I recently built a spad combat plane from SPADtothebone.com. It is the classic dogfighter. I got it to fly very well (trim wise/cg wise) but when i try to pull back on the elivator hard, the plane wobbles up and down. it can do a roll very well but it loops poorly. It gets to the top of the loop vary wobely and then it stalls or flips over. also when i do a sharp banked turn it wobbels to. any time i give alot of elevator input. I just can't figure it out. I'm running a GMS .25 running a 8/6 at 13,000 RPM and a 9/4 at 15,000 RPM. I think the tail (corrigated plastic) starts to wobble becouse it is week. Could it be the controle rod bending? i just can't figure it out.
any insight would be great
Thanks
-Matt

Your problem is too much elevator travel..........take it down a notch on the control horn, or if you have a computer radio.........dial it down..fly it...........pull full elevator......if it snaps out............dial out a little more! A simple fix.

The wooble part is your stab..........cut some height off the top...........start with an inch..problem solved!!

You can thank me later

You might find that a bigger stab will allow you to loop tighter though. Maybe lower the top of the stab but add area chord-wise. Of course the stab being on top of the square fuse means that at a high angle of attack, it can get in to the wash of the fuse and there's not much you can do about that with that design.

You might try moving your CG back.

r

fwiw, I actually don't think your stab is too tall. Mine are huge, and they do flex a bit, but they don't cause that kind of rocking. If you're concerned, put a single bamboo skewer down the flutes. I assume you ran the flutes more or less veritcally? Instead, the rocking is more likely just caused by the near-stall condition and the turbulance. Making the stab taller might actually fix it by getting more stab area up in to clean air. You might also try a sub-fin.

I agree with playing with the CG, btw.

Those coroplast planes fly.....but they are pretty heavy compared to a plane built with wood or foam. You gotta keep the speed up, and too much elevator travel will stall the plane. What is this planes' max climbing angle that it can maintain?

not sure, I had a meat with it and had three mid airs and on the third on it went streight in and kaboom! i could only save the radiostuff. Now i have a Lainar Slasher, it is much better than a cloro plane