Guest writer John Beamer examines how Ferrari and McLaren have closed the gap to Red Bull.
The RB7 has not won for three races, its lead in qualifying has been cut, and on race pace McLaren and Ferrari have often had faster cars.
It pays to be careful when making sweeping statements about performance, especially when track layout and tyre performance can have a dominating effect on race results.
But consider the Hungarian Grand Prix, where last year Red Bull were a second clear in qualifying, while this time Sebastian Vettel took pole position by less than two-tenths of a second partly because Lewis Hamilton made a couple of small errors on his final run.
The top teams’ recent technical developments gives some insight into how the battle for victory has changed.
Exhaust blown diffusers
Ferrari won their only race of the year so far at Silverstone – a weekend clouded by the row over exhaust-blown diffusers.
Prior to the race the FIA mandated that teams restrict off-throttle blowing to 10% of the full amount.
However, during Friday practice it emerged that Renault had permission to run up to 50% off-throttle based on a historical analysis of how it used its engines to aid valve cooling. This was in response to Mercedes being allowed to fire four of its cylinders off-throttle to relieve crank case pressure.
These changes remained in place for the race but were rescinded afterwards. That Ferrari won the race and McLaren struggled gave a lot of insight into the design of their 2011 cars.
The EBD restrictions were to limit the amount of hot-blowing, which many believed is what helped Red Bull secure such a large qualifying advantage, especially when it turned up the engines in Q3.
It turned out that Red Bull does not use hot-blowing. The team had tried hot-blowing in testing and free practice but it wrecked the rear tyres.
McLaren’s ‘octopus’ exhust
McLaren , on the other hand, spent most of the off-season designing the MP4-26 around the infamous ‘octopus’ exhaust system, which did hot-blow the diffuser floor. The octopus exhaust was designed to release gasses across the full width of the diffuser but created too much aerodynamic sensitivity.
So they switched back to a conventional EBD layout before the Australian Grand Prix and picked up over a second a lap in time.
Although the diffuser was changed to accommodate the new exhaust system the aerodynamic principles relied on hot-blowing the exhaust. Fast-forward to Silverstone where hot-blowing was banned and McLaren suffered the most as the delicate balance of the car so apparent in the ‘octopus’ days returned.
Ferrari were off the pace early in the year partly because of wind tunnel calibration issues. That changed when they brought a radical upgrade package at Silverstone consisting of new rear bodywork, a revised exhaust layout, a new rear wing and floor.
That Ferrari got the harder compound working so well after struggling in previous races is a testament to the increased downforce generated.
One significant performance differentiator in 2011 is rear wing design. This is intrinsically linked to the Drag Reduction System, which has a significant effect on laptime, especially in qualifying where DRS can be used feely.
To achieve this the wing needs to stall more aggressively in DRS operation. The trade-off is that this typically results in worse performance in total as airflow struggles to reattach when the DRS is deactivated – Mercedes suffered from this issue in the first few races.
Ferrari extended the main plane and increased its camber. In turn the flap cord length is reduced. When DRS is activated the effect of the flap slot disappears and the air under the main plane stalls causing downforce to drop away more quickly.
The wing was updated for Hungary practice. The flap chord was further shortened to give even greater drag reduction but so as to avoid losing too much downforce a Gurney was attached to the flap’s trailing edge. We may see this wing return at Spa, where drag reduction is especially important.
The other feature of the RB7 which Ferrari have tried to replicate is its distinctive coke-bottle rear bodywork, which allows cleaner airflow to the diffuser. Ferrari altered their rear bodywork, reworking the exhaust and radiator layout. The sidepods have also been extended rearward.
Normally designers try to create as much space as possible so superficially this seems an odd choice. There are two possible factors: first, the airflow wasn’t staying attached to the bodywork so by lengthen the sidepod this phenomena is being encouraged. Second, this new arrangement allows the exhaust construction to be simplified – it is now sunk into the floor.
Ferrari’s front wing has also been modified, with the most recent version appearing in Hungary. They have wavered between using a two- and three-element front wing. In one sense this allows them to choose the wing depending on the circuit but this approach is likely to be more expensive in development time and resources.
The outer section of the wing has reduced camber, which will cut downforce but feel more consistent and stable to drivers when steering. There have been changes to the cascades which now appear a lot more detailed than in the past – the cascade is now dual element with a separator midway across its length.
Also, the forward-facing camera is mounted directly behind the central section where it looks like a second section. The two cameras appear to join so it looks like a single section – presumably the FIA is happy with this construction.
Red Bull’s rake
A noticeable trend over the last few months has been the degree of rake the Red Bull cars run. For the uninitiated, rake is the nose to tail angle that the car runs. A car with a lot of rake has its nose closer to the ground while its tail is higher.
Why is this an advantage? The theory is that by running a lot of rake the front wing is closer to the ground where it is more effective. In addition the diffuser is at a steeper angle. Both phenomena, in theory, create more downforce. Let’s look at both of these in more detail.
Rake and the diffuser
Downforce in the diffuser is a function of height above the ground and slope. The steeper the diffuser the greater the downforce. A higher diffuser creates less downforce and also raises the centre of gravity. Both of these are only true up to a point – push them too far and all performance is lost. Adding rake to a car is trading off these phenomena.
One of the reasons why increasing diffuser height cuts downforce is because the diffuser becomes more prone to stalling. Red Bull realised that it could harness the power of the exhaust blown diffusers to mitigate this.
The exhaust gasses add energy to airflow in the outer part of the diffuser and prevent turbulent air from rear tyres entering the diffuser (acting as a seal). This reduces the effect of increasing the height of the diffuser.
Rake and the front wing
The 2009 technical regulations allowed the front wing to be run much closer to the ground than in previous seasons. This meant that the ground effect came back into play.
Ground effect is the same phenomena associated with changing the diffuser height. The lower the wing is to the ground the more downforce is generated – this is commonly known as the Venturi effect. Adding rake in conjunction with exhaust blown diffusers results in a considerable downforce benefit.
Teams follow Red Bull’s lead
Red Bull has run a lot of rake for the best part of a year, and in recent races that McLaren and Ferrari have begun to follow suit. Is this a factor in the more competitive running order? Almost certainly.
This was particularly so in Hungary where Vettel abandoned a new front wing and floor design after Friday practice. The team had to break the FIA-imposed curfew to return the car to its Nurburgring configuration.
The main problem was the revised front wing and under-chassis turning vanes. The front wing pillar was wider and consequently the turning vane was deleted. In addition the trailing edge of the front wing flap sported a gurney and the cascade profiles were changed.
The addition of the gurney was interesting as this is usually a quick way to increase grip at low speeds. Although these changes seem minor, a small change at the front of a car can have a significant effect further back.
The updated diffuser, which was in all probability updated to work with the new front wing, sported a few subtle changes (externally at least). The central section below the rear crash structure contained a new fence structure and the vanes in the primary diffuser channel were lengthened.
It’s unclear what Red Bull is trying to achieve with these updates but presumably by adding/extending these vanes the intent was to better control and direct airflow exiting the diffuser.
This is a very sensitive part of the car as the pressure gradient aft of the diffuser determines how much downforce it generates. Too steep a gradient and the diffuser is more prone to stalling.
Don’t miss part two of this article tomorrow which will look at McLaren’s progress this year and significant changes in the midfield teams.
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