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Aviation History
1963
1963 - 1144.PDF
FLIGHT International supplement, 23 May 1963 Air-Cushion Vehicles obstacle, such as this 3ft 6in rock groyne, which is being traversed at 30kt. Skirt abrasion under these conditions is virtually nil. Indeed, after 430 hours of operation, wear of the rubberized fabric is negligible. "When operating over water without skirts, severe impacts occur when the wave height becomes much greater than the day light clearance. When skirts are fitted the over-wave performance is increased by an amount almost equal to the length of the skirts. "Thoraey Island, an RAF airfield about 30 miles from Cowes, is surrounded by saltings with gullies up to 4ft deep and 20ft wide. Whilst manoeuvring over these on a low-speed approach to the airfield, the machine appeared to pitch and roll in an exaggerated manner, but the cushioning effect of the skirts made the ride relatively comfortable. To make the transitions from the airfield to the saltings and back again, SR.N1 had to negotiate a 2ft wall and a 6ft grass bank. Throughout these manoeuvres the solid structure of the machine never came into contact with the ground. "In a recent air crash at night at Thorney Island, rescuers took nearly three hours to reach the scene of the accident, and the crew were lost in the soft mud around the carry up to 20 people, compared with only two that were carried on SR.N1—an increase in payload almost ten times that of SR.N1. Model studies of this vehicle have been completed, and detailed engineering design is committed. SR.N5 incorporates the fan and propulsion system which has been developed on SR.N2. Although SR.N5 is designed to have a quarter of the payload and only a quarter of the power of SR.N2, its performance capabilities and its direct operating costs are closely related to those of SR.N2. "Four-foot skirts are by no means the practical limit of development. This is a model of Westland's new project for a 170 ton ferry—SR.N4. This craft has 8ft skirts and is operating under conditions simulat ing a speed of 70kt and 7ft waves. This is a sea state that is only exceeded in the English Channel for approximately 5 per cent of the year. The 8ft skirts allow the model SR.N4 to pass easily over a 20ft gully and a sheer drop of 13ft, which dwarfs the model motor cars. "To sum up, the skirts on a hovercraft are analagous to the pneumatic tyres on a motor car, and have comparable durability. Without tyres a car would be a totally im practicable vehicle. Without the Westland important breakthrough by the develop ment and successful engineering of a specially designed flexible structure between the craft and the surface over which it travels. This device, known as a 'skirt,' will give a significant increase to the hovercraft's capability to operate over solid obstacles, ditches and rough seas. As a result Westland ACVs will now have a considerable amphibious performance without an appropriate increase in power, or size. "This outstanding advantage can be applied to smaller craft to operate over terrain impassable to any known wheeled or tracked vehicles of similar capacity. The latest Westland ACV, the SR.N5, has an all-up weight of only seven tons, yet with its long skirts it will have a per formance over obstacles and waves better than a 40 ton craft designed without skirts. For the future, this Westland development means that it is possible for ocean crossings to be made with a 200 ton craft fitted with 10ft-15ft skirts, whereas a year ago the minimum size hovercraft for this performance was km. r Eric Mensforth Mr E. C. Wheeldon Mr D. C. Collins Mr L. Boddington Mr M. H. C. Gordon Mr R. Stanton Jones saltings. SR.N1 simulated a rescue opera tion at the scene of the incident, which was about a mile from the airfield. It took only 3min to reach the area of the crash, and the craft was back at the control tower after a total elapsed time of 7min. "Further evidence of the marsh-crossing capabilities of SR.N1 was obtained over the saltings at the mouth of the Beaulieu River in Hampshire, where there is a large area of this marshy ground. These low-angle aerial shots give a very good impression of the action of the skirt as the machine crosses the saltings and gullies without any loss of height, at speeds up to 40kt. "These experiments with 4ft skirts have been so successful that they have thrown a completely new light on the practicability of all air-cushion vehicles, and of small machines in particular. This has led West- land directly to the development of a new machine called the SR.N5. This is not just another research or demonstration vehicle, but a practical design for a small, really high performance hovercraft with a very wide range of applications. SR.N5 is 35ft long, and has an all-up weight of seven tons, which is about the same as the present SR.N1. With a payload of two tons SR.N5 can skirts the hovercraft could not have ad vanced beyond the stage of an interesting idea with very limited practical application. Skirt development has given a seven-ton hovercraft like the SR.N5 the same capa bility as a 40 ton vehicle without skirts. At the other end of the scale, instead of needing a 1,000 ton hovercraft for ocean-going operations, Westland believes that this can be achieved with a 200 ton vehicle fitted with 10ft or even 15ft skirts." The company's thinking and planning were outlined in a statement which we print in full. It ran:— "Westland has been working inten sively on the development of hovercraft, and one of the more important problems has been the improvement of the over land obstacle and the over-water wave performance. As recently as a year ago it was considered that improved obstacle performance could only be achieved by larger craft, since the power required is directly proportional to the clearance between the craft and the ground datum. "Experiments at the Saunders-Roe Division at Cowes have resulted in an considered to be at least 1,000 tons. "The following range of civil hover craft offered by Westland all feature the flexible skirt:— SR.N2: weight, 27 tons; passengers, up to 70; freight, 8 tons; max cruising speed, 80kt. SR.N2 Mk 2: weight, 37£ tons; passengers, up to 150; freight, 12 tons; max cruis ing speed, 74kt. SR.N5: weight, 7 tons; passengers, up to 20; freight, 2 tons; max cruising speed, 70kt. "The SR.N2 has been operating in 4ft to 6ft seas and an improvement on this performance, extending the amphi bious capabilities both of the SR.N2 and SR.N2 Mk 2, can now be offered. "Westland announces that deliveries of the SR.N2, SR.N2 Mk 2 and SR.N5 can be made by March 1964, or nine months from receipt of orders. To ensure these deliveries Westland is planning and tooling for batch produc tion. The prices for these hovercraft are: SR.N2, £325,700; SR.N2 Mk 2, £450,600; SR.N5, £75,600. "The SR.N2 Mk 2 is a civil version of 73
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