauge, pipe to | | | | |
engine | | | 540| |
| | | | |
14 Exhaust pipe | | | 143| |
| | | | |
15 | | | | |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp) | | | 1950| |
| | | | |
18 Tail (without clamp) | | | | |
| | | | |
19 Rudder | | | 350| |
| | | | |
20 Guy sticks, each, 57 | | | 114| |
| | | | |
21 Propellers | | | 800| |
| | | | |
22 Extra length of midrod, 308; drop | | | | |
piece for rudder, 40 | | | 348| |
| | | | |
23 Wood Bowsprit | | | 74| |
| | | | |
24 Other things | | | | |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (at starting flight) | | | 200| |
| | | | |
28 Water (at starting flight) | | | 900| |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |11,775| 26 |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |68 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs. | | 2.6 | | |
| | | | |
40 Total area of horizontal tail sq. | | | | |
ft. | | | | |
| | | | |
41 Total area of rudder (vertical) | | | | |
sq. ft. | | 6 | | |
| | | | |
42 Horse-power at brake. Horse-power | | | | |
by formula* .72 | | 7 | | |
| | | | |
43 Minimum pressure during 40 secs. | | | | |
lift, 150 lbs. | | | | |
| | | | |
44 Lift at pendulum (during 40 secs. | | | | |
absolute) 5772 | | | | |
| | | | |
45 Lift at pendulum (during 40 secs. | | | | |
in terms of wt.) 49% | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn, 10 lbs. | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings† F. W., 1575; R. W., 1383.5 | | | | |
| | | | |
48 Time of getting up full steam, 1 | | | | |
minute | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1/11 | | | | |
| | | | |
51 Root angle of wings, 9° | | | | |
| | | | |
52 Tip angle of wings, 9° | | | | |
| | | | |
53 Position of wings, Front rib on F. | | | | |
W., 1607; R. W., 1415.5 | | | | |
| | | | |
54 How guyed | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail | | | | |
| | | | |
59 Angle of tail | | | | |
| | | | |
60 Co-efficient elasticity of tail | | | | |
| | | | |
61 Position of rudder, center, | | | | |
1288.3; rear end, 1229.8 | | | | |
| | | | |
62 Line of thrust, 2500 | | | | |
| | | | |
63 Line of thrust, 1500 which is 9 | | | | |
cm. below the center of midrod | | | | |
| | | | |
64 Center of gravity_1 of whole, 1497 | | | | |
| | | | |
65 Center of gravity_2 2501, i. e., 1 | | | | |
cm. above line of thrust | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate, 1498 | | | | |
| | | | |
67 Center of pressure_2, 2536 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+-----+------+------+

Parts. Remarks.

1 Front end of bowsprit, 1686.3.

2 Front end of midrod, 1611.6.

5 Front edge of F. W., 1607.

8 C. of P. on F. W., 1575.

11 Back edge of F. W., 1527.

14 Back edge of cross frame, 1509.

17 Line through center of propellers, 1500.

21 C. of G., 1497.

24 Front edge of R. W., 1415.5.

27 C. of P. on R. W., 1383.5.

30 End of mid-rod, 1360.5.

33 Front end of rudder, 1343.8.

36 Back edge of R. W., 1335.5.

39 Center of rudder, 1288.3.

41 Back end of rudder, 1229.8.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

† This is calculated on the assumption that the center of pressure
on each wing or on pair of wings at a motion of 2000 feet per minute
is in ordinary curved wings 2-5 the way from front to rear, that for
wings of usual size the rear wings have 2-3 of the efficiency per
surface of the front ones and that the tail proper bears no part of
the weight; but if rear wing is smaller or larger this efficiency is
smaller or larger per unit of surface.

[p298]

DATA SHEET No. 2.

Weight of Aerodrome No. 6.
Certified to by R. L. Reed, November 27 and 28, 1896.

-------------------------------------------+-----------+-------------+
Parts. | Sizes. | Weight. |
-------------------------------------------+-----+-----+------+------+
|‹m.› |‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of metal, | | | | |
permanent and undetachable, such as bed-| | | | |
plate, cross-rods for the support of | | | | |
propellers, bearing points for clutch, | | | | |
etc. | | | 1178| |
2 Engine, gears, shafts, etc. | | | 1043| |
| | | | |
3 Pump, pump shaft | | | 190| |
4 Hull covering | | | 345| |
5 Gasoline tanks, valves | | | 306| |
6 Smokestack, 302; burner, 172 | | | 474| |
7 Float | | | 275| |
8 Reel | | | 77| |
9 Wing clamps, 238; drop piece for rudder, | | | 278| |
40 | | | | |
10 Other things | | | 156| |
11 Boiler, frames, mica cover | | | 694| |
12 Separator, steam gauge, pipe to engines | | | 535| |
13 Exhaust pipe | | | 82| |
14 | | | | |
15 | | | | |
16 | | | | |
17 Wings (without clamp), wet | | | 2154| |
18 Tail (without clamp) | | | | |
19 Rudder | | | 375| |
20 Guy sticks, each 53 | | | 106| |
21 Propellers | | | 644| |
22 Extra length of midrod | | | 398| |
23 Wood bowsprit | | | 135| |
24 Counter | | | 75| |
25 | | | | |
26 | | | | |
27 Fuel (at starting flight) | | | 250| |
28 Water (at starting flight) | | | 2350| |
29 | | | | |
30 | | | | |
31 Sundries unknown | | | | |
32 | | | | |
33 | | | | |
34 Total flying weight | | |12,120| |
35 | | | | |
36 | | | | |
37 | | | |
38 Total area of support (not including | | 54| | |
tail) sq. ft. | | | | |
39 Total area of support in feet, divided | | | | |
by total flying weight in lbs. | | 2 | | |
40 Total area of horizontal tail sq. ft.| .6 | | | |
41 Total area of rudder (vertical) sq. ft.| .6 | | | |
42 Horse-power at brake Horse-power by | | | | |
formula* | | | | |
43 Minimum steam pressure during 40 secs. | | | | 130|
lift | | | | |
44 Lift at pendulum (during one minute | | | | 7,211|
absolute) | | | | |
45 Lift at pendulum (during one minute in | | | | |
terms of wt.) | | | | |
46 Minimum pressure with which wheels turn | | | | 10 |
47 Position of center of pressure of wings†| | | | |
48 Time of getting up full steam, 75 secs. | | | | |
49 Angle of midrod with horizon, 2° 17′ | | | | |
50 Curvature of wings, 1 in 18, 1/4 from | | | | |
front | | | | |
51 Root angle of wings, 10° 30′ | | | | |
52 Tip angle of wings, 10° 30′ | | | | |
53 Position of wings | | | | |
54 How guyed | | | | |
55 | | | | |
56 | | | | |
57 | | | | |
58 Position of tail | | | | |
59 Angle of tail | | | | |
60 Co-efficient elasticity of tail | | | | |
61 Position of rudder | | | | |
62 | | | | |
63 Line of thrust 1500 | | | | |
64 Center of gravity_1 of whole, 1483.8 | | | | |
65 Center of gravity_2, 2482‡ | | | | |
66 Center of pressure_1 of whole | | | | |
estimate, 1487 | | | | |
67 Center of pressure_2, 2520 | | | | |
68 | | | | |
69 | | | | |
70 | | | | |
71 | | | | |
72 | | | | |
-------------------------------------------+-----+-----+------+------+

Parts. Remarks.

1 Front end of bowsprit, 1797.

2 Center of float in first trial, Nov.

6 Front end of midrod, 1613.7. 9 Front edge of F. W., 1595.7.

12 Center of float in flight, Nov. 28, 1896, 1575.8.

16 C. of P. on F. W., 1563.7.

19 Back edge of F. W., 1515.7.

22 Line through center

of propellers, 1500.

26 C. of G., 1484.4 (old C. of G., 1486.3).

29 Front edge of R. W., 1406.

32 C. of P. on R. W., 1374.

35 End of midrod, 1351.3

38 Front end of rudder, 1334.5.

41 Back edge of R. W., 1326.

43 Center of rudder, 1279.

46 Back end of rudder, 1220.5.

49 Reed wings, 80 cm.×185 cm. in rectangle.

53 Weight in shop, 1982 g.

56 On day of flight they weighed 2154 g. because they were damp.

60 Area 54 sq. ft.

63 Spread of wings, 359 cms. or 11′ 9-3/8″.

67 Weight of aerodrome in flight, 12,120 grs.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

‡ This is undoubtedly incorrect, as if it were true, the C. G. would
be just at the center of the separator, and this would be impossible.
Mr. Reed states that the C. G. was 2 cm. below the side frame, and if
this is correct, we would have C. G. = 2486.

[p299]

DATA SHEET No. 3.

Weight of Aerodrome No. 6, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 7, 1899.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for clutch, etc. | | | 2867| |
| | | | |
2 Engine, gears, shafts, etc. | | | | |
| | | | |
3 Pump, 123; pump shaft, 49 | | | 172| |
| | | | |
4 Hull covering, including apron and | | | | |
piece behind separator | | | 274| |
| | | | |
5 Gasoline and air tanks, 167, 114; | | | | |
air valve, 16 | | | 297| |
| | | | |
6 Smokestack, 319; counter, 95; | | | | |
burner, 165 | | | 679| |
| | | | |
7 Float, 275; pipe from pump to | | | | |
boiler, 40 | | | 315| |
| | | | |
8 Reel, with fork and float | | | 128| |
| | | | |
9 Wing clamps, 188; guy-post clamps, | | | 212| |
24 | | | | |
| | | | |
10 Boiler, 764; steam gauge and | | | | |
connections, 79 | | | 843| |
| | | | |
11 Front lower bearing post, 75; | | | | |
clutch post, 58; rear bearing points, | | | 288| |
155 | | | | |
| | | | |
12 Separator and pipes leading to | | | | |
engines and pump | | | 502| |
| | | | |
13 Drop piece for rudder, 57; | | | 75| |
guy-post for rudder, 18 | | | | |
| | | | |
14 | | | | |
| | | | |
15 | | | | |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp) | | | 2077| |
| | | | |
18 Superposed wings, 3448 | | | | |
| | | | |
19 Rudder | | | 323| |
| | | | |
20 Guy sticks, each 53 | | | 106| |
| | | | |
21 Propellers | | | 620| |
| | | | |
22 Extra length of midrod | | | 377| |
| | | | |
23 Wood bowsprit | | | 128| |
| | | | |
24 Canvas keel, 36; rudder, 76 | | | 112| |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (at starting flight) | | | 175| |
| | | | |
28 Water (at starting flight) | | | 1525| |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |11,995| 26.44|
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |54 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs. | | 2.04| | |
| | | | |
40 Total area of horizontal tail sq. | | | | |
ft. | | 9.5 | | |
| | | | |
41 Total area of rudder (vertical) | | | | |
sq. ft. | | 7.75| | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute) | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.) | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings† 40% from front | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1 in 18 | | | | |
| | | | |
51 Root angle of wings, 10° | | | | |
| | | | |
52 Tip angle of wings, 10° | | | | |
| | | | |
53 Position of wings--front edge of | | | | |
front wing, 1595.7; of rear wing, | | | | |
1406.5 | | | | |
| | | | |
54 How guyed--with wires from wing to | | | | |
wing on top and to guy-post on bottom | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of center of rudder, | | | | |
1279.5 | | | | |
| | | | |
59 Angle of tail, 10° | | | | |
| | | | |
60 Co-efficient elasticity of tail | | | | |
| | | | |
61 Position of rudder | | | | |
| | | | |
62 | | | | |
| | | | |
63 Line of thrust, 1500 | | | | |
| | | | |
64 Center of gravity_1 of whole, | | | | |
1484.4 | | | | |
| | | | |
65 Center of gravity_2 | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate | | | | |
| | | | |
67 Center of pressure_2 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |

Parts. Remarks.

