It must oscillate back and forth within very narrow limits. A very little tilt up or down will restore it to its normal position, so that a plane with high aspect ratio is more stable than one with a deeper surface.
The efficiency of a curved surface over a flat plane was analyzed in a former volume. Such a curve, when well drawn, adds to the lifting power as well as the stability. Since a curved plane does more work than a flat surface, its size may be reduced and its aspect ratio increased. In other words, the curved plane may be narrower than a flat surface, and may be made thinner in proportion to its width.
The height of the curve, or camber as it is called, has been worked out by elaborate mathematical equations, but we may take the general results without following the calculations. For a plane six inches in depth, the camber should be about one-half an inch, or one in twelve, or in this proportion. The curve should be a parabolic with the highest point well forward, one-third the way from the front edge. The front, or entering edge, of the plane should be the thickest point. It should be tapered off to a thin edge in the rear.
In theory, it is possible to model a plane so delicately that it will fly against the wind by the pressure of the wind itself. It is extremely important that both sides of the plane be brought to this curve as accurately as possible. An efficient plane must, therefore, be covered smoothly on both sides. Such a plane again offers very little skin friction to the wind.
It is difficult to lay down any hard and fast rules for the relation of weight to wing surface, since the types of aeroplanes differ so widely. It has been found, however, that in large models one square foot of surface will support about one-half a pound of weight, when traveling at a high rate of speed.
You will find that your model, if its wings have a spread of thirty inches os thereabouts, will approach one pound in weight. The figuring will show you that two wings, whose combined area is less than 150 square inches, will be comparatively small and certainly well under those generally employed a year ago.
The planes used on this season's models are marvels of lightness and strength. Much has been learned by studying the methods employed by the builders of man-carrying aeroplanes. It is a simple matter to build a three-foot plane which weighs complete less than one ounce, and is strong enough to withstand many a violent shock.
A geared model built by Leslie V. Robinson
