Ground effect

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Colin Chapman made the biggest performance gain in modern Motorsport when he turned his attention to harnessing underbody aerodynamics. Keith Howard charts the process of using suction to blow away your rivals

The history of innovation is suffused with supposed imposters. John Boyd Dunlop didn’t invent the pneumatic tyre, Michelin didn’t invent the radial and Mr Ackermann did not invent the steering geometry that bears his name it was actually his self-effacing boss.

But so what? Having a good idea is in many respects the easy part of innovation. The tough part resides in taking that spark of inspiration, transforming it into a working reality and persuading the world of its worth. It’s no surprise, then, that popular history recalls the movers and shakers: they breathe life into the inventive process.

Colin Chapman is sometimes portrayed as a plagiarist, a man who copied the ideas of others rather than conceiving his own. If you’re determined on this accusation, you can find evidence to support it Evidence, for instance, that he didn’t invent the monocoque racing car. But if it was really so facile a development, why did nobody else in F1 make a success of it first?

Chapman’s other great racing innovation, ground effect aerodynamics, is also a case of disputed provenance. It has even been suggested that they were first deployed as long ago as the late 1930s 40 years before Lotus exploited the idea on the Auto Union record car in which Bernd Rosemeyer met his death, a claim which rests principally on the car’s use of deep skirts to contain underbody airflow. But engage brain for a moment Why should a car designed to travel as fast as possible in a straight line generate much downforce? Downforce is used to increase cornering speed. What’s more, its generation exacts a drag penalty, which compromises top speed. If the Auto Union streamliner developed any downforce at all, then, it wouldn’t have been much.

Much more likely is that it actually developed lift, just like Mercedes’ competing car which had to be ballasted with lead. A stronger claim to prior art comes from Can-Am racing or, to be more accurate, the USAC sportscar series that inspired it where, primarily through Jim Hall’s Chaparrals, downforce aerodynamics flowered before being adopted in Formula One. I say ‘downforce aerodynamics’ because there is no question that the most significant innovation in Can-Am was the use of wings, itself not strictly a first. America’s claim to the pioneering of ground effect derives from the Chaparral 2 of 1963 which Hall designed with a relatively high nose and curved ‘chin’ section beneath, the intention being to mimic the front portion of an inverted aerofoil.

Borrowed from GM’s Corvair Monza GT sportscar, it wasn’t a new idea Frank Costin had rather more expertly deployed a broadly similar concept in the reworked Vanwall of 1956and what’s more it didn’t work. In fact, in original form, the C2’s nose generated considerable lift. Fitment of a large chin spoiler, at GM’s suggestion, counteracted this and generated front downforce, but this is a far cry from ground effect as evinced by the Lotus 78 of 14 years later. There was no attempt to utilise as much of the underbody as possible to generate negative lift; no venturi tunnels; no side skirts; no grappling with the problem of how to control the centre of pressure to balance downforce between front and rear axles.

Hall went on to develop the famous 2J ‘sucker’ car which certainly did demonstrate the potential of downforce created by lowered underbody air pressure. But it used fans to produce this, not airflow management, which if anything makes it a predecessor of the Brabham ‘fan’ car. It and the Brabham were also both banned, cementing the likeness.

Other designers toyed with underbody aerodynamics or stumbled upon unusual ground-related aerodynamic effects, but there’s no question it was Chapman who conceived ground effect as we know it His influences might have been many (including the de Havilland Mosquito) but he alone foresaw the concept’s full potential, set in train the research and development necessary to realise it, and brought the result to the track with stunning effect. His first attempt, the Lotus 78, was good but not quite great; his second, the 79, sent everyone in F1 scuttling back to their drawing boards.

The basic concept was the same as Hall’s had been with the C2 to lower the air pressure beneath the car by accelerating it through a venturi, rather as in a carburettor but Chapman and his development team, which included Tony Rudd, Peter Wright and Ralph Bellamy, approached the task much more thoroughly and scientifically. Crucially, they had at their disposal a vital tool denied their predecessors: a moving floor wind tunnel, without which it is impossible to simulate underbody airflow with any accuracy. Famously, it was when the moving floor of the Imperial College tunnel lifted up and attached itself to the underside of the model that they realised they were on to something big. It is worthwhile repeating the figures quoted in a classic paper Peter Wright contributed to the International Journal of Vehicle Design in ’83, which for the first time put hard figures to the forces being generated by underbody antics in F1. At a speed of 150mph the Lotus 79 generated downforce of 100lb from its front wings, 2001b from its rear wing and 400lb from ground effect 7001b in total on a car weighing 16501b.

By 1980, such was the pace of development, wings were developing 600lb at the same speed and ground effect’s contribution had vaulted to 24001b, a total double the car’s weight If the Lotus 78, to borrow Mario Andretti’s famous description, was ‘painted to the road’, then the F1 cars of a few years later were bolted to it In more senses than one, the world of racing had been turned upside down. Talk was of being able to drive a ground-effect F1 car on a ceiling and of drivers coming to terms with the parallel universe experience of having more grip the faster they went Step changes in racing technology are rare, and ground effect was arguably the rarest of all the most significant motorsport development ever. Ignore those siren voices who try to dilute Colin Chapman’s claim to it.

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