The Second Boy's Book of Model Aeroplanes

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Title: The Second Boy's Book of Model Aeroplanes
Author: Collins, Francis Arnold
Language: English
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[Illustration: A model aeroplane rising from the water.]

THE SECOND BOY’S BOOK

OF MODEL AEROPLANES

FRANCIS A. COLLINS

AUTHOR OF "THE BOYS’ BOOK OF MODEL AEROPLANES"

ILLUSTRATED WITH MANY

PHOTOGRAPHS AND DIAGRAMS

BY THE AUTHOR

NEW YORK

THE CENTURY CO.

1911

The Century Co.

Published October, 1911

THE SECOND BOY’S BOOK OF MODEL AEROPLANES

FOREWORD

It is assumed that the reader is familiar with "The Boys’ Book of Model
Aeroplanes." Some knowledge of the history of aviation and the early
models, big and little, will be found helpful, but not essential, as a
preparation for the present volume.

Within the year so much has been learned of the science of model
aeroplane construction that an entirely new and more detailed treatment
of the subject seems to be justified. Since the length of model
aeroplane flights has been increased ten times, their improvement is
comparable to that of the large man-carrying machines. The science has
become more exact, and the chance of failure reduced, until to-day
successful flights are within the reach of all.

In the preparation of this volume thanks are due to the New York Model
Aero Club, to Mr. Edward Durrant, Percy Pierce, Cecil Peoli, W. S.
Howells, Jr., and to the young gentlemen whose models are illustrated
herewith, who, singly and collectively, are doing much for the
development of the science in America.

THE SECOND BOY’S BOOK OF MODEL AEROPLANES .........................
FOREWORD ........................................................
LIST OF ILLUSTRATIONS ...........................................
CHAPTER I MODEL AEROPLANES OF 1911 ..............................
CHAPTER II MODEL AEROPLANE TOURNAMENTS ..........................
CHAPTER III PARLOR AVIATION .....................................
CHAPTER IV TOOLS AND MATERIALS ..................................
CHAPTER V THEORY AND PRACTICE OF PLANE CONSTRUCTION .............
CHAPTER VI SCIENTIFIC PROPELLER BUILDING ........................
CHAPTER VII ASSEMBLING THE MOTORS ...............................
CHAPTER VIII DIRECTIONAL CONTROL ................................
CHAPTER IX MODEL AEROPLANE DESIGNS ..............................
CHAPTER X DESIGNING THE SKIDS ...................................
CHAPTER XI GEARED MOTORS ........................................
CHAPTER XII LESSONS OF THE MAN-CARRYING AEROPLANES ..............
CHAPTER XIII SELECTED QUESTIONS FOR BEGINNERS ...................
CHAPTER XIV AMONG THE MODEL BUILDERS ............................
CHAPTER XV CURIOSITIES OF THE AIR ...............................
CHAPTER XVI RULES FOR CONDUCTING MODEL AEROPLANE CONTESTS .......
CONSTITUTION AND BY-LAWS OF A MODEL AEROPLANE CLUB ..............
DICTIONARY OF AERONAUTICAL TERMS ................................
The Full LibraryBlog License ................................
Section 1. General Terms of Use & Redistributing Project
Gutenberg™ electronic works .....................................
Section 2. Information about the Mission of LibraryBlog™ ..
Section 3. Information about the LibraryBlog Literary
Archive Foundation ..............................................
Section 4. Information about Donations to the LibraryBlog
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Section 5. General Information About LibraryBlog™ electronic
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LIST OF ILLUSTRATIONS

A model aeroplane rising from the water. ..........................
A good specimen of plane building. ................................
"Finish one end of the blade before cutting away the opposite end."
Model aeroplane. Designed by Cecil Peoli. .........................
A variation on a familiar form. ...................................
An excellent model designed and built by H. Wakkins. ..............
An original design by Harry McAllister ............................
An interesting experiment in stability ............................
An early model built by E.G. Halpine ..............................
An interesting experiment in stability ............................
An early model built by Monroe Jacobs. Note the Ailerons. .........
A Simple Model Glider .............................................
An effective glider built by R.S. Barnaby .........................
An efficient sling-shot glider built by John Roche ................
Designs for Sling-Shot Gliders. ...................................
Paper Gliders. Antoinette Monoplane and Wright Biplane ............
An excellent glider with wooden planes ............................
A covered-frame sling-shot glider .................................
Percy Pierce launching a model ....................................
A French model built of aluminium .................................
Diagram for making the planes .....................................
Working drawing of the Flemming Williams model ....................
An imported Flemming Williams model. English record 2600 feet. ....
Storing energy for a long distance flight .........................
A geared model built by Leslie V. Robinson ........................
An ingenious biplane ..............................................
A well-proportioned model built by Reginald Overton ...............
A good model intended for long distance work built by A. C. Odom ..
A beautiful monoplane built by R. Mungokee ........................
Detail of a model built by R. Mungokee ............................
An ingenious application of the dihedral angle ....................
Diagram Showing How To Make A Propeller From A Wooden Blank .......
Design of Metal Propeller .........................................
A test of high aspect ratio planes ................................
A modified Bleriot built by Cecil Peoli ...........................
Langley Propeller Blade ...........................................
A combination of several interesting features .....................
A skilful adjustment of the front plane and skid built by Percy
Pierce ............................................................
Wright Propeller Blade ............................................
An efficient model, showing excellent construction, designed by John
Caresi ............................................................
One of the best minimum plane models of 1911 ......................
A Metal Motor Anchorage ...........................................
A Metal Motor Anchorage ...........................................
A notable model possessing unusual stability. Built by W.S. Howell,
Jr. ...............................................................
Front view of model built by W.S. Howell, Jr. .....................
A Metal Skid ......................................................
An ingenious adjustment of ailerons ...............................
Tuning up the model for a flight. .................................
Showing Construction And Mounting Of Propeller And Axle. ..........
An excellent monoplane capable of long flights. ...................
Long-distance model built by Percy Pierce. ........................
Showing An Excellent Way Of Fastening The Propellers To The
Framework. ........................................................
Model built by Rutledge Barry, winner of spectacular flight contest.
A model by Percy Pierce, winner of the indoor long-distance record.
A Motor Anchorage .................................................
A serviceable model showing excellent workmanship built by Cecil
Peoli .............................................................
A serviceable model showing excellent workmanship built by Cecil
Peoli .............................................................
Various Steering Devices. "a" and "b," simple aileron forms. "A"
novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical rudder
(Bleriot type). "D" "Blinkers," an effective rudder. "E" stability
planes not unlike the runners of a sleigh. ........................
An excellent piece of workmanship. Model by R. Mungokee ...........
Model with minimum plane surface. Built by A. C. Odom .............
A — The Famous "one Ouncer." B — A Small Experimental Model. C — A
Modified Burgess Webb Model. ......................................
Model With Minimum Plane Surface. .................................
An American Fleming Williams built by C. McQueen ..................
One of the earlier models built by Cecil Peoli ....................
A Model With Adjustable Stabilizer. ...............................
An Efficient Three-ounce Model. ...................................
An All-metal Model Frame. .........................................
One of the best models of the year, built by John Caresi ..........
An excellent model, showing careful attention to details. Built by
L. V. Brooks ......................................................
A model with limited plane area built by R. Barry .................
An interesting experiment in metal frame building by R. Fisher ....
An aeroplane of simple construction that flies remarkably well,
built by R. S. Barnaby ............................................
Percy Pierce, winner of the distance record .......................
A well-proportioned model, capable of long flights ................
A well designed aeroplane built by James MacPherson ...............
A beautiful model built by Stewart Easter .........................
A successful model of 1910 built by E. G. Halpine. Note contrast in
plane area ........................................................
Percy Pierce launching a prize-winning model ......................
Launching the sling-shot gliders ..................................
A tractor with large plane forward built by F. W. Curtis ..........
Model built by William Robinson ...................................
Front view of the De Lion model ...................................
Two of the earlier Peoli models ...................................

CHAPTER I MODEL AEROPLANES OF 1911

For the average boy there is no more stirring music than the brisk,
whirring note of his model aeroplane. Let the propellers spin steadily
for ten glorious seconds, and the journey spans a couple hundred feet or
more. Double the time and the flight becomes a triumph. Out of the
ingenuity of thousands of boy aviators, the world over, has come a
surprising development of the model aeroplane. The experimental stage is
passed. Any bright boy may now build a model aeroplane which is certain
to give results. The distance qualities of your model may even rival
your endurance as a runner in keeping pace with it.

Working along different lines, the builders of model aeroplanes, widely
scattered, seem to be gradually developing much the same type of air
craft. The tendency is toward the construction of much lighter and more
logical models than last year. In place of the complicated models
supported by several broad planes, we find the most successful amateur
aviators expending all their ingenuity upon simple monoplane forms. The
biplane forms are being abandoned by model builders, as well as the
biplane form of elevating planes. In place of the models made from fifty
or more members, we now find excellent models, capable of much longer
flights, formed of but a dozen pieces. The builders of model aeroplanes
are keeping pace with the development of the man-carrying machines, if
they are not passing them, in developing the flying machine of the
future.

Improvement in the distance qualities of the model aeroplanes, in the
past few months, has been remarkable. At one of the first model
aeroplane tournaments, held in New York, less than two years since, the
longest flight was under sixty feet. In less than one year, flights of
more than 200 feet had become common. To-day the improved racing model
aeroplanes have flown more than 2,500 feet. As a result of the labors of
the boy aviators, it is much easier to build a successful model flying
machine to-day than it was a year ago.

What may be called the 1911 type of model aeroplane looks every inch a
racer. Every unnecessary stick and string has been cut away. When skids
are used they are of the lightest possible material and the simplest
construction. The miniature rubber-tired wheels, with ball bearings,
which made many of last year’s models so attractive, are rarely used.
The plane surface has been reduced fully one half. One great secret of
success is in the cutting down of weight. When your propeller has but
half the work to do, the length of the flight is, of course, greatly
increased.

Our amateur aviators are attacking one great problem of aviation which
the pilots of man-carrying crafts are perhaps neglecting. Model
aeroplanes are built to maintain their equilibrium in the air
automatically. They must not only rise from the ground, prepared for a
long flight, but must be contrived to resist all manner of baffling air
currents aloft. Watch the successful model as it gains its altitude,
settles down to a horizontal flight, is perhaps knocked off its course
by a cross current, and steadies itself with a graceful curve and
proceeds on its way.

All these problems must be anticipated. The young aviator must
ingeniously arrange his planes and ballast in advance. The regular sky
pilot, on the other hand, meets the problems of the air as he encounters
them, by flexing his wings against disturbing currents or by banking to
maintain an even keel at a turn. If the man-carrying airship had to be
prepared to meet all these problems before it left the ground, the
problem would be, of course, much more complicated.

In other words, if the motor of a large machine were started and the
aeroplane launched without a pilot, would its chances of flight be as
good, in proportion to its size, as those of our best model aeroplanes?
A model aeroplane which flies 300 feet performs as remarkable a feat as
would a large machine flying, unguided, a mile or more. The progress in
the construction of model aeroplanes, in brief, already deserves serious
scientific consideration.

The last twelve months have brought out a surprising number of new
aeroplanes, while notable progress has been made in the standard types.
To realize the immense strides or flights forward in the construction of
heavier-than-air machines, one need only set the 1911 models beside the
aeroplanes of a year or two years since. Even to the eye of the layman
in such matters, the older machines are beginning to appear obsolete. In
a previous volume, it was suggested that within a few years the
aeroplane of to-day would appear like cumbersome stage coaches to one
familiar with racing automobiles, and certainly the prophecy is being
quickly realized.

The general tendency is in the direction of greater simplicity in design
in passenger-carrying craft, as in model aeroplanes. Both the monoplane
and biplane types are being developed side by side, and each continues
to have its enthusiastic advocates. The increase in the
passenger-carrying qualities is realizing the most sanguine hopes.
Aeroplanes have carried fifteen passengers for several miles. The speed
qualities of machines have developed correspondingly.

If the development of model aeroplanes leads the way in perfecting
heavier-than-air machines, as many believe, the monoplane form seems
destined to replace all multiplane types. During the past year
practically all of the biplane forms have been abandoned by model
builders. As a result of wide experiments, it has been found that the
monoplane exerts more sustension per unit of surface than any two or
three-plane machines. In theory, it is, of course, possible to increase
the sustained force by setting one plane above another, but in practice
it has been found that the planes must be set so far apart that the
arrangement is impracticable. When planes are separated, they must, of
course, be stayed and trussed to keep them rigid, and all this adds to
the weight and complexity of the machine.

[Illustration: A good specimen of plane building.]

[Illustration: "Finish one end of the blade before cutting away the
opposite end."]

[Illustration: Model aeroplane. Designed by Cecil Peoli.]

The builder of model aeroplanes has a great advantage over the designer
of man-carrying crafts. The spread of the wings of his model is
comparatively small, and the problem of staying and trussing is greatly
simplified. The monoplane, especially in a model, requires practically
no staying at all. Then again the skin friction is greatly reduced in
the monoplane form. Simple as it is, there are great possibilities in
the arrangement of these surfaces. The effect of outline upon resistance
again may be more closely observed in the monoplane than in the
multiplane forms. In other words, if your model goes wrong, it is far
easier to locate the fault and rectify it than in the more complicated
arrangement of planes.

The flights of the English models this year are longer than those made
in America, but, on the other hand, we are solving many practical
problems of aviation, in our model building, which the English have not
attempted. Even in the case of our single-stick frames built in America,
the tendency is toward more stable construction than abroad. The best
English models would not qualify for an American model tournament, since
they could not rise from the ground.

The best American models, on the other hand, would be outdistanced in an
English meet, but their flights would show them to have far greater
automatic stability than their English rivals. It is extremely
interesting to speculate whether the American or English types of model
aeroplanes will survive, and which is contributing more to the solving
of the great mysteries of aviation, but, after all, it is a question
which only time can answer.

Compare typical flights of the American and English models, and the
contrast becomes obvious. The English model is usually held and thrown
forward. The starter thus gives it its altitude and direction. Being
extremely light, they gain a great deal from the wind. Their flights are
usually in straight lines, or in slightly undulating curves. Under
favorable conditions, their distance qualities are remarkable. Flights
of six or eight hundred feet are common, while the present record is
over 2,500 feet or nearly half a mile.

In an American model tournament, the models are set upon the ground and
left to themselves. As a rule, it is not even permitted to give them a
slight push. The motor must be powerful enough to carry them onward and
upward unassisted. In many cases they must be clear of the ground within
twenty feet or the flight is disqualified. It is, of course, obvious
that the motors must be far stronger than in the case of the English
models, and that their frames must therefore be correspondingly heavier
to support the weight. The plane surface, in turn, must be increased to
support this weight. The average English models, even with American
skids, would not leave the ground at all.

Once in the air, the behavior of the American model, again, is entirely
different from its English rival. Our aeroplanes are off with a rush.
The first part of the flight is at a more or less sharply drawn angle of
elevation. It usually rises to an altitude of from ten to twenty feet in
a straight line. To secure a good rise requires a much more scientific
adjustment of the planes and weighting than in the case of the English
models. As it reaches its altitude, it adjusts itself, and here the
problem of stability comes in. The marvelous little craft balances
itself with the least possible loss of time and power, comes to a
horizontal position, and is off on its flight. If its adjustment is not
all it should be, it will, of course, fail to right itself and fall
backward, or, as the phrase goes "sit on its tail." It is estimated that
one-third of the power of the motors is used up in leaving the ground
and rising to its maximum altitude.

Our American model builders believe that their flights are far more
scientific than in the case of a hand-launched model, and that they are
doing more for the actual development of the art of aviation than their
English cousins. Whether one prefers to watch an American or English
tournament is, of course, largely a matter of taste; certainly both are
fascinating.

Much has been learned about motors. It has been found that the rubber
motor is capable of great development. Since a flight of one-half a mile
may be made by twisted bands of rubber, the average model builder may be
content to let clock work and miniature gasoline engines take care of
themselves. By building and flying thousands of models, we have found
what form of rubber strand is best, just how heavy the strands should
be, and the most efficient point of winding. Instead of short heavy
bands, we now use much longer and more slender motors. The efficiency of
rubber motors has been greatly increased by arranging them in series and
connecting them up by gear wheels. It is even possible to buy miniature
gasoline motors suitable for model aeroplanes. Flights of more than one
mile have been made in this way.

All the best models this year are equipped with twin propellers. It is
very little more trouble to build two motors than one, and the model
thus equipped will not only travel much further, but will insure much
more stable flights. A common trouble in model building has been the
lack of stability. Your model has been likely to capsize, even under
favorable conditions, spoiling the flight, while a chance gust of wind
would knock it out of its course in spite of everything you could do. To
overcome this tendency, the surface of the planes might be increased,
but this added to the weight of the model, thus cutting down the length
of the flights. The twin propellers cut at the root of the problem. They
balance the thrust, thus making the flight even and stable. The planes
may also be made much smaller with a gain in weight which, in turn,
lengthens the flight.

[Illustration: A variation on a familiar form.]

[Illustration: An excellent model designed and built by H. Wakkins.]

CHAPTER II MODEL AEROPLANE TOURNAMENTS

Within the year, exhibitions and contests of model aeroplane flights
have become an established form of entertainment. The attractions of the
flights of man-carrying machines are borrowed in a large measure by the
model aeroplanes. The building of models has progressed so rapidly,
bringing the little air-craft under such control, that a definite
program of flights may now be carried out. The programs may be
considerably varied to include distance flights, weight-lifting
contests, and spectacular flights in which the models loop the loop and
perform other amazing feats.

The first formal exhibition or professional appearance of the model
aeroplane in public as an entertainment was made in connection with the
first aviation meet held at Asbury Park, New Jersey. Two of the most
successful model builders, Percy Pierce and Frank Schoeber, of the New
York Model Aero Club, were engaged to give exhibition flights for one
hour a day in the intervals between the flights of Arch Hoxey, Johnston
and other aviators of the Wright Brothers staff.

[Illustration: An original design by Harry McAllister]

[Illustration: An interesting experiment in stability]

[Illustration: An early model built by E.G. Halpine]

The models were flown for more than 200 feet and were enthusiastically
applauded. The aeroplanes in miniature imitated the flights of the
man-carrying craft with wonderful fidelity, rising from the ground and
soaring aloft in long, graceful curves. They came as a very welcome
variety, and could be watched without breaking one’s neck gazing aloft,
or the unpleasant possibility of a serious accident. The applause of the
thousands gathered for the meet may be said to have definitely
established the model aeroplane as a feature of these tournaments.

The model aeroplane has one great advantage over the man-carrying
machines. It makes possible indoor aviation, and may be enjoyed the year
round, and is especially effective for evening entertainment. The
fortnightly meets in one of the great New York armories, some time
since, attracted the attention of the officers, and the boys were
invited to give exhibition flights in connection with athletic games.
The first of these meets was held under the auspices of the New York
Model Aero Club, in connection with the Greek athletic games, in the
interval between the games and the ball which followed.

An audience of fully 3,000 people, crowding the armory, witnessed the
flights. Some twenty members of the club entered the contest. In a
public contest of this kind, much depends upon the system of flying. The
floor must be kept clear and the flights follow one another so quickly
that the interest will not lag for a moment, and the audience have no
opportunity to tire. The flights on this occasion went with a rush and
proved in every way so successful that the rules which made this program
are given in full on another page.

Few in the audience had ever seen a model flight, and the contest held
the great crowd’s attention more closely than had any of the evening’s
athletic events, which had come before. There was a breathless moment of
suspense when the whistle had sounded for the first flight. A beautiful
white monoplane led off, but in the excitement of the moment, it had not
been properly adjusted, and failing to get its altitude, spun daintily
across the floor. The second model yawed sharply and flew into the crowd
at the side.

The third model found itself, however, rose perhaps twenty feet and,
settling down to a steady horizontal, darted across the arena. Every eye
followed it. A burst of handclapping greeted its graceful rise, which
increased in volume, and as it reached the farthest corner of the great
armory, more than 200 feet distant, there was a perfectly spontaneous
cheer.

The program was so well organized and carried on that the flights
followed rapidly without a break. There was scarcely a moment when an
aeroplane was not aloft, and the interest never faltered. There were
Scores of excellent straight-away flights of 200 feet or more, at
various altitudes. Occasionally a model would fly wild, even refuse to
rise, but the flights followed one another so continuously that a
failure was quickly forgotten in the delight of watching the next
flight.

The rapid development of the model aeroplane was shown particularly in
the spectacular flights. The thrilling volplanes and daring aerial feats
of the famous air pilots were imitated by the model aeroplanes. The
models were made to dart about at unexpected angles, and, while keeping
clear of the ground, perform many astonishing feats. The prize for these
spectacular flights was won by Henry Ragot whose aeroplane actually
looped the loop repeatedly, in obedience to skilful adjustment of the
planes and weights.

In launching the model for this flight, the model was held well above
the ground and launched at a sharp upward angle. It rose with
astonishing speed, in a vertical line, fully twenty feet, when it turned
and descended with accelerated speed. The crowd naturally expected a bad
smash, but with a good clearance of the ground the model suddenly swept
around in a narrow semicircle, rose and repeated the performance. It
seemed to many spectators that the model was enjoying a miracle of good
luck, but they were mistaken. The flight was repeated several times.
Indoor aviation was an instantaneous success.

Unless well-thought-out rules are carefully observed, a public
exhibition may fall into confusion, and be seriously marred. A large
audience grows quickly impatient of delays between flights. There is, of
course, the danger that the models will follow each other too quickly,
perhaps collide in the air. The distance and spectacular flights again
must be kept separate.

The rules followed by the New York Model Aero Club in these exhibitions
worked well in practice. First of all, the floor was kept absolutely
clear except for the director of the flights, who took up a position at
the center. The distance flights started from one corner only, and the
spectacular nights from the center of one side, the weight-lifting
contest from another corner.

An official starter, a measurer, and an entry clerk are stationed at
each point from which the flights are started. When a model was wound up
ready for a flight, a starter waved a small flag to attract the
attention of the director out on the floor. From his vantage point, the
director could see if the floor was clear and signaled to the starter to
go ahead. He blew a whistle by way of signal, one blast for the start of
a weight-lifting contest, two for a distance flight, and three for a
spectacular flight.

Instantly the whistle sounded, the model signaled was released without a
moment’s delay. In this way no two models were ever started at the same
time, and all confusion was avoided. The whistle was clearly heard in
all parts of the hall, and the audience quickly learned to recognize the
signals and look to the point from which the start took place. In the
distance flights the one flying the model and the measurer alone were
allowed to go after the machine. This was done on the run. It is
important that any delay be avoided in measuring, since this does not
interest the public in the least, and may make the exhibition drag.

[Illustration: An interesting experiment in stability]

[Illustration: An early model built by Monroe Jacobs. Note the
Ailerons.]

The only other person allowed on the floor while the flights were in
progress was the owner of the model, who must follow it and bring it
back. He was allowed to cross the floor, but once he had secured his
model, he must carry it quickly to the nearest point at the side, and
find his way back to the starting point along the outer lines. It is
confusing both to the flyer and the spectators to have a single
unnecessary figure on the floor during the flights. The crowd is kept
back by members of the club, wearing the club colors.

The regular fortnightly model aeroplane meets held in New York are
doubtless the most largely-attended and best-organized meets of the kind
in the world. The 22nd Regiment armory, a spacious structure admirably
suited for indoor aviation, has very courteously been thrown open for
the purpose on every other Saturday afternoon.

Throughout the season, each of these meets brings together several
hundred boys and spectators, and on the average about 100 model
aeroplanes. The meet is conducted with intelligence and sympathy by the
Y. M. C. A., and is open to all. Of late these exhibitions have become
so popular that the crowds actually threaten the convenience of the
flyers, and the boys have been required to present credentials on
entering, consisting simply of a model aeroplane.

There are few more animated spectacles than the model aeroplane
tournament. There is a great sunlit floor, measuring 250 by 150 feet,
roofed with glass. The aviation fields are reproduced here in miniature,
without loss of animation. Along the sides are continuous lines of
"camps," corresponding to the hangars where scores of boys are busy
tuning up their machines. They have brought tools and a variety of extra
materials, planes, propellers, motors, and strips, which are spread
about them.

In each camp the machines,—and there are no two alike,—are being
assembled or repaired. Groups of the boys’ friends and admirers are
gathered about each camp, earnestly discussing the merits of a
particular model and its chances in the approaching contest. To stroll
down the line of camps is in itself a liberal education in aeronautics.

The records of all flights are carefully preserved, to be counted
against the several important trophies which will be awarded at the end
of the season. Any one of the scores of contestants can tell you at any
moment how the score stands. During this tuning up process, the
galleries have filled and an enthusiastic audience is assured.

One of the great beauties of indoor aviation is that it is entirely
independent of the weather. The air of the great armory is practically
at rest, and the aeroplanes escape the baffling side currents and air
gusts. In England, for instance, indoor aviation is practically unknown.

A whistle sounds above the hum of many voices, and at the signal
everyone scurries to the sides, leaving the broad floor clear. The
judge, starter, and measurer take their positions, and the aviators,
with their models tuned up to concert pitch, stand ready at the starting
line. The starter announces whether the flight is "official" and if it
is to be counted in the competition for the trophies, or is merely a
practice or exhibition flight.

The start is made from the extreme corner diagonally across the armory.
Only last year the start was made from a point well out in the middle of
the floor, but that was when the flights were much shorter. To-day the
boys have actually outgrown the armory, and even by flying from corner
to corner there is not enough room. The aeroplanes are no longer
launched from the hand or even pushed along the ground. They are
required to start without assistance and rise in the air without being
touched.

"Official flight."

Everyone’s attention is attracted by the announcement. Hundreds of boys
crowd to the lines. The starter is doubtless known to all, as well as
his record and standing in the various competitions. Hundreds of
critical eyes are upon the model. It is a thrilling moment. The
propellers are released, and the aeroplane starts forward under its own
power.

