Mercedes AMG: Engine Build Challenge


During my visit to Mercedes AMG before Christmas, the company set us a challenge that’s been put to other more notable visitors. In the engine build area, two engines were arranged in each bay, but without the coil pack, heat shield and exhausts fitted. Our task was to fit these parts to one side of the engine, along with tightening each fastener to the correct torque setting. A dozen journalists attended the day, the challenge being made even greater as the two current Mercedes AMG drivers had also previously completed the challenge.

The coil pack is handed over and the challenge starts...

The first job was to fit the coil pack. The four-pronged carbonfibre cased unit is a press fit atop each spark plug, then the we needed to connect CAN electronics interface near the front of the airbox.

Next the heatshield goes on... (eventual challenge winner watching intently behind)

A small reflective coated carbonfibre heatshield goes over the coil pack, attached with three small bolts, one of which is smaller and requires a different torque setting.

Access to the 24 exhaust studs under the engine was surprisingly good

Then onto the exhaust system, weighing about 3kg each exhaust is hand made from thin sections of inconnel welded together. Although the 4-into-1 exhaust is one assembly, there is some play in the primary pipes joints with the collector, so fitting the four exhaust pipes to the studs on the engine requires a little fiddling. Each exhaust pipe bolts to the exhaust port with three nuts, two above and to the side of the exhaust pipe, and one centrally below.

A blur of hand movement gets each nut threaded on...

Each of these 24 nuts being tightened to the same torque setting. With the engine up on the stand and being able to kneel below the engine, getting access to each fastener was surprisingly easy, none of the exhaust pipes being particularly obstructive. I’m sure doing the same job with the engine in the car and the floor fitted is a very different story.

A quick check that each nut is torqued correctly and the job's done.

I completed the challenge in 4m 30s and I was satisfied I’d done a good job. However ex Racecar Engineering magazine editor, Charles Armstrong Wilson completed the challenge in an impressive 3m 30s! Even though one (un-named) journalist took as long a 7m 57s, as group us journalists were confident we’d done a good job. But the teams Drivers had soundly beaten us all. Nico Rosberg did the challenge in 3m 15s, while Michael Schumacher did it thee minutes dead!

The job of the F1 engine builder and mechanic is a difficult and skilled one, the skills of the F1 driver are ever impressive and I’ll stick to drawing racecars and not working on them!

Mercedes AMG: KERS development

One of Max Mosley’s lasting legacies in F1 was the introduction of his vision of a green initiative in F1. As a result KERS (Kinetic Energy Recovery System) was introduced 2009, as part of a greater package of rule changes to change the face of F1.
KERS is a system which harvests energy under braking and stores it to provide the driver with an extra power boost each lap. A simple technical summary of KERS is here (http://scarbsf1.wordpress.com/2010/10/20/kers-anatomy/ ).
During the 2009 season McLaren were applauded for running Mercedes KERS at every race and it was widely reported as the best KERS in use that year. Along with a few other journalists, I was invited along to Mercedes AMG Powertrains in Brixworth, UK to hear about KERS development since 2009. With Managing Director Thomas Fuhr and Engineering Director Andy Cowell giving a presentation on the range of work Mercedes AMG does with its F1 teams.

Mercedes AMG Powertrains reside on the site that was previously Mercedes Benz High Performance Engines (MBHPE). Now renamed to reflect the wider application of the groups knowledge, both to uses outside F1 and to areas other than engines. Powertrain is a catch all term covering; engine, transmission, electronics and of course KERS Hybrid systems.
The company have built a purpose designed Technology Centre on the site, which historically was the Ilmor engine plant and positioned just a few miles from Cosworth in Northampton. Clearly this area has a rich seam of Engine knowledge.
Formed around three buildings the entire F1 engine and KERS development is carried out on site, only specialist functions such as the casting of the crankcases is carried out off site. Additionally other Mercedes AMG work is carried out here, such as the AMG E-cell car.

KERS 2009
Mercedes AMG (MBHPE as it was known then) developed their first KERS for 2009 in house. At the time McLaren were the primary customer for the system, although Force India and at the last minute Brawn GP were also customer teams that year.  Force India had a chassis prepared to run KERS, but chose not to during the season.  Brawn had a chassis designed before their switch to Mercedes engines, so their car was not designed to accept the Mercedes KERS.

Mercedes AMG: 2009 Battery pack and water cooling radiator

In designing the system, Mercedes AMG had a specific requirement from McLaren. As the effectiveness of KERS was unknown, McLaren didn’t want to compromise the car if KERS was removed. So the system was packaged to fit into a largely conventional car. Whereas other KERS suppliers went for a battery position under the fuel tank, McLaren and Mercedes AMG placed theirs in the right hand sidepod. Low down and far forward, on the floor between the radiator and the side impact structures. The battery pack contains not only the array of individual cells, but also the pump and pipe work for its water cooling circuit. As well as the electronic interfaces for its control and monitoring. The assembly is around 7cm high, 12cm wide and 40cm long. The KBP is probably the single heaviest KERS component. In 2009 this sidepod package was acceptable as the teams were still on Bridgestone tyres and seeking an extremely forward weight distribution. Thus the 5cm higher mounting in the sidepod was offset by its forward placement.

