How the Red Bull RB8’s exhaust feeds its diffuser

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To no-one’s surprise the race-specification exhaust for the Red Bull RB8 appeared on the penultimate day of the last pre-season test.

The team went to considerable lengths to cover it up, as the video above shows. But now the design has been seen we can get a look at how it works.

As the FIA has restricted where teams can place their exhausts, designers are striving to continue using the hot air to make their diffusers more powerful.

Red Bull’s approach is similar in principle to McLaren’s exhaust concept in that it tries to pull the exhaust plume downwards from the exhaust exit over the side of the diffuser to create a sealing effect.

The Red Bull design appears quite different and more elegant. But we won’t know until Melbourne whether it is more effective.

The Red Bull RB8 exhaust

Red Bull RB8 exhaust diagram
The first illustration shows Red Bull’s new set-up. I’ve left out the pull-rod suspension arm and lower wishbones to make the image a little clearer.

The grey zone where the exhaust exits is covered in heat-resistant paint to prevent damage to the carbon fibre. The exit contains a channel indent to drag the plume downwards using the Coanda effect, as described in the McLaren exhaust article.

This area is shaped to continue to drag the exhaust gas downwards towards the diffuser. In addition, air coming over the sidepod is also used to create a high pressure zone around the exhaust exit, further helping the Coanda effect and shaping the exhaust plume. The red lines show the exhaust flow.

The issue designers face is that this potentially interferes with how the undercut sidepod works.

Over the past couple of years teams have aggressively undercut the sidepod to feed fast-flowing air to the coke bottle zone. This helps the diffuser to be more effective by creating a low pressure zone above it, which in turn reduces flow separation in the diffuser.

Dragging the exhaust plume to the floor will reduce the effectiveness of the coke bottle zone. The bulge in McLaren’s exhausts is designed to direct the exhaust gas over this flow.

Red Bull have adopted a different solution which is visible in the image. They have carved a duct at the bottom of the sidepod for the undercut airflow to go through. This duct exits in the coke bottle zone, missing the exhaust plume.

Replicating the exhaust-blown diffuser effect

Red Bull RB8 exhaust diagram
The second illustration shows a similar picture of the RB8’s exhausts in plan view.

The exhaust exit is circled in yellow and again I’ve added the exhaust flow (red) and undercut flow (blue).

From this angle it is possible to see the shape of the exhaust indent in the bodywork. It is built in such a way that the exhaust gas appears to split – one stream spills over the side towards a vane on the floor ahead of the inner part of the rear tyre.

This will create a vortex and is primarily aimed at sealing the diffuser – this part replicates the effect of last year’s exhaust blown diffuser.

The second stream adds energy over the diffuser, which will help reduce the pressure gradient above the diffuser exit and hence reduce the risk of airflow separation under the car.

It is thought by some that the exhaust flow may partly feed a duct in the floor that houses the starter motor hole. However, it is unclear at this point whether this is for exhaust gasses or air flowing through the sidepod duct. Given the restrictions on starter motor hole size the effect is likely to be small.

As exhaust solutions are developed we’ll get a feel for the most effective solution. Last year teams quickly converged on Red Bull’s solution to optimise the exhaust blown diffuser.

Ferrari technical director Pat Fry suggested the same could happen again this year, assuming Red Bull’s design is considered legal, telling Sky: “It comes down to what re-ingested exhaust gas is really and that’s a question for Charlie [Whiting].

“I think it’s the obvious direction to go in. We gave it a shot; we didn’t quite get it right. The issues we had, we weren’t going to solve for at least the first four races, so that’s why we had to back up and change course.”

At this point the Red Bull solution is visually neater but doesn’t completely eliminate the exhaust/undercut interaction. McLaren’s solution likely does a better job in this respect but could face trade-offs on drag or quality of exhaust flow to the diffuser. The first weekend of running in Melbourne will yield more clues.

