ORIGINAL: mjfrederick
If you put a shim in to point the engine up, it will exacerbate the problem. Right now you already have negative wing incidence in relation to the thrust line. Shimming the engine as you have shown will increase the negative incidence, requiring an even more nose-high attitude to maintain level flight. The reason you're getting porpoising right now is because that nose-high attitude, while allowing the wing to produce lift, is stalling the tail, causing it to drop. Then you have to add down elevator to unstall the tail, then the wing stalls, causing you to pull up, stalling the tail. Like I said, you need to adjust the incidence of the wing. Your engine is already mounted at an angle that will make the fuselage look level during level flight, the problem is that the wing is not in a position to produce lift at that attitude. Remember, the ONLY way for a symmetrical airfoil to produce lift is for it to have a positive incidence in relation to the thrust line. You can test the incidence relative to a level fuselage, but that really has absoluteley no bearing on whether or not the airplane will fly.
The shim is to actually make the thrust line level and not up. Looking at the second set of pictures [link=http://www.rcuniverse.com/forum/fb.asp?m=6070018](previous post)[/link]you can clearly see the engine pointing downward in the first and level in the second where I added a folded piece of paper to eye ball it. The first picture I posted was not lined up properly and the plane was not level on the bench so it give the appearance of negative wing incidence. Additionally, the plane flies ok at low speeds it is when you throttle it up that the crazy characteristist start. As one test a pilot inverted the plane and increased throttle the plane immediatly did an outside loop all by itself.
Sneasle: I actually went back when we had the placement of the engine discussion the first time and raised the position of the engine so it is higher up then center of the plane. [link=http://www.rcuniverse.com/forum/fb.asp?m=5791124](previous post)[/link]