2009 KERS and the batteries sidepod location relative to the engine

Conversely the smaller Power Control Unit (PCU) was placed in a similar location in the other sidepod, ironically the PCU is around the size and shape of road car battery. This left the monocoque uncompromised, aside from the smaller cut out for the MGU in the rear bulkhead.

The 2009 Zytek developed MGU

Then the Motor Generator Unit (MGU) is mounted to the front of the engine.  This device generates and creates the power for the KERS. Its driven from a small set of gears mounted to the front of the crankshaft.  the unit remains with the engien when the car is dismantled and is oil cooled along with the engine.

All of the components are linked both to the SECUs CAN bus and to each other by High Current Cable. The latter taking the DC current between the Batteries and MGU. With this packaging Mercedes AMG quotes the total system weight as 27kg.
Designed and developed by Mercedes AMG, but other partners were involved; the unique battery cells were supplied via A123 and the MGU was partnered with Zytek. Although the power control electronics were solely a Mercedes AMG in house development.
Through the 2009 season both McLaren drivers had a safe and reliable KERS at each race. The system was safe even after crashes and was fault free despite rain soaked races. Safety was designed in from the outset, all electrics were double insulated. Teams can also measure damage to the unit via accelerometers and insulation sensors, so any impact or incidental damage can be monitored and the car retired if the need arises. Additionally each cell in the battery has its temperature monitored. KERS batteries are sensitive to high and low temperatures, each cell needing to operate in a specific thermal window. Too low and the unit is inefficient and too hot and there’s the danger of explosion.
Perhaps the only criticism was the sidepod battery mounting, despite several incidents, this never put any one in danger, so this never proved to be an unsafe installation.

KERS 2011

2011_Mercedes_AMG_engine

For a variety of non technical reasons KERS was agreed not to be raced from 2010 until the planned 2013 rules. However this plan changed, but not before Mercedes AMG had made new strategic plans around KERS.
Mercedes AMG set out a longer term strategy to work on research for KERS in preparation for 2013, as well as working with AMG to develop the road car based E-cell technology.
(Link Mercedes AMG E-Cell chassis  )
This changed when the plans for the 2013 engine were pushed back to 2014 and KERS was agreed to be reintroduced for 2011. Thus the 2013 development plans had to rebased and deliver a refined version of the 2009 KERS for 2011. Moreover there were now three teams to be supplied with KERS. There was no Christmas for Mercedes AMG staff 2010!
As a result of the research work carried out after 2009, Mercedes AMG now solely design, develop and produce the entire KERS package, aside from the Battery cells. So now the MGU is a wholly Mercedes AMG part.

The MGU fits to the front of the engine and driven from a small set of gears

With KERS effectiveness proven in 2009, it was possible to have the cars designed around it, rather than it be an optional fitment. So the packaging was revised and the entire system integrated into just two units. The MGU remains attached to the front of the engine, still driven off a spur gear on the nose of the crankshaft. While the KBP and PCU are now integrated into a much smaller single package and fitted under the fuel tank. The unit bolts up inside a moulded recess under the monocoque, the unit being attached using four vibration mounts, and then a closing panel and the cars floor\plank are fitted under it.

The 2009 battery pack (yellow) is now integrated with the power electronics (not shown) in a single unit under the fuel tank (red).

It’s this integration of the batteries and power electronics that has has really slimmed the 2011 system down. Mercedes AMG now quote 24kg the entire KERS, much of the 3kg weight loss being down to the reduction in the heavy power cabling between these units.
Not only is the packaging better, but the systems life and efficiency is too. Round trip efficiency stands at a stated 80%, which is the amount of power reapplied to the engine via the MGU after it has been harvested and stored. Improvements in efficiency being in both the charge and discharge phases.
Battery pack life was extended to as much as 10,000km, several times the 2009 predictions that batteries would need replacing every two races (2,400km). Over this period, the cells do not tend to degrade, as the team manage the unit’s condition (‘State of Charge’ & temperature) throughout the GP weekend to maintain their operational efficiency.
The 80hp boost KERS provides, stresses the engine. This was well known back in 2009, but for 2011 along with DRS the car can be several hundred revs higher than the usual EOS (end of straight) revs. Mercedes AMG quoted 15-25% more stress for a KERS and DRS aided lap, this needing to be taken into account when the team monitor the engines duty cycle, thus deciding when to replace it. Mercedes conducted additional dyno development of the engine being kept on the rev limiter to fully understand and counter this problem. This work paid benefits; Hamilton ran many laps at Monza bouncing off the rev limiter along the main straight, while chasing Vettel.

