fan assisted ground effect

[greggy_thommo]

Was just looking at the mclarencars website - it said that the mclaren f1 road car had "fan assisted ground effect" aerodynamics. I know it has probably been covered before, but what is the story with "fan assist" in downforce - I know that the f1 fan car was banned years ago - I'm wondering what the principle is...?

[Monstrobolaxa]

The principle is quite simple....reducing the amount of air (and with it the pressure) under the car in order to "suck" the car onto the ground!

[greggy_thommo]

but where does the fan come into it? is it to accelerate the airflow underneath the car?

[joseff]

The fan in the Mac F1 is much much smaller than the BT46 one. Its main purpose is to suck out the turbulent boundary layer off the diffuser, allowing a more laminar airflow out of it and hence more downforce.

The BT46 however had huge skirts meaning it actually vacuums the car to the ground. I particularly liked how the FSAE teams employed this in the Road & Track skidpad challenge: they attached a leaf blower to a kart.

[Steven]

aren't moving aerodynamic devices forbidden in formula one?

[joseff]

This was well before the flat-bottom era, so teams were very much allowed to put holes in the floor. Also Gordon Murray originally insisted that the HUGE fan on top of the body was a "cooling aid"

Of course it was swiftly banned after a "clarification" of the rules

[manchild]

but where does the fan come into it? is it to accelerate the airflow underneath the car?

It was located behind the gearbox and directly driven via output shaft.
http://8w.forix.com/fancar.html