#2368: Annulift

Contra-rotating propellers are a neat idea in that they they can be arranged to generate no reactive torque when the blades spin up or down (and thus remove the need for a tail rotor, in the case of a helicopter).

One problem, however, is that the turbulence created by the upper set tends to disrupt the lift efficiency of the lower set.

contras

Today’s invention attempts to lessen that problem by having one collection of blades which consists only of an outer(upper) length and another set which are shorter (and slightly lower), as shown.

The outer set’s speed and size can be chosen so that the best possile combination of lift and balance is obtained.