Feats on the ground
How primitive testing morphed into serious downforce
Back in the 1960s pretty much the height of Formula 1 sophistication had been Ron Tauranac and Brabham putting their 1½-litre F1 car in the full-size MIRA wind tunnel at former RAF Lindley, Warwickshire – for tuft tests of airflow around it. Ron donned a crash helmet, and slipped into the cockpit. Tuft photography did the rest. The shape proved quite clean. Maybe the fuel-injection air intake benefited – but that is as far as it went.
The downforce effect of underwing surfaces was even then being explored by a handful of inquisitive – and now largely forgotten – pioneers, not least Giotto Bizzarrini in Italy and (where strutted wings are concerned) by Indycar constructor Jerry Eisert in the US. American researcher Shawn Buckley was retained briefly by Colin Chapman in 1969 to explore ‘wingless’ downforce generation. Coincidentally, at BRM in Bourne, chief engineer Tony Rudd had detailed the young Peter Wright
to do the same.
By 1976-77 Peter had rejoined Tony Rudd – then at Lotus – and Colin Chapman had plumb forgotten about Shawn Buckley’s findings, proven on a Citroën DS rigged with a shaped underfloor but without any skirts to prevent aerodynamic in-fill diminishing the effect.
Peter recalls how pioneers John Stollery and W K Burns had proved the efficacy of a moving belt within a wind tunnel to mimic the reality of a car operating in ground contact. Fackrell and Harvey followed on with a moving ground belt in their Imperial College wind tunnel.
Peter Wright and Team Lotus designer Ralph Bellamy were then dispatched to Imperial “working with a quarter-scale model to define what would become the Lotus 78. We noticed it was increasingly difficult to get consistent load readings and then realised that the more we modified our model’s sidepod sections the more inconsistent it seemed to get. We could see the sidepods sagging and rebounding, and then ‘Eureka!’ – when they sagged the gap between their undersurface and the moving ground closed-up and the loadings spiked. When they rebounded the effect was lost. And so we identified the significance of ‘the gap’. I spent the rest of the year hanging out of the back of a Minivan driven by Eddie Dennis around the Hethel test track, reading loadings on a downforce test section.”
In succeeding years the norm for wind-tunnel racing car development progressed from quarter-scale (25 per cent) models to more accurately read 40 or 50 per cent models. At low wind-tunnel airspeed and small scale, laminar flow across the model’s surface extends farther back than on the real car. If the ratio of inertia forces to viscous forces is too low, the small model’s downforce-generating surfaces will stall. The crucial ratio is represented by the ‘Reynolds number’. Testing at too low a Reynolds number risks misleading tunnel results so the ambition has been to work at a Reynolds number as close to the full-size car’s as they can achieve. Plainly larger-scale models and higher-speed wind tunnel airflows were required.
In 1998 Benetton F1 tried a short cut, launching its new 50 per cent-scale tunnel at Enstone. Its builders claimed that its moving belt and fan were designed for 250kph – 155mph – requiring 10,000hp and a refrigeration plant to maintain constant tunnel temperature, outstripping available electrical supply. Running at 215kph – 134mph – should have represented a Reynolds number equalling one-third that of the full-size F1 car at its maximum 350kph – 218mph. But the tunnel designers had gone a stage further, since it could be pressurised to 1 bar, doubling the density of the air within and thereby doubling the Reynolds number to 0.6 that of the actual car.
This seems to have proved a step too far, since the tunnel’s entire steel structure emerged as a massive 700-ton pressure vessel. Its multiple welds reputedly leaked, so that pressurising it adequately could take the best part of an hour. When F1 test teams feel cheated by only 24 hours per day and seven days per week, this was a significant time waster.
That Benetton tunnel cost a claimed $20 million, and as recently as 2012 Mercedes-Benz approved £2 million to update its unpressurised tunnel from 50 to 60 per cent model size.
It’s all a far cry from the embryonic Williams GP Engineering team buying what had been Peter Wright’s Specialised Mouldings wind tunnel and re-erecting it at Didcot. One of their staff perfecting it then had been young Ross Brawn. He recalls how when they put the first ground-effect car model of what would become the Williams FW07 into the newly installed tunnel, their download measuring device – like a chemist’s-shop weighing machine with sliding counter-weights on a pivot bar – just recorded no load at all. “We tried repeatedly to make some sense out of it, and then thought ‘Hang on a minute – maybe the measurement range needs resetting’ – so we slid the weights along to a higher range and tried again. It was no better. No reading. But then we tried again – choosing what to us was an unbelievably high range – and Bingo! There were our readings. That was our Eureka moment. We suddenly realised just how massive ground-effect download could be and how effective Lotus had been in covering it up all year, leaking rumours of trick diffs and other such stuff to put us all off the scent.”
