Title: How To Build A 20-Foot Bi-Plane Glider
Author: Morgan, Alfred Powell
Language: English
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BI-PLANE GLIDER ***



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                         HOW TO BUILD A 20-FOOT

                           *BI-PLANE GLIDER*


        _A Practical Handbook on the Construction of a Bi-plane_

           _Gliding Machine, Enabling an Intelligent Reader_

           _to Make His First Step in the Field of Aviation;_

                         _With a Comprehensive_

              _Understanding of the Principles Involved._


                                   BY

                          ALFRED POWELL MORGAN


          _Editor Mechanical and Electrical Department of the_

                          _“Boy’s Magazine.”_


                          NEW EDITION, REVISED



                                NEW YORK

                  SPON & CHAMBERLAIN, 123 LIBERTY ST.

                                 LONDON

             *E. & F. N. SPON, LIMITED, 57 HAYMARKET, S.W.*

                                  1912



                          Copyright, 1909, by

                          Spon & Chamberlain.



HOW TO BUILD A 20-FOOT BI-PLANE GLIDER



PREFACE


Gliding flight is a comparatively new field for the amateur to delve in,
but the time has arrived when it is being extensively taken up both as a
sport and a means of experiment.

Many very costly aeroplanes have failed to fly because of man’s total
inexperience in the art of flying. All of the great aviators now before
the world, whose machines are the result of their own genius _learned to
fly_ before succeeding in a motor driven machine.

The Wright brothers spent no less than three years on the sand dunes
near the coast of North Carolina making gliding flights. They approached
the difficulties in a methodical manner, working out each problem and
determining which was the best means of accomplishing a certain result.

To control the tendency to pitching, they devised an elevation rudder
and attached it to the front of their machine. The next step was to
determine whether equilibrium should be maintained by shifting the
centre of gravity or if there was not a better method and they
introduced what is probably the most valuable feature of the modern
aeroplane, namely the warping or twisting of the ends of the planes to
secure lateral stability when a gust of wind strikes one end of the
machine.

In this manner the Wright’s continued their experiments until every move
had become a matter of habit and to balance and guide an aeroplane was
almost an instinct.

A gasoline engine was then fastened in the machine and connected to
drive two screw propellers at the rear. Dec. 17, 1903 the machine flew
for a few seconds.

The leaps and bounds with which aviation has since progressed both in
the hands of the Wrights and others is a matter too well known to be
repeated.

There is therefore no excuse necessary to be made for this little book,
coming as it does at this time and it is sincerely hoped that it may
interest and lead many to experiment first and build their aeroplane
afterward so that when their machine is complete it may be practical and
not intended to operate in some "lift-yourself-by-your-boot-straps"
manner.



    HOW TO BUILD A 20-FOOT BI-PLANE GLIDER ............................
      PREFACE .........................................................
      CHAPTER I. The Framework. .......................................
      CHAPTER II. Covering the Planes. ................................
      CHAPTER III. Trussing. ..........................................
      CHAPTER IV. Gliding. ............................................
      CHAPTER V. Remarks. .............................................
      BOOKS FOR AVIATORS ..............................................
      BOOKS ON AERONAUTICS. ...........................................
      MODEL AEROPLANES. ...............................................
      GOOD BOOKS FOR WIRELESS OPERATORS. ..............................



    Fig. 1 Horizontal Beam ............................................
    Fig. 2.—Strut. ....................................................
    Fig. 3.—Position of Struts. .......................................
    Fig. 4.—Strut clamp. ..............................................
    Fig. 5.—Stanchion. ................................................
    Fig. 6.—Stanchion socket. .........................................
    Fig. 7.—Eyebolt. ..................................................
    Fig. 8.—Assembly of stanchion, socket beam, strut and clamp. ......
    Fig. 9.—Rib. ......................................................
    Fig. 10.—Rib clamp. ...............................................
    Fig. 11.—Plan View of Planes showing Ribs. ........................
    Fig. 12.—Arm piece. ...............................................
    Fig. 13.—Parts of rudder framework. ...............................
    Fig. 14.—Corners of horizontal rudder plane. ......................
    Fig. 15.—Complete framework of rudder. ............................
    Fig. 16.—Cross bar. ...............................................
    Fig. 17.—Rudder Sockets, or Clamps. ...............................
    Fig. 18.—Arrangement of Armpieces and Rudder Cross Bar. ...........
    Fig. 19.—Complete Framework Ribs on Lower Plane Not Shown .........
    Fig. 20.—Method of hemming up edge of cloth. ......................
    Fig. 21.—Section of cloth hemmed, and reinforcing strips sewn on. .
    Fig. 22.—Trussing Of Cells. .......................................
    Fig. 23.—Plan and Elevation Views of Piano Wire Bracing. ..........
    Fig. 24.—Method of anchoring wires ................................
    Fig. 25.—Bicycle spoke turnbuckle. ................................
    Fig. 26.—Top view, showing how streams of air divide. .............
    Fig. 27.—Showing how air currents pass over objects. ..............
    Fig. 28—Action of aeroplane. ......................................
    Fig. 29—Ready to Start ............................................
    Fig. 30—Lines of Flight ...........................................



CHAPTER I. The Framework.


