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Aviation History
1963
1963 - 1093.PDF
Air-Cushion Vehicles FLIGHT International supplement, 28 February 1963 V ' '5fS Tf#v4 /--; suitable ACVs for the Army may continue to be debated" ACVs FOR THE ARMY... rudders at the rear would also assist in control at higher speeds. In this system it should be possible to obtain more continuous propulsion in the required direction of movement, though the craft may move somewhat crabwise. It is emphasized that these ideas are only provisional and that practical research would be required to determine the most suitable methods for overland use. By-pass or ducted-fan jet engines may also prove suitable for propulsion or be necessary as extra power for climbing gradients. Braking and Stopping As explained in Part I, this is easily achieved over water owing to the air "keel" under the craft below the "hump" speed and to the ability to "ditch" the craft in emergency, thereby providing reason able braking. Overland, some thought must clearly be given to these subjects. Several possible methods come to mind. These include wheels, tracks, air bags beneath the craft and telescopic feet or jacks. All are liable to damage if the craft moves against them in the wrong axis. Using the general configuration already suggested, it seems that a suitable system of skids or skis could be incorporated. The primary load bearing skis could be situated in line with and close to the main girders of the craft's "bridge," with subsidiary skis of lighter construction under the long side-edges of the craft (see illus tration). Such skis may have to be retractable and the exact system for their suspension would require research, but they would seem to be located suitably both for braking and resting the craft on the ground. As mentioned previously, the bow could be strengthened to deflect scrub and light obstacles beneath the craft. It should also be designed to link to the ski system so that obstacles are not deflected between the skis and the craft. Stability With craft designed to hover at a maximum — ratio between 0.08 to 0.09 the annular jet requires subsidiary aids to compensate for the relatively deep "air cushion" and the high centre of gravity of the craft above the surface. Additionally, land obstacles may well cause the craft to oscillate, or even worse, temporarily to lose a part of the air cushion. Two systems are normally used to compensate for this—concentric annular jets and vertical stability jets. Both systems split the cushion into sections in order to compensate for any sudden tilts of the craft or temporary loss of a portion of the curtain. BRIDGE MAIN GIRDERS :r • Perhaps the better system for over land use is to split the cushion into sections, so vertical stability jets in addition to the annular jet may be suitable. These should also counter the "cross-flow" conditions which tend to occur under the craft. Increasing Surface Clearance Flexible skirts, flexible jet extensions and side- walls are systems designed to increase the surface clearance of the main base of the craft. For ACVs with a signifi cant overland role, the skirt is probably preferable to the flexible jet extension, as the latter may tend to become partially blocked or damaged, especially when the craft is resting on the ground (however, practical trials may prove this is not to be so). For the three ACVs proposed, therefore, the flexible skirts are suggested as preferable. On the Assault Craft ACV retractable sidewalls would be attractive, as these would save on lift power and would offer an extra overload capacity under calm sea conditions. They would be retracted both overland and at sea when it was thought that their use was slowing the craft (e.g., over the higher speed bracket) but they might often prove useful at medium speeds to save fuel and thereby increase range. Three Army ACVs: Engines It is difficult to generalize over power units, especially as the three ACVs being considered vary in size. For the largest craft (the Tank Carrier) gas turbine engines may be the most suitable. These have the advantage that they can be significantly overrun to increase power for short periods, e.g., in order to overcome occasional high obstacles. Tank Carrier ACV This craft could have ten lift engines placed round its periphery. Maximum total power is estimated at some 70,000 h.p. with a probable cruise power of some 55,000 h.p. Four propulsion engines are sug gested, located as shown in the artist's impression on page 26. Maximum total propulsion power might be of the order of 28,000 h.p. with a probable cruise power of about 22,000 h.p. SKI5 Schematic arrangement of a system of skids or skis 28
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