F1 2009-13 part four: the exhaust-blown diffuser

The word innovation is usually applied to a new idea. But innovation can also be a new application of an old idea - and that is exactly what happened with the exhaust-blown diffuser, arguably the defining design concept of the 2009-2013 rules cycle.

The shorthand term really refers to the way in which high-speed exhaust gases were used to generate downforce. This involved variously blowing the diffuser, downforce-producing brake ducts and the way in which the airflow could be used to make the aero at the rear of the car work more effectively, for example by creating 'virtual' skirts.

But the idea of using exhaust gases for performance is far from new. Back in 1983, Renault introduced the concept by blowing exhaust gases directly into the diffuser (see bottom) in a way that was no longer possible once rules preventing running exhaust pipes through the floor came in.

Even so, such designs were not unusual for some time before disappearing from Formula 1.

But at the final pre-season test ahead of the 2010 season, the Red Bull RB6 introduced a new exhaust design, replacing the periscope-style ones used during the first three winter tests. This blew exhaust gases over and through the diffuser to generate downforce.

It was the start of something big, with exhaust-blown downforce remaining crucial until the end of the 2013 season even though attempts were made to mitigate the effect. But why did this concept make such a sudden comeback?

Red Bull pioneered the return of exhaust blowing with its RB6 © LAT

"When we were researching the 2010 car and the things we wanted to do around the back, it seemed like the exhaust was a wasted opportunity and we weren't getting much out of them," says Red Bull chief technical officer Adrian Newey.

"So we decided to try and get it down low, where the exhaust served two purposes. One was to energise the flow around the rear tyre. The other thing we were able to do, which I don't think many people realised at the time, was we slotted the double diffuser vertically at the rear axle.

"That extra slot meant that we could effectively blow the diffuser as well, in a similar manner to the old 1980s cars, but in a manner that was legal because the exhaust was on the top surface rather than the bottom in its exit position - although not in its aerodynamic effect."

Red Bull had stolen a march on its rivals. Ferrari, Renault and Mercedes relatively quickly attempted their own versions, albeit only blowing over the top of the diffuser to boost the airflow passing through it, with McLaren following shortly after.

It soon became clear, even to Red Bull, that the potential of this technology was enormous. The downside was that it was incredibly difficult to master. Sam Michael, then technical director at Williams, suspects that this concept had been ignored because nobody realised just how effective it would be in previous years.

"What everyone really underestimated at the start was just how much power there was in the exhausts," he says.

"When people started doing it, the early ones blew right down next to the spat and basically sealed the diffuser. And remember the diffuser had been shortened by 330mm as well. So 10 years earlier it may not have worked quite as well as before that change.

"The diffuser went from the back of the rear tyre to the axle line and at that point the tyre wake started to make the diffuser stall more, so there was the bigger incentive to make the seal between the diffuser and the tyre.

"But I am sure if you put exhaust-blowing on a car of 10 years ago, you would gain a serious amount."

McLaren was one of several teams frustrated to be playing catch-up © LAT

Michael isn't the only one surprised that everyone ignored this idea for such a long time after the major rule changes of 1994 made it impossible to do the more straightforward form of Renault-pioneered exhaust-blowing. Then-McLaren technical director Paddy Lower admits to plenty of frustration at ignoring the potential of the exhaust gases.

"I hate seeing an innovation on another car before my own because you want to be first to market," says Lowe.

"But what was super-depressing was that we were blowing floors in the '80s, so I don't understand why this trick was missed even though we stopped blowing exhausts when you could no longer stick them through the floor.

"The exits blew just above the diffuser for many years after that, then in the early 2000s Ferrari was the first to take the exhaust high and started that trend. And there they remained. But the exhaust gas has always been there to work with."

Infamously, McLaren over-stepped the marked with the hugely complicated design it tried to make work on its 2011 car pre-season. Widely known as the octopus exhaust, it was actually dubbed the 'bagpipe' exhaust by some internally and while fundamentally a sound idea it was quickly abandoned after a disastrous pre-season.

"McLaren had this exhaust that blew along the slot [in the diffuser] that was quite big," says Michael, who joined McLaren well after the bagpipe exhaust debacle. "It blew outboard and had two exists.

"I have seen some bits of that system inside McLaren and it is a monster! It's horrendous. Not a horrendous idea, in fact it was a great conceptual idea, but the engineering implementation was so hard to do.

"Ultimately, they couldn't get it to work which is why they were off the pace in testing. But between the last test and the first race they made a Red Bull-style exhaust and were strong in Melbourne. Before that, they were nowhere; 2.5s off the pace. And they had aerodynamic and overheating problems.

"It was a very good example of a McLaren-style recovery in a short period of time."

Even if teams' perfected the layout, the work was far from over. You can point the tailpipe in the right direction but the exhaust airflow, and therefore the effect produced, is related to what the engine - controlled by the driver's throttle foot - is doing. In crude terms, at 100 per cent throttle you have maximum benefit, at zero per cent throttle you have none.

