Ground Effect and the Fan Car
Author
- Darren Galpin
Date
- 8W Special, May 3, 1999
Related articles
- Gunnar Nilsson Memorial Trophy - The fan car raced twice!, by Mattijs Diepraam/Tom Prankerd/Michael Ferner
Who?Niki Lauda What?Brabham-Alfa BT46B Where?Anderstorp When?1978 Swedish GP |
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Why?
The 1978 Swedish GP will remembered for just one thing. The race itself being rather uneventful, it was the winning car that created its own footnote in history by dominating the meeting, thus to great lengths contributing to its uneventfulness in the first place. Responsible for this overwhelming coup was some clever thinking by Brabham's Gordon Murray, who was trying to eclipse Colin Chapman's ground effect invention on the Lotus 79, the skirted car that had swept the front row since its debut at Zolder. Center of the BT46B concept was a huge fan taking ground effect to a higher level (at least engineering-wise) by pulling a vacuum from under the bottom of the car, thereby creating an enormous amount of downforce. From its skirts up the car stuck on the track like glue, allowing the reigning champion to win conclusively. Immediately after, the fan was deemed illegal, contravening the rules on moving aerodynamical devices, although the Brabham team claimed its use was primarily for cooling - which wasn't far from the truth, actually. In typical FIA style the win was allowed to stand, however, which cost Arrows their chance of victory in its debut season.
There's no doubt you can't explain the Brabham fan car without explaining the reasons for it. The reasons for it were caused by Ground Effect and Team Lotus, and you can't really explain the importance of Ground Effect without going over its history...
Putting it simply as possible, Ground Effect is the art of creating a low pressure area underneath the car so that the atmospheric pressure pushes the car to the ground, which is the reverse of what happens with an aircraft wing. The way this is achieved is by utilising the Bernoulli Effect - if a moving fluid or gas is accelerated, its pressure falls correspondingly. This was achieved by creating a upside-down wing profile underneath the side panniers of the racing car. A fixed amount of air flows into the front of the side-pods of each car, where the side-pods are closest to the ground. As you go further back beneath the side-pods, the underside of them rises. The air entering the side-pod the accelerates to fill this increased area, generating a lower pressure. The outside air then pushes the car towards the ground.
The origins of Ground Effect in racing go back to 1961, when Jim Hall was experimenting with a front-engined Chapparal-Chevrolet V8 sportscar. Jim Hall, in conjunction with the aerodynamicists of Chevrolet, built a car whose entire body shape was that of an inverted aerofoil, with both the nose and the tail upswept to form half-venturi tunnels at either end of the car (rather like the modern-day diffusers seen on F1 cars), the idea being to speed up the airflow beneath the car. The problem was that the front venturi caused the car to lift, the weight of the engine being the only thing stopping the car from flipping. A massive air-dam was then fitted to counteract this, but it generated so much downforce that the wheels started to grind their way through the top of the bodywork. The concept was not fully understood, and the idea was left to languish.
However, in the 1968-'69 off-season, an anonymous fan sent Jim Hall a sketch of a car with a fan on the back of it, the fan being used to extract the air from underneath the car. Hall again worked in conjunction with Chevrolet and its parent company General Motors, who developed the idea of having a skirt around the side of the car to stop the outside air rushing in from the side of the car to break the low pressure created by the fan. The result was the Chapparal 2J sucker-car (seen here with Jackie Stewart driving), which was raced in the 1970 Can-Am series. The car worked so well that it was promptly banned - an omen of what was to come.
The concept bubbled under the surface for a number of years, Robin Herd designing wings into the side-pods of the March 701, and Gordon Murray playing with airdams and splitters with the Brabham BT44. The concept finally saw its re-emergence with Peter Wright's brilliant Lotus 78 and Lotus 79.
The evolution of Ground Effect on the Lotus 78 came about by accident. Peter Wright was at Imperial College, London, testing out the idea of putting water radiators in the leading edge of the side-pods. In a bid to try and improve on the unsuccessful Lotus 77, Wright was using a wind tunnel with a rolling road, a novelty at the time. However, the instrumentation began to show some unrepeatable results. Closer examination showed that the side-pods on the model were sagging, and as they got closer to the floor of the wind tunnel, the downforce increased.
Wright then proceeded to cut up bits of cardboard, extending the side-pods right down to the ground - the downforce level doubled. This accidental discovery showed the importance of maintaining an air-tight seal along the bottom of a car with profiled side-pods, and resulted in the successful Lotus 78 of 1977. The prototype, known as JPS/15 or 78/1, was first driven by Eddie Dennis, the shop foreman, at Hethel, but subsequent development work was done by Gunnar Nilsson. This car was later sold to Hector Rebaque, while Team Lotus raced JPS/16 and JPS/17 (78/2 and 78/3). Andretti, in 78/3 (here in the car's debut race in Argentina), won four races for Lotus, but had many reliability problems through the year. As the advantage of the car wasn't clear cut, most of the other teams hadn't cottoned on to the technical advantage. Colin Chapman himself publicly attributed his team's success to the special differential and its preferential tank-draining system - anything in fact but Ground Effect, in order to hide the discovery.
