Technical Red Bull's (asymmetrical) blown rear diffuser

Blog Zbod

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I posted in the archived 2013 Singapore thread about speculation from Giancarlo Minardi regarding the odd exhaust note Vettel's car was heard making during that race, insinuating it might be some form of traction control. (ROOTERSPORT, OTOH, are claiming it could be torque control). At the time it was more baseless rumour than anything (after all, Minardi's old F1 team since has become Toro Rosso, so Mateschitz is as much as sleeping with Minardi's old lover) but the story since has grown legs, so I thought I should create a new bespoke thread in the Technical forum.

What Red Bull are doing allegedly isn't traction control but rather a very clever exhaust blowing of the rear diffuser. The story goes that the TR (5.6.1) allow for a delay of a maximum of 50 ms after throttle application before fuel must must be introduced. And as a holdover from the blown diffuser days, the Renault engines still feature a cylinder deactivation scheme, which they claim is essential to cooling, but which also is reported to boost fuel economy. Some sources -- like Auto Motor und Sport -- believe Red Bull somehow are merging the cylinder deactivation with the 50 ms delay to create more or more energetic exhaust gasses which, thanks to the Coandă exhausts, produces all the greater downforce.

Vettel already has taunted us, claiming we'd never figure it out, but I have concocted one scenario that might work (which might bear absolutely no relation to reality). When the driver applies throttle, what if for that 50 ms, fuel only is increased to the deactivated bank of cylinders, and the ignition timing to those cylinders simultaneously is drastically retarded? There would be no significant rise in power delivered to the crank, but there would be an extra shot of gasses spewed out the exhaust ports. At 10,000 rpms, 50 ms is enough for about 17 ignition cycles from the bank of four deactivated cylinders. I doubt they ever get that low in the revs, even through the Lowe's hairpin at Monaco, but even just 17 combustion cycles comes to near as makes no difference five litres of hot, burning, expanding fuel-air mix, coursing through the exhaust, into the manufactured slipstream and across the rear diffuser.

This would increase the Coandă-generated downforce before the car changes speed in response to the change in accelerator position, which means the downforce would arrive before the added torque at the wheels. It would be a novel solution because cars ordinarily are dependent on increased speed for increased downforce. The extra downforce would reduce the tendency to wheelspin under throttle, allowing power to be applied all the sooner on corner exit. Just like traction control. And the 50 ms delay is minute enough the driver should have no difficulty adjusting the timing of his accelerator pedal applications.

Anyway, another clue was reported at Singapore. In free practices, Vettel's car was seen with FlowViz only on one side and Webber's car was seen with it only on the opposite side. Which gave rise to speculation that this new system might somehow be being "focused" on one side of the car or the other, presumably the side inboard to the corner, as body roll tends to lift and "unseal" that side of the rear diffuser. Which fueled further speculation about how they controlled which side of the car was receiving the additional Coandă.

F1 Analisi Tecnica claim to have been told by Franco Nugnes (Spanish driver currently in the Porsche Cup series) that the system is not automatic but is manually activated by the driver, who selects which side of the car is to receive the extra downforce. They claim it is good for 0.1-0.2 seconds per lap.

Which reminds me of the story a couple of weeks ago stating Lotus had abandoned their passive double-DRS, claiming it only was good for 0.2-0.4 seconds per lap, which was too little to close the gap to the Red Bulls. Red Bull, OTOH, do not seem too proud to accept lap time increases in even smaller denominations.

Niki Lauda has remarked that the FIA reviewed the Red Bull system during developmental testing, and initially ruled against it, but RBR modded it to satisfy the FIA's concerns. Which is why Charlie Whiting et al have been so unequivocal in stating the system is within the regulations.

