WIG AirflowWing-in-Ground Effect

A ground effect vehicle (also known as a Wing-In-Ground Vehicle or WIG) is a machine that uses aerofoils or other horizontal plane surfaces to lift it from ground or water by compressing the air between the wing's lower surface and the ground or water, but not sufficiently to enter free flight.  As long as the gap between the wing and ground or water is less than the wingspan, three benefits result:

  1. The air is compressed more than it would be for an aerofoil in free flight, as the wing's lower surface and ground/water form a convergent nozzleWIG No Vortices
  2. The ground/water surface keeps the airflow level behind the trailing edge, reducing induced drag
  3. The ground/water surface blocks the generation of wingtip vorticies, increasing the amount of lift

The cumulative effect of these three, is typically a 40% increase in lift to drag ratio, making them more environmentally-friendly, cost effective and fuel efficient than a similar aircraft in free flight.

Pitch control is provided either by a high-position elevator tail or less frequently, canards.

A ground effect vehicle has a hull that either aquaplanes on water or rides on an air cushion, depending upon the design.  The latter is called a "Hoverwing", if which there are two versions; one uses an air feed between catamaran hulls and the other uses a skirted hovercraft with wings attached.

The International Maritime Organization classified larger ground effect vehicles thus:

  • Type A: Operation only in ground effect
  • Type B: A craft that can temporarily increase its altitude to a limited height outside the influence of ground effect but not exceeding 150 m above the surface
  • Type C: A craft which is certified for operation outside of ground effect and exceeding 150 m above the surface.

You can usually identify a Type B or C craft from a Type A by the position of the lift wings.  Types B and C usually have the lift wings positioned further back, like a conventional aircraft, whilst a Type A will have the lift wings further forward.  This is because a Types B & C need to be stable in free flight, which is normally achieved by having the centre of lift slightly behind the centre of gravity and the tail pushing downwards to keep the nose up.  Type A craft have the centre of lift slightly forward of the centre of gravity and the tail providing positive lift.  This maximises lift to drag ratio as all surfaces are working together to lift and provides an inbuilt deterrent to go into free flight as the tail causes the nose to lower with increasing speed.

Background information on ground effect vehicles can be found typically in the public domain at sites such as http://en.wikipedia.org/wiki/Ground_effect_vehicle.