The "problem" with the Lotus 78 was that the centre of pressure was too far forward in the car, which resulted in the drivers having to run with lots of rear wing in order to prevent too much oversteer, with a corresponding lack in straight-line speed. This was rectified in the Lotus 79.
Apart from construction differences (sheet aluminium being used rather than aluminium honeycomb, as Ralph Bellamy, the main advocate of the material, had left for Copersucar), the major difference was in the treatment of the rear suspension, everything being moved in order to reduce the amount of drag in the air exiting the side-pod. This resulted in the aerodynamic load being generated over the whole car length, rather than mostly at the front, and gained the Lotus 79 25% more downforce than the Lotus 78. The prototype, JPS/19 (or 79/1), was rolled out at Paul Ricard in December 1977.
The effect of the huge increase in downforce had not been anticipated, and the car fatigued extremely quickly. A second version, much strengthened (JPS/20, or 79/2), was entered in the BRDC International Trophy at Silverstone on 19 March, the first three Grand Prix having been entered with Lotus 78s. The race was flooded out, but Andretti soon took his car into the lead before aquaplaning off at Abbey, damaging the car extensively. It may have been an inauspicious start, but the concept had been proved, and once the Getrag gearbox was swapped for a Hewland, there was no stopping it. Once Peterson had set stunning times practising at Anderstorp, the car was taken to Zolder for the Belgian GP, its first World Championship race. It (JPS/20) was originally meant to be Andretti's spare car, but the team engineer Nigel Bennett reckoned it could be made into a race car. Andretti talked to Chapman, and both put $500 into a kitty to be split between the mechanics if the 79 survived the race distance without a failure. Andretti qualified on pole by over a second, and led from start to finish... At the next Grand Prix in Jarama, Andretti and Peterson qualified 1st and 2nd, and finished 1st and 2nd, taking fastest lap along the way. The rest of the field was left standing. However, Brabham designer Gordon Murray had an idea.
At the beginning of the season, the interim BT45C, with a full-width nose section, according to Niki Lauda was suffering from acute oversteer. For years Murray had been experimenting with skirts on the underside of the BT44, but he hadn't realised that the full-width nose was creating a ground-effect downforce at the front of the car. Then he saw the Lotus 79 at Monaco (it was taken as a spare car, but not raced), and it clicked into place. He then knew how Colin Chapman achieved his speed.
The problem for him was that the Brabham used a flat-12 Alfa Romeo engine, and the heads of the engine projected into the area where the venturi tunnels would ideally be located. However, he spotted a loophole in the regulations - an extractor fan, as used on the Chapparal 2J, could be used to reduce air pressure as long as its primary function was not aerodynamic as defined in the rules. He was going to claim that the primary function of the fan was to draw air through the car to cool the engine, rather than accelerating the air to gain downforce. The fact that this beneficial effect occurred was purely coincidental... This approach was declared legal by the racing authorities.
The technical problems involved were quite huge. The whole engine bay was sealed, so that air couldn't be drawn through the engine and break the low pressure area beneath the car. Flexible skirts were developed which extended to the road surface, as well as extending back and around the suspension arms. A thermodynamics expert, David Cox, was even employed to work out the number of fan blades, pitch and optimum rotation speed!
The fan was driven from the gearbox via a series of shafts and clutches, the clutches being used to prevent the fan from over-driving the gearbox on gear changes. The material the fans were made from proved to be problematic. While testing at Brands Hatch, the original plastic blades disintegrated, followed quickly by glass-fibre versions. Magnesium versions were then cast, but these were only available in the week preceding the Swedish GP at Anderstorp.
The system worked brilliantly. During first practice the front skirt started to wear away, but once a skid was placed on the bottom of the skirt, no further problems were encountered. The fan was so effective, that the car could be seen to suddenly squat downwards when the throttle was blipped in the pits. Its illegality was soon protested, but it was allowed to race, Lauda and Watson (here seen with Gordon Murray) qualifying 2nd and 3rd behind the Lotus 79 of Andretti. Andretti eventually dropped out due to valve spring caps breaking under load, causing a valve to break, allowing Lauda into the lead. Once a back-marker dropped oil onto the track, the Brabham was in a race of its own, seemingly unaffected by the slippery surface. Lauda went on to win by 34.6 seconds.
Rumour had it that Colin Chapman (here seen inspecting the BT46B) had sketched desigs for a twin-fan Lotus 79 on his flight back home, but although the Brabham car was declared legal, Bernie Ecclestone (team manager/owner of Brabham) decided that it was better to sacrifice the short term advantage of the fan car than to compromise the Formula One Constructors Association (FOCA), of which he was president. This proved to be a wise move in the event of the FOCA/FISA wars of 1980 and '81.
The 1978 Swedish GP weekend
