Trends 2011 – Exhausts and Diffusers

This year the technical talk has largely been about exhausts.  How teams have adapted to the ban on double diffusers and the added restriction on Exhaust blown diffusers. Just to aid understanding going into the new season, I have explained how these solutions work and how they look from beneath.

Double Diffusers

Force India 2010 Double Deck Diffuser (DDD)

Since 2009 the regulations regarding the floor have been interpreted in a literal sense to allow the double deck diffuser (DDD). Indeed the very same rules were exploited to a lesser extent under the previous rules, but this only produced small extra channels in between the outer and middle diffuser tunnels. With the major cut in aerodynamic aids for 2009, several teams sought to find a way to gain more expansion ratio from the smaller diffusers. In essence the loophole exploited the definition of surfaces formed between the step and reference planes. Multiple surfaces allowed fully enclosed holes, which fed the upper diffuser deck that sat above the 175mm lower diffuser. This allowed diffuser to be significantly larger in order to create more downforce. Notably Brawn, Williams and Toyota launched 2009 cars with DDDs. Other teams soon followed suit in 2009 and last year every car exploited the same loophole. Over the winter the FIA acted to close the loophole, by enforcing a single continuous surface across a 90cm span under the floor. In a stroke this banned the double diffuser, there being no scope to create any openings in the floor to feed the upper deck.

Single Diffuser

Double Diffuser

 

Exhaust Blown Diffusers
Another approach to regain lost downforce was the re-invention in 2010 of the exhaust blown diffuser (EBD). This used high energy exhaust gasses to blow the diffuser, the faster throughput of flow under the floor increased downforce. Two methods of EBDs were used in 2010, one blowing over the diffuser and the second blowing inside the diffuser. This latter solution was more effective at driving flow through the diffuser and created more downforce. However this necessitated a hole made into the diffuser to allow the exhaust gas to enter, I‘ve termed this method an ‘open fronted diffuser‘.

2011: No openings allowed in the yellow 90cm zone, outside certain holes are permitted

A by product of the 2011 rules intended to ban the DDD, also stopped this open fronted diffuser solution. However the rules enforced the continuous surface only across a 90cm width of floor and the diffuser is allowed to be 100cm wide. Thus a 5cm window was allowed each side of the diffuser.

Outer Blown Diffuser – Solution

Red Bull Diffuser: Flow passes under the outer 5cm of floor into the diffuser

Red Bull and Ferrari appear to have found this loophole simultaneously. Recently Sam Michael pointed out this was probably the most efficient way to blow the diffuser under the new rules. As Red Bull appeared with this set up first, its often termed the Red Bull Blown diffuser.

What these teams have done is to open up the floor 5cm either side of the diffuser, then route the exhaust towards this opening. The exhaust gas gets collected by the coved section of floor and this directs the high energy gasses under the diffuser, to recover some of the losses from the more open diffuser allowed last year.

Front Exit Exhaust

Renault Front Exit Exhaust: Flow passes wide around the floor before entering the diffuser

Renault meanwhile turned the problem on its head. As the aim of the EBD is to increase flow under the car, they pointed their exhaust at the front of the floor. I’ve had it confirmed to me by two ex-Renault sources that the exhaust does indeed mainly flow under the floor.

The exhaust pipe outlet sits above the step plane just ahead of the leading edge of the floor. This is not simply blowing out horizontally and across the floor, but is ducted slightly to blow downwards and backwards, this is roughly in line the with the flow trailing off the “V” shape above the splitter. Along with the strong vortices set up by the splitter, vanes and bargeboards, this makes the floor appear wider than it is. The flow will go out beyond the floor and then curl back in and under the floor. Some flow will inevitably pass over the floor, but the most of the energy will be driving more flow under the floor to the diffuser.

McLarens Slit Exhaust

The slit above the floor is visible. Copyright: Liubomir Asenov

No conversation about exhausts this year, would be complete without some speculation about McLaren. Amongst the several exhaust systems run by McLaren over the pre-season tests was a “slit” exhaust. This appeared at the first Barcelona test, but did not seem to appear for the second Cataluña test. The exhaust collector could be seen to duct towards a double thickness section of floor ahead of the rear wheels. This section was also interesting for its longitudinal slot, this slot was not large enough to be the actual exhaust outlet, This might be a cooling slot, or to improve the flow from above to beneath the floor.  I beleive the Exhaust is actually below the floor.  As when the car ran the same floor with a conventional exhaust outlet, there appeared to be a removable section of floor ahead of the rear wheels. Being just outside of the 90mm opening rule, the floor ‘could’ be opened to allow an exhaust to blow through to underneath. If sculpted correctly, the exhaust could be ducted back inboard and blow towards the diffuser from under the floor. It’s possible that this could be in interpretation of a legal opening, assuming it met the maximum fillet radius rules.
I’d expect the resulting exhaust outlets to be a long wide slot, this wider outlet would be needed to meet the maximum radius rules and also reduce the back pressure from the tight curve of the exhaust outlet. As the exhaust would have a tortuous bend, to curl back under itself to direct the flow inboard, rather than out wide around the rear tyre.

