Why exhaust blowing was a game changer in 2011

Exhaust-blown diffusers have been around for many years, and are a very powerful tool in changing a car's aerodynamic characteristics with on- and off-the-throttle applications.

As long as the driver knows what he wants from it and how he can achieve it, it will help the overall car performance and reduce lap times.

In the old days, nearly every team had exhaust pipes blowing into the diffuser area, and when on full throttle, this high-energy exhaust flow would help increase the speed of the airflow underneath the car, creating more overall downforce.

It could also be positioned in such a way as to reduce any areas of airflow separation on the diffuser surface, making the diffuser work much more consistently.

However, with the regulations not allowing the exhaust to actually encroach upon the diffuser surface, and with clever engineers not wanting to forget the advantages that this style of exhaust-blowing system offered, a lot of work would have been put in to settle upon a positive concept.

In the early part of 2011 it looked like Renault had been the first to find an advantage. Its forward-facing exhaust system, which had the outlet blowing across the leading edge of the sidepods, had everyone heading back to their CFD and windtunnel engineers to investigate the concept.

If the system had proved to be as positive as it initially looked, then it would have been very difficult for other teams to implement it, as it would have meant an almost completely new package.

Renault's radical forward-mounted exhaust © sutton-images.com

But in reality there appears to have been very little potential for further development with this approach, and although it started the season strongly, improvement was limited.

Red Bull, on the other hand, went down a more conventional route, with the exhaust pipes on top of the floor blowing across the diffuser foot, which is just inside of the inner wall of the rear tyre.

Having the exhaust exit in this area helps to reduce the airflow from going under the sides of the diffuser as the rear tyre rotates. If this airflow is allowed to spill underneath, it reduces the efficiency of the diffuser, which in turn reduces the performance of the entire underfloor.

There were various detailed developments of this concept during the season, but the reality is that this system was the best for overall performance, and most of the other teams followed suit.

There were very different opinions regarding the merits of hot- or cold-blowing.

Basically, cold-blowing is when the engine is used like a compressor under braking. So the throttle is kept open, and the retardation is achieved by cutting the spark and fuel.

This air is then fed through the exhausts, and its velocity helps increase the speed of the airflow around it, improving the diffuser performance.

But some teams were using hot-blowing, which means that fuel was introduced into the system.

With a highly retarded ignition, the fuel would not burn until it got into the exhaust system. This would generate just that bit extra performance from the diffuser, especially under braking when the rear of the car is higher, which normally makes rear grip more nervous on corner entry.

Managing the very high temperatures in the exhaust system and the tailpipe area is no mean feat, so the negatives of this approach can very quickly outweigh the positives.

McLaren followed Red Bull's lead with its exhaust-blowing concept © sutton-images.com

Any difference in performance of these different systems is negated when the driver comes back onto the throttle and wants positive torque.

The one other area that exhaust-blowing also helps is the amount of downforce that can be created from the wing sections that are mounted on the inboard surface of the rear brake ducts, because this unit generates its forces directly upon the tyre contact patch.

There is no time lag created when the suspension is moving because of the load reduction when the driver hits the brake pedal. The forces acting directly on the rear tyre contact patch give the driver a more consistent sense of rear grip, allowing him to have more confidence in the rear of the car.

As all of the teams other than Renault adapted the Red Bull concept, you could say that this was the best solution.

But since Red Bull had it as part of its initial concept and the rest of the car was optimised around the characteristics of this exhaust-blowing concept, it still had the upper hand on outright performance.

McLaren was very swift to copy Red Bull's system. It started its initial testing with a very complicated exhaust outlet located somewhere in the middle of the car's rear floor, but I get the impression that the team quickly encountered the problems inherent in trying to manage the high temperatures.

By the time of the Australian Grand Prix, it was following what would become the de rigueur exhaust-outlet concept for 2011.

The FIA has banned this style of downforce-producing device for 2012. Why? I am not sure. Everyone has it now, the money has been spent on development, and it is working.

The only thing I think should have been banned is hot-blowing, as this basically is wasting fuel and does not send out a very good message of leadership in innovation when everyone is trying to reduce our carbon footprint.

The new regulations essentially return the exhaust tailpipe location to where it was a few years ago, on the upper trailing edge of the sidepods.

We'll have to wait until 2012 testing starts to learn what the consequences of this will be, and whether anyone can find a solution that will improve their performance. But I am not expecting any team to discover any great exhaust concept that will render other cars redundant.

As always, it will be the sum of all the parts that translates into a car's overall performance - and for the last three years, Red Bull has been pretty good at that.