Can a major engineering upgrade of the MP4-28 rescue McLaren's season?

Sky Sports F1's Mark Hughes explains the problems that have afflicted McLaren this season and ponders if they can return to form in China.

By Mark Hughes.   Last Updated: 01/04/13 12:19pm

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Jenson Button's entire 2013 season probably hinges on what happens at the McLaren Technology Centre in the three weeks between the Malaysian and Chinese Grands Prix.

Will he be a contender this year, winning races just as in his previous three McLaren seasons, or is he consigned to be a bit-part player in a fundamentally flawed machine?

A major engineering upgrade of the troublesome MP4-28 is underway. The alternative - that of bringing last year's car out of retirement - has for now been cast aside, though it was considered. The team is confident it has identified the main shortcoming of the car as an aerodynamic one, unconnected with the radical pull-rod front suspension and centring around the underfloor.

The way airflow behaves in the small gap between the ground and an F1 car's underfloor is extremely sensitive and very aerodynamically powerful. The lower to the ground it can run, the more downforce that can be produced as the air pressure difference between the underfloor air and that in free-flow around the upper surfaces of the car increases - and it is this difference in pressure that sucks the car harder to the ground.

A 1mm reduction in ride height can give a downforce increase worth around 0.1s per lap. The normal limitation is the car grounding out as the downforce through the faster corners grinds the car into the ground. Allowance has to be made for the addition of around 150kg of fuel at the start of the race - and for the fact that parc ferme regulations do not allow a change of ride height between qualifying and race. If that were not the case, the cars could be run much lower during qualifying when they are running light, with low fuel levels.

At the ride height range in which an F1 car normally runs, the McLaren's underbody airflow detaches, separating off and dispersing rather than following the downforce-inducing form of the floor and diffuser. As this happens, much of the downforce is released, the car moves up on its springs as a result and thereby moves out of the critical ride height window where the air detaches. With the airflow now working as it should once more, so the downforce builds again, forcing the ride height back down to the critical level and triggering the detachment. Hence the car behaving like a bucking bronco, particularly around the bumpy Albert Park circuit in Australia.

Just as the McLaren's airflow can be made to behave normally above a certain ride height window, so it seems there is a ride height below which it will also work. But that ride height is too low to use in race conditions - and therefore cannot be used in qualifying either, because of the parc ferme regulations. It is believed the car was running with this super-low ride height when it set the fastest time of the first day at Jerez testing.

At Malaysia the car was improved compared to Australia by the team running the car relatively high, above the ride height that triggers the most severe of the buffeting phenomenon. Although such a ride height sacrifices downforce to rivals that can run lower without problem, reducing the bouncing brought more gain than the loss from reducing peak downforce.

"We were at least 1.5s off the pace in Australia," said Button in Malaysia, "but if qualifying had remained dry here I think we would be maybe 1s off, maybe even slightly less. It's helped by the fact that Sepang is a smoother track than Albert Park, but it's also from improvement in the car from the way we're running it." Obviously, the aim is to be able to ruin a conventionally low ride height but without triggering the airflow detachment.

The team believes it learned a lot about why the detachment problem is arising from on-the-hoof modifications made in Sepang, including crudely 'cutting and shutting' the contours of the diffuser, in order to energise the flow better around the crucial areas where it is detaching.

Whilst it's surprising that the powerful simulation tools of McLaren did not pick up on the aerodynamic problem before the car actually ran, the team is running absolutely flat-out in the break before China to have heavily upgraded cars in Shanghai for Button and Sergio Perez. Don't bet against a total transformation of form.

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