KERS in use
Although the max 60KW (~80hp) output can be reduced from the steering wheel, its normal for the driver to use the full 80hp boost each time they engage the KERS boost. With a reliable KERS, the driver will use the full 6s boost on every lap. Media reports suggest Red Bulls iteration of the Renault KERS does not use this full 60kw. Instead something like 44kw, providing less of a boost, but allowing smaller batteries to be used. The loss in boost being offset by the overall benefit in car packaging.
The driver engages a KERS boost either via a paddle or button on the steering wheel, or by the throttle pedal. The latter idea being a 2009 BMW Sauber development, where the driver pushes the pedal beyond its usual maximum travel to engage KERS. Nick Heidfeld brought this idea to Renault in 2011 and the over-extended pedal idea has also been used for DRS too.
Once the driver is no longer traction limited out of a turn, they can engage KERS. Usually a few small 1-2s boosts out of critical turns provides the ideal lap time. It’s the driver who has to control the duration of the boost, by whichever control. As with gear shift the drivers can be uncannily accurate in their apportioning of the boost around the lap. It’s suggested that the 2009 Ferrari system apportioned the duration of the KERS boost via a GPS map, the driver simply presses the button and the electronics gives them the predetermined amount of boost. This solution came as surprise to Andy Cowell, so one wonders if this is legal or perhaps if the report is true.
From on board shots, we’ve seen the steering wheel has an array of LEDs or numerical displays to show the driver the boost remaining for that lap. The SECU will have control code written to prevent overuse of KERS around a lap.
Typically the battery will hold more charge than a laps worth of harvesting\discharge. So that any unexpected incidents do not leave the driver without their 6s of boost.
In use KERS can be used in several different ways. When lapping alone KERS typically gains 0.45s per lap, although this varies slightly by track. Along with DRS is can boost top speed by 12kmh. As explained the driver uses a pre-agreed amount of boost, decided from simulation work done at the factory before the race. So the planned strategy of KERS usage will be used in practice, qualifying and in parts of the race. However in the race the driver can use KERS tactically to gain an advantage. Drivers are able to use more a KERS boost to either overtake or defend a position. One feature of 2011 along with the Pirelli tyres being in different condition during the race, was the driver’s freedom to alter their racing line and use their grip and KERS to tackle their rivals.

KERS future
KERS continues in its current guise for another two years, then for 2014 along with all new engine regulations there will be a new format KERS. Energy recovery will be from different sources, so the overriding term for the hybrid technology on the car will simply be ERS (Energy Recovery Systems). However KERS will still exist, harvesting energy from braking, but will have a greater allowance for energy stored and reapplied. But, there will also be TERS (Thermal Energy Recovery), which a MGU harvesting energy from the turbocharger. Overall ERS will provide a third of the engines power for some 30s of the lap. No longer will the driver press a button for their KERS boost, it will be integrated in their demand for power from the throttle pedal. The electronics will be constantly managing the Powertrains energy, harvesting and applying energy based on whether the driver is on or off the throttle. In 2014 Powertrains and ERS is set to become very complicated.

Analysis: Abu Dhabi Test – 2012 Exhausts

Image via Williams F1

Last weeks Young Driver Test was the first chance for teams to try exhausts systems designed to the revised 2012 rules. Next year teams will have to place the exhaust exits in a specific region of the car, with further restrictions on the pipes shape and angle. These changes have been introduced to ban the blowing of the diffuser for aerodynamic gain. While I have detailed these rules previously (http://scarbsf1.wordpress.com/2011/10/26/2012-exhaust-position-and-blown-effects/), we can start to look at what the teams have been doing in Abu Dhabi.

Three teams brought revised exhausts, most notably Williams who ran their exhaust in all three days of the test, while Mercedes did less running with their interim set up and Ferrari tried a non legal exhaust on just one of the testing days.

Williams

IR cameras point upwards towards the wing and pods on the wing house sensors (Image via Williams F1)

Shunning any running with an Exhaust Blown Diffuser (EBD), Williams ran in Abu Dhabi with an exhaust positioned within the correct area and orientation as demanded by the 2012 rules. Their exhaust is a simple interpretation of the new rules, with the exhaust placed close to the cars centreline and as rearwards as possible. Most interestingly the exhaust is tipped up at the maximum 30-degree angle. This positioning suggests the team are trying to blow the centre of the underside of the rear wing. While I have proposed more radical solutions in my previous article, this does show that teams are to look at blown rear wing effects, as opposed to purely aero neutral exhaust positions. Exiting the exhaust pipe at great speed and temperature, the exhaust plume will hit the underside of the rear wing. This would have the effect of speeding up the airflow under the wing decreasing pressure and creating more downforce.

Williams Exhaust is low and rearward within the legality zone (yellow) and points upwards at a max of 30-degrees

However this effect is more complex than a simple jet of gas hitting the rear wing. Gordon McCabe’s Blog (http://mccabism.blogspot.com/2011/10/exhaust-blown-diffusers-in-2012.html) highlighted some research by Prof. K. Kontis & F. L. Parra from the University of Manchester on the effect of exhaust gasses on an F1 car. They found the exhaust plume passing at an angle out into the airflow created its own drag and moreover was bent backwards by the airflow at greater speeds. When this theory is applied to the Williams set up of a steeply inclined exhaust pointed towards the wing suggests some very interesting effects come into play. Firstly at lower speed the exhaust plume (jet) will be far stronger than the flow over the car. Thus this jet passes upwards through the crossflow over the car, will reach the rear wing to create more downforce.