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Illustrations ?? John Beamer for F1 Fanatic

50 comments on “How the Red Bull RB8’s exhaust feeds its diffuser”

  1. It will be interesting to see which exhaust system will be preferred by most teams: McLaren’s, Red Bull’s. Both designs fulfill the same role: directing the exhaust gasses towards the diffusor, but still energising it with the high-velocity air with undercut.

    Red Bull’s system will generate more drag, because squeezing air into a funnel is always tricky. I wonder how Red Bull’s system would fair with McLaren’s U-shaped sidepods: then they wouldn’t need a funnel but still get the same result.

    1. The reason Mclaren haven’t got L-shaped pods this year is that they went for the RedBull style “blowhole” at the back of the engine cover to exhaust the air from radiators etc. Since RB haven’t abandoned that, they won’t be able to run the L shaped pods

    2. Is it a ‘funnel’ or a tunnel? If it’s a tunnel, then any extra drag will just be surface effects as the air is not being ‘squeezed’, just turned.

      1. tunnel, you’re right (my English is terrible…)

    3. People we are ripping off Sauber, Sauber was the one who invented this new exhaust, at least it was the first team using it which made Peter Sauber quite confident about his own team.

      1. Although Sauber did not come up with the trick of those openings the air going around the side-pod flows through to avoid it mixing with the exhaust flow.

        And nobody knows if this thing was planned by Newey from the start or not. He might have had something like this in mind and then when he saw the Sauber the pieces fell in place for him, but it could have been planned all along.

  2. Thanks, John. This was an excellent article. I was struggling to come to grips with this, but you explained it wonderfully.

  3. Thanks John for the article.

    Hmmm, won’t all of this be dependant on the velocity of the jet exiting the exhausts which I presume to be variable now that elaborate mapping is outlawed? In that case, the blowing is going to be sporadic at best even with the nice bridge that may or may not work (although as it’s Newey, let’s assume it does work). My point is that it is definitely going to test the drivers somewhat more this year than last year to get a handle on these variable systems.

    Gordan McCabe wrote a nice article in October about it ( and more recently this month ( with a nice Milton Keynes comparison ;)

    1. This is what is most interesting for me, i can see how at high speed the effect of this will work, and i can see how when the accelerator is depressed and gasses are being blown with more velocity this will have an effect, but at lower speed and turn in will there be as big a benefit (think Scarbs wrote coanda works better at lower speed but then you have less energy in the flow), certainly without the elaborate mappings to keep the gas flowing this will surely lower the impact, would it also make it more unstable as the grip would change through the corner?

  4. Sounds a little more complex than the McLaren solution (to me at least) but the principal remains the same. Now I have an idea of how they both work it will be interesting to see which fairs up better (if it’s possible to tell)!

    I wonder which will be better for development?

  5. The exhaust rule is really cracking me up ,may be because of my naive understanding of rules and aerodynamics. As I effectively recall, exhaust positioning cannot be used for aerodynamic gains, if yes, then what Red Bull and other’s are doing? Aren’t these solutions illegal at first place?

    1. I may be wrong, but I believe that as it stands Red Bull is complying with the current rules as to how and where their exhaust can be placed and directed. They are ‘simply’ trying to take what they have learned about EBD from last year, and are still trying to apply it somewhat, albeit in a much more restricted and inevitably less effective way, which is why all the teams seem to be saying they are all suffering from less downforce and grip this year due to the changes in the EBD rules. But Red Bull et al are not going to simply ignore all they have learned about the benefits of EBD.

      What I find intriguing is that Whiting may call what Red Bull et al are trying to do as going against the spirit of the rules, which is why they might still tweek the rule, but to me if Whiting truly wanted to eliminate EBD the regs would be even more restrictive. Part of the story is that drastic changes to the rules vs. more subtle changes from one year to the next can cost the teams tons of money in having to go completely back to the drawing board every year, and can keep the field from being more close like everyone is hoping for and expecting this year. So perhaps we are seeing a gradual backing away from EBD (although it really has been a big step in reducing EBD’s effectiveness from last year) and as I say the teams can’t unlearn what they now know about EBD and it’s effectiveness.

