If the model has a flat bottom wing, then it will climb under throttle even if you have added down thrust. If the wingplan is symmetrical or semi-symmetrical, it won't do this. If you have a laminar flow airfoil (only Pica used this on their P-51) all bets are off.

I use no down or right thrust on my planes. I use the flight controls, and throttle management to fly the plane, not let the plane fly itself.

Bill, AMA 4720
WACO Brotherhood #1