Ground-plane influence on airplane wings

The present study discloses a very material ground-plane influence at small incidence and ground gap. The lift is augmented, the drag diminished; the lift-drag may be increased 30 to 40 per cent. Thus a sea gull or a suitably designed monoplane may skim the surface of smooth water with considerably greater economy than it can fly at a few wing depths aloft. But the pitching moment is only slightly affected by the presence of a ground plane.