Jet in Crossflow - low speed: unimpeded the exhaust plume blows the rear wing

At lower speeds the jet obstructing the crossflow will create drag and there will be drag induced by the greater rear wing mass flow, but being at lower speeds this drag will not be detrimental to aero performance. Then at higher speeds when the crossflow over the car has more energy the exhaust jet will start to bend backwards. Most likely moving the jet away from blowing the wings under surface. Thus the blown rear wing (BRW) effect will reduce, the car will lose some downforce and the drag induced by the blown effect will also reduce. Thus at higher speeds the car will shed drag, further boosting top speed.

Jet in Crossflow: High Speed - the faster airflow over the car bends the exhaust plume downwards away from the wing

Williams Abu Dhabi Test exhaust is not a clear sign that they will have this exact positioning for 2012, but the test will have proven the blown effect and just as importantly provided data on the heat passed over the rear wing. It was clear that the rear wing was set up with numerous sensors for vibration, heat and pressure measurement. Many of these sensors were within the rear wing flap itself, the shear number of sensors run on the wing required two aerodynamic pods mounted to the rear wing endplate to house the wiring to send the data back to the onboard data-logger. Additionally Williams ran several different kind s of thermal cameras, mounted to the rear crash structure and pointed upwards looking at the underside of the rear wing. This would not only provide actual temperature measurement, but also highlight which areas are being blown by the exhaust, somewhat like a thermal flow-viz test.

Mercedes

Another one of the teams late to the blown diffuser in 2011 and in particular blowing the outer section of floor by the rear wheel, Mercedes also tried a non-EBD set up in Abu Dhabi. According to earlier comments by Ross Brawn on autosport.com (http://www.autosport.com/news/report.php/id/96276), the Mercedes test exhaust was not a definitive 2012 set up “”The car will be testing next week with our first interpretation of what the regulation will be.”, but merely a revised exit location to remove the exhausts effect from the rear ends aerodynamics, “This is compromised because we’re fitting it around the existing car, but we’re removing the effect of the blown exhaust to see how the car will work without that.”

The set up that Mercedes tested with was similar to Williams with the exhaust outlet focussed towards the inner\rear of the regulatory box it needs to sit within. Flanked by bodywork the exhaust did not appear to be as steeply inclined as the Williams set up. Reinforcing Brawns comments about removing the blown effect.

Pictures in F1talks.pl gallery http://www.f1talks.pl/2011/11/17/ostatni-dzien-testow/

Ferrari

Like Mercedes Ferrari run an alternative exhaust on the last day of the test. However unlike these previously two teams they did not fit a 2012 spec exhaust. Instead the cars left-hand exhaust was routed dramatically sideways to exit ahead of the rear tyre. This set up would not be legal either in 2011 or 2012, but was probably a simple to completely remove the blown effect from the rear of the car. With the right hand exhaust apparently in its normal EBD set up, the team would be able to measure the difference in pressure left to right to access the effect the exhaust is having. While a large part of development for 2012 will be aimed at getting the exhaust to do some useful work elsewhere eon the car, such as a blown Rear Wing (BRW), the team salsa need to get the diffuser and rear brake ducts working without the artificially accelerated airflow blowing over the from the exhaust. As the test exhaust does not fit into the current regulations this test would be the one place where they could do this, with permission to run such an exhaust being unlikely for a Friday practice session. So although preparation is underway for their exhaust development, Ferraris plan for their 2012 remains hidden.

Ferrari: A Chamber has been added to the Exhaust system (yellow)

One area of Ferraris exhaust development that has recently been exposed is the exhaust chamber. These devices have been rumoured for many months. Most of the rumours attributed to Mercedes engined teams, although no evidence has appeared of the system on any of their three teams cars. As reported by Giorgio Piola at the Abu Dhabi race, Ferrari had this system in place for the Grand Prix and the system remained fitted for at least part of the test. What at first appears to be another exhaust outlet joined to the secondary exhaust pipe, is in fact a closed ended pipe. This picture of the exhaust removed from the car (http://www.f1talks.pl/2011/11/17/ostatni-dzien-testow/?pid=7210 via F1talks.pl\Sutton Images), shows the large extension, which acts as a pressure accumulator when the exhaust is blowing. Then when the driver is off the throttle the pressure built up in the chamber is release, which smoothes the blown diffuser effect between full and part\closed throttle.

When on the throttle the chamber is pressurised along with the exhaust system

..

When off the throttle the chamber maintains some exhaust flow

Similar systems were common on Japanese 2-stroke motorbikes in the eighties, albeit placed on the inlet side of the engine (often termed ‘boost bottles’), Fords WRC car also featured a chamber on the inlet side for similar effect.