      Same with the other day Whiting saying that teams shouldn’t have flexy front wings, yet the rules allow for some flex, so the teams design their wings to the limits of the tolerances, and to pass the FIA’s test for flex, and yet Whiting still calls that going against the spirit of the rules…Most around here said if you don’t want them to have flexy wings, then don’t allow flexy wings…why still give them some parameters that still have them ending up with flexy wings to some degree come the end of the day?

      1. Correct Robbie. CW going from 5mm tolerance to 3mm is share stupidity tbh.

      2. Its Schumachers fault Robbie, & that answers everything ;-) He taught people how to bendd the rules in f1 after all hahahaha!

      3. As far as I understand @robbie, the issue of this RB solution being illegal is not so much about the rules in exhaust placing but the fact teams are not allowed to funnel it somewhere after that.
        With the “tunnel” etc. setup air enters the car and then exits at a different place. And that is air that is not used to cool either driver, engine, gearbox or whatever, its only for aerodynamic benefit.
        Therefore it might be considered to be breaching some rules, depending on interpretation of them.

      4. It’s the same old FIA problem. A badly conceived, worded and implemented rule. To save all these issues they should have simply decided to extend the flat bottom to the rearmost edge of the car and insist the exhaust exits directly on top of this. Yes there may have been some positive aerodynamic effect but the opportunity for rule interpretation and exhaust gas exploitation would have been significantly reduced.

    2. All of this sounds similar to the now banned Lotus passive ride height suspension. FIA makes a broad interpretation that it’s meant for aerodynamic benefit, not for suspension benefit, thus is banned. How is blowing exhaust at the diffuser different in this case? What can RBR and McLaren say is the “intent” for this layout other than aero benefit? Seems that the FIA can just say, “this is built for aero benefit, and since we know that using exhaust blowing for aero benefit is not allowed, this design is banned despite the exhaust being in the right place.”

      Personally I hate that kind of rationalization of the rules where they make a judgement on “intent”, but they just used it on Lotus and their suspension solution.

      1. Well, if they ( FIA) wanted to get rid of it they would make it a rule to put the exhaust somewhere else. With the rules being what they are there will inevitebly be aero-benifits from the exhaust. And getting that position optimized and designed around it correctly will gain you df vs drag etc. Only a stupid team would just place the exhaust on random. Everything on these cars are designed with a purpose and are well thought through. So the only solution to get rid of it ( aero-benifits from exhaust ) is to use the periscope exhaust the suggested sometime last year.

        1. Interesting points folks, about funneling/tunneling the exhaust to still retain some aero benefit, which might be considered against the spirit of the rules. I just think that Whiting et al could not have expected them to just ignore all they have learned about EBD, so unless they have made strict rules about funneling, one can’t blame the likes of Red Bull for attempting this. Obviously the rule must be vague enough that they believe what they have done is legal.

          1. I just looked at the rules at a fairly quick glance, and I certainly don’t see anything saying you can’t funnel or tunnel air but there are certainly many restrictions to the dimensions and placings of any bodywork ahead of the rear wheels etc etc. So I think if anyone has to tweek their ideas it will likely be the ‘against the spirit of the rules’ thing rather than that they literally broke a rule by infringing beyond an allowed dimension.

          2. @robbie, replying to this one, because I can’t to the one below this one (?)

            BTW, I’m not blaming RBR for exploiting a loop hole in the rule. That is par for the course in F1.

            My annoyance is with FIA interpretations and banning tech based on “intent”.

            Wasn’t the Lotus ride height ban due to a violation of the “spirit of the rule”? It sounded like someone opened their big mouth and said its primary purpose is for aero and they banned it even though it was a passive suspension system within the written rules.

  6. Nice article… lovely diagrams

  7. i feel a major exhaust row coming up in Melbourne. Dont know why but i have a feeling we might see protests from some teams and possibly Charlie banning some solutions.

  8. I’ve made this point before, but maybe the driver could use his gas-pedal to add some revs to the exhaust. The only thing is, you must be able to have a clutch or neutral position or something like that, to prevent extra revs resulting in extra drive.

