Historia y Arqueología Marítima
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JOHN COBB'S ATTACK ON WATER SPEED RECORD IN NOVEL HYDROPLANE
TRAGIC END TO PROMISING AND WELL ORGANIZED ATTEMPT ON WORLD WATER SPEED RECORD
Fuente: Yachting World- 1952
EVER since Gar Wood pushed
the water speed record into three figures in Miss America IX with
a speed of 102.25 m.p.h., the water speed record has gone up in
surprisingly small steps compared with land and air records and in the
last 13 years has increased less than 40 m.p.h. to the present record of
178.4 m.p.h. recently made by Stanley Sayres in Slo-Mo-Shun. From
this it is not difficult to appreciate that there is little room for
further development in the types of boat which have been used.
To raise the water speed record any appreciable amount, and, to make it worth while, it should be over 200 m.p.h., it is obvious that a radical change would be necessary in both hull form and motive power. The three-point suspension Apel type hulls which have been used so successfully on both sides of the Atlantic in recent years suffer from one major snag and this is a tendency to become airborne. With their much-curved deck surfaces these boats have grown from a hydrodynamical dream into an aerodynamical nightmare. At speeds of more than 150 m.p.h. the lift on the curved fore-deck is such that any small change in the angle of incidence due to a wave would increase the lift so that the boat would take off and possibly turn over.
There are difficulties also with a propeller, the efficiency of which is inversely proportional to its speed through the water, and at speeds over 200 m.p.h. the losses are so great that a very big engine would be needed.
It was because of this that Reid Railton, John Cobb's technical adviser, whose instinct in anything to do with speed is almost uncanny, suggested an entirely new approach to the problem and the result is Cobb's new boat. She has been designed by Commander Peter du Cane and is being built by Messrs. Vosper, Ltd., Portsmouth. To appreciate reasons for the final shape of the boat, it is interesting to follow the lines of development from Railton's original conception which resembled a small seaplane hull on floats or skis.
To stop it taking off it was essential to have an aerodynamically stable hull which would not be sensitive to small changes in angle of incidence, while a jet aircraft engine was logically chosen, because of its light weight, its efficiency at high speeds, all its thrust being used and, of course, the elimination of all propeller troubles.
Permission was given by the Director of Naval Construction to use the Haslar experiment tank and in 1950 tests were started with one-sixteenth scale, rocket propelled models about 2ft long. The top two photographs show the type of model which was first used. A cigar shape was chosen because any alteration in the angle of incidence would cause the centre of lift to move behind the centre of gravity and thus provide a righting couple. The air njdder was solely to keep the model straight during the tests.
Having decided on the approximate shape and type of engine, the big job began, that of finding the shape and position of the planing surfaces, and this is where Commander du Cane's great experience of planing hulls was invaluable. The first major problem to overcome was that of porpoising. With the jet-engined Bluebird II, in which Sir Malcolm Campbell made a vain attempt on the record in 1947, porpoising took place at speeds of less than 100 m.p.h., which proved that the cause was hydrodynamic and not aerodynamic as many people thought at the time.
Thus the first model had four skis, with two on either side providing lateral stability, while one forward and another aft were intended to stop any tendency to porpoise. It was soon found that the after ski was unnecessary and so the layout took on the form of a water tricycle. During these early tests a considerable amount of data was collected about the positions .and angles of the skis; but one problem remained unsolved, and that was how to lift the boat out of the water and to ride on her skis. By substituting floats for skis and fairing the forward one into the hull the final shape of things began to emerge and, early in 1951, tests were made with a one-sixth scale model (about 5ft long) to get an idea of its hydro- and aerodynamic qualities. Driven by a rocket, developing a thrust of 301b for 20 seconds, which was made and calibrated by the Rocket Propulsion Division of the Royal Aircraft Establishment at Farnborough, this 5ft model was accurately timed at 97i m.p.h. From this, the designers calculate that the full-scale hull might be capable of 240 m.p.h. They say might because there will be many factors to be considered in the full-size boat which will not necessarily be present in the model; but the performance of the model gives some indication of what may be expected when John Cobb makes preliminary trials at Loch Ness at the end of this month or the beginning of next.
