Hovercraft as we know them today started life as an experimental design to reduce the drag that was placed on boats & ships as they ploughed through the water. The first recorded design for an air cushion vehicle was put forward by Swedish designer and philosopher, Emmanual Swedenborg in 1716. The craft resembled an upturned dinghy with a cockpit in the center. Apertures on either side of this allowed the operator to raise or lower a pair of oar-like air scoops, which on the downward strokes would force compressed air beneath the hull, thus raising it above the surface. The project was short-lived and it was never built, for Swedenborg soon realized that to operate such a machine required a source of energy far greater than that which could be supplied by a single human occupant.
In the mid 1870s, Sir John Thornycroft built a number of model craft to check the 'air cushion' effects and even filed patents involving air lubricated hulls. But also he failed on the still missing HP to push enough air under his craft. From this time on both American and European engineers continued work on the problems of designing a practical craft. Not until the early 20th century was a hovercraft practically possible, because only the internal combustion engine had the very high power to weight ratio suitable for hover flight.
In the mid 1950s Christopher Cockerell (later Sir Christopher), a brilliant British radio engineer and French engineer Jean Bertin, worked along similar lines of research, although they used different approaches to the problem of maintaining the air cushion. Cockerell, while running a small boatyard on the Norfolk Broads in the early 1950's, began by exploring the use of air lubrication to reduce hydrodynamic drag, employing first a punt, then a 20 knot ex-Naval launch as a test craft. The limitation of this approach quickly became apparent, and before long he was fired with a far more ambitious idea, one in which a thin layer of lubricating air gave way to a deep air cushion which would raise the craft above the surface, enabling it not only to clear small waves, but also to make the transition from water to land and back again.
To check his own theory Cockerell used little more than a couple of tins ( tin-cans ), a blower and a pair of scales. By inserting a cat food tin into a coffee tin, and blowing a jet of air through the gap between the walls of the inner and outer tins, he demonstrated the possibility of a machine that could one day travel on a cushion of air. Aimed at the scales, the blower's jet pressure alone was 1lb (0.45kg). The jet coming out of the tin assembly when brought near the scales gave 3lb (1.36kg).
Unlike earlier plenum-type air cushion vehicles, in which air was simply forced by a fan into a larger
chamber beneath the vehicle and allowed to escape, Cockerell's concept was that air would be taken in through a large fan and separated, a percentage being directed to the cushion via a system of slots around the underside perimeter of the craft, with the nozzle aimed downwards and inwards to form a continuous air curtain. This would create a jet of high pressure air that would move under the hull and be retained to a certain extent by the jet line that formed the curtain effect, the balance of the air being ejected through ports at the rear of the craft for propulsion. It was this idea, an air-flow system, that was the key to progress.
1956 / 1957
Christopher Cockerell had a neighboring boat builder produce a working model hovercraft. His idea worked very well in model form, but as was later found, considerable power was required to maintain the cushion, and also the hard structure clearance was not ideal.
It was the duty of anyone who thought an invention had any military value to contact the Service ministries and give them first refusal. Accordingly, the model hovercraft flew over many Whitehall carpets in front of various government experts. It was promptly taken out of it's inventor's hands and put on the secret list where it languished for over a year, no-one having any idea what to do with it. News gradually filtered in from abroad of similar projects, particularly that of a Swiss engineer, and Britain seemed to be in danger of losing the lead so far held. A member of the Ministry of Supply staff, Mr R A Shaw then took a step which was to have important consequences, by authorizing a small contract to the aircraft company Saunders Roe to check the design of the vehicle.
The Saunders Roe report was favorable and Cockerell gained permission to approach the National Research and Development Corporation (NRDC) to see if they might be prepared to give the hovercraft backing if the project could be freed from the secret list. This Corporation was financed by loans from the British Board of Trade to develop and exploit (where the public interest is involved) British inventions to the manufacturing stage.
Cockerell took a film of the model performing various maneuvers to show the NRDC in April. The next morning they made their offer; they were prepared to put up £1,000 immediately for securing Cockerell's patent rights. With the eventual object of forming a British Hovercraft industry, NRDC ordered an experimental craft, the SR.N1, from Saunders Roe (Aviation) in the autumn after having eventually got the craft off the secret list. Hovercraft development for civilian use could now go ahead as its value for military purposes had not yet been proven.
Saunders Roe threw themselves in to the project with great enthusiasm, with the result that the craft was completed two months ahead of schedule, only eight months from starting work. The Cockerell designed research vessel Saunders Roe Nautical One (SR.N1) appeared in May at East Cowes, Isle of Wight - the first flight taking place on 11th June. The press were present in force and watched with astonishment as the model craft was demonstrated to them on a lawn and over a small 'obstacle course'. It was then the turn of the full-sized craft to demonstrate its capabilities, and this was carried out on the concrete slipway. It was obvious that this was not going to be enough though, so the craft was then towed out in to the East Cowes yacht basin by a launch; a nervous time for its engineers as the craft had not taken to water before. All went well though and that craft performed flawlessly, having photographs taken against the Queen Mary which was passing at the time. This first skirtless craft could operate only in calm seas up to 1½ft in height and negotiate obstacles of 6 to 9 inches.
