X-ray spec: Williams FW07

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“Ground effect is not very sensitive to ride height as long as sliding skirts are permitted. FW07 had 75mm of spring travel and could be run soft. But once sliding skirts were banned and we went to flexiskirts, the necessity for a good seal did make the cars movement-sensitive as the skirts now only had a useful range of about 15mm, compared to 75mm with sliding skirts. Flat bottoms were still worse, even producing lift at quite tiny nose-up incidences. Whomever thought the flat bottom was a good idea, and would make better cars, was an idiot. I believe it was a French journalist’s Idea, which Balestre read and believed. It got a touch better with the plank following Senna’s death, and better still now with the stepped plane rule”

Although the FW07 was closely modelled on the dominant Lotus 79 of 1978, it was designed with a better appreciation of the high loads imposed on the car’s body by the development of significant negative pressure beneath – a lesson that Dernie thinks Lotus failed to learn with the disastrous 80: “Our sidepod and skirt box were much stiffer than on the Lotus. Ours was aluminium honeycomb with considerable section: theirs was polyester glass with local blocks of foam laminated-in for stiffness – probably nowhere near enough. The skirts would probably jam at high loads, which I believe was the main cause of the 80’s porpoising. Peter Wright thinks that porpoising was an aerodynamic phenomenon caused by the airflow detaching and reattaching at different ride heights. But I did sufficient experimentation to conclude that it was caused by jamming skirts”

“One of the most important aspects of FW07’s success was its skirt and skirt box design. The initial skirt system was a carbon/structural foam composite plank fitted with a polyethylene seal, ceramic rubbing strips and Tee slot guides: the later system used roller guides to reduce friction. I reasoned that the inward load on the skirt was highest on the inner skirt as the car rolled off it, so to keep it on the road more force was needed at long skirt extensions. The skirt suspension we had to develop to achieve this was more sophisticated than the suspension of the car itself! We could immediately tell if the skirts weren’t working properly because we got porpoising”

“We used two different underbodies, depending on the circuit. The one with a more rearward centre of pressure had less downforce and the resultant car, together with its smaller rear wing, was quite a bit worse, so we did not use it often: Hockenheim and Monza spring to mind. I think they were the Mk4 and Mk27 – these are wind tunnel numbers, we did not make them all full-size. No standard wing profile is appropriate for ground effect, so we started from scratch. The underbody shape was carved in wood. We fitted a row of pressure tappings to it and used a manometer bank to monitor the underbody pressure. I then modified the shape following what I observed on the pressure profile. Later we had a hollow pod with a built-in scanivalve and pressure sensor, which was much neater”

Most people’s diffusers stopped at the rear suspension. It was very difficult to keep the flow attached any further back, so all you got was more weight and less accessibility. I am told the Brabham BT49 never had attached flow rearward of the chassis because they never found a solution to keeping the flow attached after the sudden change of section. If so, it must have had a much better rear wing than ours! We sorted this just before Silverstone in 1979. The fairing that achieved it was discovered that week at Imperial. It was such a big gain that I came back from the tunnel, drew it full-size overnight and got It made and fitted in time for the race. It was worth 1.5 seconds a lap!”

“I don’t really remember how much the underside and rear wing contributed to the overall downforce – probably about 80/20 per cent. But since the rear wing was a significant part of defining the wake pressure which drove the underbody performance, it is impossible to separate them. The rear wing was not at the legal limit because overall performance was better with the underbody and wing coupled. The lift-to-drag ratio was between 6 and 7, I think. The thing I really remember was FW08 at 8.2 – which was the best we raced before flat-bottom cars”

More grip gives the brakes a hard time – it was very difficult to get them to live in a 13-inch wheel. The toughest circuit was Montreal. We usually just fitted ducts to suit.” In fact the grip at high speed was such that, with no power assistance, drivers could no longer lock-up wheels everywhere within the car’s performance envelope; this meant its full braking potential could not be exploited. “The limiting factor was a driver’s leg strength! Maybe we couldn’t use all the grip potential of a ground-effect car back then, but the braking was still massively better simply because of that grip”

The case for the persecution

“I don’t think any driver who experienced real ground effect did not like it: Alan Jones loved it. Sadly, the most famous and Influential drivers, Scheckter and Villeneuve, were at Ferrari, who never engineered a working skirt. Their car must have been horrible to drive. They assumed that all ground-effect cars were as bad as theirs, and their opinion was a big part of the journalists’ false view that ground effect was dangerous”

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