Under Norbert Singer’s leadership, the Porsche 956 emerged as a car with remarkable aerodynamic properties for its era.
Two specific technical details had a significant influence on possible cornering speeds: the ‘Singer dent’ at the front of the underbody, named after Norbert Singer himself, and a long diffuser, which started ahead of the centre of the vehicle and extended all the way to the rear. As speeds increased, this created an ever-stronger vacuum, which quite literally sucked the 956 to the ground. This enabled very high cornering speeds and gave Porsche a decisive advantage during races.
Wind tunnel work took place at the University of Stuttgart’s Research Institute for Automotive Engineering and Vehicle Engines (FKFS) and at Volkswagen.
But getting there was a labour-intensive and time-consuming process. This is partly because Porsche did not have its own wind tunnel at the time. So work began using models in the 1:5-scale wind tunnel at the University of Stuttgart’s Research Institute of Automotive Engineering and Vehicle Engines (FKFS) on the premises of Mercedes-Benz in Untertürkheim. This was where, at the end of the 1960s, even the legendary Porsche 917 had to prove itself when it came to aerodynamics.
At the time of the development of the 956, wind tunnel tests using full-scale models or finished vehicles were much more complex. These were carried out at Volkswagen in Wolfsburg, for example, and followed a strict timetable. “If we wanted to use Volkswagen’s wind tunnel for a day, we had to have everything ready to go at seven in the morning,” recalls Singer. “And the tests finished at 5:30 pm sharp. Then we had another half an hour to leave the building before it was locked at exactly 6 pm. It was very time-consuming to transport everything we needed to Wolfsburg,”.
Ground effect
The declared objective of the aerodynamic development of the 956 was to create ‘ground effect’, which was already being applied to Formula One cars at this time. The basic idea behind ground effect is to create a vacuum between the vehicle floor and the road surface, which effectively sucks the car to the tarmac, thereby allowing higher cornering speeds.
“To begin with, we copied Formula One, with inverted wing profiles under the car and skirts that sealed this configuration to the sides. The ground effect in a Formula One car is mainly created by an airflow coming from the front. Our results were disappointing,” says Singer, explaining the particular problems associated with the aerodynamic development of the 956. “We were forced to admit that ground effect only built up properly under the comparatively wide monocoque of a sports prototype if air also flowed in from the sides and the underbody was designed accordingly.”
Eventually, a solution was devised that featured two or three diffusers, depending on the track. The short-tail version of the car, designed for high downforce on twisty circuits, had a diffuser ahead of the front axle in the form of an upward curvature of the underbody. This profiling accelerated the airflow, creating negative pressure and therefore downforce. This diffuser has gone down in the Porsche history books as the ‘Singer dent’.
In the area below the cockpit, the underbody was flat, in line with Group C technical regulations. To the left and right of this flat area were two diffusers in the form of elongated channels that extended to the rear of the vehicle. These two channels were designed so that air could flow in from not only the front of the vehicle, but also from the sides.
After completing this wind tunnel work for the short-tail version of the 956, Norbert Singer and his team turned their attention to the long-tail version. The aim was to reduce drag, thereby enabling a higher top speed. To achieve this, the profile of the two rear diffusers had a flatter shape for lower drag, but also lower downforce. To maintain the aerodynamic balance, the ‘Singer dent’ at the front of the front axle was closed.
As the values of the first 956 long-tail from 1982 show, when compared with those of the 936/81, 20 per cent more downforce was built up with identical aerodynamic drag; this highlights the effectiveness of ground effect in the long term. By way of comparison: the short-tail version of the 956, which was designed for twisty circuits with short straights, generated twice as much downforce as the long-tail version. In essence, the 956 short-tail would have been able to drive upside down on the ceiling above 180 km/h, while the 956 long-tail version could only have been driven upside down above 321.4 km/h.
Narrower tyres for even more downforce on the 962 C
When the 962 C was created as a result of the changes to the regulations for the 1985 season, Porsche took the opportunity to optimise its Group C racing car in aerodynamic terms as well. Since the flat wide six-cylinder boxer engine did not allow for an optimal design of the diffuser channels in the rear area, Norbert Singer was on the lookout for a new solution. “The wind tunnel had shown that we could improve downforce with narrower tyres and wider diffuser channels,” he explains.
With the support of tyre partner Dunlop, the 962 C therefore now had wheels that were only 14 inches wide instead of 16, but their diameter was increased from 18 to 19 inches. In terms of high cornering speeds, the tyre contact area was therefore roughly the same, but the reduction in tyre width meant that the diffuser channels can be made 50 mm wider, providing even more downforce.
With thanks to Porsche Motorsport, Porsche Heritage and the Porsche Museum.