1 Front edge of bowsprit, 1702.7. Weight 2867 gm. for part 1
includes also part 2.

2 Center of float with small wind vane rudder, 1628.9.

6 Front edge of midrod, 1613.7.

9 Center of float with small rudder off, 1609.2.

12 Front edge of F. W., 1595.7.

15 C. of P. on F. W., 1563.7.

18 Back edge of F. W., 1515.7.

21 Line through center of propellers, 1500.

25 C. of G., 1484.4.

28 Front edge of R. W., 1406.5.

31 C. of P. on R. W., 1374.5.

34 End of midrod, 1351.8.

37 Front end of rudder, 1335.

39 Back edge of R. W., 1326.5.

42 Center of rudder, 1279.5.

45 Back end of rudder, 1221.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

[p300]

DATA SHEET No. 4.

Weight of Aerodrome No. 6, Superposed Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 13, 1899.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for clutch, etc. | | | 2867| |
| | | | |
2 Engine, gears, shafts, etc. | | | | |
| | | | |
3 Pump, 123; pump shaft, 49 | | | 172| |
| | | | |
4 Hull covering, including apron and | | | | |
piece behind separator | | | 274| |
| | | | |
5 Gasoline and air tanks, 167, 114; | | | | |
air valve, 16 | | | 297| |
| | | | |
6 Smokestack, 319; counter, 95; | | | | |
burner, 170 | | | 584| |
| | | | |
7 Float | | | 315| |
| | | | |
8 Reel, with fork and float | | | 128| |
| | | | |
9 Wing clamps, 188; guy-post clamps, | | | | |
24 | | | 212| |
| | | | |
10 Boiler, 764; steam gauge and | | | | |
connections, 79 | | | 843| |
| | | | |
11 Front bearing point, 75; clutch | | | | |
post, 58; rear bearing points, 155 | | | 288| |
| | | | |
12 Separator and pipes to engines and | | | | |
pump | | | 502| |
| | | | |
13 Drop piece and guy-post for rudder | | | 75| |
| | | | |
14 | | | | |
| | | | |
15 | | | | |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp), 2077; | | | | |
superposed wings | | | 3448| |
| | | | |
18 Tail (without clamp) | | | | |
| | | | |
19 Rudder | | | 323| |
| | | | |
20 Guy sticks | | | 106| |
| | | | |
21 Propellers | | | 620| |
| | | | |
22 Extra length of midrod | | | 377| |
| | | | |
23 Wood bowsprit | | | 128| |
| | | | |
24 Canvas keel, 36 | | | 36| |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (at starting flight) | | | 175| |
| | | | |
28 Water (at starting flight) | | | 1525| |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |13,275| |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |87.4 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs | | | | |
| | | | |
40 Total area of horizontal tail sq. | | 9.5 | | |
ft. | | | | |
| | | | |
41 Total area of rudder (vertical) | | 7.75| | |
sq. ft. | | | | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute) | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.) | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings†, 40% from front | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1 in 18 | | | | |
| | | | |
51 Root angle of wings, 10° | | | | |
| | | | |
52 Tip angle of wings, 10° | | | | |
| | | | |
53 Position of wings--front edge of | | | | |
front wing, 159 | | | | |
| | | | |
54 How guyed | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail | | | | |
| | | | |
59 Angle of tail, 7-1/2° | | | | |
| | | | |
60 Co-efficient elasticity of tail, | | | | |
1240 grammes at center to deflect to | | | | |
the horizontal | | | | |
| | | | |
61 Position of rudder | | | | |
| | | | |
62 | | | | |
| | | | |
63 Line of thrust, 1500 | | | | |
| | | | |
64 Center of gravity_1 of whole, | | | | |
1484.4 | | | | |
| | | | |
65 Center of gravity_2 | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate | | | | |
| | | | |
67 Center of pressure_2 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+-----+------+------+

Parts. Remarks.

1 Front edge of bowsprit, 1702.7. Weight 2867 gm. includes parts 2.

2 Center of float without small wind vane rudder, 1666.1. (Center of
float with wind vane rudder on, 1627.)

8 Front edge of midrod, 1613.7.

11 Front edge of F. W., 1585.

13 C. of P. on F. W., 1563.7.

16 Rear edge of F. W., 1531.7.

19 Line through center of propellers, 1500.

23 C. of G., 1484.4.

26 Front edge of R. W., 1395.8.

29 C. of P. on R. W., 1374.5.

32 End of midrod, 1351.8.

35 Front end of rudder, 1335.

38 Back edge of R. W., 1342.5.

40 Center of rudder, 1279.5.

43 Back end of rudder, 1221.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

[p301]

DATA SHEET No. 5.

Weight of Aerodrome No. 6, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 22, 1899.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for clutch, etc. (bowsprit, 78g) | | | 2867| |
| | | | |
2 Engine, gears, shafts, etc. | | | | |
| | | | |
3 Pump, 123; pump shaft, 49 | | | 172| |
| | | | |
4 Hull covering, including apron and | | | | |
piece behind separator | | | 274| |
| | | | |
5 Gasoline and air tanks, 167, 174; | | | | |
air valve, 16 | | | 357| |
| | | | |
6 Smokestack, 319; counter, 95; | | | | |
burner, 170 | | | 584| |
| | | | |
7 Float | | | 315| |
| | | | |
8 Reel, with fork and float | | | 128| |
| | | | |
9 Wing clamps, 188; guy-post clamps, | | | | |
24 | | | 212| |
| | | | |
10 Boiler, 764; steam gauge and | | | | |
connections, 79 | | | 843| |
| | | | |
11 Front bearing post, 75; | | | | |
clutch-post, 58 | | | 133| |
| | | | |
12 Rear bearing points | | | 155| |
| | | | |
13 Separator and pipes to engines and | | | | |
pump | | | 502| |
| | | | |
14 Drop piece and guy-posts, 18; for | | | | |
rudder, 57 | | | 75| |
| | | | |
15 | | | | |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp) | | | 2077| |
| | | | |
18 Tail (without clamp) | | | | |
| | | | |
19 Rudder | | | 323| |
| | | | |
20 Guy sticks | | | 106| |
| | | | |
21 Propellers | | | 620| |
| | | | |
22 Extra length of midrod | | | 377| |
| | | | |
23 Wood bowsprit | | | 128| |
| | | | |
24 Other things | | | | |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (at starting flight) | | | 175| |
| | | | |
28 Water (at starting flight) | | | 1525| |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |11,948| 26.3 |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |54 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs. | | | | |
| | | | |
40 Total area of horizontal tail sq. | | | | |
ft. | | 9.5 | | |
| | | | |
41 Total area of rudder (vertical) | | | | |
sq. ft. | | 7.75| | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute) | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.) | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings† 40% from front | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1 in 18 | | | | |
| | | | |
51 Root angle of wings, 10° | | | | |
| | | | |
52 Tip angle of wings, 10° | | | | |
| | | | |
53 Position of wings | | | | |
| | | | |
54 How guyed | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail | | | | |
| | | | |
59 Angle of tail, 7° 30′ | | | | |
| | | | |
60 Co-efficient elasticity of tail, | | | | |
1240 grammes at center to deflect to | | | | |
the horizontal | | | | |
| | | | |
61 Position of rudder | | | | |
| | | | |
62 | | | | |
| | | | |
63 Line of thrust, 1500 | | | | |
| | | | |
64 Center of gravity_1 of whole | | | | |
| | | | |
65 Center of gravity_2 | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate | | | | |
| | | | |
67 Center of pressure_2 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+-----+------+------+

Parts. Remarks.

1 Front edge of bowsprit, 1685.7. Weight 2867 gm. includes Parts 2.

2 Back edge of cylindrical part of float, 1606.5

5 Front edge of midrod, 1613.7.

8 Front edge of F. W., 1595.7.

11 C. of P. on F. W., 1563.7.

14 Back edge of F. W., 1515.7.

17 Line through center of propellers, 1500.

21 C. of G., 1484.4.

24 Front edge R. W., 1406.5.

27 C. of P. on R. W., 1374.5.

30 End of midrod, 1351.8.

33 Front end of rudder, 1335.

36 Back edge R. W., 1326.5.

38 Center of rudder, 1279.5.

41 Back end of rudder, 1221.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

[p302]

DATA SHEET No. 6.

Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 23, 1899.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for clutch, etc. | | | 3050| |
| | | | |
2 Engine | | | 464| |
| | | | |
3 Pump, 334; pump shaft, 55 | | | 389| |
| | | | |
4 Hull covering | | | 398| |
| | | | |
5 Gasoline tanks, air tanks, valves, | | | | |
etc. | | | 348| |
| | | | |
6 Smokestack | | | 373| |
| | | | |
7 Float, 275; drop piece for rudder, | | | | |
57; guy-post, 18 | | | 350| |
| | | | |
8 Reel, 128; steam gauge, 81 | | | 209| |
| | | | |
9 Wing clamps, 200; guy-post clamps, | | | | |
32 | | | 232| |
| | | | |
10 Boiler, 764; burner, 170; counter, | | | | |
95 | | | 1029| |
| | | | |
11 Rear extension to midrod | | | 174| |
| | | | |
12 Separator and pipes to engine and | | | | |
pump | | | 502| |
| | | | |
13 Exhaust pipe | | | 84| |
| | | | |
14 Front lower bearing point, 84; | | | | |
clutch post, 41 | | | 125| |
| | | | |
15 Rear bearing points, 146; extra | | | | |
strengtheners, 32 | | | 178| |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp) | | | 2342| |
| | | | |
18 Tail (without clamp) | | | | |
| | | | |
19 Rudder | | | 322| |
| | | | |
20 Guy sticks, each 56 | | | 112| |
| | | | |
21 Propellers | | | 837| |
| | | | |
22 Extra length of midrod at front | | | 129| |
| | | | |
23 Wood bowsprit | | | 132| |
| | | | |
24 Other things | | | | |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (375 at starting flight) | | | 200| |
| | | | |
28 Water (2100 at starting flight) + | | | | |
616 in boiler | | | 1400| |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |13,370| |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |68 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs | | | | |
| | | | |
40 Total area of horizontal tail sq. | | | | |
ft. | | 6.94| | |
| | | | |
41 Total area of rudder (vertical) | | | | |
sq. ft. | | 7.64| | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute) | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.) | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings† | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings | | | | |
| | | | |
51 Root angle of wings, 10° | | | | |
| | | | |
52 Tip angle of wings, 10° | | | | |
| | | | |
53 Position of wings | | | | |
| | | | |
54 How guyed | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail | | | | |
| | | | |
59 Angle of tail, 7° 30′ | | | | |
| | | | |
60 Co-efficient elasticity of tail | | | | |
| | | | |
61 Position of rudder | | | | |
| | | | |
62 | | | | |
| | | | |
63 Line of thrust, 1500 | | | | |
| | | | |
64 Center of gravity_1 of whole | | | | |
| | | | |
65 Center of gravity_2 | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate | | | | |
| | | | |
67 Center of pressure_2 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+-----+------+------+

Parts. Remarks.