*A gliding machine*, more often popularly termed a glider, is simply a
motorless aeroplane, operating by force of gravity to carry its
passenger sailing through the air from the top to the foot of a slope.

*The glider* described herein is the type developed by Octave Chanute
and may be considered as the parent of the biplane machines with which
the world has lately become so familiar. The machine is known as a
biplane since its supporting surface is in the form of two superimposed
trussed planes vertically above each other and having a tail in the rear
for the control of direction.

There is always a tendency among experimenters to depart from the design
and dimensions of any machine or apparatus offered for construction.
This, since it develops originality is a good indication, but most of
those who will undertake to build a glider are attempting something
altogether new and so any radical change from the instructions in this
little booklet are unadvisable.

It is better at first to benefit by the experience of others. The glider
here described is considered as the "standard" of the biplane type. It
has an active supporting surface of 152 square feet which is sufficient
to carry the weight of an ordinary man. A machine having a larger
surface will support the same weight when moving through the air at a
slower speed, but larger surface means an increase in some of the
general dimensions. An increase in surface by lengthening the planes
will make the machine much harder to keep on an even keel, while
increasing their depth in the direction of flight will require greater
agility on the part of the operator to keep the centre of gravity in the
proper position. A larger machine also means more weight and a heavy
machine is hard to make a landing with.

On the other hand a light glider is dangerous and will not stand any
rough usage.

*The cost of the glider*, provided the construction is accomplished by
the intending owner is so low as to place it within the reach of any
person of ordinary means. The expenditure for raw materials varies
greatly. It is usually a little less than $20.00 and should not exceed
$35.00. A finished glider is worth from $50.00 to $100.00 depending
whether or not more than one is made at a time.

*Housing.* One of the first considerations is usually the housing and
storing of the glider, but the machine under consideration is so
designed that it may be quickly taken apart or "knocked down" and be put
away in the cellar, under the porch or in some other out of the way
place.

*The framework* is composed entirely of selected spruce, straight
grained and free from knots. Spruce is very dense and tough but yet one
of the lightest of woods.

*The dimensions* given are for the finished pieces after they have been
planed up. The usual method of finishing wood for aeronautical work, so
that it has a hard glassy surface and offers little resistance to the
air is first to give it a thorough brushing over with hot glue and
water. It is rubbed down after drying, using fine sand paper. The wood
is then given a coat of thin shellac.

This is rather a tedious operation and instead some may prefer to first
smooth up the wood by sand papering and giving it a coat of spar
varnish.

The corners of all the woodwork are rounded off so as to reduce the
resistance offered to the air.

*Horizontal beams*. The principal members of the planes when smoothed up
should measure 20 feet long, 1 1/2 inches wide and 3/4 inches thick.
Four of these beams are required. In some lumber yards, twenty foot
spruce free from knots is very hard to secure and so instead, two 10
foot pieces may be spliced together at the centre as shown in Fig. 1.

The splicing strip is 5 feet long and has the same cross section as the
beams, save for a distance of one foot from each end where it begins to
taper down to 1/4 inch thick. Six holes are bored through the splicing
strip and the beams so that they may be fastened together by means of
six 3/16 inch round headed stove bolts. The holes are located so that
the space between the two centre bolts is six inches while the others
are located one foot apart.

A large washer having a small hole in the centre is placed under the
head of each bolt as well as the nut.

[Illustration: Fig. 1 Horizontal Beam]

*Struts.* Each pair of horizontal beams are held parallel to each other
and three feet apart by six horizontal struts. The form of these struts
is illustrated in Fig. 2.

They are three feet long and 1/2 x 1 1/4 inches in cross section. A
notch 1 1/2 x 3/4 inches is cut in each end so as, to form a projection
1 1/2 x 1/2 x 1/2 inches.

The location of the struts in the plane is illustrated in Fig. 3. The
two in the centre are two feet apart and the others respectively 4 feet
6 inches and 9 feet on either side. The struts on the upper plane are
placed so that the projections come above the horizontal members. Those
on the lower plane are placed just the opposite, that is so that they
come on the under side.

[Illustration: Fig. 2.—Strut.]

They are fastened with one or two small wire nails and then secured by
means of a clamp. Two dozen clamps are required. They are bent out of a
strip of sheet brass one sixteenth of an inch thick, 3 7/8 inches long
and 1 inch wide. The ends are rounded and a 1/4 inch hole located and
bored in each as in Fig. 4.

[Illustration: Fig. 3.—Position of Struts.]

The clamp also serves to protect the under side of the beam from the
action of the nuts on the ends of the eyebolts. The method of fastening
the clamp is detailed a little later.

[Illustration: Fig. 4.—Strut clamp.]

*Stanchions*. The planes are separated by twelve stanchions, four feet
long and 7/8 of an inch in diameter.

[Illustration: Fig. 5.—Stanchion.]

They are rounded and smoothed up so that the ends will fit snugly into
the socket illustrated in Fig. 6. These sockets may be purchased¹
already bored and finished or can be procured at a foundry. They are
preferably made of aluminum which metal is at once light and strong but
brass or even iron may be used if it is necessary to avoid expense.

[Illustration: Fig. 6.—Stanchion socket.]

There are other methods of joining the stanchions to the beams but the
use of the socket is recommended because it is the strongest method and
also permits the glider to be readily taken apart.

