THE EVOLUTION OF THE "CORNICHE" BENTLEY

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THE EVOLUTION OF THE ” CORNICHE ” BENTLEY

Mr. W. A. Robotham, of Rolls-Royce, Ltd., describes the conception and development of one of Britain’s most advanced high-performance cars IN 1931, when Rolls-Royce first took over the Bentley Company, some wind-tunnel tests were made on the first 3i-litre saloon car. The results were ilhuninating, but not very helpful towards improving the top speed of a motor car which must suit the average Bentley customer. Briefly, it was found that small excrescences such as lamps, horns or mascots on the fiont of a car have little or no effect on its speed. Making drastic alterations to the front as a whole, however, cut down the drag considerably. The best shape appeared to be something on the lines of the Lancia. The main point about this design is that there are no sharp edges and the gap between the wings and the body is filled in. 1.1nfortunately, in 1931, we particularly wished to retain the original Bentley appearance, and therefore any sweeping alterations to the radiator were out of the question. We found that, unless we altered the front, nothing we could do at the back made very much difference. With the altered front, however, a measurable improvement was obtained by a sweeping back an d tail. When we had combined all the improvements (which produced an entirely unconventional-looking car), we got a figure of merit for this and then turned a model of the standard saloon back to front in the wind-tunnel. We were somewhat disgusted to find that a lower drag figure was produced than with our streamlined vehicle 1 Nothing further was done, therefore, to reduce the windresistance of the car sold to the public until just before the war. As soon as the Germans began to build their motor roads, it became evident that a vehicle designed for the winding lanes and congested main roads of Britain would have to be modified if it was to take advantage of this new road engineering. Before we started to design a car suitable for the autobahnen, therefore, we looked round to see if we eould get any full-scale results which would be of value from ears that had already been built for private customers. We found that an enthusiast, the late Monsieur Embirieos, had, IA ith the assistance of a French engineer, Monsieur Vaulin, produced quite a practical streamlined Bentley, which seemed to be considerably faster than the standard p ro( t

In doing this he had taken liberties with the radiator, and this in no way resembled the standard Bentley. However, the tout ensemble was not altogether unpleasant.

Mr. Embiricos very kindly agreed to lend us the car for experimental work, and we carried out a few minor modifications to improve the power-output of the engine and make the gear ratios more suitable for high speeds. When the modifications were eomplete, the car could be driven without excessive pinking on any No. 1 petrol available in England, and was free from detonation on Ethyl or any other premium spirit.

The car was fitted with 6.5 in. by 19 in. tyres and geared to give the following road-speeds at 4,000 engine r.p.m. :

Overdrive 127k m.p.h. Direct —108 17 2nd speed 72 7, 1st speed =151 „ The body was very light and the high first gear seemed quite practicable for starting and hill-elimbing,. Indeed, the car was so fast, tractable and economical that an extended continental tour was arranged, to demonstrate these virtues to

representatives of the technical press. The car averaved lit) m.p.h. for five miles over Germtui roads, limier favourable conditions. It also gave the following consumptions at constant speed on the autobahnen :—

40 m.p.h. = :32 m.p.g. 60 = 26 80 „ =21 90 „ =11 „ To demonstrate that, in making this vehicle suitable for the German motor )1 roads, it had not been spoilt tor ordinary high-speed touring, some stretches were timed on the French roads between Paris and Metz. Montniirail to Chalons-surMarne was covered at an average speed of 76 m.p.h. and 60 in.p.h. was averaged over the 180 miles from Paris to Metz. At, the conclusion of these road tests the car was taken to NIontlhery and covered 107 miles in one hour, the fastest. In being at just over 110 m.p.h. These results Ate-were interesting and a. few more modifica

tions were made to the power plant. George Eyston then took the car round Brooklands and covered 114 miles in the hour. These results were just what we wanted technically, but we were not satisfied w ith the appeitranee of the car, and also it was a two-door saloon, with rather cramped luggage-space and rear passenger accom modation. Monsieur therefore, Continued on page 415

set to work to redesign the appearance and convert the body into a commodious four-door saloon, with plenty of luggageroom. The result of his efforts was what the company’s engineers considered to be a very good-looking motor car, and a wind-tunnel model WIIS made. The drag tests were most encouraging since, in spite of the increased body/dimensions, the wind resistance figure was exceedingly low. A full-size car was built and confirmed the wind-tunnel tests. Since it had been decided to put the car on the market as a definite model, no liberties could be taken with the power plant at all. Nevertheless, the car in full touring trim, with a driver and passenger, lapped Brooklands at 109i miles per hour. The car was then taken to France and the continent, where every new RollsRoyce chassis has been subjected to a run of at least 15,000 miles of high-speed continental motoring. As this car was intended to be especially suitable for the new motor roads, a considerable amount of this run was carried out on the autobahnen and autostrada. The major problem which immediately presented itself was that of tyre life. It was almost impossible to get a standard tyre to last more than a few miles if the car was driven flat out. Another disconcerting result was that, if one indulged in a short Spurt of speed and then came back to 90 m.p.h., the tyre never got over its high-speed treatment and, if these speed spurts were repeated, it was found that the tyre burst after exactly the same

number of miles as would have been the case if the same distance had been covered continuously. With the assistance ot the tyre companies, we at once started to do the necessary development work to get a tyre to suit these extreme conditions, and were well on the way to success at the outbreak of war. Unfortunately, even our experienced test drivers took some time to get accustomed to the very high maximum speeds, and the first ” Corniche ” was completely smashed up just before the war started. This was the only example in existence, and it will, therefore, be some time after the war before anyone can once again handle one of these rather surprising vehicles. It seems improbable that there will be any basic difficulty in accustoming the average Bentley driver to speeds of between 100 (1 110 m.p.h. on autobahnen specifically built for the purpose. The danger lies in such speeds being used without discretion on normal roads. One other point is worth emphasising. Speeds of 100 m.p.h. are frequently claimed for conventional standard touring-cars. Such speeds are very rarely attained. In reviewing the march of progress, it is interesting to remember that the RollsRoyce “Phantom I” had a top speed in still air of something less than 70 m.p.h., and its engine dimensions were 50 per cent. bigger than those of the existing Bentley. There is no doubt that this streamline Bentley is the forerunner of a new breed of motor-car built to take advantage of the changing read-conditions.