Invented in the 1950s, hovercraft (or ACVs) have recently enjoyed a resurgence among people looking for new and innovative ways of spending their leisure time. Until recently, although large versions have been built and used by the military and certain commercial carriers, it hasn't been cost effective or safe enough to built small personal hovercraft. New materials and designs have made this now possible and we see air cushioned craft being used for racing (very exciting), rescue, survey and also leisure activities.
The fascinating thing about these hovercraft of all sizes is that they don't travel on the ground or on water, but hover above it on a cushion of air pressure. A large craft might hover a foot or so off the ground, and a small personal hovercraft just a few inches. If you want to buy a small hovercraft, it's very important to check the safety features before making the sale. All designs use a propeller mounted underneath the vehicle to direct air down to the ground and also out the back to propel it along, called forward thrust.
Downward thrust, or lift, is provided by the air pressure underneath the craft, which has to be contained within a skirt surrounding, and fastened to, the hull. It isn't possible to contain the air completely however - it needs to leak out from under the skirt around the edges to maintain an even air pressure underneath the hull. The skirt is made from very tough material and in the case of larger craft is very substantial indeed.
The hovercraft is pushed forward by re-directing some air, if there is only one engine, to the rear of the ACV. A large version may need two or several powerful engines to carry a big payload of passengers or equipment. Hinged flaps are mounted in the air flow leaving the rear and can be turned so that air flow is re-directed by the pilot's steering mechanism. As you might imagine, a quick and tight turn is just not possible, but it's true that larger boats and ships cannot turn quickly either.
Hovercraft for leisure purposes also have flaps for steering, but also rely on the pilot's body weight. Most versions have handle bar type steering controls. When the pilot turns the handles, he also leans heavily on the side of the craft in the direction he wants to go.. The combination of the two actions can effect quite a rapid turn and racing ACVs can be quite nimble around tight turns, both on land and water.
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