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Short History Of The Hovercraft

A hovercraft is a vehicle supported on a cushion of air supplied by a powered fan mounted on the craft. Hovercraft SK-5The hovercraft was invented by Christopher Cockerell in 1956. The theory behind one of the most successful inventions of the 20th century, the Hovercraft, was originally tested in 1955 using an empty KiteKat cat food tin inside a coffee tin, an industrial air blower and a pair of kitchen scales. Sir Christopher Cockerell developed the first practical hovercraft designs, these led to the first hovercraft to be produced commercially, the SRN1.



Christopher Cockerell's idea was to build a vehicle that would move over the water's surface, floating on a layer of air. This would reduce friction between the water and vehicle. To test his hypothesis, he put one a smaller can inside a larger can and used a hairdryer to blow air into them. The downward thrust produced was greater when one can was inside the other rather than air just being blown into one can.

Christopher Cockerell - Biography (information provided by NASA)

Christopher Sydney Cockerell was born in 1910. He worked for the Radio Research Company until 1935 and then for the Marconi Wireless Telegraph Company from 1935 until 1951. During the war years, Christopher Cockerell worked with an elite team at Marconi to develop radar, a development which Churchill believed had a significant effect on the outcome of the Second World War, and Cockerell believed to be one of his greatest achievements. While at Marconi, Christopher Cockerell patented 36 of his ideas. Christopher Cockerell was knighted for his achievement in 1969.

Power-to-weight-to-strength - The hull of the hovercraft

The next consideration for a properly functioning hovercraft is the power-to-weight-to-strength ratio, which affects lift, propulsion and handling as well.This deals with the structural strength of the raft to be light enough to be lifted by the air cushion created underneath, yet strong enough to carry the weight of the engine, its passengers or payload. More information can be found on this site http://leisure-hovercraft.com

Air cushion vehicle hull construction is more closely based on aviation rather than marine constructions for the simple reason that aviation hulls are a combination of strength and lightness as opposed to strength as a priority. Although wood and plywood are often used, many hovercraft hull structures are made of aluminum (aluminium) skin, welded or riveted onto an aluminum web or frame. Enclosed spaces are sealed to provide airtight compartments for natural buoyancy.

Problems Associated With Leisure Hovercraft

On the face of it, a hovercraft has a simple principle - simply provide a pressurized cushion of air underneath the hull, contain it with a skirt attached to the periphery of the hull and it will fly. As with most things in life, it's never as easy as all that. There are many things that hovercraft design needs to take into account, both in terms of safety and practicalities. Assuming that we have a good theoretical design and a working prototype machine, what are the practical tests required to ensure correct operation in all conditions?

An air cushioned craft can lift off from two basic types of surface either dry or wet. The thrust power required to lift off from the two are just not the same. In fact, it takes more power to lift a craft from the surface of a river, lake or the sea than it does from dry land, ice or any other solid surface. Lifting off from water is known as 'getting over the hump' and is a particular problem for hovercraft designers. The power to weight ratio is important and unfortunately an engine needs to be designed with extra capacity to give up to 25% more power than needed for normal flight, just to lift off from a wet surface if needed.

A low powered vehicle may have difficulty lifting off from water, but this is generally an inconvenience. Lightening the load a little will ensure lift off and it's not a safety issue unless you happen to be stranded miles out to sea. However, there is one feature that is potentially hazardous and this is called 'Plow-In'. When an ACV is moving at full speed over the sea, or other turbulent water, the surface may not always be flat. On the sea, waves are an important factor for smooth hovercraft flight. Similarly over river rapids, the same principles apply. Actually, the problem on river rapids is probably more acute because rocks may be jutting up or just below the surface of the water.

On the sea, it's common for a wave to rise up and strike the bow of a small boat or hovercraft. A boat will simply bounce over the top of it, but in the case of an ACV this can have disastrous effect. Hovercraft design is crucial - if not designed correctly, the wave will cause the front to dip into the water, which is called 'Plow-In'. The bow plows into the water, raising the stern and coming to a very abrupt stop. This is obviously a major safety concern, as any passengers will be thrown violently into the sea, or come into contact with the craft causing injury.