F1 2009-13 part two: Brawn and the double diffuser

In just one week, less than a month before the first race of Formula 1's brave-new-regulations era in 2009, Ross Brawn's eponymous team didn't so much move the goalposts as completely change the game.

Honda had pulled the plug on its works team in December 2008 and by the time the Brawn-led management buy-out was completed in the first week of March '09, its rivals had long since been out testing.

The much-vaunted double diffuser was already in the news, as both Williams and Toyota had been testing with it. But Brawn had gone even further with maximising the effectiveness of its design through the way the whole rear of the car was conceived.

This one design concept was decisive in the remarkable story of a phoenix-from-the-ashes team triumphing in 2009 despite a winter of discontent.

After a shakedown at Silverstone on March 6, the Brawn BGP 001 joined the rest of the teams in testing at Barcelona a few days later. Jenson Button topped the first day, setting a respectable pace of 1m21.140s before team-mate Rubens Barrichello went second fastest on day two with a 1m20.966s.

The pace of the car looked good straight out of the box, but it was on day three of the test, March 11, that the Brawn showed its true colours. Button banged in a 1m19.127s, a second faster than anyone else.

The Brawn crew went from facing unemployment to blowing their rivals away © LAT

"We're all f****d," was one top driver's private conclusion after that day of running. Barrichello's fastest time of 1m18.826s on the fourth and final day of the test did little to undermine that conclusion.

A glance at the three fastest times was telling. Behind Button, Williams driver Nico Rosberg was second fastest ahead of Toyota's Timo Glock. The 'diffuser gang' teams had stolen a march.

The Red Bull RB5 was the car that set the aerodynamic template for the five seasons of the 2009-13 rules cycle. But while Adrian Newey's car won six races in 2009 and took second in the constructors' championship - five places better than Red Bull had managed a year earlier - it was Brawn's team that stole a march and dominated the early stages of the season with Button.

Six wins in the first seven races gave Button a 26-point advantage over Barrichello, with Sebastian Vettel a further six behind. Despite only standing on the podium twice in the final 11 races, Button went on to seal the world championship with a race to spare.

The concept of the double-decker diffuser was simple. The architecture of the diffuser itself was relatively easy to justify based on the regulations, even though the intent of the rules was not to allow this to happen. But the key to this was how to get sufficient airflow to the diffuser to make it worthwhile.

The regulations were designed to stipulate that the floor be impervious, hence with no way to feed extra airflow from under the car into the diffuser. To that end, article 3.12.5 of the technical regulations stated that "fully enclosed holes are permitted in the surfaces lying on the reference and step planes provided no part of the car is visible through them when viewed from directly below".

Brawn's use of "spaces between transitions" proved fruitful © XPB

But by capitalising on the transition between the parts of the car sitting on the reference plane (basically the lowest plane of the car with the exception of the wheels) and the slightly higher step plane that governed, among others, the rear of the car, a hole could be created. Or rather, not a hole. It was more a gap between two things. Or "spaces between transitions", as the FIA put it.

The FIA heard an appeal against its ruling that the double diffuser was legal after the first four races of the season, and maintained that it was legal. The arguments were very detailed and a 7000-word document explaining the legal debate was released by the FIA at the time. It is well worth a read in combination with the original regulations.

Brawn, of course, had seen all of this coming. He had a good idea that his team had stolen a march on the rest by optimising its car around the double diffuser. He claims that he made attempts to tackle the loophole only to be dismissed by his rivals.

They probably should have listened. After all, the megabucks and then-unsuccessful Honda team had committed much of its 2008 development budget to working on the '09 car that became the Brawn. It was way ahead of the curve.

"I said that we were not achieving the reductions in downforce that we were asked to do and that I thought we needed to have another run at the regulations," says Brawn. "That was rejected and I was told the numbers I was intimating were scaremongering. So that gave me some idea [of how far ahead we were].

Because Honda spent so much of 2008 doing this, the team had plenty of time to prepare for the '09 rules © XPB

"We had the benefit of being able to start really early that year. The slope is steep when there are new regulations and if you start early, you get the benefit if you do a sensible job.