The base of the socket is 3 1/4 inches long, 1 1/4 inches wide and 1/4
of an inch thick. The cup has an internal diameter of seven eighths of
an inch and an outside diameter of one inch and one quarter. It is one
inch high above the base. Two 1/4 inch holes are bored 1 7/8 inches
apart in the base. Two smaller holes 1/8 inch in diameter are bored 7/16
inch nearer the ends of the base than the larger holes.

*The wooden pattern* is made from the dimensions indicated in Fig. 6. It
is thoroughly smoothed up by rubbing with sand paper and then given a
coat of shellac. All parts should have a very slight taper towards the
top so that the pattern may be withdrawn easily from the sand mould.

[Illustration: Fig. 7.—Eyebolt.]

If the interior of the mould is coated with lamp-black, the castings
will require no other finishing than boring the holes.

Two dozen of these sockets are required. Six are fastened to each of the
four horizontal members by means of round headed wood screws which pass
through the smaller holes in the base. The sockets are located exactly
opposite the ends of each strut so that when the stanchions are in
place, they will be separated by the same distances but all lie in a
plane at right angles to that in which the struts are.

A 1/4 inch hole is bored through the horizontal beam directly under each
one of the 1/4 inch holes in the base of the socket. These holes permit
an eyebolt to pass through. The eye bolt is illustrated in Fig. 7. The
stock is 1/4 inch in diameter and should be at least two inches long
under the eye.

[Illustration: Fig. 8.—Assembly of stanchion, socket beam, strut and
clamp.]

The diameter of the eye is one half an inch. These eye bolts are
obtainable already threaded and ready for use with a nut and washers,
but can be procured somewhat cheaper in blank form and threaded by the
purchaser. Four dozen are necessary, two for each socket. The eye bolts
pass through the socket and beam, coming out on the under side directly
opposite the holes in the strut clamp. A nut placed on the under side as
in Fig. 8 will then hold the clamp tightly against the under side of the
beam and secure the position of the strut.

*Ribs.* Forty one ribs support the cloth forming the surfaces. They are
each one half an inch square in cross section and four feet long.

[Illustration: Fig. 9.—Rib.]

They are fastened to the horizontal members one foot apart, flush with
the front and projecting one foot in the rear. One or two small wire
nails are used to fasten the front ends and then a clamp placed over
them and screwed down with two No. 5 round headed wood screws, one half
an inch long. A small brad awl should be used to make a hole before
starting the screw and so avoid any possibility of starting a split in
the wood.

The clamps are bent out of sheet copper strips, 2 1/4 inches long and
5/8 of an inch wide. The ends are rounded and a hole bored through which
the screws may pass.

The surfaces of the planes are curved to give them an increased carrying
capacity and add to the gliding power.

[Illustration: Fig. 10.—Rib clamp.]

The best method is to steam the ribs and then bend them so that when
they dry they will retain their curve and not tend to push the
horizontal beams apart. Only a very slight curve should be given and the
amount of curvature should be the same for all the ribs.

Some designers construct gliders having flat planes, intending that the
pressure of the air underneath the fabric shall produce a natural curve
but such a method is exceedingly poor practice and results in a very
inefficient machine.

The ribs must be perfectly rigid and the frame of the whole machine
strongly trussed so that it cannot possibly be distorted by the air
pressure. The following extract from the report of the Smithsonian
Institute well illustrates this point.

"This new launching piece did its work effectively and subsequent
disaster was, at any rate, not due to it. But now a new series of
failures took place, which could not be attributed to any defect of the
launching apparatus, but to a cause which was at first obscure; for
sometimes the aerodrome, when successfully launched would dash down
forward and into the water, and sometimes (under apparently identical
conditions) would sweep almost vertically upward into the air, and fall
back although the circumstances of flight seemed to be the same. The
cause of this class of failures was finally found in the fact that as
soon as the whole machine was up-borne by the air, the wings yielded
under the pressure which supported them, and were momentarily distorted
from the form designed and which they appeared to possess.
"Momentarily," but enough to cause the wind to catch the top, directing
the flight downward, or under them, directing the flight upward, and to
wreck the experiment. When the cause of the difficulty was found the
cure was not easy, for it was necessary to make this great _sustaining
surfaces rigid_, so that they could not bend.”

The report in question refers to the experiments conducted with
Professor Langely’s model aerodrome.

Some experimenters claim that the parabolic curve gives the greatest
lift with the least power required for propulsion but it can be safely
doubted. The Wright machine is probably the most efficient in existence.
Their curve is very nearly the arc of a circle and is not of the
parabolic form.

Four per cent is about the proper curve to give the planes of a glider.
This is about two inches for ribs four feet long. After fastening the
front end of the ribs, curve them up in the centre by pressing down on
the loose and at the rear. Then nail the rib to the rear beam with a
small wire brad and screw on the clamp. The nails prevent the ribs from
slipping longitudinally while the clamps serve to prevent them from
moving sideways or pulling off when the fabric is under the pressure of
the air.

Fig. 11 is a plan view of the top and bottom planes. Twenty one ribs,
each one foot apart are used on the upper plane. Only twenty ribs are
required on the bottom surface because an opening two feet wide must be
left in the centre for the body of the operator.

