Page:Aerial Flight - Volume 2 - Aerodonetics - Frederick Lanchester - 1908.djvu/438

App. VIIIb. other curves. A further effect of wind is that if opposed to the direction or projection it increases the energy of flight, so that the total time of flight may be greatly prolonged. A well-thrown boomerang in a high wind will return at a considerable height over the thrower's head with a velocity like that of driven grouse.

The whole question of wind effect, unless the weather is exceedingly boisterous, is a mere matter of relative motion, but even as such it possesses some subtleties. Thus, as remarked, the initial energy is enormously increased, in some cases being more

Fig. 204.

than doubled by the boomerang being thrown in the teeth of a gale. Also, the greater the head wind the more important it becomes to give an effective initial spin to the boomerang, for the wind adds to the velocity without adding to the rotation, and thus, unless the additional spin be given by the thrower, the behaviour of the boomerang in a high wind is not satisfactory. The author has found that in the case of boomerangs copied from Australian models, in which the angle is very open, and the principal axis consequently ill-defined, it is often easy to throw down wind (although it will not then return), but impossible to throw against even a moderate breeze, owing to the insufficiency of the initial spin.