The Brabham BT46B, better known as the “fan car”, was a Formula One car introduced at the 1978 Swedish Grand Prix as a counter to the dominant ground-effect Lotus 79. The BT46B generated an immense amount of downforce by means of a large, vertically-mounted fan located at the rear of the car.
By Graham Duxbury
The fan, whose claimed primary purpose was to cool the engine by drawing air through the rear-mounted radiators, was driven by the Brabham’s Alfa Romeo engine through the lower shaft of the gearbox.
Downforce was created by the fan sucking air from beneath the car, creating a low-pressure area. This gave the BT46B a substantial advantage in terms of tyre grip and cornering ability.
The BT46B was the brainchild of renowned South African designer Gordon Murray, who was forced to exploit the advantages of ground effect aerodynamics in a novel way. This was because of an inherent problem associated with the Brabham.
The broad architecture of the Alfa Romeo three-litre, flat-12 “boxer” engine meant any attempt to create conventional, under-body ground effect venturi tunnels – as pioneered by Lotus – was fundamentally compromised by intrusive cylinder heads. This led to the idea of the fan car which would obviate the problem.
The (then) Alfa Romeo engine boss Carlo Chiti described the concept as “posterior ventilation”, which he said produced the same physical aerodynamic advantages as the ground-breaking Lotus 79.
The BT46B won on debut at the Anderstorp circuit in the hands of Niki Lauda who dominated the race, leading from start to finish and lapping the entire field up to second place.
However, the BT46B did not race again, being voluntarily withdrawn by the Brabham team. This was mainly for political reasons and not because, as many pundits suggested, the fan contravened the rules forbidding moveable aerodynamic devices.
There are many interesting stories associated with the BT46B.
One might expect that positioning a large fan at the rear of a F1 car is a relatively simple exercise. Not so. It is reported to have required significant input from a thermodynamics specialist in order to perform optimally.
What’s more, the fan blades, originally sourced from a military tank and manufactured in glass-fibre-reinforced nylon were prone to failure. They had to be replaced with much stronger – and heavier – cast magnesium items.
On a lighter note, it was reported that the Brabham team went to great lengths to ensure secrecy, covering the fan at all times. But whereas today’s teams would manufacture a custom-fitted shroud, Brabham’s mechanics found a much simpler solution in the form of a dustbin lid.
Undoubtedly, the Brabham BT46B fan car made a profound impact on F1 and is celebrated to this day as one of the best examples of technical ingenuity.
However, it was not Murray’s only F1 fan car design. In secret, he was working on the Brabham BT47. This car was never built, but there was an important update in the nascent design.
The speed of the fan was variable, governed by car speed. On the straight, variable pitch fan blades would feather. As Murray explains, the BT47 design would generate ground-effect downforce in the corners but not create drag or sap so much engine power on the straights.
Perhaps unsurprisingly, this thinking was more than four decades ahead of what will appear in the F1 rule book for 2026 when the new age of active aerodynamics will be introduced. This time, however, the concept is primarily motivated by the desire to reduce drag in a straight line to hit fuel/thermal efficiency targets.
F1 aside, the BT46B/ BT47 fan car chapter in the automotive history book has recently been reopened with the aim of once again showcasing the innovative thinking and technical prowess of Gordon Murray.
He recently revealed a stunning new road-going supercar. Dubbed the T.50 Fan Car, it features a naturally aspirated V12 engine delivering 650 horsepower and an advanced active aerodynamic system incorporating a 400mm ground-effect fan which is a throwback to his famous Swedish GP-winning Brabham design.
What’s more, the T.50 employs sophisticated dynamic underbody ground effect systems which adapt to road conditions and demands for speed or adhesion – in a similar vein to the requirements of F1’s upcoming rules. The price of the T.50? An eye-watering R60-million.