MP4-25 - The infamous snorkel
It has now emerged from comments by Martin Whitmarsh to Autosport.com that McLaren do indeed have a link between their rear wing and the snorkel on the top of the chassis. While a link between the two parts emerged during testing as they were both fitted with the same aero testing set up, it is only now that the full picture has emerged. Using the driver to interact with the snorkel feeding the rear wing and its attendant slot, the wing can ‘stall’ increasing straightline speed when the driver needs it.
How its done…
The snorkel on the top of the chassis feeds a duct passing down inside the footwell, its position is some where around the pedals, most probably it runs down alongside the brake pedal\footrest so as to avoid the mandatory padding inside the cockpit. This duct has a ‘hole’ in it to ‘cool’ the driver inside the cockpit. However the duct continues inside the chassis, past the fuel tank and up and over the airbox (probably passing by the hatch fitted high up on the engine cover), then through the shark fin and into the rear wing flap.
When the driver places his foot\leg over the ‘hole’ the flow is diverted into the rest of the duct and this feeds the slot on the rear wing flap. There is enough airflow through the convoluted duct to disrupt the airflow under the rear of the wing, effectively breaking up the flow around the wing. This is what F1 aerodynamicists term a ‘stalled’ condition, although this is different to the term ‘stall’ used in aeronautical aerodynamics. In this ‘stalled’ state, the strong spiralling flows coming off the wing, that lead to the huge drag penalty a highly loaded F1 wing incurs, break up. With out these flows and their resulting drag penalty, the car is able to get to a higher top speed, by around 3-4kph.
When the driver is ready to brake for the next corner, he releases foot\leg and the airflow passes back into the cockpit and the rear wing flow reattaches, creating downforce and its attendant drag. In this format the car can lap normally with its wings delivering maximum downforce.
This set up is legal as the rear wing slot in itself is legal (used by McLaren, BMW Sauber last year). There is no specific working to prevent wing stalling in the rules. There are no moving aerodynamic parts, except perhaps for the drivers foot\leg. It’s a piece of interpretive genius, but perhaps as far removed from the spirit of the rules as you can get.
Of course now its deemed legal, teams can either formally protest it or adopt it themselves. Doing the the latter is possible for most teams, as they have apertures in the footwell area to fit a snorkel, while the shark fin and rear wing are easily created. But, finding a route for the duct out of the tub might prove the headache, as the monocoque may not have any openings sufficiently large enough. This year the monocoque is also is subject to homologation and hence cannot be altered until the 2011 season. Of course ‘where there’s a will, there’s a way’, teams will not want to lose a straight line speed advantage.