I've flown the 1/4 scale G.P. Spacewalker for the last 3 yrs with an Y/S 91 A/C. I turn a 16- 6 APC prop aprox. 8400rpm. I also use 15% Cool Power. This gives the plane a lot of authority in the air. We have members in my club that use Saitos, Thundertigers and OS 91's that really don't compare. Also with my Y/S , I was able to put my battery pack on the CG and I added NOOOO lead to this plane to get it to balance. I love this plane....It's my every day flyer.........Mike