Some leap into the air, others take the full twenty feet permitted them
in getting off the ground. There are surprisingly few failures. The
length of the take-off, the angle at which it rises, the altitude in the
first rise, are critically observed by the young experts.

To the whir of the propellers, which form two blurred circles in the
air, the model quickly climbs upward, rights itself and speeds away on
its long flight. The young aviator’s skill is revealed to every eye by
the angle of the ascent, the altitude and the ability to gain
equilibrium aloft. The more you know about aviation, the more absorbing
is your interest in a flight.

A good rise is usually observed in silence. By the time the model has
reached the middle of the armory, more than one hundred feet from the
starting line, enthusiasm is aroused. When two-thirds the distance has
been covered, the applause begins. Let the model continue without
swerving to the farthest corner, and a perfectly spontaneous cheer
sweeps the crowd. It is a well-deserved reward of hours of patient
effort.

The official measurers take the floor on the run, dragging their tape
after them. The crowd overruns the floor to gain a closer view of the
model, and the young aviator receives congratulations. The distance is
announced at once, and there are more cheers. There is never a dull
moment at the meets. One or more machines are almost always aloft. It is
as thrilling as a three-ringed circus.

CHAPTER III PARLOR AVIATION

A model glider, or aeroplane without a motor, will be found perhaps as
entertaining a toy as the power-driven machine. It is much simpler, of
course, to build and adjust a successful glider even than the most
elementary model aeroplane. With the problem of the motor and propeller
removed, the cost of construction besides is reduced to practically
nothing. Here is excellent entertainment for those who have not the time
or patience for model building. A graceful glide of successive waving
lines makes a beautiful spectacle. Incidentally it is a good plan to
work out the designs of large models in this way.

Fascinating little paper models, reproducing the famous man-carrying
machines, the Wright, Bleriot, and others, may be put together in a few
minutes. With a little adjustment, they may be made to fly from fifty to
one hundred times their length. A paper Bleriot biplane six inches in
length, for instance, may be made to sail for from twenty-five to fifty
feet, and so on. This will be the actual horizontal distance traversed;
the actual distance measured in long, undulating curves may be
considerably more. Such flights do not consist merely of a long diagonal
to earth, but of several surprising upward sweeps, well worth the
trouble of construction. It is interesting to note the remarkable
stability of their gliders.

[Illustration: A Simple Model Glider]

An hour’s entertainment, no less interesting than instructive, may be
enjoyed with a series of these paper gliders. A different model might be
prepared for each guest, and a prize or favor offered for the longest or
best spectacular flight. The little gliders will cross a large room
before coming down. The various aeroplanes nowadays are so familiar that
in any gathering will be found several who favor, for instance, a Wright
over a Curtiss take a lively interest in the rivalry of the various
models.

[Illustration: An effective glider built by R.S. Barnaby]

[Illustration: An efficient sling-shot glider built by John Roche]

Begin with a very simple model. You will soon learn the trick of judging
the size of the supporting surfaces and the spacing. The Antoinette
aeroplane is probably the easiest one to imitate. From a sheet of
ordinary writing paper, cardboard or fine wood, cut the form indicated.
If the paper be rather heavy, it may be made six inches in length. By
folding the paper and making one cutting, it will be found much easier
to make the wings even and symmetrical.

The two sides should be fixed at a broad dihedral angle. To keep the
little glider on an even keel you will need to add a weight to the
front. A large pin or paper clip will answer. Launch the glider by
holding it horizontally and throwing slightly forward. If it darts
downward, lighten the ballast. If it falls backward, "sitting on its
tail," add more weight at the front or bend the tail up.

Your glider will, of course, travel to the ground along the line of
least resistance, and the trick is to adjust the center of gravity and
center of pressure that this descent may be as gradual as possible. The
center of gravity should come a little in front of the center of
pressure. The gliding angle, as it is called, or the angle between the
course of the model in flight with the ground should be about one in
twelve. In other words, the glider descends one foot for every twelve
feet it travels forward. Practically all the famous monoplanes may be
reproduced in this way.

A variety of gliders may be made in a general arrow form. These arrows,
or darts, as they are called, may be made about a foot in length and
three or four inches in width. The horizontal surface, it should be
borne in mind, is the supporting surface, while the vertical surface
gives the flight direction. These gliders will also require weighting at
the forward end. They should be thrown forward with rather more force
than in the case of the Antoinette.

The biplanes such as the Wright and Curtiss aeroplanes may be reproduced
very easily in paper. They fly best when made about six inches in
length. Cut the two sheets of paper for the main planes one inch by six
inches and round off the corners on one side. Two similar sheets, one by
three inches, will be required for the smaller plane in the rear.

The planes are held in position by a series of paper struts, or
toothpicks, and should be separated by a distance equal to their width,
in this case one inch. Cut the slips of paper to form the struts one and
one-half inches in length and bend over the corners at right angles,
one-quarter of an inch from either end. These should be pasted in
position, always keeping the edge of the struts lengthwise so that they
will offer the least resistance in flight.

Connect the two biplanes by strips of paper six inches in length pasted
on the lower planes or main deck of the little aeroplane. The forward
planes should be fixed at a slightly elevated angle by running struts
from the connecting strips to the upper plane. The accompanying picture
will show how simple this all is.

The biplanes as a rule require no weighing. To launch them, hold them
high in the air and merely let go. They fly best with their smaller
planes forward. By varying the angle of the front plane, you can soon
bring it to an even keel. A vertical rudder placed three inches behind
the main plane will increase the model’s directional stability.

An amazingly clever little glider may be made of a piece of reed or
cane, say five inches in length, and a sheet of writing paper. With a
pair of scissors cut two planes, one three by one inch and the second
two by half an inch. You will also need a vertical rudder one inch
square. Round off the corners slightly and glue the planes at either end
of the stick and exactly on a level. Now fasten the rudder at right
angles to the planes beneath the larger plane. If it dips, the front
plane is too far back, while if it rises too quickly and settles back,
the front plane must be brought back.

The paper gliders form an excellent kindergarten preparation to the
study of aviation, leading up to the construction of large model
gliders. You will thus gain a skill in adjusting the planes and fixing
the centers of gravity and of pressure, which will prove valuable later
on. The possibilities of glider building come as a surprise to the
laymen in such matters.

THE SLING-SHOT GLIDER.

A fascinating field of experiment is opened by combining the sling-shot
principle with the ordinary glider. The speed with which one can launch
a glider from the hand is, of course, limited. Now use a small strand of
rubber to launch the planes, and the increased speed will not only
lengthen the flight surprisingly but make possible a really remarkable
spectacular flight. A small glider may be made to return to the starting
point or even loop the loop two or three times before touching the
ground. By a simple adjustment of the planes, these curves may be varied
indefinitely.

[Illustration: Designs for Sling-Shot Gliders.]

When you have adjusted your glider to fly well, try the same arrangement
of planes on a piece of reed, say eight inches in length, and bend the
end over in the form of a hook. By heating the cane over a flame, you
can make it turn without breaking and hold its position. Now loop a
single rubber band over your thumb and forefinger, and passing the hook
over the rubber, pull back exactly as you would use a sling shot. As you
release the glider, pull your other hand quickly out of range. By using
a heavier paper, one which will hold its shape, and turning the forward
edges up slightly, the glider may be made to travel upward in a variety
of graceful curves.

[Illustration: Paper Gliders. Antoinette Monoplane and Wright Biplane]

[Illustration: An excellent glider with wooden planes]

[Illustration: A covered-frame sling-shot glider]

The best glider for launching on the sling-shot principle is made from
planes cut from thin metal sheets. Aluminum is the best material, but a
very thin wood will answer. A one-foot model glider will be found the
easiest size to manage. Cut one plane eight inches in length by three in
width, and the second five inches by two inches. Round off the corners
on one side of each plane, leaving a straight line for the front or
entering edge.

Mount the planes on a strip of reed, cane or bamboo about eighteen
inches in length. In all these gliders the forward plane is made the
smaller, thereby reducing the head resistance as far as possible. The
metal planes should be slightly flexed by bending them to a slight
concave above the horizontal and just back of the front edge. The
forward end of the stick should be bent into a large hook by heating or
first soaking in water. If your glider falls quickly to the ground bend
the frame a trifle upward.

Since your glider is intended to travel at a comparatively high speed,
the planes may be mounted much further apart than in the case of a
glider launched from the hand. Try them first ten inches apart and
afterwards adjust them to suit. The rubber used for launching the glider
should be fairly heavy, say three strands of one-eighth inch rubber or
its equivalent. The end of the hook may need adjusting so that it will
escape from the rubber on being released.

It will be found an easy matter to obtain long, graceful glides from
this model from the first. By launching it upward, it may rise to a
considerable height. When you have caught the trick of launching your
glider with sufficient force, try a spectacular flight. Set your forward
plane at an angle by inserting a block of wood between the stick. In the
case of metal planes, bend up the front edge.

A very slight upward elevation will answer. Gradually increase this
angle until the model sweeps upward and turns on itself. You will soon
be able to make the glider describe a complete circle or loop the loop
twice before landing. When traveling at such a high rate of speed, your
glider is likely to be dangerous and might inflict a bad cut, and the
flight should only be attempted where one has plenty of room.

These flights may be still further varied by adjusting the rear edge of
the vertical plane or rudder. By turning the rudder to the right, for
instance, the glider may be made to travel to the right or the direction
may be reversed. In this way the glider may be made to describe a
complete horizontal circle or several circles. By launching the glider
upward with this adjustment, it may be made to fly in a graceful spiral.

The success of a glider depends more upon its modeling and finish of its
planes than in the case of the model aeroplane. It must gain as much
support as possible from the air, since it has no motive power to keep
it aloft. Its head resistance must also be cut down. The ordinary
cloth-covered planes, which serve well enough for an ordinary model
aeroplane, will not carry a glider far. The planes must, therefore, be
of metal or wood, or when built-up planes are used they must be of the
most careful workmanship.

The simplest form of glider, excepting, of course, the paper model, is
made entirely of wood. A glider two feet in length will be found a good
size to experiment with. The model should be much heavier than an
aeroplane so that one need not take the care in its construction to
reduce weight which may make the construction of a model tedious. A
glider of this size may weigh upward of one pound. Under favorable
conditions, it will glide for two hundred feet, when launched from the
hand, while if it is thrown from an elevation, an upper window or a hill
top, it may travel considerably further.

Select a stout stick for your base, one inch square and two feet in
length. The main plane should measure fifteen inches in width by six in
depth, and the smaller plane ten inches by four inches. A thin board
about three-sixteenths of an inch thick may be used for the planes.

The front corners should be slightly rounded, and the rear edges cut
sharply away. These planes may be flexed by steaming. Hold the section
to be bent over the spout of a tea kettle until the wood is soft and
pliable enough to bend. If it does not soften sufficiently, immerse the
wood in boiling water. The plane should be flexed slightly upward just
back of the forward edge. A good curve may be obtained by heating the
under surface over a flame.

To hold it in position until it has dried and assumed shape, bend it
over a stick laid on a board and fasten the plane down by driving brads
around the edges and bending them over to keep it down. Leave it in this
position until it is dry and hard.

Your glider will fly better with a vertical rudder, as in the case of
the paper models. The rudder should be cut from a thin board of the same
material about six inches square. Round off one corner and plane or
sandpaper this front edge, which will be the entering edge. The entering
edges of the front plane should be prepared in the same way to reduce
the head resistance as much as possible. Nail this rudder to the side of
the stick directly beneath the rear or larger plane. It will be still
better if you mortise it neatly into the center of the stick.

The glider is thrown with the smaller end forward. For the trial flight,
mount the smaller plane at the extreme forward end and then move it
backward as you test it out, until the glider moves on an even keel. To
launch the glider, grasp the central stick from beneath at the point
where it balances, and throw it forward with all your might. Since it
travels at a much higher speed than a power-driven model aeroplane, it
requires much less supporting surface, while the planes may be spaced
much further apart.

When you have adjusted the planes, try throwing your glider at an upward
angle of say forty-five degrees. It should rise swiftly to a height of
upwards of fifty feet, turn backward on itself, and even describe a
graceful upward curve before coming down. Now try throwing it into the
wind or against a moderately strong breeze. Its course is likely to be
very irregular. It will dip and rise at many unexpected angles, and
probably travel several hundred feet in all before landing. During the
past year, a model glider has been built by Mr. W. H. Howell, Jr., to
glide a horizontal distance of 650 feet, while the actual length of the
flights has been upwards of 2,000 feet.

CHAPTER IV TOOLS AND MATERIALS

A well-stocked tool chest will be of great assistance to the builder of
model aeroplanes, but it is by no means essential. A few simple tools,
easily obtained, will be found to answer. First of these comes a
serviceable pair of nippers. You will need them to bend the axles of
your propellers, in adjusting the motors, and for a score of uses. A
pair of nippers with a cutting edge is best. Always be sure to slip
these in your pocket before flying your model, for you are sure to need
them.

A fine gimlet, or a needle drill, will be found useful in a score of
ways. They cost but a few cents. A handle which may be adjusted to
drills of different size is best. A drill one thirty-second of an inch
in diameter will be found especially useful. The parts of your model are
likely to be delicate and easily split, even while driving a small brad.
You can avoid the danger of splitting by first using the needle drill,
even for small brads, and then enlarging the hole, if necessary, with a
larger drill or a gimlet.

[Illustration: Percy Pierce launching a model]

[Illustration: A French model built of aluminium]

A fine saw will be found very useful,—the finer the better. The timber
used for the frame is so light and soft that it is likely to split. A
gig saw will be found just the thing for cutting out propeller blanks
and other parts, but it is not essential. If your model be made of
metal, a small soldering iron will, of course, be found
indispensable,—the smaller the better. The metal parts are very
delicate, and the iron should have as fine a point as possible. Such an
iron can be obtained at a hardware store for a few cents. If you do not
know how to solder neatly consult some tinsmith.

[Illustration: Diagram for making the planes]

In addition to good cutting tools, a good half-inch chisel is most
important. A concave chisel will be found handy in carving propellers.
Some of the best propellers have been whittled out with an ordinary
penknife, and sometimes a dull one at that, so that after all a good
penknife is the most essential tool of all. With this little handful of
tools, you will find you can build up the most delicate models.

The world has been ransacked for material which will give the greatest
possible strength for its weight. The use of aluminum is, of course,
familiar. The search has also brought out the comparatively unknown
metal, "magnalium," which, although a trifle heavier, is believed to be
much more desirable on account of its greater strength. In a search for
strong, light wood the builders of aeroplanes have searched the tropics.

One of their discoveries has been balsic wood, which is of a feather
weight. It is exceedingly soft and easily worked, but has the drawback
of being rather pithy and easily split. A severe jar is likely to
discover some weak point. It will be found valuable, however, for the
shorter members of the model. Some model builders use balsic wood as a
filling for hollow sticks. The wood may be strengthened by covering with
cloth glued firmly about it. It is also used as a filling for thin
aluminum tubing.

In all the search for materials nothing has been found to compare with
bamboo for lightness and strength. A number of successful model
aeroplanes have been built this year in which the central sticks and
frames are built entirely of bamboo. Bamboo is especially valuable in
constructing the smaller members. It can be bent either by the dry-heat
process, described elsewhere, or by steaming. Bear in mind that the
strongest part of the stick lies just beneath the hard glazed outer
surface. The only drawback of bamboo is a tendency to split at the ends.
The extreme lightness of the material on the other hand makes it
possible to make rigid joints by glueing and winding with fine thread
touched with glue.

[Illustration: Working drawing of the Flemming Williams model]

[Illustration: An imported Flemming Williams model. English record 2600
feet.]

The lighter woods, whitewood and poplar, are much used by model
builders. They are easy to work, especially whitewood, because of its
freedom from knots and cross grains. Some builders prefer ash on account
of its strength. Beech has rather less strength, some fifteen per cent,
while spruce is little more than half as strong as ash. The quality of
the wood varies considerably according to its nearness to the bark of
the tree. The wood used for model aeroplanes should be well seasoned; a
year is not too long.

Motor bases are of two general divisions. The "single stickers," or
bases consisting of one member, are commonly called "spars," while the
more complicated frameworks are designated as "built-up" frames. The
spar type is, of course, the simplest to construct, and, as many
believe, the most efficient of all forms. The simpler the design, as a
rule, the less chance will there be of breakage. For the beginner the
use of plain, honest sticks is, of course, to be recommended.

The built-up motor bases, on the other hand, make a more attractive
model to the eye. There is besides an opportunity to reduce the weight
of the frame while retaining the same strength. An examination of the
models illustrated elsewhere will show to what an art such construction
has been brought. By ingenious bracing it is possible to construct motor
bases of strips one-sixteenth of an inch, or even less, in width, and
yet render the whole sufficiently rigid to withstand the pull of
powerful twin motors.

Your frame may be considerably lightened by using hollow sticks or
shafts in place of solid members. A stick three-fourths of an inch wide
formed of light lath one-eighth of an inch thick will weigh no more than
a solid piece one quarter of an inch square. Such a member is stronger
than the small, solid stick; it bends less readily under the pull of
your motors, and renders the entire frame far more rigid. It will also
be found much more satisfactory to mount the planes upon such a frame.

A little practice will enable you to make a very satisfactory stick of
this pattern. Secure a light strip one-eighth of an inch thick and of a
width one-eighth of an inch less than that of the stick you intend to
build. A one-inch stick is probably larger than you will need. The
following directions are intended for a stick three-fourths of an inch
square.

First cut three square plugs one-half an inch square and one-fourth of
an inch thick, and placing one at either end and one in the middle to
form a core, build your frame about them. The edges should overlap and
be glued continuously together, and the plugs fastened in position with
brads driven from the middle of the four sides. When dry, cut away the
glue, sandpaper and varnish.

Some model builders prefer a T-section-shaped spar, which is almost as
light as the hollow stick, besides being easier to construct. We assume
that you are working with eight-inch strips, which will prove heavy
enough for ordinary purposes. Prepare one strip one-half an inch wide,
the desired length of your base, and the second strip three-eighths of
an inch wide, the thickness and length being the same.

Now fasten the smaller strip at the center of the long strip, glueing it
first in position. When dry, drive a series of fine brads along the
center of the back of the larger strip. Cut away the glue and sandpaper.
The T-shaped stick will be found strong enough for all ordinary demands.
The rubber strands of your motor may be carried either above or below
it.

The H-shaped-section stick is rather more difficult to build, but it
will be found somewhat stronger, weight for weight. If you are using
one-eighth strips, cut two lengths one-half an inch wide, and a third
length three-eighths of an inch wide. Fasten the smaller pieces to the
middle of one of these strips, as in the case of the T stick, with glue
and brads. When dry, attach the remaining strip opposite, glueing and
nailing as before. Some builders prepare these strips by cutting out the
grooves with a chisel, thus making a one-piece strip. This requires very
careful workmanship, however, and is scarcely worth the trouble.

The motor frame may be still further lightened by using a trussed frame.
The weight of this member may be cut in two in this way without
sacrificing its strength. To build such a part secure two strips of wood
one-eighth of an inch thick, one inch in width, and cut to the desired
length. Now from the same material cut six blocks, one-half an inch in
length, and set these at regular intervals along one side of the strip.
They may be glued or nailed in position, or both. A small brad will hold
them in place. In working with such delicate material it will be well to
first drill the holes with a fine drill. Next fasten the second strip
above them, nailing and glueing as before.

[Illustration: Storing energy for a long distance flight]

CHAPTER V THEORY AND PRACTICE OF PLANE CONSTRUCTION

THE planes of your model aeroplane need no longer be a blind experiment
whose merits or defects may only be learned by actual test. The science
of wing-building is much better understood to-day than a year ago.
Without going into the complicated equations dealing with aspect ratio,
pressure, and gravity, it is important that one bear in mind a few
definite rules in designing even the simplest planes. A great many
useless experiments may be avoided.

In a previous volume, it was pointed out that a narrow plane, or one
with a high aspect ratio, driven with its broader side forward, would
yield greater support than a square surface of the same area. (The
aspect ratio, it may be well to repeat, is the relation between the
width and depth of the plane. A wing, for instance, whose width is five
times its depth, is said to have an aspect ratio of five.)

It has been found that on small planes the center of pressure is
situated about one-third the distance back from its front or entering
edge. The center of pressure in flexed planes occupies about the same
position.

As long as a plane remains horizontal, or nearly so, a very narrow
surface,—one, that is, with a high aspect ratio,—will exert greater
lifting power than a deeper plane of the same area. An examination of
the successful model aeroplanes of 1911 will show that the depth of the
planes has been cut away. Planes are used with an aspect ratio as high
as ten. The speed at which such a plane travels is a very important
factor. As the speed increases, the efficiency of the plane surface
increases, so that a model aeroplane driven rapidly may be sustained by
less wing area than in the case of one which flies slowly.

As the front edge of a plane is raised, the center of pressure travels
backward. By the time the plane has reached an angle of about fifteen
degrees, its lifting power has diminished about one-half. A very narrow
plane, or one with a high aspect ratio, should, therefore, be set near
the horizontal. The model should, moreover, rest upon skids at as low an
angle as possible.

In starting off, the planes will thus exert their maximum lift, or
nearly so. If the narrow planes be elevated too much, the center of
pressure will come nearer the rear than the front edge, and tend to
force the aeroplane downward, or, as the phrase is, make it "sit on its
tail." As long as a plane is traveling horizontally, or at low angles,
its rear portion exerts very little sustaining power and may be cut
away.

A plane with a high aspect ratio is much more stable in flight than a
surface of greater depth. The center of gravity of a flat plane would,
of course, coincide with the center of the surface when the plane is in
motion. When the plane tilts, the center of pressure, as we have seen,
moves backward or forward. If the plane has little depth or a high
aspect ratio, this center of pressure cannot move far.

It must oscillate back and forth within very narrow limits. A very
little tilt up or down will restore it to its normal position, so that a
plane with high aspect ratio is more stable than one with a deeper
surface.

The efficiency of a curved surface over a flat plane was analyzed in a
former volume. Such a curve, when well drawn, adds to the lifting power
as well as the stability. Since a curved plane does more work than a
flat surface, its size may be reduced and its aspect ratio increased. In
other words, the curved plane may be narrower than a flat surface, and
may be made thinner in proportion to its width.

The height of the curve, or camber as it is called, has been worked out
by elaborate mathematical equations, but we may take the general results
without following the calculations. For a plane six inches in depth, the
camber should be about one-half an inch, or one in twelve, or in this
proportion. The curve should be a parabolic with the highest point well
forward, one-third the way from the front edge. The front, or entering
edge, of the plane should be the thickest point. It should be tapered
off to a thin edge in the rear.

In theory, it is possible to model a plane so delicately that it will
fly against the wind by the pressure of the wind itself. It is extremely
important that both sides of the plane be brought to this curve as
accurately as possible. An efficient plane must, therefore, be covered
smoothly on both sides. Such a plane again offers very little skin
friction to the wind.

It is difficult to lay down any hard and fast rules for the relation of
weight to wing surface, since the types of aeroplanes differ so widely.
It has been found, however, that in large models one square foot of
surface will support about one-half a pound of weight, when traveling at
a high rate of speed.

You will find that your model, if its wings have a spread of thirty
inches os thereabouts, will approach one pound in weight. The figuring
will show you that two wings, whose combined area is less than 150
square inches, will be comparatively small and certainly well under
those generally employed a year ago.

The planes used on this season’s models are marvels of lightness and
strength. Much has been learned by studying the methods employed by the
builders of man-carrying aeroplanes. It is a simple matter to build a
three-foot plane which weighs complete less than one ounce, and is
strong enough to withstand many a violent shock.

[Illustration: A geared model built by Leslie V. Robinson]

[Illustration: An ingenious biplane]

It will be found a good plan first to lay out the exact form of your
plane on a smooth board. Make the depth of the plane one-fifth of its
length. It will be noticed that this plane is much more slender than
those used last year. Next draw a line at the center the entire length
of the board, and mark off one-tenth of the length of the plane from
either end. From this center describe a quarter circle at either end, on
the same side of the line. This will form your main or entering wedge.
The rear corners should be cut sharply away and only slightly rounded.

There is no better material for the main frame than a thin reed, cane or
bamboo. The longer ribs may be made of any light lath and the cross ribs
of a thin flat strip of the same material. Soak the reed overnight to
make it as pliable as possible, or heat it over a flame. Now lay the
reed over the outline of the plane, and hold it in this position by
driving thin brads on both sides and bending them over the cane. When
the outer edge is complete, mortise the ends slightly and tie and glue
firmly together.

With the outer frame held rigidly in position, it will be found a much
easier matter to introduce the ribs. If you are building a flexed plane
first, insert a stick of wood from end to end before placing your cross
ribs in position. The thickness of this temporary stick will, of course,
determine the curve of your plane. For a three-foot plane, a height of
one-half an inch will answer.

The ribs may now be bent over this obstacle and fastened securely to the
outer rim by glueing, tying, or nailing. The cross ribs may also be
raised by inserting small wedges between them and the longitudinal ribs.
When your frame is complete, loosen it from the board and you will find
it regular and rigid. Cover it with a very thin cloth pulled tightly
over the frame, and glue or sew it in position. A small plane may be
covered only on the under side.

Excellent results are being obtained in England with planes built up
entirely of wire. If aluminum wire is used, the weight of the wings is
considerably cut down, but even ordinary wire will be found lighter than
wood. For a plane thirty inches in width, or thereabouts, the wire used
should be at least one-sixteenth of an inch in diameter, and should be
soft enough to bend easily and hold its position.

It will be found a good plan to plot out the exact shape of your plane
on a sheet of paper, and then bend the wire over this outline. The ends
may be fastened together readily by binding tightly with fine wire, such
as florists use, and touching the joint with solder. Be careful, of
course, to keep the joint smooth. The cross ribs of these metal frames
may also be made of wire. Bend the ends at right angles and attach to
the inner sides of the plane with fine wire, and touch all the joints
with solder.

