Correct me if I'm wrong, but I was under the impression the ROD was controlled by the pitch on the main rotor blades? If the engine is at idle or stopped, surely the rotor blades and weight of the a/c will still determine ROD?
Is someone telling me if the engine stops on the way down during a practice autorotation the ROD suddenly increases? Or because a possible increase in friction on the spragg will slow the rotor rpm thus requiring more down lever which then becomes the reason for increased ROD?
Having said that, slowing the rotor RPM a little during the descent would reduce ROD, no?