The fact that a considerable amount of knowledge can lie gained by experiments with weighted model gliders does not at present appear to be sufficiently appreciated ; only with model gliders, for convenience sake, a less weight is used per square foot of carrying aëroplane surface. A ¼ lb. per square foot area is a convenient demonstrating weight, giving a Speed of about 8 m.p.h., with a drop of about one in six ; with man-carrying machines the usual weight varies between ½ and 1½ lbs.

If a single aëroplane be released in the air it will simply fall anyhow to the ground, but on fixing a steering plane fore or aft, let us say in front as in Fig. 1, there will be a tendency for it to glide, but sooner or later one side will dip downwards, owing to the two planes not being in the same straight line or being improperly balanced.