HOW TO BUILD A “GLIDER”
The simplest form of heavier-than-air machine is the stiff card or
letter which you may spin across the room. If you give it just the
right twirl it will glide on a level for many feet. There are many ways
besides of folding a sheet of stiff paper which will convert it into
a surprisingly clever little airship. With a little practice these
gliders may be made to fly ten or twenty times their own length, which
would be a very creditable flight for the best aëroplane models.
There is no better way to begin the construction of a model aëroplane
than by study and experiment with these paper ships. The most famous
aëronauts of the day, the Wright brothers, Curtiss, Herring, and many
others, have spent years working with gliders before attempting to
build or fly an aëroplane. It is in this way that they discovered what
form of wing would support the greatest weight, whether the passenger
should stand up or lie down, how to place the propeller and the rudder,
and hundreds of other details which have made possible the actual
conquests of the air.
Following in their footsteps, or rather their flights, the amateur
aëronaut should first build and fly only gliders or aëroplanes without
means of self-propulsion. The simplest form of glider may be made by
cutting a broad oval from a sheet of stiff letter-paper and creasing it
down the middle. The experiment may be made more interesting, however,
by cutting out the plane like the outstretched wings of a bird, as
suggested in the accompanying illustration. Try as you may, this sheet
will not fly. Now add a trifling weight to the front of the plane. This
may be done by fastening one or more paper clips to the edge, pasting a
match or a toothpick, or by dropping a little tallow or sealing-wax.
At first you will underestimate the weight your little airship will
carry. Add more weight in the same way, and test its gliding powers
until the little airship will glide gracefully across the floor. Keep
the length of these models under six inches. If you increase it beyond
this, the model loses steadiness and flutters about ineffectively.
An interesting model may be made by folding a sheet of stiff paper in
an arrow-like form. The idea is to form a series of planes which will
support the weight of the tiny craft and, at the same time, enable it
to fly or dart in a straight line. It will be found that the vertical
surfaces lend stability and keep the ship moving in a straight line.
You will soon learn, in this way, more of the principles of aëroplane
construction than mere reading from books can teach you. Be careful,
meanwhile, to remember just how you have launched the various forms
of models, whether you have thrown them with an upward or downward
motion, and how hard a push you have given them. The skill you acquire
in this way will be valuable later on when you come to launch your
regular model aëroplane.
[Illustration: Dowel Strips of Different Sizes.]
We are now ready to begin the construction of the frames of aëroplane
models. The first model will be merely a glider. The frame and wings or
planes of an aëroplane are built much the same as a kite. The idea in
all such work is to combine the greatest possible strength or stability
with extreme lightness. Remember, however, that the aëroplane during
its flights is racked and shaken by its motor, and is likely to land
with a bump. The materials used must be stronger than in the case of
an ordinary kite, the joints more securely formed, and the entire
structure braced in every possible way.
The best materials for constructing these gliders or aëroplanes are
very cheap and easily obtained. At almost any hardware-store you will
find a variety of “dowel-sticks,” which seem especially made for this
work. They are smooth, round sticks a yard in length and of a variety
of diameter. The sticks three sixteenths of an inch in diameter will
be found most serviceable, while the larger sticks are just the thing
for the backbones of your aëroplane. These sticks will not split at the
ends and may be readily worked. They cost one cent apiece.
Some boys find that the reed or cane suits their purpose better than
the dowel-sticks, since it is more flexible and a trifle lighter. The
cane is easy to work when you wish to build planes with curved lines.
It can be readily shaped to any desired form by first wetting it and
allowing it to dry after working. Care must be taken in using it,
since the ends are likely to split. Bundles of this cane may be bought
at most hardware-stores or in department-stores. Enough material for
constructing a model may be bought for a few cents.
The lightest of all available materials is bamboo. It is difficult to
procure, however, and requires more working up than the others. The
best plan is to buy a stick of bamboo, a dry piece, and split it into
strips of the desired length and thickness. The grain is so straight
that there is practically no waste material as in ordinary wood. The
strips may be readily planed or sandpapered. The wood is extremely
light and strong enough for all practical purposes of the model
aëroplane builder. An old bamboo fishing-pole may answer your purpose.
The first gliders constructed should be of the monoplane form, that
is, with a single surface. The biplane or multiplane models will come
later. Meanwhile, one is not losing time in working only on these
simple models, for the experience is valuable and nothing is lost,
since when the frame is properly constructed the motor and propeller
may be added. The work throughout is extremely simple, and there are no
problems of which the average ingenious American boy need be afraid.
[Illustration: DIAGRAM FOR PLAN OF THE AËROPLANE ON PAGE 58.]
[Illustration: DIAGRAM--SHOWN IN PERSPECTIVE. PLATE A.]
To construct the model shown in Plate A first make two frames of
dowel-sticks, bamboo, or reed, or, if these be lacking, of light lath,
the smaller frame 8½ by 19½ and the larger one 10½ by 36½ inches.
Care must be taken to have the sides of the rectangle exactly the same
length and the joints closely and neatly finished. Some boys prefer to
lay one stick over another, then wrap the joint tightly with thin but
strong linen thread, and over this brush a coat of thin glue, without
using any brads or nails.
In kite-building, to be sure, it would be enough to lay the strips
over one another and fasten roughly with a tack. Nor did the lengths
of the stick, when covered with paper, make much if any difference.
