A raft of updates appeared on several of the front-running cars in Valencia.
As in 2009 when Brawn dominated the first half of the season with its double diffuser, Red Bull has enjoyed a similar performance advantage this year. The key difference is that in the first few races no-one could put a finger on why the RB6 was so quick.
Having previously suspected a trick ride-height control system was responsible for the RB6′s speed, the teams are now trying to emulate its clever exhaust and diffuser arrangement.
What is different about Red Bull?
At the rear of the RB6 there we find an unusual pullrod suspension set-up. Pushrod suspension, used by most other teams, connects from the lower part of the upright to a point roughly a foot above the floor, effectively ‘pushing’ the rocker, which activates a spring and damper system. A pullrod does the opposite.
This creates more space on the inside of the lower upright (there is no connecting arm) but potentially compromises the diffuser as the rocker is close the floor where the double diffuser inlet should be. At the start of the season many thought Newey would revert to a traditional pushrod system but he didn’t, believing that the pullrod allows tighter rear end packaging that gives a net increase in downforce (look at how tight the Red Bull is around the engine cover).
Second is the placement of exhausts low down on top of the diffuser. The theory is that the fast exhaust gasses help keep airflow attached in the diffuser which increases downforce by (a) making the diffuser work better and (b) allowing aerodynamicists to run a more extreme design (i.e., a bigger diffuser). It is these so-called exhaust blown diffusers that rival teams now believe is the root cause of Red Bull’s considerable speed advantage.
The difficulty in emulating Red Bull’s design is that the speed of the exhaust gas is variable. When the driver is on the throttle the gas speed is high. During braking it is is low. This variance causes inconsistency in diffuser downforce (effectively reducing downforce when cornering, which is when you need it most) so in the early 2000s constructors abandoned similar designs in favour of more stable downforce.
In addition there are significant heat problems too – the carbon fibre bodywork won’t take kindly to being blasted for 90 minutes with 800C fumes. In one sense it is no surprise that Newey had the vision to bring back the exhaust-driven diffuser given the last car to sport it before the RB6 was the 2003 McLaren MP4-18 – another Newey car.
How does Red Bull’s diffuser work?
The RB6 exhausts exit immediately below the forward lower rear wishbone, a few centimetres in front of the rear tyres. About 5-10cm aft of the exhaust exit is a small inlet slit that feeds the outer channel of the diffuser. This allows some of the exhaust gas to bleed into the diffuser channel adding to the energy of the air inside the diffuser, which helps downforce. It works in a similar fashion to the slots many teams have in the front wing endplates.
The rest of the gas passes the slot and blows over the outer edge of the diffuser aft of the rear tyre. Higher air speed equals lower air pressure, so as the exhaust gasses blow over the diffuser the pressure gradient behind the diffuser is lower than it would be otherwise. The diffuser is less likely to stall so downforce is higher.
Airflow in this area is often affected by the bulk of the rear tyres which creates unpredictable and turbulent flow. The exhaust-driven diffuser reattaches and smooths the flow behind tyres.
The detail at the diffuser trailing edge is critical for managing the airflow. Over the past few races Red Bull has been extremely active developing this area. The standard solution is to place a gurney flap on the rear edge to scavenge the air more effectively from the diffuser.
Ferrari, Renault and Mercedes
At Valencia all of Ferrari, Renault and Mercedes sported new exhaust arrangements.
The Ferrari upgrade was the most high-profile and extensive. The exhaust was moved to the floor to an opening below the sidepods. The Scuderia sported a raised gearbox and attached the lower wishbone suspension arms slightly higher to protect them from the exhaust heat.
In addition the radiators and oil cooler were updated partly to help cool what the engine but also to make the coke-bottle zone more effective. Massa’s was the only car that sported the full upgrade as Alonso was in the middle of a four-race gearbox cycle.
Unlike the Red Bull solution Ferrari did not cut a slit into the diffuser. This meant that exhaust gas blew over the top of the diffuser only. The diffuser looked largely unchanged from the Canada version except for the addition of a gurney flap.
Despite Alonso and Massa failing to score a front row grid slot the upgrade was thought to have performed well. Failure to properly dial in the soft tyres in qualifying that prevented Alonso from being closer to pole although it is unlikely that had the softs worked he’d have usurped either of the Red Bulls.
Mercedes’ and Renault’s implementations were similar to Ferrari’s albeit with some subtle differences to manage airflow. Mercedes added some vanes atop the diffuser to help guide air past the tyre to prevent it overheating. Renault’s exhaust exit blew onto a heat shield that was then directed over the diffuser where a gurney helped scavenge airflow from under the car.