There are several advantages in the metal planes. It is a very simple
matter to flex the plane by bending the cross ribs and the ends upward
to the desired curve, much easier than when working with wood. Such a
frame will stand almost any amount of knocking about without injury. A
swift volplane to earth, which would smash any ordinary wooden frame to
"smithereens," would have little effect on a model plane. Such frames
again are very easy to cover.

It will be found a good plan to sew the cloth to one edge, draw tightly
across and sew fast to the opposite side, while a few stitches around
the metal cross ribs will give it any curve you desire. A metal frame
makes it possible to experiment with various curves. It is an easy
matter to bend the ribs up or down and alter the line of the plane at
will.

Small stability or guiding planes may be made of a sheet of metal,
although such construction is not advisable for the main plane. When
your front or entering plane is the smaller one, it is possible to turn
it into a very efficient motor anchorage.

The plane should be cut from a sheet of aluminum, preferably. Fasten
this securely to the front of your motor base with nails, or tying in
position. The wires of the hooks holding the ends of the motors may be
passed through the holes cut to the back of the rear edge of the plane
and bent over. Of course it is very simple to anchor double motors, or
even multiple motors, in this way.

One of the novelties in plane construction is a narrow wing with ends
brought well back. It may be built either flat or flexed, and promises
to afford unusual stability. The form is very popular among model
builders in England, where it is made very narrow, its depth often
equaling its width.

In many of the English models, these planes are placed far forward and
raised well above the main stability plane. They are built with the
entering edge either straight or slightly curved. Such front planes
behave especially well in the open air and even against a considerable
wind pressure.

There is still considerable difference of opinion as to the best
material for covering planes. Several specially prepared aeroplane
cloths have been placed upon the market which are guaranteed to be
practically airproof. The cloth is rather heavy, however, and better
suited for large machines. A thin silk answers the purpose perhaps as
well as anything.

Some model builders select the thinnest possible silk and then render it
airproof by varnishing or covering with a thin solution of wax or
paraffin. When this is neatly done, the planes are very taut and
shipshape. Several preparations are offered for sale for coating planes,
which are excellent.

In the search for the lightest possible covering, some builders have
gone a little further and use a very thin paper known as bamboo paper.
Even the thinnest paper will be found as impervious to air as a rather
heavy cloth. Its weight is practically nothing, even for a large plane.
It requires no varnishing or preparation, although it is sometimes
painted to render it more rigid.

There is, of course, a very obvious objection to paper that it is easily
punctured, but on the other hand, such accidents are very easily
repaired. A bad rip may be patched up with a touch of paste, or, the
plane may be re-covered very quickly. With this paper care must be taken
to fasten it to the frame of the plane as securely as possible, as a
loose sheet will flutter and increase the head resistance.

[Illustration: A well-proportioned model built by Reginald Overton]

[Illustration: A good model intended for long distance work built by A.
C. Odom]

In order to lighten the plane, the outer frames at the ends and rear may
be cut entirely away. An appreciable saving of weight is thus obtained
without weakening its structure. This plan is especially to be advised
in comparatively small planes. Design your plane and lay out its exact
form on a board. A thin strip of wood should be cut the width of the
front or entering edge, and similar straight lengths for the longer
ribs.

It will be found a good plan to use a heavier piece back of the front
edge or at the top of the curve. In building your plane, follow the
former directions of laying a stick on the board to give you the height
of the curve. The shorter cross ribs may then be fastened by glueing to
the longer ribs. By using a light lath or strip for the cross ribs, it
will be possible to make them sufficiently rigid merely by glueing
without the trouble of nailing. A skeleton frame of this kind has the
advantage of being very elastic.

In covering the frame, draw the cloth tightly across the upper side of
the frame and touch with glue at regular intervals along the ribs. When
dry, trim away the cloth between the points of the ribs and the open
ends. The rear edge may be held in position merely by the shorter cross
ribs. Trim the cloth along the edge.

In such a plane it is well to stiffen the cloth covering by painting
with shellac or varnish. This also lends a semi-transparent effect which
improves the general appearance of the plane. By cutting away the side
and end pieces of the frame such a plane three feet in width may be made
to weigh less than one ounce.

Since it is very important that the covering of the planes may be
perfectly smooth, it will be well to experiment with several different
methods of attaching the cloth or silk or paper. By covering with paper,
a taut surface like a drumhead may be had. Use a rice or fiber paper and
moisten the sheets by laying them between damp cloths, as was explained
in detail in a previous volume. In drying, the paper contracts and
tightens.

In covering a frame with cloth, the angle of the two sides may be
altered by stretching the covering over the raised ribs on one side and
drawing it tightly from edge to edge on the reverse side. If you have
difficulty in making your surface smooth, try lacing it to the sides.
You will need a strong hem at the edge. By using a thread, you will be
able to pull the cloth taut much the same as tent flaps are tightened.

The proper curve for a flexed plane is still a matter of dispute. The
highest part of the curve should come well forward, while the rear
surface is drawn straight. A good camber may be plotted very simply.
Draw a rectangle with a length sixteen times its height. Now mark off a
point on the upper side one-fourth of the way from the left-hand corner
and draw diagonal lines from this point to the two lower corners. Next
round off the broad angle formed by the two lines and you will have a
good curve to imitate in flexing your planes.

CHAPTER VI SCIENTIFIC PROPELLER BUILDING

Ever since windmills were first set up, men have been studying the
merits of different propellers. By the time steamships came to be driven
through the water by rotary blades or screws, their modeling had become
a science. The builders of rotary fans in turn contributed still further
to our knowledge on the subject. Drawing largely upon all this
experience, the aviator has learned to build fairly efficient
propellers, although there is probably no department of aeronautics
to-day so little understood.

In a windmill a current or cylinder of air flows, of course, against the
propeller. The blades must be shaped and spaced with this in view.
Reverse the action of the windmill, and the propeller proves
inefficient. The broad blades will stir up a current of air, to be sure,
but a very weak one. A revolving fan solves a very different problem in
detaching a cylinder of air from the atmosphere and propelling it with
the greatest possible momentum. Here, again, the propellers must be
differently modeled and spaced. Neither the reversed windmill propeller
nor the electric fan, however, would serve to drive an aeroplane.

[Illustration: A beautiful monoplane built by R. Mungokee]

[Illustration: Detail of a model built by R. Mungokee]

[Illustration: An ingenious application of the dihedral angle]

The propeller of an aeroplane must cut its way smoothly, pressing the
air backward without splashing. It is only when an aeroplane is held
fast that its propellers kick up such a fuss and blow your hat off. The
aeroplane propeller’s work is much the same as that of a steamship,
although the air through which it travels has many tricks not yet
understood. The density of the air compares to that of water as one to
eight hundred, but the friction encountered by the air propellers is
much greater than 1-800th that of water. It may be laid down as a
general rule, however, that the driving force of an aeroplane propeller
varies as the square of the number of revolutions per minute.

There is at present no standard form of propeller for the man-carrying
or model aeroplane. One school of designers favors a small blade
revolved at high speed, while others claim that a larger propeller
driven more slowly is more efficient. As a general rule it may be laid
down that a model with a span of thirty inches should be driven by twin
propellers eight inches in length or diameter. They should have a speed
of about 1,200 revolutions per minute, or at the rate of some 200 turns
every ten seconds. To test the strength of your motor, give the
propeller 200 or 400 turns, and watch in hand, find how long it takes to
run down.

[Illustration: Diagram Showing How To Make A Propeller From A Wooden
Blank]

There is much difference of opinion as to the proper modeling of the
propeller. It has been worked out by elaborate equations that the blade
should be concave and yet in actual tests it has been found that some
machines are driven faster by a flat blade propeller. By a flat screw we
mean a straight pitch propeller, or one in which the angle does not vary
from the hub to the tip. When Mr. Glenn H. Curtiss made his famous
record flight at Rheims, he used a straight pitch propeller, and when,
later, his machine was equipped with propellers scientifically curved,
his aeroplane lost speed. Evidently the exact relation of propeller
forms to the machine still remains much of a mystery.

[Illustration: Design of Metal Propeller]

A very simple test of the efficiency of propellers of various modeling
may be made by running them in heavy smoke. By burning a piece of oily
cotton waste, you may watch the action of the propellers on the smoke,
while, at the same time, this greasy smoke will leave its mark on the
section of the propeller blade which does the most work. The speed of
the blades near the hub of the propeller is, of course, much less than
at the tips, and consequently the work they perform in sending the
aeroplane forward is small. At the extreme end of the propellers, the
air, of course, tends to slip off.

The most efficient part of the blade, according to these tests, is about
one-third of the radius distant from the center. Less than two-thirds of
the propeller seems to do effective driving work. On the propellers
driven against greasy smoke, the blades near the hub remain
comparatively clean while the portion most soiled extends outward from
this point. The test would seem to indicate that a broad blade narrowing
to the hub would develop the maximum thrust. It would also seem that it
is unnecessary to carry the lines of the blade close to the axle,
thereby possibly weakening the propeller.

To understand the theory of the propeller, bear in mind the principle of
the action of the wings, for the analogy between the two is very close.
The forward, or entering, edge of the propeller is curved so that it
will cut its way smoothly and offer less resistance than a straight
entering edge. The blade of the propeller is made slightly concave for
exactly the same reason that the plane is curved. Like the plane, such a
surface takes advantage of the resistance of the air.

The curve of the propeller blade near the hub is made much higher than
further on because this part travels more slowly, and it is important
that the cylinder of air set in motion by the blade should have the same
velocity throughout its diameter. The blade is made widest at its outer
end, since this is the most effective surface and is expected to do the
greatest amount of work. The other end of the propeller blade is rounded
off in order that the air may slip away, thus avoiding skin friction,
which at this point is naturally high.

[Illustration: A test of high aspect ratio planes]

[Illustration: A modified Bleriot built by Cecil Peoli]

The width of the propeller blade has been the subject of an immense
amount of investigation and discussion. The friends of both the wide and
narrow blade back up their arguments with complicated equations, which
it would only be confusing to repeat. It is argued by some authorities
that since the narrow blade does not stir up the air as long a time as
the wide blade, therefore one blade does not stir up the air enough to
interfere with the action of the second blade.

[Illustration: Langley Propeller Blade]

A small blade may be driven by a much lighter motor, and is, of course,
capable of much higher speed. On the other hand, the wide blade drives
the model much further ahead per turn than the narrow blade, while
making a much greater demand upon the motor.

Briefly a narrow propeller is best for speed and the wide blade
propeller for power. There is an immense amount of difference of opinion
concerning the form and position of the propeller so that it is
impossible to lay down any hard and fast rules. It is argued by several
well-known aviators that a propeller is more effective when driven with
its straight edge forward and there is scarcely a point not in dispute.

One of the most novel propeller designs, the Cowley, is a blade bent in
the form of an arc of a circle, the radius of the curve being equal to
the diameter of the propeller. The propeller is mounted with the convex
surface forward. The theory of this propeller is that it focuses the
air, as it were, which it throws back forming a cylinder of air which
travels at a higher speed than one set in motion by the horizontal
blades.

The tendency for the air to slip off the ends of the propeller blades is
probably reduced. This form of propeller may be made by steaming the
blades and bending them into position. A mould may be prepared and the
steamed blades forced to take their shape and held in position until
they have dried.

A series of experiments have been made in England with boomerangs to
discover the effect of curved surfaces on flight. The Langeley
propeller, which embodies the information gained in this way, has a flat
back while the face is concave, following the general stream line form.
The ends of the propeller blades are practically square. Some of the new
propellers are covered with a thin canvass glued smoothly over the
greater part of the blade. The covering guards somewhat against
splitting and splintering.

In the latest Percy Pierce models, for instance, the blade is carried
out in a semicircle at the end of the propeller, thus practically
doubling its surface. The driving power of this blade is very high. It
is argued for this design that the blade being very thin is forced
slightly backward at the beginning of the flight, while the model is
gathering motion, but later, when the tension is removed, springs back
thus increasing its effective surface and the thrust. The propeller thus
automatically adjusts itself for the work it has to perform.

Since it is so difficult to fix upon the right pitch of a propeller, the
builder of model aeroplanes had best work out this problem for himself.
The propeller blank described later on, with a depth of three-fourths of
one inch to an eight inch diameter, will give you a comparatively
low-pitch propeller. An eight-inch propeller cut from a block one inch
in depth will give you as high a pitch as you are likely to need. As you
increase the pitch, you, of course, increase the power of your
aeroplane, while at the same time you make a greater demand upon your
motor. Try the propellers of different pitch until you find the one
which gives you the greatest stability and the highest speed. It is well
to remember that in increasing the width of your propeller blade you add
to the skin friction.

Some designers carry the curve of the propeller blade to the center of
the axle, while others leave the center blank. It is argued by the
former that the longer the blade the greater is the thrust. Others
believe that the blade exerts little or no thrust near the center and is
weakened by being cut away too much. The builder of model aeroplanes has
one great advantage over the designer of passenger-carrying craft. The
model does not have to carry fuel. After all, the difference in the
power required for the various models is so slight that an extra strand
or two on the motor will probably solve the problem.

Many successful builders of model aeroplanes now carve their propellers
from solid blocks of wood. This method, to be sure, allows the designer
to shape the propeller blades with more freedom than with the ordinary
or built-up propeller, and of course does away with much of the
preliminary work. So great is the demand for the one piece propellers
that the manufacturers of accessories now prepare "propeller blanks" or
pieces of wood in a variety of sizes ready to be carved. The one-piece
propeller is likely to split, but they are easy to make, and this work
is a very fascinating kind of whittling.

[Illustration: A combination of several interesting features]

[Illustration: A skilful adjustment of the front plane and skid built by
Percy Pierce]

Propeller blanks are easily prepared in case you find it inconvenient to
buy them. The following directions refer to a propeller eight inches in
length, but the same proportions hold good for any size. Select a piece
of some straight-grained wood, white pine is best, which will not split
readily, and is easy to work. The original block for an eight-inch
propeller should be eight inches in length, two inches in width, and
three-fourths of one inch thick. Now draw a line lengthwise, exactly
bisecting the block, and mark off the middle of the line, and two points
one inch from either end. With one of these outer points as a center,
describe a quadrant of a circle above the line, and from the
corresponding point, draw a similar circle below the line. From the
center of the blocks draw a complete circle one-half of one inch in
diameter. Draw straight lines from the ends of the arcs to the vertical
diameters of the circle, and saw away the wood to these lines. In
carving your propeller, first cut away the wood from the longer straight
lines of the block on opposite sides. The blades should be slightly
concave. It will be found a good plan to finish one side of the blade
before cutting away the opposite side. Cut away the wood until the blade
is less than one-eighth of an inch thick, and sandpaper away all marks
of the knife or chisel. The wood should then be oiled or covered with a
light coat of varnish. It is very important that the two ends of the
propellers should be uniform both as to their modeling and weight. To
mount the axle, drill a hole at the center just large enough to admit
the wire. The outer end may be bent over and inserted into the hole to
keep it rigid. If the axle does not fit tightly, drive in small wedges
of wood, such as a toothpick, at both sides.

The propeller used by the Wright Brothers on their machines is very
simple to construct. Prepare a propeller blank eight inches in length,
two in width and three-fourths of an inch in depth. Draw two lines
parallel with the longer sides, the first seven-eighths of an inch and
the second one and one-eighth inches back. Now at the upper right-hand
corner mark off a point one and one-half inches from the end, and from
the opposite corner on the lower base the same dimension. Connect these
two points.

[Illustration: Wright Propeller Blade]

The blank is completed by cutting away to these lines, leaving the
blades each one and one-eighth inches in width. The axle should be left
a little full, say three-eighths of an inch across. Round off the outer
corners. In modeling your propeller cut away or bevel the sides formed
by the two intersecting lines, which will form the entering edge of the
propeller. The blade should be cut to a very slight concave, although
some prefer a flat blade. The propeller is mounted by drilling a hole at
the center and mounting in the usual way.

The propellers of a model aeroplane are subject to more wear and tear
than those of a regular passenger-carrying machine. At the end of every
flight, they face a possible catastrophe. In the search for some durable
form of screw, a number of interesting discoveries have been made. One
builder has succeeded in coating a wooden propeller with bronze by
subjecting it to an electroplating process, but this is much too
complicated for the amateur. The lighter metals, aluminum and magnalium,
naturally suggest themselves for the purpose. Such propellers weigh no
more than wood and may be readily bent to the required shape.

Procure a thin sheet of aluminum, or, if this cannot be had, a smooth
piece of tin will do. It must, however, be heavy enough to hold its
shape. The design of the propeller may be laid out on the tin, and the
metal trimmed away. To make an eight-inch propeller, draw a rectangle
eight inches in length and two inches broad, and draw a line joining the
middle of short sides. At the center, draw two vertical lines half an
inch on either side of the center lines, half an inch above and below
the center, forming a small inner rectangle. Now from a point on the
bisecting line, one inch from either end, draw two semicircles. Next,
connect the top of one of these circles with the nearest point of the
inner rectangle and draw another line from the point below to the
corresponding corner of the large rectangle. Repeat the diagram on the
other end of the rectangle, reversing the curve as indicated in Fig. A.

In cutting out the design, allow the straight sections running to the
sides of the larger rectangle to remain. They will be needed to hold the
central piece in position. This consists of a block of wood measuring
one inch by one-half an inch and one-quarter of an inch in thickness.
The strips at the center should be bent tightly over the corners,
overlapped, and nailed firmly down with brads. Next, at the center,
punch a small hole and drill through the block a shaft large enough to
hold the axle of the propeller which is then firmly imbedded in it. One
great advantage of the metal propeller is the fact that you may readily
alter its pitch.

An efficient propeller may be made by mounting metal blades on a wooden
shaft. Procure a stick one quarter of an inch square and three inches in
length, and saw through both ends for a distance of three quarters of an
inch. Prepare your propeller blades by plotting them out on a sheet of
aluminum, as described above, and cut away the middle section. The
blades may then be inserted in the open ends of the stock and nailed
securely in position. The edges of the wood may then be rounded off and
the axle inserted firmly at the center. The metal sheet should be bent
into the proper pitch as in the case of other metal propellers.

FABRIC PROPELLERS

The most nearly indestructible propellers are the fabric screws. They
are also doubtless the lightest form. The blades will, of course, be
perfectly flat, making straight pitch propellers. You will need a small
cylindrical piece of wood one half an inch in diameter, and one half an
inch in height, of some tough, hard wood. The blades may be made of reed
or cane, or, still better, of wire. Aluminum wire being very light is
probably the best for the purpose. Bend the wire into the form of a
triangle two inches in width and four inches in length. Determine at
what angle you wish them to be set, and bore holes in the hub and fix
wires of each frame firmly in them. Cover the frames neatly with cloth
and mount it in the usual way.

[Illustration: An efficient model, showing excellent construction,
designed by John Caresi]

[Illustration: One of the best minimum plane models of 1911]

THE LANGELEY BLANK.

Many model builders still retain the Langeley propeller. It is a very
simple one to build. To prepare a blank secure a block, as before, eight
by two inches and three-fourths of an inch in depth. Connect the four
corners with diagonal lines. Parallel to the longer side draw two lines,
one three-fourths of an inch inside and the second one-half inch below
it. Cut away the block forming a double fan-shaped piece. Some prefer a
wider center and the hub may be made a trifle broader if desired.

In shaping the propeller cut away from opposite sides of the blank. The
original Langeley is a flat blade propeller so that the modeling is very
simple. You may use your own judgement as to the thickness of the blade,
although about one-eighth of an inch is suggested. The Langeley is
mounted in the usual way. To heighten the pitch of your propeller secure
a thicker blank.

CHAPTER VII ASSEMBLING THE MOTORS

In the present stage of model aeroplane building, rubber strand motors
satisfy every demand. Models have been flown for more than 2,500 feet by
the force of these twisted strands, and doubtless their efficiency will
be still further increased. Such motive power is besides very easily
obtained and applied. Careful tests have shown that more energy may be
stored up in twisted rubber strands than in the same weight of springs
of steel or any other metal.

In gauging the strength of your motor, much depends upon whether your
model is to rise from the ground or be launched from the hand. In the
model tournaments in England, the flying machines are almost invariably
thrown across the starting line, while in America they are required to
rise unaided. It is obviously unfair, therefore, to compare the distance
records of the two countries.

[Illustration: A Metal Motor Anchorage]

It requires a comparatively powerful motor to raise a model from the
ground, whereas a lighter motor would be sufficient to propel it through
the air. Many models, capable of flights of several hundred feet when
thrown will refuse to rise, while, on the other hand, some models which
rise well enough have poor distance qualities.

It should be borne in mind that the length of the motor, speaking
broadly, controls the distance qualities, and its diameter the speed of
the model aeroplane. A long slender motor, capable of from five hundred
to one thousand turns which will revolve the propellers for thirty
seconds or more, should insure a flight of several hundred feet. As you
increase the number of strands of rubber, building up the diameter of
the motor, you cut down the number of turns and therefore its duration,
although you increase its speed.

A motor capable of one thousand turns must be about forty inches in
length and consist of but six, or at most eight, of these strands. A
model which may be driven by this motor, it will be found, must be very
light. A model aeroplane weighing upwards of one pound, on the other
hand, will require motors composed of fourteen strands or more to raise
it from the ground. It is a very simple matter, of course, to add
strands of rubber until your motor develops sufficient energy for the
work it is expected to do.

The length and diameter of your motor, again, has a direct influence on
the height of the flight. Too much power tends to raise the aeroplane
higher than necessary above the ground. Since it requires more energy to
drive a model aeroplane upward than along a horizontal direction, this
is obviously a waste of energy.

If it is desired to fly the model as far as possible, it must be kept
close to the ground. In the case of weight-lifting contests, the problem
of altitude is, of course, entirely different. Overwinding is even worse
than underwinding, since it shortens the life of the motor.

Try out your aeroplane with ten strands on each motor and increase them
later. The motor, as previously explained, is formed by looping the
rubber strands loosely between the hooks, just as zephyr is wound on a
skein. Keep the strands very loose and fasten them to the hooks by tying
with a strand of rubber. In winding, do not turn the propeller after the
rubber has a double row of knots for its entire length. Such a motor
should take up from three hundred to five hundred turns, perhaps more.
Do not keep the elastic wound up too long before starting your flight.
The strain is great and it quickly wears out.

[Illustration: A Metal Motor Anchorage]

The rubber strands should not be allowed to come in contact with any
metal parts of the model. The copper that is often used for wiring is
especially injurious and tends to decompose the rubber. The hooks of
both the propeller and motor anchorage should be covered with a piece of
rubber tubing. This serves a double purpose. With this protection, the
rubber when tightly twisted is in no danger of being cut by the wire or
of taking up the oxides which quickly eat through it.

[Illustration: A notable model possessing unusual stability. Built by
W.S. Howell, Jr.]

[Illustration: Front view of model built by W.S. Howell, Jr.]

It requires an expert to pick out the best quality of rubber. If the
strands be examined under a magnifying glass, it will be found that the
edges of fresh rubber of the best quality are clean-cut, whereas the
cheaper rubber, and that which is worn, has commenced to granulate,
giving the edges a ragged appearance.

A simple test is to stretch the rubber over a ruler. A good rubber, in
first-class condition, will stretch about seven times its length, and on
being released instantly spring back to its original size. The same
rubber should stretch to ten times its length without breaking.

There is a great difference of opinion among the most successful model
builders as to the best shape of rubber strands. Some prefer the flat,
band rubber, while others are obtaining satisfactory results with rubber
cut in square strands. The strand used by the English model builders is
seldom more than one-sixteenth of an inch square, while in America
one-eighth of an inch strand is commonly used.

Experiments have been made with a single strand of rubber one-fourth of
an inch square, but the results have not been satisfactory. One theory
is that the corners of the square rubber tend to cut into one another
and quickly wear out, and that a perfectly round strand would be the
more efficient. At present there are no such strands on the market. It
is argued by some that the square strand in twisting must be turned on
itself further than the flat strand, and is therefore placed under an
unnecessary strain. After all, the advantage of one form over another is
fractional, and an extra strand added to the motor will balance any
possible defects.

Figures have been prepared giving the exact relation of the size of
rubber to the number of turns, although such statistics are elastic. The
problem may be worked out with your own motor. Differences of
temperature will be quickly noted. The rules prepared by V. E. Johnson,
M.A., an English authority on aviation, are as follows: The motive power
is doubled by increasing the number of rubber strands one-half; by
doubling the number of strands, the motive power is increased more than
two times; and the tripling of the strands increases the motive power
seven times. As regards the number of turns the same authority states
that the doubling of the number of strands diminishes the number of
turns by one-third to one-half.

[Illustration: A Metal Skid]

It is also found that each strand will have doubled knots of 310 turns;
four strands, 440; sixteen strands at 200; and eight at 210. This is
working with strands one-sixteenth of an inch square. As a rule, rubber
should not be turned after the second row of knots is formed. And by the
way, you will find that the rubber, after being tightly twisted, tends
to stick together, and should be carefully separated after a flight so
that the air can reach all surfaces.

According to the experiments made by Mr. Johnson, one pound of rubber
may be made to store up 320 foot pounds of energy, while one pound of
steel, in the form of springs, will only store up 65 pounds.

In the early model aeroplanes much valuable energy was lost through
friction. There has been a marked improvement in the construction of the
propellers, axles, and bearings. Friction has been reduced to
practically nothing. It is possible, of course, to drive a propeller
with the shaft turning in a hole drilled at random through a stick, with
a glass bead for a washer. It is very important, however, that the axle
should turn exactly at right angles, and to hold it in position requires
careful adjustment. To meet the demands of model aeroplane builders,
several shaft mechanisms have been prepared, even to a very complete
arrangement of miniature ball bearings.

