A serviceable model showing excellent workmanship built by Cecil Peoli
The vertical rudders or fins, as they are sometimes called, are, of course, intended to control the movement to right or left and keep the model from sliding sideways. They have no counterpart in the wings of birds, and are believed by some aviators to have little effect. At any rate, they can do little harm since their head resistance is practically nothing. Unlike the horizontal forward planes, these fins should not be carried too far forward.
In practice it is found that they often get in the way, and a slight side gust of wind striking them, with their great leverage, will knock the aeroplane completely off its course, perhaps upset it. The best position for such rudders is either above or below the main plane, or behind it, where they are out of the way of cross currents. In last year's models, these vertical surfaces were often very large, presenting as much surface as the planes themselves. It has been found that they may be cut down in size, thus saving weight without losing their efficiency.
A long vertical fin, or keel, has the disadvantage of presenting a dangerously broad surface to any cross current of wind. The question of the position of the rudder was taken up in a previous volume. A glance at the successful model aeroplanes of the year shows that the vertical rudders have been adopted very generally. Considerable ingenuity is displayed in adjusting them.
The use of wing tips of any form is intended to control both the horizontal and vertical movement. The general theory or equilibrium, of course, applies in both cases. The most perfectly adjusted model is subject to many forces which tend to tip it to one side or the other. A gust of wind,—and the air is never perfectly quiet,—will tip one end of the plane up or down.
Various Steering Devices. "a" and "b," simple aileron forms. "A" novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical rudder (Bleriot type). "D" "Blinkers," an effective rudder. "E" stability planes not unlike the runners of a sleigh.
In the early models, this tendency was met by fixing the plane at a dihedral angle. An examination of last year's models will show how common was this design. The dihedral angle lowers the center of gravity. Now, after one side of the model is raised and the plane rights itself, the center of gravity swings through a considerable arc, like a pendulum, before it can come to rest, so that the center must swing back and forth several times.
This tendency to tipping is fatal to a steady flight. It was first observed by the Wright Brothers while studying the early Langeley type of machine. The Wrights abandoned the dihedral angle entirely, as all the world knows, and replaced it by the horizontal plane with a straight entering edge. The keel will in a measure overcome this side motion.