*Arm pieces.* The operator is supported in the machine by two strips of
wood passing under his armpits. These armpieces are 3 feet long, 1 inch
wide and 1 3/4 inches deep.

[Illustration: Fig. 11.—Plan View of Planes showing Ribs.]

They are fastened to the horizontal beams by means of a 3/16 inch round
headed stove bolt. The distance between should be just wide enough to be
comfortable and is variable with the breadth of the operator between his
shoulders. Thirteen inches is about the proper distance for the average
person. The upper side of the arm pieces is rounded so that they will
not be quite so uncomfortable as they would be if left square. It is not
a good plan to pad these pieces by wrapping them with cloth for it will
impede the movements of the body in balancing.

[Illustration: Fig. 12.—Arm piece.]

*Rudder.* The rudder is composed of two planes at right angles to each
other and in the rear of the main surfaces. The vertical portion keeps
the machine headed into the wind and causes it to glide in the direction
in which it is started or head on into the wind. The horizontal rudder
steadies the machine longitudinally and prevents the machine from
suddenly diving or pitching. Neither of the rudder planes are movable.

The separate parts composing the framework are illustrated in Fig. 13.

[Illustration: Fig. 13.—Parts of rudder framework.]

The cross section of all the sticks is the same, namely one inch square.
The two long beams, _A_, are 8 feet 11 inches long. The two uprights,
_B_, each 3 feet 10 inches long from the vertical members of the
directional plane. The horizontal plane is made up of six horizontal
strips, two of them, _C_, six feet long and four, _D_, two feet in
length.

*The horizontal plane* is fitted together with half and half lap joints.
It is first fastened with nails and then reinforced with brass corner
braces.

[Illustration: Fig. 14.—Corners of horizontal rudder plane.]

Corner braces are also used to strengthen the vertical plane.

[Illustration: Fig. 15.—Complete framework of rudder.]

*The rudder beams* are stepped into sockets on the body of the machine
so that the rudder is detachable.

*A short cross bar* 2 feet inches long and 1 1/4 x 3/4 inches in cross
section, is fastened between the two centre struts of both planes at a
point eight inches forward of the rear beams.

These cross bars carry one of the sockets mentioned above as also do the
rear horizontal beams. The cross bar and sockets in the upper plane
should be directly over those in the lower plane but in an inverted
position.

[Illustration: Fig. 16.—Cross bar.]

*The construction of the sockets* is illustrated in Fig. 17. The smaller
one is fastened to the cross bar and is bent out of a strip of 1/16 inch
sheet brass 4 1/2 inches long and 3/4 of an inch wide. The larger socket
is the same length and thickness but is 1 1/4 inches wide and is
fastened to the horizontal beam. Two of each size are required. The ends
are rounded and a 3/16 inch hole bored in each so that a 3/16 inch round
headed stove bolt may be used to fasten the sockets to the framework.

[Illustration: Fig. 17.—Rudder Sockets, or Clamps.]

[Illustration: Fig. 18.—Arrangement of Armpieces and Rudder Cross Bar.]

[Illustration: Fig. 19.—Complete Framework Ribs on Lower Plane Not
Shown]

A hole is bored in the centre of the top of the smaller sockets so that
a bolt may be passed through the rudder beam and cross bar to prevent
the former from pulling out.

The two sockets in each plane must be in perfect alignment and lie on a
line drawn at right angles to the horizontal members through the centre
of the planes.

In Fig. 15 it will be noticed that four bolts pass through each plane
near the corners. The bolts are 3/16 inches in diameter and serve to
fasten the piano wires which brace the vertical and horizontal plane to
each other.

The complete framework of the glider without the tie wires and the ribs
on the lower plane will appear as in Fig. 19.

    ¹ From Spon & Chamberlain



CHAPTER II. Covering the Planes.


The surfaces of a motor driven aeroplane are usually made of some
material which is practically air tight. The Herring-Curtiss Co., use
Baldwin’s rubberized silk, while most of the foreign aviators prefer a
balloon cloth known under the name of "continental."

Ordinarily the surfaces of a glider are not covered with any preparation
to make them air tight and is not necessary, but since it will
considerably increase their efficiency it is offered as a suggestion to
those who are able or care to undergo the expense.

*Aero varnishes* for this purpose are obtainable in the market and may
be applied with an ordinary brush or by immersing the fabric. One gallon
will cover approximately 100 square feet of ordinary Cambric, although
much depends upon the weave. The more open or coarser the goods, the
more varnish it will require, while fine fabrics take the least amount.

Varnish is expensive and is not considered in the estimate of cost made
at the beginning of the book.

*The surfaces* are formed of cambric or muslin stretched tightly over
the ribs. Thirty yards of material, one yard wide will be sufficient to
cover the machine, including the rudders.

Seven strips 4 feet 6 1/2 inches long are cut and sewed together along
the selvages so that a surface 4 feet 6 1/2 inches wide and a little
over 20 feet long is formed. Twenty one strips, 4 feet 6 1/2 inches long
and 1 1/2 inches wide are cut and sewed to the surface at right angles
to the long edges and one foot apart, between their centre lines. The
edges of these strips are turned under 1/4 of an inch on each side so
that they form a reinforcement 1 inch wide which will come directly
above each rib.

