The Kadet Senior will fly well on a 50 sized 4C. OS, Magnum, and Saito all have 4C engines in this range. Put a 12X5 prop on it and have fun! I do beleive you'll have to move some radio gear forward if you get one of these lighter engines.... I flew a Kadet Senior last weekend that had a 46 2C on it and I never went over half throttle...