    Otherwise, I’m doubting if the effect is big enough.
    Maybe it’s the other way around? Maybe they try to have clean air from the undercut, not spoiled by exhaust fumes?

    Or maybe, they make us look the wrong way…

    1. Have you ever driven through any corner (barring extremely slow-speed ones) at high velocity, even in your road car while having your engine disconnected from the transmission (i.e. clutch engaged)? If you did, you’d know that is not the safest way of doing it. And if you happen to be pressed for time like most racing drivers are, definetly not the fastest way of doing it as well.

      1. Hm, that’s right. But maybe that can be reduced by using some kind of double-clutching. Here my english is insufficiënt, but I mean that you give some extra revs before you re-engage the clutch. The reason for heel-toe technique, I mean. Hope you understand what I mean.

    2. JPS mate, thats what the off throttle engine mapping does. Because the driver throttle is actually only a switch requesting that amount of throttle from the computer, the computer is simply programmed to give the engine revs etc on the off throttle without the driver having to even press the throttle at all.

      1. Hence why people say “the cars drive themselves nowdays” which is not really fair, although the computers etc do take care of alot of things the driver used to, eg gear changes, clutch bite, engine mapping & driveability, off throttle exhaust generation overrevs, engine stalling when car spins etc etc etc etc

      2. sorry original comment is a reply to Verstaphen, not JPS :-)

  9. I really hope that McLaren have the better option here, and it definitely seems like their solution is less complicated, and might just be more reliable in yielding more general performance, rather than different results throughout the season.

    I also wonder if this is why the ‘winglets’ have been introduced to the rear of the RB8. In the F1 show on Sky, they took a look at how Red Bull have introduced, I think it was between 6 and 8 little winglets that help feed into the diffuser, and I reckon we could see a lot more of these being designed for and after Melbourne.

  10. Well, from my Layman’s POV, the solution does not look or sound logical. I assume the cold air blowing over the exhaust will be heavier and slower than the exhaust air. We also know that hot and fast moving air will tends to go up rapidly or not? So, if all these are correct, how come the exhaust hot blows downwards? What forces it downwards? For sure not the cold overhead air?

    I have read the Coanda-effect on the MP4-27 and it sounded more logical to me as the bulge causes a deflection but the RB8 does not have the same bulge, so I find it difficult understanding the process. I guess not being an Engineer contributes to my misery :(

    1. We’re only taking about a few feet. Just imagine if your standing in a 120mph gale. Your breath will be half way down the street before it realises what temperature it is. Whipping all these vortices and flows around the tail-end of an F1 car means that you make stuff blow almost anywhere regardless of temperature.

  11. From the penultimate and final days of testing it seemed that Red Bull were struggling to come to grips with their new system. If I remember correctly they did not run much on those two days. Could it be that they find themselves in a similar situation as McLaren were in last year?

    But yes it looks unlikely that Red Bull are going to give up on EBD technology for the time being.

    1. RB reported their lost testing time on the last two days was because Vettel went off and damaged his front wing, then had gearbox problems. Apparently nothing to do with the new exhaust system.

      1. Then again, they would say that, wouldn’t they @pault :-)

  12. Fantastic article, John. I’m still scratching my head here because, while I think the science and analysis is logical, I’m wondering about the real use of fresh-air duct on the side pod. It seems to me that the benefit of this duct is there whether or not there is the exhaust blowing across it, in its separate space in a different direction. Indeed, the segmentation of the two flows only begs the question as to what that sidepod duct is doing.

    You always will want to aid the coke-bottling in that area, as you say, to get low pressure, high-speed air going over top of the diffuser. The question is, always how much can you do this efficiently by sticking vanes in that area or punching holes in the body work? If it were efficient, we would see much more of this venting back there. Vanes are banned, so probably big holes, fed by NACA ducts, etc. So to me, that hole has to be influenced by the exhaust directly, or it would not be there,. Either exhaust is somehow being ingested (the lower red line should, in part, join the green line), or it is being used to drag the air out the back side, by lowering pressure at the exit of the duct . Or both. In any event, it seems to me that RBR effectively is blowing their diffuser with exhaust via that duct, albeit in a different way than last year.

