F1 2009 Technology: Rear wings, diffusers – and the inevitable controversy

Posted on | Author John Beamer

McLaren have had lots of problems with their rear wing and diffuser
McLaren have had lots of problems with their rear wing and diffuser

As we head into the first race of 2009 a row is brewing over the diffusers used by Toyota, Williams and Brawn GP.

F1 Fanatic guest writer John Beamer takes a look at the diffuser row and offers his thoughts on what’s gone wrong at McLaren.

Hands up who finds that rear wing attractive? Uh… thought not. What is the FIA playing at? In two words: not sure.

We all know that the objectives of the 2009 regulations were to reduce the wake and aerodynamic sensitivity of the car. A high, squat rear wing was the FIA’s response to its own challenge.

By raising the rear wing it works in cleaner air so the plane should be more efficient. More downforce is available for a given angle of attack which, all else being equal, makes the associated wake smaller. However, the reduced plan area cuts total downforce and teams may simply reclaim lost grip by running more cambered profiles. Drag increases slowing the car – some in the paddock contend that this was the true intent of the FIA’s regulation.

The other consequence of raising the wing is to decouple it from the diffuser ?ǣ moving the diffuser back helps too (more on that later). How does raising the wing help? The 2008 regulations cause the rear wing to generate a low pressure zone at the base of the car, thereby creating a shallower pressure gradient for the diffuser to work against.

In theory, raising the wing pushes this low pressure zone higher so upwash from the rear wing/diffuser combination is muted. So far the profile shape and integration with the endplates are nothing that hasn’t been seen in the last couple of seasons.

More interesting is the interpretation of the diffuser regulations. Compared to 2008 the diffuser has move aft, to the rear wheel centre line, is raised, with a severely restricted central section.

The diffuser controversy

Timo Glock's Toyota - diffuser highlighted (click to enlarge)
Timo Glock's Toyota - diffuser highlighted (click to enlarge)

That teams can run a central section at all is of some contention. However a close reading of the rules suggests that a 150mm central section extending beyond the main diffuser is permissible. Toyota was the first team to take advantage of this, with its small central tunnel.

The theory is simple. By increasing the overall volume of the diffuser air can be slowed in a more controlled fashion which reduces the odds of flow separation. I find it hard to believe that the FIA will outlaw this central tunnel as it is a fair interpretation of the rules

More controversial are the subsequent interpretations by Brawn GP, Williams and Toyota. These teams have so-called ‘double decker’ diffusers and likely contravene the spirit of the regulations if not the letter. The regulations for the diffuser rely on bodywork visible from the ground. This means that bodywork behind that which is visible from the ground sits outside the rulebook governing diffusers. Hey presto, a few canny designers have exploited this loophole.

The Williams and Brawn diffusers do exactly this. A lower surface tracks a higher, wider upper surface, which creates a more voluminous device. As we head to the first race of the season it is unclear whether the FIA will permit these.

McLaren’s problems

McLaren’s woes likely originate in the diffuser, which is one of the reasons why green flow-vis paint was plastered all over the device in recent testing. Flow separation here is pernicious, causing stall and a loss of downforce. Not only will this make the car a lot more susceptible to oversteer but the rear tyres wear out a lot faster.

The problem with flow separation in the diffuser is that it is hard to pinpoint the root cause. The issue may be with the diffuser but equally may be to do with the splitter. After all the diffuser must work with the flow patters it is given – all of which is heavily influences by what happens at the front of the car.

Given the Kovalainen set the MP4-24’s fastest lap despite not being a fan of oversteer suggests the Woking-based outfit has overcome its back-end issues. However, that doesn’t mean McLaren will be on the pace in Australia.

It’s taken the team several weeks to get to the bottom of the problem, if indeed it has. Development on other aspects of the car will have slowed. Although the boffins at HQ are capable of developing the car at a prodigious rate, in the current environment of restricted testing it won’t be before the European rounds that Hamilton and co. are back on the pace.

John Beamer also writes for Race Tech magazine.

Images (C) www.mclaren.com, Toyota F1 World