I was going to avoid this conversation because I'm not very good at this aerodynamic stuff.
BUT...I've done something very similar to what PF#1 and Chuck are suggesting. A while back, some asshole wanted to put three 300ft wind turbines in a field on a hill above the lovely valley where I live. Our action group against it wanted to prove that they'd be seen from just about everywhere in the valley. Having checked as to safely etc, I offered to circle in a helicopter at 300 ft above that field, so that people could find out if they could see me. There was about a 15 kt wind, and I orbited at 30-40 kts till I got dizzy. When I was into wind we hardly moved over the ground, and when we had a tailwind we practically shot off the hillside, or that's what it felt like. But we didn't fall out of the sky...why should we, since no matter what the groundspeed, the airspeed was still 30-40 kts. The only danger would have been if I'd estimated my speed with reference to the ground, and reduced my airspeed when turning downwind. That's the only problem with downwind turns, in either f/w or helicopter - if you look at the ground and think you're going too fast. At least, that's how I see it...and I'm here to tell the tale, so I guess it was right.
Oh, and we won the battle, and didn't get the wind turbines to spoil the view.
