 The edge of the aileron directs air flow from the underside of the wing to the upper surface of the aileron, thus creating a lifting force added to the lift of the wing.This reduces the needed deflection of the aileron.Both the Canadian Fleet Model 2 biplane of 1930 and the 1938 popular US Piper J-3 Cub monoplane possessed Frise ailerons as designed and helped introduce them to a wide audience.