15 years ago, we used OS 25s in them and put them on trike gear - and flew combat with them! I've flown them with the following: Veco .19; Fox .15 and .19; OS 25FP, 25FSR, 32, and 40FP. All flew well, but be ready to turn as it gets tiny QUICK! My favorite was the Fox .19 without landing gear. The lighter you keep them the better they fly. Best to have a nother person to launch it and help trim it on the maiden flight.