This system works on the backpressure created within the exhaust. It’s worth noting Ferrari have recently switched to the nozzle type exhaust outlets, these being narrower in cross section to that of the main exhaust pipe. Most probably these nozzles work to increase backpressure to smooth the exhaust plume at different throttle openings. Just as interesting is the switch of the Mercedes powered teams to nozzle type exits mid season, suggesting the exhaust chamber rumours may be true. It would be logical to assume that the back pressure created within the exhaust both by the nozzles and the chamber would affect top end power. But any time loss being made up by the less senstive aerodynamics.

In some respects this exhaust chamber is similar to what appeared to be a one-way exhaust valve fitted at several GPs this year. The belief being that the exhaust valve allowed the exhaust to suck in air when the driver was off the throttle, to maintain exhaust flow to the diffuser. This being a mechanical alternative to the off throttle mappings (Hot Blown\Cold Blown), which were to be banned mid season. There appears to be a move to again enforce engine mapping restrictions for 2012, so the teams will need to find ways to smooth the exhaust plume over the bodywork. But this one-way exhaust valve will be expressly banned under the 2012 Exhaust Regs. So the exhaust chamber solution appears to be a design what will become present on the many cars exploiting blown exhaust effects in 2012.

Mercedes F-Duct Front wing

Note: Updated 24th Oct

Mercedes GP are rumoured to be running a novel front wing. This has been reported in the three major F1 magazines (AMuS, Auto sprint and Autosport). It seems the front wing uses the nose hole to blow a slot under the wing. Although this is a completely passive system (i.e. no moving parts or driver intervention), the fact that it alters aero performance at speed, has seen it dubbed as an F-duct Front Wing.

This solution was first heard of by Michael Schmidt of German magazine ‘Auto Motor und Sport’ (AMuS). Schmidt passed the tip off to Giorgio Piola who spent hours in the pitlane observing the Mercedes car and how mechanics handled the different wings. A task made additionally difficult, as he could not arouse suspicion by Mercedes and give away the fact he was researching the tip off.
He found only two noses had the nose-hole with the splitter and that these wings were only carried parallel to the ground when moved around the pitlane. The final piece of the jigsaw was when he saw a mechanic inspect the wing with his hand leading to understand the slot placement and this information allowed him to work out the system and draw it for the aforementioned magazines. Its remarkable such a tiny detail can be observed and goes to show the hard work that went into Piola exposing this innovation.

Description
AMuS article

Autosprint article

As described in the illustrations and texts, the wing assembly (including the nose) is as follows. The nose hole is used to pass air down through the front wing pylons into a slot on the underside of the wing. It appears that the slot has a wide span and is very narrow.

The nose hole feeds air through a duct into a slot under the front wing

This design is somewhat similar to Mercedes early 2010 F-duct rear wing, which was passive. The driver didn’t have a control duct, as with the McLaren system. Instead the ductwork would only blow with enough force to stall the rear wing at a certain airspeed. Tricky to design and tune, this system worked well for Mercedes last year. Its not improbably that just such a system could be made to work on the front wing.

Aiding downforce or stalling the wing?
Typically slots in the wing are for two purposes; aiding or stalling the flow over the wings surface. How the slot creates these two very different effects depends on the slots angle to the wings surface.

To aid the airflow, you need a slot blowing nearly inline with the surface and airflow. Known as Tangential flow, this flat entry angle creates a relatively wide slot when viewed externally.

To stall the airflow, you need a slot blowing at near right angles to the surface. This creates a narrow slot when viewed externally.

Looking at what you need to aid or stall the airflow also requires different placement of the slot.

To aid the airflow, you would inject the flow from the slot in an area downstream on the wings surface where the boundary has slowed and thickened. On a front wing this would arguably be somewhere on the flap towards its trailing edge.

To stall a wing, you want to upset the airflow where it’s moving quite fast, for a front wing it would be placed towards the leading edge of the wing. Last year with F-ducts we saw the stalling slots initially placed on the flap, until Renault placed theirs on the main plane for a better stalling effect.

This analysis suggests the narrow slot towards the leading of the front wing is for stalling not aiding the airflow.

Why stall the wing?
However, while we have got this far in reverse engineering the Mercedes front wing. We now need to work out what the benefit of stalling the front wing is. When stalling aerodynamics there are two possible benefits. Reducing drag for more top speed or reducing downforce.

Drag Reduction
For a front wing the drag loss wouldn’t be that beneficial on top speed. Sitting within the frontal area of the cars silhouette the front wing has very little form drag. However, induced drag from vortices produce particularly at the outboard ends is a factor, but far less than with rear wings. With teams increasingly bending their wings down at speed to gain greater downforce, they are creating most of the load towards the wing tips. By making the wing more aggressive at its outer ends, means that more vortices will be produced and sent around the front tyre. This flow structure creates drag and stalling the wing, especially near the tips would reduce this drag and boost top speed. Martin Whitmarsh was quoted in the AMuS article as suggesting a 5/8kph gain from stalling the front wing.

Drag is induced by the vortices created at the wing tips

With the front wing stalled, some of the energy it robs the airflow can pass towards the underfloor, increasing the pressure at its leading edge, forcing more flow under the floor for more downforce. With more downforce from the underbody, a smaller rear wing can be raced, which also creates less drag for more top speed.

