I'm using the OS 70 4-stroke. You will deffinately be able to take off in 20 feet on pavement. I would say 10 feet with 3/4 throttle, maybe less with flaps and also depending on CG. With full flaps and 3/4 throttle im off in less than 10 feet on grass. I have the CG a little far back though. about 3.5 inches from leading edge.