McLaren Snorkel: How it works

MP4-25 - The infamous snorkel

http://www.autosport.com/news/report.php/id/82001

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 pedalfootrest 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 footleg 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 footleg 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 footleg.   It’s a piece of interpretive genius, but perhaps as far removed from the spirit of the rules as you can get. 

What now

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.

McLaren: Legality and Bahrain spec

MP4-25 - Rear wing scrutineered and declared

Correction the diffuser has again appeared in its full guise in FP1, we all make mistakes…!

Incidentally McLaren arrived with major revisions around the rear of their car. firstly the diffuser shown in the pitlane for scrutineering was devoid of the upper deck bodywork that extended to the beam wing. this slotted panel effectively stretched the diffuser into a longer and higher device for more dowforce. While the diffuser below this panel is the same version as McLaren ran late in their testing programme. above the diffuser the crash structure and slotted beam wing remain the same, but the added duct to vent the oil cooler has gone.

McLaren Developments: Snorkel rumour

NOTE: Update on McLarens SnorkelRear wing here http://wp.me/sNdA9-235 

As McLaren continue to use testing rigs to map their cars aerodynamics, the importance of the snorkel on the top of the chassis is becoming apparent.  On Friday The car lapped with an array of sensors attached to the rear wing.  However, there was an additional sensor mounted inside the snorkel.  Raising the question why would you want to test rear wing and driver cooling simultaneously?

This Snorkel, is an apparently innocuous looking part, which was at first believed to be solely an inlet to cool the cockpit.  Several teams add similar inlets in this area to supplement the inlet in the tip of the nose.  The cockpit houses the power steering rack, hydraulic lines and electronics boxes, so cooling is often required.  However the initially simple inlet has been superceded by at least two more shapely snorkel-like derivatives each with an apparently unnecessarily complex double wall construction creating smooth narrow inlet and a streamlined outer surface.  This snorkel has been present ont he car through out all the cold and wet testing sessions, suggestion its purpose goes beyond a simple primary purpose of cooling.

One rumour around the internet suggests the inlet is linked by a duct to the shark finblown rear wing.  At first appearing to be simply a wild rumour, that the snorkel is blocked by the drivers knee to alter the rear wing airflow.  However the presence of the airflow sensor along with the rear wing test rig, suggests there might be a link after all.  The rumours suggest the drivers left  braking leg, which sits unused on long straights could be used to alter the flow from the snorkel to the rear wing duct, where a valve alters flow through the blown slot to stall the rear wing.  This would reduce downforce and also drag, which would allow a higher top speed.  Then the driver moves his leg to start to brake for the next turn the valve switches airflow back to normal, the wings airflow reattaches and provides the downforce needed for the turns.  This sounds both feasible and far-fetched at the same time.

It would be hard to link the rear wing and snorkel with any certainty, but any input from the driver that would alter the cars aerodynamics as the rumours suggest would certainly be an area of greyness in the rules and liable to protest come Bahrain.