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.
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.