The world’s record for speed on land was for many years held by Sir Malcolm Campbell. In November 1937 George Eyston, in his powerful and heavy car Thunderbolt, achieved a new record, with a speed of 312.20 miles an hour over the measured kilometre
A SPEED OF MORE THAN FIVE MILES A MINUTE was achieved by George Eyston, in Thunderbolt, over the flying kilometre on the salt lake at Salduro, Utah. The car weighed more than 7 tons. The front track was 5 ft 4 in, the mean rear track 5 ft 7 in and the overall length 30 ft 5 in. At 312 miles an hour the tyres were revolving 2,580 times a minute.
THE chapter “The World’s Land Speed Record” describes how Sir Malcolm Campbell, with his Blue Bird car, broke successive world records for speed on land. On November 19, 1937, the world’s land speed record changed hands once more, but still remained in the keeping of Great Britain. Sir Malcolm Campbell’s record of 301·129 miles an hour was broken by a substantial margin by Captain George Eyston, who covered the flying kilometre in two directions at an average speed of 312·20 miles an hour.
Eyston’s giant car, Thunderbolt, was largely his own creation. It was a car evolved for the express purpose of travelling for a few brief seconds at a higher speed than anything had previously travelled on land, and it achieved this object with little trouble.
Campbell’s Blue Bird used a Rolls-Royce aero engine of 36,582 cubic centimetres capacity; Thunderbolt was powered by two similar engines, developing some 4,700 horse-power and installed side by side in the centre of an enormous chassis which, as soon as its details had been made public, was subjected to a great amount of criticism. Thunderbolt was condemned as an unwieldy car which must be extremely difficult to handle; as an unnecessarily heavy design; in short, as a freak. Most of the cars, however, which have, at some time or other, broken the land speed record have been subjected to similar criticism. Eyston’s wonderful car vindicated itself triumphantly.
Little attempt was made to save weight — the car weighed more than seven tons, compared with the five tons of Campbell’s Blue Bird. The two huge twelve-cylinder supercharged engines were mounted in the centre of the chassis, all the power being transmitted through the twin-tyred rear wheels. Each engine had its own clutch, coupling it to a short shaft and a train of gears transmitting the drive to a huge gearbox. From this gearbox the drive was taken to a bevel and crown wheel driving the rear axle, in which no differential gear was used.
The front layout of the car was completely unconventional. Just in front of the driver, who sat in front of the engines, were two independently sprung wheels. From these wheels two driving shafts led to the centre of the chassis, at which point the hydraulic brake mechanism was mounted. Ahead of these wheels was another pair of wheels with a narrower track, and the two pairs of front wheels were connected together by a complicated and ingenious steering gear which permitted each wheel to turn through a different arc as the car was steered round a curve. The rear axle was of the independently sprung type, each universal-jointed driving shaft carrying a wheel with twin tyres. Huge transverse leaf springs were used. In addition to the hydraulic brakes acting on two of the front wheels, a transmission brake was installed, acting on the shaft which transmitted the power from the gearbox to the rear wheels.
The streamlining was more perfect than that of previous high-speed cars, even the wheels being enclosed. It was the decision to use this type of body that governed the main details of the layout, which were largely planned with perfect streamlining in view.
In the nose of the car was a large opening through which air was admitted to the radiator; at the tail was a fin to give lateral stability. The only projection from the body was the small sloping windscreen in front of the driver’s cockpit, behind which was a streamlined headrest.
Underneath, where streamlining was even more important, the body was virtually flat, with a ground clearance of about eight inches. The intakes to the engine superchargers were brought out to the top of the body as a precaution against the possible sucking in of dust and salt spray from near the ground. The front track of Thunderbolt was 5 ft. 4 in, the mean rear track 5 ft. 7 in. and the overall length of the car 30 ft. 5 in. The overall height from the ground was only 3 ft. 10 in. and the overall width 7 ft. 1½ in.
1931 Malcolm Campbell Blue Bird Napier engine 245·73 mph
1932 Malcolm Campbell Blue Bird Rolls-Royce engine 253·97 mph
1933 Malcolm Campbell Blue Bird Rolls-Royce engine 272·11 mph
1935 Malcolm Campbell Blue Bird Rolls-Royce engine 276·81 mph
1935 Malcolm Campbell Blue Bird Rolls-Royce engine 301·13 mph
1937 George Eyston Thunderbolt Rolls-Royce engine 312·20 mph
Thunderbolt’s fuel tanks had a capacity of forty gallons and the oil tanks held eighteen gallons. On the flanks of the tail were the planes of special air brakes used to assist in pulling up the enormously heavy car at the end of its fast run.
The chief problems facing the designer were those of acceleration and braking; its run at constant speed was to be a matter of only a few seconds. To accelerate a mass of 7 tons to 300 miles an hour and then to check it in a reasonable distance were no mean engineering problems, and their successful solution was a great tribute to the designer and to all those who worked with him.
At the time when the record was broken, the “dry lake” at Salduro, Utah, was far from dry. At times the surface was too slippery for an attempt on the record to be considered. On one occasion the car succeeded in averaging 310 miles an hour in one direction, but one of the clutches began to slip and the return run was a failure. The tyres also gave rise to problems of their own, and their short life set a strict limit to the number of test runs that were possible. Heavy treads would be ripped from their cord bases by centrifugal force at these tremendous speeds, a fact which accounts for the fact that tyres used for this kind of work have virtually no tread, and therefore a short life.
Once the clutches had been rebuilt to withstand the loads imposed on them, however, Thunderbolt gave no further trouble and, although Eyston was a little disappointed by the margin over the previous record, he had no doubt that Thunderbolt was capable of at least 320 miles an hour.
At 312 miles an hour the tyres were revolving 2,560 times a minute and increased in diameter by 1¼ in; the effect of braking in these conditions was an unknown quantity, but the combination of hydraulic braking and of the auxiliary air brakes in the tail proved splendidly efficient.
It is an indication of the driving skill necessary in record attempts of this kind that the change from first gear to second is made at about 100 miles an hour, and that from second to top at over 200 miles an hour.
In addition to covering the kilometre at 312·20 miles an hour, Thunderbolt took the measured mile at 311·42 miles an hour, thereby breaking the world’s record for the mile.
SECTIONAL DIAGRAM of Thunderbolt. The driver’s seat is in front of the two twelve-cylinder supercharged Rolls-Royce aero engines. In front of the driver are two pairs of wheels, of different tracks, connected by an ingenious steering mechanism.