1 Front end of midrod, 1611.5.

2 Front edge of F. W., 1609.7.

5 C. of P. on F. W., 1577.7.

8 Back edge of F. W., 1529.7.

11 Line through center of propellers, 1500.

15 C. of G., 1494.6.

18 Front edge of R. W., 1411.7.

21 C. of P. on R. W., 1379.7.

24 Rear end of midrod, 1360.3.

27 Rear end of R. W., 1331.7.

* H.P = (Rev.×diam.×pitch ratio×thrust)/33000

[p303]

DATA SHEET No. 7.

Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 12, 1899.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for gears, clutch, shafts, etc. | | | 3050| |
| | | | |
2 Engine | | | 464| |
| | | | |
3 Pump, 334; pump shaft, with gear | | | | |
and eccentric and end rod, 55 | | | 389| |
| | | | |
4 Hull Covering, 264; apron 115; | | | | |
piece behind separator, 19 | | | 398| |
| | | | |
5 Gasoline and air tanks, 167, 165; | | | | |
air valve, 16 | | | 348| |
| | | | |
6 Smokestack, 310; piece to protect | | | | |
midrod, 63 | | | 373| |
| | | | |
7 Float, 275; drop piece for rudder, | | | | |
57; guy-post, 18 | | | 350| |
| | | | |
8 Reel, fork and float, 128; steam | | | | |
gauge with pipe, 81 | | | 209| |
| | | | |
9 Wing clamps, 200; guy-post clamps, | | | | |
32 | | | 232| |
| | | | |
10 Boiler, 764; burner, 170; counter, | | | | |
95 | | | 1029| |
| | | | |
11 Rear extension to midrod | | | 174| |
| | | | |
12 Separator and pipes to engine and | | | | |
pump | | | 502| |
| | | | |
13 Exhaust pipe, 84 | | | 84| |
| | | | |
14 Front lower bearing point, 84; | | | | |
clutch post, 41 | | | 125| |
| | | | |
15 Rear bearing points, 146; extra | | | | |
strengtheners, 32 | | | 178| |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp) (2180 in | | | | |
1896) | | | 2342| |
| | | | |
18 Tail (without clamp); part of | | | | |
rudder | | | | |
| | | | |
19 Rudder reduced (No. 2 or new one, | | | | |
299) | | | 322| |
| | | | |
20 Guy sticks, each 56 | | | 112| |
| | | | |
21 Propellers (95 cms.; wood, 837; 95 | | | | |
cms. canvas, 548) | | | 837| |
| | | | |
22 Extra length of midrod (front), 129 | | | 129| |
| | | | |
23 Wood bowsprit (complete), 132 | | | 132| |
| | | | |
24 Other things | | | | |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (375 at starting flight) | | | 200| |
| | | | |
28 Water (2100 at starting flight) + | | | | |
616 in boiler | | | 1400| |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |13,379| |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |68 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs. | | | | |
| | | | |
40 Total area of horizontal tail sq. | | 6.94| | |
ft. | | | | |
| | | | |
41 Total area of rudder (vertical) | | | | |
sq. ft. | | 7.64| | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute) | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.) | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings† | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1 in 12 | | | | |
| | | | |
51 Root angle of wings, 10° | | | | |
| | | | |
52 Tip angle of wings, 10° | | | | |
| | | | |
53 Position of wings | | | | |
| | | | |
54 How guyed | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail | | | | |
| | | | |
59 Angle of tail, 7° 30′ | | | | |
| | | | |
60 Co-efficient elasticity of tail, | | | | |
1240 grammes at center of rudder to | | | | |
bring it to a horizontal; 490 grammes | | | | |
at point same distance from front | | | | |
end of rudder as length of rudder of | | | | |
1896, to bring to horizontal | | | | |
| | | | |
61 Position of rudder | | | | |
| | | | |
62 | | | | |
| | | | |
63 Line of thrust, 1500 | | | | |
| | | | |
64 Center of gravity_1 of whole | | | | |
| | | | |
65 Center of gravity_2 | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate | | | | |
| | | | |
67 Center of pressure_2 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+-----+------+------+

Parts. Remarks.

1 Front end of bowsprit, 1700.5. Front end of midrod 1611.5.

3 Front edge of F. W., 1609.7.

6 C. of P. on F. W., 1577.7.

9 Rear edge of F. W., 1529.7.

12 Line through center of propellers 1500.

16 Front edge of R. W., 1411.7.

19 C. of P. on R. W., 1379.7.

22 End of midrod, 1360.3.

25 Front end of rudder, 1343.5.

28 Back edge of R. W., 1331.7.

31 Center of rudder, 1288.

34 Back end of rudder, 1229.5.

* H.P. = (Rev.×diam.×pitch ratio×thrust) / 33000

† This is calculated on the assumption that the center of pressure
on each wing or on a pair of wings at a motion of 2000 feet per
minute is in ordinary curved wings 2-5 the way from the front to the
rear, that for wings of usual size the rear wing have 2-3 of the
efficiency per surface of the front ones and that the tail proper
bears no part of the weight; but if rear wing is smaller or larger
this efficiency is smaller or larger per unit of surface.

[p304]

DATA SHEET No. 8.

Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 19, 1899.

Parts. Remarks.

1 Front end of bowsprit, 1683.5.

2 C. of float, 1614.5.

5 Front end of midrod, 1611.5.

8 C. of reel and float, 1577.5.

11 Front edge of F. W., 1609.7.

14 C. of P. on F. W., 1577.7.

17 Rear edge of F. W., 1529.7.

20 Line through center of propellers, 1500.

24 C. of G., 1498.

27 Front edge of R. W., 1406.7.

30 C. of P. on R. W., 1374.7.

33 End of midrod, 1360.3.

36 Front end of rudder, 1343.5.

39 Back edge of R. W., 1326.7.

41 Center of rudder, 1288.

44 Back end of rudder, 1229.5.

47 N. B.--Distance between C. P. on F. W., and C. G. = 79.7.
Distance between C. P. on R. W. and C. G. = 123.3. If the mean C. P.
is to be over the C. G. we should require an efficiency for the rear
wings of 64.6%.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

[p305]

DATA SHEET No. 9.

Weight of Aerodrome No. 6, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 27, 1899.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for clutch. etc. | | | 2867| |
| | | | |
2 Engine, gears, shafts, etc. | | | | |
| | | | |
3 Pump, 123; pump shaft, 49 | | | 172| |
| | | | |
4 Hull covering, including apron and | | | | |
piece behind separator | | | 274| |
| | | | |
5 Gasoline and air tanks, 167, 174; | | | | |
air valve, 18 | | | 361| |
| | | | |
6 Smokestack, 319; counter, 95; | | | | |
burner, 170 | | | 584| |
| | | | |
7 Float | | | 290| |
| | | | |
8 Reel, fork and float | | | 128| |
| | | | |
9 Wing clamps, 188; guy-post clamps, | | | | |
24 | | | 212| |
| | | | |
10 Boiler, 764; steam gauge and | | | | |
connections, 79 | | | 843| |
| | | | |
11 Front bearing point, 75; clutch | | | | |
post, 58; rear bearing points, 155 | | | 288| |
| | | | |
12 Separator and pipes leading to | | | | |
engine and pump | | | 502| |
| | | | |
13 Drop piece and guy-post for rudder | | | 75| |
| | | | |
14 | | | | |
| | | | |
15 | | | | |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp), repaired | | | 2123| |
| | | | |
18 Tail (without clamp) | | | | |
| | | | |
19 Rudder | | | 299| |
| | | | |
20 Guy sticks | | | 106| |
| | | | |
21 Propellers | | | 628| |
| | | | |
22 Extra length of midrod | | | 377| |
| | | | |
23 Wood bowsprit | | | 78| |
| | | | |
24 Other things (canvas keel, 36; | | | | |
rudder, 76) | | | 112| |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (at starting flight) | | | 175| |
| | | | |
28 Water (at starting flight) | | | 1525| |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |12,019| |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |54 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying | | | | |
weight in lbs | | | | |
| | | | |
40 Total area of horizontal tail sq. | | | | |
ft. | | 9.5 | | |
| | | | |
41 Total area of rudder (vertical) | | | | |
sq. ft. | | 7.75| | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute) | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.) | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings† | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1 in 18 | | | | |
| | | | |
51 Root angle of wings, 10° | | | | |
| | | | |
52 Tip angle of wings 10° | | | | |
| | | | |
53 Position of wings. | | | | |
| | | | |
54 How guyed. | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail | | | | |
| | | | |
59 Angle of tail, 5° | | | | |
| | | | |
60 Co-efficient elasticity of tail, | | | | |
200 grammes at center to deflect it | | | | |
to the horizontal | | | | |
| | | | |
61 Position of rudder | | | | |
| | | | |
62 | | | | |
| | | | |
63 Line of thrust, 1500 | | | | |
| | | | |
64 Center of gravity_1 of whole | | | | |
| | | | |
65 Center of gravity_2 | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate | | | | |
| | | | |
67 Center of pressure_2 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+-----+------+------+

Parts. Remarks.

1 Front end of bowsprit, 1695.7. Weight 2867 includes Parts 2.

2 Front end of midrod, 1623.7.

5 C. of float, 1618.2.

8 Reel and float, 1576.7.

11 Front edge, F. W., 1595.8.

13 C. of P. on F. W., 1563.8.

16 Rear edge F. W., 1515.8.

19 Line through center of propellers, 1500.

23 C. of G., 1485.5.

26 Front edge of R. W., 1406.7.

29 C. of P. on R. W., 1374.7.

32 End of midrod, 1352.2.

35 Front end of rudder, 1333.9.

38 Rear edge of R. W., 1326.7.

40 Center of rudder, 1280.6.

43 Back end of rudder, 1219.9.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

† This is calculated on the assumption that the center of pressure
on each wing or on pair of wings at a motion of 2000 feet per minute
is in ordinary curved wings 2-5 the way from front to rear, that for
wings of usual size the rear wings have 2-3 of the efficiency per
surface of the front ones and that the tail proper bears no part of
the weight; but if the rear wing is smaller or larger this efficiency
is smaller or larger per unit of surface.