The oddest aspect of all this is that the 2012 exhaust overrun-driven EBD was banned because it constituted a moveable aerodynamic device (undoubtedly the most tortured interpretation of the TR I ever have come across). Material differences? The old system blew extra exhaust gas beneath the rear diffuser on throttle lift. RBR's new system (if speculations are accurate) blows extra exhaust gas across the top of the rear diffuser on throttle application. So I am baffled the latter has been ruled legal when the former was not.
Surely if it's driver activated/selectable it should be illegal, as I was under the impression that any driver actived aerodynamic device other than drs was banned, hence the banning of the f-duct?
Good stuff Blog Zbod

I think most people realize there is an unknown, underlying element to the RBR domination. It may be romantic to think that it's Seb's hard work and determination that is making the difference, but that's nonsense. Newey, Red Bull, and Renault have developed an almighty machine that only a handful of people truly know the secrets to. Vettel decided to tweak everyone's giblets a bit when he taunted them in Korea saying "They'll never figure it out".
The bad news for the other teams keeps getting worse. Last week Vettel told, "...I am sure for the races to come that we will be able to enhance the system even further..." :o

Pre last season, Lotus were testing an antidive/ride height control at the front that ultimately was ruled illegal because it was driver-operated (via his left foot) and its primary benefit was to the aerodynamics (front wing height), not to the braking. Unless RBR can argue this asymmetrical diffuser blowing isn't primarily of benefit to the aerodynamics, and since it is controlled by the driver's right foot, I am finding less and less reason to side with the FIA's decision.

KekeTheKing, can't argue with that. Messrs. Horner and Newey might not have read Benjamin Franklin but I'm sure they both understand the principle that three only can keep a secret if two of them are dead.

Remember the alleged ('automatic' but no moving parts) ride height adjustment that Red Bull had? It supposedly maintained the same ride height with a qualies fuel load, and with a full race load, all by its lonesome. It was reported in the press that the FIA had a talk with RBR about it and it went away, but we still never heard the particulars of how it worked. Or how the flexy front wing managed to pass tech inspection, even after the FIA had doubled the weight of the static test load.

When those lads are done with F1, there might be a place for them with the Ministry of Official Secrets.
I'm assuming that in that theory Road of Bones , the method of controlling traction is via management of the rate of discharge so that KERS can be deployed earlier than is normal.

There are a couple of dubious suggestions reported in the article about how the KERS is used (it refers to "drag on the engine" and using "sensors in the suspension"). Harvesting kinetic energy from braking and deceleration ceases as soon the car is no longer decelerating. Therefore it is questionable as to how it can be used to put "drag" on the engine when one is trying to "drive" a turn and then accelerate out of it. The advantage of traction control only comes into play when throttle is applied and one wants to limit wheel spin but nothing the suspension does will relay reliable information about wheel spin or loss of traction. That is because of the variability of track surfaces and variations in compression due to downforce acting on the car. The lateral and longitudinal movements of the suspension do not correlate with the rotational velocity of the wheels in relation to the power train which is what the software needs to "understand".

So, this leaves us with the question of how KERS could be used to control traction. Deploying KERS too early causes a loss of traction which is where the skill of the driver ought to come into play. The driver hits the button when he thinks it will give the boost he needs without spinning the drive wheels. How much latitude the teams legally have to control the rate of discharge I don't know although I believe there are prescribed limits. However, doing something to get round those and enable KERS use earlier than the competition could be the key to the Renault engined cars secret, if there is one..

If the initial rate of discharge is low and used in concert with the so called "Torque Control" method (i.e. preventing ignition in some cylinders to limit the engines power output), in theory, the driver could have his foot hard pressed on the throttle leaving the ECU to manage (and optimise) the power transfer to the engine from the KERS and overall output to the drive until the threshold at which full throttle control is in the "foot" of the pilot.

A strict interpretation of the technical reg's implies such a manipulation of the system would be illegal.*

A strict interpretation can be found in Rootersport or look it up on the Official Formula 1 website but that won't be half as much fun :D
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Another theory is emerging as to the secret of Vettel's dominance:
Odd that should cite El Confidencial, because the article in El Confidencial refers to fair plagiarises an article in the November print issue of Racecar Engineering, which I have a copy of and believe probably is the origin of the KERS-as-TC theory (story on page 14). It probably would provoke a visit from the copyright police if I were to post the article here but, if you can read the Spanish (or can muddle through the Google transmutilation), the meat of it is faithfully reproduced in El Confidencial.

The theory in Racecar Engineering came from someone called David J. Dodge, who I am unfamiliar with. His supporting details are rather convoluted, and some of his premises I can not agree with, but it isn't entirely implausible.

