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Fig. 4. Morane Umbrella Type Monoplane. Courtesy of "Flight."

Multiplanes

Fig. 4-A. Deperdussin Monoplane with Monocoque Body. Gordon-Bennett Racer.

Biplanes

Fig. 5. S. P. A. D. Tractor Biplane Speed Scout.

A distinct disadvantage of the two superposed surfaces of the biplane is due to the fact that there is "interference" between the upper and lower wings, and that the lift for equal areas is less than in the case of the monoplane. With a given form of wing, 100 square feet of monoplane surface will lift considerably more than the same area applied in biplane form. The amount of the "drag" for the support of a given load is increased, and with it the amount of power required. The greater the separation or "gap" between the wings, the greater will be the lift, but when the gap is unduly increased to obtain a great lift the length of the interplane bracing is increased to such an extent that the resistance of the bracing will more than overcome the advantages due to the large gap. There is a fixed limit to the gap beyond which it is not practical to go. The bracing has a very material effect on the air resistance, no matter how small the gap.