    By stripping off the vanes and flips, F1 has taken race car aero to an entirely new level, were “secondary” effects are now much more important and apparently just as powerful. Also I’m sure it takes more wits and faster computers to work out this kind of solution, rater than sticking a piece of CF in the breeze.

  13. And Charilie can blow them away by specifying that no bodywork should be around last two inches of the exhaust pipes. In that case Coanda would become just another interesting fragment of F1 history.

  14. ha, that video is funny, the lengths they go to cover up the car. like a man on the beach trying to change his trunks under a towel.

    1. lol i agree, its utterly pointless anyway, after the 20 or so guys come running out and cover it with boards, umbrella’s and the entire linen cupboard, seb then drives off to get himself in a position to be wheeled back into the garage and stops bang in the middle of no where, any professional photographer is fast enough to get the shots they want in that time space.

  15. Thanks for this analysis. I love reading technical articles about F1, even if I understand only a fraction of the concepts. I hope there are many more of them on F1 Fanatic over the course of the season :)

  16. Amazing amount of effort to go to for what seems (to me at least) to be very little gain.

    And it’s against the spirit of fairness that the FIA are (supposed to be) endorsing. Once again the wealthier teams can afford to explore the edges of performance while the newer teams have to make do.

    1. At least the newer teams can take comfort that the benefits if EBD that the wealthier teams particularly had gotten a good handle on, have now been curtailed. While Red Bull and Mac seem to be perhaps the ones who will still benefit a little bit from channeling their exhaust gases, the benefit is much less than last year, and the stability in the rules otherwise should help the lesser teams. I think the greatly restricted parameters of what they can do with the exhaust should also help the lesser teams more easily duplicate the wealthier teams efforts.

  17. I know secrecy has always been part of F1 but Red Bull have taken it to a whole new level. They’re a little hypocritical too if you ask me… Complaining about McLaren copying them last year, when I still have photos of Vettel & Webber practically climbing into the McLaren cockpit (& various other team members crowding around snapping photos) trying to get to grips with how the f-duct worked. The way those guys moan, you’d think they’d never try to copy anyone themselves. Obviously we know better though.

    1. While I take your point, I think that what happens is that before the season starts the teams have a better chance of hiding things from others with things like the screens in the video. I think that is fully within their rights and they should, having spent tons of money trying to find an edge, try to hide their secrets for as long as possible while they can. I think we all know, and they all know, that once the season begins (Friday practice) and all the teams have their latest greatest kit out there for the world to see, there is only so much hiding anyone can do any longer. And then yes it is fair game and you see drivers checking out each others cars in parc ferme etc etc. But while they can control the viewing of their car, they are going to do it.

      1. I don’t disagree with you… not even a little bit. My complaint isn’t about them hiding their innovations,it’s more about them acting as if they’re not guilty of blatantly trying to copy others as well. The way they spoke with disdain about being copied, you’d think they’d refrain from doing the same… & of course they won’t. In light of this, my position is that they should complain less, that’s all.

  18. This seems to be a similar way of directing the exhaust gases like Sauber rather than the McLaren. Looking forward to this season!!!

  19. I think Iran could learn a thing or two from the Red Bull boys about how to conceal their latest tricks from prying eyes.

    1. Mclaren should hire CIA and Mossad, then we’d see what RBR’s secrecy is worth. Should be no problem at all-just tell them you suspect they’re hiding a nuclear weapon in there. Since many Newey’s cars are indeed an F1’s equivalent of a nuclear weapon it wouldn’t even be a lie!

  20. This is why I love F1!!!

  21. Whatever the merits of the system, this was pathetic to watch, the FIA need to step in and say, ‘ Guys, once you break cover at the test you break cover’, to see mechanics scurrying around with makeshift barriers to prevent pictures was ridiculous, reminds me of a school boy covering up his answers to an exam….grow up.

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