Gordon Murray T.50 rear fan mechanism.

One of the main features of the GMA T.50 supercar is the downforce-producing rear fan, and in two videos produced by GMA, founder Gordon Murray and development driver Dario Franchitti explain this unusual aerodynamic device.

The fan is a reference to the 1970s Brabham BT46B "fan car" F1 racer designed by Murray. Exploiting a loophole in the rules, Murray used a rear-mounted fan to create a vacuum that sucked the car onto the track and generated downforce without the drag penalty of a large spoiler. The setup was so effective that the fan car, which entered (and won) the 1978 Swedish GP just once, was preemptively withdrawn before it was banned.

However, Murray insists that the T.50 fan had nothing to do with the BT46B. In the first video, Murray claims that the T.50's design is similar to his other big hit, the McLaren F1. That supercar had two small fans that acted on a small area of the rear diffuser, Murray says, and 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 and spins at up to 7,000 rpm, acting on the rear spoiler and rear diffuser. The standard T.50 has six settings: auto, high downforce, streamline, braking, test, and V-Max boost.

This allows for more downforce with less drag, as well as more consistent downforce regardless of speed, Murray says. The large rear wing and the ground-effect bodywork that many F1 teams used in the late 1970s are speed-dependent. They only work when sufficient speed is available.

In contrast, Murray claims that T.50 drivers can increase downforce by 50% simply by turning on the high downforce mode. Braking mode adds downforce under braking and can reduce stopping distance from 150 mph by 98 feet, according to the car's published specs; V-Max Boost adds ram air capability and boosts the car's power output to 690 hp; and V-Max Stream Boost increases the car's power output to 690 hp.

Streamline mode actually limits downforce when it is not needed. By lowering the spoiler and stalling the diffuser, it creates what Murray calls a "virtual long tail" effect, minimizing downforce and keeping the T.50 stable when driving straight at high speed. This, Murray claims, reduces overall drag by 12.5%.

As Murray explains in Part 2, this all works because the fan can pull air out from under the car more easily than the diffuser alone. The diffuser cannot be so large, because otherwise the air would stagnate and create vortexes, which would disrupt the downforce.

While these videos cover the standard T.50, GMA has also produced a circuit-specific version. Named T.50s Niki Lauda in honor of the late triple F1 champion, it skips all fan modes except high downforce. The fan works in conjunction with other aerodynamic devices, such as the large rear wing and spinal fins, to generate tremendous downforce.