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Aviation History
1963
1963 - 1126.PDF
FLIGHT International supplement, 25 April 1963 Air-Cushion Vehicles water craft may operate in direct competition with existing ones. A figure (reproduced at the top of page 23 of this journal's February issue and reproduced again on page 56) illustrated a typical vehicle which may be used for regular transport of per sonnel and equipment, over completely unprepared terrain, including soft ground and stretches of water. At first sight, one might consider it an amphi bious type of craft. But, whereas the very high cost of sophisticated craft can be justified for marine ferry services with high utilization factors, overland vehicles are unlikely to achieve such high usage; and, if they are to be successful they must be built at very much lower cost. Furthermore, main tenance facilities are likely to be con siderably less accessible, so that the simplest of designs is called for. The result of these considerations is that simple plenum-chamber designs become very much more attractive; and the simplicity of structure and systems, and associated low capital cost, make such designs economically desirable. As with marine vehicles, flexible elements are fundamental to efficient operation. On the other hand, the types of obstacles encountered are very different. The size of overland obstacles is more predictable, and the larger ones may be avoided. Critical stretches can be tackled at reduced speed. The flexible elements are not required to respond to the very high accelerations which are experienced in high-speed overwater operation, although the wear and tear they en counter on hard ground may be a greater problem. The hypothetical craft referred to has an air propulsion system for water and very soft surfaces. It may also have wheels to give partial support on harder surfaces, and some degree of propulsion, steering and stability. The INDUSTRY SIX TYPES TO THEIR CREDIT Instruments for no fewer than six types of air-cushion vehicle have been supplied by Sangamo Weston Ltd of St Georges Court, 22-26 New Oxford Street, London WC2. These have included resistance-type thermometer bulbs, circular-scale ratiometer indicators, 270°- scale indicators, pressure transmitters, position transmitters, and circular-scale temperature indicators. vast stretches of muskeg in Northern Canada provide a good example of ground over which the ACV may operate but where virtually no competitive vehicles exist. Typical operating data for a vehicle of this type might be: payload, 25 tons; speed, 50kt; obstacle clearance, 5ft; installed horsepower, 3,000; slope-climbing ability, 1 in 6. The Land-Rover Conversion Mr Eggington went on to describe the now-familiar Vickers Land-Rover con version. He said that, for vehicles which spend most of their operating life on metal roads or good tracks, with occasional operation on soft ground, there is a very good case for taking a standard vehicle and adding air-cushion equipment as an extra. Three major advantages are obtained on bumpy ground: (1) the shocks to the suspension, and hence to passengers, are very much reduced by the inherent softness of the air cushion, which in fact becomes part of the suspension system; (2) the reduced bearing-pressure under the wheels them selves means that the soil is but lightly compacted—which, on agricultural land, means considerably reduced damage to germinating crops; and (3) the fact that optimum wheel loading may be selected for all soil conditions, and that such a vehicle may operate in conditions in which its conventional counterpart might become bogged. The speaker went on to describe details of the Land-Rover conversion, a full description of which is given else where in this issue. Going up in size, said Mr Eggington, similar conversions may be made to larger load-carrying vehicles—for ex ample, 3 ton lorries. It is expected that, as the size of the vehicle increases, the porportion of the load-carrying space employed by the cushion-providing equipment will become much smaller. THE VA-3's SPLITTER-PLATE A sizeable component of the Vickeis VA-3 is the duct splitter-plate, which measures 15ft X 12ft. In order to achieve low weight with high strength and great rigidity it has a basic core of furnane-treated Dufaylite structural honeycomb, together with a section of Dufaylite laminated between two skins of 24-gauge alloy sheeting. A U-section made from the same gauge of metal is used for edge filling and the bonding and sealing of core and skins is accom plished with cold-setting epoxy resins. A photograph, provided by the manufacturers — Dufaylite Develop ments Ltd, of Essex Road, Boreham Wood, Herts, England^is reproduced. It is by no means impossible to produce a kit of parts which may be attached to a standard vehicle to convert it to the AC-assisted type. Yet another possibility involves a mobile platform, which may be likened to a large low-loader from the sides of which skirts are suspended, forming a plenum chamber in the usual way. This may be used as a trailer towed by a tractor vehicle carrying the blowing equipment. Such platforms could be designed for the low-speed transport of very heavy loads over unprepared surfaces. Large one-piece items of equipment—which are carried into such places as oil refineries and power stations during construction—might otherwise require expensive roads, the use of which would be confined almost entirely to the construction period. With reasonably flat surfaces, and speeds not exceeding 5 m.p.h.. the air gap under the skirt can be reduced to a fraction of an inch, so that the lifting power require ment can be reduced to a few horsepower per ton. A particularly interesting application is that AC-assistance would enable heavy loads to be taken over bridges which would be unable to support the high bending moments imposed if the same load were applied as a number of point axle-loads. (It seems that at last that hypothetical condition beloved by examiners of student structural engi neers—the moving uniformly distributed load—may now become a practical achievement.) Summing up, the Vickers speaker suggested that the overland ACV future is by no means clear. The case for the ACV in the commercial field depends on one of two things; either removal of the necessity for expensive surface prepar ation, or considerable reduction in the adverse effects on the surface itself. To be concluded
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