Advantages and Disadvantages

The advantage of an air-cushion vehicle over conventional craft is that it can travel over water faster than most ships.

О u. s. Marines load a Humvee onto a Landing Craft Air Cushioned (LCAC) during a 2006 exercise in North Carolina. Two huge propellers are visible at the rear. The skirt will inflate with a cushion of air supplied by four fans when the craft leaves the shore.

Amphibious ACVs have the added advantage of being able to travel over­land, too, and they can do so faster than most trucks or military vehicles. Amphibious ACVs can cross deserts, swamps, lakes, or ice with equal ease.

At first, ACVs seemed to offer enor­mous potential for public transportation and military use. Problems in their use reduced their commercial value, how­ever. The airscrews were too noisy for ACVs to move around cities. At sea, ACVs traveling fast over the ocean put out a lot of spray, and the salt spray damaged the gas turbine engines. The engines also used a lot of fuel, making ACVs expensive to operate. While com­fortable for passengers in calm water, even big ACVs could not cope well with rough seas. These disadvantages caused the early optimism about them to fade.

The military in Britain and the United States experimented with ACVs as amphibious assault and patrol craft. The U. S. Marine Corps and U. S. Navy use an ACV designed in the 1980s as a landing craft (a vessel used for taking troops and equipment to shore). The Landing Craft Air Cushioned (LCAC) is carried inside a large naval ship. Offloaded from the ship, the LCAC can move inshore and up a beach to land troops and supplies. The LCAC has four engines (two for propulsion, two for lift) and four fans; its top speed is about 45 miles per hour (72 kilometers per hour).

While some ACVs are used in public and private transportation, the ACV has not yet developed into the widespread system that its inventors expected. The air-cushion principle has been tried in other forms, however. High-speed hovertrains have been tested for railroad use. Enthusiasts and model makers enjoy building small ACVs as a hobby.

RAM WINGS

An interesting vehicle that uses the ground-effect principle, rather like flying boats did in the 1920s, is the ram-winged craft. It looks like an airplane, but it never takes off. Instead of flying, it skims over the surface. The Japanese and the Russians have built ram-winged machines, which are good at travel­ing over lakes and icy terrain.

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SEE ALSO:

• Aircraft, Military • Flying Boat and Seaplane • Lift and Drag • Pressure

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