[Illustration: Fig. 20.—Method of hemming up edge of cloth.]

*Reinforcing.* The long edges of the surface are then doubled back and
hemmed, turning under 1/4 of an inch and forming a 3 inch hem as
illustrated in the upper part of Fig. 20. This 3 inch hem is then
doubled back one inch and sewed again so that the result is a two inch
hem, composed of two thicknesses of cloth save for one inch back from
the edge where it is made up of four thicknesses.

This reinforcing is necessary to avoid ripping and tearing the cloth out
from under the tack heads when it is under pressure during a flight.

[Illustration: Fig. 21.—Section of cloth hemmed, and reinforcing strips
sewn on.]

*The bottom planes.* The cloth on the bottom planes is made up of two
sections, divided by the space in the centre of the lower plane which
the operator occupies. These sections are made and reinforced in exactly
the same manner as that for the top plane just described but are one
foot less than half as long.

*The cloth is tacked* over the front horizontal beam and then stretched
tightly over the curved ribs and fastened with tacks at the ends. Fasten
the corners of the cloth first and smooth it out before driving the
tacks in the ribs. Ordinary brass headed upholsterer’s nails are used
but they should not be long enough to pass all the way through the ribs.

A strip of felt 3/8 of an inch wide and four feet long is laid on the
cloth directly over each rib so that it comes between the head of the
tack and the cloth. This precaution may seem unnecessary to some, but it
greatly reduces the liability of having the cloth tear when under
pressure. The tacks along the ribs are spaced about 4 inches apart A
heavy weight held against the under side of the rib by an assistant,
when the tacks are driven in will provide a firm foundation to hammer
against.

A very good method of fastening the cloth to the ribs is to sew a pocket
on the under side of the surface and into which the ribs may be slipped.

The rear ends of the ribs may be fitted with metal tips by tapering the
end down until it is round and measures 1/2 inch in diameter. A 1/2 inch
brass ferrule such as that used on file handles is then forced on.

*The rudder planes* are covered on both sides. The fabric is stretched
tightly over the frame and then tacked along the edges. The edges should
be turned under before tacking so that there is no possibility of the
cloth tearing out.

The cloth at the ends of the planes should be securely fastened to the
struts by means of tacks. This will relieve the ribs of some of the
strain and correct a tendency for them to pull in towards the centre.



CHAPTER III. Trussing.


The strength of the glider lies in its proper trussing with piano wires
which when tightened up should so brace the framework that it will
support without appreciable sag or strain, a heavy man hanging from the
arm pieces and the ends of the planes resting on a pair of carpenters’
horses.

Two methods of trussing the planes are illustrated in Fig. 22. The
machine is divided into five cells the vertical boundaries of which are
formed by the stanchions. .

*The first method* illustrated is the one used in this case for the
glider. It is somewhat simpler than the second and does not require the
use of any turnbuckles.

Each wire is fastened to one of the eyebolts on the horizontal beams and
then run diagonally across to the socket on the opposite beam in the
other plane, considering front and rear to be opposed.

Four of these diagonal wires, represented by _J_ in Fig. 23 brace each
of the four large cells. The middle cell cannot be trussed up in this
manner because the wires would interfere with the body of the operator.
So the rectangles formed by the two centre struts with the upper
horizontal beams and the two centre rear stanchions with the rear
horizontal beams of the upper and lower planes, are braced by means of
wires running across their diagonals.

[Illustration: Fig. 22.—Trussing Of Cells.]

*The rudder* is stiffened and trussed to the planes by sixteen wires.
Two of these _F_ and _H_ run from the top of the vertical rudder plane
to the lower sockets in the rear, 4 1/2 feet from the ends of the
planes. The corresponding pair _E_ and _G_ run from the bottom of the
rudder to the top sockets of the same stanchions. Four wires _A_, _B_,
_C_, _D_ steady the horizontal plane and run from its corners to the
sockets in which the rudder beams are stepped on the frame of the glider
itself. The remaining eight, indicated by _I_ in the illustration brace
the horizontal and vertical planes of the rudder to each other.

Fig. 24 illustrates the method of anchoring piano wires.

The wire is first passed through a short piece of 1/8 inch copper tubing
about 3/8 of an inch long, then through the eyebolt. The end is doubled
back passed through the tube again but now in a reverse direction. By
bending the extreme end of the wire over in the form of a hook and
shoving the tube down close to the eye bolt, the wire is secured and
cannot pull out. The other end of the wire is fastened in the same
manner but before the end is bent over into a hook, the wire must be
first pulled tight.

[Illustration: Fig. 23.—Plan and Elevation Views of Piano Wire Bracing.]

After fastening all of the wires their tension may be regulated by
turning the nuts on the lower ends of the eye bolts. It is very
necessary that the frame should be perfectly true and not warped or
twisted. Otherwise the machine will be very hard to balance and manage
when making a glide. Especially must the rudder be true with the rest of
the machine.

[Illustration: Fig. 24.—Method of anchoring wires]

Since there are no eyebolts about the rudder which could be used to
tighten or loosen the truss wires, a turnbuckle must be included in each
wire for that purpose.

