How Gordon Murray T.50's rear fan works

One of the GMA T.50 supercar's most distinctive features is a downforce-generating rear fan. In a pair of GMA-produced videos, founder Gordon Murray and development driver Dario Franchitti give the lowdown on this unusual aerodynamic device.

The fan references the Murray-designed Brabham BT46B "Fan Car" Formula One racer of the 1970s. Exploiting a rules loophole, Murray used a rear-mounted fan to create a vacuum to suck the car down onto the track, generating more downforce without the drag penalty of larger spoilers. The setup worked so well that after entering (and winning) just one race—the 1978 Swedish Grand Prix—the Fan Car was preemptively withdrawn before it could be banned.

However, Murray claims the T.50's fan had nothing to do with the BT46B. In the first video, Murray claims the T.50 design is actually closer to another one of his greatest hits—the McLaren F1. That supercar actually had two small fans that acted on a small area of its rear diffuser, Murray said. The T.50 essentially takes that concept and supersizes it. 

The 15.7-inch carbon-fiber fan is driven by a 48-volt electric motor, spinning at up to 7,000 rpm and acting on rear spoilers and a rear diffuser. The standard T.50 includes six settings: Auto, High Downforce, Streamline, Braking, Test, and V-Max Boost.

That not only allows for more downforce with less drag, but also generates for a consistent amount of downforce regardless of speed, Murray said. A big rear wing, or the ground-effect bodywork used by many F1 teams in the late 1970s, is speed-dependent. It only works if you're going fast enough.

In contrast, a T.50 driver can simply switch on High Downforce mode and get 50% more downforce, Murray claims. Braking mode can add downforce under braking, shortening the stopping distance by 98 feet from 150 mph, according to the car's published specs. V-Max Boost adds a ram-air function, raising the car's output to 690 hp. 

Streamline mode actually limits downforce when it isn't needed. It creates what Murray calls a "virtual longtail" effect by lowering the spoilers and stalling the diffuser, minimizing downforce to keep the T.50 stable during high-speed straight-line runs. That reduces overall drag by 12.5%, Murray claims.

As Murray explains in part two, this all works because the fan can pull air out from under the car more readily than a diffuser alone. A diffuser can only be so large, otherwise air stagnates and creates vortices, which disrupt downforce.

These videos cover the standard T.50, but GMA is also building a track-focused version. Named T.50s Niki Lauda, in honor of the late triple F1 champion, it will skip all of the fan modes except high downforce. The fan will work with other aerodynamic devices, including a large rear wing and spinal fin, to generate what could be a staggering amount of downforce.