Air-cushion Machine

air-cushion machine, also called ground-effect machine, or hovercraft, any of the machines characterized by movement in which a significant portion of the weight is supported by forces arising from air pressures developed around the craft, as a result of which they hover in close proximity to the Earth’s surface. It is this proximity to the surface that chiefly distinguishes such craft from aircraft, which derive their lift from aerodynamic forces created by movement through the air.

Two main classes of air-cushion vehicles exist: those that generate their own pressure differential irrespective of forward speed; and those, more closely related to true aircraft, that require forward speed before the pressure differential can be generated. The former are classed as aerostatic craft (ACVs); the latter are called aerodynamic ground-effect machines (GEMs).