*Turnbuckles.* The construction of these turnbuckles which are very
simple and inexpensive is illustrated in Fig. 25. They are made of a
bicycle spoke and nipple by cutting off one end of the spoke and using
the part which is threaded. The end of this piece is bent back and
twisted into an eye. A piece of 1/16 inch sheet brass 1/2 x 3/8 inch has
a hole bored in its centre, the diameter of which is such that it will
just admit the spoke nipple. The nipple is prevented from passing all
the way through by the shoulder on one end. A piece of sheet iron 1/2
inch wide and 3 inches long has a similar hole bored in its centre. The
ends of this strap are rounded and bored so that the piano wire may be
passed through. The turnbuckle is then assembled and connected as shown
in the illustration. The tension of the wire is regulated by turning the
spoke nipple while the spoke itself is held rigid.

[Illustration: Fig. 25.—Bicycle spoke turnbuckle.]

*The second method* of bracing illustrated in Fig. 22 requires that a
turnbuckle be included in the diagonals of every rectangle, except those
formed by the stanchions with the horizontal beams. This method is used
on almost all aeroplanes and is considered the strongest but the first
method is plenty strong enough for an ordinary glider. If after
trussing, the machine is found to be warped or twisted, it must be trued
up. By sighting along the horizontal beams and tightening or loosening
the necessary wire any curvature may be easily corrected.

*The second method* of trussing is considerably harder to true up than
the first, since when one diagonal of a rectangle is tightened, the
other must be loosened. But since it makes an exceedingly firm and rigid
structure, it may be well recommended to those who care to undergo the
added expense and labor involved by the extra turnbuckles and wires.

*To take the glider apart*, first remove the bolts holding the rudder
beams in the sockets on the machine. Then unfasten the wires which brace
the rudder to the machine by loosening the turnbuckles until the spokes
and nipples unscrew and come apart. The rudder may now be removed from
the machine.

Next take off all the nuts on the eye bolts in the lower plane and pull
the eyebolts out of the sockets. The two planes will then come apart.
Remove the stanchions by pulling them out of the sockets. The two planes
are then laid one on top of the other and will occupy very little room.



CHAPTER IV. Gliding.


The first words which may well be said upon this subject are to
emphasize caution. But by this I do not wish to imply that gliding is
exceedingly dangerous. Neither do I by caution mean timidity but rather
judgment and common sense.

Canoeing is generally considered a safe sport, but who would think of
canoeing on the ocean in a storm. It is exactly the same extreme to
glide from a very high object, or experiment in a high wind.

*The atmosphere* near the earth is a mass of whirling and swirling
currents which are constantly rising and falling and become very
pronounced in a high wind. Even in a comparative calm these eddy
currents exist but of course not to a dangerous degree. Evidence of this
may be seen by watching the little dust particles floating in the air
and made visible by a sunbeam coming through the window of a quiet room.
Although the sense of feeling cannot detect the smallest air current,
these little particles are whirling around and constantly changing their
direction.

When the wind strikes some natural object such as a tree or a stone, the
streams of air divide, part of them passing to the sides and part going
over the top. The air begins to divide some distance before it reaches
the object and the result is a rising current on one side and a falling
current on the other.

These currents are the bugbears of aviators for when one end of their
machine passes into such a current that end rises or falls depending
whether or not the current is rising or falling.

[Illustration: Fig. 26.—Top view, showing how streams of air divide.]

Other rising and falling currents are caused by the sun passing behind
clouds. Portions of the atmosphere are thus chilled and commence to fall
while others upon which the sun is reappearing are heated and rise.
Balloonists constantly encounter these changes in temperature and the
gas in the bag expands or contracts so rapidly that it often requires a
skillful pilot to prevent disaster.

These rising and falling currents caused by changes of temperature may
be clearly seen on the surface of a lake if the observer is stationed at
a height where he may look down on the water. In some places the water
is covered with smooth glassy streaks which run in various directions.
These smooth streaks are evidence of rising currents of air at those
places. The rough spots which suddenly spread out and run across the
water are caused by descending currents.

Therefore it is not good judgment to attempt gliding over ground broken
by trees or other natural objects or when the wind is blowing over 12-15
miles per hour.

[Illustration: Fig. 27.—Showing how air currents pass over objects.]

Do not under any consideration jump off from a height which rises
prominently from surrounding objects. Otto Lilienthal, the brilliant
German investigator and engineer who made over two thousand gliding
flights specifically warned experimenters against starting glides from
precipitous cliffs or buildings. There are two excellent reasons for
this. First, because when jumping from such an elevation, a gust of wind
rebounds from the sides and strikes the machine so that it requires
great skill to counteract its influence. Second, because, the operator
and machine are suddenly suspended high in the air.

Be satisfied at first by running against the wind on level ground and
making short jumps. After some practice, operations may be transferred
to a gentle slope and the length of the glides considerably increased.
If the experimenter thus proceeds slowly without impatience, there is no
danger in gliding. It is said that the Wright brothers never so much as
turned an ankle in the hundreds of flights they made, before building a
power driven machine.

[Illustration: Fig. 28—Action of aeroplane.]