In a nutshell, he says there's more to meet the eye in the way the RB9 goes fast around corners, is faster on the lap and faster out of the corners, yet is slower in top speed. He claims that superior aero should mean more downforce with near equivalent top speed, so you can't put it all down to better aero. And he thinks there's some jiggery-pokery going on with RBR's KERS, because no other Renault-powered team has such persistent problems with theirs, and why should such bright lads not be able to suss it out and mend it?

He concludes this means RBR are using their KERS as rather a buffer for excess engine power, controlled by load sensors on the rear dampers. A compressed damper is taken as a sign that there's traction a-plenty and the full measure of torque is applied to the prop shaft. An uncompressed damper means that traction is scarce and more power is diverted to charging the KERS. This cycle could occur several times each wheel rotation so the load on the KERS is more sporadic and more intense than that experienced by the other teams, hence more stress on the system.

Mr. Dodge says that it must be providing the driver some measure of feedback regarding the availability of traction, which could be a breach of the TR. And that statement, IMHO could be a mild understatement.

I can't for the life of me figure how this would not contravene the regulation against TC. Then again, I can't see how the F1 Analisi Tecnica theory doesn't contravene the TR as well.

I also find it noteworthy that Mr Dodge's theory doesn't go anywhere near the asymmertry claims, but it is entirely possible that Franco Nugnes doesn't have a clue and the one-sided FlowViz thing is overblown and completely unrelated. Maybe they simply were running short of the paint :whistle: . He notes that it is the RBR's habit to apply KERS power for acceleration at corner exit rather than using it for more top speed, which would seem to argue against the process of applying torque to charging of the KERS in the event of wheel slippage under acceleration.

And the objective is not to reach the highest speed on the straightaways, it is to cover their distance in as little time as possible. Red Bull might have found an aero balance to do this through higher cornering speeds and earlier throttle application that negates the need for high top speed. Aero drag, after all, increases at the square of the increase in speed, so high top speed is quite costly in terms of fuel consumption. Mr. Dodge discounts this possibility, stating all the other teams have smart guys too, so if simply increasing downforce ad infinitum resulted in the lowest lap times, they all would be doing it.

He also mentions the now-famous dashed tyre marks the Red Bulls left exiting the corners at Montreal. Which we have already discussed in this forum, noting they look very much like normal limited slip diff acceleration tracks, and if it's leaving tyre marks, it isn't a very good traction control. Could just be undulating tarmac.


Curious marks leading from one corner on one circuit in 14 races means Red Bull are using TC??? :facepalm:

But he overlooks the fact that Red Bull knowingly have selected a less powerful but more fuel efficient engine. I suspect the Red Bulls -- especially Vettel -- have a not insubstantial weight advantage on the start grid (at least over the non-Renault powered cars), which reduces the handicap to them of being underpowered, which is why Vettel so rarely is out-drag-raced to the first corner by more powerful Mercs and Ferraris.

The more powerful cars must start with more fuel, the extra mass of which only compounds their fuel consumption disadvantage. The Renaults are rumoured to be down by 25-50 bhp. If true, and if the fuel consumption relationship is completely linear (but I suspect it's a bit more in the Renault's favour), that means the Renault-powered cars can be lighter by 5-10 kg on the start grid (but that advantage reduces to near zero as fuel burns off and cars near their spec weight).

A lighter car generating the same lateral load in a corner is putting less load on its tyres. Which also would explain why Lotus have managed to be so easy on the rubber.

I think the chief argument against the KERS-as-TC theory is that the Red Bulls haven't only just hit upon this model. They have been slower but quicker ever since switching to the Renault lumps (2010, IIRC), but also have been winning the entire time. So how did they manage to win in those past seasons without Mr. Dodge's KERS-as-TC?
There is much to be agreed with in the above article but a couple of thing can be queried.

Firstly, the statement that Vettel is rarely out-drag-raced by Mercedes and Ferrari. As far as I can see the reverse is true with Ferrari, at Monza Massa was very close to getting past Vettel at turn 1, this is not an isolated incident as can be seen from the starts by Alonso ; these have been so quick at times that I have expected to see him penalised for a jump star until the slo-mo replay shows what happened.

The second is that if the fuel position becomes less of an advantage as the race goes on then why can Vettel put in blindingly fastest laps near the end, as he does in almost every race.

