I used a YS91FZ. Plenty of power for me. After I learned to land the plane reasonably smooth, no problems with the retract gear. I had fun with the plane and flew it about six months before moving on to a GP Giles 202 (1/4 scale). I like the Giles better, but the Chipmunk was a nice plane, well built. My only real problem with the plane was with the elevator which has a counter balance. Over time it would warp a bit at the joint where the counter balance meets the main part of the elevator, so that one side of the elevator would always be different from the other. I would try to get them both the same with a heat gun, but after a day in the sun, the problem would reappear. I'm not sure this made a big difference in flight but it bugged me. All the stickers look great in the beginning but as the fuel causes the edges and corners to loosen, can become pretty ragged over time too.