Loss of kinetic energy when you turn downwind, very interressant subject Shawn!
let's see the case of a downwind turn just after takeoff when the wind is more than 25% of your airspeed
I can found the following factors: (I maybe wrong!)
There is a variation of wind velocity and direction near the ground which affect lift, drag and moment of the aircraft. This horizontal gust or shear vary with altitude and are due to the friction of the air over the ground (sort of boundary layer).
In my view this ground boundary layer can have different profiles:
LAMINAR: low thickness, low velocity near the surface, gradual velocity change. (Mojave desert early in the morning!)
TURBULENT: greater thickness, higher velocity near the surface, sharp velocity change.
We also have to think about the effect of leaving ground effect:
— increase in induced drag and thrust required
— increase in angle of attack to maintain the same lift
— reduction in climbing performance (more drag with the same thrust)
I have experienced this problem while towing big gliders in summer: (180 Hp tug with a 750+ Kg glider), we had to do a turn just after takeoff (200 feet max) to avoid some house (noise). We always used to turn upwind and One day I decide to turn downwind towards a great cumulus and I never made it......As I was turning , I lost around 10 Kt of airspeed and start to descent.....unable to recover.......I had to release the glider in a crop field (pilot and glider OK). Wind speed was around 30% of towing speed and turbulent.
stardust