Model shown in Plate V. Ready for a Flight.
A good working idea of the aëroplane is clearly shown by the builder of the biplane with triangular wings ([Plate 17]). His model is not successful and will not fly, yet it embodies several good features. The biplane form of the lifting plane is excellent in itself as we have seen in earlier models. The spacing of the two planes is good, and the bracing of the model throughout is well planned. The triangle does not make a good soaring plane even when its broad side is made the entering edge. The triangle serves well enough however for the rear stability plane. The chief fault of the model is that it is much too large. The motor although well proportioned is much too weak to propel so large a frame.
An interesting variation from the common type of aëroplane is made by varying the angle of the sides of the planes ([Fig. 18]). Here is a well constructed model, and, with a single exception, fairly well proportioned. The mistake, and it is likely to prove a serious one, is in the size of the vertical rudders. They are well placed above the main plane, but their size is likely to defeat the purpose for which they were designed and knock the model off its course rather than keep it steady. It is a question again if one of these rudders would not serve the purpose better than two and thus minimize weight and resistance.
The best point of this model is the ingenious method of enlarging the surface of the planes without increasing the size of the planes or adding to their weight. This is done by cutting the covering of the planes at an angle and keeping the entire surface taut by bracing. It is of course very important that the cloth should be held tight without wrinkling. The plan of having the wings taper slightly outward is good. Such a model combines more lifting surface with less weight than any other model of this general group.
CHAPTER VIII
BUILDING A BIPLANE
EVERY one knows, of course, that the box-kite flies better than a plane surface, and many believe that the box or cellular type of aëroplane has a similar advantage over the monoplane. The enclosed end keeps the air from slipping off the edges of the plane, and makes for stability. There is all the difference in the world, or rather in the air, between an actual flight and the movement of a model aëroplane. The aviator, by flexing his planes, and adjusting his rudders fore and aft, may balance his craft to suit the air currents. In the model aëroplane, the adjustment must be made before starting once and for all. Several interesting principles are involved in the cellular or box form of aëroplanes which will well repay study (Plates [19]-[20]).
In disturbed air, which is of course the usual condition of the atmosphere, the cellular model is likely to be deflected, and since the elevating plane or planes cannot be adjusted, it will soon fall off its course. Such models are easy to construct, and any one who has built a monoplane will have little difficulty with them. No attempt is made to flex the planes. The cellular type must be equipped with a lifting-plane forward, which may be easily adjusted to any angle, and held in position. It is indispensable that you have two propellers placed aft behind the main plane. The model may be made much more effective by adding a third stability-plane or rudder at the rear. It may be either vertical or horizontal and should be easily adjusted. The models illustrated, herewith, are very simple forms and clearly indicate the necessary frame work. It will be found that these models require considerable ballast, skilfully distributed.
