In 2009 the Brawn team won the FiA Formula 1 World Championship. They had a controversial device dubbed a double diffuser fitted to their cars. For years, I was convinced that allowing it was all a conspiracy, both to damage the big manufacturer teams and to help some vulnerable teams step forward, but I now realise that probably wasn’t the case.

To understand the various sides of this requires a bit of digging and a little technical understanding as well, but it is the political side and the ramifications the decision had that are most fascinating – you could say that this single interpretation changed the face of Formula 1. Perhaps that’s why it is still being dragged up again from time to time today – it has left some people very sore indeed. One real political twist in the tail, particularly for Honda, was that they gifted the idea for the double diffuser, and hence a chance at the world championship, to what would be the Brawn team. They then did the right thing by the many people in the team by paying a huge amount for the new team’s 2009 campaign. So, Honda had virtually all the financial pain of competing, with none of the glory that passed to the “new” team.

Any of you from inside F1 with views from other teams or just with different perspectives – please let me know what you think. My aim is to use feedback from other inside experts to add to the depth of this review. I also don’t mind including conflicting views if the source and text can be quoted. I’m also willing to consider your views if you feel you cannot officially “go public”. I know how hard that is while you’re inside the sport. Questions and comments from everyone else also welcome, of course.

Background.

For 2009 there was a substantial change to the regulations. For example: the introduction of KERS, engines could no longer be replaced without limits, bodywork was changed dramatically. All of this meant a reduction in aerodynamic forces and had teams scrambling for any tricks they could find to increase downforce. The double diffuser was a clever interpretation of the rules which gave more of that extra downforce efficiently. Many teams felt (and still do) that the interpretation should never have been accepted and that the real solutions raced were actually illegal.

After a lot of pre-season discussion failed to resolve the issue, double diffuser cars were protested after the first two races. These protests were rejected, first by the Stewards and then at the appeal hearings.

This is a bit of a long one so I’ve got some headings here to show you what there is....

Rules and interpretation of rules.

Formula 1 has technical and sporting regulations which are accessible to the public. http://www.fia.com/regulation/category/110 However, this is only part of the story. The FiA issue “clarifications” or Technical Directives which explain how they will interpret the rules as well as private teams correspondence with the same objective. These are expressed as opinions but they are generally considered to be part of the regulations and are also used by the Stewards of race meetings and by appeal court judges as part of their suite of decision making information. Going against these interpretations of the regulations is rarely successful.

The rules and the conventional interpretation of them.

From the middle of 1994 a “plank” was introduced under the floor to stop the cars being run “on the ground” and in 1995 a stepped “parallel plane” floor was introduced (to try to reduce downforce) and make sure air was always passing under the cars. Bodywork in the middle of the car between the rear of the front wheels and the front or centre of the rear wheels (rules have changed over the years) has to be “shadowed” by a flat section of floor. The two floor levels are 50mm apart – the central 300mm to 500mm (largely team choice) of the car is shadowed on the lower reference plane. Outboard of that the car is shadowed on the raised “step” plane. If there is no bodywork to shadow there is no need to put floor there. A radius tangential to both surfaces of up to 25mm may be used to blend the two.

The conventional view. A cross section through the car forward of the start of the diffuser. The optional radius sweeps between the two levels of flat floor.

The rules and the liberal interpretation of them.

The loopholes used to allow the double diffusers were the facts that, if there was nothing to shadow, you didn’t need a floor and the fact that you didn’t need to shadow suspension. The interpretation used then circumvented the regulation stating that the floor had to be “impervious” (the word used in the regulations). Ross Brawn had obtained written approval for the double diffuser loophole idea. However, he was cautious about designing his whole car around the idea and came to one of the regular Technical Working Group (TWG) meetings with his aero expert to try to clarify the situation without giving the game away to the other teams. He offered a change to the regulations which would close the loophole. Most teams were completely in the dark and were suspicious of a late change in regulation thinking Ross had a loophole with the new wording rather than the old. The double bluff worked. I was in the meeting representing BMW Sauber. To be approved, the new wording proposed would have required unanimous agreement.

This is a cross section through the car, ahead of the diffuser showing one of the ways a double diffuser was given an air entry. It is clear how dramatically different this is to the more conventional interpretation of the rules. Not only is an air entry opened but the size of it is increased by the radius that is used outboard of the slot (this is a regulatory consequence of the interpretation allowing the slot). There must be no bodywork anywhere directly above the void between the reference and step planes and there must be a void. If the distance in plan view between the two is zero, the two must be jointed together and be impervious.