[p306]

DATA SHEET No. 10.

Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 27, 1899.

---------------------------------------+-------------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+--------+------+------+
|‹m.›| ‹ft.› |‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, gears, shafts, | | | | |
etc. (such as guy-wires and turn | | | | |
buckles, 26g). | | | 3342| |
| | | | |
2 Engine. | | | 476| |
| | | | |
3 Pump, 301; pump shaft, 55; support | | | | |
to pump, 33. | | | 389| |
| | | | |
4 Hull covering: front, 47; sides, | | | | |
92; top 46; small side pieces, 44. | | | 229| |
| | | | |
5 Gasoline and air tanks, 167, 165; | | | | |
air valve, 18; netting, 30; piece | | | | |
rear of separator, 20. | | | 400| |
| | | | |
6 Smokestack, 310; piece to protect | | | | |
midrod, 63. | | | 373| |
| | | | |
7 Float, 290; drop piece for rudder, | | | | |
57. | | | 347| |
| | | | |
8 Reel, fork and float, 128; counter, | | | | |
95. | | | 223| |
| | | | |
9 Wing clamps, 202; guy-post clamps, | | | | |
33. | | | 235| |
| | | | |
10 Burner, 170; boiler 759. | | | 929| |
| | | | |
11 Separator with tubes brazed to it. | | | 513| |
| | | | |
12 Steam pipe, 87; steam gauge and | | | | |
connections, 81. | | | 168| |
| | | | |
13 Exhaust pipe, 90; wooden plugs in | | | | |
nose of frame, 10 | | | 100| |
| | | | |
14 Upper front bearing point and | | | | |
clutch post. | | | 136| |
| | | | |
15 Lower front bearing point, 84; | | | | |
lower rear bearing point, 146; | | | | |
clutch, 41. | | | 271| |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp), front, | | | | |
2×662; rear 2×605. | | | 2534| |
| | | | |
18 Tail (without clamp). | | | | |
| | | | |
19 Rudder. | | | 299| |
| | | | |
20 Guy sticks 65; rear, 50. | | | 114| |
| | | | |
21 Propellers, 100 cm. round ends, | | | | |
30° blade. | | | 757| |
| | | | |
22 Extra length of midrod, front, | | | | |
174; rear, 227. | | | 401| |
| | | | |
23 Wood bowsprit (heavy one). | | | 130| |
| | | | |
24 Other things. | | | | |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (390 at starting flight). | | | 225| |
| | | | |
28 Water (2000 at starting flight). | | | 1500| |
| | | | |
29 | | | | |
| | | | |
30 Lead on bowsprit to balance. | | | 13| |
| | | | |
31 Sundries unknown. | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight. | | |14,704| 1 03 |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail). sq. ft. | |68 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs. | | 2.1935 | | |
| | | | |
40 Total area of horizontal tail. sq. | | | | |
ft. | | 6.94 | | |
| | | | |
41 Total area of rudder (vertical). | | | | |
sq. ft. | | 7.64 | | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute). | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.). | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn. | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings†. | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1 in 12, but | | | | |
about 1 in 11 now. | | | | |
| | | | |
51 Root angle of wings, 10°. | | | | |
| | | | |
52 Tip angle of wings 10°. | | | | |
| | | | |
53 Position of wings. | | | | |
| | | | |
54 How guyed. | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail. | | | | |
| | | | |
59 Angle of tail, 5° elevation at | | | | |
rear end. | | | | |
| | | | |
60 Co-efficient elasticity of tail, | | | | |
200 grammes at center to deflect it | | | | |
to a horizontal. | | | | |
| | | | |
61 Position of rudder. | | | | |
| | | | |
62 | | | | |
| | | | |
63 Line of thrust, 1500. | | | | |
| | | | |
64 Center of gravity_1 of whole, 1498. | | | | |
| | | | |
65 Center of gravity_2. | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate. | | | | |
| | | | |
67 Center of pressure_2. | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+--------+------+------+

Parts. Remarks.

1 13 grammes of lead on end of bowsprit.

2 End of bowsprit, 1708.

4 C. of float, 1622.

6 Front end of midrod, 1619.

9 Reel and float, 1601.5.

12 Front edge of F. W., 1609.7.

15 C. of P. on F. W., 1577.7.

17 Rear edge of F. W., 1529.7.

20 Line through center of propellers, 1500

24 C. of G., 1498.

27 Front edge of R. W., 1404.7.

30 C. of P. on R. W., 1372.7.

33 End of midrod, 1350.3.

36 Front end of rudder, 1333.5.

39 Back edge of R. W., 1324.7.

41 Centre of rudder, 1279.5.

44 Rear end of rudder, 1222.

47 Distance between C. P. on F. W. and C. G., = 79.7. Distance
between C. P. on R. W., and C. G. = 125.3. If the mean C. P. is to
be over the C. G. we should require an efficiency of 63.6 for the
rear wings.

* H. P. = (Rev.×diam.×pitch ratio×thrust)/33000

† This is calculated on the assumption that the center of pressure
on each wing or on pair of wings at a motion of 2000 feet per minute
is in ordinary curved wings 2-5 the way from front to rear, that for
wings of usual size the rear wings have 2-3 of the efficiency per
surface of the front ones and that the tail proper bears no part of
the weight: but if the rear wing is smaller or larger this efficiency
is smaller or larger per unit of surface.

[p307]

DATA SHEET No. 11.

Weight of Aerodrome No. 5, Superposed Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, August 3, 1899.

---------------------------------------+----------+-------------+
Parts. | Sizes. | Weight. |
---------------------------------------+----+-----+------+------+
|‹m.›|‹ft.›|‹gr.› |‹lbs.›|
1 Frame, including everything of | | | | |
metal, permanent and undetachable, | | | | |
such as bed-plate, cross-rods for the | | | | |
support of propellers, bearing points | | | | |
for clutch, etc. | | | 3556| |
| | | | |
2 Engine, complete | | | 476| |
| | | | |
3 Pump, 301; pump shaft, 55; support | | | | |
to pump, 33 | | | 389| |
| | | | |
4 Hull covering, 276; apron, 117; | | | | |
piece behind separator | | | 393| |
| | | | |
5 Gasoline and air tanks, 167, 165; | | | | |
air valve, 17 | | | 349| |
| | | | |
6 Smokestack and piece to protect | | | | |
midrod | | | 385| |
| | | | |
7 Float, 290; drop piece for rudder, | | | | |
57; guy-post and clamp, 17 | | | 364| |
| | | | |
8 Reel, fork and float, 128; steam | | | | |
gauge with pipe, 81 | | | 209| |
| | | | |
9 Wing claps, 202; guy-post clamps, 33 | | | 235| |
| | | | |
10 Boiler, 775; burner, 171; counter, | | | | |
100 | | | 1046| |
| | | | |
11 Rear extension to midrod | | | 227| |
| | | | |
12 Separator and pipes to engine and | | | | |
pump | | | 513| |
| | | | |
13 Exhaust pipe | | | 90| |
| | | | |
14 Front lower bearing points, 84; | | | | |
clutch post, 41 | | | 125| |
| | | | |
15 Rear bearing points, 146; extra | | | | |
strengtheners, 32 | | | 178| |
| | | | |
16 | | | | |
| | | | |
17 Wings (without clamp) | | | | |
| | | | |
18 Tail (without clamp), part of | | | | |
rudder | | | | |
| | | | |
19 Rudder | | | 309| |
| | | | |
20 Guy sticks, each 60 | | | 120| |
| | | | |
21 Propellers, 100 cm. round end | | | 757| |
| | | | |
22 Extra length of midrod, front | | | 174| |
| | | | |
23 Wood bowsprit | | | 130| |
| | | | |
24 Other things, 248 grammes of lead | | | | |
on end of bowsprit | | | 248| |
| | | | |
25 | | | | |
| | | | |
26 | | | | |
| | | | |
27 Fuel (at starting flight) | | | | |
| | | | |
28 Water (at starting flight) | | | | |
| | | | |
29 | | | | |
| | | | |
30 | | | | |
| | | | |
31 Sundries unknown | | | | |
| | | | |
32 | | | | |
| | | | |
33 | | | | |
| | | | |
34 Total flying weight | | |14,354| |
| | | | |
35 | | | | |
| | | | |
36 | | | | |
| | | | |
37 | | | | |
| | | | |
38 Total area of support (not | | | | |
including tail) sq. ft. | |87.5 | | |
| | | | |
39 Total area of support in feet, | | | | |
divided by total flying weight in lbs. | | 2.75| | |
| | | | |
40 Total area of horizontal tail sq. | | | | |
ft. | | 6.94| | |
| | | | |
41 Total area of rudder (vertical) | | | | |
sq. ft. | | 7.64| | |
| | | | |
42 Horse-power at brake Horse-power | | | | |
by formula* | | | | |
| | | | |
43 | | | | |
| | | | |
44 Lift at pendulum (during one | | | | |
minute absolute) | | | | |
| | | | |
45 Lift at pendulum (during one | | | | |
minute in terms of wt.) | | | | |
| | | | |
46 Minimum pressure with which wheels | | | | |
turn | | | | |
| | | | |
47 Position of center of pressure of | | | | |
wings† | | | | |
| | | | |
48 | | | | |
| | | | |
49 | | | | |
| | | | |
50 Curvature of wings, 1 in 11 | | | | |
| | | | |
51 Root angle of wings, 10° | | | | |
| | | | |
52 Tip angle of wings, 10° | | | | |
| | | | |
53 Position of wings | | | | |
| | | | |
54 How guyed | | | | |
| | | | |
55 | | | | |
| | | | |
56 | | | | |
| | | | |
57 | | | | |
| | | | |
58 Position of tail | | | | |
| | | | |
59 Angle of tail | | | | |
| | | | |
60 Co-efficient elasticity of | | | | |
tail, 200 grammes at center gives | | | | |
deflection of 5° | | | | |
| | | | |
61 Position rudder | | | | |
| | | | |
62 Elasticity caused by rubber bands | | | | |
| | | | |
63 Line of thrust, 1500 | | | | |
| | | | |
64 Center of gravity_1 of whole | | | | |
| | | | |
65 Center of gravity_2 | | | | |
| | | | |
66 Center of pressure_1 of whole | | | | |
estimate | | | | |
| | | | |
67 Center of pressure_2 | | | | |
| | | | |
68 | | | | |
| | | | |
69 | | | | |
| | | | |
70 | | | | |
| | | | |
71 | | | | |
| | | | |
72 | | | | |
---------------------------------------+----+-----+------+------+

Parts. Remarks.