Aero Balance
But that may not be the greater goal of stalling the front wing. Instead the aim may be managing the balance of the car through out its speed range. This would be done by the loss of downforce altering the cars Centre of Pressure.

Firstly, let’s review what the front wing does for the cars dynamics at different speeds. An f1 cars downforce is produced largely by the front wing, rear wing and the floor. With the front and rear wings being the main tuning elements. By tuning the front and rear downforce you alter the cars Centre of Pressure.
Centre of Pressure (CofP) is the balance of downforce at the front and rear axles. As such it’s analogous to being the aerodynamic equivalent of Longitudinal CofG (balance of mass between the axles). CofP is also known as termed as aero balance.
Typically the CofP position closely matches that the CofG. Starting from around 1-2% behind the CofG, then as the car gains speed the car gets lower making the front wing and diffuser work better. Fairly soon the stepped bottom\plank choke flow into part of the diffuser, this robs the diffuser of some downforce. While as the front wing gets closer to the track, it works in ground effect to create even more downforce. The combined effect of the loss of some rear downforce and gain in front downforce is that the CofP moves further forwards.

Such is the potential of the front wing and the near equal tyre sizes front to rear; an F1 car is largely limited on corner entry by the rear grip available. In low to mid speed turns the car needs a slight rear bias to the CofP, this prevents the car suffering corner entry oversteer. Where the car wants to spin as it approaches the apex. Too much front wing in these corners will make the car too pointy and hinder laptimes.
In faster turns the front wing can lead the car. The drivers turn in gentler to fast turns, which creates less lateral acceleration at the rear axle. So it’s rare for the rear to step out on turn-in to fast corners. Thus, at higher speeds you can have a CofP biased towards neutral or the front. Last year with the adjustable front flap, (rather than used for the overtaking balance adjustment for which it was designed) teams would use alter the front flap angle into a fast turn.

So typically you wouldn’t want to shed front downforce for fast turns, by stalling the front wing. Stalling the front wing will reduce front downforce and drive the CofP rearwards, robbing the driver of front axle load just when he needs it.

But, the move towards a rear biased high speed set up could be a response to other problems with the chassis. We knew the 2010 Mercedes W01 suffered understeer and Michael Schumacher didn’t like that facet of its handling, even though Nico Rosberg could cope with it. Perhaps Schumacher’s style of being aggressive on initial turn in, helps the car to rotate into turns more to gain speed through slow\medium speed corners. This tendency corner entry oversteer wasn’t present in the 2010 chassis.
The 2011 W02 is shorter and designed to rotate better, it certainly isn’t a natural understeer. We can suggest this forwards bias, as a possible reason for the car being hard on its rear tyres.
So if the W02 has a forward biased aero balance, this would move the car closer towards corner entry oversteer. We’ve also seen the mid season wing upgrade displays some flexibility, as with many teams front wings. This would have the effect of moving the front wing in yet closer proximity to the track and create even more front downforce at higher speeds.
So with the W02, as speed increases and the CofP moves forwards. Now the corner entry oversteer create a danger of high speed spins, the team need to calm the chassis down a little. So when the wing stalls, the CofP moves rearwards and gives the drivers more confidence with a little understeer. In Michaels case his naturally aggressive turn in is tolerated and as we’ve seen Rosberg can cope with understeer. So both drivers benefit. This might also save the tyres from slip in high speed turns, which could be detrimental to the tyres grip.

Front Ride Height

Another possibility with the stalling front wing is that it’s allowing an opportunity to play with the linearity of the cars ride height. In particular the proximity of the splitter to the ground at different speeds.

As has been much discussed, the front wing needs to run as low as possible to create downforce. To achieve this teams run as lower front ride height as possible. The limitation of a low front wing ride height is the front splitter grounding, this becomes an increasing problem as speed increases and the aero load builds up and compresses the front suspension. So at the ‘End of the Straight’ (EOS) at very high speed the car is at its lowest and splitter is grounding. This forces the car to have a higher ride height, to keep the plank from wearing away in the EOS condition. Thus at lower speeds the front ride height is correspondingly higher, compromising the potential of the wing.

If Mercedes stall the front wing as the car reaches top speed, hence above the speed of any corner on the track. Then when the wing stalls, the load on the front axle will suddenly decrease and the front ride height will increase. Effectively the ride height\speed map is no longer linear. Ride height will decrease linearly at lower speeds, then above the speed of the circuit’s fastest corner, the wing stalls and ride height increases.
What this allows the race engineers to do is shift the ‘ride height curve’ down the map for a lower initial (static) ride height. Knowing that the splitter will not ground in the end of straight condition. Therefore with the unstalled wing having a lower ride height, more downforce can be generated. When the wing is stalled the lack of downforce is less consequential as the car is on the straight. Plus there may still be the small boost in top speed from the lack of induced drag from the stalled wing.

One other potential of such a solution is the front wing grounding. We have seen the midseason version of the Mercedes front wing ground quite easily in some turns this year. So as with splitter ride height, endplate ride height at top speed may become the limiting factor in benefiting from the wing flexing at lower speeds. Stalling the wing on the straight will see the load on the wing decrease and the wing will naturally flex upwards. Giving the opportunity to flex more at slow speeds and have the stall prevent grounding on the straight.

