> The folks who absolutely know and understand this are the
> model airplane folks. Their airspeeds are very low and even the
> slightest wind affects them when they turn. Who knows, might
> be a good master's thesis subject...
As a model flyer...
I don't think many model pilots do understand the 'downwind turn' issue. The debate surfaces regularly in the magazines and newsgroups. Usually we're too worried about the effect a downwind turn has on ground speed to notice if the sink rate is any higher/lower. The downwind turn has a bad reputation because the high ground speed fools the pilot into thinking he's going too fast. Pilot tries to slow up which causes a higher sink rate or worse a stall and spin in.
As a early solo glider pilot (lapsed)..
I never noticed the wind while circling in a thermal drifting downwind. Sure if you look down you can see your track isn't a circle on the ground but I can't say I noticed any "up's and downs" are you go round and round. Not even when you are sharing a thermal with another glider.
However it's clear that gliders have innertia or wind shear wouldn't be a problem, the plane would instantly accelerate to maintain it's flying speed.
Jury still out.