"We'd prioritised 2009 and we were well up the slope of development, so had a lot of confidence that we had a good car.

"When testing started, it appeared to us that we may have achieved a lot more than some of the other teams who were running out there. That proved to be the case."

Until the car ran at Barcelona in that fateful test, nobody realised just how serious Brawn had been about his downforce figures.

"Ross was quite distinctive in terms of his flagging up that he thought these rules were going to generate far more downforce than expected," confirms Paddy Lowe, then McLaren's technical director and now at Mercedes.

"He started quoting numbers and the general feedback in one meeting was that either we don't believe you, or if you are right you're in a very good place! But there was a mixture of resource applied to the project. Honda worked pretty much 100 per cent on that [the new rules] for all of 2008, whereas McLaren and Ferrari were fighting for the championship and put in less than a normal amount of effort."

Most tellingly, the three teams who had adopted the double diffuser were confident it would not be especially controversial. Brawn explains that the genesis of the idea came from within Honda, specifically in a Japanese aero group that would feed ideas both to the works team and to the offshoot Super Aguri squad that never made it to the '09 season.

Brawn was given a free hand by Honda © LAT

"One of my objectives had been to utilise the power of Honda more effectively because when I arrived there was a pretty disparate effort going on in Japan and in the UK and they weren't joining up very well," he says.

"It seemed to me that you either reject and close down what was going on in Japan completely, which would have been a great shame because there's a lot of very bright people there, or you integrate it properly into the programme and manage it properly and make use of it.

"Because I came in with carte blanche from the board of Honda to do what was needed, I was perhaps the first person to have authority over both groups. There was an aero programme going on in Japan which was what I'd call an advanced conceptual programme. One of the Honda engineers came back with this concept and John Owen - who was in charge of the aero development - looked at it and initially didn't think it would work.

"But as we worked on it we realised it was viable, that the engineer in Japan had opened up this opportunity and the more we looked at it and the more we thought about it the more we liked it."

Then-Williams technical director Sam Michael explains that his team also hit upon the idea independently.

Williams was one of the first to hit the track with a double diffuser when it began testing in February 2009 © XPB

"It was a Williams aerodynamic group, it didn't come from outside the company," he says. "We knew it was a good step, but the Williams team was quite shocked during winter testing to find out how few other people had done it. That was a surprise."

Toyota is believed to have hit on the concept thanks to staff movement from Honda. But like Brawn and Williams, it too believed that the design was legal. As Michael explains, his team did not even feel the need to run it past F1 technical supremo Charlie Whiting. Michael believes key to victory in the case was precedent connected to other holes in the floor elsewhere on the car.

"It was deemed so uncontentious inside Williams that the team never even checked with Charlie Whiting," says Michael. "The first time I spoke to Whiting about it was after the Algarve test in January. I told him what the team had done and he said it was fine. The rules were so clear that I didn't even think it was something to check.

"What won the case was that there were what people call 'holes' in other parts of the step plane and reference plane already. As there were holes in the front of the car around the bargeboard that had been there since 1993.

"The fact it was applied to the rear was new, but not at the front of the floor. In fact, it was being used by a number of the teams that filed the complaint. That precedent was powerful."

The arguments over the legality of the double diffuser did prove contentious. But Brawn insists he has no regrets given that he had tried to flag it up.

Williams had no doubt that Whiting would accept the concept © LAT

"My conscience is clear because I put my hand up and said, 'Look guys, I think we need to tighten these regulations up', and everyone said, 'Go away'. And that was at a very early stage of this interpretation, so from that point on we just pressed the accelerator and got on with it.

"You can never be absolutely sure, but we had as strong a case as we could have. When you read the wording of the regulations, an appeal court was convinced that our interpretation was acceptable.

"And the fact that two other teams actually came independently to the same concept I think proved the case even more. If we'd been out there on a limb, perhaps it would have been a little more precarious, but we weren't. We had Williams and we had Toyota who had both taken virtually the same interpretation of the regulations.