Summary
Looking at the options listed above, I would definitely say the cars wing is stalling.  with little to be gained from drag reduction the stalline is most likley to create another effect on the chassis.
In comparison to the manipulation of the CofP to resolve handling problems, the speed sensitive ride height control would be a more likely purpose of the stalling wing. Perhaps more importantly this would be a universal solution, one that other teams could legally adopt in preference to flexible splitters or excessive rear ride height to achieve lower front ride heights.

Legality
So if we now accept that this theory is how the might wing work, we need to look at the legality and construction of the set up. Firstly a passive system that involves no moving parts or driver intervention is legal. Secondly the rules on the closed sections forming the front wing are much freer than those applied to the rear wing. So slots can be legally made across the side spans of the front wing. Clearly it would be legal in both of these respects, that the stalling slot can be made to blow at certain speeds.
The biggest issue is with the nose hole itself. This is covered in the rules and is allowed for the purposes of driver cooling. This being worded into the nose cone regulations for 2009 to prevent Ferrari style slotted noses. We know the nose hole is used to blow the front wing for several reasons. Firstly Mercedes do have the nose hole, but rarely use it, instead the duct moulded into the access panels atop the chassis are normally used for driver cooling. Most of the time the nose hole is sealed up with clear tape.
But one crucial picture in the AMuS gallery accompanying their article, was of the car with the nose removed, showing a black carbon fibre cover going over the front bulkhead. This would seal the nosecone, such that air entering the nose hole would not pass into the cockpit and instead pass down the wings support pylons. With this panel in place the nose hole cannot function as driver cooling and goes against the rules. Perhaps this set up using the nose hole was just at Suzuka for testing, as Teams are unable to do much full scale testing away from the circuit. It could be legally run in a Friday practice session, as teams are given some leeway to test parts which might otherwise be unacceptable to the scrutineers. As long as the parts aren’t run for qualifying, then apparently illegal parts can get limited Friday running.
So for 2012 the wing might gain its inlet from another position. At Suzuka, the use of the nose hole might have been a good way to disguise the system when it was tested.

I have to thank the many people who aided me in my countless questions on this design. Thanks for your patience.

Mercedes: Innovative Linked Rear Suspension

As we get towards the end of the season we often see teams start to get relaxed with the usual secrecy in the pitlane. This weekend in Korea was no different with several technical details being bared to the cameras for the first time.
In particular was the first picture I’ve seen of the Mercedes rear suspension, http://www.f1talks.pl/?p=11598&pid=6274  (Credit to F1Talks.pl and SuttonImages.com for the picture)
The surprise is that Mercedes appear to have adopted a hydraulic solution for managing rear roll and\or heave stiffness. Nothing is new in F1, this solution closely matches the aims of the 1995 Tyrrell Hydrolink system, which I hope to cover in detail in a future blog post. Indeed this is not even new in current F1, as several other teams already run similar and perhaps even more developed systems. But this is the first evidence I’ve had of teams interconnecting the suspension with hydraulics.
I spoke to renowned race car designer and suspension expert Andy Thorby about the use of just such a system, “I think most or all the teams are using linked hydraulic actuators on the corners.” adding “they allow you to tune the attitude change of the car under aero load, independently of corner spring rates” by altering both heave and roll stiffness.

Background
Mercedes were one of the many teams to switch to pull rod suspension for 2011, to gain the aero benefits and a lower CofG. With space at a premium at the back of an F1 car, compromises in packaging the various suspension elements need to be made. At its launch it was clear the Mercedes pull rod arrangement placed the rocker quite rearward, in comparison to other pull rod arrangements which place the rocker towards the front of the gear case. The conventional forward rocker placement, puts the heave spring and antiroll in the space at the front of the gear case, packaged around the clutch.
In Mercedes case the rocker is packaged the other side of the gear cluster, just under the gearboxes cross shaft. This leaves little room for the antiroll bar and heave spring. It does however place the rocker and torsion bars very low for the benefit of packaging, aero and CofG. Albeit these are small benefits, perhaps Mercedes choice of a short wheel base did not leave space for the suspension to be packaged around the clutch, as the gearbox length is a critical factor in wheelbase length.
So left with the lack of space to place either a mechanical heave element or a antiroll bar, it appears that Mercedes have opted to create a passive hydraulic system. This is not to be confused with any form of active suspension or the cars high pressure hydraulic systems, this system will be entirely self contained to remain within the rules on suspension design. As the system reacts only to suspension loads, it is clearly legal and there is no question of interpretation in its acceptance by the FIA.

