Jim said:
... a small amount of power (up to about 15 hp) to the rotor will flatten the coning and increase performance.
Good point, Jim, but the coning angle isn't what flattens, its the disk angle.
Adding partial power to the rotor should actually
lower rotor rpm, interestingly, and the coning remains the same.
Think of it this way: If you were to prerotate fast enough, you would lift off.
Lets say this happens at 320 rpm. You would need a lot of rudder, probably more than what's available, but pretend you are hovering at 320 rpm.
Now , as you move into forward flight, you turn off the prerotator. Power to the rotor has to come from somewhere, so the rotor tilts back about 10 degrees to drive air through the rotor. The rotor must now make additional lift to maintain altitude, because rotor thrust is at a 10 deg angle to vertical.
This additional loading drives rpm up to maybe 350, the normal flight rpm fpr this machine.
If you engage partial power from the prerotator, the disk can fly flatter and the rpm will decrease back towards the 320 rpm that you hovered with, settling at something greater than 320, but less than 350. I'm just guessing at these numbers.
Coning stays the
same oddly enough, due to the way centrifugal force relates to rpm change.
It is more efficient to power the rotor meachanically than it is to power it aerodynamically. The rotor is lousy at converting wind energy to usable thrust. If you add too much power, then you need a tail rotor for ant-torque, (and the rotor will need more pitch and won't be in autorotation)so the best combo is a gyro with some power coming from autorotation and some coming from prerotation.