aerodynamic ground-effect machine

An aerodynamic ground-effect machine (GEM) is a vehicle that uses forces from air pressure to hover close to the Earth's surface. Unlike aircraft that use aerodynamic forces from moving through the air, GEMs rely on air pressure generated around the craft.1

There are two main types of air-cushion vehicles:
* Aerostatic craft (ACVs): These generate their own pressure differential regardless of forward speed.1
* Aerodynamic ground-effect machines (GEMs): These require forward speed to create the necessary pressure differential.1

The term "ground-effect machine" is often used synonymously with "hovercraft". This effect is observed when an aircraft flying near the ground experiences an apparent increase in aerodynamic lift, typically up to a distance above the ground equal to its wingspan.23