It is not generally realised that the ground effect principle on which the air cushion vehicle is based was first expounded by a Scandinavian scientist some hundred years before Sir George Cayley grasped the basic principles of flight and two hundred and fifty years before the hovercraft went into commercial service. The basic principle of the air cushion vehicle is extremely simple, but, as in many branches of engineering, simplicity of principle and ease of achievement do not go hand in hand!

How does a hovercraft hover? Let us take a vehicle with a weight of 1000 lb (454 kg) and a flat undersurface of 100 sq ft (9m2) in area. If we increase the air pressure under the machine by 10 lb/sq ft (478 N/m2), the total reaction pushing upward from the undersurface of the machine will be 10 x 100 = 1 000 lb (454 kg). This, being equal to the weight of the machine, will cause it to leave the ground.