The model builder who cannot avail himself of these parts can,
nevertheless, imitate their action with reasonable fidelity. The axle
attached to the propeller should be heavy enough to resist bending in
ordinary wear and tear. A bicycle spoke is just the thing. When you have
decided upon this axle, procure a piece of metal tubing in which the
axle will turn freely, without binding or rattling about. The tubing
should then be passed through the frame supporting the propeller exactly
at right angles, and extend out at either side about half an inch. To
fasten it securely in position, glue and if necessary drive small
wedges,—a match or toothpick,—about it.

Several metal washers should be strung on the axle between the upper
edge of the shaft and the propeller. These may be punched from a sheet
of metal. A section of this tube may also be inserted part way in the
propeller, and washers introduced where they meet. The second tube will
insure smooth action.

The projecting tube will serve also to remove the propeller far enough
from the frame to prevent its striking. By freely oiling these parts,
the propeller may be made to turn very freely.

[Illustration: An ingenious adjustment of ailerons]

[Illustration: Tuning up the model for a flight.]

In bending the axle into a hook for holding the rubber strands of the
motor, care must be taken to keep the ends of the strands on a line with
the axle. After turning the wire into a hook, bend back the shank to the
proper angle. It will be seen that if the motor carries the axle about
from side to side, the friction will be considerably increased. Over
this hook, slip a piece of rubber tubing before attaching the strands of
rubber, since the metal is likely to cut and wear the motor. It will be
found a good plan to tie the strands together just below the hook to
keep them from slipping off. And, by the way, do not keep your motor
wound up any longer than you can help before a flight, since the strain
on the rubber in this position is very great.

As motors have increased in power and distance qualities, the process of
winding up has become a serious problem. The simple method of turning
the propeller by hand takes too long, and a slip with a powerful motor
may give one an ugly cut. An ordinary machine drill will do the work
much more quickly. Some drills are geared so that a single turn of the
wheel will give you ten revolutions of the propeller.

To arrange your motor for winding with a drill, run the axle through the
propellers and turn in the form of a closed hook. A small hook should
then be fixed to the end of the drill, which may be inserted in this
loop. Some boys use a double hook on the propeller, detach the strands
of rubber, wind them up, and then attach them to the propeller.

A very simple and ingenious method of winding up has been adopted in the
remarkable model constructed by Mr. Mungokee. The motor is anchored by
running the wire holding the strands through the supporting stick of the
base, and bending the end into a hook which, as the rubber pulls, is
held securely in a second hole at the side.

[Illustration: Showing Construction And Mounting Of Propeller And Axle.]

To wind up, it is only necessary to draw out this hook, attach it to the
winding drill and turn. When wound up, the pull of the motor will
obviously hold the end of the hook firmly in the hole, making it
impossible for it to turn. This does away with extra hooks and the
trouble of hooking up the motor when once it has been wound.

The life of your rubber motor may be lengthened by careful winding. As
long as you wind up by turning the propeller by hand, it is safe to turn
it as fast as you can, since the process is slow at best. In case the
turning is done with a machine drill or some similar geared wheel, there
is danger at some points of winding too fast.

It is safe to wind as quickly as you can until the first row of knots
has formed in the rubber strands, but at the moment the double strands
begin to appear the winding should proceed very slowly. You will find
that if you wind very quickly the double knots will appear in tight
groups or bunches, and that only after considerable winding do these
begin to spread out evenly. This puts the rubber under a severe and
unnecessary strain and shortens its life.

The simplest way of locking the propellers when once wound up is to
thrust a piece of cane or reed through the hooks. The twist of the motor
will hold it tightly in position, so that you can carry your model
about, even shake it vigorously without danger of dislodging it. If you
have twin propellers, use a strip long enough to pass through both
hooks. Remove the strip just before starting. Be careful, of course,
that your axles have not been thrown out of plumb.

It will be found very convenient to equip your model with a single clasp
for holding the propellers after they have been wound up, which may be
easily released. It is awkward to keep them from slipping. An effective
break may be made by attaching two strips of reed or cane, such as you
use for skids, to either side of the motor base, so that the free ends
will pass between the propeller blades and the frame, thus locking them
fast.

These bands should spring outward and be held in position by rubber
bands running from one to the other. To release the propellers, simply
pinch the two free ends together, and the propellers will be freed at
the same instant. Do not keep your motor wound up a moment longer than
you can help. It is very trying to the rubber to be held in this
tightly-twisted position.

In mounting your propeller, it is well to make the support for the
bearing of the propeller axle as long as possible. An axle turning in a
shaft one inch in length will meet with much less resistance than in a
half-inch shaft, and with a good motor an inch-and-a-half shaft is still
better. The rear stick of your motor base, which often holds the
propeller axle, is usually made as thin as possible and rarely gives you
more than a half-inch support.

It is a good plan to lengthen the shaft by attaching a block of wood to
the frame and passing the axle through it. Cut from a strip one-half an
inch square a piece one inch in length, or whatever seems necessary.
This may be mortised slightly into the stick and glued at right angles.

[Illustration: An excellent monoplane capable of long flights.]

[Illustration: Long-distance model built by Percy Pierce.]

Now drill a hole through the stick, with the grain, and the stick of
your motor base and pass the tube holding the propeller shaft through
both. To make this look shipshape, round off the edges. A great
advantage of this stick is that it enables you to mount the propeller as
far as you like from the frame, thus preventing it from striking.

[Illustration: Showing An Excellent Way Of Fastening The Propellers To
The Framework.]

In mounting the propellers above or below the frame, you will need
similar supports. The blocks should measure half an inch in width by one
and a half inches square and should be cut with the grain of the wood
running lengthwise. The hole for the propeller shaft is drilled near the
top, and the block is securely fastened to the frame.

It will be found a good plan to mortise the frame slightly in order to
make the joint perfectly rigid, even in the face of a bad smash-up. Many
boys merely glue the stick in position and bind it securely to the motor
base with fine strong thread, and paint it with glue or shellac to hold
it in position. These blocks may be fastened either above or below the
frame or at the sides.

In mounting the propellers, bear in mind that a position above the
planes tends to drive the aeroplane downward, while the thrust exerted
below tends to throw the aeroplane upward. The builders of model
aeroplanes differ as much as to the best position of the propellers as
the designers of man-carrying machines. Excellent models have been built
with the propellers in either position. It is obviously impossible to
lay down a rule for all models, since the properties of the planes vary
so widely.

A very simple and efficient support for the propeller shaft may be made
of metal to correspond to the motor anchorage. Procure a sheet of heavy
tin—a piece of sheet aluminum is still better—one-half inch in width and
three inches in length. Now mark off a one-half inch, one inch, two
inches, and two and one-half inches, and bend over the ends at right
angles, as shown in the accompanying drawing.

This support may be nailed or screwed rigidly to the end of the motor
base, and a hole for the shaft of the propeller drilled through the two
uprights. The propeller must be mounted so that the blades will, of
course, be free of the base. The size of the support may be altered to
suit the frame. In case you are using a heavy propeller, say an inch
blade, the metal must be heavy enough to resist the pull of the
propeller.

The forward ends of the motors may be held by a cross piece cut from a
sheet of aluminum six inches in width and two inches in depth, which is
bound rigidly to the end of the motor base with shoemaker’s thread.
Aluminum suitable for this purpose costs about fifteen cents a square
foot, and is soft enough to be cut with heavy shears.

An ingenious motor anchorage of metal construction has been hit upon by
the builders of model aeroplanes in France. We are all familiar with the
difficulty of raising the hook, holding the rubber bands, high enough
above the main frame, or fusilage, to be perfectly free. Instead of
attaching a wooden block, the French boys bend a piece of tin, or some
such metal, very simply into a support for the hook.

You will need a sheet of metal heavy enough to withstand the full force
of the motor when wound up. The tin used in cans, as a rule, is not
heavy enough. For each support you will need a rectangle of tin or metal
measuring three by one and one-half inches. Parallel to the longer base,
draw a line one-quarter of an inch above. From the center, erect a long
rectangle one-quarter of an inch wide, extending to the opposite side.
Now connect the ends of the line above the base with the points at which
the upright rectangle intersects the top line, round off the edges
neatly and cut away this triangle. Four holes should be cut or punched
in the tin, as indicated in the drawing.

Now bend the tin on the two upright lines until the two sides are
parallel. This support is fitted to the end of a motor base and secured
by driving nails through the three holes at the base covering the wood.
The end of the hook which holds the rubber strands of the motor should
be passed through the opening at the end, bent over and fastened into
position with a drop or two of solder. Such a support adds practically
nothing to the weight of the frame, and obviously anchors the motor
rigidly.

[Illustration: Model built by Rutledge Barry, winner of spectacular
flight contest.]

[Illustration: A model by Percy Pierce, winner of the indoor
long-distance record.]

The efficiency of a rubber-strand motor may be considerably increased by
careful adjustment. If the strands first be wound rather loosely, as a
rope is formed, and strung between the propeller hook and the motor
anchorage, you will find that about thirty per cent. more rubber may be
added without increasing the length and that a five to ten per cent.
increase in the number of effective turns may be gained as well. By
increasing the amount of rubber, you will, of course, add accordingly to
the power of the motor. It is safe to say that the efficiency of your
motor is increased upwards of twenty-five per cent. by this adjustment.
The credit of this ingenious arrangement is due to Mr. W. Howell, Jr.

It will be well to experiment with a short-strand motor, using a single
strand of rubber for the test. Let us assume that your motor is twelve
inches in length, thus making a double strand twenty-four inches long.
First knot this, string it between the two hooks and turn it, counting
the revolutions until the first row of double knots begins to appear.
Note the number of turns.

Now untie the strand and, holding one end, twist it until the lines of
the edges make a continuous loose spiral throughout its entire length.
The easiest way of twisting them is to lay them on a flat surface and
rub with the palm of the hand.

Now bring the two ends together and let the strands twist and wriggle
until they come to rest. Fasten the ends and measure the double twisted
strand. You will find that it measures less than ten inches.

To prepare a strand for a twelve-inch motor, you must therefore begin
with a piece of rubber fully thirty inches in length. It is clear,
therefore, that the new plan enables you to gain considerably more
rubber length for length. Now string your twisted rubber on the hooks of
your motor so that to wind up you must turn against the twisted strand.
You will find that a number of turns are required before the rubber
strands are untwisted and lie parallel, which is pure gain. Count the
number of turns up to the time the first line of the double knots
appears, and you will find that it is about five per cent. greater than
in the case of the single strands.

The power exerted by your motor is meanwhile increased in direct
proportion to the amount of rubber added. Still another advantage of
this adjustment lies in the fact that such a motor will unwind to the
first turn. In preparing a multiple-strand rubber, each strand must, of
course, be twisted in the same direction and exactly the same number of
times before being installed.

The builders of model aeroplanes may profit from the experience of the
automobile tire manufacturers in studying the properties of the rubber
used for motors. Rubber is at best comparatively short-lived. It suffers
a surface deterioration on being exposed to the air, which in time
affects the entire mass.

This process of decay goes on fastest in very warm weather and in very
bright sunlight. It is believed that sea air and the rarified air of the
mountains are bad for rubber. On the other hand, a very low temperature,
as you may perhaps have discovered, robs the rubber of much of its
elasticity.

It will pay you to take some trouble to protect the rubber strands as
far as possible. Lay them away in a can or jar in some cool, dry and
dark place when they are not in use. Some boys cover the rubber with
powdered chalk. When the surface of the rubber begins to granulate, its
best days are over. Rubber is originally white in color, while the
refining process gives it the familiar gray tone.

The Para rubber is generally considered the best of the many kinds now
on the market. As a rule, any oil or grease tends to decay the rubber,
as any motorist can tell you. This is particularly unfortunate for the
aviator, since the efficiency of the rubber motor is increased by
slightly lubricating the strands. Many boys prefer to chance injuring
their motors in order to gain the advantage of the oiled strands.

The strands thus prepared slide smoothly on one another and do not grip
each other even when tightly wound. The simplest preparation for
greasing the strands is a solution of ordinary soap and water. A few
drops poured over the strands will suffice. When your motor unwinds, be
careful to keep your face out of range, since a few drops might be flung
into your eyes. Several preparations for lubricating the motors have
been placed upon the market.

The direction flights may be controlled very easily by winding the
motor. If you care to fly your model in circles or spirals, the simplest
plan for influencing its direction is to give different power to your
propellers. It often happens that a model must be in a restricted place,
perhaps a straight-away flight is out of the question.

The model may be deflected to the right or left by the use of vertical
propellers, but they require delicate adjustment, and a gust of wind may
destroy their effect. B y winding up one double the number of turns of
the other, a circular flight is assured. To gauge the diameter of the
circle merely alter the relation of the number of turns. You will soon
find that you can control the diameter of the circle with remarkable
accuracy.

[Illustration: A Motor Anchorage]

CHAPTER VIII DIRECTIONAL CONTROL

THE unerring flight of birds is, of course, the model for the builders
of heavier-than-air machines. Much of the birds’ skill in directing
their motive power remains a mystery to us, but we are learning to
analyze and, in a measure, imitate them. The builder of model aeroplanes
again must not alone imitate the methods of the birds; he must make
their system of maintaining stability automatic. A study of a variety of
successful models shows that there is great difference of opinion as to
the best plan for stabilizing the aeroplane.

Directional stability is gained by the use of horizontal elevators or
tails for controlling vertical movement, by vertical rudders or fins for
steering to right or left, and by flexible wing tips to guard against
tipping.

In designing any system of rudders, or ailerons, for gaining stability,
one should always have in mind the general principles upon which such
surfaces act. The movement of the horizontal planes or ailerons has an
important effect upon the direction of the flight, because they change
the angle of incidence.

In other words, they alter the angle of the plane with the line along
which the aeroplane is flying. If you bend the rear edge of the plane,
or aileron, downward, the angle of incidence is increased. What happens
is this. As the plane is lowered, the air is compressed beneath it,
which tends to lift the plane, throwing up the front edge and changing
the course of the flight.

This method of securing stability, which was invented and patented by
the Wright Brothers, has been widely imitated. In their later machines,
the Wrights have even abandoned the front elevating surfaces and depend
upon the movement of the main plane and a small elevating plane placed
just back of the rear rudder for their directional control.

They have thus done away with the friction encountered by the front
planes, which has resulted in giving the machine greatly increased
speed. Now in the model aeroplane, it is, of course, impossible to flex
the planes up or down during flight. Some adjustment must be hit upon
which will give the machine automatic stability. The principle of the
action of the stabilizer remains, of course, exactly the same.

In designing rudders for controlling horizontal flight, it should be
borne in mind that their stabilizing power varies largely in proportion
to their distance from the center of gravity. In most models the further
they are removed, either front or back, the greater is their leverage,
and the smaller need be their surface. By placing the rudder on an
outrigger carried far out, a very small plane will suffice.

[Illustration: A serviceable model showing excellent workmanship built
by Cecil Peoli]

The vertical rudders or fins, as they are sometimes called, are, of
course, intended to control the movement to right or left and keep the
model from sliding sideways. They have no counterpart in the wings of
birds, and are believed by some aviators to have little effect. At any
rate, they can do little harm since their head resistance is practically
nothing. Unlike the horizontal forward planes, these fins should not be
carried too far forward.

In practice it is found that they often get in the way, and a slight
side gust of wind striking them, with their great leverage, will knock
the aeroplane completely off its course, perhaps upset it. The best
position for such rudders is either above or below the main plane, or
behind it, where they are out of the way of cross currents. In last
year’s models, these vertical surfaces were often very large, presenting
as much surface as the planes themselves. It has been found that they
may be cut down in size, thus saving weight without losing their
efficiency.

A long vertical fin, or keel, has the disadvantage of presenting a
dangerously broad surface to any cross current of wind. The question of
the position of the rudder was taken up in a previous volume. A glance
at the successful model aeroplanes of the year shows that the vertical
rudders have been adopted very generally. Considerable ingenuity is
displayed in adjusting them.

The use of wing tips of any form is intended to control both the
horizontal and vertical movement. The general theory or equilibrium, of
course, applies in both cases. The most perfectly adjusted model is
subject to many forces which tend to tip it to one side or the other. A
gust of wind,—and the air is never perfectly quiet,—will tip one end of
the plane up or down.

[Illustration: Various Steering Devices. "a" and "b," simple aileron
forms. "A" novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical
rudder (Bleriot type). "D" "Blinkers," an effective rudder. "E"
stability planes not unlike the runners of a sleigh.]

In the early models, this tendency was met by fixing the plane at a
dihedral angle. An examination of last year’s models will show how
common was this design. The dihedral angle lowers the center of gravity.
Now, after one side of the model is raised and the plane rights itself,
the center of gravity swings through a considerable arc, like a
pendulum, before it can come to rest, so that the center must swing back
and forth several times.

This tendency to tipping is fatal to a steady flight. It was first
observed by the Wright Brothers while studying the early Langeley type
of machine. The Wrights abandoned the dihedral angle entirely, as all
the world knows, and replaced it by the horizontal plane with a straight
entering edge. The keel will in a measure overcome this side motion.

Much of the advantage of the dihedral angle may be borrowed, however, by
turning up the extreme ends of the plane, without materially lowering
the center of gravity. In several of the successful models of the year,
these tips have been made equal to about one-fifth the width of the
plane, and are raised as high as forty-five degrees.

The theory is that, when the oscillation commences, these surfaces damp
out the swinging tendency, and bring the model to an even keel.
Sometimes the tips are rounded off, although in some cases they are made
triangular and brought to a point. As a rule, they are added to the rear
plane, although one notable exception is the case of the Lester Robinson
model, which carries these tips on both planes.

The tips, or ailerons, at the ends of the planes maybe made of the same
material as the planes themselves. In case you are using wire frames, it
is, of course, a very simple matter to bend up the tips to any desired
angle. When the frames of the planes are made of reed, as is generally
the case, the tips should be made separately. Bend your reeds to the
desired shape and cover them with the same material used for the planes.

It is quite as important that they be covered smoothly as in the case of
the planes. They may then be attached to the ends of the planes by
wiring rigidly in position. It will be found convenient to adjust them
so that they may be bent up or down to suit conditions. The same plan
should be followed in building and attaching the ailerons to the rear of
the main stability planes.

Some interesting experiments have been made by placing several vertical
surfaces above the main stability plane. A series of four or six
vertical rudders are sometimes spaced apart at equal distances,
extending from the front to the rear edge, with a height of about half
their length. In some cases the corners are rounded off, while others
prefer to cut away the front edge sharply.

In the Vinet monoplane, the vertical fin appears in an entirely new
form. The fin is attached near the outer edge of the main plane and the
upper edges curled inward, forming an arc of a circle. The theory of the
curve is that it tends to keep the air from slipping off the ends, after
the manner of the curtains of the Vaison biplane.

As a rule, these curled fins are about three-fourths the depth of the
plane and are attached with the front ends on a line with the entering
edge of the plane. These curled planes may be stretched on frames of
light wire or thin reed. As the model tilts to one side, the air
striking the curved surface of the outer side of the fin meets with
little resistance, while the fin at the opposite side, acting with its
concave surface against the wind, offers considerably more resistance,
thus tending to check the side motion and bring the aeroplane to an even
keel.

An effective form of aileron consists of an "L" shaped plane set closely
against the rear corner of the main wing. These ailerons are made in
pairs and hinged to a rear edge. The side should extend about half the
width of the plane. The action of the hinged plane at the rear is, of
course, familiar.

The extension at the side, which should be kept rather narrow, not more
than one-fourth the depth of the main plane, is likely to prove very
efficient. If the aileron be turned too far either up or down it will
offer considerable resistance. In one of the new English models, these
ailerons are so connected that as one rises the opposite aileron is
lowered. Here is a fascinating field for experiment in automatic
control.

The vertical rudder used on the new Bleriot, the result of an immense
amount of experiment, suggests interesting possibilities for the model
builder. The rudder is built in the form of a long triangle and is
mounted by hinging one of its shorter sides to the upper surface of the
rear plane, so that its corner will extend upward and outward. In this
position it suggests a fish’s fin. The receding angle of the front edge
offers very trifling resistance.

The new Baby Wright racer depends for its lateral control largely upon a
novel form of rudders known as "blinkers." These rudders are triangular
in shape and extend out in front of and below the forward planes with
their longer edges forward. They act much the same as the jib of a
sailing vessel, and, because of their position well in front of the
center of gravity, act with considerable leverage.

The design appeals especially to the builder of model aeroplanes, since
they can be added with very trifling weight by curving the front skids
forward and stretching the cloth across their forward corners. The
Valkyrie monoplane is equipped with similar rudders, in the form of half
circles carried in the same position.

In addition to the vertical and horizontal stability planes, many
aeroplanes are now equipped with stability planes extending diagonally
from the vertical axis. These are placed below the main planes,
extending outward not unlike the runners of a sleigh. This box-like form
tends to confine the air and affords increased support.

There is even an upward tendency from this pressure of air. These planes
are usually rectangular in shape, the forward or entering edge being cut
away sharply. By mounting these planes on the skids, their additional
weight is practically nothing. Several interesting applications of this
principle are shown in the accompanying illustrations of models.

CHAPTER IX MODEL AEROPLANE DESIGNS

Whether one be designing the simplest paper glider, a model or a
passenger-carrying aeroplane, the problem of stability is the same. To
keep afloat, your air craft must be supported, as a rule, by at least
two surfaces to provide longitudinal stability. To understand the
principle of longitudinal stability, picture to yourself a very
delicately-balanced board or "seesaw." The center of gravity naturally
falls between these two planes at either end, and the wings therefore
tilt up or down, or seesaw, on this invisible fulcrum. With this
principle in mind, the movement of your aeroplane, which may seem so
capricious, will be seen to follow definite laws.

When a gust of wind forces the front plane upward, the rear plane swings
down. This movement increases the angle of both planes to the
horizontal; they offer much greater resistance to the air, and the speed
of the machine is checked. As the aeroplane slows down, as a rule, it
tries to right itself, that is, to seesaw back to balance at a
horizontal position. This in turn reduces the resistance the planes
offer to the wind, and the flight is continued at its original speed.

[Illustration: An excellent piece of workmanship. Model by R. Mungokee]

[Illustration: Model with minimum plane surface. Built by A. C. Odom]

The trick, therefore, is to adjust your planes with regard to the center
of gravity so that they will always seesaw back to a horizontal
position; in other words, to secure automatic longitudinal stability.

In designing a motor base bear in mind that it must be made as long as
possible for installing the motor, and broad enough to afford stable
support for the wings, the whole being kept as light and as rigid as
possible. Since the length of the flight depends directly upon the
length of the motor, the frame of your model should be at least two feet
in length. The width of the frame may vary widely, as a glance at the
successful model aeroplanes of the year will prove. For racing model
aeroplanes, the base may be increased to four or even five feet in
length.

THE FAMOUS "ONE OUNCER."

The one-ounce models, which have been brought to such perfection in
England, are among the simplest aeroplanes to build. Fig. A models have
a record of 1,500 feet. The adjustment is delicate, however; it is a
very "tricky" affair to manage, and whether you can get the remarkable
flights made abroad is another matter. For the stick, select a piece of
straight-grained ash or some light wood three feet in length and
one-quarter of an inch square. The planes should be cut from a thin
board one-sixteenth of an inch thick. The main plane should measure
fifteen inches by three inches, and the smaller plane eight by one and a
half inches, thus giving them a high aspect ratio. They should taper
slightly towards the ends. Round off the corners of both planes and
sandpaper the edges down. If the wood will stand it, work it down, using
a sharp plane or sandpaper. The planes should be bent by steaming
slightly across the middle and set at a slight dihedral angle.

[Illustration: A — The Famous "one Ouncer." B — A Small Experimental
Model. C — A Modified Burgess Webb Model.]

The model is driven most efficiently by a six-inch propeller. If it be a
one-piece blade, prepare a propeller blank six inches by one inch, cut
from a half-inch board. Cut away to the thinnest possible blade. Use a
very simple support for your propeller shaft as well as for the motor
anchorage at the extreme forward end. The planes should be tied with
rubber strands to the stick and glued in position when properly
adjusted. Try out your model with a motor consisting of two strands of
one-eighth-inch rubber, and increase if necessary. You will need all
your ingenuity and skill and workmanship to construct a stable model
even of so simple a design which will come within one ounce. Throw it
with the wind.

A MODIFIED BLERIOT.

In improving the lines of the various self-raising models, many of the
designs have been greatly simplified. With the number of members
reduced, the construction of a successful model becomes much easier and
the chances of failure more remote. A simple rectangular frame with two
planes driven by twin propellers requires very little skill or
experience to put together. It is very easy to locate and correct the
trouble in such a model, and quickly adjust it to rise and fly for
considerable distances.

There are many forms of such planes this year which are marvels of
lightness and strength, but the beginner should try the simplest. Begin
by building a simple rectangular frame, three feet in length and ten
inches in width of half-inch or quarter-inch strips. Mortise the corners
half way through each stick and glue them in position. Increase the
steadiness of the frame by a cross piece at the center, without
mortising. Mount your motor above the frame, selecting some simple,
strong support for the axle and the anchorage.

A model which rises unassisted requires considerable power and your
propellers should have eight-inch blades and be carved from blanks one
inch thick. You may find it advisable later on to install propellers
with very broad blades. First install motors of considerable power, each
consisting of twelve or fourteen one-eighth-inch rubber strips. You will
not get more than two or three hundred turns out of them, but with a
high-pitch propeller this will give you an excellent flight, say 200
feet.

[Illustration: Model With Minimum Plane Surface.]

For the early trials use planes with a rather high aspect ratio. Make
one of the planes four by sixteen inches with square corners, and the
second, which will be carried forward, about the same size with rounded
corners. Both planes should have a slight camber.

Attach the planes to the under side of the motor base. The theory of
this adjustment is that the planes thus rest upon undisturbed air and
are more stable. The planes above the frame come in contact with air
which has been churned up more or less by the passage of the frame. A
small vertical rudder may be added below the rear frame and well back of
the center of gravity. The model should be supported at a slight
elevation by a simple skid. By adjusting the angle of the forward plane,
this model may be made to perform a number of spectacular flights. A
model very similar to this was the winner of a cup offered for the best
spectacular flights at an important New York tournament.

