Ten light hovercraft covering a wide spectrum of craft from the best current (1972) racing designs to older designs approaching obsolescence have been put through a standard series of tests to provide a fund of data for future comparisons, and to test the accuracy of various simple theories in pre¬dicting the characteristics.nThe average craft emerges as being 134 ins. long, 75 ins. wide with a cushion pressure of 13.3 1b/sq. ft, which is 1.5 times the value obtained by dividing the weight by the struc¬tural area. The structural clearance is 6.5 ins, the mean air gap beneath skirt 0.5 ins, and the stiffness in heave 450 lb/in. The stiffness in pitch and roll is a function of the skirt design, the values for finger skirts being about one third of those for bag skirts. The stiffness in roll is about half that in pitch. Petrol engines with maximum outputs of around 10 h.p. are used to provide cushion air, but direct drive systems usually absorb much less than this maximum. The thrust to weight ratio is 0.11, the skirt drag 9 lb., which enables the craft to reach 25 m.p.h. in 300 ft. from a standing start over short grass. At this speed it takes 2.7 sees, to rotate through 180 in yaw, and the noise level is 96 dBA at 7.5 m. The average installed propulsive system power is 16 H.P., but shows a very wide variation from 9 H.P. to 36 H.P., and little direct correlation with performance.
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