'Medium Turns' is usually the first exercise a student QFI learns to teach.
And with it comes the acronym KISS!
None of the grandiose 'energy concept' bolleaux is worth a rat's - it's utter boffinry and irrelevant. Ignore frictionless particles, kinematic viscosity and the time of day on Saturn's moons - and keep it simple!
Aircraft in turn requires more lift because only the vertical component of lift opposes weight. The increase in lift is achieved by increasing the angle of attack; this also increase drag. An increase in thrust is necessary to avoid deceleration.
As for 'downwind turns' and relativistic mechanics or whatever, if you really want to complicate matters and you remember that the angle of attack is the angle between the chord line and the relative airflow, if some external factor such as a vertical gust changes the relative airflow then angle of attack will also change as a result. Mention that during a medium turns brief to a trapper and the pen will start to make notes - followed by "Why's that, sir?".....
The illusory effect of wind on apparent speed is covered during low level intro - but only demonstrated if there is a significant wind during the air exercise.
I found that my Aero Eng degree was worth the square root of sod all when it came to teaching P of F - the CFS way was infinitely simpler and easier for all to understand....
