Lets get back to parshally powered rotors then... Would it be more efficient to take some engine power, go through an alternator or generator to a motor and gearbox, and then to the rotor, or to route engine power through a prop for thrust to power the rotor with wind? It seems like you might gain some efficiency with the motor, but would the additional complexity be worth it? I had a hydraulic prerotator on my HKS gyro that I could apply power to the rotor inflight, but the output of it was so low I really couldn't detect much difference.
I get .98 for the belt .65 for the alternator .85 for the motor+ESC .92 for the reduction just for napkin figures so it winds up being a bit less than 50% efficient. The other way is even more of a guess, .75 for the prop and .40 (?) for wind to rotor for a conversion efficiency of .3 ? Sound about right?