At Le Mans in 1952, during the practice sessions Daimler-Benz tried an air brake on a 309SL coupe. This consisted of a metal flap mounted above the roof and hinged to move through 90 degrees. It was operated by a foot pedal through the horizontal position. It was never seen in a race, nor again that year, but it had obviously provided the Daimler-Benz engineers with some useful data.
When the Mercedes-Benz team returned to Le Mans in 1955 the 300SLRs had air brakes on the rear of the body. Now the flap was the width of the body and some 20 inches in height and when it was ‘down’ it fitted the body like a second skin. It was operated by hydraulic rams actuated by a lever on the scuttle. The sensitive operation lever worked an hydraulic valve, permitting the brake to be raised or lowered to any angle, although the intention was to raise it to the vertical at the end of the straight.
With practice, the drivers could make use of it on all three corners at Le Mans, and during practice took lap times braking with the air brake alone and even with the wheel brakes alone.
Stirling Moss played with their new gadget and discovered he could make use of it on far more occasions than at the end of the straight, where maximum braking is called for. On some bends he found that raising it half-way it gave sufficient braking for him to keep his foot on the throttle, maintaining a more balanced cornering technique.
An example was the bend after the pits, under the Dunlop Bridge. Without the air brake he had to lift the throttle and approach on the over-run and then open up round the bend. He found he could now take this bend without lifting his foot, losing the requisite speed by raising the air brake. As he got more experienced and courageous, so he raised the air brake by smaller amounts until he found the ideal. This resulted in more balanced cornering, less strain on the car and a more relaxed situation for him. Discussing this with engineer Uhlenhaut gave the German technician great satisfaction, for he had designed this ‘air spoiler’ as a brake that would not wear out, but was aware of the effect it had on the car.
It was designed to act through the car’s centre of gravity so that, when raised, it transferred wind pressure into a downward as well as a retarding force, and the downward component increased the loading on the tyres. By using it to ‘balance’ the car on a fast comer, Moss had been increasing the cornering power of the car.
Uhlenhaut had not been prepared to give his drivers so much complication to think about and at first had told them to use it only in a straight line for braking from high speed. But Moss was always pleasing Uhlenhaut by this sort of thing, for he had not worked with a driver that could do so many things while driving fast, and he naturally encouraged Moss to use the ‘air spoiler’ for all sorts of circumstances.
Later in 1955 the 300SLR cars were raced in Sweden and the air brake was useful over a bad jump on one of the straight. This jump could not be taken flat out and Moss found the car was much more stable when he lost speed using the air brakes, and it ensured the car landed rear wheels first. In addition there was no fear of a wheel locking on while in mid-air to make the landing a dicey business. After only one season of sports-car racing Daimler-Benz withdrew from the scene and turned their racing department back onto production designing, so the air brake did not develop any further.
In 1956 two young Swiss engineers, Pierre and Michael May, built an adjustable aero-foil wing fortheir open Porsche Spyder, and this could be tilted from -3 degrees to +17 degrees. They had no ideas of using this device as a brake to supplement the wheel brakes, but designed it as a thrust producer, giving a downwards force through the c. of g. of the car. They had calculated the forces involved to provide an additional downwards load on the tyres to balance out the loss of adhesion due to cornering forces.
Their intention was to use this spoiler on very fast bends, experimented with it at Nürburgring and found it very effective on curves where the contour of the road lifted the car and reduced the weight on the tyres as the car was cornering. They took the Porsche to Monza for a long-distance sports-car race, certain in the knowledge that they would be able to take the Curva Grande some 6-8 mph faster than a normal Spyder. Unfortunately the scrutineers were not bright, and did not comprehend the principles behind the design, being sure it was an air brake, even though Mays insisted it could not swing sufficiently to become effective as such. The scrutineers refused to accept the mechanism so this brilliant design was lost to the motor-racing world.
For years Ferrari and Aston Martin determined the pattern of sports-car racing, and neither firm was noted for brilliant design and research, preferring well-proven ideas. It was not until 1961 that thought was given to ‘messing about with the air flow’. Frank Costin, Vanwall and Lotus had made great strides in smoothing the passage of the air over their cars, but when Ferrari changed to rear-engined sports cars he inadvertently started up interest in ‘air spoiling’.
During testing of the rear-engined sports car in 1961 Richie Ginther was troubled by instability at speed on the straights at Monza, and Ferrari’s engineers could not account for it. By chance someone gave Ginther a photograph of the Ferrari taken at full speed on the straight; the car had a nose-down appearance as if Ginther had the brake hard on. This turned his thoughts to the air flow over the tail of the car and the possibility of some aerodynamic phenomena lifting the rear at speed, which would account for the instability. A spoiler was made that had the effect of turning up the end of the body, and this was sufficient to cure the trouble. It turned a negative pressure into a positive pressure, so there was no tendency for the rear to lift.
When Ferrari cars appeared with this tail, just about everyone copied it and a spoiler became accepted fashion. Some cars that were hardly fast enough to stir the air had rear spoilers and the whole affair became a bit of a farce.
However some experimented with the idea in serious vein, and experimenting has been done in the sphere of the V8-engined sports car. At the end of last year Jim Hall’s Chaparral appeared with a larger than usual spoiler, and it was adjustable from the cockpit. It was said the reason for adjusting the angle was to apply greater or lesser downwards thrust on the rear tyres at the will of the driver.
This is where we came in. The Chaparral is rightly praised as an advanced sports car, with lots of novel features about it. Yet it would seem that the Daimler-Benz engineers have quite a good lead on their American rivals. I wonder when someone will ‘discover’ high pressure direct fuel injection and desmodromic valve gear? DSJ
CONTENTS., September 1926
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