Correct me if I'm wrong, I don't think using the brake will make it turn faster, it should actually made you turn slower. The best way to turn is actually transform gerwalk for turning, when done transform back to fighter.
If you only want to play with the fighter mode, using the thrust should actually make you turn faster, but the angle may be wider.
I don't know about the physics of this game, but if you're flying a real aircraft, speed makes for wider turns, using the airbrake and slowing down willmake you turn tighter, in effect slower means you turn faster.