One design example. This is an isometric view from below the car looking at the floor with the (arrow) opening for the double diffuser starting behind the transition between the reference and step planes. There were many ways to do this and the solution chosen was different for each team. All, though, had an entry forward of the start of the conventional diffuser and an exit linked to a low pressure zone of the car (the rear of the car or under the lower rear wing or both).

The realities of making the double diffuser work

But the design and aerodynamic challenges are just beginning. Finding the optimum shape for the entry and exit for the double diffuser was compromised by the need for the legalising slot as well as just finding space – especially for those teams that had already designed their cars around a standard diffuser. At first we considered using a slot 5mm wide (that was the tolerance accepted by the regulations at the time) by the length of the entry for the double part of the diffuser. That clearly wasn’t going to do anything at all positive for the flow which, however you design the system, is operating in an area of very low static pressure and in an area where the air will detach from the surfaces if given half a chance. The legalising slot looked like it might make the whole concept useless.

However, if we took advantage of the difference in pressure above the slot (positive pressure), the negative pressure underneath, a really tiny slot and flexible materials, combined with some surface shaping inside the tiny slot we could effectively close it once the car was rolling at low speed. You could not see through the slot because it was less than 0.5mm wide on the official design and in reality was smaller. With a bit of force it was possible (flexible materials are wonderful!) to force a small steel rule through the slot to “prove” it was “open”.

Note when looking at these illustrative airflow lines that the air mainly moves from the front of the car towards the rear so the flow angularities involved are nowhere near as extreme as they look in this cross section.

Now, honestly the airflow inside the double diffusers wasn’t as simple as I have sketched it here, but to show fully realistic flow patterns (these are influenced by height, pitch angle, aerodynamic yaw etc,) would not help the conceptual understanding of the devices. These were (illegal now in F1) interesting things to investigate. The airflow is a little like a half way house between the rotating flow of a (by now) normal motorsport diffuser and the simpler flow of a ducted diffuser.

This picture shows evidence of a tape over back to back. The white marks on the slot surround show the adhesive from race (duct) tape left behind when the tape was removed. I believe that the aero people and race engineers were checking that the sealing mechanism was working correctly.

Out on the race track the versions of the double diffuser I know a lot about would certainly have been illegal once the car was up to speed as the slot was closed.

Why the conspiracy theory?

More than 10 years before this loophole was exploited the same regulatory loophole had been used by a small team in another area of the car. Slots and radii were introduced into the floor of the car with the slots mirrored in the bodywork upper surfaces (so you didn’t fall foul of the floor’s “shadow rule”). It was not allowed because Ferrari (I was there at the time and responsible for asking the polite question to my boss who asked the FiA) pointed out where this loophole would lead. Most of the time you need to take note of historical interpretations but sometimes it is a disadvantage to remember these old interpretations and assume they are still valid – this was one of those rare occasions. Today of course correspondence is shared electronically and is easier to distribute – so questions about new interpretations that don’t correspond with an older one are more likely. We have also all learned to ask in writing – verbal responses are easily forgotten or denied. I had that personal bias in a way that I remembered the much earlier interpretation and wrongly assumed that it would also be remembered by the rule makers.

Adding to the feelings of a conspiracy was that there was a bit of a “war” going on between the rule makers of the time and the major manufacturers. The teams, led by the big players, set up the Formula 1 Teams Association (FOTA) and used this to counter a big push from Max Mosley of the FiA to introduce a budget cap. Alternative, and in my opinion completely fictitious, cost saving ideas were put forward and adopted. Ultimately the teams succeeded in countering the budget cap idea – but totally failed to contain costs. Example – aero testing restrictions. Introduced to cut spend on aerodynamic research. Have failed in part because the rules don’t prevent re-allocation of spending and in part because engineers always have counter strategies. It may have reduced the subsequent escalation in spend on aero. For those who would say “no, no, you’re wrong, the restrictions have worked” – just look at the size of aerodynamics groups in Formula 1 today. They are huge and have been growing in all the medium-sized teams during the aero testing restriction period.

