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MenuHomeAviationHumansOriginsScienceWeb LinksSite MapContact At cruise, a non-negligible amount of the drag of a modern wing is induced drag. Parasite drag of a Boeing 747 wing is only equivalent to that of a 1/2-inch cable of the same length. One might ask what affects the efficiency of a wing. We saw that the induced power of a wing is proportional to the vertical velocity of the air. If the area of a wing were to be increased, the size of our virtual scoop would also increase, diverting more air. So, for the same lift the vertical velocity (and thus the angle of attack) would have to be reduced. Since the induced power is proportional to the vertical velocity of the air, it is also reduced. Thus, the lifting efficiency of a wing increases with increasing wing area. The larger the wing the less induced power required to produce the same lift, though this is achieved with and increase in parasite drag.

There is a misconception by some that lift does not require power. This comes from aeronautics in the study of the idealized theory of wing sections (airfoils). When dealing with an airfoil, the picture is actually that of a wing with infinite span. We have seen that the power necessary for lift decrease with increasing area of the wing. A wing of infinite span does not require power for lift since it develops lift by diverting an infinite amount of air at near-zero velocity. If lift did not require power airplanes would have the same range full as they do empty, and helicopters could hover at any altitude and load. Best of all, propellers (which are rotating wings) would not require much power to produce thrust. Unfortunately, we live in the real world where both lift and propulsion require power.

MORE (Power and Wing Loading)

David Anderson,
Scott Eberhardt

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