[Openurmind]

Cool... How does it turn around when at a static hover? torque convertors on the counter rotating hubs? Asymmetric pitch in the tail rotor? Or can it only turn when flying forward like a plane?

[SJSAMPLE]

Dissymmetry of torque caused by opposite changes in the pitches of each rotor.

[going hot]

The rotors give opposite torque to the shaft which is connected to the frame, thus the tail rotor is needed to counteract the torque of the blades.

With two rotor discs, the tail rotor is not needed, as the net torque cancels.

I think if one set of rotors were to be given a little bit more of pitch, and the other set a little less, the bird would stay as same altitude, but the net torque to the shaft would no longer be neutral, thus causing the tail to come around.

I have not quit my current day job, so this is just speculation based on previous infor from another life. (!)