A SIMPLE EXPERIMENTAL MODEL.

A great deal of pleasure and profit may be had from a small experimental
model aeroplane. The beginner who is constructing his first model will
find a small machine by far the most satisfactory. The more experienced
model builder, on the other hand, will find that so simple a model will
enable him to try out new theories quickly and cheaply. A simple Bleriot
form, one foot in length, driven tail foremost is recommended. Many
successful model builders keep such a model constantly in their
workshops.

A model aeroplane of this type and size can be made to fly from the very
first. Many of the problems which appear so difficult in constructing a
three-foot model, such as balance, head resistance, and the proper
adjustment of power, practically are avoided in this miniature
aeroplane. There is a great advantage again in the fact that the small
model may be flown indoors in the average room, where the air problems
are almost negligible. Fig. B.

Let the motor base consist of a single stick one-fourth or three-eighths
of an inch square and one foot in length. At one end of the base, attach
a block of wood one inch square and of a thickness equal to that of the
stick. Glue this in position and bind it securely by wrapping with
thread touched with glue. At a point three-quarters of an inch above the
stick, drill a hole parallel to the frame for the axle of your
propeller. A hooked wire should be attached to the opposite end of the
base. One end may be run through the stick and fastened, or it may be
imbedded in a block fastened to the stick corresponding to the axle
block. A simple and effective motor anchorage may be made of metal
(described elsewhere).

Your propeller should measure four inches in diameter. A propeller cut
from a blank one by four inches and one-half of an inch thick will give
a good pitch. Either a propeller of wood or metal such as has already
been described will answer. The propeller should be mounted upon an axle
and adjusted to the bearings, and the hook after passing through the
bearings in the support turned into a hook for the rubber strands.
Select from the detailed instructions the method which appeals to you.
Be sure that the propeller spins smoothly. It should be so delicately
adjusted that it will turn literally at a breath.

Before stringing the rubber strands between the two hooks of your motor,
be sure that the hooks are bent back, so that the strands will be in a
line with the bands. The bearings should be carefully oiled. In flying
out of doors, there is danger of getting fine sand or dirt in the
bearings which, of course, greatly increases the friction. Try out your
motor with four strands of rubber one-eighth of an inch square. The
rubber sold for one-eighth inch is often a trifle under this
measurement. The propeller should, of course, be mounted with the
shorter or curved edge forward. In winding your motor, never turn it
after the second row of double knots begin to appear, and do not keep
your propeller wound a second more than is necessary before a flight.

[Illustration: An American Fleming Williams built by C. McQueen]

[Illustration: One of the earlier models built by Cecil Peoli]

For a model of this size, wooden planes are entirely practical and very
simple to construct. Much depends upon the modeling of the planes and
the smoothness of both of their surfaces. For the planes you will need
two thin boards, one eight by two inches and another four by two inches,
each one-eighth of an inch thick. Select a wood such as poplar or
spruce, which will not split easily. The ends of the planes should be
rounded in front and cut sharply away at the rear edge, as described
elsewhere. If the wood will stand reduction without breaking, plane or
sandpaper away the surfaces until they are about one-sixteenth of an
inch thick.

The planes may be flexed by steaming, but there is a still simpler
method. Paint your planes with a thin glue or varnish, and while they
are still wet and pliable, bend them to the desired shape. To shape
them, procure a strip of wood one-quarter of an inch square, tack it to
a board and bend the planes over it, and fasten them in position with
brads driven about the edges and bent over to hold it down. The stick
should be placed parallel to the entering edge and one-half an inch back
of the line. This will give you planes flexed with a dipping edge. Later
you will probably want to experiment by changing this curve, which is
very easily done by bending over a stick of different size and altering
its position.

The model is driven by the propeller with the small plane forward.
Attach the planes to the stick with the curved or entering edge forward
by tying them with a rubber band. This will hold them in position and
allow them to give when they fall. Slip the planes back and forth until
the proper position has been found. A small block of wood may be
inserted between the planes and the stick to raise the wing to the
desired elevation. Practise throwing the model as a glider until it
sails across the room on an even keel, when the motor may be installed.

Directional stability may be gained by adding a vertical rudder. It may
be made from a thin board similar to that used in the planes. Cut a
piece two inches square and round off the corners, and shave to a knife
edge. Attach this, curved edge downward, to the edge of the stick
directly beneath the rear plane, taking care that the motor does not
touch it. To complete the model, attach skids to the under surface at
the front and rear. These should be of light reed, cane or bamboo, glued
to the main frame and curved downward and backward like runners.

MODEL WITH MINIMUM PLANE SURFACE.

In the experiments in building models with very narrow planes, some
amazing results have been produced during the past year. The limit in
this reduction would seem to have been reached in the model with planes
with a ratio of eight separated by a distance equal to ten times their
width. The forward part of this amazing model is a modified biplane, and
in this respect it resembles a successful model of last season. The two
models are reproduced side by side, for the sake of comparison. The
economy of weight and resistance is instantly obvious to the most
inexperienced eye. The model rises quickly and flies for nearly three
hundred feet in a perfectly straight line.

The motor base, which has a length equal to six times its width, or
eight by forty inches, is constructed of one-quarter inch strips. A
light cross piece at the center braces the two sides. The supports for
the propeller axles extend out horizontally from the sides. This
arrangement makes it possible to mount two ten-inch propellers on an
eight-inch base. The front ends of the frame are joined by a
semicircular piece of reed which acts as a shock absorber and does away
with the weight of the cross piece. The workmanship in every detail of
this frame must be exceedingly delicate.

The planes have an aspect ratio of eight and measure two inches in depth
by sixteen in width. The outer ends of the rear plane are three inches
in their fore and aft dimensions, thus making the outer rear edge a
slight concave. The front is cut sharply away at an angle of forty-five
degrees. The upper plane lies flat upon the motor base. The lower plane
is not set directly below it as in the ordinary biplane form, but to the
rear, its front edge being on a line with the rear edge of the upper
plane, after the manner of the Valkyrie machine. The two planes are
separated by a space slightly greater than their width. Two small
rudders, elliptical in shape, are carried just behind and below the rear
plane. The model is mounted on very delicate skids built of reed, and is
inclined at a very slight angle. Six strands of one-eighth-inch rubber
are used for each motor. The unusual length of the motor makes it
possible to give six hundred turns.

THE BURGESS WEBB MODEL.

An ingenious method of lightening the front end of the motor base and at
the same time reducing the head resistance is employed in the Burgess
Webb model. A single stick frame is used with a base equal to one-fourth
its length. The cross piece is mortised to the central stick and braced
by the diagonal sticks, joining at the main frame. This cross piece is
carried out beyond the braces and pierced for the propeller shafts,
where two twin propellers are mounted. Fig. C.

The front plane is elliptical in form, with a width equal to two-thirds
the width of the base. It has an aspect ratio of two. The propeller
motors are strung on hooks attached to the outer sides of this frame.
The plane must be unusually strong to stand the pull of the motors,
which is naturally great. It is fixed to the extreme outer end of the
central stick. The main plane, which is mounted well forward in this
model, is an almost perfect semicircle. One can, of course, carry out
his own ideas in selecting the design of the planes.

A very light central stick is used which is strengthened by wires
running to a vertical strut at the center. It is claimed that the
ingenious arrangement of the forward plane cuts away from one to two
ounces in the weight of the model, and the decreased head resistance
adds both to its stability in flight and distance qualities. The
simplified form of front plane may be adopted on a variety of models.

A MODEL WITH ADJUSTABLE STABILIZERS.

A serviceable model may be built up with flat planes equipped with
ailerons both at the rear and outer ends of the planes. These tips make
it possible to control both the horizontal and vertical movement, and
permit a great many adjustments impossible with other models. The motor
base may be borrowed from some earlier model. It should be fairly heavy.
A rectangle measuring ten by forty inches built of one-half inch strips
will be found sufficiently rigid. The sides should be braced by a cross
piece at the middle. The ends and central strut may be made of some form
of truss, if desired. One of the simplest means of providing supports
for the axles of the propellers is to carry the stick at the rear, one
and a half inches beyond the side pieces, and pass the axle through a
hole drilled one-half an inch from the end.

[Illustration: A Model With Adjustable Stabilizer.]

The pull of the motors when wound is thus well distributed and, as has
been pointed out, permits of a larger propeller being used without
danger of their striking in turning. Still another advantage is that it
keeps the strands of the motor from interfering with the planes. When
the motors are strung above the planes, they have a tendency to force
the machine downward.

Construct two serviceable planes the same size, six by eighteen inches.
These should be flat and covered as smoothly as possible. Now attach to
the rear edges of each plane a series of three ailerons each two by five
inches, fastening one at either end and the third at the middle. Make
the frames of the ailerons of a very light lath strip and wire them to
the rear edge in such a way that they may be swung up or down through a
small arc. At the outer ends of each of the planes, attach semicircular
tips, each with a base of six inches and a radius of six inches. These
may be rounded off or cut away to sharp points as desired. They should
also be attached so that they may be bent up or down and will hold their
position. Mount the model on some simple arrangement of reed skids, so
that it will be elevated at a very slight angle above the horizontal.
The model complete should weigh about eight ounces. Equipped with twin
motors of fourteen strands of one-sixteenth-inch rubber each, the
propellers should be turned about four hundred times. A medium-pitch
propeller will best serve your purpose.

In flying this model, bear in mind that the flight will be directed in
an opposite direction from the angle of the ailerons, or rudders, just
as a boat answers its helm. The wing tips should be bent up or down
until the flight is stable. The complete equipment of ailerons enable
one to correct any defects in proportion which are likely to be needed
in models built by beginners.

AN EFFICIENT THREE-OUNCE MODEL.

(Record 900 Feet)

A surprising variety of designs may be carried out in models of the
three-ounce class. One of the easiest to control is a broad adaptation
of the Bleriot model, flown with its small surface forward. For a
three-foot model, first build two planes of very light material. Wire
frames are especially suited for this model. The main plane should
measure two feet in length by four in width, or with an aspect ratio of
six. The smaller plane, carried forward, should be one foot in length
with the same aspect ratio. It will be found a good plan to carry the
outer edges of this plane back, forming two inch squares at the rear
edges. A plane with a slight camber will prove the more stable.

For the frame secure two light sticks three-sixteenths of an inch square
of some fairly strong wood; a straight spruce is good. Attach the motors
to these sticks before completing the frame. Select some rigid support
for the propeller axle. Prepare two ten-inch propellers, carving the
blades from propeller blanks three-fourths of an inch thick. The motor
will probably work best when made up of six strands of rubber,
one-eighth of an inch square, although this should be finally determined
by actual test flights. Keep all parts of the motors extremely light.

To assemble the model, connect the forward ends of the sticks carrying
the motors by a piece of reed bent to a half circle, by merely binding
the ends firmly together. The sticks should diverge so that the
propellers will be about ten inches apart, giving plenty of room for the
propellers to turn without striking one another. Next fasten the larger
plane in position across the top of the sticks, and about two inches
away from the propellers, making the plane serve as a cross piece to
hold them firmly in position. The strands of the motor should preferably
be carried above the plane. This plan does away with the rear stick of
the motor base, thus saving this weight. Adjust the parts very
carefully, that the frame will be rigid enough to stand the strain of
the motor.

[Illustration: An Efficient Three-ounce Model.]

The model will require careful adjusting to be brought to an even keel.
The forward plane should be attached in such a way that it may be tilted
up or down as desired. With care, the weight of the model may be brought
within three ounces, although a fraction over will not matter. Models
built on these lines have flown in a perfectly straight line for 900
feet.

AN ALL-METAL MODEL FRAME.

In a previous paper, it was suggested that the motor base be made of
tubes of aluminum. The idea has been carried further, and attractive
frames are now constructed in which not only the main frame is
constructed of metal tubing, but the cross piece supporting the
propellers and the braces as well are of the same material. The new
metal, "magnalium," has been used successfully for this purpose. It is a
trifle heavier than aluminum, but much stronger, and almost as easy to
work. In England, the motor base is sometimes made of metal tubing one
inch in diameter, and the rubber motor is passed through the tube
itself.

[Illustration: An All-metal Model Frame.]

Such a frame may be made readily by one who has had no experience in
tinsmithing or metal work. The metal frames are sometimes constructed by
driving wooden blocks into the ends of the tubes and letting them
project one-half an inch or more. The plug may be cut off flush, and the
cross piece fastened by wire and stout nails through the cross tube into
the plug of the main tube. A convenient brace may be constructed by
cutting the tubes to the proper size, fasten the ends and pass the rivet
through both tubes at the point of intersection, and screw the nut down
firmly on the opposite side. Such a frame is practically indestructible.
There is one possible drawback, however, in the tendency of the metal to
bend if the rubber motor pulls too strongly. Once bent, it is difficult
to get back into shape. This tendency may be overcome when twin
propellers are used, by winding alternately, giving one propeller one
hundred turns and the other propeller one hundred turns, then the first
another hundred, and so on until the motor is wound up. The planes,
propellers and skids may be of any reliable design.

AN EFFICIENT SINGLE STICKER.

A very light single-stick model may be built of bamboo rods, which will
stand an immense amount of wear and tear. It consists of a single
longitudinal member with crossed pieces at either end, braced against
the central stick to withstand the pull of the motor. Select a bamboo
stick about half an inch in diameter and three feet long. An old fish
pole will answer. The cross pieces at the ends should be of some light,
strong wood, such as poplar, whitewood or ash, since they must be
mortised and drilled, and the bamboo is likely to split under the
operation. Use a three-eighth-inch strip, cutting a piece ten inches
long for the rear and another six inches in length for the front of the
base. Fasten these rigidly in position at right angles by mortising,
glueing and tying in position. Run diagonal pieces cut from quarter-inch
strips from the ends of both cross sticks to the central frame. Be
careful not to cut away the wood in mortising it, for a bad break is
likely to occur at the weakened point.

Build two serviceable planes. The larger one, which should be carried in
the rear, should measure about twenty-four inches by eight, and the
front plane twelve by four inches. Since your frame is very light and
strong, there is no need to economize weight. By carrying the braces
running from the cross sticks well out on the stick, you can provide a
broad support for the planes. Tie the wings on the motor base with
strands of rubber. In landing they will then give enough to save a bad
smash.

[Illustration: One of the best models of the year, built by John Caresi]

[Illustration: An excellent model, showing careful attention to details.
Built by L. V. Brooks]

The propellers are mounted by passing the axles through holes drilled
through the center of the rear stick about one inch from the ends. The
rubber strands may be simply passed around the front stick and tied in
position, or may be looped about a hook inserted in the stick. Use a
fairly high pitch propeller, since the base will carry a powerful motor.
Select some simple form of skid, for the model will be comparatively
light, say within ten ounces.

A ONE-PLANE MODEL.

Interesting experiments have been made this season by altering the angle
at which the main planes are set to the motor base. The theory of these
designs is, of course, that the resistance offered by an entering angle
is less than that of a straight edge. In some models, the main planes
are carried backward until the rear tips are on a line with the
propellers. The model is driven tail first by twin propellers. The
planes are besides set at a slight dihedral angle so that the angle of
incidence is greater at the ends.

A rectangular base is suggested, with a central stick. The planes, which
may be either flat or cambered, are attached to the central stick and
slightly raised by inserting strips of wood above the outer edges of the
motor base. In this way, it is possible to fix them rigidly. Wire braces
running from the outer ends to the rear of the motor base will add to
its strength. The angle of the wings to the motor base may be altered to
suit conditions. A plane of high aspect ratio works best in this
position.

THE CANNING MODEL.

There is much to be said for the model with propellers placed near the
centers of gravity and pressure. Many authorities believe that the
successful aeroplane of the future will carry propellers somewhere near
the center of the motor base. Since the thrust is exerted near the point
where the aeroplane balances, it is argued that its stability is greatly
increased, while with the propellers far removed, either to the front or
rear, the torque gains a leverage from its position which it is
difficult to control. The main difficulty with this arrangement all
along for rubber-strand motors has been that the length of the motor
must be cut down to about half, and their efficiency reduced.

In the Canning model, this difficulty has been overcome, and a motor
extending the entire length of the motor base is hitched up to twin
propellers placed near the center of gravity. A powerful motor extends
along the center of the motor base, attached to a gear wheel at the
forward end. This wheel turns two smaller gears at either side. In this
way, a motor running the entire length of the frame may be used with an
increased number of turns. A third gear wheel should be introduced to
make the propellers turn in opposite directions.

THE FLEMMING WILLIAMS MODEL.

An immense amount of curiosity has been aroused regarding the famous
Flemming Williams model. This machine has completely outdistanced all
rivals, and set a new and amazing distance record. Its builder
frequently gets flights of eighteen hundred feet with his model, and has
made the astonishing record, under favorable conditions, of one-half a
mile. In order to study this model at first hand, the writer has
imported one of the machines, built by Ding, Sayles & Company, one of
the leading model builders of England.

The distance qualities of this model will be recognized at a glance. It
is a single sticker, extremely light in all its members, combining an
extraordinarily long motor base with well-adjusted plane surfaces. The
arrangement of the wings is original. The main stability plane is set
forward in front of the center of pressure. The rear plane is formed by
filling in the space between the rear stick and the braces, thus saving
the weight of the frame usually carried in this position. The model is
driven by two seven and a half inch propellers of very high pitch. The
model is without skids and is launched from the hand.

The central member measures four feet two inches in length. The stick is
one-half by one-fourth of an inch, with the forward part tapering
gradually to one-fourth of an inch square. The base stick is eight
inches in length, cut from a strip five-eighths by one-eighth of an
inch. The diagonal pieces forming the triangle are cut from the same
material, and meet at a point eight inches from the rear, thus affording
a surface of twenty-four square inches. The wooden parts are glued and
tied together, no nails or brads being used.

The main plane is an exceedingly refined piece of workmanship. A glance
shows that it is very speedy. The frame consists of steel wire one
thirty-second of an inch in diameter. The plane measures sixteen and
one-half inches in width and four and one-half inches in depth at the
narrowest point at the center, and five and one-half inches in the
widest part at the ends. It has four cross ribs of the same wire. The
frame is covered, on the upper side, with oiled silk. The camber is
slightly higher at the sides than the middle.

The plan of fixing a rigid shaft for the propeller axle is very simple
and effective. A piece of aluminum tubing is forced over the ends of the
rear stick and glued firmly in position. A hole for the axle is then
drilled through this tube, and the wooden stick which forms its core.
The axle thus turns in what is really a metal shaft, and the friction is
reduced to a minimum. A piece of tin tubing, a putty blower, for
instance, will serve as well. In this particular machine, the propellers
are cut from a board one-sixteenth of an inch thick and bent by steaming
to the desired curve.

The shafts of the propellers are formed of a very light steel wire, less
than one thirty-second of an inch in diameter. This is passed through
the hole in the rear stick and bent into a hook in the usual way. The
motor anchorage consists of a wire passed through the central stick and
bent back, and turned into two hooks. The rubber-strand motor consists
of twenty strands of strip rubber one-eighth of an inch broad. A special
preparation resembling cosmoline is used to lubricate the rubber, thus
increasing the number of turns. The motor will take on one thousand
turns without undue strain.

CHAPTER X DESIGNING THE SKIDS

Much more attention is paid to designing the skids for model aeroplanes
in America than abroad. Since the American model usually rises from the
ground under its own power, this detail of construction naturally has
come to be of vital importance. By attacking the problems faced by the
designers of large aeroplanes, our work is helpful in developing the
science of aviation as a whole.

Nothing has been found better for building skids than cane or bamboo. A
chassis may be made of these materials which will weigh but a fraction
of an ounce, so that even the most elaborate skids will add but little
weight. They are, besides, exceedingly elastic, which makes them easy to
work, while this quality enables them to take up the shock of a violent
landing. The thinnest sizes are best for our purposes. The reed
one-eighth of an inch in diameter will answer for all ordinary models.
To prepare reed for working, soak it for an hour. Another plan is to
heat it slightly over a flame, when it may be bent with little danger of
breaking. In case of a bad smash during a meet such skids may be readily
pieced out and repairs made so quickly that the model need not be kept
long out of the contest.

[Illustration: A model with limited plane area built by R. Barry]

[Illustration: An interesting experiment in metal frame building by R.
Fisher]

The simplest skid is made by splitting a section of reed, or splicing
it, to form a Y, and attaching the upper ends to the bottom of your
motor base. The lower end is then bent into a half circle. Wrap the reed
tightly at the crotch to keep it from splitting, and touch the wrapping
with glue. To make such a skid stable, join the two pieces by a cross
brace. The skid should slant backward at a slight angle to reduce the
friction on starting. Several methods of bracing such a skid are
suggested in the accompanying photographs of models.

A stronger skid is formed by turning the reed to form ellipses and
attaching them to the motor base. The curved parts will require bracing.
Two diagonal braces will keep them in position. Some model builders
prefer to shape the skids at the bottom, so that only a single point of
the reed comes in contact with the floor. This plan makes it possible to
shape the skids into several graceful forms which help to make the model
attractive.

Still another plan, followed by some of the most successful model
builders, is to shape the skids like the runners of a sleigh. In some of
the Percy Pierce models this year, about six inches of the rear skids
come in contact with the ground. It might be supposed that the friction
in this case would be considerable, but this particular model is one of
the quickest to rise. This design has the great advantage of being
extremely elastic and letting the rear of the model down gently after a
considerable fall.

Some model builders still retain the wheel skid in a much simpler and
lighter form. The miniature bicycle wheels do very well for scale
models, but since they are likely to add an ounce or two to the weight
of the aeroplane, they are prohibitive. To avoid this weight, the wheels
may be made of simple disks of wood cut very small. A wheel one-half an
inch in diameter, cut from a board one-eighth of an inch thick, weighs
practically nothing and affords sufficient support. These may be mounted
very simply on axles made of bent wire attached to the feet of the
skids. Sandpaper the rims to an edge in order to reduce the surface
presented to the air. Since their surface is edgewise to the line of
flight, they will offer very little resistance.

The wheels on some of this year’s models are formed of wire disks
covered with silk. The weight of these wheels is practically nothing,
and they add much to the appearance of a well-finished model. Wire disks
which may be covered in this way may be bought from the supply houses.
It requires rather a skilful hand to shape the wire into perfect circles
which will run easily. The covering again is a very nice operation. The
silk wheel is not recommended for the beginner; but for one who is
anxious to finish his model to the last detail as attractively as
possible, they form an interesting feature.

Ping-pong balls make serviceable skids. Since they are carefully
rounded, they will turn easily. To mount them, drill a hole for the wire
shaft or axle, taking great care to have it pass through opposite points
of the sphere. The wire may then be bent above it and attached to the
skid. The celluloid turning on the wire axle produces practically no
friction, and the ball offers very little resistance to the air. The
balls are, of course, extremely light and add little to the weight of
the model.

By combining the skid and wheel form of support, your model will gain
the advantage of both these devices. The general form of the Farman skid
may be followed. The skid in this case should be fairly heavy, strong
enough to hold its shape, although elastic enough to take up a
considerable shock. The simplest plan is to connect the two skids by a
cross piece, and use this as the axle for two small wheels, mounted on
the outside of the skid. This plan enables the aeroplane to rise with
the minimum amount of resistance and land at the end of a flight with
protection.

In the collapsible skid we find one of the most interesting novelties of
the year. This ingenious mechanism, which is very easy to adjust, and
which is placed under the front of the model on rising from the ground,
is drawn into a horizontal position extending out before the machine and
acts as a buffer, an aerial cow-catcher. Any simple form of skid may be
adjusted in this way. The upper end or ends are merely fastened to the
motor base so that they will swing easily back and forth. From a point
half way down the skid, a rubber band is run to the front end of the
motor base. When the model is set on the ground, after winding up, the
skid is pulled back to form the forward support. It will be found
necessary to adjust it to stand at a trifle less than the vertical. The
rubber bands must be just strong enough to permit the skid to stand in
this position when held down by the weight of the machine. As the
machine rises, the skid is, of course, released and instantly snaps up
to a horizontal position.

A new interest is lent to model aeroplane building by mounting them on
pontoons contrived to float them on the water. Several large men
carrying machines have risen from the water, notably the Curtiss model.
It is believed by some aviators that since the water offers less
friction than the earth or than a wooden runway, it is easier to rise in
this way.

The builders of modern aeroplanes have been quick to adopt this idea.
The models are mounted on miniature pontoons, and after winding up the
motors are released in the usual way. An actual photograph of a model
thus mounted in the very act of rising clear on the surface of the water
is reproduced as a frontispiece of this volume. The pontoons, it will be
noticed, consist of two small pieces of board, placed almost directly
beneath the planes. The model is mounted on these pontoons by ordinary
skids of reed. The angle of the planes with the surface of the water is
the same as in the ordinary mounting. The pontoons are kept as small and
light as possible.

To start the machine, the propellers are wound up in the usual way. It
has been found that a model would rise rather more quickly from the
water than from the land or within a few feet. As our photograph shows,
the pontoons leave a slight wake behind them in the water. Once started
to rise, however, the machine rapidly gains its elevation. One advantage
of the pontoon skid flying over the water is the safety it insures on
landing. At the end of such a flight the model drops into the water, but
with little danger of breaking any of its parts. It will be found
interesting to experiment in mounting the model loosely on pontoons, so
that when it rises it will leave them behind, thus doing away with the
increased load.

CHAPTER XI GEARED MOTORS

A MORE accurate control may be gained over a strand motor by using gear
wheels. Both their speed and duration may be increased indefinitely. The
gear will restrain a powerful motor from "racing," acting much the same
as the governor of an ordinary engine. Still another advantage is the
steadiness they insure to a machine in flight by cutting down the
vibration.

The geared wheels and the frames for mounting them will be found to add
very little weight, and they make possible a saving of rubber in the
motor which renders such equipment no heavier than the ordinary
direct-drive motor. Gears may be installed upon any ordinary motor base.
Here is a fascinating field for experiment.

