Hovering Closer to Success

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.

Transatlantic? By 1963, British engineers had solved the clearance problem by equipping hovercraft with rubberized canvas skirts several feet long. Although the skirts were strong enough to contain the pressurized air--enabling hovercraft to rise several feet above the ground--they were flexible enough to brush over solid obstacles and high waves. The development of skirts converted the hovercraft from an experimental device into a practical means of transportation. The British Hovercraft Corp. has already built and sold seven-ton, 18-passenger hovercraft and nine-ton, 38-passenger models like those in operation at Expo 67. Both have a 4-ft. clearance. Two larger versions will soon come off the company's Isle of Wight production line: a 40-ton model that will carry eight autos and 160 passengers, and a 165-ton craft that will carry 32 autos and 250 passengers and have skirts long enough for a 12-ft. clearance on land. Two of the 165-tonners will be in regular service across the English Channel by 1968, making their runs at speeds as high as 85 m.p.h. By the end of 1970, the company expects to have developed 300-to 400-ton air-cushion ships that will be capable of operating on the open seas. Inventor Cockerell visualizes a 10,000-ton atomic-powered craft that will cross the Atlantic at high speeds with 2,000 passengers aboard.

Bell Aerosystems, British Hovercraft's licensee in the U.S., has manufactured hovercraft that have been used success fully in an experimental ferry run across San Francisco Bay and as high-speed gunboats to hunt down Viet Cong in the Mekong Delta. It has just sold its first two commercial craft to an Alaska firm that will use them to supply offshore drilling operations. Using the hover principle on land, a French hover train, suspended above a monorail by a thin cushion of air, has already reached speeds of 190 m.p.h.

Esoteric Future. The hover principle has equally good prospects in industry. British Hovercraft is producing hover pallets, air-cushion platforms that can be used to move heavy industrial loads. In a recent British Hovercraft demonstration, for example, a 41-ton machine tool on a hover pallet was easily pushed several feet by two men. By fixing a skirt around a 14-ton oil-storage tank at a military depot and pumping in air, hovercraft technicians were able to move the tank on a cushion of air across a road and a railroad line to a new location. A hover transporter, designed for Britain's Central Electricity Generating Board, has already been used to carry a 155-ton transformer over a bridge that otherwise would have failed under the load: a hover platform built into the transporter suspended the transformer on a cushion of air, reducing its effective weight by about 70 tons.

Engineers foresee even more esoteric uses. They have already designed a hover kiln, in which pottery is suspended over a moving conveyor belt by the hot gases used to bake it. And they are attempting to perfect a hover bed for badly burned patients who would actually lie on a thin film of air, thus avoiding painful contact with the bed sheets and allowing healing on all sides.

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