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Aviation History
1963
1963 - 1168.PDF
- - ; >~ FLIGHT International supplement, 27 June 1963 Air-Cushion Vehicles "intimate contact with the water." In other words, it tries to replace Mr Cockerell's air curtain by an all-round mechanical wall, which consumes no power. The planing surfaces bear about 10 per cent of gross vehicle weight, and may be divided into left and right halves to provide lateral control. These skis are supposed t«j follow local wave profiles, "without transmitting an ex cessive amount of acceleration." In his opening, Mr Ford comments on the fact that an ACV needs high lift 1.0 NORMALIZED WAVE . DRAG-TO-LIFT RATIO Mdez- l •LENGTH TO BEAM, RATIO;/ /I\\ ft. < .t , PB / L WAVEPRAG BVBBLE LENGTH DENSITY OF FLUID GRAVITATIONAL CONSTANT BUBBLE PRESSURE ATUOSPHER1C PREJ > -VELOCITY ABSOLL'T SURE. ABS ^-—i NORMALIZED VELOCITY OR FROUDE NO. iffZ Wave drag for length .beam ratios from zero two-dimensional) to eight Drag]:[speed for typical CAB; DT is total drag,'comprising wave drag and friction]drag IMO 100 VP 40 100 SPEED Lift: drag plotted against speed for various craft, showing gap said to be filled by CAB vehicles HYDROFOIL „. PR°P Afc ' -=££JE l_.JgLICQPTERS PLANING BOATS 40 60 80 100 120 140 160 KNOTS Enlargement of central portion of previous figure as linear plot, suggesting that the best CAB craft will be very large _i_ 5 10 . VELOCITY - FPS 0.5 1.0 15 FROUDE NO. V/ J~jfV Correlation between theory and experiment for smooth-water towing tests horsepower even with zero forward speed, and that increasing its loading density results in an increase in overall h.p. per pound. Conversely, the CAB lift consumes less than 20 per cent of total power. The resulting high-density craft suffers less sidewall drag, less air drag and less ram intake drag, and is penalized only by a rise in wave drag. Any pressurized region over smooth water generates its own depression and, if it has forward motion, wave. Static ally the CAB resembles a bottomless barge. At low speeds a wave begins to be generated, and the length of the wave increases with vehicle speed. The hump speed is that at which the rear seal rides in the bottom of the wave trough. Further rise in speed results in a decrease in angle of attack and wave drag. The last-named is the most difficult drag term to determine, and the accom panying drag : lift plot is based on work by Dr Nicholas Newman of the David Taylor Model Basin. The next set of curves shows drag plotted against speed for a typical large vehicle. Yet another portrays the CAB plot against other overwater vehicles (GEM = ground-effect machine, an American ACV appellation), and the next diagram is an enlargement of the region between 40 and 160kt. Actual experiments were made at NAEC with models roughly 5ft long and weighing 121b to 501b, and these tow-tank results are repeated here. Mr Ford states that work is now in hand in the fields of configuration, air require ments, stability and control, response to waves, applied loads and motion alleviation. Construction has also begun on a manned research craft, the XR-1, and this is to start operating at about the time this issue appears. Although photographs of XR-1 are not yet available, a clear idea of its design is afforded by the artist's impression below and the two drawings on the facing page. The basic design has been prepared to facilitate the installation of extensive instrumentation and future alterations to skis, side boards and control system which are almost certain to be required in the course of research and development programmes. A simple aircraft-type turbojet has been chosen for propulsion to provide a light and self-contained thrust source; obviously, a water or air propeller would have higher efficiency. Artists impression of XR-1, showing a small plume of spray just behind the front planning surface 97
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