The great advantage of the geared motor lies, of course, in the fact
that it enables you to divide up your rubber motor into smaller groups
of strands. As you increase the power by adding more rubber, you of
course cut down the number of the turns it will take. A motor forty
inches in length, comprising six strands of rubber, one-eighth of an
inch square, may be twisted to about one thousand turns. Double the
number of strands and you will find that you cannot get more than five
hundred turns with safety. Double the diameter of your motor one more
and it cannot be twisted more than to two hundred times.

Now it is clear that if the motor consists of two groups of six strands
each, and the axles be geared together, it may be wound up with one
thousand turns while the power exerted will be that of the twelve
strands. A motor with three groups of strands in turn will give you one
thousand turns with the propelling force of the combined number, or
eighteen strands, and so on.

As a general rule, it may be laid down, that by dividing your motor you
double the number of revolutions. The heavier the motor the greater is
the vibration in unwinding, and as you have doubtless discovered, a
model which vibrates in flight offers a greatly increased resistance to
the air. The geared motor cuts the vibration in half, or a third, as the
case may be. Incidentally, this renders your motor practically
noiseless.

The resistance offered by a set of smoothly-running geared wheels is
slight, and may be compensated by adding more strands to the motor. In
mounting them use the same care as used in the shafts of ordinary
motors. By mounting them on a simple metal frame the friction may be cut
down still further. This mechanism, moreover, is so slight that you can
afford to select substantial material for the purpose. The clock wheels
used in most of our American clocks are too thin for the purpose and
easily slip apart.

A wheel one-sixteenth of an inch thick will add little weight to your
model and will run much more smoothly. They may be bought very cheaply
from clockmakers. The ingenious miniature ball bearings constructed for
model aeroplanes are excellent for mounting gears, but they are not
essential by any means, and the ordinary arrangement of washers used for
motor axles will be delicate enough for gear adjustments. Complete sets
of gear wheels mounted on metal frames, ready to be attached to the
motor bases, may be purchased from the supply houses, but they are so
simple that almost any bright boy can construct them for himself.

In experimenting with gears it will be well to begin with but two sets
of strands with gears of the same number of teeth. Several models
equipped in this way have been flown with success in America. The best
flights are those made by a model built by Mr. Frank Schoeber of New
York, a winner in several competitions. Mr. Schoeber’s model is driven
by two motors of three strands each. He uses wheels of the same size and
number of teeth. The support on which the gear wheels are mounted must
be perfectly rigid, since any play will result in a serious loss of
power through increased friction.

Compressed-air motors have not yet been developed to a form practical
for use in small model aeroplanes.

[Illustration: An aeroplane of simple construction that flies remarkably
well, built by R. S. Barnaby]

A number of inventors are at work on this problem and high hopes are
entertained that a practical form of compressed-air engine will soon be
invented. An unlimited supply of compressed air may of course be carried
without adding to the weight of the model. It costs nothing again to get
a supply. Anyone with a bicycle pump can get up enough energy for his
model as easily as he can inflate a bicycle tire. The best
compressed-air engines at present weigh from one-third to one-half as
much as the model they drive, and will run only from ten to thirty
seconds.

Spring motors hold out a promise for the model aeroplane builder. A
number of fascinating experiments have been made to utilize the power of
a coil spring. One young aviator mounted the spring of an ordinary shade
roller upon a model aeroplane. The spring was connected up for a direct
drive, a single propeller being used. It was found that such a spring
could turn fifty times, storing up a relatively large amount of energy.
Once released, however, it unwound with startling rapidity. The
unwinding process was so rapid that the propeller spun through the air
without taking hold or exerting any appreciable driving power.

A propeller of very high pitch was employed, but with the same results.
Evidently a spring of this nature is not practical. Experiments have
been made in Germany, however, with coil springs better suited for model
aeroplanes, with satisfactory results. Since trolley cars have been
driven for considerable distances by energy wound up in coil springs,
the model aeroplane should be able to take advantage of this elasticity.
Doubtless another year will find model aeroplanes flying by energy
stored in this way.

The Petrol motors are now offered for sale in sizes suitable for model
aeroplanes by several firms. A motor developing one-half of one
horsepower weighs but little. The principal difficulty of these little
power plants is that they set up a more or less violent vibration which
racks the entire machine and renders a stable flight difficult. To set
up one of these engines and adjust it to so delicate a task requires the
highest engineering skill. Unless one has had such experience it will be
well to avoid such experiments for the present at least. As a rule the
engines are used to equip scale models which are not intended to fly.
The beautiful model illustrated on the cover of this volume built by Mr.
Karl H. De Leon is equipped with a rotary Knome engine especially
imported.

CHAPTER XII LESSONS OF THE MAN-CARRYING AEROPLANES

THE builder of model aeroplanes will do well to keep in touch with the
development of the passenger-carrying air craft. The development of both
types of machines will always be more or less parallel. It is especially
important that you watch the design and position of wings, and the
modeling of propellers, since here the problem confronting both classes
of builders is practically the same. The use of ailerons and vertical
surfaces and all improvement in steering the large machines again may
have a direct application on model aeroplane buildings.

The photographs of the new models of the large machines published in the
newspapers will often give valuable hints, while the technical
aeronautical papers will, of course, give more detailed information. In
a few years, at the present rate of model aeroplane development, the
designers and pilots of large machines may be looking to the new designs
of model aeroplanes with much the same interest.

There is at present but one passenger-carrying monoplane, the Valkyrie,
flown "tail first." It is built in two sizes, the smaller, fitted with
high-powered engines, being intended for racing. The general lines of
the Valkyrie resemble those of many of the model aeroplanes, but there
are some features which deserve careful study. The main plane of the
Valkyrie is set at a pronounced elevation, and has a high aspect ratio.

The front and rear planes are separated by a distance equal to about
five times their width. Both planes have a slight camber. One of the
most novel features of this model is that the forward plane is tilted
upward at a positive angle, while the rear plane is elevated
considerably less, thus giving the machine a longitudinal dihedral
angle. This arrangement makes for fore and aft stability much the same
as the dihedral angle of the wings makes for lateral stability, and
suggests an interesting field of experiment.

The new type of Bleriot XI follows the general lines of the famous
machine which first crossed the Channel. The fuselage of the new
machine, however, is completely covered, tapering to a broad flat
surface at the rear. This plan of gaining more surface by covering the
frame is becoming general. In model building, it is unsafe to follow
this plan, unless the motor base be comparatively small. The new Bleriot
carries a larger horizontal rudder than formerly, placed aft, while the
vertical rudder above it has been increased in size. The general design
of the main plane, which is placed forward, remains unchanged. A single
tractor screw is carried in front as usual.

In the new Blackburn aeroplane, the fuselage is covered with wood as far
back as the pilot’s seat, and with cloth to its extreme end. The use of
thin board for this purpose suggests interesting possibilities. One of
the most novel features of this model is the light skid attached to the
outer ends of the main plane. The skid is very light, adding little to
the weight or head resistance, and prevents the end of the plane from
digging into the ground on landing. Such an attachment may readily be
added to model aeroplanes when they will save many a broken wing.

A novelty in plane-designing is shown in the Handley Page monoplane. The
main plane, carried forward, as in the Bleriot, is cambered just back of
the entering edge, flows back to a flat surface at the middle and then
tilts upward toward the rear edge. The two sides, in turn, are set at a
slight dihedral angle to the horizontal. This modeling is believed to
secure automatic stability in two dimensions, both longitudinal and
transverse. The planes are unusually broad in their fore and aft
dimension, extending back nearly one-half the length of the motor base.
The horizontal and vertical rudders are very small. The design should
work well in models.

Builders of biplane models will find some interesting suggestions in the
new Bristol biplane. The forward planes are of the biplane form, the
lower surface being much narrower than the superimposed plane, the
comparative width being one-third wider. Another original feature of
this machine is that the planes are connected by only four struts
instead of by rows of struts along both the front and rear edges. The
planes are held rigid by a series of braces. It is believed that this
arrangement decreases the head resistance, at the same time insuring
considerable lateral automatic stability. The rear plane is of the
monoplane type.

The friends of the Dunn monoplane believe that the question of automatic
stability has been practically solved in this ingenious machine. The
Dunn machine has flown on an even keel for five miles without the pilot
once touching the controlling levers. The trick is in the design of the
main wings.

The greater part of the wing, extending out from the central stick, has
a slight camber and is slightly elevated, besides being set at a
dihedral angle. Near the outer edge the wings are bent sharply down,
much as the wings of a swallow are bent, and are given a considerable
negative angle both forward and outward. The tips, therefore, form
pockets at either end under the arched tips.

Wings modeled in this way are remarkably stable even when traveling
across the wind. When a gust of wind strikes the outer edge of the
plane, it tends to thrust it down rather than up, as is the case when a
gust gets under a wing of the ordinary design. The wing quickly rights
itself, however, since the angle of the plane tends to lift it. The
pockets in turn by compressing the air tend to counteract this tipping
tendency. These pockets are besides closed to an extent by ailerons or
flaps, which may be pulled down, thus confining the air still further.

An effective device for securing lateral control appears in the new
Grahame-White machine. Narrow ailerons are placed on the forward edge of
the front plane near the outer tips. The tips at the opposite ends are
hinged and so connected that as one is raised the corresponding tip is
lowered, or the other way about. Now as one of these tips is lowered,
tending to lift the machine, the opposite aileron working in the other
direction tends to depress it.

The increased resistance offered by the lowered flap again tends to keep
the machine from swinging around in the direction of the side on which
the other aileron is lowered. The lateral control is thus much more
quickly applied than in the case of the rear ailerons. In applying this
principle to model construction, it must be borne in mind that the
resistance of these forward tips is tending to retard the machine and
must be used with care when the motive power is limited.

As far as general appearance is concerned, the Piggot monoplane is
probably the greatest novelty of the year. It is the first aeroplane to
carry a cabin, as it were, in which the pilot sits completely enclosed.
In general appearance it suggests a great whale with exaggerated fins.
The pilot looks out through elliptical windows at the sides and bottom,
covered with mica, to protect him from the wind.

The wings of the Piggot aeroplane resemble the Bleriot machine, the
propeller, or rather tractor, being carried forward. It is extremely
interesting, however, since it suggests for the first time what the
appearance of a cabined, passenger-carrying aeroplane of the future may
be.

On the Farman aeroplane, the arrangement for providing stability is very
interesting. The ailerons in this case are attached to the rear of one
of the main planes, the lower one, by hinges. This general plan will be
followed in the case of the model aeroplanes. In a number of successful
model aeroplanes, the Farman ailerons have been closely imitated. The
Curtiss biplane depends for its stability upon ailerons mounted midway
between the two main planes and partly within them. This plan is
scarcely practicable in the case of model aeroplanes, since they
increase air resistance and are difficult to control.

The Baldwin biplane has introduced a new feature for obtaining stability
which may be closely imitated. A large plane is set vertically, directly
above the upper main plane which may be swung from side to side by the
pilot. The theory of this stabilizing surface is that it will restore
equilibrium from side to side, since it works in undisturbed air while
meeting with very little head resistance.

Many builders of model aeroplanes have introduced a similar vertical
plane directly above the main plane, or have placed it well forward at
the extreme front of the motor base. By removing this rudder as far as
possible from the main supporting surface, it exerts a greater leverage,
and a very small plane carried well forward will be more effective than
a larger plane directly above the main supporting surface. It has the
disadvantage of catching any chance side current and thereby knocking
the aeroplane off its course.

[Illustration: Percy Pierce, winner of the distance record]

[Illustration: A well-proportioned model, capable of long flights]

[Illustration: A well designed aeroplane built by James MacPherson]

The same principle has been carried somewhat further in the case of the
new Herring biplane, which carries six triangular stabilizing fins set
vertically above the upper plane. It is believed that these fins offer
considerable resistance to any tipping motion of the planes, and if the
machine slants to one side or the other, for any cause, there is a
tendency, of course, to dart downward at an abrupt angle. The fins
retard this motion as far as the upper plane is concerned, and the lower
plane without such an equipment tends to swing back like a pendulum,
thus bringing the aeroplane to an even keel.

In the case of the Antoinette aeroplane, of a monoplane type, a somewhat
different device is depended upon for stability. The ailerons in this
case are attached to the outer edges of the rear wing and are hinged so
that they may be raised or lowered at will. One of these may be turned
up while the other is turned down. Although these resemble the Farman
ailerons, they are believed to be twice as effective since they may work
in opposite directions, while those of the Farman aeroplane may only be
inclined downward.

It will be noticed in the photographs of many successful model
aeroplanes that the tips of the wings are flexed upward at an angle
often as much as 45 degrees. These planes, it is believed, tend to lower
the center of gravity, and in the case of a turn tend to bring the
aeroplane to an even keel. Their head resistance in a straight flight
is, of course, rather great. It is claimed that the Antoinette aeroplane
is the easiest of all aeroplanes for a beginner, largely because of this
adjustment of ailerons.

One of the most novel devices for gaining stability which has appeared
during the year, is that of the Pfitzner monoplane, which gains lateral
stability by means of an ingenious sliding wing tip which may be pushed
out or drawn back at will. When the aeroplane begins to fall from its
level, one of these wing tips is shot out, while the other is pulled in.
This increased surface tends to throw one plane upward while the shorter
plane, which for the time exerts less lifting power, falls
correspondingly. The Pfitzner monoplane makes many sharp turns with very
little tipping.

A New York aviator has succeeded, it is reported, in building a
practicable aeroplane, which combines the best features of both the
lighter and heavier than air machines. In the earlier stages of the
development of aeronautics many believed that the solution of the
problem was to be found in some such combination. The attempts usually
consisted in adding large planes to dirigible balloons. Gradually,
however, the combination was given up as impossible. The great
dirigibles of to-day carry considerable plane surface, but this is
intended to lend stability for guiding and not support.

The New York aviator, however, reverses matters and retaining the
aeroplane form attempts to gain additional support from gas pockets. He
does this by building his plane after the general Bleriot model but with
a considerable space between the upper and lower surfaces, which he
fills with gas. The machine has not yet been exhibited, but it is
understood that this space is upwards of one foot in thickness and as
wide and long as the planes. The front entering edge is kept sharp so
that the wings, for all their size, meet as little resistance as
possible. Whether the support gained from so small a body of gas is
worth while, and counteracts the increased resistance of the enlarged
wing, is of course an open question. The dirigible aeroplane has been
flown successfully several times, however, with a passenger and is
reported to have behaved well.

The new Paulhan biplane introduces an entirely new form of plane which
is being watched with great interest. The wings have the appearance of
being fluted or corrugated. The frames of the planes consist of a great
number of ribs, running from front to rear, placed but a few inches
apart. These ribs are made very flexible. The canvass covering of the
planes is sewn with a series of pockets, exactly corresponding to the
ribs. The wings are covered by merely pulling the canvass on the ribs
and fastening it rigidly in place. This gives the canvass a tendency to
arch between the ribs so that the planes consist of a series of
corrugations. It is believed by some aviators that the supporting power
of the aeroplane is increased in this way. It has the advantage at least
of being very easy to adjust. A model aeroplane built on these lines
should fly well and have a distinctive appearance.

Another feature of the new Paulhan which should appeal to the builder of
model aeroplanes is its ingenious trussed girder. It is known as the
Fabre girder. It is interesting to note here that the built-up girder
was used in the model aeroplanes even before it was adopted in the
man-carrying machines. The Fabre girder consists of two long strips of
light wood connected by crosspieces of steel running diagonally. This
form of construction gives unusual strength and is very light. It has
its parallel in the beautifully built-up trusses to be found for
instance in the models built by Mr. Mungokee. In this case the girders
are made entirely of wood.

The question is often asked whether the rear edge of the front plane
should be straight or brought back and tipped at either end. A study of
the various models of the standard manufacturers shows that there is
considerable difference of opinion among the experts. The builders of
model aeroplanes in America still retain the straight line, while in
England the tips are brought well back in a great many of the designs.
The theory of this form is, obviously, that this tip tends to damp out
any lateral motion, and makes for stability. In the most successful
American models the rear line of the plane is kept straight without
apparent loss of stability.

Turning now to the large machines, we find a similar contrast. In none
of the Bleriot models is the rear line broken. The Wright, Curtis and
Antoinette machines, even in their latest form, still retain the
straight line. The Etrich monoplane has had good results with rear wing
tips. The model has been accepted by the Austrian Minister of War who
has ordered a fleet of twenty of these craft for the army.

The rear tip was first suggested by Lilienthal. The friends of this form
claim that it more nearly approaches the form of a bird’s wing than any
of the other planes now in use. The depth of the main plane is nine and
three-quarter feet and at the tips twelve feet. The entire tip is so
adjusted that it may be flexed at will from the pilot’s seat. It will be
seen that this arrangement makes it possible to imitate the flight of a
bird very closely. In adopting this idea in model aeroplanes it will be
well to attach the extension by a hinge so that it may be turned up or
down at will. Since it is placed well out from the main axis of the
machine its leverage is naturally great.

In the large machines as well as in the models there seems to be a
general tendency to increase the aspect ratio of the main planes. The
Bleriot XI still retains its broad deep plane, but in several of the
models the depth of the model has been greatly reduced. In the new
Voisin monoplane the main wing has a width of thirty-seven feet and a
depth of but five feet, thus giving it an aspect ratio of nearly one to
eight. The machine flies with great ease, its resistance is very low and
it answers well to its stabilizing devices. The Cody biplane again has
supporting planes measuring fifty-two feet by only seven feet six
inches.

The same tendency to reduce the size of the planes is noticeable in the
recent Wright models. The Wright machines (model R), are the smallest
yet used on an aeroplane. They have a spread of but twenty-six feet six
inches and a chord of only three feet seven inches, giving them an
exceedingly high aspect ratio. In the racing machines the spread has
been cut down to twenty-one feet six inches. Attention has been called
in an earlier chapter to this same tendency to reduce the wing area in
model aeroplanes. It is interesting to find our amateur aviators
increasing the aspect ratio of their planes although working
independently.

In many of the large machines the front and rear planes are brought much
closer together in the more recent models. It would seem that as the
front and rear planes are brought closer together there would be a loss
in fore and aft stability, but on the other hand the reduction in weight
made possible by shortening the frame is very important.

A careful report has been prepared in France recently of all the serious
accidents to aeroplanes with the idea of classifying them. The record of
fatal accidents shows a total of thirty-one up to the beginning of the
present year, resulting in thirty-four deaths. Although these figures
taken alone are appalling, they are found on analysis to indicate that
aviation is nevertheless growing safer and not more dangerous. In 1910
there were twice as many fatal accidents as in the previous year, but on
the other hand there were more than five times as many flights made, so
that the percentage of accidents, as a matter of fact, was but forty per
cent. as great as for the preceding year.

The commonest cause of accidents according to these tables has been
faulty construction. Next in turn came the accidents due to the errors
of the pilots. Atmospheric conditions rank third in the list and fourth
the carelessness of the spectators. There were in all some forty-seven
accidents in 1909, and 101 in 1910. An increase is to be noticed last
year in the accidents due to atmospheric conditions. This was caused in
most cases by the unusual daring, even foolhardiness of the pilots. In
their attempts to amaze their audience by performing hazardous dives and
volplanes from great heights many machines were wrecked and several
aviators met their death.

Since the main cause of fatal accidents has not been structural weakness
or the carelessness of the pilots, it is clear that the science of
aviation itself cannot be blamed. It is of course a comparatively easy
matter to build machines sufficiently strong to fly without breaking
down. The number of accidents, especially fatal accidents, due to the
inherent danger of flying, to dangers which cannot be overcome, has been
very trifling, and is steadily diminishing.

CHAPTER XIII SELECTED QUESTIONS FOR BEGINNERS

How can I find the center of pressure of my model aeroplane? The
simplest plan is to adjust the planes so that the model flies on a
perfectly even keel, and then balance the machine. Since the center of
pressure and the center of gravity must coincide to produce horizontal
flight, this point of balance will be the center of pressure. As a rule,
the center of pressure will be found to be near the front edge of the
main plane, perhaps slightly back of this forward edge.

What is the best position for the propeller?

In the case of a model driven by a single motor, the propeller shaft
should pass through the center of gravity and center of pressure of the
machine. It is very important that the alignment should be perfect or
you will have great difficulty in securing a horizontal flight. In case
of a double propeller machine, the line midway between the two propeller
shafts must pass between the center of gravity.

My aeroplane starts off all right but often begins to rock from side to
side like a cradle and then flutters to the ground. How can I prevent
this?

[Illustration: A beautiful model built by Stewart Easter]

[Illustration: A successful model of 1910 built by E. G. Halpine. Note
contrast in plane area]

This "rocking" motion is probably caused by a too low center of gravity
in your machine. If your planes are set at a dihedral angle, they should
be brought nearer to the horizontal. Another plan is to place them lower
down. A side gust of wind will start this rocking or vibration, and in
order to right itself the machine loses momentum and falls. This
difficulty is seldom experienced with horizontal wings, especially if
their aspect ratio is high.

I have no trouble in getting my model off the ground, but it seems to
rise too fast and fall backward or uses up the power before it really
gets under way. Is the trouble with the propeller or the planes, for my
motor seems all right?

If your model rises quickly, the planes are probably well designed and
built, the motor is effective, and the propeller sufficient for all
needs. The trouble is likely to be with the angle of the planes. Perhaps
your front plane is elevated too high. The rear plane should be kept
horizontal or very nearly so. An aileron at the rear of the main plane
will help you to properly adjust same. As a rule, the angle of ascent
should be a little more than that of the front plane. If it still acts
badly, strengthen your motor and bring your large plane back a trifle.

What is the best place to put the keel?

The greatest stability is usually gained by fixing the keel at the
center of gravity. There is great difference of opinion as to whether it
should be above or below. Try both ways. What is stability for one
aeroplane may mean disaster for another.

Why should an aeroplane pitch and roll when rising or even traveling
horizontally, but sail in a bee line when it begins to descend?

The stability of a model is greater when its course is downward than
when in a horizontal flight. In this position, the center of pressure is
much less likely to shift, and the pole of gravity has rather a
steadying effect. For this reason a glider thrown from an elevation
travels much more evenly than a power-driven machine. Try reversing your
planes.

Why is it that my aeroplane sails all right, but when I increase the
power of my motor it falls off and darts about until it reaches the
ground?

It has been found in experiments of man-carrying machines that an
increase in the speed of a flight would often render an ordinarily
steady machine unstable. It is argued by some authorities that the air
is churned up, as it were, by the forward planes, and that the rear
wing, therefore, rocks just as will a boat in rough water. If your model
flies well at a certain speed, you had better stick to the motor, and
try a larger plane.

How far apart shall I place the two wings of my monoplane?

There is no general rule possible. Some designers believe that the two
planes should be separated by a distance equal to four times the width
of the main plane. An excellent model which makes long flights is
illustrated herewith, in which the distance is equal to nearly twenty
times the width of the main plane, while another successful model has an
open space of only twice the width of the main plane. Much depends, of
course, upon the speed at which the aeroplane flies. The wings may be
much further apart on a high-speed than on a slow-flying model.

Are there any simple equations for working out the relation of the
proportion of the size and weight of model aeroplanes?

There are many such equations, but none of them are simple. The formula
which obliges one to solve a complicated problem in algebra or calculus
to know where to cut off a stick is obviously absurd in the case of
small models. These formulas which may be found in technical books on
aviation seem to savor too much of certain school books to be brought in
for the builder of model aeroplanes. A good rule to remember is that the
thrust should equal the weight of the machine.

Some of the large aeroplanes are driven by propellers made up of four
blades. Would you try this arrangement on a model aeroplane?

By no means. As explained in the chapter on propellers, the work
performed by your propeller blades is entirely different from that of an
electric fan. It is true that fairly efficient propellers made up of
four blades have been used on some passenger-carrying aeroplanes. This
form might prove effective on a model aeroplane, but increased weight is
prohibitive. By carefully designing your two blades, you can get equally
as much work out of them and at the same time reduce the weight by
one-half. It is argued by some authorities that the single blades act
upon undisturbed air and are therefore more efficient than a four-blade
propeller, as the air is always churned up.

How can I calculate the speed of my machine from the size and pitch of
my propeller?

It is practically impossible to do so. If you multiply the pitch of a
propeller by the number of turns at a given time, you will arrive
theoretically at the speed.

In practice, however, the slip of an aerial propeller is from
twenty-five to forty per cent. It is very difficult to determine just
what the slip is. Your calculation is likely to be a matter of thirty
per cent off and is of little value.

I am troubled with my machine trembling a great deal during flight. What
can I do to make it steady?

The framework of your model is probably too light for your motor.
Strengthen your machine if it will stand it, or take off some strands of
your motor, if it will stand it. The frame may be strengthened by using
wire braces. This method so commonly used last year is being abandoned
by the successful builders, as it makes it necessary to attach struts at
right angles to the frame, which add to the weight and resistance. The
wire in vibrating also offers an appreciable amount of resistance to the
air. In a large passenger-carrying machine, these wire braces are
absolutely necessary, but the model being so much smaller it is better
to make the frame heavy enough to remain rigid. A great deal of extra
work and annoyance is saved by doing away with wires. This trembling
again may be caused by your propeller not being properly balanced.

What is the lightest metal I can use?

Aluminum has less specific gravity than any metal now available. Its
cheapness also makes it practicable. Magnalium is a trifle heavier than
aluminum but considerably stronger, and is preferred by many model
builders. There are still others who prefer steel to either of these.
Steel is three times as heavy as aluminum and about five times as
strong. If you can get the metal in the proper size for model aeroplane
building, steel is probably the lightest after all. Some model builders
have great success with umbrella ribs, which is probably the most
available form of steel for our purpose. As most of us have discovered,
a steel bicycle spoke is by far the best axle for propellers.

Should the propeller be in front or behind the machine?