"It's one of those moments in F1 where you either get it or you don't get it. If you don't get it, you do your best to stop those who have got it because what can you do?

"I've been on both sides. Someone's had a smart idea, you look at it and you think, blimey. You either pat them on the back and get on with it or you think, well, let's have a run at this because maybe we can stop it and it wasn't what was intended and we've done what was intended."

In 2009, Newey and Horner's plans for F1 domination were only just bearing fruit © LAT

Needless to say, those on the other side of the fence were less convinced. Red Bull's Adrian Newey did evaluate the architecture of the double diffuser for '09 but did not - and still does not - believe it was legal. And the race to incorporate it into the car was a huge problem for his team.

It's overwhelmingly likely that, had the double diffuser been ruled to be illegal, Red Bull would now be sitting on not four, but five consecutive drivers' and constructors' championship doubles.

"We had a quick look at a tiny version of what the three teams came up with [before '09], but it didn't look that promising and we really didn't think it was legal, so we didn't pursue it any further," says Newey.

"Whether it was deemed legal or not wasn't really an engineering decision. It became a political battle where Max Mosley, who was FIA president at the time, wanted to give McLaren and Ferrari a slap. They hadn't got double diffusers. He changed from unofficially saying, 'No, there's no way it's legal', to effectively saying, 'Yes, it is legal'.

"But for us it was a great season. As Red Bull Technology we had managed to win Monza the previous year with Toro Rosso and Sebastian and we were starting to go in the right direction. But the rule change for us was a great opportunity.

"The old rules had been in existence, in essence, all the way back to 1998 and it was, therefore, quite difficult for new teams coming in to claw back all the iterations and knowledge that the existing big teams had accumulated in all those years.

"So the rule change was our opportunity and we managed to grab it with both hands. We obviously didn't win the championship, which was a shame, but having said that if you'd said going into 2009 that we were going to win several races and finish second in the world championship, we would have probably all fallen around in disbelief!"

Red Bull interrupted Brawn's dominance when Vettel gave the team its first win in the rain in China © LAT

Unsurprisingly, Lowe agrees with Newey's position on the double diffuser ruling. But he does accept the rule was ambiguous. As always, any vagueness in the rule allows for interpretations that some might call against the spirit of the regulations to prevail.

Did the regulations intend to allow airflow to be channelled through the floor? No. Was there just enough wriggle room to claim that they did? Yes. But there was a feeling it suited the powers that be for that conclusion to be drawn. Lowe believes that the ambiguity allowed conclusions to be drawn that were non sequiturs.

"Obviously, you justify your own position, don't you?" says Lowe. So the people that were thinking it was alright think it's alright. But I personally felt it was an ambiguous rule [about fully enclosed holes]. And in the presence of ambiguity then you must refer to custom practice and original intent. And custom practice and original intent was to understand that rule completely differently, which was you're not supposed to put a hole in the floor.

"When the rule was originally conceived the floor was actually flat and then the step plane was put in, in 1994. It was at that point the rule may not have been written as clearly as it should have been and that's what caused the ambiguity. As in all these things there's a bit of cleverness and there's a bit of politics.

"My reading of that was that despite the thickness of the [full verdict] document, when they actually got to the crux of it - as much as the single phrase that is ambiguous - they didn't deal with it. They didn't recognise that something wasn't clear and they said it was.

"The court of appeal ruling didn't actually address the fundamental point. It glossed over it, which would tell me it was a political point. It just sort of said, 'Well that clearly leaves this', and I thought, 'It doesn't, that's the point'."

The result of all this was that Brawn won eight out of 17 races and Button was crowned world champion. Red Bull emerged as a race-winning force with the car that was, at heart, the best aerodynamically, but without being designed around the double diffuser that was later hastily adopted. And McLaren and Ferrari, who had fought for the '08 title, won three races between them and finished a distant third and fourth in the standings.

With a major rule change coming in F1 next year, and many predicting acrimony over the interpretation of the rules, what happened in 2009 might be a harbinger of what's to come next season.