In the Noughties, Peter Wright saw Jim Hall with his Chaparral ‘Fan Car’ at the Goodwood Festival of Speed: “I suggested that between us we had wrecked motor sport. He grinned and just about agreed…”
The VW Group scandal simply reflects a firm with traditional racing guile
There are plainly many more headlines to come in the VW emissions scandal. Observing its progress from the touchline I can’t escape the feeling that a racer was initially involved. Bending a regulation, or weaving an arguably permissible route around one, is deeply embedded into any real racer’s DNA.
Consider the 1981 ban on F1 cars’ sliding skirts. It heralded the fleeting age of so-called ‘clearance cars’ by demanding a 6cm clearance between an F1 car’s lowest suspended part and the road surface. FIA luminaries had been reassuring teams that skirts would still be allowed, but apart from the 1981 South African GP (deprived of world championship status) the 6cm clearance rule applied. Gordon Murray of Brabham said at the time: “We had discussed such a rule and rejected it as unenforceable. Now we had a month to build clearance cars before Long Beach” so he and colleague David North “took the rules and read them closely again…”
They were confident every team would fit soft springs and allow aerodynamic loads to force their cars closer to the track, whereupon fixed-skirt ground-effect sections would begin “to suck”, exerting their download, overcoming the lack of sliding skirts to provide consistent sealing against ambient-air in-fill.
No part of the car would be closer than 6cm to the ground except wheels and tyres “when measured”. Certainly “no part would systematically or permanently touch the ground” as had the old sliding skirts (as prohibited by the new ruling). Even had sliding skirts been retained, if the car hit a bump or more so a kerb then the skirt would surely leave the road surface for a moment, which would alone constitute “not permanently touching the ground” – clearly demonstrating the new rule’s semantic limitation.
So it was simply unenforceable. It said nothing about measuring the car’s clearance at speed. As Gordon said: “If you set a Ford Escort at 6cm clearance when stationary and then drive it on the road, it’s going to squat and at some time it’ll clear only 5.99cm, so did that mean we had to set cars at 7cm static, so they would go no closer than 6cm at speed? That’s not what the rule said. It was stupid. We told them it would be unpoliceable but we built a system that complied with it to the letter – confident everyone else would be doing the same thing.”
Murray and North selected a soft air spring that stored the energy by driving down a hydraulic piston – piped to cylinders on each suspension corner – compressing air in a central reservoir. By carefully choosing orifice sizes, fluid could be bled back to the cylinders, pumping the suspension back up. So the car would in effect be blown down by download as it gained speed. Fluid would be forced out of the cylinders, load the piston, and compress air in that central reservoir. “Then if we got the bleed rate right, the car would stay down through slow corners without springing up suddenly as download diminished. Once the car slowed on its way back in, the compressed air would force back the reservoir piston, fluid would bleed back into the cylinders on each suspension corner and the car would rise.”
And there’s the key – compliance could only be verified at the moment of measurement. The clearance cars of 1981 complied. At Long Beach, to Brabham’s astonishment, they found their cars were the only ones so equipped. But using plastic hydraulic lines to save weight was a mistake. They blew off or melted. Fluid leaked and the car sank, so Nelson Piquet ran finally with conventional suspension.
In Brazil problems persisted, but Nelson qualified on pole. The team’s fixed skirts attracted attention, made from a material that could not survive extended ground contact. Williams and other rivals protested to establish what was considered legal and what was not. They objected to the skirts’ floppiness, which enabled them to suck in and run on an air-bleed bearing that kept them effectively airborne, barely above the road surface. This movement was considered to contravene the requirement “to remain immobile in relation to the sprung part of the car”. Gordon argued “Everything moves to some degree. How rigid is rigid? How do you define it?”
So for the Argentine GP everyone ran some kind of skirt system. But Brabham’s lowering devices remained troublesome. A Mark II system used in Buenos Aires would not stay down out of slow corners – but Nelson gained so much time round the quick bits that it compensated and he won.
For Imola a Mark III system proved reliable until the last 10 race laps, when Nelson rocketed past the pits “like a power boat with the car’s nose jammed up and its tail still down”. He still won.
A FISA meeting then issued one of its famous ‘clarifications’, specifying uniform skirts, maximum 6cm deep and 6mm thick. It was plain that lowering systems, though ethically illegal, could not be policed. Brabham’s system needed no switches but at Monaco they put a switch on one car and kept the defensible system on the other. Gordon: “I wanted to put a big notice on the switch saying ‘suspension height correction switch’ but Bernie wouldn’t let me…”
The cars had gone from some 6.5 inches total wheel movement to 1.5 inches, half of that provided by tyre flexure. What had been brought about allegedly by the drivers’ plea to ban skirts to provide slower, safer cars had resulted in the cars battering themselves and their drivers apart. The law of unintended consequences had struck again – but where a legal requirement can only be measured by a one-time test, a racer will always find a way around it. Competitive forces mean they can’t help themselves. Transfer that mentality into major industry and it’s asking for trouble.