Gwyvern

My problem is simple, whenever i use the firespitter helecoptor rotor, my helecoptor always tilts backwards with varrying strengths (after messing with placement for a while using the centers of mass and thrust) the best i can hope for is a violent tip forward on takeoff which is pulled backward in the air, but this still makes it nigh-impossible to land, because as soon as i slow the rotor thrust the helecoptor tilts forward again. thanks for any assistence.