As the technology evolved, so did the engine mapping strategies needed to exploit it.

"We didn't explore that as much in 2010 as we could have done, with hindsight," says Newey of the engine mapping requirements.

Red Bull compensated for the loss of double diffusers through engine mapping in 2011 © XPB

"When the double diffuser was taken away in '11, the opportunity to blow the diffuser itself was taken away. But we managed to get an effect which actually gave, certainly in low-speed corners, more downforce than the 2010 car by positioning the exhausts just in front of and inside the rear tyre.

"With the 2010 exhaust, it was a little bit like the 90s cars in that without the exhaust blowing, you weren't worse off.

"With the '11 car, if you didn't have exhaust blowing you were actually worse off than if you had no exhaust parts at all. So it became necessary to keep the exhaust running at all times. That's where working with Renault was so important.

"Funnily enough, it was work that we had started on when I was at Williams back in 1993 with [Renault's] Bernard Dudot. I had given him the challenge of, more or less, getting rid of the butterflies [the throttles] and just running the engine on spark and ignition timing. When it came back with the '11 car, Bernard had long gone but Renault dug back through their archives and picked the work back up again."

So the challenge was two-fold. You needed to get your aerodynamic design work right, but this was of limited use without the trick engine maps that started to become prevalent in '11.

There were some fascinating concepts attempted during this season, notably at Renault which through a tortuous feat of engineering managed to get its exhausts to exit at the front of the sidepod to blow more of the floor.

It worked, to a point, but diminishing returns and struggles on slow tracks meant that the team became increasingly uncompetitive as the potential of a more orthodox design started to become clear.

And it wasn't only the team themselves that faced a big challenge.

"It wasn't just an aerodynamic problem, it was an engine problem," says Sam Michael. "You wanted as high a mass flow rate through the engine as possible despite not having the power. That meant opening the throttles to 100 per cent and cutting power.

"That was a challenge for the engine guys. The only way you can do that is to retard the engine and every time that puts a lot of heat and stress in the engine. So it required lots of dyno hours.

"Effectively you had throttleless engines that were being driven on fuel and ignition. The third parameter [throttle] was completely removed.

Williams was strengthened by the 2011 British GP rule tweaks © LAT

"At the end of 2011, that's when the big hit came. The FIA really tightened up on it by tightening up on the throttles, and they also controlled retard as well. But the big hit was by saying that they had to match, in certain conditions, what the pedal was doing. And they moved the exhaust position as well."

F1 had a sneak preview of this at the 2011 British GP, where rules came in that effectively allowed only 10 per cent of engine over-run when off the throttle.

For various political reasons, combined with the fact that this did pose legitimate reliability problems for some teams, the ban lasted only one race before a wider raft of rule changes came in for '12. But it changed the competitive order dramatically.

Williams is arguably the best example of how important this technology had become. With its Cosworth powerplant, which lacked trick engine maps, the car was poor in 2011, but Silverstone was its strongest showing.

The fact a very similar machine won a race the following season indicates that generating the maximum exhaust blown downforce was critical.

Fortunately for the strugglers, exhaust-blown downforce was effectively outlawed for 2012 - at least, it was meant to be. But it came back with a vengeance.

An eminently sensible proposal to sling the exhaust exit out the back of the car, 50mm behind the rear-wheel centre line (a theoretical line from one side of the car to the other running through the centre of the rear wheels) was tabled.

The mooted rule was not dissimilar to the regulation that should finally knock out exhaust-generated downforce in 2014. It was, of course, prevented from happening amid behind-the-scenes politics.

"Some teams felt they were in a stronger position with exhaust technology, others a bit weaker," says Mercedes team principal Ross Brawn.

"Those that were a bit weaker wanted a draconian regulation, those that were stronger wanted some latitude. Those things get argued.

"But the compromise we ended up with still gave probably more scope than the majority of people thought there would be. And that includes the FIA. But once you've written a regulation, it's there in black-and-white and you have to respect it.

"Whatever the intent, the spirit and so forth, it's what is written in the regulation that matters and we didn't do a good enough job or writing a regulation to stop the exhaust system.

"We gave the potential for Coanda systems and we didn't know about them then. Sometimes, new technology comes along that nobody envisages."

F1 politics have influenced the genesis of exhaust-blown diffuser rules © XPB

For 2012, the exhaust position regulations dictated that the permitted two exhaust exits would have to face rearwards, with the positioning and diameter of the last 100mm of the tailpipes mandated in terms of location and angle. The theory was that by stipulating they must point upwards (at an angle of between 10 and 30 degrees), the exhaust gases could not be redirected for anything other than a tiny aero gain.

It wasn't the case, especially as the rules still allowed the exhausts to exit forward of the key downforce-generating areas at the rear of the car. The Coanda effect became easily the most talked-about aerodynamic effect of '12.

