ORIGINAL: captinjohn
ORIGINAL: Super08
I would go with the 55 in that airframe. It is a little overpowered, but the 30 will be underpowered and will have weak vertical. It will fly fine as long as you are not into 3D. The 55 will give fantastic vertical but the GP Yak is not the best choice for 3D as the wing loading is a bit on the high side. Their is a good thread on it in the 3D forum.
If it does balance better with the 55cc engine...use it....you can always throttle back to the power of the 30cc engine. Thats the way I look at it. Easy balance means a lot!
Capt,n
Yup that would be my choice. I have the SU-31 with the 55 and it is a rocket. The power of the 30 can't be underestimated though. I have mine on a GP Giant Stick weighing just shy of 14lbs and it surprised everyone at the field including myself with it's performance.