It was 50 years to the day that Louis Bleriot made the first crossing of the Dover Strait by airplane. Although the SR.N1 was the first hovercraft to make the trip successfully, it was plagued with slow performance and the inability to traverse even very small waves easily with a hover height of only 23cm. At first it had seemed as if the peripheral jet would provide sufficient clearance height to allow a medium size craft to negotiate coastal waters, at least, without employing more than one half or one quarter of the power required by a conventional aircraft or helicopter of similar capacity. But in practice, the clearance height was only one twentieth or one thirtieth of its beam. This meant that craft 40ft wide and 80ft long would have a clearance between the base of their hard structure and the surface beneath of only 1 to 2 ft. Had this situation continued, the air-cushion vehicle would not have advanced beyond the stage of an interesting aerodynamic phenomenon, but with very limited practical application.
At the same time the US pioneer Dr. Bertelsmann developed his kind of Hovercraft with the intend to use it for patient visit in his vincent - as both gentleman were working on the same kind of project - they encountered the same kind of obstacles and development of the Hovercraft needed a better solution for ground clearance.
Further work by another inventor, C H Latimer-Needham, on the flexible skirt produced the breakthrough required to enable the craft to maintain a deep enough air cushion for the negotiation of waves and obstacles. After reading about Cockerell's experiments, he thought about the size of the waves that these craft would likely encounter in the English Channel and the Atlantic, and was convinced that this clearly called for some form of flexible skirt to contain the air cushion and enable vessels to traverse significantly rougher surfaces. On contact with the obstacle, the skirt would tend to collapse, but by reducing the peripheral diameter at the base, either by built-in taper or curvature, there would be a downward component of force tending to keep the skirt extended.
1960 / 1961
In October 1961, Latimer-Needham sold his skirt patents to Westland, the parent company of Saunders Roe Ltd, which built the SR.N1. The earliest Westland skirts were simply extensions of the inner and outer edges of the peripheral air ducts at the base of the hard structure, made in two sheets of rubberized fabric and feeding air in to the cushion through the gap that separated the skirts at the hemline. Air from the lift fan simply entered between the two walls of the skirt, which then inflated, and was discharged in to the cushion at its base. As the skirt concept was developed, so easily replaceable 'fingers' or loops of material were fastened at the hemline. to reduce water drag and take the wear.
The introduction of the skirt was a vital engineering breakthrough. It meant that the total depth of the air cushion beneath the solid structure was now equal to the depth of the skirt, plus the daylight clearance or hover gap between the skirt hemline. and the ground. Engineers at Westland soon ascertained that, for a given power, the obstacle clearance height was ten times greater. Apart from being subjected to very considerable wear and tear, particularly at high speed over water, it was felt that it would offer few operational problems. It would deflect on coming in to contact with waves, rocks and jetties, and since afterwards it would return promptly to its normal inflated shape, air leakage would be minimal.
The SR.N1 was now fitted with a Rolls Royce Viper jet engine for forward propulsion, and now made 50kt with ease instead of it's earlier piston-engined maximum of 35kt. With a 4ft skirt fitted around the perimeter of the craft, the craft could cope with 6 to 7ft waves, cross marshland with gullies up to 4ft deep and traverse obstacles up to 3ft 6in high. Moreover, the craft was now operating at twice its original weight, with no increase in lift power. With this new configuration, hovercraft developers around the world took note and high performance craft started to appear.
The craft was gradually modified over time both in hull shape and by the addition of a propulsion air intake 'shed' as well as cushion air bleed control ducts. Being of such important historic interest, the SR.N1 is now in the care of the Science Museum in London.
On 20th July, the 12.5 ton, 24 seater, Vickers VA 3 started the world's first experimental passenger hovercraft service between Moreton (on Leasowe Bay in the Wirral) across the Dee estuary to Rhyl in North Wales. Though the service was extremely popular, landing sites, unreliable 400 hp engines and bad weather made it an inauspicious start. 23 of the 59 operational days were canceled, almost ending with the craft being dashed to pieces against the Rhyl seawall when it broke free from its moorings during a storm. The skirtless VA 3 only had a hover height of 20 cm. This experimental two month service was operated by British United Airways.
A passenger service was started from Eastney, Portsmouth to Ryde on weekday mornings from 11th to 24th August using the larger and more robust 48 seat SR.N2 craft. This was operated by Southdown Motor Services and Westland Aircraft, who took over from Saunders Roe in 1959. The continued development of skirts (in which to trap an air cushion beneath the craft) enabled the potential of hovercraft to be exploited commercially.
The 27 ton SR.N2 was operated on an experimental service across the Bristol Channel between
Weston-super-Mare and Penarth, South Wales, by P & A Campbell from 23 July until 30 August. The same year, Westland laid down a production line at its East Cowes factory to produce the SR.N5 and SR.N6 craft which had been designed. from here on also the military got more and more interested in the use and development of Hovercraft.
The US military took several Hovercraft to vietnam - used it extremely successful and developed during 1970's the LCAC which with a weight of 100 tons and 16.000 HP are at current time the major craft in size and capacity.
Till Russia build the Zubr Class – World’s Largest Military Hovercraft currently in service.
Since you had so much patience and read this file till all to the end - here a small treat - Hovercraft history from National Geographies ...enjoy :
Related external Links