Big problem is, the flap,elevator deflection is proportional to airspeed. As a scenario, drop flap to 15 degrees. take off. as the plane accelerates flap affect starts to lift the plane.Lift off say, to 20 ft. Now to maintain that height, as the plane accelerates you would have to keep adding more down el. because of the added lift with speed. Now throttle back you will have to gradually back off on the up el. till it slows down enough to the point where el. is at neutral. as it slows down more you would have to add up el. to maintain flying speed just before touchdown. When we used maneuvering flaps on controlline yrs. back, rule of thumb was flaps would move 1/3 of el. travel.