Mac Slit: The exhaust might exit beneath the floor in a long narrow outlet

Spring-Less Rear Suspension – A Quiet Revolution

In the latter part of the year suggestions were that teams were discarding the rear side springs to allow very soft rear ends.   This has proved to be the case, in the past few years teams have been removing their rear torsion bars to gain greater control of suspension set up.  This revolution has been quietly spreading as many teams have gone this route.

An early sign springs were being removed was  the I-Racing game, which accurately modeled the FW31 with the Williams teams assistance, the game provided no scope for rear springs.   Equally comments made by Anthony Davidson over the Abu Dhabi Grand Prix weekend suggested that McLaren’s extreme stiff front\soft rear was due to this set up. Leading to Buttons problems locking up the inside wheel under braking. Closer investigation with technical people close to the sport prove this to be case and the practice is widespread amongst several teams, already McLaren and Williams are highlighted as adopting this practice, but Toyota and red bull are sporting this set up, by virtue of their gearbox supply this suggests that force India and Toro Rosso have the option too. Although this seems to be a relevantly recent practice as most teams first designed this into the 2009 cars, albeit it may have been tested or raced before then.

Suspension on F1 cars has the joint purpose to control the cars attitude both for aerodynamics and tyre dynamics. These often contradictory requirements have lead to compromises, largely against tyre performance and more to the benefit of aero control. Aerodynamicists want the car to run flat (or raked) with little change in roll or ride height. For mechanical grip the car needs softer attitude control. This has lead F1 cars to run quite stiff front ends and softer rear ends, both in roll and heave. A soft rear ARB creates more mechanical grip, which then in turns needs to be controlled by a stiff front anti roll bar. For aerodynamics reasons the front wing and splitter like to be flat to the track surface to gain most downforce, thus this also tends to require a stiff anti roll bar.
At the extreme end of this set up characteristic this has been exhibited most clearly in McLarens handling. The car gains traction from the soft rear anti roll bar, but the stiff front roll bar means that the rear heavy car tends to roll at the rear and this picks up the inside front wheel going into turns.
On a side point although McLaren run what has been called a stiff front axle, their apparent problem with grip over bumps going into turns is not necessarily a reflection of this set up, more that the cars aero requires tight ride height control, it is possible to run stiff anti roll bar and still have a compliance for coping with bumps.

Heave is when the car moves vertically, thus both wheels are rising or falling together
In a typical rear suspension the effect of heave is that the heave spring (blue) and each side spring (yellow) is providing stiffness. The dampers (Red) damp the motion.

Roll is when the car tilts, thus one wheel is rising and one is falling
In a typical rear suspension the effect of Roll is the ARB (orange) and the side springs provide the stiffness. Again, the Dampers (Red) damp the motion

Single wheel bump, which tends to be for riding kerbs or bumps in the track is a secondary requirement to heave and roll control, spring rates are not normally tuned for this requirement, instead the cars dampers allow freer suspension movement when the wheel suddenly rises up at a greater rate than normal, the damper has different rates for the wheel rising at different speeds, known as low speed (the cars chassis moving slowly i.e. pitch roll) high speed (bumps) and often a tertiary setting known as ‘blow off’ where the damper will provide a far lower damper rate for extreme wheel speeds such as kerbing.

Hence in both heave and roll the side springs are providing additional stiffness to the effective spring rate, thus both roll and have are coupled to the rate of the side springs. If we can do away with the side springs then both roll and have can be totally independent and controlled by their relevant springs. If you need a softer ARB rate, then the side springs are the limiting factor.

When you do away with the side springs, the heave and roll bar rates are higher in order to replace the spring rate added by the side spring. As long as each of these devices has a wide enough range of springs then there is no loss in control.