Who was correct about the best way forward for the future of F1? Well, that depends on your perspective. The biggest, manufacturer-backed teams will almost always win if resources are not restricted because they have the spending power to blow the privateer teams off the race track if and when they choose to do so. It takes some time but the big spending usually works. Sometimes apparently “unlimited” resources are a disadvantage and too much money breeds inefficiency, but a well-organised and efficient large team will always beat a good small one. The FiA’s approach would have meant closer racing and stronger privateer teams. The big teams’ approach has allowed them to maintain their advantage – and hence some have stayed in F1. The price has been poorer racing and small teams on the brink of bankruptcy. I am not a politician and have focused on the technical side but you could see that a very different F1 may have been stronger today without some of the big players.

Some literal interpretations of the rules which do, cleverly, comply with the letter of the law are rejected. Teams tried lots of ways to get more air to the diffusers, especially for 2009. For example the curves joining the step and reference planes had to be tangential to the surfaces where they met but nothing in the letter of the law said they had to be tangential in the same direction. So we asked for, and had approved, the following concept :-

Unfortunately for us, despite having approval in writing from the FiA during 2008 for 2009 and working to that, approval was withdrawn early in 2009. The truth is that it would have been difficult to manufacture – but so was the legalising slot on the double diffuser. This was one of the reasons we felt there was a conspiracy – that change of mind. We felt, quite strongly, that our interpretation was in complete agreement with the letter of the law and therefore was legal.

How was it that 3 teams started with double diffusers in 2009?

The loophole that was used had been in the rules for years. How could it be that 3 teams miraculously and coincidentally came up with the same concept all of a sudden in 2009. Despite protestations of the time, it wasn’t a coincidence. Honda had announced their withdrawal from Formula 1 and many people, fearing the worst, left the team looking for new opportunities. The normal notice periods for transfer had been waived to save the team money. You can’t take designs of listed parts from one team to another but you don’t normally unlearn something you’ve learned! So, this came about due to personnel movement. I will not name names and I don’t think anything illegal was done – knowledge transfer is one of the reasons teams poach people and it is one of the reasons that experienced personnel are valuable to others.

Why did Brawn have the best overall double diffuser package initially? There are many reasons but the main one is that they had more development time on it than any other team. Once a person leaves and starts at another team development has to start from scratch. By the end of the season the Brawn team were no longer the fastest but their early point scoring took them over the line.

Politics

The diffusers were permitted in 2009 with the technical people in the FiA focussing on the concept of the interpretation. Having gone through Stewards and appeals it would have been embarrassing to change your mind. Having had the interpretation slapped in our faces the unsuccessful teams had no qualms in taking the interpretation to the limit. By the time rule makers representatives realised we were all “taking the piss” (laughing at the letter of the law in this case) and that actually it had been a bad idea, the rules could not be changed for 2010 (needs unanimous agreement after a certain time the year before). The rules were changed for 2011 with the specification of a large area of the floor which could contain no fully enclosed holes even where there was nothing to shadow. This then forced our devious minds to work on other potential loopholes......

There is another view one could consider. By the time the first races were underway and the protests had been lodged it was clear that the Brawn team had an advantage. Now with the best will in the world it must have seemed quite funny, and good for the sport, to the rule makers that their regulatory interpretation was causing such an upheaval. Having once formed an opinion rule makers like everyone else are human and don’t want their opinions challenged – especially not publicly. The teams with the double diffusers were all teams “in trouble”. Toyota was threatening to leave (and did in the end). Brawn had zero sponsorship and would not exist in the future if they were not reasonably successful – there had been no buyer for the team remember – only a management buyout and Honda money got them to the grid. And Williams had a dreadful year in 2008 and were looking dodgy. Hence, even if from an engineering perspective you might be tempted to change your mind, there were also good reasons why you should not.

Now we are into opinions, so this is an interpretation.... Why did the Stewards side with the FiA? Well, they are independent (and occasionally show it), but where do you think they get their expertise from? Few really have engineering expertise at the necessary level. They are likely to ask the FiA technical people for an opinion and for background information. Of course they read the rules but they are a minefield and help is needed. Why was the appeal lost – doesn’t bode well when you go against your technical delegate and stewards does it? – not a great precedent to set. The members of the appeal council also have to be briefed on the details of the technical regulations – and where do they go – same source. Of course they also read the rules for themselves as well and try to make a sensible call. Once the protest was lost at the race track it was lost and the other teams should have moved on.

