Explained: The ingenious innovation that propelled Brawn GP title glory

The year 2009 in Formula 1 will be remembered as one of the most entertaining and exciting seasons in the history of the sport, with Brawn GP synonymous with that season for its incredible story and the tremendous success it achieved.

This is the story of a team that rose from the ashes and won both championships in 2009, thanks to one of the greatest inventions in Formula 1 – the double diffuser.

Here is a look at how that solution came to be, after almost never making it onto the grid in the first place after Honda’s near-collapse in 2008.

Changes to F1 regulations before the 2009 season

Major rule changes announced for the 2009 season were intended to significantly alter the dynamics of Formula 1 racing.

The goal of the new rules was to reduce the amount of downforce that cars could generate. Less downforce also meant less dirty air, theoretically making it easier for cars to follow each other closely and creating more exciting races.

Additionally, the new rules substantially increased the overall safety of drivers on the track by implementing numerous new safety systems.

At the same time, the world was grappling with a significant economic crisis that had a considerable impact on Formula 1 teams.

The racing team Honda bore the brunt of the situation, deciding to withdraw from the fastest motorsport competition in the world. The Japanese brand lacked the necessary funds, then through a combination of events led to the formation of Brawn GP at a cost of just £1, led by team principal Ross Brawn, which saved the Brackley-based team from outright collapse.

Brawn faced significant financial challenges throughout the season, however, clearly making them the poorest constructor at the time.

However, this did not prevent them from maintaining their team and creating a championship-winning car that season.

How the double diffuser came to be at Brawn GP and others

Even in 2008, engineers were exploring ways to make their cars faster for the following season. Reducing aerodynamic components meant paying much more attention to every detail to maintain a high level of downforce.

It is believed that the idea of the double diffuser came from a young Japanese aerodynamicist working for Honda. Reading the new rules in his language, he noticed poorly defined rules regarding the size of the diffuser.

In addition to the clearly defined dimensions of the diffuser, clause 3.12.7 of the regulations stated:

“No bodywork which is visible from beneath the car and which lies between the rear wheel centre line and a point 350mm rearward of it may be more than 175mm above the reference plane. Any intersection of the surfaces in this area with a lateral or longitudinal vertical plane should form one continuous line which is visible from beneath the car.”

As the rules required engineers to consider the size of the diffuser from a specific viewpoint, it opened up other options.

The young Honda engineer noticed that additional openings could be implemented on vertical surfaces, serving as static support for the car’s floor and plank. In other words, a completely legal method was found to increase the size of the diffuser.

To understand why this is a big deal, we must recall the basic principles of the diffuser and its role.

What is the aerodynamic role of the diffuser on F1 cars?

The diffuser is one of the most crucial aerodynamic components on a Formula 1 car. Without it, the car’s floor would be entirely inefficient. Its main role is to expand the airflow coming from beneath the car and gradually increase the pressure to atmospheric pressure.

Due to the car’s geometry, i.e., the narrow space it creates with the asphalt, the air passing underneath accelerates, simultaneously creating a low-pressure area. The difference between this low pressure and atmospheric pressure above the car actually generates a force that pushes the entire car down to the asphalt—known as downforce.

Therefore, a well-designed diffuser will make the airflow passing under the car even faster, thus increasing downforce. The larger the diffuser, the greater the expansion, and consequently, the greater the acceleration of the airflow. However, when designing the diffuser, two things must be carefully considered.

The first is that an excessively large diffuser can lead to excessive airflow acceleration, which may detach from the surface of the floor, rendering the entire system inefficient. This increases the chance of turbulent flow, which is undesirable.

The second thing is that the FIA determines the maximum size of the diffuser, and attention must be paid to the angle at which the diffuser is designed. If we implement too steep an angle, there is a high risk of flow separation on the diffuser, and the entire system falls apart.

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Why is the double diffuser so ingenious?

A loophole in the regulations allowed engineers to create another diffuser, which could start much further forward and thereby increase the overall volume of the diffuser. This leads to greater expansion and lower pressure underneath the car, directly affecting the amount of downforce. And most importantly, the engineers of the then-Honda, or Brawn GP a year later, managed to design the diffuser lines in such a way that flow separation did not occur.

This added a significant boost of downforce, enabling the car to be much faster and more stable in corners. However, Brawn GP was not the only team to start the 2009 season with a double diffuser due to the crisis faced by Honda.

Many engineers left Honda for other teams, primarily the other Japanese team Toyota and Williams, which was collaborating with Toyota at the time. Therefore, these three teams were the only ones to begin the season with a double diffuser.

What set Brawn GP apart was how the diffuser functioned alongside other aerodynamic components.

While the double diffuser provided a massive boost of downforce to the rear of the car, if the front end was not equally aerodynamically developed, the aerodynamic balance crucial for stability on the track would not be achieved.

Already in the first race of the season in Australia, it was clear that the Brawn GP car was the fastest on the grid. Soon after, a lawsuit from major teams followed, but it was ultimately unsuccessful. The FIA officially declared the double diffuser legal.

Other teams quickly started developing and implementing this clever system on their cars. But of course, this required a significant amount of time.

Jenson Button took advantage of the performance advantage of their car and secured six victories in the first seven races. Subsequently, the lack of finances and the inability to develop the car led to other teams becoming more competitive.

However, it turned out that this was not enough, and Jenson Button won the driver’s title, while Brawn GP was the best constructor that year.

Truly an incredible story from many perspectives that will be tough to replicate in this sport again.

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