You need downthrust...
Placing washer in the top 2 holes will pitch the thrust angle of the engine down (in relation to the planes thrust line)...
Most often planes that "balloon" when increasing throttle need downthrust... however, wing and horz. stab incidence can cause it too... most planes has equal incidence in the wing and stab, but not always...
Say the hstab is slightly negative in pitch (i.e. it slants UP a bit and acts like down elevator) You can trim it out at lower speeds but at higher speeds the effect is exponential and the trim isn't enough to prevent the nosing up of the plane...
Again it is more likely the thrust angle of the engine... Most design's wings provide lift that will "pick up" the nose of the plane instead of lifting the whole plane... a bit of downthrust couteracts the "over-lift"...
Kindof like 2 guys pulling a sign up with 2 ropes on each end over pullies... If one guy is pulling with more force his end will rise before the other, but get the forces equal and the sign will rise level... Make any sense?
Originally posted by jpeters
My plane is a little tail heavy and wants to climb when increasing the throttle. I have to trim in some down elevator. If i shim out the motor do i shim the top or bottom. If i shim out the top is that called down thrust because it will cause the nose to push down or am i backwards and its called up thrust because it pushes air up? Anyway what do i do if i do not want the plane to climb when increasing the throttle.