1 C. P. on F. W., 1577.7.

2 Line through center of propellers, 1500.

6 C. of G., 1498.

8 C. P. on R. W., 1372.7.

* H. P. = (Rev.×diam.×pitch ratio×thrust) / 33000

[p308]

DATA SHEET No. 12.

Weight of Aerodrome, One-Quarter Model.
Certified to by Chas. M. Manly, June 11, 1901.

* H.P. = (Rev.×diam.×pitch ratio×thrust) / 33000

† This is calculated on the assumption that the center of pressure
on each wing or on pair of wings at a motion of 2000 feet per minute
is in ordinary curved wings 2-5 the way from front to rear, that for
wings of usual size the rear wing have 2-3 of the efficiency per
surface of the front ones and that the tail proper bears no part of
the weight; but if rear wing is smaller or larger this efficiency is
smaller or larger per unit of surface.

[p309]

INDEX

Abbreviations and symbols for points on aerodrome … 14, 15

Accidents, in launching large aerodrome … 126, 184, 185, 265–281

― loss of model aerodrome … 17, 94, 154

Aeolipiles, alcohol … 55, 56, 59, 60, 65, 66, 112

Aerial navigation, report of Board of Ordnance on … 276, 279

Aerodrome, balancing of … 45–52, 81, 90, 109, 134, 211, 212

― construction of … 53–80, 164–187, 234–250

― definition of word … iii

― dimensions of (‹see› aerodrome models and data sheets).

― eighth-size model … 133, 134, 154

― engines (‹see› engines and motors).

― experiments with models … 6–14, 16–24, 133–155

― field trials (‹see› trials).

― first flight of model, May 6, 1896 … 2, 3, 107, 108, 117

― first trial of a “flying machine” in free air … 97

― flight (‹see also› trials).

― ― first model, May 6, 1896 … 2, 3, 107, 117

― ― large machine (1903) … 126, 127, 255–282

― ― photographs of … 108, 259, 260

― large … 126, 127, 129, 130, 156, 183, 225, 255–282

― ― construction of … 164–187, 234–250

― ― launching apparatus for … 156–163, 183

― ― shop tests … 251–254

― ― trials (1903) … 126, 181, 255–282

― ― weight of … 277

― launching apparatus for models … 92–122, 133, 134

― ― ― ― large aerodrome … 156–163, 183

― man-carrying (‹see also› aerodrome large) … 123, 125, 129, 130,
151, 153, 156–187, 234–250, 255, 282.

― model, descriptions of (‹see also› data sheets).

― ― ― ― No. 0 … 21, 30, 31, 36, 38, 40, 53, 55, 75

― ― ― ― Nos. 1, 2, 3 … 28, 29, 38, 40, 53

― ― ― ― No. 4 … 53, 62–67, 69, 70, 72, 75–79, 81–83, 86, 92–109, 120

― ― ― ― No. 5 … 26, 64–66, 69, 70, 75–79, 81, 82–84, 86, 88, 89,
90, 92–109, 110–122, 130, 131, 134, 135–155, 158, 174, 188, 189,
208–210, 231, 257, 281.

― ― ― ― No. 6 … 49, 61, 62, 78–81, 89, 90, 92–109, 110–122, 130,
131, 134, 158, 174, 188, 193, 208, 210, 231, 257, 281.

― ― ― ― rubber pull … 11–20

― ― eighth-size … 133, 134, 154

― ― frames of … 39, 53–80, 90, 112, 119, 129

― ― launching apparatus for … 92–112, 134

― ― quarter-size … 158, 159, 170, 226–233, 234, 255, 257–261, 281

― ― results from … 17, 129

― ― steam driven (‹see also› Nos. 5, 6) … 122, 164, 165, 224, 281

― ― trials, of Nos. 0, 1, 2, 3 (1892) … 29, 53

― ― ― ― Nos. 4, 5, 6 (1893) … 63, 92–106

― ― ― ― Nos. 5, 6 (1896) … 2, 79, 106–109

― ― ― ― No. 6 (1898) … 61

― ― ― ― Nos. 5, 6 (1899) … 49, 79, 135–155, 231, 257

― ― ― ― Nos. 30, 31, and others … 6–14, 17, 19

― motors (‹see› engines and motors).

― quarter-size models (‹see› aerodrome models).

― rubber-power models … 5, 8–24, 44

― weights of (‹see› weight and data sheets).

Aerodromics, science of … iii, 7

Aerodynamics … 7, 30, 43, 44, 80, 91, 99

― experiments in … 1, 6, 7, 19, 21, 32, 41, 80, 98, 128, 150, 153

Aeronaut (‹see also› aviator) … 130

Air, compressed … 11, 24, 25, 26, 68, 112

― liquid … 154

― resistance of … 6, 8, 9, 142, 165–167

Air-chamber … 64, 68, 69, 98, 112, 113

Air-cooled engine … 226

Alcohol and hydrocarbons, use of, as fuel … 24, 25, 35, 55, 57, 66,
72, 73

Alcohol aeolipiles … 55, 56, 60, 66, 69, 112

Allegheny Observatory, experiments at … 11, 13, 31, 150

Allotment, Government, for man-carrying aerodrome … 124–126, 132, 278

Aluminum-bronze, use of … 114, 116, 173, 174

Aluminum in engine construction … 32, 114, 243, 252

― sheathing of hull … 69

― wires … 84

Aneroid barometer for determining height … 186

Anemometer cups … 143

Angle, diedral, of wings … 45, 82, 89

― of inclination … 41, 43, 83, 99, 100

― ― rotation … 61

― ― wings, root angle … 83, 89, 91, 97, 98, 100, 101, 103

Area, relation to weight and power … 43, 44, 64, 90, 99, 101

― supporting (‹see also› surface) … 82, 87–89, 91, 93

Asbestos, use of … 35, 63, 67

Associated Press statement to … 266, 280

Aviator, equilibrium of … 161, 169, 253

― weight of … 130, 210, 256

Aviator’s car … 185–187, 214, 251, 252

― jacket … 273

― seat … 185

― wheel … 214, 216, 265, 266, 272

Bagging or pocketing of wings … 84, 86, 100, 195, 203

Balance (‹see also› equilibrium) … 82, 165

Balancing of aerodrome … 45–52, 81, 90, 109, 134, 211, 258

― ― engine … 246, 247

― ― wings and rudder … 211, 255

Ball-bearings on launching car … 160, 175, 177, 252, 253

Bamboo ribs for wings … 200

Barometer, aneroid … 186

Barus, Dr Carl, boiler experiments by … 58, 70–75, 93–95

Batteries, electric … 11, 24, 26, 27, 162, 212, 220–222, 237, 240,
241, 257, 262, 263

Bearings, ball, on aerodrome and launching car … 160, 175, 177, 252,
253

― bronze, on model aerodromes … 177

Bedplates … 116, 168, 175, 273

“Beehive” boilers (‹see› boilers).

Bell Alexander Graham … 4, 96, 102–104, 106, 108

Bessemer steel guy wires … 172

Bevel gears … 174, 177, 241

Bird-wings, construction of … 7, 188, 200, 201

Birds, soaring, study of … 7, 9, 88, 287

Blazer, S. M., engineer … 126

“Bleeder,” feed tube for burner … 67, 113

Blériot aeroplane of Langley type … 283

Blower for artificial wind … 61, 97, 225

Board of Ordnance and Fortification … 124, 126, 132, 250, 255, 271,
276, 278, 279, 280

Boat, house … 92, 93, 136, 148, 149, 156–163, 269

Body, construction of (‹see also› hull) … 32, 60

Boiler, “Beehive” type … 34, 39

― coil of … 34–39, 70, 71, 113–116

― development of … 55–59, 65, 68, 70–75, 102, 114–116

― pressure … 58, 59, 63, 68, 69, 101, 102

― report on, by Dr. Barus … 70–75

― serpollet type … 56, 57

― spray type … 70

― tests of … 70–75, 135

― tubing of … 70–75, 114, 141

― water-tube type of … 34, 35, 70–75, 114

Bolometer, development of … 123

Brake, horse-power … 28, 37, 58, 61, 64–69, 117, 223, 224, 230, 233

― Prony … 38, 61, 65, 66, 117, 179, 222, 228, 233, 249

Brass, use of … 54, 63, 113, 180

Brazing … 117, 173, 175, 235, 236

Bronze, aluminum … 114, 116, 171, 173, 177, 234, 237–240

Burners, Bunsen type … 35, 68, 72, 113

― gasoline … 56, 60, 61, 62, 65, 67, 68, 70–75, 112–116, 149

― shield for … 60, 67, 95, 115

Bushing, cast-iron … 114–117, 121

Buzzard, American, and “John Crow,” study of … 285

Cameras, telephoto … 260, 261, 273

“Canvas-covered” propellers … 84, 178

Car, aviator’s … 185–187, 214, 251, 252

― launching (‹see› launching apparatus).

Carbon, energy developed by the use of … 27

Carbonic-acid gas as motive power … 11, 24, 26, 28, 29, 39, 53, 54

― liquid … 24, 28

― ― freezing of … 28–29

― ― latent heat of … 28

Carburetor, development of, suitable type of … 224, 225, 239, 240,
248, 249, 251, 253, 259

Carpenter, Frank G., witnesses flights … 108

Cast-iron, use of (‹see also› iron) … 114–117, 121, 234–236, 240

“Cast-off” apparatus … 96, 110

Center of gravity … 10, 13–16, 45–52, 61, 64, 80, 91, 103, 143, 144,
150, 209, 210

― ― ― in relation to pressure … 10, 11, 15, 46, 48, 64, 98, 99, 101,
103

― ― pressure … 7, 10, 11, 13, 15, 45–52, 78, 80, 84, 87, 88, 90, 91,
200, 209, 210

― ― ― formulæ for … 49, 87, 88, 90

― ― wings and tail … 16

― ― rotation … 62

― ― thrust … 62

Centrifugal pump … 241, 248

Charcoal, as fuel … 57

China silk (‹see› silk).

Chopawamsic Island, Potomac River … 93, 135, 153, 183, 256

Chronograph attachments … 162, 163, 229

Circulating pump … 114, 244

Clamps, wing … 82, 89, 145, 183

Coast and Geodetic Survey … 93, 145, 256

Coefficient of elasticity … 146

Coil, spark (‹see› sparking devices).

Compressed air … 24, 25–26, 68, 112, 113

Condenser, steam … 65

Construction and tests of large engine … 234–250

Construction of frame and engines … 53–80

― ― ― of large aerodrome … 164–187

― ― supporting surfaces … 188–206

Control, equilibrium and … 77, 78, 119, 207–217

― gyroscopic … 78, 211

Cooling systems, (‹see› water and air cooling).