At its most basic level, this is the tendency of a jet of air to be attracted towards a surface. McLaren had some familiarity with this, having struggled with it with its 2010 exhaust.

"McLaren's solution came out at Silverstone in '10 and it didn't work because the Coanda effect caused the exhaust flow to stay attached to the Coke bottle line rather than going outwards and into the diffuser," explains Lowe.

"There was quite a lot of work done and science put into understanding Coanda to solve that problem, so when it got to the end of '11 and the second form of exhaust-blowing with the engine restraints and the exhaust position constraints in' 12, it was a help."

The rule change did hold Red Bull back for the first half of 2012, when famously seven different drivers won the first seven races. But it did not take long for Red Bull to hit its stride.

"We did struggle at the start of 2012," admits Newey. "We'd been on the exhaust technology right from the start of 2012 and had evolved our aerodynamics around it and had perhaps gone further down that route than others had. So when it was taken away, we had more to relearn.

"It was very similar to when I was at Williams and we had active suspension for two years and when it was taken away [in 1994] we had to relearn than those who had only been on it for not time or perhaps one year.

Newey had to contend with significant rule tweaks while at Williams © LAT

"It's funny how quickly things change and move on and those lessons that others have been learning and that you haven't take a bit of re-doing.

"So the start of last year was a struggle. Suddenly we had all sorts of problems that we just weren't expecting. And when problems pop up that you don't expect it takes a while to go away and understand them.

"When you've actually understood them, you've got a chance of coming up with solutions."

Red Bull's solution was, inevitably, extremely effective. Even when the rules were modified to prevent engine maps being changed dramatically, it did not significantly hold the team back, culminating in nine wins on the bounce at the end of 2013.

Red Bull harness the Coanda effect to attach the high-speed exhaust airflow to a 'ramp' behind the exhaust. This directed it in the direction it wanted. The key to generating downforce here was through the aerodynamically-profiled brake ducts, and making the diffuser work better by sealing it.

Others opted for what might be termed as a less literal Coanda effect exhaust without a ramp of bodywork to attach the airflow to. This relied on the downwash effect of airflow already travelling over the car to direct the exhaust gases downwards.

This remained difficult to execute, even with the curbs on the trick engine maps. Again, Williams is a superb example of the dangers of an exhaust that isn't giving stable results.

When it removed the exhaust effect in free practice at Abu Dhabi near the end of the 2013 season, the car was actually improved. Considering this was a design that should be worth a second a lap or more, that was a dire indictment of how effectively it was working. Williams saw out the season without exhaust-blown downforce and Valtteri Bottas claimed eight place, entirely on merit, at Austin.

For next season, the chances of exhaust-blown downforce being resurrected are vanishingly small. But from 2010-2013 it was arguably the key to success in F1.

And remember what Newey said about what happened in '94 when Williams lost active ride and suffered aerodynamic problems?

That is a reminder that, no matter how brilliant a team Red Bull is, it is as big a challenge to stay at the front in F1 as it is to get there in the first place.

ORIGIN OF THE EXHAUST-BLOWN DIFFUSER

Originally published in AUTOSPORT magazine on March 10 2011

Jean-Claude Migeot was a 29-year-old Renault aerodynamicist when he conceived the exhaust-blown diffuser in 1982. The system made its debut on the Renault RE40 at the Monaco Grand Prix a year later.

"We knew that skirts were going to be banned and flat bottoms were coming for 1983, and our tests showed that we would be left with perhaps one third of the downforce we had," says Migeot.

"So we were looking for ideas to generate downforce. The idea of blowing wings was not new in aircraft history, but I don't remember it being done on a car before. We also thought about trying to use exhaust gases to simulate skirts, which was tested on track with absolutely disastrous results!"

Migeot settled on a multi-pip design that fed air directly to the diffuser and also drew air from both the turbo and the wastegate of the 1.5-litre powerplant. A titanium plate was used for heat shielding.

Renault pioneered blowing technology in F1 in 1983 © LAT

"It was obvious that it was very good for traction out of the slow corners," says Migeot. "It was worth something like 80kg of downforce, which was huge, and there was no way you could do that with conventional bodywork.

"But it was very throttle-dependent and on tracks with long corners the car could be so throttle-sensitive that it was slower, despite having more downforce."

With Alain Prost and Derek Warwick not always happy with the performance of the exhaust-blown-diffuser-equipped Renaults (the Brit nicknamed the system 'the blowjob'), Migeot found himself increasingly sceptical of its merits, although he tried the philosophy again when he went to Ferrari in 1986.

"It made my name known in F1 for the first time, and not necessarily in the most brilliant way," says Migeot. "It worked, but it was not all good. Now, with not so many long, fast corners and the ability to use the ECU to manage the throttle, it is maybe easier.

"Today the effect of the exhaust-blown diffuser is perhaps not proportional to its visibility, and it's just one of the cocktail of 10 things that make a good car."