#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.


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.

One Comment:

  1. I’ve thought of a better way to implement this idea. Think of a ball bearing. Imagine that the inner rotor blades end on a ring like the inner surface of a ball bearing. A set of planetary gears would run on this ring, held in place by a cage attached to the fuselage. Another ring on the outside of the the planet gears would carry the second set of blades. This would allow contra-rotation, but without the outer blades having to be mounted on fine struts attached to the central axle, since this would probably cause some unwanted turbulence for the inner blades to overcome.

    It might even be possible to have multiple annuli of blades arranged in this way, rather than just two.

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