It will require some years of experimenting to answer this question
definitely. On one hand it is argued that the forward propeller, or
tractor as it is called, works in undisturbed air and is therefore more
efficient. Most of the large passenger-carrying aeroplanes are driven by
tractors. Others argue that the propeller churns up the air and that the
planes would therefore balance themselves against the gusts thus set in
motion, which makes their flight unstable besides requiring additional
power. Practically all of the successful model aeroplanes this year are
driven by propellers.

What is the lightest practical model aeroplane?

The English aviators who excel in constructing very light models have
had great success with what are termed "one ouncers." Some of the models
of this type weigh even less than one ounce. The distance qualities of
these machines are marvelous. Mr. Burge Webb claims a record of 1,500
feet in a straight-away flight by one of his one-ounce models.

Can I make a model fly by turning the propellers in the same direction?

It is doubtful. In using twin propellers the blades should, of course,
revolve in opposite directions although they are wound up by turning
them away from the center. Be careful, of course, to mount the right and
left propeller in the proper position. Some aviators believe that the
propellers should be turned at the same time,—there are machines to do
this,—in order that the thrust may be exactly balanced.

What is the longest flight ever made by a model aeroplane?

Mr. Flemming Williams, the English expert, claims to have made a flight
of almost exactly one-half a mile. His machine, which is illustrated in
this volume, weighs ten ounces. It was launched by throwing it in the
air, and in making this record flight travelled with the wind.

What is the best weight for a model?

Here is a very difficult question. It depends entirely upon what you are
trying to accomplish. In England, where everything is sacrificed to the
distance qualities of the model aeroplane, the best models vary from
five to ten ounces in weight. In America, where much more is required of
a model aeroplane, since it must rise from the ground under its own
power and possess considerable automatic stability, the average weight
is much more.

What is the average speed of a model aeroplane in flight?

About twelve miles an hour. When sailing with the wind this speed may be
increased indefinitely. In sailing against the wind, a model aeroplane
may creep along while remaining almost stationary.

Will tandem propellers make my model swifter or steadier?

Little has been accomplished either in America or in England with the
tandem propeller. Several small French models have been flown in this
way, but without striking results. Theoretically, the torque of the
propellers balance one another in this position; the forward propeller
creates a considerable backwash, and the second propeller works at a
disadvantage. Further experiments may discover an advantage in this
arrangement

How hard should I throw my machine when starting it?

It is not a good plan to launch the machine at a higher speed than that
at which it travels under its own power. By increasing its speed, you
are likely to set up violent oscillation, and, as explained elsewhere, a
model becomes unstable with increased speed. It is better to start it
too slowly than too rapidly. In the case of a glider, of course, it is
well to throw it with all your might. This is a problem, incidentally,
which does not occur when the models rise by their own power.

My machine flies very well indeed, but I cannot make it start from the
ground. When I add more power it swerves to one side and will not fly
off. What would you advise?

[Illustration: Percy Pierce launching a prize-winning model]

[Illustration: Launching the sling-shot gliders]

This is a common experience. Our advice is to return to the original
motor and make the most of the successful flights. Your model may not be
adapted to rising at all, that is, it is too light to carry the motor
required to raise it from the ground. If your frame is made strong
enough, it may be able to stand the increase in power, if it vibrates
violently, as is probably the case with a heavier motor.

What is the best time to release the propellers, just as it starts or
before?

Try both ways. Some model builders allow their propellers to get under
way a second or so before the flight commences, and release them and
push the machine forward at the same instant. One amateur secures his
propellers by means of a thread which he breaks by touching it with a
match, but it is rather fanciful.

What is the best height for a model aeroplane to fly?

In the principal model tournaments held in New York the models were
seldom more than twenty feet from the ground at any time. Most model
builders have this altitude in mind in designing their machines. It
seems to be generally agreed that when a model rises higher than this
too much power is used up in gaining altitude and there is a
corresponding loss in the distance qualities. On the other hand in the
remarkable 1,600 foot flight made by Cecil Peoli in July, the model rose
to a height, it is believed, of more than 100 feet and gained
considerable distance in gliding down. After all it is a problem which
must be decided by the individual. Incidentally it is estimated that a
large man-carrying aeroplane on rising to an altitude of one mile can
safely soar with all power shut off for twelve miles. This means of
course that an aviator has the choice of landing anywhere within a
circle twenty-five miles in diameter, which gives him a rather wide
choice.

What is meant by "critical soaring speed?"

It is claimed by some aviators that every aeroplane has a certain speed
at which it flies best and beyond which it is unsafe to push it. If more
power is put on, they argue, it will only tend to send the machine up in
the air and will not increase its speed. This is probably true in a
measure of model aeroplanes as well. When you have found the speed at
which your aeroplane flies best do not change the number of rubber bands
of your motor or the number of turns in winding.

Do the tails of birds serve as rudders to guide them in flying?

It is an open question. Some aviators who have made very careful
observations of birds in flight deny that the tails have anything to do
with their direction. The theory is advanced by some scientists that the
birds used their heads to change their course, operating them as a
forward rudder, much as do some types of aeroplanes. They argue that
since a rudder is much more effective when placed forward the smaller
surface presented by the flat heads and necks of birds has more effect
than a comparatively large tail.

What is the relation of the wing surface to the weight and horse-power
of the biplane as compared with the monoplane?

The Wright biplane carries a trifle more than two pounds of weight for
each square foot of lifting surface. The Bleriot monoplane carries about
five pounds weight to every square foot of lifting surface. On the other
hand the Wright machine carries about forty pounds per horse-power,
whereas the Bleriot will only carry about twenty-seven pounds. These
figures do not work out for all biplanes or monoplanes but they indicate
broadly the relation between the two general types of aeroplanes.

What would be the effect of bending down the outer ends of the wings of
an aeroplane as the wings of some birds droop?

The experiment is well worth trying. It would seem that this angle would
give increased stability, although if the model were knocked off its
course it might increase the resistance considerably. An elaborate test
of this form has been made by an aeronaut named Weiss in England, who
believes he has gained automatic stability in this way. Mr. Weiss has
built and flown a number of aeroplanes, varying in size from one
weighing five pounds to one which carried a weight of 140 pounds, and
the tests are reported to have been very satisfactory.

What is meant by the phugoid path of a model aeroplane?

The line described by the machine in flight. Every aeroplane left to
itself flies in a series of waves swaying more or less up and down from
the horizontal. In a aeroplane under the control of an aviator this is
largely overcome by manipulating the rudders controlling the vertical
motion. Every model aeroplane or soaring machine has a phugoid path
peculiar to itself which is affected by the power of its motor, the form
of the wings, its ability to right itself, etc. It is obvious of course
that if the path of your model aeroplane is irregular the machine must
travel more slowly and its distance qualities are therefore reduced.

Is a variable wing surface an advantage and can it be applied to model
aeroplanes?

In theory at least there is a great advantage in the variable surface
plane. As yet but one aeroplane has been flown in which the pilot may
increase or cut down the spread of his wings at will. When such control
is possible the aviator may employ the maximum spread of the wings for
rising, for instance where it is needed, and then reduce their area when
aloft, thus gaining in speed qualities. At the present stage of the
development of the model aeroplane a variable wing does not seem
practicable, although it is reasonable to suppose that the improvement
will come in time. The control would of course have to be automatic,
which renders the problem rather complicated.

What is a vortex pack?

Literally a small cyclone or eddy of the air. The term is used by
aviators to describe a turbulent section of the atmosphere. It is very
common in flying, especially at low altitudes, to run into a very
turbulent eddy of air, such as is set in motion by high buildings or
deep valleys. They are extremely dangerous since they cause the
aeroplane to dip and roll about violently, and call for quick and
skilful handling of the aeroplane to keep it from being upset. The term
might be used to describe an eddy of air which brings a model aeroplane
to grief.

What form of propeller will give the highest efficiency?

It is impossible to lay down a hard and fast rule. Much depends upon the
form of the machine. The Voison propellers have been found in actual
practice to give only about forty per cent efficiency. This is said to
be partially due to the fact that their parts are held together by bolts
and projecting nuts which offer considerable skin friction. The Wright
propellers are believed to be the most efficient propellers for large
machines since their efficiency is about seventy per cent. The
accompanying photographs of the standard model aeroplane types in
America will show that there is great difference of opinion as to the
diameter and pitch of the screws.

What is meant by a variable speed machine?

Merely an aeroplane whose speed may be increased or reduced by degrees
at the will of the aviator. This will enable the pilot to use a slow
speed for rising, for instance — and on reaching a desired altitude
increase his speed. On encountering high winds, for instance, the speed
might be increased so that the aeroplane would cut through them almost
undisturbed. The variable speed aeroplane will doubtless soon make its
appearance. Many aviators expect that it will be the next great step in
the advancement of the science of aviation.

Has any model aeroplane been fitted with an automatic stability device
and what is it like?

No such equipment has attracted public attention up to the present
writing. An interesting method of securing automatic control has been
suggested by H. L. Twining, the well-known writer on aviation. His plan
is to attach a geared wheel to the propeller shaft in such a way that it
will not begin to move until the propeller has made about 100
revolutions. A string is then run about this wheel which is pulled back
as it turns. The pull of this string in turn is made to raise or lower
the horizontal rudder of the model, but only after the machine
propellers have made 100 turns and the model is presumably well up in
the air. In this way the propeller may be set to send the model upwards
at a sharp angle and then made to take the proper angle for a horizontal
flight. The attachment suggests very interesting possibilities. It may
be possible, if the device works, to alter the angle of the rudders
either vertical or horizontal several times during a flight.

What is the record flight for a motor-driven model aeroplane?

A flight of upwards of one mile is reported to have been made by a motor
driven model in India, while in the United States the mile mark is
claimed to have been passed. Neither of these flights are official. The
most advanced work with motor-driven models is at present being done in
France. At a recent model tournament at the Velodrome du Pare des
Princess, Paris, a number of model aeroplanes equipped with engines of
various types were flown. One of these, a biplane measuring nearly seven
feet in length, was fitted with a petroleum two-cylinder motor which
developed one-third of a horse-power. It rose beautifully, cleared a
high building and was flying well when it unfortunately collided with
some telegraph wires and came to grief. Before the accident it had flown
nearly three hundred feet in a perfectly straight line. Another model at
the same meet equipped with a carbonic acid motor flew very well for a
time but was injured in a collision.

How long has a model aeroplane remained in the air?

The American record for time aloft is held, we believe, by Cecil Peoli
of New York, whose model has remained in the air for sixty-five seconds.
Several records of from thirty to forty seconds are reported from
France. It is probable that the best record has been made in the long
distance flights in England when 26,000 feet was covered.

Has the model aeroplane any practical commercial utility?

Probably not, unless we take seriously the suggestion of a writer on
aerial warfare, who believes they will some day be so perfected that
they may be used to drop bombs or high explosives over forts or besieged
cities. His suggestion is that hundreds of model aeroplanes equipped
with miniature engines might be released in a swarm, each carrying a
deadly explosive which would be dropped automatically at a certain time.
It would be impossible, he argues, for gunners to bring down an entire
fleet of these swiftly moving machines, and so while many of them might
fall short enough would succeed in dropping their missiles to make them
an exceedingly dangerous weapon. The writer points out that the expense
of such a mosquito fleet would be trifling compared with the cost of the
ordinary engines of warfare and might be operated without risking any
lives.

[Illustration: A tractor with large plane forward built by F. W. Curtis]

[Illustration: Model built by William Robinson]

How large may a model aeroplane be made with good results?

None of the successful strand motor models at present exceed five feet
in length. This would seem to be the practical limit at which a model
may be carried with this motive power. Flights of more than 1,500 feet
have been made with models but two feet in length. When regular engines
are installed there is of course no limit to the size of models.

When was the first model aeroplane constructed?

Crude machines propelled through the air by twisted rubber strands were
used as playthings more than a century ago. The model built and flown by
Langeley in 1887, was probably the first machine to appear on the lines
now generally followed by aeronauts. Successful model aeroplanes have
been used as toys for less than five years. Their development in this
period has been remarkable.

Are the equations for calculating the thrust of propeller in terms of
wing area and skin friction and general proportions useful in designing
model aeroplanes?

Only in a general way. When the dimensions are very small these
complicated equations are misleading. They are for the most part
extremely complicated and for this reason we have avoided them entirely
in the present volume. Much better results may be obtained by proceeding
merely by the rule of thumb, and testing out the proportions of your
aeroplane by actual practice.

What is the American indoor record for model aeroplanes?

A flight of 265 feet was made at a New York tournament by Stewart
Easter, the model rising from the ground under its own power. This was
made diagonally across the hall as far as it could go. Many flights have
been made at the New York meets in which models have flown the entire
length of the hall and struck the further wall with their motors far
from run down. In other words, model aeroplanes have reached a state of
development where they have outgrown the largest indoor enclosures
available for flying.

CHAPTER XIV AMONG THE MODEL BUILDERS

A number of model aeroplane builders in America have developed
distinctive designs which have come to be accepted as standard types.
Among thousands of boy amateurs these models are looked upon much as, in
the larger field of aeronautics, the Wrights, Curtiss, or Bleriot are
accepted as authoritative. Like the famous designers and pilots of
man-carrying craft this younger generation of designers give their names
to their machines. Our young designers, as a rule, confine themselves to
developing a particular type of machine. A comparison of the models of
the same builder for a year or more will usually show that the same
general form and arrangement of the planes remain the same.

The Percy Pierce model, which borrows the name of its designer, is
probably the best known of these model aeroplanes. The designer is a New
York schoolboy seventeen years of age, who has won distance records both
for indoor and outdoor flying. His machines rise from the ground under
their own power. The Pierce model of 1911 is equipped with wings much
narrower than those used last year, spaced well apart on a four-foot
frame. The planes, which are slightly flexed, are covered with silk, or
bamboo paper drawn taut and varnished. Twin propellers of high pitch are
used and the motors are carried above the planes. They are wound more
than five hundred times. The planes are carried beneath the main frame.
Directional stability is obtained by carrying back the edges of the rear
plane and by a vertical rudder placed beneath. The model is mounted on
skids of bent reed and is elevated very slightly above the horizontal.
It starts off very fast, often leaving the ground within five feet. The
model reaches its maximum altitude, traveling at an angle equivalent to
its position at starting, and maintains its height throughout its
flights.

The later Pierce machines, while preserving the same general lines, are
considerably lighter and have developed surprising distance qualities.
The planes are made of light lath or bamboo covered with specially
prepared paper, while the pitch of the propellers has been increased as
has the power. The latest models have flown for 1,600 feet.

Another prize-winning model which has attracted considerable attention
of late is the aeroplane designed and built by Cecil Peoli. It shows an
intelligent appreciation of the principles involved and excellent
workmanship. It is a monoplane, flying with the smaller plane forward,
and has recently flown for nearly 1700 feet. Planes are used with both
silk or paper covering. The success of the model is largely due, no
doubt, to the careful workmanship and finish of the planes.

The models are usually high powered and are driven by twin propellers of
high pitch, carved from especially designed blanks. The aeroplane rises
very quickly and will successfully combat a high wind. It is doubtless
due to this fact that the model has won in a contest for altitude. It
has repeatedly flown over a thousand feet. It does not follow, of
course, that the beginner can equal these records since much depends
upon the skilful adjustment of the model which comes only with
experience.

Another prize-winning aeroplane which has been much admired is the
Leslie Robinson model. This model, which is of an original design, makes
long and remarkably stable flights. In no other model has metal been
used so extensively in construction. The propellers are made of aluminum
as is the framework of the planes. Both planes are built in the
proportion of about one to five, the smaller wing being carried forward.
A novel feature of this model is the turned wing tips of both planes,
which are slightly tapered and bent upward and outward at a slight
angle. The model is beautifully finished in every detail.

Skids of reed are used and the model is tilted upward sharply at an
angle of nearly forty-five degrees. The motors, three feet in length,
are composed of ten strands of square rubber, which will take about 400
turns. The model rises quickly at a sharp angle but soon comes to a
horizontal position and flies with great steadiness. It weighs complete,
ready for flight, nine ounces. Its metal construction makes it very
durable and proof against many of the smaller accidents. The later
machines have been equipped with geared motors, which work well in
practice.

The models built and flown by H. L. Watkins always give a good account
of themselves. A comparison of the Watkins models of 1910 and 1911 shows
that their inventor has kept closely to his original design and has made
remarkable progress in lightening his machine while keeping it
sufficiently strong to support two powerful motors. The wings have been
cut down in size and made extremely light, the smaller wing being set
well forward. Directional stability is gained by a small vertical and
horizontal rudder, carried far in the rear of the rear main plane. Every
part of the frame is kept extremely light. The model complete weighs but
four ounces.

The Watkins model stands on very light skids so arranged that a single
point comes in contact with the floor, thus reducing the friction on
rising. In many of his models Watkins covers his planes with thin red
paper. The machine rests almost horizontally but rises very quickly on
being released. Its extreme lightness often gives its flights a slightly
waving form. Twin propellers, with unusually broad surfaces are used for
driving, although, in some models, a single propeller is carried just
back of the rear plane. It is an extremely graceful model in flight.

In the models built by Stewart Easter the wing surface has been reduced
still further. The surfaces are no more than knife blades and are
mounted surprisingly far apart on a rectangular frame. Every part of the
frame has been cut away where possible to economize weight and
resistance. Although four feet in length the model weighs less than
three ounces. The front planes are flat with straight entering edges and
the sides are cut slightly away. The rear edge of the rear plane is
slightly concave. In some of his models two thin blades are carried
forward, the upper one being placed slightly in front, thus ingeniously
varying the biplane form.

Two slight vertical rudders, elliptical in form, are carried back of the
rear plane. The frame stands in a practically horizontal position. The
skids used are very light, touching the ground at a single point. With a
six-strand motor the twin propellers are wound about six hundred times.
The propellers are broad and of a high pitch. The Easter model clears
the ground instantly, rises rather high and makes a beautiful flight.
The model shows extremely fine workmanship in every detail.

The model built by John Caresi contrasts strikingly with these extremely
light frames. They are of excellent workmanship and illustrate many new
ideas in construction. The Caresi model flies well and has acquitted
itself specially in the weight-lifting contests. It is safe to say that
no other American model aeroplane shows a more comprehensive knowledge
of the scientific principles involved in model building or a higher
standard of workmanship in every detail of their construction. The
planes are large, thus affording unusual stability. The frames are
marvels of delicate and ingenious construction. In contests in which the
workmanship and design are considered as well as the distance qualities,
the Caresi model stands in a class apart.

No list of the successful model aeroplane models of the year would be
complete which did not include the prize-winning machine built by J.
Ragot. The aeroplane carries two planes of about equal size and shape
mounted on a simple frame. It is driven by twin propellers of rather low
pitch and a high-powered motor. By skilful adjustment of the planes and
weights the model performs the most amazing spectacular flights. The
model is well made. The unexpected course of the machine is controlled
by flexing the ends of the planes. The Ragot model "loops the loop" and
performs other amazing feats.

In point of workmanship few of the model aeroplanes which have appeared
at the meets this year compare with those built by R. Mungokee. The
genius of the Japanese for delicate construction finds an admirable
opportunity in such work. These models are unusually large, and their
wing area considerable, yet so delicate are all the parts that they
weigh less than one pound. The sticks used for the motor base are
hollow, being built up of a light veneer one-sixteenth of an inch thick.
The joints are so cleverly arranged that they would deceive the average
eye. The main sticks of the frame are joined by a series of trusses of
the same delicate construction which form an exceptionally rigid base of
amazing lightness. Every detail of the model shows the same delicacy of
construction. The planes are built up of thin strips of bamboo covered
with Japanese silk on both surfaces, the curve being drawn perfectly.
The models are driven by two very wide propellers of high pitch, placed
back of the rear plane. The smaller plane is carried forward. The model
rises to considerable height, often fifty feet or more, and flies
horizontally with unusual stability. The frame is braced by fine wires
running through struts placed midway above and below the main sticks.

The finest scale model aeroplane in America to-day is doubtless the
biplane built by Mr. Karl H. De Leon, illustrated on the cover of this
volume. Its great size is indicated by comparison with the boys standing
about it. The most delicate workmanship is to be found in every detail.
The planes are controlled by a complete system of wires and levers
centered at the driver’s seat, exactly as in the large man-carrying
machines.. The wings may be flexed and the guiding rudders turned from
side to side or their angle elevated or depressed by the slightest
movement of the controlling devices. The model is equipped with a
miniature Gnome engine especially imported for the purpose. The
materials employed in constructing this model alone cost upwards of
$500. The model embodies several original features, the inventions of
the builder.

[Illustration: Front view of the De Lion model]

Several of the most interesting models of the year have been designed
and built by Mr. W. S. Howell, Jr., a very painstaking and intelligent
student of aeronautics. Mr. Howell has done much valuable original work
in building scientific gliders. One of his gliders weighing nearly two
pounds, has been thrown for more than 600 feet measured in a straight
line, while the actual distance traversed was probably two or three
times this distance. The model is of exquisite workmanship in every
part. Mr. Howell is the inventor of several devices for increasing the
efficiency of rubber-strand motors by reverse winding.

CHAPTER XV CURIOSITIES OF THE AIR

Until the summer of 1911, the longest model aeroplane flights officially
recorded in America remained under 300 feet. From England meanwhile came
disquieting reports of 1,000 foot flights and better, made by a number
of aeroplanes. A comparison of the best American and English models
showed that, both as regards form and workmanship, American boys were
holding their own against their English cousins, and utterly failed to
account for the much greater distance qualities of the foreign models.

In July, 1911, the American distance record was suddenly jumped to 1,691
feet, 6 inches, by Cecil Peoli of New York. The model used had been
flown in the regular indoor meets for very much shorter distances. This
sensational advance in the distance record was made at an outdoor
tournament at Van Courtland Park, New York City. Of the thirty-four
models entered for the contest, including the familiar models built by
Percy Pierce, H. Watkins and others, several showed a similar increase
in distance qualities. The model aeroplanes were the same as had flown
but 200 feet indoors, their rubber motors exerted no more power than
before, the pitch of the propellers remained unchanged.

What then is the secret of the suddenly acquired distance qualities?
Evidently the difference lies in the quality of the air the little ships
navigate. It is commonly said that the air indoors is dead as contrasted
to the live air found out-of-doors. The variation in the quality and
movement of the air forms a very interesting study which no aviator can
afford to neglect. To the actual navigator of the air this study is just
as important as life and death, while to the designer even of model
aeroplanes it is of course of vital importance.

Although the composition of the air and its behavior under various
conditions has been the subject of scientific examination for centuries,
"it is only within the past few years that it has been studied with the
idea of bringing it under control. The long painstaking experiments of
Langeley and Lilienthal, referred to in the previous volume, for
determining the resistance of the air and its effect on the surface of
the aeroplane, opened a new field of scientific research. Within the
past few years, even months, the advancement in our knowledge of the air
has been greater, it is safe to say, than in the previous century.

It is not generally realized by the laymen how rapid has been the
development of "aerology," nor how practical are the results obtained.
There have already been established in Germany three scientifically
equipped stations for observing air conditions for the benefit of
aeronauts, just as the weather bureau observes weather conditions and
informs ships at sea of approaching storms. One of these, established by
Dr. Polis at Aachen, is now in operation. In addition to this the Public
Weather Service Stations of Germany have been equipped recently with the
necessary apparatus for making daily observations of the upper air for
the special benefit for aerial navigators.

The resistance offered by the air to the passage of an air ship of any
type depends upon its density. The air is obviously an exceedingly
variable medium, as capricious as quicksilver, as both the sky pilot and
the flyer of model aeroplanes have learned. The density and therefore
the resistance depends upon the temperature, the pressure and the state
of equilibrium. We are in the habit of thinking of density and pressure
as affecting enormous volumes or areas miles in extent, such as are
reported in the weather forecasts from day to day. To an extent these
same conditions are found changing within a few feet. It is this
tendency to rapid change of conditions which makes the problem of
stability in aeronautics so baffling.

The pressure upon an aeroplane, whether a man-carrying machine or a
model, varies considerably between the level of the seashore and the top
of a mountain. An aeroplane in rising from the level of the sea for
several thousand feet therefore meets new and unexpected conditions. The
density is reduced fully one-half at an altitude of 18,000 feet, and
since aeroplanes have risen more than 10,000 feet this must be taken
into consideration. Even at a height of 300 feet, which is often reached
by aeroplanes in flight, the difference in the pressure calls for
skilful manipulation on the part of the sky pilot.

The density varies again according to the temperature. Let an aviator
suddenly run into a hot or a cold strait of air and the pressure upon
his planes will instantly change. The effect of temperature must be
taken into consideration by any one flying model aeroplanes. It may
happen that a draft of cool or of hot air, by changing the pressure on
the planes, will throw a model aeroplane out of balance and mar an
otherwise promising flight. A difference of a few degrees of temperature
will often affect a very sensitive model. The only way to combat this is
of course to build your model with the greatest possible stability.

The presence of high buildings or other violent inequalities will also
affect the density of the air and in turn the pressure exerted on the
wings of an aeroplane. Among aviators it is generally believed that a
great city is one of the most dangerous possible objects to fly above.
In the case of New York with its many sky-scrapers, for instance, the
danger is vastly increased. Even in the open country the presence of a
deep valley or other depression will so affect the density of the
atmosphere that an aeroplane is likely to be drawn down from its course.
These areas are known among aviators as "pockets," and are often large
enough to swallow up a large man-carrying craft, at times with
disastrous effects. The chance of your model aeroplane running into such
a pocket is of course considerable.

A striking illustration of the effects of these chance currents was
afforded during a recent model aero tournament in New York. A model
aeroplane which had flown with remarkable steadiness for more than 150
feet chanced to pass over the head of a boy who was walking slowly
across the course. This moving object served to set up a small whirlpool
of air. The model on striking it was instantly checked, when it turned,
skirted the column of air and passed on. In an indoor flying, an open
window, merely by changing the temperature slightly in its vicinity,
will often cause a model to be seriously deflected, perhaps to be thrown
completely off its course. It will often be noticed in outdoor flying
that a model, in passing over a stream or body of water or a mass of
dense foliage, will encounter a change of temperature which will
appreciably affect its course.

