Effects of wingtip-mounted propellers on wing lift and induced drag.

It is proposed that aircraft can be designed using propellers at the wingtips in such a way that the L/D ratio can be varied by changing the effective aspect ratio in flight. An experimental program testing a wing with propellers mounted at the wingtips is reported. It is shown that the use of a propeller at the wingtip, turning in the direction opposite to that of the wing vortex, shifts the trailing vortex core outboard, decreases the wing drag coefficient, increases the maximum lift coefficient and increases the effective aspect ratio. Rotating the propeller in the opposite direction has the reverse effect. A functional relationship is shown to exist between ACD/CD and Tcd/CLS-