Crab,
Does the Main Rotor have a way of knowing it is in a "Down Wind"?
The aircraft is designed for a certain direction of airflow that exists in forward flight thus is more efficient and offers less drag when the relative wind aligns with that aircraft orientation.
Of course when we talk about "down wind" we are referencing a certain and definable ground reference.
Is that what is causing the difference in power demand?
Drag alone...which is increased due to the airframe is what produces the demand for extra power as compared to being "into" wind with the most efficient orientation of the aircraft....or is it?
I seem to recall Mr. Lappos held forth on this topic at a time. period he was doing the flight testing on the Commanche....where they were doing 75 MPH sideways hovering and related testing.
If we do some searching...maybe we can resurrect that thread from right here at Rotor Heads.