Simulating aerodynamics with Physics2

I am getting a lot of grief with the Physics 2.0 engine - or at least my attempts to use it to fly an airplane.

I am trying to simulate lift and drag with 2 different polar forces at right angles that should act opposite to the direction of travel, and should increase with the square of linear velocity, and the sine and cosine of the angle of attack (calculated in a variable), as appropriate.

My aircraft quickly accelerates to nearly 12000m/s, apparently the maximum value the scene could handle, and drag seems to apply in the wrong directions. I don’t know what other griefs this craft has, but I’ve tried to fix this for a day or more. I have made sure that all the degree angles I used have been converted to rad.

EDIT: I found one more problem; if the Y velocity is POSITIVE (descending) at around 15 m/s or less, the aircraft climbs.

Sorry for my disorderly game, and my incomplete explanation. But can someone please download the game linked above and see what is going so wrong?

Note: the hidden part is very small and contains things unrelated to drag.