The structure is composite, of birch plywood and high tensile aluminium alloy, and great care has been taken to get the hull as light as possible. Mr. Peter Crewe, chief hydrodynamicist to Messrs. Saunders Roe, was consulted about the loads on the planing surfaces; while data on stresses in the hull, which is not unlike that of an aircraft, was obtained from Messrs. Vickers Super-marine, Ltd.
The main hull consists of two skins of tVin birch plywood, doped fabric covered and highly polished, glued to multiple fore and aft stringers, which, in turn, are lugged to fin and iin birch plywood frames sawn to shape. Aluminium (D.T.D. 610B) has been used for all highly stressed surfaces and members, while the planing surfaces have been reinforced with N.P. 5/6 aluminium alloy sheeting. It is interesting to note that these planing surfaces, which are flat in section, with no V or dihedral, are the same as those used on the early models. The power unit, which has been lent by the Ministry of Supply, is a De Havilland Ghost, which develops a static thrust of 5,0001b, or nearly 2\ tons.
Although it may be some time yet before an attempt will be made on the record, and it is more than probable that minor modifications will be found necessary before the boat is ready to do so, the results achieved by rocket propelled models are very encouraging. All those interested in high-speed craft will wish John Cobb, Reid Railton, Peter du Cane, and all those associated with them, a successful outcome of this venture and may all their hard work result in regaining the water speed record for England.
Some of the 1/16 scale models used in development. The top two photographs show original three-ski model with cigar-shaped aero-dynamically stable fuselage. (Bottom /eft) An early attempt with floats and (bottom right) the final shape. Installation of rockets, madefy Messrs. Wilmot, Mansour & Co. is dearlyseen
TRAGIC END TO PROMISING AND WELL ORGANIZED ATTEMPT ON WORLD WATER SPEED RECORD
(Above) Cobb signals the success of the larger rudder (Left) Crusader leaving Temple Pier for her last run
AS reported in last month's Yachting World John Cobb was killed on September 29 when Crusader broke up on Loch L Ness at the end of the first run of his second attempt at the world water speed record—a few seconds after becoming the first man to exceed 200 m.p.h. on water, with a speed of 206.8 m.p.h. Unfortunately this does not constitute a record because, under the international rules, an average has to be taken of two runs in opposite directions.
After the first attempt on September 19 when a cross wind, which made it difficult to keep Crusader straight, had robbed Cobb of the record, it was more than a week before he could take Crusader out again to try the larger rudder fitted to give greater directional control. This was a great success and, for the first time, he was able to turn Crusader round at the end of a run without coming off the plane, thus ensuring that neither time nor fuel was wasted between the two runs.
On September 29 it seemed as if patience had been rewarded and conditions on Loch Ness looked perfect for the attempt. Starting farther back than on previous runs, Cobb worked up to a speed very much faster than ever before which, all factors haying been considered, must have been in the region of 240 m.p.h. Everything seemed to be set for the record when, just over halfway down the measured mile, he slowed considerably. Then, just after passing the mile post, Crusader buried her nose and disintegrated. Cobb was thrown clear but was killed instantly.
What went wrong can never conclusively be proved because there was not much left of Crusader to pick up. Several theories have been put forward based on photographic evidence, mainly in the form of " stills " taken from cine films. It seems certain that Crusader hit some small waves, or " swells," just before she came to pieces. Whether this was the cause or whether it was the straw which broke the camel's back, is difficult to say, although probably the latter. From the British Newsreel sequences taken by Pathe News cameraman Jock Gemmell, it was obvious that Crusader was "pattering" considerably more than on previous occasions. This was probably largely due to the great speed at which she was going, which must have placed a terrific strain on the forward planing surface.
During trials earlier in the month the forward planing surface had shown signs of working and, although it had been strengthened internally, it may well not have been strong enough. Cobb obviously had some indication that something was wrong because he slowed down, but when Crusader hit the waves, which can clearly be seen in the photographs, something gave way. The second photograph in the sequence shows spray apparently coming out of the cockpit, which seems to confirm the theory that something had collapsed in the forward part of the vessel. This would also account for her sudden nose dive and final disintegration.
Thus ended tragically one of the most promising and well-organized attempts ever made on the water speed record. Never has a boat been so logically thought out, carefully designed, tank-tested and built, and in memory of John Cobb, whose name is added to the ever growing list of those who have given their lives for speed and progress, it is to be hoped that those who made the attempt possible will not be discouraged.
Este sitio es publicado por la Fundacion Histarmar - Argentina
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