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Aviation History
1963
1963 - 1169.PDF
Air-Cushion Vehicles FLIGHT International supplement, 27 June 1963 THE COCKERELL PAPERS Part Four Ripplecraft Report No 3/58; March 18, 1958 IN THIS BRIEF DOCUMENT Mr Christopher Cockerell presents a series of notes and general comments on the hovercraft project:— The invention consists of an at-present unexploited and, to quote a Saunders-Roe report, "an entirely new concept of lift different from that of existing vehicles," and it could lead to a new sort of vehicle for travelling over the sea at about 100 knots, and in sizes of up to perhaps 500 tons, and which is "steered" and not "flown"; which can hover, and run up a beach, and be loaded and serviced on land without the use of harbours. . . . He then presents arguments in favour of further investigation of the hovercraft principle:— At the moment freight can be trans ported over the oceans, or over the Channel, by displacement craft, at a maximum speed of about 20 knots. It can be stated without error that such craft will never be able to travel at 40 knots. It is probable that underwater craft, with atomic power units, will be developed; but such craft must have a maximum Figs 3, 4 and 5 from Hovercraft Report No 7/58 are reproduced in that order below. The accompanying text appears near the beginning of the abstract starting in column three economic speed, and this is certainly less than 50 knots. Planing craft, hydrofoil craft and heli copters are, and will remain, incapable of attaining the efficiency required to enable them to be used as freighters; since their efficiency is not, to a first order, a function of size. Aircraft, the efficiency of which in the ultimate is a function of incidence drag and skin resistance the overall drag being inde pendent of size) are capable of carrying small loads over a speed range of, say, 200 to 1,000 m.p.h.—but the strength of materials and other considerations result in a proper maximum size of perhaps 500 tons. There is therefore an unfilled gap in the speed range between about 50 and 200 knots. That is, between those craft which are supported by and travel in or through water, and those craft which are supported by and travel in air. The gap should properly be filled, as it is on land, by a class of vehicle which travels through air, but is supported by the surface of the denser medium. Such a vehicle is a hovercraft, which is supported on a cushion of air, the cushion of air being supported by the denser medium beneath it—lift at zero incidence. More specifically, he suggests the design of a New York or cross-Channel ferry, or a river boat, after suitable development work, would not appear to contain any insuperable or very difficult design problems, and even assuming that there is no development potential, looks very attractive as a stabilized passenger and car ferry. In considering ocean-going hovercraft Cockerell reminds us yet again of the need for a flexible arrangement for the undersurface of such a craft:— The design of an ocean-going hovercraft is not simple, and seems to contain two quite separate and distinct problems. The first is to lift the craft above the surface of the water. This is comparativ ely simple. The second is the problem brought about, not so much by the roughness of the surface over which it must travel, but by the speed at which It travels over this roughness. This would appear to mean that a flexible, sprung arrangement must be used to enable the bottom of the craft to conform to the surface beneath it* It will be seen that by this time, and before the design of the SR.N1 had \\\\\\\\\\\\\\\\\\\\ Fig 6 from Hovercraft Report No 7/58, showing an apparently efficient form of vortex produced by an internal jet commenced, Cockerell was convinced that flexibility was an essential ingredi ent in the hovercraft concept—although, as will be seen from his remarks, he had not succeeded in convincing other people of this fact. Nevertheless the recent news from Westland Aircraft (May 30 issue) shows that they are now of the same view. At the Westland hovercraft presentation at Grosvenor House on April 18, it was said that, in their view, hovercraft without flexible skirting "would remain no more than an interesting idea." If this is a prece dent, then it may well be that the addi tion of a dynamic control system— which Cockerell has been advocating for some time—may also become common practice, together with the introduction of more complicated flex ible systems. Hovercraft Ltd Report No 7/58, July 4, 1958. This report deals with various meth ods Cockerell investigated in an attempt to improve the efficiency of the hover craft lift idea. These investigations began in October 1956, and centred around the possibility of using the jet air over again, thereby making use of the energy which is thrown away in the exhaust in simple non-recirculatory curtain schemes. Cockerell starts with a discussion of how a vortex flow system can achieve a recirculation of the jet air. He conducted experiments in which the pump inlet extracted air from the vortex, and hence obtained a closed, or forced, system as shown in the accompanying illustra tions (Figs 3, 4 and 5 of the original report). He found that positive cushion pressures (Pc) could be obtained, no matter which way the vortex was arranged to travel. He then experimented with another configuration (Fig 6), obtaining similar results with an "inter nal" jet and noted that very little energy was being imparted to the vortex. Further testing of this nature led to work on multi-jet systems. Fig 9 shows his double-jet rig, which can be recognized as basically the system employed on SR.N1. In the following extract Cocker ell outlines his work on this rig, and * The writer seems to be alone in this view. 98
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