Copper, use of … 27, 39, 63, 72, 112–115, 162

Copper tubing … 35, 56, 57, 59, 112, 115, 140, 141, 248

Counter, speed … 62, 120, 185, 243, 249

― ― propellers … 178

Covering for tail … 86, 103

― ― wings … 54, 63, 77, 81, 86, 88, 90, 148, 194, 195, 205

Crank bell … 110

― starting … 244

Crank-pin … 237–239, 243–247

Crank-shaft … 237, 239, 244–246, 250

Cube, law of the … 129, 130, 222, 244, 249

Currie, Rolla P., report on American Buzzard … 289

Curved surfaces (‹see also› wing curvature) … 18, 44, 47, 99

Cylinders (‹see also› engines, cylinders).

― aluminum in construction of … 114

― brass in construction of … 54

― steel tubes in … 116, 121, 234, 235, 239, 240

― construction of … 112, 114, 116, 121, 212, 213, 232, 235, 239,
240, 246

― five, engine … 245, 246, 250, 255

― high-pressure … 33

― low-pressure … 33

― multiple, engine … 226

― oscillating … 33, 38

― tests of (‹see also› engine tests) … 55

― walls of … 239

― weight of … 246, 247, 250

Daniell, on energy in storage batteries … 27

Data sheets … 297

Definitions of terms and symbols … 14, 15

Deflection, absence of … 269

de Lucy, on sustaining surfaces … 19

Diedral angle of wings … 45, 82, 83, 85, 89, 96, 146

Dimensions (‹see› aerodrome descriptions and data sheets).

Distance of flights … 103, 107–109, 135–155, 258

Distortion of wings … 82–84, 91, 98, 105

Dry batteries … 262

Duration of flights (‹see also› time) … 103, 107, 108, 137, 145,
148, 258

Dynamometer, use of … 222, 228, 229, 230, 242, 247, 249

Eagle quill and spruce rib, comparative strength of … 201

Early steam motors and other models … 30–40

Efficiency of wings … 87, 89, 91, 144, 192, 193

Eighth-size models … 133, 134, 154

Elastic limit of rubber … 9, 22, 23

Elasticity of tail … 78, 90, 144, 152

― coefficient of … 51, 144, 146

Electric batteries … 24, 26, 27, 212, 262, 263

― circuits … 70, 212, 220–223, 237, 241, 257

Electricity as motive power … 24, 26–28

Energy in foot pounds (‹see also› lift) … 23–27

Engine (‹see also› motors) … 112–116, 179, 180, 222–225, 226–233,
234–250, 281

― American builders … 131, 180, 219, 228

― air-cooled … 226

― automobile … 219

― balancing of … 246, 247

― carbonic-acid gas … 24, 26–29

― compressed air … 11, 24–26, 68, 112

― construction of, and frames … 53–79, 114, 116, 219, 223–233

― ― ― ― tests … 234–250

― contract for … 126

― cylinders of … 33, 38, 54, 112, 114–116, 121, 212, 213, 232,
235–239, 246, 250, 255

― description of one-horse-power … 37, 116

― electric … 24, 26–28

― European builders … 131, 140, 219, 234

― experimental … 218–225

― five-cylinder … 224, 232, 234–250, 255

― gas (‹see also› gasoline) … 26, 28, 131, 133

― gasoline … 24, 37, 65, 125, 131, 179, 210, 218, 219, 224, 277

― gunpowder … 24, 25

― horse-power (‹see also› brake, horse-power) … 37, 58, 116, 233

― hot-water … 24, 25, 68

― large, construction and tests of … 133, 234–250, 281, 282

― ― weight of … 247, 250, 256

― Manly … 219–225

― multiple cylinder … 226

― oscillating … 33, 38

― radiator … 252

― steam … 24, 30–40, 64, 69, 116, 120

― ― dimensions of … 116

― Stringfellow … 30, 31

― tests … 37, 55, 61, 69, 102, 133, 148, 234–250, 281, 282

― water-cooled … 220, 235, 236, 241, 247, 248, 252

― weight of … 116, 126, 130, 209, 247, 250

Equilibrium, maintenance of … 6, 31, 45, 51, 144, 213–216

― of aviator … 161, 169, 213, 253

― and control … 77, 78, 119, 207–217

― lateral, and longitudinal stability … 31, 45–52

Evaporation, rate of gasoline … 65, 66

Evaporators … 37, 65, 67, 114, 148

“Factor of safety” … 111, 186

Feathers, pliability of … 188, 200

― toy-propeller, blades made of … 8

Feed, gravity … 239

Fibre insulation … 241, 257

Field trials, eighth-size … 133, 134, 154

― ― large and quarto size models … 126, 158, 170, 181, 226–234,
255–282

― ― models Nos. 0, 1, 2, 3 … 29, 53

― ― ― Nos. 4, 5, 6 … 63, 92–106

― ― ― Nos. 5, 6, 2 … 61, 79, 135–155, 231, 257

Fire-proofing preparation … 148

First flight of heavier than air machine … 107, 108

First trial of a flying-machine in free air … 97

Flexure of wings … 82–84, 91, 98, 105

Flight (‹see› aerodrome and aerodrome model flights).

― bird, study of … 7

― of large machine … 126, 181, 255–282

― ― May 6, 1896 … 2, 3, 107–108

― ― models Nos. 4, 5, 6 … 2, 63, 79, 92–109, 135–155

― ― quarter size model … 259

― ― rubber-driven models … 16–20

― ― quarter-size models … 158, 170, 226–233, 243, 255, 257–261, 281

Floating the models … 64, 68, 69, 99, 103, 119, 120

Fly-wheels of engine … 242, 243, 247, 252

Flying aerodrome model as a kite … 133, 154, 155

Flying-weight of aerodromes (‹see also› data sheets) … 15, 62, 63,
76, 77, 81, 89, 91, 148, 247, 250, 256

Foot-pounds, definition of … 15

― energy in (‹see also› horse-power) … 22, 27, 62

Force-pump … 57

Formulæ:

― area … 19

― center of pressure … 49, 87, 88, 90, 101

― drift … 41, 43

― efficiency … 47

― Harting’s … 19

― horse-power … 15, 62

― lift or weight … 41, 43, 62

― Manly’s, for changing center of pressure … 51

― Maxim’s, for horse-power … 15

― resistance … 41

― soaring speed … 91

― tandem wing … 87

― work (‹see also› horse-power) … 18, 23, 27, 62

Frame, construction of, model … 39, 53–80, 90, 112, 119, 129

― ― ― large aerodrome … 164–187, 253

― main … 165–168, 170

― resistance of … 165–167

― testing of … 79

― transverse … 77, 165, 174–178

― work … 118

French academy, communication to … 3

Fuel, alcohol and hydrocarbon … 24, 25, 35, 55, 57, 66, 72, 73

― carbon … 27

― carbonic acid gas … 11, 24, 26, 28, 29, 39, 53, 54

― charcoal … 57

― gas … 26, 28, 37

― gasoline … 24, 25, 36, 37, 65–68, 112, 125, 224, 248, 259

― quantity of … 68

Fuel-tank … 36, 65, 67, 68, 112, 113

Funds for experiments … 124–126, 132, 257, 278, 279, 281

Gaertner, Mr., instrument maker … 93, 95

Gas, carbonic-acid … 24, 26, 28, 36, 68, 113

Gas-burners … 35, 55, 60, 65, 70–75, 112, 113

Gas-engine (‹see also› engines, gas and gasoline) … 26, 28, 37

― Five cylinder … 224, 234–250, 255

― large … 234–250, 277

― model … 26–28, 65, 131, 133, 232–234

Gasoline-burners … 56, 60, 62, 65, 67, 68, 70–75, 112–116, 149

Gasoline-engines … 24, 37, 65, 125, 131, 179, 210, 218–225, 232–234,
248, 259, 277

Gasoline-evaporator … 37, 65, 148

Gears … 114, 117, 136, 137, 168, 174, 175, 177, 237, 241

Gibson, Captain, recorder … 250

Goldbeater’s skin, for wings … 77

Goode, G. Brown … 97

Government allotment (‹see also› Board of Ordnance and
Fortification) … 124–126, 132, 279

Gravity, center of … 10, 13–16, 45–52, 61, 64, 80, 91, 98, 101, 103,
143, 144, 150, 209, 210

Gravity-feed … 239

Guiding (‹see› equilibrium and control; sustaining surfaces; and
rudder).

Gun-metal … 174

Gunpowder … 24, 25

Guy-posts … 184, 189, 199, 266, 267, 268, 270, 274, 275

Guying, early systems of … 81, 84–91

― wire … 81, 84–90, 99, 164–173, 189, 191, 196, 199, 264, 266

Gyroscopic control … 78, 211

Harting’s formula … 19

Head resistance … 142, 165–167

Heating apparatus (‹see› burners).

Herring, A. M., assistant … 104

Hewitt, Mr., at rescue of Mr. Manly … 273

Hodgkin’s fund, aid from … 257

Holmes, W. H. … 286, 289

Horizontal flight, velocity required to sustain … 1, 16–19, 43, 91

― rudder … 8

Horse-power, exerted by rubber … 9, 22

― Maxim’s formula … 15

― required to sustain flight … 1

― developed … 28, 37, 55, 58, 64–69, 117, 179, 223, 233, 249

Hot-water engine … 24, 25

House-boat and launching apparatus … 92–109, 110–122, 148, 149, 156,
163, 269

Huffaker, E. C. … 44, 46

Hull, construction of … 30, 32, 36, 53, 60, 69, 75, 112, 118–121

― forms of … 30, 31, 32, 38, 60, 69

― resistance … 49, 69

― steel tubes for … 39, 69, 75, 112, 118, 120

Ignition (‹see› electric batteries and circuits).

Indian rubber for power (‹see also› rubber) … 21, 40

Internal work of the wind … 6, 42

Inclination, angle of … 41, 43, 83, 99, 100

Insulation … 144, 241, 257

Iron, use of … 63, 64, 114–117, 234, 236, 240

Jacket, cork, aviator’s … 273

― water … 220, 234, 236, 241, 247, 252

“John Crow” (bird of Jamaica), study of … 285

Kite, model flown as … 133, 154, 155

Langley. S. P. … 3, 4, 9, 18, 76–79, 93, 95, 102–108, 112, 123–126,
128, 131, 133, 135, 153, 156, 161, 179, 183, 184, 188, 211, 212,
219, 223, 230, 231, 257, 266–268, 270, 271, 287, 280, 281

― statement of … 124, 280

― letter of instructions from (‹see› appendix).

― study of “John Crow” bird (‹see› appendix).