It’s noteworthy that both rear dampers are used, in the nineties we saw monoshock front ends, which utilised both a single spring and single dampers. But monoshocks only have one damper so the control of roll is undamped. With a side spring-less set up there’s two dampers, controlling roll motion. Which is an obvious improvement in vehicle control over Monoshocks.
Although there are some set backs with a side spring-less set up, some suspension designers want a non linear rate to the heave and wheel rates and sometimes different rising rate curve for each of these elements. This is achieved by the linkage (pushrod or pullrod) and the rocker geometry, going for side spring-less set up prevents having differing wheel and heave spring rising rates. In some engineers opinions, this is the removal of a needless layer of complexity.
A heave element not only supports the rear axle heave motion, but the element provides a non linear rate. Ground clearance is used up through downforce compressing the suspension as speed increases. The heave element has a range of free movement, this is taken up as ride height lowers until the then the heave spring itself (or Belleville stacks or bump rubbers) come into effect and add considerable rate to the heave motion. This prevents grounding or choking the underfloor through low ground clearance.
Equally making set up changes is both simplified and complicated. Engineers can now change either roll or heave rates independently, before changing a changing torsion bar effectively altered both. But changing a torsion bar, while not a quick task was the switch of an isolated component. Now teams will need to change the entire heave spring or ARB assembly.
An additional benefit is if a team wants to commit fully to the side spring-less set up, the packaging of the suspension becomes far easier, no longer having to package long torsion bars. This is perhaps a reason why Red Bull were able to effectively package the pullrod set up, as the pivot for the rocker is near vertical, fitting a torsion bar in this position would have been be tricky.

With the design of next years car leading towards a widespread adoption of pullrod, the option to adopt side spring-less will be attractive to aid packaging. Although the side spring-less pushrod set up will also allow dampers and rockers more freedom to be packaged at the front of the gearbox casing. Adoption at the front of the car is possible too, there is lesser need as the front roll rate is higher and the torsion bars can add to the effective rate. But simpler packaging and tuning may still be attractive for a designer.

Octobers Technical Updates

I’ll compress this months work into one post for simplicity. For updates on F1 technology have a look at the following outlets: Automoto365.com and Motorsport Magazine.

Automoto365.com – Korea & Japan

This is my major outlet, with my images and writing on race-by-race developments

Japanese GP http://bit.ly/AM365_Japan

Red Bull – Rear wing, beam wing and front wing endplates

McLaren – New F-duct

Renault – Slotted footplate

Williams – Slotted beam wing

Sauber – New diffuser

Force India – New diffuser

http://f1.automoto365.com/news/controller.php?lang=en&theme=default&month=10&seasonid=21&nextMode=ExclusiveNewsForm&news_id=42674

Korean GP http://bit.ly/AM365_korea

Red Bull – New front brake ducts

McLaren – Slotted front wing endplate

Ferrari – Ridged splitter

http://f1.automoto365.com/news/controller.php?lang=en&theme=default&month=10&seasonid=21&nextMode=ExclusiveNewsForm&news_id=42861

Motorsport Magazine – Composite Monocoques

I’ve illustrated this article on composite monocoques

http://www.motorsportmagazine.co.uk/2010/10/25/latest-issue-%E2%80%93-december-2010/

Valencia: Technical review now Automoto365.com

 

My Technical review is now online at Automoto365.com.  With the latest updates across the grid.

http://bit.ly/aGG7yC
or
http://f1.automoto365.com/news/controller.php?lang=en&theme=default&team_id=0&month=07&seasonid=21&nextMode=ExclusiveNewsForm&news_id=41314

Force India: Barcelona Rear End Update

Force India: New beam wings and enlarged cooling outlets

Continuing their current theme of innovation Force India (FI) produced a revised rear end for the VJM03 in the latter days of the Barcelona test.  This included a revised beam wing set up and enlarged cooling outlets.

Originally it appears that the FI used a very tall diffuser and a split rear beam wing. In Actual fact the car used a lower diffuser, but what appears to be the top section of diffuser was a second full width beam wing, sat ahead of the split one.  Although the rules demand ‘one closed section’ (i.e. one element) for the area containing the beam wing, there is a free zone for bodywork sat ahead of it.  Last year both Ferrari and Toyota exploited this area for a second beam wing sat in tandem ahead of the other one.

With the update there are now two full width beam wings, the rearward one no longer split but instead hooking up over the rear crash structure.  However the forward beam wing remains (yellow) and sits in a cascade with the diffuser, to create a high expansion ratio diffuser by effectively making a taller exit (light grey).  Also aiding the diffuser exit are a pair of fins attached the outside faces of the diffuser and stack of winglets affixed the rear brake ducts.

