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Aviation History
1963
1963 - 2337.PDF
Air-Cushion Vehicles FLIGHT International supplement, 26 December 1963 COGKERELL ON HOVERCRAFT A Valuable Paper Read Last Month in Stockholm One of the principal members of the British delegation to last month's sym posium on air-cushion vehicles organized by two Swedish societies (see "Inter national News" in this issue) was Mr Christopher S. Cockerel], the man who has done more than any other person to turn the ACV into accomplished fact. While in Sweden he received the Thulin Bronze Medal of the Swedish Society of Aeronautics; and he also read the paper which is here abstracted. MANY PEOPLE HAVE IDEAS, but I WOUld say that in order to convert ideas into realities, it is necessary to have a lot of luck, time, facilities, the ability to live on air, and a very patient wife. One must not be born too late, or too early, or in the wrong place; and if the idea has anything to do with marine experts, it is wise to plan to live for a very long time. Now I would like to single out T. J. Kaario of Finland, who started develop ing his ram wing as long ago as 1935, and who I understand is still hard at it. I would also like to mention J. C. M. Frost and his team in Canada for their work on what one might describe as cushion-take-off aircraft. Then there is Melville Beardsley, who I think was the first man in the United States to do work on air-supported vehicles. And then when it comes to practical design, there is Dick Stanton Jones and his team, who have done more than anyone else to thrust the Hovercraft into being. The Ministry of Supply and I first tried to interest Shorts of Belfast; but they turned it down, and so we tried Saunders-Roe, who took it on. This might be regarded as a bit of luck for Dick, but here is the point, and this isn't luck. Given the opportunity, Dick and his team jumped in with both feet, and grasped the problem with both hands. It is usual in giving an introduction to the general principles of Hovercraft to start by talking about lift systems, plenum chambers and annular jets, and then go on to talk about wave-drag, stability, etc, all with respect to per formance over a flat sea. This is not really the problem at all. A Hovercraft is essentially a surface vehicle, and is an attempt to extend the use of land surface vehicles, to achieve operation over soft surfaces such as water, and over unprepared tracks such as a rough sea. It is proposed, therefore, to start with a pictorial representation of the major power components (Fig 1). The first component is body aerodynamic drag, and all that need be said here is that developed Hovercraft are likely to be run true to the water, and somewhat angled to the airstream. Suspension system aerodynamic drag, could proper ly be included as part of the first com ponent—except for that part which is an air clearance, the drag of which is felt in the form of a nose-up incidence drag at speed. The third component represents the hydrodynamic lift resulting from con tact with the surface, and/or displace ment lift, as for example in the case of a sidewall craft. This lift decreases the cushion-power requirement, may slightly increase wave drag, and results in a surface contact drag. The fourth component, body aerodynamic lift, is a material factor at lOOkt, and it decreases both the cushion-power and the wave-drag components. Missing out the fifth component for the moment, induced wave drag has been the subject of a number of papers and is now reasonably well understood. This paper is therefore concerned with the effect of rough water on the Fig 1 Hovercraft power components BODY AERODYNAMIC \ DRAG \ SUSPENSION SYSTEM AERODYNAMIC DRAG ' V////////////////77777fy I AERODYNAMIC — DRAG POWER SURFACE CONTACT \ LIFT \ /////////////A | IODY AERODYNAMIC \ 6 o £^ n CUSHION AIR SUPPLY & MOMENTUM DRAG ,•> mV KTJKZ. „ CUSHION 7777nn numb—— SURFACE CONTACT DRAG POWER HYDRODYNAMIC — DRAG POWER FIG 1 LIFT POWER Pc = 60lb/sqft MOMENTUM DRAG POWER CUSHION AIR SUPPLY POWER Pe-30 FIG 2 -SPEED » K)0 tot Fig 2 Calm water power/speed characteristics (constant air clearance) Fig 3 Calm water lift-power I air-clearance characteristics (constant speed) LIFT POWER FIG 3 ° AIR CLEARANCE - 86
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