When they first hear the roar, visitors at Canada's Expo 67 look skyward, expecting to see a low-flying airplane. Instead, shooting spray from all sides, an ungainly contraption speeds by on the nearby St. Lawrence River, carrying 38 passengers on one of the fair's most popular rides. For most visitors, it is their first glimpse of the hovercraft, a British amphibious vehicle that suspends itself on a cushion of air and skims with equal ease over land, ice or water.
Although hovercraft are still a novelty in North America and in most other parts of the world, they are becoming familiar in Britain, where they work as ferries between coastal resort towns and ply the cross-Channel route between England and France. Experimental military and civilian hovercraft skim along waterways and across marshes in Britain. And the hovercraft principle of using a thin layer of air to move heavy loads is finding increasing applications in British industry and transportation.
Air Curtain. Hovercraft were born in the fertile mind of British Aeronautical Engineer Christopher Cockerell in 1954. Testing his notion in true pioneer-inventor fashion, he attached a hose to the exhaust of an ordinary vacuum cleaner, stuck it through a hole in the top of an open-bottomed tin can, and watched fascinated as the can floated off the floor; the increased air pressure inside the can had pushed against the floor through the open end, lifting the can. Recognizing that the unhindered escape of air from the bottom of the can—and from the bottom of early experimental craft—made it too inefficient and unstable for any practical use, Cockerell then conceived the idea of constructing craft with double walls and blowing air down between them. This, in effect, produced a peripheral curtain of air that slowed the escape of compressed air under the hovering vehicle.
Before long, several British firms had produced working prototypes of the peripheral-air-wall hovercraft, lifted by pressure produced by the air stream from horizontally mounted fans and driven laterally by aircraft-type propellers. Although the ingenious craft could skim almost effortlessly along smooth highways and waterways at automobile speeds, even the most powerful could not rise more than a foot above the sur face; the air curtain could not effectively contain pressurized air above this height. As a result, hovercraft could not operate over choppy seas or rough ground, where they might smash into jutting rocks or wave tops.