Allied to the diffuser changes the hump enclosing the rear of the sidepods around the gearbox was cut open to allow for greater cooling in the opening flyaway races. Allied to the rear end of the coke bottle shape, the exhaust outlets and a gaps made for the suspension that allow hot air to escape the sidepods (all shown dark grey).

Force india: Closer look at their splined wheel mounting

Splines on the silver axle engage with those on the wheel, to connect the pair together

Specially machined splines on the front wheel centre hole mate to the axle

A typical hub uses these pointed drive pegs to connect the wheel to the axle

Force India: Developments

Force India: The undernose hump may reduce lift and also house ballast

Not new developments, merely ones not spotted on the car at its launch.

Under the nose the car sports a hump, similar to that employed in 2009 by Renault and Williams (in early testing at least). This is used to offset the lift created by the neutral central section of the front wing (as mandated by the rules). Additionally Force India appear to have an access hatch in this hump, which suggests that there might be Ballast placed inside it, not as effective as ballast mounted in the wing by usefully a few centimeters lower than inside the main nosecone.

Force India: splines to mount the wheel to the hub speeds pitstops

Then the front wheel and hub assembly is innovative. usually the front wheel is prevented from rotating on the hub by four or so drive pins. In fitting the wheel during pitstops, the holes in one need to correspond with the drive pins in the other. Thus four drive pins means the wheel will fit the hub in four orientations each 90-degrees apart. Thus the more drive pins the less the mechanic has to rotate the wheel to fit it to the hub. This year Force india have specially made wheels with a splined detail, to match that on the hub. I can around 20 splines on the wheel suggesting the wheel will fit in one of 18 positions. making the aim of the sub three second pitstop that little bit easier.

Force India diffuser

Force India have added this unusual diffuser design. The upper deck of the double diffuser rises up to 400mm tall (yellow), the rear crash structure (green) now sits inside the diffuser, with the beam wing (blue) split to allow the diffuser to exit without obstruction.

VJM03 diffuser detail

Force India VJM03: Initial observations.

Entering their second year with McLaren\Mercedes rear end, Force India have continued to focus their efforts solely on the chassis. The results of this w`ere apparent after last years car was able to set the pace at several races. With the new car some of the more anachronistic features of the VJM02 have been altered for more conventional designs, largely noticable with the raised chassis\nose and sidepods. While these elements may even look conservative, their treatment of the diffuser is clearly a unique interpretation of the rules.

Perhaps the only team to have a lower nose than their 2009 design, the car sports a more bulbous flatter nose than that of their previous car. With a clean zero keel set up to the front of the raised chassis, the two bulges on the top of the chassis are not an attempt at a “V” nose, simply clearance for the rockers operating the springs\dampers inisde the chassis. As with last year the steering rack is mounted midway twixt the upper and lower wishbones. Below the raised chassis, the car retains the front wing and small bargeboards fitted to a “T” piece, both seen on the 09 car.

Unusually the sidepod entries are low and the top edge of the sidepod rounded, but below a typical shape of undercut is used. Present on the launch car were two serated fins mounted in place of the mirrors and the mirrors themselves joined to the pod wings. Again, the roll structure is undercut, now using four pillars to provide the rollover protection. With the space behind this used Williams-style to feed ducts leading to an oil cooler, saving space within the sidepods. As with the cars format late year, the engine cover sports small shark fin affixed to the rear wing.

Even if the full diffuser cannot be seen clearly, the launch version can be seen to be a narrow set up, making the most of the permitted bodywork height. Normally teams bend the rear impact structure to avoid obstructing the diffuser and beam wing. Force India appears to have done the opposite, by placing the structure low and passing inside the upper deck of the diffuser. Thus the diffuser can rise up above the space normally taken by the structure.

This creates a narrow, but very tall, steep diffuser. Which is a valid alternative way to gain a higher expansion of the airflow, just as making the diffuser longer or wider. In achieving this layout, the lower beam wing is now split in two with its centre missing. The gap spans the exit of the upper deck of the diffuser, a small endplate on the inner tip of the beam wing probably creates a vortex to help draw more flow through the upper deck. Without the beam wing connecting the endplates to the rear end, the rear wing relies on just a single mouting pillar for support. one curious element appears to be the placement of the rear toe link, normally this sits behind the driveshasft and sports an extended aerofoil profile. force india look like they’ve moved it to a lower position forward of the drive shaft.