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Aviation History
1963
1963 - 2273.PDF
Air-Cushi»n Vehicles FLIGHT International supplement, 22 August 1963 is practically completed, and it should begin to operate this summer. Its design is based upon extensive tunnel testing, in the course of which a lift/drag ratio of 24 has been recorded. This compares with 18 for a modern jet airliner and from two to eight for conventional ACVs, say the authors of the paper mentioned. Moreover, they assert that this value of 24 "should be capable of improvement." If determinations of stability, control and Reynolds number with the manned test craft prove satisfactory, the next stage will be the construction of an un furnished, instrumented example of the from each of the two pairs of lift engines are coupled to a mixed-flow fan on the centreline, both fans discharging into a common plenum space. This is said to enable the craft to run with either fan shut down, there being no mechanical connection between front and rear fans. Deflection vanes in the side jets provide control for braking and yaw, supple mented by the two propellers (and, apparently, rudders and an elevator). In addition, the big central fin is to pro vide "a side force for turning" at high speeds. Structure is expected to cost $5 to $10 per lb (presumably in a production craft), and will be partly of metal and partly glass-fibre. High-strength alu minium alloy in standard forms will be used for primary structure, with corro sion-resistant aluminium alloy for cer tain areas. Glass-fibre will be used in secondary areas, especially those with compound curvature. This big and ambitious vehicle I regarded as being of "the minimum economical size"; and the considerable calculated reserve of power is expected to lead to future growth in terms of payload. We shall watch the progress of the MARAD/VRC programme with interest. Fig 1 The basic concept of the surface-effect ship rests upon the airflow over an aerodynamic lifting body operat ing in ground effect. In the left-hand illustration the streamlines indicate a reduced pressure above the body (and around the convex sides) and uniform increased pressure over the entire undersurface. In the right-hand sketch the channel-flow lift system is depicted applied to a vehicle with side air curtains AIR flow r|(U> CHANHU FLOW UFT 5I5TEM ! t t ^^J-^^tMf^y CHANNEL. FLOW HtCM MKVHNK definitive 200,0001b ship. The latter is envisaged as a commercial (or military) transport vehicle for overwater opera tion. Most of its characteristics are tabulated in the data, but some narrative amplification of the design is of value. The most noteworthy feature of the full-scale craft will be a system of flexible side jet nozzles capable of auto matically adjusting their height so that they should just clear the water surface. How this may be achieved at speeds greater than lOOkt is not explained— indeed Rethorst and Potter admit that the system "still requires considerable further development"—but it is to function without any external power, merely by virtue of "the reaction pres sure caused by proximity of the jet nozzles to the surface." At the same time the main belly of the ship is to ride as high as possible, for lift is "only slightly dependent on the height of the body above the surface." The flexible nozzles will meanwhile keep adjusting their height so that they just clear the water, and are to be stressed to pass through the top of the occa sional wave. Lift power is twice the propulsion power, and the free-turbine outputs 26 MARAD/VRC Surface-Effect Ship Type Research prototype capable of eventual conversion to transport use, with design payload of 150 passen gers or 80,0001b cargo over a range of about 500 miles. Dimensions Very approximate overall length and width, 180ft and 80ft, respectively. Weights Gross weight, 200,0001b; max payload, 80,0001b (four 8ft x 8ft x 20ft containers); max fuel, 20,0001b; by inference, basic equipped weight, about 100,0001b. Lift system Fore and aft mixed-flow fans, not coupled together, each driven by two GE T64 turbines each rated continuously at 2,270 s.h.p.; total lift power, 9,080 s.h.p. Propulsion system Two variable-pitch propellers, each driven by a 2,270 s.h.p. T64, supplemented by variable rearwards deflection of the side jets. Performance (estimated) Max speed, I50kt; operating speed for best performance, 100 to I20kt; nominal operating height over rough water, 4ft to the jet nozzles and 9ft clear under the belly, using 9,350 total s.h.p- to cruise at I02kt; operating height over calm water, Ift (6ft under the belly), requiring only 3,700 total s.h.p.; with development, the suspension system will have a full vertical extension of 6ft, so that the body will ride 12ft above the water with a nozzle clearance of only Ift. Fig 2 Most previous ACVs or GEMs) have been supported almost entirely by their air cushions, and this has limited their speed to about 80kt. In contrast, a low-aspect-ratio wing in ground effect has no immediate limit to speed, but poses stability and control problems. VRC believe they have solved these problems, and are about to demonstrate this with a manned vehicle, shown in cutaway form below, Its superficial similarity to the developed Cushioncraft CC-2, to be used by the RAE in aerodynamic-lift experiments, is noteworthy
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