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Aviation History
1964
1964 - 1940.PDF
FLIGHT International supplement. 25 lune 1964 Air-Cuthion Vehiclas The True Originator? John Isaac Thornycroft—Designer, Patentee, Constructor and Demonstrator of an Air-Cushion Vehicle in the 1870s BY THE EDITOR Sir John Isaac Thornycroft (1843-1928)—a picture taken in 1909 THE STORY which I have to tell is so extraordinary in its circumstances and, I believe, of such historical significance that, unless it can be contradicted, it could bring unqualified acknowledge- • ment of John Isaac Thornycroft as the true originator of the air-cushion vehicle—or "hovercraft" to use the term now popularly accepted. Not only did this gifted Englishman take out a patent on his scheme for a plenum- chamber craft, but he built models of sizeable dimensions, tested them in his tank at Bembridge, Isle of Wight, and observed the reduction in resistance afforded by the air cushion. When I add that this took place as long ago as the 1870s and that the experiments concerned HMS Lightning, the Royal Navy's first torpedo boat, the full importance of Thornycroft's work will, I hope, be appreciated. Some people may share my concern and indignation that these experiments of nearly a century ago should never have become widely known, thus preventing the name of a great British engineer to be accorded the honour it I deserves. | I should be doing Christopher Cock- s' erell scant justice if I failed to place his own achievements in what I believe to be a true perspective. The plain facts, as I see them, are that, after tentative experiments with the air lubrication of boats, Cockerel] hit on the idea of lifting a craft bodily on a cushion of air. Thornycroft anticipated this by over 80 years. Cockerell's own historic achieve- ment appears to have been the invention of a means—the peripheral jet—of containing the air cushion. There are other claimants, however, and the truth of their contentions must ultimately be established. What is immediately important is that, if the work of Thorny- croft should now be acknowledged, as I believe it deserves to be, then it should not be viewed as any diminution of Cockerell's reputation. Rather it should come as a fresh stimulus to a new industry, first created in Great Britain for the exploitation of Cockerell's ideas. Not the least remarkable aspects of the matter are that, in his own inde- pendent researches, Cockerell should have pursued such similar lines of inquiry to those of Thornycroft; that he should have envisaged as one of his immediate goals the building of a very fast torpedo boat; and have expressed his thoughts in such strikingly similar terms. For instance, we have Thornycroft observing: ". . . if the air can be carried with the model"; and Cockerell musing: *'If air were induced under it and could be kept in place ..." And both of them coming to their own conclusions, Thornycroft:"... there must be an advantage in this system"; and Cockerell: ". . . it would appear to be ... advantageous . . ." To dispel any ambiguity let us be perfectly clear that Thornycroft's scheme was not mere lubrication by a film of air, but the bodily "lifting" or "support" of a craft by pneumatic means—by the confining of a "body" of air within a cavity. John Isaac Thornycroft was born in 1843, the son of Thomas Thornycroft, a sculptor who was himself an amateur engineer of uncommon talent. While employed in the drawing office of John Elder's Fairfield Shipbuilding Co on the Clyde, John Isaac calculated the resist- ance of the curious "Popofga" ships (they were circular in plan form); and one finds, incidentally, that a few years later ships of this form were mentioned in the context of air lubrication, in a letter which passed between Britain's great hydrodynamicist William Froude and Dr Tideman, Member of the Academy of Amsterdam and chief constructor to the Royal Netherlands Navy. This letter is now displayed at the David Taylor Model Basin, Washington DC. In 1864 Thornycroft established a launch-building and engineering yard at Chiswick, and in 1871 constructed Miranda, apparently the first truly "high-speed" boat of which there is record. She attained 16.4 knots and was followed in 1873 by the torpedo boat No 23 for the Norwegian Govern- ment. The 85ft HMS Lightning was delivered at Portsmouth in May 1877, and was succeeded by a profusion of successful torpedo boats and launches which ultimately led to the famous Thornycroft "CMBs" of the First World War. The leading character in our story was later to distinguish himself also in other fields of activity—notably in the pro- duction of lorries and buses; but for the present we are concerned only with a patent that was granted to him in 1877. We quote the Specification for "An Improved Method of Reducing the Friction of Vessels when Travelling on the Water." "According to my Invention," de- clared young Thornycroft (he was then 34), "in order to reduce the friction of a vessel when travelling on the water I interpose a layer or body of air between the bottom of the vessel and the surface of the water, which air I confine within a cavity of the bottom of the vessel so that the air shall be carried along with the vessel over the surface of the water, the air being in direct contact with the exterior of the bottom of the vessel and with the surface of the water below it. To this end the bottom of the vessel is formed with an external cavity into which air is forced so as to displace water from the cavity, and the air is maintained at such pressure as to keep the cavity filled, or nearly so, with air, such air as may escape being replaced." As a concise and lucid description of a plenum-chamber ACV that would be difficult to improve upon even today. Two distinct forms of hull were described and shown in drawings. One, circular in plan, appeared in side eleva- tion as a stepped planing craft, having an air cushion bounded by the step and
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