In flying model aeroplanes the performance of a machine will often vary
unaccountably from day to day. With the same motor and winding, the
model will fly much higher and more freely at different seasons of the
year. It is well to bear in mind that in the summer months the heat
causes a low density. The pressure exerted by the atmosphere is
therefore correspondingly small; the model, or for that matter a large
machine, travels much faster. A dry day also tends to cause low density.
This will account for the excellent flights on warm, dry days and the
crankiness of the machine when the weather is damp.

Cold weather on the other hand tends to increase the density of the air.
The speed of an aeroplane is materially reduced but on the other hand
the air will be found more buoyant. Such weather is better for heavy
models, although they fly much more slowly. It will be seen that at high
altitudes, where the density is least, models should fly both faster and
higher than they will nearer the sea level.

One of the curiosities of the air is the effect of eddies created by the
passage of aeroplanes. Let an aeroplane move fast enough through the air
and it will create high density above its course, and low density below
its line of flight. This condition may also be found in the wake of
model aeroplanes. It will often be noticed when two models are flying
near together that the disturbance caused by one will seriously
interfere with the second machine. The contrast between the air above
and below the models in flight in especially noticeable when the planes
are flexed.

[Illustration: Two of the earlier Peoli models]

A great deal has been learned of the action of the air upon aeroplanes
by photographing the air currents. The smallest eddies of the air have
been made visible by taking instantaneous photographs of thin smoke as
it passes obstacles of various size and form. It has been found that a
square object causes a great deal of disturbance when in an air current.
The air is compressed in front of it and eddies for some distance in its
wake before finally coming to rest. An elliptical object causes less
disturbance, but the air continues to splash in its wake for some
distance. Even a perfectly spherical object offers a surprising amount
of resistance to the air. In the case of a long narrow ellipse the
disturbance is considerably reduced. A curved surface however, such as
is used for the planes of an aeroplane, cuts the air with practically no
resistance, and the air flows smoothly about and joins behind it with
very little wake or splashing. A form which suits the air in this way or
a "stream line" body as it is called is obviously just the right design
for the wings of an aeroplane.

Even the experts in aeronautics differ so widely, however, that it is
impossible to lay down any definite rules. One of the greatest
authorities on the science of aviation, Mr. Horatio Philips, of England,
believes that aeroplanes gain more support from the entering edges of
their planes than from the rest of their surface. He argues that it is
this edge, meeting the air currents, which serves to hold the aeroplane
suspended.

This theory is founded on the experiments made with a machine of
original design flown by Mr. Philips as far back as 1890. It consisted
of a series of planes mounted one above the other at regular intervals,
much the same as the strips of a Venetian blind. The lifting power of
this model in proportion to its surface and the power exerted was
enormous. This theory is borne out in part by the success of the model
aeroplanes with very narrow wings which have been flown with great
success during the year. The beautiful model built by Stewart Easter,
for instance, which is illustrated on another page, depends for its
support on planes which are no wider than ordinary window blinds.

There is an immense difference of opinion again as regards skin
friction. Some writers believe the air has a tendency to stick to
certain materials more than to others, and that this difference is so
great as to materially retard some machines in their passage through the
air. A complicate series of tables has been worked out in great detail
to show the exact amount of this friction on various bodies. Some
aviators go to great pains to make every part of their aeroplanes as
slippery as possible. This is done by polishing the surfaces exposed to
the air and in some cases enclosing the foreward part of the aeroplane,
like a ship’s prow, to diminish friction.

On the other hand we find some of the greatest authorities on aviation
disregarding this question almost entirely. In the Wright machines, for
instance, the surface of the wings is usually left comparatively rough,
and the sticks and wires are placed without any attention to diminishing
friction. This is true as well of the Delegrange, Voison and Farman
machines. Still other aviators design every detail of their machines to
cut down this so-called skin friction. The uprights, for instance, are
made elliptical in shape, with the sharp edges turned forward so that
they will cut their way the more smoothly through the air.

Several interesting attempts have been made to design a prow for an
aeroplane which will cut the air with the least possible amount of
friction. It is noticeable in these designs that the prows are very
blunt, like the prow of a canal boat, and not as might be expected,
sharp and narrow like that of a racing craft. The blunt-nosed prow is
considered best for the air ship, because the air being one eight
hundredth as dense as water offers very little resistance to its
entrance. It is so much easier, in other words, to push an air ship
through the air than a boat through water that there is no object in
sharpening its nose.

The air, however, in flowing along the sides of a rapidly moving body
sticks to it, and retards its progress relatively more than water
retards a boat. It is important, therefore, that the body of the
aeroplane be made very short, so that the sides will offer as little
friction as possible. This reverses the proportions of a water-borne
ship. We are so accustomed to see fast boats with long, narrow hulls,
that it comes as a surprise to find that a fast air ship must have a
very broad beam and as short a hull as possible.

It is probable that, as air ships develop, this general characteristic
will become more marked. As aeroplanes become larger and faster they
will therefore depart further and further from the conventional ideas
concerning water-borne craft. It is impossible to prophesy at present
what form the great passenger-carrying air ships of the future will
take, but it is certain that their hulls or the closed-in portion
carrying the machinery and passengers will be very short, snubbed-nose
affairs. The world will be obliged to change its mind as to what
constitutes a speedy-looking craft.

Man has learned to fly. More than 1,000 aeroplanes have been built which
have successfully risen above the earth. It is estimated that these
aeroplanes have flown in all more than 250,000 miles, or a distance
equal to ten times the circumference of the earth. But no machine has
yet been made which will fly alone, without the skilful manipulation of
planes and rudders. The model aeroplane which soars gracefully aloft,
suiting itself to the varying air conditions, perhaps comes nearest to
the automatic flying machine.

A great advance will be made in aviation with the appearance of some
practical contrivance for securing automatic stability. The aeroplane as
it stands to-day shows a wonderful advance in the improvement of its
general lines, and the mechanical perfection of its parts, but the
question of stability remains practically the same as it was when the
Wright Brothers made their first flights. The machine has been brought
under a remarkable control, but only as it is directed by the practised
hand of the sky pilot. Let him take his hand even for a moment from the
levers, which control the planes and rudders, and there is danger of a
bad spill, perhaps a fatal accident. Practically nothing has been
accomplished in building machines which will fly unaided.

It has been pointed out, elsewhere in this volume, that the experiments
with the model aeroplanes are certain to have an important influence
upon the development of aeronautics as a whole, because they address
themselves particularly to this problem of stability.

It is believed by many aviators that the problem of automatic stability
will be solved by some form of the gyroscope. A great many experiments
are being made with various forms of the gyroscope, although no machine
has as yet been actually fitted and flown with such a device. The
general principle of the gyroscope is very simple. It consists of a
wheel which is made to revolve at very high speed. When such a wheel
turns fast enough it will remain in a fixed position. Every one is
familiar for instance with the gyroscope top. You wind it up and place
it at any angle, and it will support itself and retain the position
until it has run down.

The gyroscope has been applied for instance to railroad trains and has
worked, experimentally at least, with remarkable success. By installing
a gyroscope on a car running on a single track the car may be kept
upright by the stabilizing force exerted by the revolving wheel. The
same principle has been applied to steamships to prevent their rolling
in heavy seas. The tipping of a car running on a single track, or of a
ship at sea, is of course very much like the rolling of an aeroplane in
flight; and it would seem that such a stabilizing device might solve the
problem. The gyroscope has a serious disadvantage, however. Since it
revolves at enormous speed any breakage would tend to throw the detached
part to one side with dangerous force. In the case of the gyroscope used
to steady ships at sea this force would be sufficient to send a piece of
metal through the hull. On so delicate a craft as an aeroplane such an
accident might readily prove disastrous.

It has been found again in experiments with gyroscopes on steamers that
the frames have been seriously strained, even when the gyroscope worked
smoothly. When a ship rolls and pitches to the motion of the waves, it
is of course under a great strain but this balances itself. When it is
held in a rigid horizontal position the pitching and rolling exert an
exaggerated strain on the hull. In one instance a vessel actually broke
its back under such a strain and was lost. An air ship, being at best a
very frail structure, could scarcely be expected to stand the strain
which has wrecked a steel ship. At the recent Paris Aeronautical show
several extremely ingenious combinations of the pendulum and gyroscope
principles were illustrated. It is of course possible that some modified
form of the gyroscope may solve the problem.

A remarkable series of tests has been made this year in France with an
automatic stability device based upon an entirely new principle. The
rudders are operated automatically, in this case by a vertical fin
opposed to the wind. As the pressure of the air varies, the rudder is
forced up or down, thus bringing the aeroplane to an even keel without
the assistance of the aviator. It is reported that model aeroplanes
equipped with this device have been flown in three hundred experiments
without a single accident.

The day is approaching when the air conditions will be observed and
announced for the benefit of aviators exactly as the weather is foretold
to-day. An aviator who is about to start on a cross-country flight will
thus be able to study the conditions of the air lanes and lay out his
route just as an automobilist looks up good-roads maps. In crossing a
particular piece of country he will therefore know whether to take a low
or a high air lane, that is, one of few hundred feet above the earth or
the one several thousand feet aloft. The pressure of the air on the
regular air lines will be announced as well. In this way aviation will
be made much safer than it is to-day, when the aviator must venture
without any knowledge of conditions aloft except those he may gain from
the ground surface weather maps. During the year 1910, fully a score of
lives might have been saved had aviators had such information.

The first of these observation stations is actually in operation in
Germany to-day. Each of these stations is supplied with a number of
rubber balloons equipped with automatic apparatus for recording
atmospheric conditions in the upper air lanes. The stations also contain
the proper apparatus for measuring the ascensional force of the
balloons, with the gas generators used for inflating the balloons. When
the balloons are sent up for great heights their altitude will be
measured by means of the theodolite.

The soundings of the air are taken twice daily at eight o’clock in the
morning and two in the afternoon whenever the weather permits. In the
summer the morning observations are made much earlier. The movements of
the balloons are then carefully observed at various altitudes until they
are lost. These observations are then telegraphed to the central station
at Lindenberg and sent out much the same as the regular weather
forecast.

CHAPTER XVI RULES FOR CONDUCTING MODEL AEROPLANE CONTESTS

PREPARED BY THE WEST SIDE YOUNG MEN’S CHRISTIAN ASSOCIATION, NEW YORK.

GENERAL RULES AND CONDITIONS FOR 1911.

1. These General Rules and Conditions shall apply to the events
conducted by the West Side Y. M. C. A.
2. Each and every contestant for a prize shall accept without
reservation the conditions laid down by the West Side Y. M. C. A.
and shall abide by the decision of the referee. Each contestant
must register his name, age and address before the event.

(a) All contestants in Class "A" must be 18 years of age or over.
(b) All contestant in Class "B" must be under 18 years.

3. Every machine competing must be made by the operator (no toys
admitted), and it must be built along practical lines, that is, a
model from which a practical man-carrying machine can be built.
4. The Committee shall have the right to reject any entry, the
rejection of which they deem advisable.
5. The flights shall be accounted level flights and no allowance will
be made for variation of height.
6. A trial shall be considered to have ended whenever the machine
touches the ground.
7. Competitors shall decide by drawing lots the order in which they
shall take their turns.
8. Any entrant not ready to commence his trial when called upon will
forfeit his turn to him who is next ready, and will fall back to
the end of the list.
9. The commencement of the distance flown shall in the case of
machines on wheels be counted not from the starting line, but from
the point which is determined by the judges as that at which such
machines actually leave the ground. In the case of machines using
the catapult, there shall be deducted from the total distance
flown the equivalent of the initial impulse of the catapult.
10. There shall be no restrictions as to the design, size, weight,
form or amount of power, but the power must be self-contained in
the model.
11. All models must start from the ground.
12. Each contestant shall have three trials.
13. The longest flight in the three trials will be counted for the
prize.
14. All awards shall be made to the owner of the model and not to the
operator, unless by special agreement between owner and operator.
15. The contests shall cover a period of two hours, unless otherwise
designated by the judges.

RULES FOR CONDUCTING MODEL AEROPLANE CONTESTS

PREPARED BY THE NEW YORK MODEL AERO CLUB.

The officials at the distance contest will be: One entry clerk, one
starter, one judge.

The officials at the spectacular flight contest will be: One announcer
and starter, a jury composed of three persons selected from spectators,
not members of the Club.

The officials at the demonstration of a lifting-power contest will be:
One entry clerk, one measurer and calculator, and one judge.

There will be a director in the center of the armory room to order the
flights.

The director will have a whistle.

Each starter will have a flag.

Starters will ask for the floor by showing flag.

The director will order the flights as follows:

Three whistles for a spectacular flight.

Two whistles for a distance flight.

One whistle for a lifting-power flight.

Contestants must keep off the floor unless following their own machine
in flight.

After they have picked up their machine, they must leave the floor in
the most expeditious manner.

Contestants will apply to entry clerks for directions.

RULES FOR MODEL AEROPLANE CONTESTS

PREPARED BY THE NEW YORK MODEL AERO CLUB.

The contests shall be open to all.

The entries are free, and shall be received at the New York Model Aero
Club, 141 Lexington Avenue, either by letter until March 18, 1911, or
verbally on March 4 & 11, 1911, from 8:15 P. M. to 10 p. M., and at the
13th Reg. Armory on March 18 from 8 to 9 p. M.

Models must be built by the contestants.

There shall be two contests: A distance contest and a spectacular flight
contest.

DISTANCE CONTEST Two prizes:

I. The first prize shall be awarded to the contestant making the
longest flight, and the second prize to the contestant making
the next longest.
II. Each contestant shall have only his longest flight recorded.
III. Models must start from the ground under their own power.
IV. Contestants are not allowed to push their models. Two special
officers of the Club shall be appointed to watch this
particular point.
V. All models must start from the same starting line, which will
be marked on the floor; they must be off the ground at a
distance of twenty feet from the starting line. In case a model
is not off the ground at said distance, it shall be
disqualified for that flight.
VI. Flights shall be measured from the starting line to the point
of landing.
VII. A one-quarter-inch rope shall be laid on the ground without
being fastened at either end, at a distance of 20 feet from the
starting line.
VIII. Models must measure at least two feet in length and two feet in
spread.

SPECTACULAR FLIGHT CONTEST One prize:

I. The cup shall be awarded to the contestant making the most
spectacular flight as previously announced.
II. A jury of five persons, selected from the spectators, shall
decide upon the most spectacular flight.
III. Power shall be optional.
IV. Models must measure at least two feet in length and two feet in
spread.
V. Models must be fitted with a landing device by which, if proper
speed was obtained, the machine would leave the ground.
VI. Each contestant, before launching his model, must announce the
object of his flight. The announcement will be made to the
public.
VII. Contestants are at liberty to fly their models from the ground
or from the hand, and start wherever they wish.

Non observance of any of the above rules shall disqualify any flight.

CONSTITUTION AND BY-LAWS OF A MODEL AEROPLANE CLUB

COURTESY OF NEW YORK MODEL AERO CLUB

CONSTITUTION

ART. I

This association shall be called the . . . . . . . . . . . . . . . . . .
. . . . . . . . . . .

The object of this Club shall be to popularize and study the Science and
Art of Aviation through models.

ART. II

_Membership_. There shall be two classes of members: 1st.—Senior
Members, who have been elected as such by the Admission and Membership
Committee; who are qualified to represent the Club at all competitions,
and shall have a vote at all meetings in the conduct of the affairs of
the Club; 2nd.—Junior Members, comprising all such that have not
qualified as seniors, and who shall have no vote.

Any person may become a member of this Club who is passed upon by a
majority of the Admission and Membership Committee, to whom all
applications, either made directly or through a member of the Club, must
be submitted.

All applicants accepted shall at once become Junior Members, and shall
remain so until elected Senior Members by the Admission and Membership
Committee.

ART. III

_Officers_. The Officers of this Club shall be a President, two
Vice-Presidents, a Secretary-Treasurer, and a Board of Governors, to
consist of said officers and the Chairman of the Patent Bureau and
Contest Committee.

The President and Second Vice-President shall constitute an Executive
Committee of the Board of Governors, with full power to act for them in
the affairs of the Club.

ART. IV

_Dues and Assessments_. The dues shall be 25c (twenty-five cents) per
month for Junior and Senior Members alike, to be collected at the first
business meeting of each month.

ART. V

_Standing Committees_. There shall be the following Standing Committees,
to consist of four members each:

_1st.—Patent Bureau_. The Patent Bureau shall investigate and pass upon
claims for any feature of a member’s own contrivance, and register and
insure to members the exclusive use thereof in the Club.

_2nd.—Contest Committee_. The Contest Committee shall arrange details
of, attend and record all competitions held by the Club. They shall also
attend and report on any other competition at the request of the Board
of Governors.

_3rd.— Admission and Membership Committee_. The Admission and Membership
Committee shall examine all applicants for membership, with full power
to accept or reject them, and shall further examine the Junior Members
who wish to qualify as Senior Members.

The Committees shall convene regularly at every business meeting and
besides, as often as their duties may require.

ART. VI

_Special Committees_. Special Committees may be appointed at any time,
by motion or resolution, to take into consideration and report upon
special matters. Unless otherwise provided for, they shall be appointed
by the presiding officer.

Art. VII

_Meetings_. Regular meetings shall be held every Saturday. The first
Saturday in October and the first Saturday in April shall be semi-annual
election and business meetings. Following these, every first and third
Saturday of each month shall be a business meeting.

All other meeting nights shall be called Social meetings. At the social
meetings no regular order of business shall be observed.

ART. VIII

_Elections_. The officers and members of the standing committees shall
be elected by written ballot.

The President and First Vice-President shall be elected at the first
business meeting in October, to serve for one year; the Second
Vice-President and the Secretary-Treasurer shall be elected at the first
business meeting in April, to serve for one year.

Two members of each of the standing committees shall be elected at the
first business meeting in October, to serve for one year; the two other
members of each of the standing committees shall be elected at the first
business meeting in April, to serve for one year.

ART. IX

_Amendment_. This Constitution may be amended by a two-thirds vote at
any regular business meeting; but, no amendment shall be entertained
unless it shall have been proposed in writing at the previous business
meeting.

By-laws may be altered, suspended, annulled or amended by the majority
action of the members present at any meeting.

BY-LAWS

ART. I

_Duties of President and Vice-Presidents_. The President shall preside
at all meetings of the Club and of the Board of Governors, and perform
such other duties as usually pertain to that office.

The Vice-President, in the absence of the President, shall in his stead
perform such duties.

ART. II

_Duties of Secretary-Treasurer_. The Secretary-Treasurer shall keep a
record of all meetings of the Club and of the Board of Governors; issue
notices to members of all special meetings, and perform such other
duties as may be assigned him by the Constitution, by the Club, or by
the Board of Governors.

The Secretary-Treasurer shall keep the accounts of the Club; receive all
moneys, fees, dues, etc.; pay all bills approved by the Board of
Governors, and preserve all proper vouchers for such disbursements. He
shall, at each regular meeting of the Board of Governors, make a
statement of the financial condition of the Club; and shall, at the
semi-annual meetings, submit a report, approved by the Board of
Governors, of the financial transactions of the preceding fiscal half
year.

ART. III

_Enforcement of Rules by the Board of Governors_. The Board of Governors
shall have full power to expel or suspend any member whose conduct shall
be pronounced, by a two-third vote of the members present at a meeting,
to have endangered the welfare, interests or character of the Club.

ART. IV

_Liabilities_. The Board of Governors shall have no power to make the
Club liable for any debts exceeding in total the amount of five dollars,
unless authorized to do so by a recorded vote of a meeting of the Club.

ART. V

_Meetings of the Board of Governors_. The Board of Governors shall hold
regular meetings on the last Saturday of each month.

ART. VI

_Non-Attendance at Governors’ Meetings_. A member of the Board of
Governors who, without satisfactory explanation, shall fail to attend
two consecutive meetings of that body, shall be deemed to have resigned.

ART. VII

_Colors_. The Club colors are Sky Blue and Red.

ART. VIII

_Arrears_. A member one month in arrears shall not have a vote at the
meetings, nor hold office in the Club.

ART. IX

_Order of Business._

1. Reading of Business.
2. Reports of Officers and Committees.
3. Unfinished Business.
4. Election of Officers.
5. New Business.

DICTIONARY OF AERONAUTICAL TERMS

Aerodrome. A tract of land selected for flying purposes.

Aerodynamics. The science of aviation, literally the study of the
influence of air in motion.

Aerofoil. A flat or flexed plane which lends support to an aeroplane.

Aeronaut. One engaged in navigating the air.

Aeronautics. The science of navigating the air.

Aeroplane. A heavier than air machine supported by one or more fixed
planes.

Aerostatics. The science of aerostation, or of buoyancy caused by
displacement, ballooning.

Aerostation. The science of lighter than air or gas-born machines.

Aileron. The outer edge or tip of a plane, usually adjustable, used to
balance or stabilize.

Airship. Commonly used to denote both heavier and lighter than air
machines; correctly a dirigible balloon.

Angle Of Incidence. The angle of the plane with the line of travel.

Area. In the case of planes, the extent of surface measured on both the
upper and lower sides. An area of one square foot comprises the actual
surface of two square feet.

Aspect Ratio. The relation of a surface crossing the direction of flight
with that paralleling the line of

flight. Automatic Stability. Stability secured by fins, the angle of the
planes and similar devices.

Aviator. One engaged in aviation.

Aviation. The science of heavier than air machines.

Balancer. A plane or other part intended for lateral equilibrium.

Biplane. An aeroplane with two supporting surfaces one above the other.

Body. The main framework supporting the plane and the machinery.

Camber. The curve measured from the cord to the highest point of the
plane.

Carriage. The part on which the main body is supported on land or water.

Center Of Gravity. The point at which the aeroplane balances.

Center Of Pressure. The imaginary line beneath the plane at which the
pressure balances.

Deck. The main surface of a biplane or multiplane.

Directional Control. The ability to determine the direction of the
flight of an aeroplane.

Dirigible. A balloon driven by power.

Down Wind. With the wind.

Drift. The resistance of the plane to the forward movement.

Elevator. The plane or wing intended to control the vertical flight of
the machine.

Engineer. One who controls the power, driving the machinery.

Entering Edge. Front edge of the forward plane of an aeroplane.

Equilibrator. A plane or other contrivance which makes for stability.

Flexed. A plane is said to be flexed when it curves upward forming an
arc of a circle.

Fin. A fixed vertical plane.

Flying Machine. Literally a form of lighter than air craft; a gas-born
airship.

Following Edge. The rear edge of the plane or wing of an aeroplane.

Fusilage. The body or framework of an aeroplane.

Glider. An aeroplane without motor power.

Guy. A brace, usually a wire or cord used for tuning up the aeroplane.

Gross Weight. The weight of the aircraft comprising fuel, lubricating
oils, and the pilot.

Gyroscope. A rotating mechanism for maintaining equilibrium.

Hanger. A shed for housing an aeroplane.

Harbor. A shelter for aircrafts.

Heavier Than Air. A machine weighing more than the air it displaces.

Helicopter. A flying machine driven upward by rotary screws on vertical
shafts.

Helmsman. One in charge of the steering device.

Lateral Stability. Stability which prevents side motion.

Loading. The gross weight divided by the supporting area measured in
square feet.

Longitudinal Stability. Stability which prevents fore and after motion
or pitching.

Mast. A perpendicular stick holding the stays or struts which keep the
planes rigid.

Model Aeroplane. A toy aeroplane, reproducing a man-carrying machine.

Monoplane. An aeroplane or heavier than air machine supported by a
single main plane which may be formed of two wings extending from a
central body.

Motor. A contrivance for generating driving power.

Multiplane. An aeroplane with more than three main planes one above
another.

Nacelle. The car of a dirigible balloon, literally a cradle.

Net Weight. Complete weight of the machine without pilot, fuel or oil.

Ornithopter. A machine supported and propelled by planes moving in
imitation of birds; a flapping wing machine.

Orthogonal. A flight maintained by flapping wings.

Plane. A surface or wing, either plain or flexed, employed to support or
control an aeroplane.

Pilot. One directing an aeroplane in flight.

Pitch. Theoretical distance covered by a propeller in making one
revolution.

Pylon. Correctly, a structure housing a falling weight used for starting
an aeroplane, commonly a turning point in aeroplane flights.

Propeller. The screw used for driving an aeroplane, plane.

Rudder. A plane or group of planes used to steer an aeroplane.

Runner. Strip beneath an aeroplane used for a skid.

Scale Model. A miniature aeroplane exactly reproducing the proportions
of an original.

Spar. A mast, strut, or brace.

Stability. The power to maintain an even keel in flight.

Starting Platform. A runway to enable an aeroplane to leave the ground.

Skin Friction. Resistance offered by planes or wings.

Slip. The difference between the distance actually travelled by a
propeller and that measured by the pitch.

Soaring Flight. A gliding movement without apparent effort.

Surface. The extent of planes measured on one side only.

Sustaining Surface. Extent of wings or planes which lend support to an
aeroplane.

Tail. The plane or planes, both horizontal and vertical, carried behind
the main planes.

Tandem. An arrangement of two planes one behind the other.

Thrust. The power exerted by the propeller of an aeroplane.

Tension. The power exerted by twisted strands of rubber in unwinding.

Tractor. A propeller placed before the main plane.

Triplane. An aeroplane with three main planes one above another.

Up Wind. Against the wind.

Wake. The churned or disturbed air in the track of a moving aeroplane.

Wash. The movement of the air radiating from the sides of an aeroplane
in flight.

Wings. Planes or supporting surfaces, commonly a pair of planes
extending out from the central body.

*** End of this LibraryBlog Digital Book "The Second Boy's Book of Model Aeroplanes" ***

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