*Action of an Aeroplane*. Before starting to glide it is perhaps well to
understand how the machine operates and supports its passenger. The
illustration shows the cross section of an aeroplane moving forward
through the air in the direction indicated by the arrow. The front edge
of the aeroplane is elevated so that the surfaces form an angle with the
horizontal. The front edge enters practically still air and causes it to
follow the curve of the planes and leave at the rear in a downward
direction. Since the action and reaction of two forces are always equal
and opposite, there is a force exerted against the aeroplane causing it
to rise.

A sky-rocket is caused to ascend by the reaction of gases formed by
burning powder escaping downwards through a small hole. The aeroplane,
by means of its curvature directs the air downwards and so rises itself.

The planes pass so rapidly on to new and undisturbed bodies of air, and
stay over one body for so brief an instant, that there is no time to
completely overcome the inertia of the air and force it downwards. This
may be likened to a skater moving swiftly over very thin ice which would
not bear his weight were he standing still, but since he is moving so
rapidly, that any one portion of the ice does not have time to bend to
the breaking point, is supported.

*Equilibrium.* A glider will remain in perfect equilibrium only so long
as the centre of gravity of the machine and operator fall in the same
vertical line as the pressure exerted by the air. If the former is
forward of the latter, the machine will incline forward and travel
downwards. If the centre of gravity is to the rear of the centre of
upward thrust exerted by the air, the head of the machine will rise,
while if it is to either the right or left side, the machine will lean
or turn over respectively to the right or left.

[Illustration: Fig. 29—Ready to Start]

The centre of pressure on the plane is somewhat in advance of the actual
dimensional centre of the plane. This is due to the curvature of the
plane and also to the disturbing action upon the air of the front edge.

*To make a glide*, carry the machine to the top of a slope. Have two
assistants hold the ends of the lower plane. Get in underneath and stand
up between the arm pieces. Grasp the front horizontal beam of the lower
plane and lift the machine until the arm sticks are snugly under the arm
pits as in the illustration.

If necessary have the two assistants prepared to run a short distance
with the machine, but as soon as you are in motion you will be relieved
of all weight and surprised at the lift exerted.

After getting the machine snugly up under the arm pits, face the wind,
elevate the front of the machine slightly, run a short, distance and
leap into the air. If you are in the right position you will sail to the
foot of the slope in free flight. To land, push yourself towards the
back of the machine, so that the glider tips upward slightly in front.
It will then rise slightly but loose its momentum and slowly settle so
that you drop gently on your feet.

*Balancing* is accomplished in flight by moving the legs and body
towards that side which is highest.

[Illustration: Fig. 30—Lines of Flight]

*Shifting the centre of gravity* by swinging, the legs forward or moving
the body in the same direction, will naturally cause the centre of
gravity to assume a forward position, and being a force exerted
downwards, the machine will dip and descend. A reverse movement of the
centre of gravity will cause the front of the machine to tip up and
ascend. But if the upward slant is continued too long the glider will
loose its forward velocity and settle.

The tendency is always to place the weight of the body too far to the
rear. After a little experience the experimenter will learn how to dip
his machine to acquire velocity for a rise and to otherwise handle it.

Fig. 29 illustrates two lines of flight in their successive stages. At 1
the operator is running along the top of the hill and the dotted line
from 1 to 2 represents his course immediately after leaving the ground.
In case the weight is back slightly too far and is not shifted much
during the glide, the machine will follow the upper line indicated by 3,
4, 5 and land at 6. If instead, at 2, the body is moved forward, the
machine will travel down as shown by 7 and approach the earth. Having
attained considerable velocity at _S_, the operator moves back and the
machine rises, travels upwards as at 9 and then settles about at the
point 6. This latter line of flight is to be preferred since the machine
does not rise quite so high in the air and moreover has more velocity so
that the operator may rise if necessary.

If during a flight a gust of wind strikes the machine from the front, it
will accelerate its vertical motion in regard to the earth. That is, if
the machine is already rising it will rise higher and if descending will
fall more quickly. A gust of wind from the rear will cause the machine
to drop suddenly and so always glide _into the_ wind.



CHAPTER V. Remarks.


In a little booklet such as this it is even impossible to cover the
subject of gliding flight fully much less power driven aeroplanes, but a
short description of such a machine built by the author, assisted by Mr.
Harold Dodd and Mr. Safford Adams will no doubt interest many since it
has been used successfully as a glider in towed flights.

The machine was attached to an automobile by means of a long piano wire
bridle. It rises at a speed of between 15 and 20 miles per hour and
remains in the air as long as the auto keeps moving at this rate. The
grounds used by the author in his experiments limited the flights to
about 800 feet.

The automobile in one flight traveled about 50 miles per hour, but the
machine soared on a perfectly even keel and without any pitching. Just
as the author was about to descend, the towing wire broke, but the
aeroplane glided so gently to the ground that it was impossible to tell
where it first touched.

The following description of the machine is an extract from an article
written by Mr. R. S. Brown.

