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Aviation History
1963
1963 - 1085.PDF
FLIGHT International supplement, 28 February 1963 Air-Cushion Vehicles THE COCKERELL PAPERS . . . be reviewed in this and subsequent articles. The papers are titled and dated as under. Rippiecraft Report No. 1/55—"Hover craft." Hovercraft Ltd Report No. 7/56—"Hover craft Mark II: Recirculation." Rippiecraft Report No. 8/56—"Hover craft: Descriptive Notes." Rippiecraft Report No. 9/56—"Hover craft: Notes on Possible Design of Cross- Channel Ferry." Hovercraft Ltd Report No. 1/57—"Notes on the Design of High-Speed Surface Craft." Hovercraft Ltd—"Letter to Mr Shaw dated November 12, 1957, discussing Deflec tors." Rippiecraft Report No. 12/57—"Notes on Uwe H. von Glahn's Technical Note 3982(22) NACA." Rippiecraft Report No. 13/57—"Note on Possible Hovercraft Development." Rippiecraft Report No. 3/58—"Notes on Hovercraft Project." Report No. 7/58—"Hovercraft: Develop ment Potential." Report No. 8/58 "Ring Vortex Curtains." Hovercraft Report No. 11/58—"Manned Hovercraft: Draft Brief Specification with Notes Attached." HDL Report No. HDL/61/2—"Some Possible Developments in the Hovercraft Field." It should be explained that "Rippie craft" is the name of Cockerell's boat building company, and Hovercraft Ltd (not to be confused with the NRDC subsidiary Hovercraft Development Ltd) his air-cushion vehicle company; also that the italics are our own, as indicating some of the more significant passages. Rippiecraft Report No. 1/55; October 25, 1955. As is now well known, Cockerell began his significant studies by investi gating the "lubrication" of the hulls of displacement craft by the injection of air between the water and the hull. From * Mr Cockerell has provided us with a personal recollection of this period:— "After I had learnt from and found out the shortcomings of "air-lubrication" experi mentally, the first idea I had was fixed side- walls with hinged doors at the ends with air pumped into the centre. The next idea, at about the end of 1954, was fixed sidewalls with water curtains sealing the ends. I stuck here for a bit, because I didn't know enough to be able to work out the probable duct this concept his mind turned to the feasibility of the air-cushion vehicle, to which he gave the name of "hover craft".* It would appear, he said, to be both possible and advantageous to support a weight on air, be it a "boat" over water, or possibly a vehicle over land, or an aeroplane during landing or taking off. The last few words are especially note worthy, for practically nothing has been published of any British work in the field of air-cushion aircraft despite their obvious potential. In contrast, Convair have conducted an extensive company- funded research programme into the same idea, which they call the GETOL (ground-effect take-off and landing). Cockerell roughly calculates cushion pressures for a vehicle like a car (0.171b/sq in) and an MTB (0.681b/sq in), and then turns to the problem of containment. After rejecting the pos sibility of employing thin rubber walls or any other solid material, he asks, the thought then arises, would it be possible to use a "wall" of fast-moving water or air which is pumped down . . . in the form of a thin curtain all round the device ? Here again, Mr Cockerell makes a suggestion which has been followed up only by Hughes in America, for a water- jet curtain. This still appears worthy of some research effort. Simple calculations follow, for a circular device discharging air from around its periphery either directly downwards or directly inwards. These have stood the test of time and are now known (in more elegant non-dimen sional form) as the Chaplin thin-jet theory, evolved by Harvey R. Chaplin of the David Taylor Model Basin in 1957. and other losses and the sort of power that would be required. "Then one Saturday evening 1 thought I would have a look at using air curtains. A simple calculation looked all right on a power basis, and so that Sunday I made up an annular jet using two tins, and found that the air did follow the 'predicted'' path and that there was a 'predicted' gain in lift—very exciting, but with nobody to share it with, very lonely. From my wife, 'There, there, In an attempt to verify the calculated performance, measurements were taken of the height of a simple piston sliding vertically within an open-sided box. Various widths of jet were chosen between 0.125in and 0.22in, with a supply pressure varying from 6in to 17.5in water gauge. In general, the measured performance lay between 10 per cent and 22 per cent below that calculated, but in some cases the correlation was close. Various minor modifications were made to this apparatus, and the basic theory of air-cushion vehicles explored more fully. Cockerell then turns to consider an actual design study of a "hoverboat," using as his basis an MTB weighing 50 tons, with an assumed slot (jet) length of 210ft and an assumed cushion area of 2,000 sq ft. The sub sequent calculations are probably the first in the world for a large ACV with an annular jet curtain. The craft is found to have an installed power of some 7,500 h.p. in order to ride at a height of 3ft. For forward propulsion it is suggested that the air leaving the curtain slot along the sides of the craft be deflected aft to give a forwards thrust component equal to 0.85 of the thrust in the direction of the airstream. It is suggested that the air mass flow and velocity will be increased by employing a forward-facing intake, but it is now appreciated that it is not possible to utilize ram effect in view of the fact that complete momentum drag is always suffered. The report concludes with a discussion of behaviour over waves and of stability about both axes. Cockerell notes that, at speed, the jet is deflected aft not only by the angle set for obtaining thrust but come and have some tea.'' Little did she know the number of letters and reports she would find herself typing—mostly in weekends and evenings—because we were trying to build up Rippiecraft Ltd, and were very short of time and cash. But note that it all happened by lots of little, simple steps. It was just a case of plodding along trying to solve a particular problem which one had set oneself; and, of course, there are still years of work ahead." Model on \est in Lord Somer-leyton's garden at Somerleyton, Lowestoft, in May 1957 20
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