As regards the starts it is evident that on the first two laps Vettel builds up a big lead, as much as four seconds, then the increase in his lead slows down to a second or less per lap. This happens even when early first stops by the leaders are likely. It looks to me as though at the end of the warm-up lap when everyone else's tyres are cooling down on the start line Vettel's are not and their temperature may even be increasing. This could give him a big advantage until the rest of the pack get their tyres up to full working temperature, which could be as much as two laps. This could be carried out by having the hot engine air, boosted by burning extra fuel, is directed at the rear tyres, then when as the car speed increases the exhaust gases are redirected to the diffuser ; this could be activated automatically or by the driver (which I would assume to be illegal). It would also explain why the difference in qualifying is less than Vettel's first and second laps gains.

Or it could be total bollocks ; if this is so then I am sure that someone will point out the flaws.
The reality of the situation is that because the Red Bull with Vettel is so much faster than the rest of the grid "he must be cheating". Maybe he is just a better driver in a better engineered car? No one is suggesting Ferrari have a launch control system but the way Alonso and Massa fly away at the start of every race it wouldn't come as any surprise to me if they had some sort of system but then they are tonking the rest of the field so no one really cares.
Matthew Somerfield (somersf1) discusses KERS and traction control in his blog but he has some interesting shots of the Red Bull diffuser that caught my attention. As Bill Boddy notes the RB9 appears to have an advantage particularly off the line and in the first lap. If you scroll down Somerfield's page there is one shot in particular which shows a subtle but important sculpting of the extremities of the diffuser close to the tyres. Exhaust gases are channeled down past the "coke bottle" and over the outer edges of the diffuser. The curvature of these edges channel hot air around the rear tyres, even when stationary, and create vortices of hot air around the tyres at speed. At low speeds such as on the warm up lap and in very slow corners the heating effect on the tyres will be quite significant. The effect will be less at higher speeds as the flow of cold air over and around the aerodynamic surfaces and the tyres will "draw" more of the heat away from the car.

So, we now have the ingredients of Red Bull's traction and downforce advantage:

1. The RBR diffuser is probably the most optimised on the grid, especially with its more efficient directing of hot gases and airflow around the rear tyres
2. The engine and torque maps work together with the deactivation of some of the cylinders to keep the power output to the drive train below the level that would induce loss of traction as throttle is applied to accelerate off the line and out of corners.
3. The sculpting of the aerodynamic shape of the coke bottle and the zones around the exhaust outlets confer a lot of the car's downforce by the way that airflow and hot exhaust gases are channeled over that and the flat areas of the floor and on to the rear wing planes.
4. Item 3 works in concert with a higher rake than is run by the other teams. The angle of the flat area of the floor acts as an additional aerofoil since it presents an additional surface area in the direction of travel. Meanwhile the area between the rear of the floor and the road road surface is greater when compared to that of the opposition. In effect it acts as additional volume for the diffuser and (I theorise) more ground effect.

These are the main areas where I believe Newey's aero' design and the tweaks of the engine and software technicians have produced significantly better, more efficient enhancements in the finer details of the car. Each area may be a relatively small detail on its own but as a package they easily account for the kind of car advantage we assume. We can also assume that the attention to detail in those areas is matched by attention to the front wing and the rest of the car. Add to that Vettel's obvious speed and there really isn't much of a mystery as to their current domination. Not to me anyway.
In this week's Autosport (Issue 41), Mark Hughes speculates it is far less involved than any of the other guesses. He thinks it is just the standard Renault cylinder deactivation, but the bank to be deactivated is selected by the position of the steering wheel. Unlike Señor Nugnes, he thinks it is the outboard bank that gets the extra blowing. Which would make sense in terms of putting more downforce on the tyres doing the most gripping, so he seems to be minimising the need to counter the loss of downforce on the inboard side due to body roll.
Toto Wolff says they have engines on the test bench trying to mimic what's going on the with the Renaults. Says he's not sure whether they have the resources to duplicate the RBR (& Lotus?) result before season runs out.

If speculations are correct, the Renault gimmick hinges on the cylinder deactivation scheme, which is a holdover from the EBDs that only is permitted by the FIA because Renault convinced them it was elemental to engine cooling. Which doesn't paint a rosy picture for Mercedes.
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