The automobile experiment naturally suggested the aeroplane, and after
much reading of magazines and animated discussions as to the relative
advantages of biplanes, monoplanes, gliders, etc., the boys decided to
try their skill on a biplane of their own design, a combination of the
features and proportions of the Curtiss and Wright machines.
The automobile was child's play compared with the problems confronting
the young aviators in designing and working out a flying machine,
and, as in the former case, the question of motive power was the most
difficult. We might add it has not yet been satisfactorily solved.
Fig. 48 shows the general appearance of the boys' model, which was
eighteen inches long from front to back, and the planes, made of light
card-board, were 14 inches long and 3-1/2 inches wide. The frame,
braces, rudder, and tilting plane were made of 1/8-inch basswood, put
together with 1/2-inch brads clinched wherever the points came through.
The parts composing the frame were made first, and all small details,
such as rudder, propeller, tilting plane, etc., cut out later.
The separate parts are shown in the drawing. Four straight pieces like
_a_ were required to support the tilting plane in front, and two pieces
each _b_ and _c_ for the rudder in the rear. Two pieces _a_, one of _b_
and _c_ were fastened together by means of two uprights _d_, forming
one complete side of the machine. This was completed, and the second
side made identical with it.
These two sides were then fastened parallel with each other, rigidly,
by means of the two rudder posts _e e_ and the cross pieces _f f_, by
brads. The rudder posts bound the two sides rigidly at the rear, the
cross pieces at the centre, and at the forward end the tilting plane
was held in position by the brads, which also acted as pivots.
This made a remarkably light and yet strong framework. The card-board
planes were not placed in position until everything else was finished,
as they could be attached easily and quickly, but were very much in the
way when experiments were being made on the propelling apparatus.
Of course there had to be a propeller, and the problem of making it
required some practice.
Ralph introduced the subject by showing Harry how to make an
old-fashioned toy, shown in the detail drawing, of two pieces, one the
propeller, the other a balancing stick.
The propeller was made of a piece of 3/8-inch basswood, 4 inches long
and 1/2 inch wide. A 3/16-inch hole was first drilled at the exact
centre. The two ends were then whittled down to the shape shown at _k_.
The balancing stick was next whittled down until one end fitted tightly
into the hole drilled in the propeller, and the rest of the stick then
rounded until it was of uniform diameter. This stick was glued into the
hole, and allowed to dry.
There was plenty of work to do while the glue was hardening, as the
cross pieces _g g_ had to be fastened to the frame to prepare for the
installation of the power plant.
When the glue was dry, Ralph took the balancing stick between the palms
of his hands, drew his right hand toward him with a quick motion, at
the same time releasing the stick. To Harry's amazement, the whole
thing flew up and struck the ceiling, and for a few minutes aeroplanes
were forgotten while the two played with this interesting but ancient
toy.
[Illustration: Fig. 48. The toy biplane]
Ralph explained that the propeller was simply part of a screw thread,
and had actually worked its way through the air just as a screw works
its way into a piece of wood. Its lifting power had been shown by the
way it carried the balancing stick with it up to the ceiling.
"Now," he continued, "when we place a propeller horizontal it will worm
its way forward through the air in the same way and carry the aeroplane
with it, for the simple reason that it is so placed in the frame it
can't get out. As the free space it has to revolve in is only 3 inches,
we shall have to cut the blades down to about 2-3/4 inches to give it
clearance."
They whittled out a shaft 1-1/2 inches long and fastened the two
notched pieces _h h_ to it after placing the propeller in position
between the two cross pieces _g g_ which had been previously drilled
with 1/4-inch holes to act as bearings.
New rubber bands were then passed over the notches, stretched out to
the front and rear of the frame, and tied to cross pieces.
By winding up the propeller, these bands were twisted tightly, and when
the propeller was released, the bands unwound, causing it to revolve
rapidly.
The rudder was now pivoted in position by brads, and the two planes
fastened by the same method.
The power derived from the bands was not sufficient to propel the
aeroplane fast enough to support it in the air, so it was necessary to
experiment with strong thread until the centre of gravity was found.
It proved to be near the centre of the planes. Small holes were made
with an awl at this point, the thread passed through them and tied.
By suspending the aeroplane from a chandelier it took up a horizontal
position.
Then the forward tilting plane was elevated slightly and the propeller
wound up. On being released the aeroplane slowly and majestically
sailed through the air in a great circle, limited by the length of the
suspending thread.
The boys never tired of this toy and all it lacked was the ability to
fly in the open air, which would require a more powerful motor. This
would more than double the weight of the machine, and therefore call
for larger planes to support it. There you have the great problem of
the aviator.
Ralph wisely suggested that as they had not yet reached the stage of
designing gasolene motors they had better leave the aeroplane as it
was, or it would be necessary to abandon their woodwork, which neither
of them had any intention of doing.