"The two supporting surfaces of the aeroplane are five feet wide in the
direction of flight and twenty six feet long. When the machine is moved
rapidly forward, the action and reaction of the still air on the lower
side of the moving surfaces, lifts the aeroplane from the ground and
supports it in the air. The curvature of the planes is that segment of a
parabola, whose depth is one ninth its length. They are spaced one
vertically above the other and about four and one half feet apart in the
middle. The ends converge slightly to make the machine less affected by
cross gusts. The longitudinal curvature of the planes is maintained by
spruce ribs half an inch square and spaced nine inches apart. Their
front ends are ingeniously fastened in brass sockets on the front
horizontal members and their rear ends project about a foot over the
rear horizontal pieces. The fabric a close woven muslin is put on over
the top and bottom of the ribs and is fastened by grommets to a wire
running through the rear ends of the ribs, and by strips of felt
fastened down to the ribs with upholsterer’s tacks.

"The stanchions are six feet apart except the middle two, which are only
eighteen inches apart. The horizontal pieces of each surface are
parallel and four feet distant from each other. All are of selected
spruce, shaped so as to give the greatest strength with the least
resistance to the air, and the least weight. All the many rectangles of
the structure are braced diagonally with steel piano wire. In every one
a small turnbuckle is inserted to adjust the length. The nuclei of these
turnbuckles consists of bicycle spokes. By this wiring a perfectly rigid
truss is formed.

"Ten feet to the rear of the main body, there is a horizontal tail,
which halves a vertical rudder of about the same area. This vertical
surface is movable and turns the aeroplane to the right and left when
moved by rotation of the steering wheel. As can be seen in the
accompanying illustration these rudders are strongly supported from the
principal structure.

"At an equal distance in front of the supporting planes is the elevation
rudder. This consists of two horizontal plane surfaces, six feet by two.
These turn about a horizontal axis transverse to the direction of
flight. Thus the angle which they present to the wind can be altered at
the will of the operator. This is accomplished by pushing and pulling on
the steering wheel. Through the middle of the horizontal surface runs a
triangular vertical plane. This is designed to prevent the turning of
the machine by a gust striking the rear vertical rudder, for if it
strikes both vertical surfaces, one in front and one behind, the two
neutralize each other and no turning takes place.

"On the ground the machine runs on three twenty-inch pneumatic tired
wheels. These were especially made for the purpose, with seamless rims
and heavy motorcycle spokes. Two are set in regular forks of tubing
under the rear edge of the lower plane, while the third wheel is
considerably in advance of the body proper. When running on the ground
preparatory to rising, the machine is carried on these little wheels.

"The operators seat is in front of the supporting planes, and as the
photograph shows is carried on two braces from the front wheel. Sitting
in the seat, the aviator can direct the aeroplane from side to side by
turning the steering wheel before him. This steering wheel is mounted on
a post hinged at the bottom, and by pushing or pulling on the wheel the
aviator is enabled to control his height above ground by means of the
elevation rudder which is connected by a wooden rod to the steering
post.

"Mid-way between the two main surfaces and at the front of each end is a
small plane. These are tilted at positive and negative angles to the
wind, by means of cords connecting them with a pivoted bar moved by the
pilots feet. In flight, if one end rises, the aviator presses down the
end of the bar on the rising side. This causes the ’balancing plane’ on
the high side, which is the name given to the movable planes just
described, to form a negative angle with the wind so that the high side
is forced down. The other balancing plane assumes an equal positive
angle, so as to force up the lower side. Thus the machine is again
brought to an even keel. After a little experience, this action becomes
almost automatic, so that no difficulty is experienced in keeping the
flyer level.

"The motor, which at present has not been installed, will be supported
between the two main planes and connected to a laminated spruce
propeller, six feet in diameter.”

Those who of until late have not been associated with aeronautics can
scarcely realize the steps by which aviation had progressed and the
trend towards building machines.

The aeroplane worker can no longer be classified with the seeker after
perpetual motion. It is therefore to be lamented that so many of these
machines partake of freak construction. Originality is always to be
fostered but must bear some degree of proportion.

Only a very few favored people in comparison to the rest of civilization
have been enabled to see an aeroplane in flight. Many times less are
those who have had the privilege of examining a successful machine.



BOOKS FOR AVIATORS


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*THE THEORY AND PRACTICE OF MODEL AEROPLANING.* By V. E. Johnson, M.A.
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BOOKS ON AERONAUTICS.


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Air-pressure on a Thin Plane Inclined at an Angle to the Direction of
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this work is here given. Contents of Chapters: 1. Introduction. Dr.
Barton’s Air-ship. Lebaudy’s Military Air-ship. The Deutsch Air-ship.
The Wellman Air-ship. Motors of the Wellman Air-ship. Chapter 2.
Dirigible Balloons. Giffard’s. Dupuy de Lome. Tissandiers’. Krebes’.
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Baulx, Zeppelin, Deutsch, Lambert, Wellman’s Air-ships. Trolanini’s
Air-propelled Boat. Chapter 3. Flying Machines. Giving a Number of those
made by Hargrave and also by Phillips, Ader, Maxim, Pilsher’s Soaring
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Machines of the Future. *134 pages, illustrations and page plates, 12mo.
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MODEL AEROPLANES.


*MODEL FLYING MACHINES, THEIR DESIGN AND CONSTRUCTION.* By W. G. Aston.
Contents of chapters:—1. General principles and their application. 2.
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*MODEL AEROPLANES, HOW TO BUILD AND FLY THEM.* By E. W. Twining.
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*THE AEROPLANE PORTFOLIO.* By D. Ross Kennedy. Containing nine sheets of
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