This Is Not a Vacuum Cleaner

The Brabham BT46B fan car shares a large, circular protrusion at its rear with the new Gordon Murray Automotive (GMA) T.50 road car. Both are fans. And both were put there by designer Gordon Murray. Despite family resemblance, the T.50 and the BT46B are dissimilar vehicles whose fans serve very different purposes. The BT46B, which the Brabham F1 team ran at the 1978 Swedish Grand Prix, was a sucker car. Its fan created a low-pressure zone under the car that pulled the BT46B toward the ground, thereby generating downforce without the drag penalty of a wing (or, if the FIA asked, it cooled the engine). The fan nestled into the T.50’s rear bodywork is part of a less radical but more sophisticated aerodynamics scheme. Those who read car manuals might remember that Murray’s 1994 Mclaren F1 used two 120-mm fans to accelerate underbody air up over a steep section of the rear diffuser, which created around five percent more downforce (and a two percent reduction in drag). The T.50’s 400-mm fan operates on the same principle but is more comprehensive.

Like the F1’s fans, it reduces turbulence and air separation over the entire width of its rear diffuser, in concert with other aerodynamic components. For example, in its highest-downforce setting, the fan activates, a set of rear spoiler flaps flip up, and the diffuser ducts open. The result is 50 percent more downforce instantly.

The system has other settings, including the low-downforce Streamline mode for Autobahn sprints, which drops the flaps below the bodywork by –10 degrees, stalls the diffuser, and cranks up the fan to its maximum 7000 rpm to create a “virtual longtail” that reduces overall drag by 12.5 percent. A Brake Boost mode extends the flaps up 45 degrees, opens the diffuser ducts, and maxes out the fan, doubling downforce and reducing the T.50’s stopping distance from 150 mph by 10 meters.

For the most brutal acceleration, V-max Boost mode reduces drag to a minimum and isolates fan power to the T.50’s 48-volt starter-generator, eliminating parasitic drag on the naturally aspirated V-12 and delivering up to 690 hp for a short period.

“The Brabham was a really simple, crude device,” Murray said in a GMA video. “It was a vacuum cleaner.”