hmm... it might have something to do with the thrust line of the engine and the angle of the wings. the engine probably has down thrust that cancels out this effect when throttle is applied. when you take it off, there is some aerodynamic effect that causes it to pitch up. check the alignment of your wings to the center and also check the elevator to make sure that is angled correctly too. it might just be, though, that it flies so well doing your aerobatic maneuvers because of some offset somewhere, and this stability for aerobatics may go away if you change it to not pitch up. its a very confusing problem you have there[&:]