Tech Analysis: Mercedes diffuser ‘u’ bend

Tech Analysis: Mercedes diffuser ‘u’ bend

Since Mercedes launched the W05, its 2014 challenger, in Jerez at the beginning of February, a number of people have been questioning what the ‘u’ bend slot in the central section of the diffuser is all about. Recently its purpose has transpired and it is, like every other component on a Formula 1 car, a unique interpretation of the rules that is totally legal.

F1 cars, surprisingly, need to be started using an external starter-motor, which runs on a huge 24V battery to produce enough torque to kick-start the engine into life. The starter-motor is fed through a slot in the diffuser at the back of the car before connecting to a small gear that attaches to the flywheel.

The slot in the diffuser is therefore needed to start the engine but it also represents an opportunity for airflow to be transferred from the top of the floor to the upward facing slop on the inside of the diffuser.

Williams have a metal, hinged flap over their starter-motor hole

Williams have a metal, hinged flap over their starter-motor hole

Since 2010, teams have been exploring the full effect of the starter-motor hole in the diffuser as an aerodynamic device. In 2010 there were little rules surrounding its shape and size so we ended up seeing long, thin slots that aided the upwash of the diffuser. The FIA have been slowly clamping down on this area since, setting specific dimensions for the hole.

For 2014, the governing body have gone a step further: the hole must either be sealed off with a hinge (which still allows access for the starter-motor but otherwise closes up) or the hole must not be seen from beneath the car.

Whereas many teams have gone for the former option, Mercedes have continued to utilise a slot by moving the central section of the diffuser forward to create a vertical opening in the shape of a ‘u’. The slot isn’t visible from beneath the car so the solution is 100% legal.

Although it takes away a small area of the central expansion zone, the slot allows a large mass of airflow coming around the sidepods into the Coke-bottle region to bleed through the diffuser. This generates a higher volume of upwash at the rear of the car.

This is a design that can be copied by other teams if they wish to as it’s relatively easy to manipulate. However this is not a “silver bullet” in terms of performance and no doubt the W05 is optimised around this design. The same principals apply for McLaren’s ‘mushroom’ suspension arms.

The slot highlighted) allows airflow to bleed from the back of the diffuser into the expansion zone behind

The slot (highlighted) allows airflow to bleed from the back of the diffuser into the expansion zone behind

Images courtesy of Octane Photographic

William Tyson

William Tyson

William Tyson - a Mechanical Engineering student at Swansea University - has been writing about the technical side of Formula 1 since February 2013. After joining the Richland F1 team for 2014 he has continued to establish himself as a more rounded technical analyst whilst maintaining a healthy following on his blog.


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