― aerodrome, War Department report on … 277, 278, 279

“Langley type” of aerodrome … 77, 164, 208, 244, 266, 276, 278–281

― ― ― rudder … 77, 86

Lateral stability … 45–52, 97

Launching, difficulties of … 10, 11, 12, 92, 94, 96, 99

― methods of … 13, 94–97, 110

― of large machine … 265–267, 271–272, 276, 282

Launching-apparatus … 92–122, 134, 149, 156–163, 183, 185, 231, 257,
261, 265–267, 270, 272, 276, 282

― overhead … 5, 92–122, 133–135, 139, 142, 143, 145, 151, 152, 154,
156–163

― underneath … 134, 135, 145–147, 151, 152, 154, 156–163, 183

― weakness of … 265, 276, 282

Launching-car … 158, 159, 183, 184, 255, 258, 262, 266–268, 271,
272, 274, 277

Launching speed (‹see also› velocity) … 135, 161, 162

Law of the cube … 129, 130

Lewis, Captain I. N. … 250

Lift of propellers (‹see also› pendulum tests) … 61, 62, 66, 69, 77,
94, 99, 102, 105, 107, 151, 189, 192

Lilienthal, Otto, on efficiency of curves … 44

Lineal velocity … 1, 43, 110, 166

Liquid air … 154

Longitudinal stability … 45–52

Lubrication … 113, 177, 234, 239, 240

McDonald, Mr. … 266, 271, 272

McKinley, President William … 123, 124

Macomb, Major M. M., report of … 276–278

Maltby, Mr., machinist … 93–95, 102, 106

Man-carrying machine … 123, 125, 129, 130, 151, 153, 156–187,
234–250, 255–282

Manly, C. M., assistant in charge of experiments … 123, 129,
218–224, 265, 266, 268, 272, 276, 278

― ― ― engine … 219–225

― ― ― formula … 51

― John M., description of flight, by … 260–261

Maxim’s formula for horse-power … 15

Mechanical flight … 2–4

― ― theory of … 1

― ― Dr. Bell on … 4

― ― Mr. Langley on … 3–4

Mica, use of … 63, 72, 115, 257

Models (‹see also› aerodrome model description and trials).

― experiments with … 1, 133–155

― ― ― small … 6–14, 17, 19

― flight of (‹see› trials).

― launching of (‹see also› launching apparatus) … 92–122, 133, 134

― rubber-driven … 5, 8–24, 76

― steam-driven (‹see also› Nos. 4, 5, 6) … 134, 135

― steam, motor, and other … 30–40

Motive power (‹see also› engines, electricity, and fuel) … 8, 11,
21–29, 118

― discussion of … 11

Motors, available (‹see also› engines) … 11, 21–29, 278

― carbonic acid gas … 11, 24, 26, 28, 29, 39, 53, 54

― compressed air … 11, 24, 25, 26, 68, 112, 113

― construction of early types of … 30–40

― electrical … 24, 26, 27, 212, 262, 263

― gas … 26, 28, 37, 131, 137

― gasoline … 24, 37, 65, 125, 131, 179, 210, 218, 219, 224, 277

― gunpowder … 24, 25

― hot-water … 24, 25, 68

― rubber … 5, 8–24, 76

― steam … 24, 25, 30–40

― weight of (‹see also› weight of engines) … 116, 126, 130, 209,
247, 250

Mount Whitney, observations on … 123

Nash, Dr. F. S. … 276

National Museum, models in … 282

Needle-valve … 56, 57, 113

Nitric acid, use of … 71

Nomenclature of parts of aerodrome … 14, 15

Oiling systems … 113, 177, 234, 239, 240

Open wind, experiments in … 42, 99, 257, 271, 272

Ordinance and Fortification (‹see› Board of).

Oxygen, necessity of … 72

Paper covering for rudder … 86, 103

Pénaud, Alphonse, toy aeroplane designed by … 7–9, 21, 22, 40

― tail or rudder … 8, 12, 13, 50, 51, 79, 82, 107, 122, 139–147,
151, 152, 153, 209, 211, 213, 214, 216, 253, 264, 270–272

“Pendulum” test for lift … 60, 61, 66, 94, 131, 135, 211, 212, 214,
232

Percaline for wing covering … 194, 195

Pinion (‹see› gears).

Piston (‹see› engines and cylinders).

Pitch of propellers … 63, 69, 76, 94, 181

Plane (‹see also› wings and surfaces).

― dropper … 150

― surface, angle of inclination of … 6, 8, 41–45, 61, 83, 97, 99, 100

― velocity required to sustain … 1, 43, 110, 166

Pocketing of wings … 84, 86, 100, 195, 203

Potomac River, location of tests on … 93

Power (‹see also› steam, fuel, and electricity).

― development of … 8, 39

― formula for … 62

― generating apparatus … 112, 125

― relation to area and weight … 43

Power-gauge (‹see› dynamometer).

Powell, Major G. H., recorder … 250, 267, 276

Press, attitude of … 127, 268

― report to, Mr. Langley’s … 280

― ― ― Mr. Manly’s … 266–267

Pressure, center of … 7, 10, 11, 13, 15, 45–52, 64, 78, 80, 84, 87,
88, 90, 91, 200, 209, 210

― ― ― rules for locating … 49, 87, 88, 90, 101

― ― ― and center of gravity … 10, 11, 15, 46, 48, 64, 98–101, 103

― steam … 24, 30–40, 53–59, 63–75, 101, 114, 117, 134, 135, 137,
141, 142, 149, 150

Pressure-gauge … 114

Prony-brake … 38, 61, 65, 66, 117, 179, 222, 228, 233, 249

Propellers … 7, 8, 11, 13, 22, 40, 68, 69, 94, 95, 102, 103, 108,
109, 118, 119, 136, 139, 143, 145, 149, 178–184, 258, 261, 262, 268,
272, 277

― construction of … 63, 76, 98, 100, 178–184

― early forms of … 7, 8, 11, 22, 33

― lift of … 61, 62, 66, 69, 77, 94, 102, 105, 107, 131, 148, 151,
189, 192

― pitch of … 63, 69, 76, 118, 181

― position of … 39, 63

― shafts of … 39, 117, 175–177, 242

― slip of … 107, 109

― speed of (‹see also› revolutions per minute) … 61, 91, 94, 99,
107, 114, 134, 264, 272

― tests of (‹see› pendulum, lift, and thrust).

― thrust of … 47, 62, 94, 119, 148, 154, 161, 174

― toy … 7, 8, 9, 21, 22

Pumps … 36, 37, 57, 59, 65, 68, 71, 75, 114, 115, 141, 241

― centrifugal … 241, 248

― circulating … 114, 244

― double-acting … 68, 114

― force … 57

Quantico, Va., flights at … 64, 66, 79, 93, 147, 255, 269

Quarter-size model … 158, 159, 170, 226–233, 243, 255, 257–261, 281

Quill, eagle’s, and spruce rib compared … 200, 201

Radiator (‹see also› engine, water-cooled) … 252

Randolph, Gen. W. F. … 276, 277

Record of flights (‹see also› data sheets) … 2, 3, 17, 107, 117,
135–155, 255–282

Reed, R. L., chief carpenter … 93–95, 102, 106, 266, 271, 272, 275

Reel attached to float … 119, 120

Relation of area to weight and power … 43, 44, 64, 81, 89, 90, 99

Reservoir (‹see› air-chamber and tank).

Resistance, air … 6, 8, 9, 142

― of frame and guy-wires … 165–167

Revolutions of engine and propellers per minute (‹see also› speed) …
33, 58, 63, 65, 66, 102, 109, 115, 249, 252

Rib, spruce and eagle’s quill, compared … 200, 201

Ribs, construction of … 37, 80, 81, 86, 89, 188, 194–206, 263, 264

Ridgway, Robert, on American Buzzard … 301

Root-angle of wings … 82, 83, 91, 98, 100, 101, 103

Rotation, angle of … 61

― center of … 62

Rubber as a source of power … 5, 8–24, 44, 76

― elastic limit of … 9, 22

― “fatigue” of … 23

― horse-power produced by … 9, 22, 23

― springs … 2, 185

― insulation … 144, 241

Rubber-driven models … 5, 8–22

Rubber-pull and rubber-twisted models … 16–24

Rudder (‹see also› tail) … 8, 9, 77, 80–91, 122, 136, 207–217, 255,
272, 275

― horizontal … 8

― Pénaud’s … 8, 12, 13, 50, 79, 87, 107, 122, 139–147, 151, 209,
211, 213, 214, 216, 253, 270–272, 275

― vertical evolution of … 81, 82, 86, 97, 101, 106

Rudder-tail (‹see› tail-rudder).

Sanding-tests of wings … 84, 85, 89, 99, 190–204

“Separator,” evolution of, for dry steam … 58, 59, 65, 68, 114, 142

Serpollet-type boilers … 56, 57

Shafts, main, construction of … 117

― propeller … 39, 117, 175–177, 242

Sharp, Archibald, on balancing of engines … 246

Sheathing, aluminum … 69

― mica … 63, 72, 115

Shop tests … 40, 218, 251–254

Silk wing-covering … 54, 63, 81, 86–88, 90, 148, 194, 195, 205

Sliding tail designed … 16, 84

Smillie, Thomas W., photographer … 260, 267, 271, 273

Smithsonian Institution … 1, 6, 17, 18, 31, 42, 124–126, 171, 174,
176, 179, 257, 260, 271, 276, 280–281

Smoke-stack … 60, 67, 74, 78

Soaring birds, study of (‹see also› appendix) … 7, 9, 88

Soaring-speed … 32, 41, 69

Sparking devices (‹see› electric batteries and circuits).

Specific gravity … 120

Speed attained (‹see also› velocity) … 31, 32, 41, 55, 61, 91, 99,
107, 114, 134, 161, 264

Speed-counter … 62, 120, 185, 243, 249, 252

Spokes, wire … 243

Spruce guy-sticks and frames … 85–87, 90

― ribs compared with quills … 200, 201

St. Louis Exposition tests … 249

Stability, lateral and longitudinal … 45–52, 77

Starter on launching-car … 94, 95

Starting-crank on launching-car … 243, 244

Steam, dry, production of … 58

Steam-chest … 117

Steam-engine … 24, 30–40, 64, 69, 116, 120

Steam-gauge … 114

― construction of frames and … 53–80

Steam-generating apparatus … 114–116

Steam-motors and other models … 30–40, 134, 135

Steam-pressure … 24, 30–40, 53–59, 63–70, 101, 102, 114, 117, 134,
135, 137, 141, 142, 149, 150

Steel, use of … 69, 112, 116, 119, 121, 172, 174, 234, 277

― tubes, for hull … 39, 69, 75, 112, 118, 120

Steering apparatus (‹see also› equilibrium and control) … 214–216,
265, 266, 272

― ― automatic … 30, 77, 211, 216

Steering wheel … 214, 216, 265, 266, 272

Storage batteries (‹see› batteries, electrical).

Stringfellow engine … 30, 31

Superposed wings … 13, 14, 17, 138, 153, 193, 231

Supporting surfaces … 11, 44, 77, 81, 99, 188–206

Supports for propellers … 112

― ― wings and tails … 36, 69

Surfaces (‹see also› planes and wings).

