This 'Downwind Turn' business is demo'd during 'Low Level Intro' to Bulldog students. It's just illusion leading to insidious pitching attitudes resulting from the perception that the cows should still be going past the window at the same rate!! Other dangers are also highlighted - but there is no aerodynamic reason for loss of speed turning into or out of wind. How does the aircraft know what the wind is doing?? It's a bit like thinking that a Thermos flask somehow knows that it's supposed to keep hot things hot and cold things cold - but not the other way round!!