I don't know about other brands, but Futaba retract servos aren't very powerful. (136G - 70oz) Unless you go with a Quarter scale retract servo and there isn't enough room in the thin F-18 wing. You could use a programmable digital like Hitec so you could set the speed. I think you're going to need a lot of torque on the LE flaps. I saw a real nice F104 crash at the SW Fan Fly several years back, because one of the LE flaps did not retract.