The momentum picture is exactly the same with wind and no wind.

If Momentum is p and Velocity is v, then:

No wind case you start with v make a 180 degree turn and you're going -v. Momentum has gone from p to -p and Deltap=-2p.

For the wind case looking from the ground you go from 2p to zero so Deltap=-2p. In the wind frame of reference you go from p to -p and DeltaP=-2p.

I think its impressive how fast you can turn a balsa wing plane without breaking it. There is a large force (F=DeltaP/DeltaT) that must be mostly elastic to turn a plane that is going 100 mph and have it come out 180 degrees with almost the same energy, WOW.

Carl