Ground Effect (cars) - Porpoising

Porpoising

Porpoising is a term that was commonly used to describe a particular fault encountered in ground effect racing cars.

Racing cars had only been using their bodywork to generate downforce for just over a decade when Colin Chapman's Lotus 78 and 79 cars demonstrated that ground effect was the future in Formula One, so naturally at this point under-car aerodynamics were still very poorly understood. To compound this problem the teams that were keenest to pursue ground effects tended to be the more poorly-funded British "garagiste" teams, who had little money to spare for wind tunnel testing and tended simply to mimic the front-running Lotuses.

This led to a generation of cars that were designed as much by hunch as by any great knowledge of the finer details, making them extremely pitch sensitive. As the centre of pressure on the sidepod aerofoils moved about depending on the car's speed, attitude and ground clearance, these forces interacted with the car's suspension systems and cars began to resonate, particularly at slow speeds, rocking back and forth - sometimes quite violently. Some drivers were known to complain of sea-sickness. This rocking motion, like a porpoise diving into and out of the sea as it swims at speed, gives the phenomenon its name. These characteristics, combined with a rock-hard suspension resulted in the cars giving an extremely unpleasant ride, so much so that Formula One world champion drivers Mario Andretti and Alan Jones left Formula One because of it.

Ground effects were largely banned from Formula One in the early 1980s, but Group C sportscars and other racing cars continued to suffer from porpoising until better knowledge of ground effects allowed designers to minimise the problem.