PLATE VI.
A Model with Both Good and Bad Features.
In building these cellular forms select some light lath for the frame rather than dowel sticks. It will be necessary to join many of these together at right angles, and the curved stick will be found difficult to work. For each box cut four sticks the desired width, and eight sticks the depth of your plane. The box should be almost exactly square so that all these shorter sticks should be the same length. Now build your box by nailing and glueing these sticks together, taking great pains to have it symmetrical. Should a single one of these sticks be too long or too short it will throw the entire frame out of plumb and make it next to impossible to get a straight flight.
In most of these models the front or rear stability-planes are made exactly like the larger frame only much smaller. When the frames are completed and thoroughly dry and smooth, stretch the cloth covering tightly over them by drawing it lengthwise, all the way around. By using a single piece of cloth it will be found easier to pull it together and hold it tight and smooth. It will be found a good plan to touch the outer edges of the frame you are covering with glue just before covering. When the glue dries the cloth will thus be held firmly in position. The cloth may be fastened to the outer edges by glueing or sewing.
A simple but effective plan for mounting the stability-planes is suggested by the models here illustrated. The frame of the motor-base may be made the width of the smaller frame and fastened between the two sticks. It should be left free so that it may be tilted up or down and fixed in any position. If the rear stability-plane is to serve as rudder it should of course be mounted vertically so that it may be turned to right or left. Be sure to make your frame sufficiently strong and rigid. A light frame which will vibrate when the motor turns or is shaken by the wind will be found very troublesome indeed.
The cylindrical forms of planes ([Plate 21]) carries the foregoing principles a step further. A surprising degree of stability is obtained by thus enclosing the air, and by throwing out several lateral stability-planes fore and aft. The models may be constructed of heavy wire, ordinary umbrella wire will answer the purpose, and may be readily bent. The planes in the accompanying model are merely suggestive. The broad planes placed forward, well above the diameter, promise well, but the rear wings appear unstable and small for the other surface. The forward or lifting-plane is again, much too narrow. The cylindrical form is equipped with a double propeller, one before and the other in the rear, both mounted on a bar, which forms the exact axis of the cylinder. This adjustment will give you a very pleasant surprise. The vibration and torque of the two propellers seem to equalize one another, and the thrust is much more steady than in the case of a single screw. The thrust is not only double, in this way, but the gain for stability is surprising. The model should be mounted on skids to assist it in rising, and to take up the force of the impact on landing.
The double propeller, mounted on the same shaft, may be used successfully in many models. A very simple monoplane form ([Plate 22]) may be equipped in this way. If two or more planes be mounted between the propellers, an astonishing soaring quality may be had. It is an excellent plan to fasten the planes to the frame at first by rubber bands, so that they may be pushed up or down readily, and adjusted and weighted to suit the conditions.
There is danger in this form, however, that the plane will turn completely over in its flight, although this will have little effect upon the thrust or direction. The model is exceedingly simple to make. The propellers should not be too large, not more than twice the diameter of the planes at most. The two propellers must, of course, be turned in opposite directions, to correct the twisting tendency.
PLATE VII.