downwind turn
Mechta Silverstrata
Quite right about climbing/descending through appropriate wind gradient
Indeed add local patches of accelerated wind above and around any hill or ridge particularly in 'stable' conditions and turning analysis gets very difficult
(There are two relationships we try to isolate in discussion, Aircraft to Air , and Aircraft to Earth , which are however linked by Air to Earth)
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I think Lyman hit on something when he said Time came into it.
During the Turn(not straight upwind or downwind)the aircraft has to be accelerated + or - with respect to the ground in order to maintain flying speed. This takes time ,and has to be paid for with engine power or gravity(potential energy= height]
If you take the extreme case of an instant turn (on the spot) you can arrive at a minus airspeed.....So??? (Dont ask, Ive been there done that )
Consider further the interesting situation you were watching from the balloon,
Perfect circle ? Constant G?? Constant angle of bank???....I dont think so
These effects most noticeable where windspeed is a large compared to aircraft airspeed
I wonder how a Jumbo fares doing a 180 downwind turn in a 200 mph wind .