Why did Formula One ban a race car the very same season it won?

Because its giant fan was a way around a rule that already banned movable aerodynamic devices, and it worked too well to ignore. In 1978, the Brabham-Alfa Romeo BT46B, designed by Gordon Murray, used a fan at its rear to suck air from under the car and press it onto the track. Brabham got past the rules by arguing the fan's main job was cooling the engine, since less than half the air it moved was used to create that suction.

The car raced exactly once, and won. Niki Lauda drove it to victory at the 1978 Swedish Grand Prix, and when the circuit turned oily during the race, rival cars had to slow down while Lauda simply accelerated, because his downforce actually increased the harder his engine worked. Brabham's owner, Bernie Ecclestone, agreed with rival teams to withdraw the car after three races, but the sport's governing body, the FIA, banned 'fan cars' with almost immediate effect anyway.

The underlying idea, called ground effect, wasn't new. In 1970, Jim Hall's Chaparral 2J used rear-mounted fans and ground-hugging skirts to the same end, and though it never won a race, rivals got it banned by the end of the year anyway. The real breakthrough came from Lotus instead: their 1977 Lotus 78 shaped its sidepods like upside-down airplane wings sealed to the ground with flexible skirts, generating huge grip without a fan at all, and the improved Lotus 79 won six races and the 1978 world championship. Other teams copied the trick until cornering speeds became so dangerously high that several serious accidents in 1982 forced regulators to require flat underbodies in 1983 — a ban on ground effect that lasted forty years, until it returned to Formula 1 in 2022.