― covering for … 77, 81, 86, 87, 90, 148, 194, 195

― curved … 44, 46

― plane, observations on velocity of … 1

― rigid … 6, 46

― supporting … 11 44, 77, 93, 99 188–206

― sustaining … 1, 5, 41–44, 80–91, 99

― ― and guiding … 5, 80–91

Surgeons’ tape, used for mending ribs … 264

Sustaining surface … 1, 5, 41–44, 80–91, 99

― ― de Lucy on … 19

Symbols … 14, 15

Synchronizing mechanism … 108, 121, 136, 137

Table, turn … 156, 165, 166

― whirling … 1, 5, 6, 7, 11, 13, 31, 42, 165, 166, 178, 189–194

Tachometer … 62, 120, 185, 243, 249, 252

Tail … 8, 9, 70, 77, 80, 91, 99, 207–217

― adjustment of … 16, 84

― connections of … 84, 213–216

― covering … 86 103

― Pénaud … 12, 13, 50, 79, 107, 122, 139–147, 151–153, 209, 211,
213, 214, 215

― sliding … 16, 84

― use as guiding and sustaining surface … 80

Tail-rudder … 77, 86, 87, 119, 152, 153

― Langley … 77, 86

Tank, air … 64, 68, 69, 112, 114

― fuel … 36, 65–68, 112, 113

― water … 252

Telephoto camera … 260, 261, 273

Tests (‹see also› engine tests, trials, and flights).

― boilers … 70–75, 135

― construction and … 234–250

― cylinder … 55

― engine … 37, 55, 61, 69, 102, 133, 135, 148, 234–250, 251–254, 281

― experimental engine … 1902–1904 … 250

― frame … 79

― power … 61, 62, 69, 102

― resistance … 165–167

― sanding, of wings … 84, 85, 89, 90, 190–204

― shop, of large machine … 40, 218, 251–254

― St. Louis Exposition … 249

― whirling-table … 1, 5, 6, 7, 11, 13, 31, 42, 165–166, 178, 189–194

― wing … 84, 85, 89, 99, 190–204

Testing ground (‹see also› Quantico) … 64, 66, 92, 93, 255, 256,
277, 280

Thrust, center of … 62

― propeller … 47, 62, 94, 119, 148, 154, 161, 174

Thrust-recording devices … 229, 230

Thurston, R. H. … 128, 129

Time of flights … 103, 107, 108, 109, 137, 145, 148, 258

Torque … 222, 242

Toy aeroplanes … 7, 9, 21, 22, 40

Transmission (‹see also› shaft and gears) … 117, 175–177, 242

Transverse frame … 77, 165, 174–178

Trials, first … 97

― (1891) … 17

― (1892) … 53, 92

― (1893) … 65, 93–96

― (1894) … 65, 96–100

― (1895) … 101–106

― (1896) … 2, 79, 106–109

― (1897) … 123–125

― (1898) … 61

― (1899) … 79, 135–155

― (1903) … 126, 181, 255–282

Tubes in hull construction … 69, 112, 116, 119, 120, 172, 174, 234,
277

Turn-table … 156, 165, 166

Turnbuckle (‹see also› guying) … 170, 171, 172

Valve-chest … 114, 213

Valves … 114, 117, 213

― exhaust … 237

― mechanically operated … 114, 213

― motion … 112, 114, 115, 213

― needle … 56, 57, 113, 212

Vaporization … 37, 67, 148, 149

Varnish, collodion … 192

― not affected by ammonia … 198

― pyroxelene … 86

― water-proof … 263, 264

Velocity … 18, 31, 32, 55, 91, 99, 107, 109, 114, 134, 150, 161,
166, 185, 264, 265

― initial … 100, 110, 150, 163

― required to sustain plane … 1, 43, 110, 166

Vertical rudder … 81, 82, 86, 97, 101, 106

Vulcanite, use of … 257

War Department, allotment … 124–126, 132, 278, 279

― ― Board of Ordnance and Fortification … 124–126

― ― ― ― ― ― ― Report of … 276–280

Washington Evening Star, report of … 274

Watches, stop, for timing flight … 109

Water, cooling, for engine … 235, 236, 241, 247, 248, 252

Water-engine, hot … 24, 25

Water-jacket … 220, 234, 236

Water-proof varnish … 263, 264

Water-tank … 252

Watkins J. E. … 39

Weight (‹see also› data sheets).

― flying, of aerodrome … 15, 38, 62, 63, 76, 77, 81, 89, 90, 91,
101, 109, 116, 148, 206, 247, 250, 256, 277

― of aerodrome … 31, 38, 40, 53, 62, 63, 116, 126, 130, 206, 256

― ― covering for wings … 194

― ― parts of aerodrome … 31, 63, 116, 190, 250

― ― engine … 116, 117, 126, 130, 156, 209, 247, 250, 277

― per horse-power … 31, 126

― relation to area and power … 43, 44, 64, 81, 89, 90, 96

― total, with aviator … 256

Wellner, Georg … 44, 47

Wheel, fly … 242, 243, 247, 252

― steering … 214–216, 265, 266, 272

Whirling-table … 1, 5, 6, 7, 11, 13, 31, 42, 165–166, 178, 189–194

Widewater, Va., experimental grounds (1903) … 255, 256, 277, 280

Wind, artificial … 42, 61

― difficulties of launching in … 94, 99, 265, 271, 272, 276, 282

― experiments in … 42, 61, 99, 257, 271

― internal work of the … 6, 42

― open … 42, 99, 257, 271, 272

Wind-shield for burners … 60, 67, 95, 115

Wind-vane rudder … 136

Wing-clamps … 82, 89, 145, 183

Wings, adjustment of, for center of gravity … 16

― angle of … 45, 61, 82, 83, 89, 91, 97, 98, 100, 101, 103

― arrangement of … 45–47, 77, 86, 89, 194, 255

― bagging of … 84, 86, 100, 195, 203

― bird, construction of … 7, 188, 200, 201

― boxes for … 263, 264

― construction of … 7, 70, 80, 81, 87, 90, 91, 99, 105, 119, 121,
138, 188–206

― covering of, cloth … 195, 199, 204, 205

― ― ― goldbeater’s skin … 77

― ― ― paper … 86

― ― ― silk … 54, 63, 81, 86–88, 90, 148, 194, 195, 205

― ― ― weight of … 194

― curvature of … 18, 44, 46, 47, 86, 87, 90, 99, 112

― distortion of … 82, 83, 84, 91, 98, 105

― double tier … 13, 14, 17, 138, 193, 231

― efficiency of … 46, 87, 89, 91, 144, 192, 193

― flexure of (‹see› distortion of).

― pocketing of … 84, 86, 100, 195 203

― quills and spruce ribs compared … 200, 201

― ribs of … 37, 80, 81, 86, 89, 188, 194–206

― single tier … 17, 142, 146, 147–151, 153, 192, 193, 231

― superposed … 13, 14, 17, 138, 153, 193, 231

― surface of … 9, 69, 81, 99

― tandem efficiency of … 46, 87

― two sets of … 13, 77, 106, 138, 231

― weight of … 190, 196

Wire guying … 81, 84–91, 99, 164–173, 189, 191, 195, 196, 199, 264,
266

― resistance … 165–167

― spokes … 243

Wooden guy sticks … 63, 81, 85

― ribs … 37, 80, 81, 86, 89, 188, 194–206, 263, 264

Wrecking of large machine … 126, 184, 265–281

Zinc, energy developed from … 27, 241

Zoological Park cameras … 260, 261, 273

TRANSCRIBER'S ENDNOTE

Original spelling and grammar have been generally retained, with
some exceptions noted below.

Illustrations are moved from inside paragraphs to between
paragraphs.

Footnotes have been renumbered and moved from the ends of
pages to the to the ends of the appropriate sections, which
are: Advertisement (page iii); Part I; and Part II, up to just
ahead of the DATA SHEETS, which have their own footnotes, which
were neither moved nor renumbered.

Pages 16–18. Page 16 ended at "with another one, No. 31, also
shown", followed by Plates 1–4, followed by page 17, which contained
two data tables, followed by page 18, which continued the original
paragraph. The transcriber has closed the paragraph, and moved the
Plates and tables to follow it.

Pages 31–32. The footnote on page 31 said only "See footnote on page
32." The footnote on page 32 had no anchor in the text. Therefore, to
simplify, the page 31 footnote has been eliminated, and its anchor is
linked directly to the page 32 footnote. Pages 46–47. The footnote
on page 47 had no anchor in the text. However, the footnote on page
46 said only "See Footnote page 47". Therefore, the footnote anchor
on page 46 has been linked directly to the footnote on page 47,
eliminating the page 46 footnote.

Page 63. The large table was split into two tables, repeating the
first column in each part. Large curly brackets "}", "{", indicating
combination of information on two or more lines, have been replaced
by Unicode box drawing characters, e.g. "│┌┘└┐". Tables in general,
and these box characters in particular, may not line up properly
unless the user is employing a monospaced font.

Page 140. The paragraph for June 23 originally ended "dotted line in
Plate". The transcriber has inserted " 34.", as a guess.

Pages 190–192. The wide tables were split into two, repeating the
first column in each part.

Page 193. The wide tables were transposed, row for column.

Page 201. The wide table was split into two.

Pages 297–308, Data Sheets. Remarks originally situated in the tables
are appended below each Data Sheet. The units of measurement were
originally spelled out—‹m.›=‹Metres›; ‹ft.›=‹Feet›; ‹gr.›=‹Grammes›;
and ‹lbs.›=‹Pounds›. In the footnotes to the Data Sheets, in the
phrases "curved wings 2-5 the way", and "rear wings have 2-3 of the
efficiency", the hyphen seems to mean division, like "/". This usage
occurs also in the caption to Plate 85, in "SCALE 1 1-16 INCH TO
STATUTE MILE".

Page 299. Item 41, "7 75" changed to "7.75".

INDEX. The original index was structured in a way not suitable for
this ebook. The white space on the printed page substituted for words
not repeated. Thus, under "Balancing of aerodrome, [ ... ]", were
indented entries for "engine", "wings and rudder", &c. This spacing
has been rendered herein as a horizontal bar "―", one for each word
to be understood as repeated. So in this case, two bars, meaning
"Balancing of". Moreover, page numbers referenced by index entries
were right-justified and preceded by dotted leaders. Herein, the
leaders have been indicated by horizontal ellipsis "…". The leaders
in the Table of Contents have also been replaced by ellipses.

Estimating from Internet Archive's stated scanning rate of 400 ppi,
the pages were about 6.2 by 9.2 inches. Body text was printed in 9
point type, with 3 point leading, and footnotes were printed in
5.4 point type.

*** End of this LibraryBlog Digital Book "Langley Memoir on Mechanical Flight, Parts I and II - Smithsonian Contributions to Knowledge, Volume 27 Number 3, Publication 1948, 1911" ***

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