The aëroplane, it must be remembered, travels edgewise, and, having no
guiding string, is at the mercy of every gust of wind. If the frames
are carelessly proportioned it will not travel true, but is likely to
be deflected. Imagine a boat whose sides are not exactly uniform trying
to travel in a straight line. It would be lopsided, and would roll and
pitch under the most favorable conditions. Now an aëroplane, since it
travels in so thin a medium as air, is far more sensitive than a boat,
and it becomes lopsided if its proportions be in the least inaccurate.
Only the greatest care in construction will produce an air craft which
will fly true and straight.
It makes little or no difference in a kite if the ends project a
little and the joints be carelessly made. Not only must your aëroplane
be perfectly proportioned, but it must be finished like a piece of
fine furniture. The question of friction is a very important one in
the heavier-than-air machine. You cannot be too careful to round off
every corner and smooth every exposed surface. If you have opportunity
to see a regular aëroplane, a Wright or Curtiss model, you will find
that every part of the machine has been sandpapered and varnished with
the greatest care. This is not done for the sake of appearances, but
because it has been found that the wind striking against the rough
piece of wood meets an appreciable amount of resistance, whereas
it slips past a polished surface with little or no friction. Your
aëroplane should be finished like a violin.
[Illustration: A Coil of Cane or Reed.]
In building these planes be careful to compare the lengths of the
corresponding sides throughout. If you prefer to use brads for
fastening the joints do so. The dowel-stick and bamboo will take the
brads with little danger of splitting. When thoroughly dry, cut away
the glue which has squeezed out, round off the ends, and sandpaper with
fine sand or emery-paper. If you use brads it will not be necessary to
place the joints in a vise while drying. Should your strips split, bore
the holes with a fine awl. Some boys after drilling the holes merely
tie and glue the sticks together, using no nails whatever.
Now cut three dowel-strips 34 inches long and slightly sharpen their
ends, so that when brought together they will form a prism whose base
is about one fourth their length. Next bend a strong piece of wire into
a hook--a hair-pin will answer for small models--and fasten it in the
apex of the prism, with the hook inside. The projecting end of wire
should then be bent over, and the three dowel-sticks glued and tied
tightly together.
At the open end of the prism next fasten two strips from end to end,
leaving the third side of the triangle open. Now fasten your two planes
on the open side of the prism, slightly mortising the sticks and gluing
and nailing them securely in position. To further strengthen the
prism, join the three sides at the middle with three sticks, forming
a complete triangle. The prism thus braced will be found as strong as
a heavy central stick, besides being much lighter and providing an
excellent base for the propeller. A strong stick about half an inch
square should be tied and glued across the middle of the triangle at
the base of the prism to support the motor.
The frame once complete, sandpapered and varnished, it is ready to be
covered. At first this may be done with some smooth paper. Almost any
thin material, muslin or linen, will answer for the purpose, although
white silk makes the most finished-looking model. Such scraps as may
be found in the family piece-bag will answer every purpose. In sewing
the cloth over the frame the advice of some big sister, aunt, or the
mother may well be taken. The idea is to fasten the cloth smoothly
and neatly over the frame, keeping the surface free from creases or
wrinkles of any kind. Boys are likely to be awkward with the needle.
The cloth may also be glued over the frames. When complete cover the
planes with a thin solution of paraffin dissolved in benzine.
In attaching the planes or wings to the central axis of the model, the
larger stick or backbone may be mortised neatly, so that the sides of
the frame will be sunk in flush with the upper surface. A fairly good
glider may be made, however, by merely nailing down the frames against
this backbone. The distance between the two planes is a complicated
problem, but the beginner had better at first imitate the model shown
in the accompanying illustration. If the two supporting planes be too
far apart or too near together, the glider will fall. The amateur must
experiment by changing their position on the central axis until he hits
the right proportion. He will be able later to carry this proportion
in his eye, and the experience will prove invaluable. Until you have
hit upon the proper position, fasten them to the backbone with rubber
bands. These permit you to slide the planes back and forth without the
trouble of nailing.
Aëroplanes, unlike kites, fly best in a perfectly quiet atmosphere. If
you make your trial flights out of doors, select a quiet day. A room,
a barn, or any large interior will be found better. In launching your
glider, hold it from beneath, so that it balances, and throw it forward
with a swift, steady movement of the arm. A little practice will make
you very expert.
[Illustration: Splitting a Bamboo Fish-Pole.]
You will now find yourself fitted to reproduce any of the simpler
forms of monoplane models, several of which are here illustrated. An
interesting model is made by attaching U-shaped wings to a central
axis. In making these curved planes the reed will be found useful.
Other effective gliders are made with triangular wings fixed at
a variety of angles. Remember that the model must be absolutely
symmetrical. In attaching the frames to the central axis, always make
the joints as smooth and rigid as possible.
The weighting of the glider will be found to be a very important
detail. As a rule the gliders require a considerable weight at the
front. The exact position of the weight can only be determined by
experiment. The simplest way is to wire a nail or a piece of metal
to the edge of the frame. If your glider does not balance perfectly,
which is likely to be the case, this fault can be largely remedied
by weighting it. The tendency of the glider is likely to be upward,
and the weight serves to keep it on an even keel. When your model
glides steadily through the air, without rolling or pitching, you have
constructed a well-balanced frame. It will then be time to take up the
problem of propulsion.