Implementing exhaust blown diffusers present three engineering challenges. First is re-routing the exhausts – not a simple task. Each cylinder has an exhaust exit that feeds into a primary pipe. The exhaust lengths are tuned to the maximise engine power and re-routing the pipe to the floor requires meticulous engineering to ensure no loss of power.
Second is ensuring that the back of the car can withstand the heat generated by the exhausts. The suspension is covered with a protective heat shield, and heat responsive paint and sensors adorned the floor and rear wing endplates of the cars in practice.
Indeed Mercedes had to modify its exhaust exit before qualifying because of excess heat. This was where McLaren ran into trouble with their MP4-18 seven years ago – the car couldn’t run for more than five laps without setting its rear bodywork on fire. The team are planning to run their version of the exhaust package at Silverstone this weekend.
The third greatest challenge is packaging at the rear. The flow in this area is important and if suspension or other components obstruct the exhaust gasses then the effect of the exhaust gases reduces.
These three factors make retrofitting an exhaust blown diffuser to a car a significant challenge. As teams understand better how it works, expect them to get closer to Red Bull. However expect Red Bull to maintain an advantage as McLaren do with their F-duct.
While teams are busy copying Red Bull the Milton Keynes-based outfit isn’t standing still. The team brought a revised F-duct as well as a new diffuser to the European Grand Prix. The main diffuser inlet was changed slightly and the outer arches were more pronounced.
Webber’s crash gave us a great insight into how the RB6 diffuser is fed from the floor. It is believed to have only been caught on video by FOM’s cameraman, who F1 Fanatic spoke to at the Goodwood Festival of Speed. He mentioned that one photographer had been shooting the straight until about ten second before the crash, when he walked away. A pity, as it could have revealed more of the secrets of the most competitive car on the grid.
However the video shows that as the RB6′s under-body narrows an inlet with a vane and large radius feeds the diffuser. The vanes extend the width of the step plane allowing a higher volume of air into the diffuser increasing downforce. This is now standard solution across the grid having being pioneered by McLaren at the start of the year.
Valencia was also the first track where Red Bull raced the F-duct – previously it had only appeared in practice at Turkey. As discussed before the F-duct is a pneumatic switch, with the driver turning the duct on or off with his hand or knee. The Red Bull system was the same as that run at Istanbul Park with a couple of internal tweaks to ensure downforce didn’t wash off when the ‘switch’ was closed.
McLaren is saving its big upgrade for Silverstone so made very few changes for Valencia. The only noticeable difference was a slight tweak to the F-duct cockpit inlet which is now by the driver’s hand, rather than next to his knee as previously. This is now becoming standard placement for all the teams and probably gives easiest access to the cockpit duct.
One significant area of development since the start of the season has been brake ducts. After the banning of outboard wheel fairings teams are now trying to recreate the flow effect of the fairing with ducts and vanes inboard of the tyre.
Teams are trying to get air to exit through the wheel smoothly and to direct it away from the sidepods. This minimises wheel drag and prevents any turbulent air interfering with the sidepod undercuts. In Valencia Red Bull produced brake ducts that stretched to the front of the tyre, allowing better air control through the tyre.
After a torrid off-season where Renault CEO Carlos Ghosn came perilously close to shutting the team down before selling it to a venture capital fund, many predicted that the R30 would toil at the rear end of the grid.
However, the technical team has infused the Enstone-based outfit with new purpose and the rate has of development has been on par with McLaren and Red Bull, as proved by how quickly the team brought an exhaust blown diffuser to the car.
Renault has apparently had 22 iterations of its front wing, with close to six different endplate designs. Valencia was no different as it brought yet another revised endplate. It was based on the version raced at Turkey (the one at Montreal was a special low downforce incarnation) with a gap between the inboard cascade and the outer winglet above the footplate. This fed a different brake duct configuration no doubt to refine the airflow around the tyres.
Ever since the RB6 stretched its legs in high-speed corners at the start of the season Silverstone has been seen as Red Bull’s race to lose. Again in Valencia the car was considerably quicker than the rest of the grid in sector 3 where there were more high-speed corners.
So what’s in store for the Silverstone? Based on Valencia there isn’t a huge amount for Red Bull to be worried about. Publicly the team has said that it won’t be bringing a huge update to its home Grand Prix while McLaren has announced it will run its revised rear package.
Odds are it will be a two-horse race. Don’t forget Turkey where the MP4-25 was quick with its conventional exhaust lay out. If the exhaust-driven diffuser is worth the half a second that most in the pit lane think then McLaren has a real shot at winning – but as we’ve seen it’s a big ask to make it reliable and efficient from its very first appearance. Also expect Ferrari in particular to be close to pace as it processes the Valencia data and starts to optimise its layout.
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Image (C) Red Bull/Getty images