overpitched,
Nobody said there was no such thing as inertia, what we have said is that the direction of the wind is of no significance at all, and when you measure the velocity relative to an intertial reference frame, it is all the same.
The idea that the aircraft depends on the wind relative to the earth is flawed, and that the aircraft, if turned quickly enough, would see some magical downwind loss of performance is quite flawed.
Imagine that you are heading east, and that the earth happens in that instant to be moving toward the Andromeda galaxy at 45,000 mph. Now turn 180 degrees, and just imagine what your "change in momentum" must be relative to Andromeda! This is EXACTLY equal to the false logic about the earth reference relative to the wind's direction.
There is NO downwind effect due to intertia, momentum, Newton's laws or even magical fairies.
Maxng,
You are absolutely right that the rotor sees no downwind. In fact, turning your tail to the wind in a hover will not cost you any performance at all in most helicopters. rotors are not wings, and helos hardly need the wind sock, except when it comes time to stop the darn machine.