Variable Speed Rotors and Prop(s)

[Graviman]

"Perhaps the action of the worm and gear is not fully understood."

Dave, i think you're misunderstanding where i'm coming from. The point is that to control the prop velocity the worm gear has to react large torques. Since Power=Torque x Rot_Vel this means that whenever the worm is "controlling" the speed a lot of engine power is wasted.

I agree with all you are saying, but you have just found another method to avoid the servo motor itself having to dissipate all this power. We have a lot of problems when drivers think the limited slip we fit is traction control - it doesn't take much Torque x Rot_Vel to cause a diff clutch burn out.

Since this is effectively a type of shunt transmission, i suggest you do a power flow calculation for different flight regimes. You'll soon begin to understand my concerns. Don't forget that wasted power in a heli is lost payload...


Regarding prop velocity, let me clarify:

Prop RPM should be proportional to SQRT(Prop_Thrust), so that dynamic pressure controls thrust at fixed blade AOA. As aircraft flight speed increases the blades will twist/pitch, so that more of the lift/thrust component becomes torque. This just means that for a given input torque Prop RPM will drop off with airspeed, resulting in a a reduction in thrust. Alternately increase torque linearly with speed, to maintain fixed prop RPM hence thrust. For ideal blade twist, design a torsionally soft blade with trailing edge trim (or servo flaps).

Mart

[Edit: hopefully to clear up last paragraph...]