Championship position vs. Year for constructors

In a year when the rules are relatively stable the average “championship position” change from year to year is somewhere near 1. For 2009 it was 3 and there were two big winners and several losers.

It is clear, from where Honda had been before, that the Brawn team took a huge step forward and that team immediately fell back a little the following year. They had benefitted from a change to the strongest engine and early commitment to the double diffuser concept. However, parts of the team had been torn apart by the withdrawal of Honda, the resulting cut back in staff and finances as well as the uncertainty that followed. It took Mercedes a little while to rebuild the team.

Red Bull also took a step forward despite not starting with a double diffuser. They invested resources quickly after the realisation that they were behind, and had been the quickest car behind the Brawn cars anyway. For BMW it was the end of the road and they withdrew at the end of the year.

Why are details like these never published?

Most teams gag the vast majority of employees. Don’t talk to the press is one common instruction (and contractual obligation) for F1 “normal” employees. People who want to keep their jobs are scared. I didn’t spill the beans at the time because I was still in F1. Partly that meant being very busy (so no time to hone the words) but partly you won’t survive long in the sport, never mind one job, if you bring the sport into disrepute. I was already always on the edge of upsetting my bosses so could not afford to go public (I was one whose communications needed to be sanitised before publication). This is true of most people in F1. It’s only a few people who can “legally” talk to journalists without a filter.

Amateurs think they can explain technical things like diffusers and front wings, but clearly have no idea what is behind the engineering side. Their well-meaning and often seemingly plausible offerings proliferate and become folklore. Professional journalists are not often engineers, are not told the truth by the teams. Race engineers rarely know about aerodynamics in detail anyway and they’d rather invent a plausible story than convey the truth because the teams don’t want the truth to be told in case it gives away an advantage. Eventually, long-standing journalists may have earned enough respect to be told the truth, but then they are told that they cannot publish that juicy fact.... I’ve read every piece I can find on double diffusers and haven’t yet found one that I think covers the technical side of the subject really well. In part that’s because most articles are short but in part because that combination of willingness to expose and availability of technical facts is missing. The fault really lies with the teams who are so obsessed with secrecy they don’t allow information to flow into the public domain.

Why they should have been declared illegal from the start.

I wish to use an example that may not, at first, appear related but is, in my opinion. Ferrari had the rules on bodywork tolerance changed after they’d been excluded from a race for an illegal barge board in 1999. It is precisely this tolerance which I wish to use to illustrate my belief. Between the wheels (precise locations have changed over the years) all bodywork has to be shadowed by surfaces on two planes under the car. The idea of this rule is to limit downforce generation. Ferrari fell foul of this rule because the barge boards were not fully shadowed. Ferrari appealed the decision in two conceptual ways. One was that they didn’t gain performance from the error and “proving” this involved opening up CFD and wind tunnel testing results to the FiA. The other was that they insisted there had to be a tolerance to the shadow rule because even they, with all their resources could not achieve infinite precision. A tolerance of 5mm in plan view was accepted and put into the regulations for the following years (it has been modified since to a smaller number).

So, given the legalising slot is somewhere between 50 and 100mm above the reference plane and is tiny, the fact that it has to be precisely aligned with the edge of the reference plane all the way along one side of the slot and given that infinite precision is not achievable even for a big team like Ferrari, it was clear that the real world installations of this concept were going to be illegal to the letter of the law. Even in the last few years some teams have claimed not to be able to manufacture things to a tolerance better than 2mm – a fact that doesn’t go so well with claiming they could make the double diffusers legal.

With the benefit of hindsight, talking to other insiders and seeing how development was pursued – I’m now quite convinced none would have passed the letter of the law out on track. Once you see what really had to be done to create double diffusers that actually worked it should be clear that it required infinite precision, a liberal interpretation of tolerances and in most cases, material deflection, to make them work really well. I am willing though, to be educated if someone knows of a legal way to seal the double diffuser legalisation slot.....

More posts from me here https://www.linkedin.com/today/posts/willemtoet1

If you've got all the way here then you really are a dedicated follower of both F1 and aerodynamics. Well done! Comments?

P.S.- there is no need to copy the double diffuser concept if rules allow a bigger conventional one. It is not as efficient as a bigger diffuser unless this is the only way to aerodynamically connect to a nice low (static) pressure area.