Air cushion vehicle (ACV) is an amphibious (land and water) craft that travels on a layer of compressed air just above any kind of surface. The compressed air serves as an invisible cushion that eliminates almost all friction between the vehicle and the surface. ACV’s, which are also known as hovercraft, can carry passengers, vehicles, and freight. Some ACV’s can travel as fast as 80 miles (130 kilometers) per hour.
How an ACV works.
An air cushion vehicle has one or more fans that suck air into the craft. The fans force the air underneath the vehicle, creating an air cushion between the ACV and the surface. ACV’s are sometimes called ground effect machines because they use the surface to help trap the air.
A flexible rubberized skirt surrounds the lower edge of most ACV’s. It fills with air forced in by the fans. The skirt enables the vehicle to travel over such rough obstacles as rocks and waves. Some ACV’s have skirts only across the bow and stern. Rigid sidehulls run along the length of the craft. Such ACV’s are called surface effect ships (SES’s). They can be used only in water.
Gas turbines or lightweight diesel engines provide the power for the fans, and propellers drive the ACV forward. Most ACV’s have small doors called puff ports and either rudders or propellers for steering. These three devices enable the vehicle to travel backward, forward, or sideways, or to hover or turn.
History.
ACV principles were recognized as early as the mid-1800’s, but the technology did not exist for building a practical model. In the early 1900’s, a limited number were built. The Austrian Navy demonstrated one in 1916. In the mid-1950’s, Christopher Cockerell, an English inventor, improved the basic design. In the early 1960’s, Japan, the Soviet Union, the United Kingdom, the United States, and other countries all tested ACV’s.
In the late 1960’s, the U.S. Navy and Army began to use ACV’s in the Vietnam War for patrol duty and rescue missions. In 1968, the British began to use ACV’s to carry passengers and cars across the English Channel. Development of hoverbarges—that is, ACV’s that are pulled or pushed by another vehicle—began in the 1960’s. In 1972, Canadian researchers discovered that ACV’s could be used to break ice on waterways.
Today, manufacturers produce a number of models that vary in size, speed, and power. Modern ACV’s accomplish many tasks. However, most ACV’s are used for military missions. Russia and the United States are the world’s largest users of the craft.
In the late 1950’s, Jean Bertin, a French engineer, invented a special train called a tracked air cushion vehicle (TACV) or air train. This train ran only on land, and it required special tracks. It did not actually touch the tracks but used them as a guide. The train had a linear electric motor, which included electromagnets in the underside of the vehicle (see Linear electric motor). The tracked air cushion vehicle was powered by magnetic forces between the track and the electromagnets. It could also be powered by an auxiliary jet engine.
A vehicle called a magnetic levitation train, or maglev train, resembles the TACV. But a maglev train relies on a magnetic force between the vehicle and the guide rail—rather than on a cushion of compressed air—to hold the vehicle above the track.
