Are We Back To Square One ?
At Le Mans in 1952, during the practice sessions, the Daimler-Benz concern tried out an air brake on a 300SL coupe. This consisted of a metal flap like an aeroplane wing mounted above the roof and hinged to move through 90 degrees. It was operated by an extra foot pedal in the cockpit through levers and cranks, and when not in use a hand lever locked it in the horizontal position. It was never used in a race, and indeed was not seen 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 300SLR open 2-seaters had air brakes fitted on the rear of the body. This time the flap was the width of the body and some 20 inches in height and when it was “down” it fitted the bodywork like a second skin. It was operated by hydraulic rams actuated by a lever on the scuttle, the hydraulic power coming from a pump driven from the gearbox. The operating lever stuck out horizontally and moving it upwards allowed the hydraulic pressure to fill the rams and raise the flap. When released the lever returned to the horizontal position and the flap remained raised until the lever was pressed downwards, whereupon the hydraulic pressure was released and the flap swung down to the horizontal. This sensitive operating lever, working an hydraulic valve, permitted the air brake to be raised or lowered to any desired angle, although the design intention was that it should be raised to the vertical position for maximum braking at the end of the long Mulsanne straight. With a bit of practice the drivers found they could make good use of it on all the corners at Le Mans, and during practice tried the effects on lap times braking with the air brake alone, and then with the wheel brakes alone.
Stirling Moss played with this fascinating new gadget and discovered that he could make use of it on far more occasions than at the end of the Mulsanne straight, where maximum braking is called for. On some bends he found that by raising it only halfway it applied just sufficient braking for him to keep his foot hard on the throttle and maintain a much more balanced cornering technique. An example was the bend to the right, after the pits, under the Dunlop Bridge. Without the air brake he had to lift off the throttle and approach on the over-run until he had the car lined up and then open up round the bend. By trial and error he found he could take this bend without lifting his foot from the throttle, but lost the requisite amount of speed by raising the air brake. As he got more experienced with its use, and more courageous, so he raised the air brake by smaller amounts until he found the ideal. This resulted in a much 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” essentially as a brake that would not wear out, but he was aware of the effect it caused on the car. The flap was designed to act through the centre of gravity of the car, so that when raised it transferred the wind pressure into a downward force as well as a retarding force, and the downward component increased the loading on the tyres. By using it to “balance” the car in a fast corner, 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, though he had been aware of its possibilities, and at first had told them to use it only in a straight line for heavy braking from high speed. Stirling Moss was always pleasing Uhlenhaut unknowingly by this sort of thing, for he had not worked with a driver that could do so many things while he was 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 came in very useful over a bad jump on one of the straights. This jump could not be taken flat out and Moss found the car was much more stable when he lost speed by using the air brake, and it made certain that 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 short 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 Michel May, built an adjustable aero-foil wing across the top of their open Porsche Spyder, and this could be tilted from 3 degrees to +17 degrees by means of a lever in the cockpit. They had no ideas of using this device as an air brake to supplement the wheel brakes, but designed it purely as a thrust producer, giving a downwards force acting 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 adjustable spoiler on very fast bends, and experimented with it at Nurburgring and found it very effective on fast bends where the contour of the road tended to lift the car and reduce 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 after the pits at some 6-8 m.p.h. faster than a normal Porsche Spyder, purely by reason of the additional adhesion provided by the spoiler. Unfortunately the Italian scrutineers were not very bright, and could not comprehend the principles behind the design, being sure that it was an air brake, even though the Mays insisted that it could not swing sufficiently to become effective as an air brake. The scrutineers refused to accept the mechanism and would riot even let Michel May practise with it, so this brilliant design was lost to the motor-racing world.
For some years Ferrari and Aston Martin determined the pattern of sports-car racing, and neither firm have been noted for anything very brilliant in the way of basic design and research, preferring well-proven ideas, so it was not until 1961 that much thought was given to “messing about with the air flow.” Frank Costin, Vanwall and Lotus, as well as most of the other British special builders, had made great strides in smoothing out the passage of the air over their cars, but when Ferrari changed to rear-engine positions for his sports cars he inadvertently started up interest in “air spoiling.” During high-speed testing of the rear-engined sports car in early 1961 Richie Ginther was being troubled by a feeling of instability at high speed on the straights at Monza and the Ferrari engineers could not account for it. Quite by chance someone gave Ginther a photograph of the new Ferrari, reputedly taken at full speed on the straight, yet the car had a nose-down appearance as if Ginther had the brakes hard on. This turned his thoughts to the air flow over the large flat tail of the car and the possibility of some aerodynamic phenomena lifting the rear of the car at speed, which would account for the feeling of instability. A spoiler was made up that had the effect of turning up the end of the body, and it was found that this was sufficient to cure the trouble. It broke up the air flow and turned a negative pressure into a positive pressure, so there was no longer any tendency for the rear of the car to lift.
When Ferrari cars appeared with this turned-up tail made in one with the body, and looking very pretty, just about everyone copied it, whether they needed it or not, and a tail spoiler became an accepted fashion. Some cars that were hardly fast enough to stir up the air had tail spoilers, and the whole affair became a bit of a farce, and still is in many cases. The heights of spoilers continues to vary and one English sports car even had a ”two stage” spoiler, a smaller one being riveted on to the original one. To be really sporty these days it is not sufficient to have “ape tape” stripes over the roof, you must have a “spoiler” on the tail as well.
However, some people experimented with the idea in a serious vein, and a lot of experimenting has been done in the sphere of the large V8-engined sports cars. Towards the end of last year Jim Hall’s Chaparral sports car appeared with a larger than usual spoiler across the tail, and in addition it was adjustable from the cockpit. It was said that the reason for adjusting the angle of the spoiler was to make it suitable for varying conditions and to be able to apply a greater or lesser downwards thrust on the rear tyres at the will of the driver. It would also turn through 90 degree’s and form a very effective air brake ! This is where we came in. The Chaparral is rightly praised by everyone as being a very advanced sports car, with lots of novel features about it, and to benefit from General Motors research knowledge. 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 ?—D.S.J.