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 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. 

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.

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36 thoughts on “McLaren Snorkel: How it works

    • Dont forget this slot applies to the low pressure underside of the wing, which is close to seperating most of the time, so it doesnt take much to upset the flow structure around the wing

      • I’m still confuzzled. So, the driver closes the port, the air then flows through the slats behind the upper element, which detaches the stream, thereby generating a stalled condition?

        Are there any good pictures, or does anyone know, if the opening in the upper element is just a cut slit, or if it is beveled out a bit so as to direct the additional air in-line with the main stream, up and along the backside of the upper element?

        It would seam to me, a complete novice, that the purpose of a beveled slit would be to motivate the main stream to remain attached longer. In which case, the driver closing the cockpit hole would increase downforce (more aggressive angles), which is a condition you want in a corner but not in a straight line. SO, why would you want the driver concentrating on closing a hole… while braking… while concentrating on his line?

        How much air would you have to introduce into the cockpit to make a high pressure bubble in the cockpit? A bubble would allow the air to pass over/around the driver with less turbulence.

        I know everyone is saying McLaren is so much faster down the straights… but is that because they have less drag in the straights, or because they carry more speed through the corners, and thus more speed down the straights? Actually, it would be interesting to compare trap speeds at the end of long straights which began with a fast corner, versus a long straight that began with a slow corner. I guess you would still need similar length straights. Anyone want to put all of this data together and compare?

      • So, I’ve been reading the various threads on this subject, and here is my conclusion.

        McLaren, in response to F1′s trend toward less technical tracks, with fewer slow sections, have opted for a blown wing. The intent is not to “stall,” but to increase wing efficiency at lower wing angles. They sacrifice downforce in the slower sections for speed in the high speed corners and straights.

        The snorkel does not feed the system, but instead acts as a switch. When the hole in the cockpit is open, air from the intake box supplies the blown wing. When the hole is covered, the air stream coming into the intake box is blocked and is entrained in the existing flow towards the rear of the car.

        Here is an interesting article in Popular Science about Fluidics, which someone else found.

        http://books.google.com/books?id=jSEDAAAAMBAJ&pg=PA118&lpg=PA118&dq=fluidics+switch&source=bl&ots=Qsb0QmziiZ&sig=j94bWOB4pZOdZU1geMw8VBaQFUU&hl=en&ei=VJCaS8SMBI38tQP1tuB9&sa=X&oi=book_result&ct=result&resnum=3&ved=0CA8Q6AEwAjgU#v=onepage&q=fluidics%20switch&f=false

        At the end of the year, it will be interesting to see which teams do well on the slower, more technical tracks, and which do well on the higher speed tracks. I guess just comparing sector times would work too.

  1. Hi Craig, this is very interesting. I’m wondering what parameters go into the design of a wing to determine whether the extra air blown through the flap aids attachment/downforce (the BMW wing and normal additional slots where unregulated) or whether it causes detachment/turbulent flow (the McLaren solution)? It would seem to someone not expert in aerodynamics that this extra slot in the rear wing flap is having it both ways.

  2. I m not convinced the snorkel provides the air that actually stalls the wing, at 200mph there’s a huge amount of air hitting that wing.

    I more inclined to believe the interpretation that says the snorkel acts as a valve that switches where air sucked in from the airbox splitter gets exhausted, when the snorkel is blowing into the cockpit (aka on position) air gets exhausted over the diffuser/gearbox duct, driver moves and closes off the “switch” snorkel acts as a valve redirecting the air from the airbox over the rear wing, thereby stalling it.

    • I think you’ve hit the nail on the head with this one Alex. That snorkel looks like an awfully small intake, and the vertical stacking of the airbox (in contrast to a clear horizontal stacking directly at intake where flow is split to each bank of cylinders) would also tend to suggest such an approach.

      Whatever it is, I’m loving it and Bob Bell should perhaps try to remember why we all love F1.

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  4. I disagree with the author when he says, “It’s a piece of interpretive genius, but perhaps as far removed from the spirit of the rules as you can get.”

    Absolutely incorrect. The intent of the formula is to provide constraints for the design of a car. It is up to the teams to design a car with competitive advantage within the constraints of the formula. Innovation requires breakaway thinking and this is an excellent example of this very thing.

    The snorkel is actually the epitome of the F1 spirit. What is far removed from the spirit of F1 is building the same car each year within a safe interpretation of the formula.

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  7. I’m not sure that the explanation given would provide enough airflow, though the duct, too “stall” the wing @ 200mph!

    Regards,

    Slowflow

    • Yes Slowflow but read Alex’s really helpful post (no.2 above). A small flow of air could be used to switch the path of a much larger flow. Sort of like an aero “relay switch”. Now that’s truly impressive!

  8. Why do you say it’s legal? I thought it was illegal for the driver to interfere with the aerodynamics of the car? Bob Bell has already said that Renault will probably apply a formal protest.

    • It’s legal because there are no moving parts. The driver manipulates a lot of things in the cockpit (like gear changes), and this is just another very clever part of the system that a modern F1 car is today. I think Bob is still in the “Why didn’t we think of that?” part of denial, anger, and acceptance…

      • the only moving thing permitted since 2009 is the front wing adjustment in 6 degrees from the cockpit, btw this year could be more usefully to look after the front tires degradation…
        for me this system in the MP4-25 is legal 100% just wondering how let pass the airflow when the driver put his leg there!!

        cheers mate

  9. It can’t be illegal, if you make it illegal you make the driver illegal. The only moving part in the system is the driver, you can’t ban the driver from moving.

  10. Hi Craig, thanks for a detailed explanation on this, i was searching and this helps a lot.

    Just to know if a get it right: basically the hole permits the air going from the cockpit to the rear end helping to have less downforce and gain some speed??

    Thanks again for your time and your info…

    Cheers from Venezuela
    Alejandro Burger

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  12. for you guys doubting that the “small duct” could actually stall the wing – remember how valuable every fraction of nearly everything is in F1. I have no doubt that the wing has been calibrated to run at the very limit of stalling at the theoretical top speed of the car. If it were not being run like this the team would be ignoring a source of potential downforce – something they that is very unlikely. Therefore adding a small amount of flow, or diverting flow could very well be “stalling” the wing.

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  14. On the point of the driver being a “moveable aerodynamic component”, they’ve been that for years with their helmets shaped and positioned to aid airflow into the airbox!

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  16. Is it likely that this snorkel was causing Mclaren’s troubles in yesterday’s qualifying?

    May be, the drivers are not covering the snorkel with their knee well enough causing the wing to stall even in low speed corners?

    BTW, excellent blog. Long time reader, first time commenter.

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  19. Might sound like a silly idea, but did anyone notice Lewis using his left hand as if he could be activating this F-duct,in the Malaysia. I know it is supposed to be the drivers leg and that they make brake balance adjustment there, but it looked as if he had the back of his hand on the hole. I have yet to see an in conclusive cockpit photo, one way or the other.

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