What Mercedes have in place of a conventional anti roll bar and heave spring are hydraulics units (yellow), which probably also act as the dampers. These are connected via fluid lines (blue) to the central valve block and reservoir (red). Springing for the rear wheels is managed by the torsion bars. One end of which is conventionally located within the rocker pivot, the torsion bar then leading forward and connecting to the front of the gear case.
There is still some hardware at the top of the gearbox, which looks like it might be the mounting for an anti roll bar (ARB). But in this set up, its hard to see how the suspension rocker will act on the ARB. So Its not clear if the car started the season with a mechanical system, or whether it was designed purely with this solution in mind.
The teams early season struggle with rear tyre wear, may or may not be attributable to this system. My feeling is that other rear suspension and car layout factors have influenced the tyre problem, to a greater degree than this hydraulic solution. Although in a car that had a difficult pre-season and fundamental design problems. Getting the hydraulic suspension to work as well, may have been just another drain on resources for a team trying to recover its pace.

How it works
A cars individual wheel dampers displace hydraulic fluid as the suspension moves, creating higher pressure in one end of the damper and lower pressure in the other. To act as a damper, valves in the damper control the rate in which the fluid moves between the two chambers to create the damping effect.

In the passive hydraulic unit, the fluid is displaced not from one chamber to another, but via pipes through a valve block and into the opposite hydraulic unit. How the upper and lower chambers are interconnected left to right make the system react differently to inputs from the suspension. These being a resistance to roll or heave.

In a simplified view we can see the system working in two modes, with the fluid lines in ‘Parallel‘, where one units upper chamber connected to the opposite units upper chamber. Or, in ‘Crossover‘, where the upper chamber in one unit is connected to the lower chamber in the opposite unit.
In each mode we can see the effect of the car in roll (tilting from cornering loads) or heave (going down from aero or braking loads).

Parallel

Heave

When the car is in heave, both upper chambers create high pressure. This creates resistance between the two systems wanting to displace their fluid. This has the effect of increasing the cars heave stiffness.

Roll


When the car is rolling, the upper chamber on one side and the lower chamber on the other side create high pressure. As these chambers are now connected to the lower pressure chambers on their opposite side, the fluid displaced with little resistance. This presents no increase in the cars roll stiffness.

Crossover

Heave


When the car is in heave, both upper chambers create high pressure. As these chambers are now cross connected to the lower pressure chambers on their opposite side, the fluid is displaced with little resistance. This presents no increase in the cars heave stiffness.

Roll


When the car is rolling, the upper chamber on one side and the lower chamber on the other side create high pressure. As these chambers are cross connected to the high pressure chambers on their opposite side. This creates resistance between the two systems wanting to displace their fluid. This has the effect of increasing in the cars roll stiffness.

If a team simply want a hydraulic system to create one suspension effect, then they can rig up a basic system based on one of these patterns. However, with a valve system connecting in the centre of the pipes, then a single pair of hydraulic units and would be able to control both heave and roll stiffness. Such a system would not need external pressurisation or any control software to operate the valve block.

Development issues
However these systems are still present handicaps to development. Friction in the valve seals and the valve block, will create heat and variances in the systems response. This heat will be an enemy of the system, as it effect on the volume of fluid in the system, thus the stiffness the system provides to the suspension will alter. As a result the system will need to be a ‘constant volume’ system. Where the volume of fluid is managed depending on its rate of thermal expansion. This is probably part of the function of the small reservoir mounted to the valve block.
Equally important is the ‘installation stiffness’ of the system, that is the flexibility of any components, especially the flexible fluid lines, as this will alter the systems response.
But these and other issues related to hydraulic systems is already well understood by the teams with similar hydraulics being used both for the braking system and the high pressure electro-hydraulic control systems.

One area which presents trouble to the teams is the modelling of these systems. The design and simulation of the hydraulic element is not necessarily covered by conventional suspension and ride simulation software. I asked , Peter Harman, Technical Director of Deltatheta Ltd (http://www.deltatheta.com) about these issues. “I have advised teams on how best to simulate them“ adding “it sounds like it is a common development“. The problem is the hydraulic elements don’t fit in with conventional suspension design software. As Peter explains “Traditionally car companies have used MSC Adams for suspension modelling, and this has been adopted for ride simulation by most F1 teams, however Adams is really just a mechanical tool and doesn’t do hydraulics well“. Thus teams need to alter their approach, needing specialist add-ons and code to augment the already well established suspension development solutions.
Of course the systems will also be physically rig tested in back to back comparisons with their mechanical counterparts on the teams multi-post rigs.

Overcoming these issues with good approach to the detail design work, a hydraulic system should be able to get very close to the response of a Mechanical system. However the potential of the Hydraulic solution does offer some other benefits over purely mechanical systems.

Other possibilities
Once you have the ability to independently tailor the damping and stiffness of the heave and roll functions. The next obvious step is to control the pitch of the car. Pitch is when the car brakes or accelerates, one end of the car moves down and the other moves up. Braking creates a forward pitch, with reduced front ride height and greater rear ride height. Acceleration is the opposite situation.
As we’ve seen for the past few years controlling pitch is critical to maintaining a low front wing ride height, with out sacrificing splitter wear or excessive rear ride height (thus rear downforce).
Linking the hydraulic units\valve blocks between both front and rear axles, will allow the same resistance to pitch, as it does to heave on just one axle. This will increase the front heave stiffness, reducing forward pitch and preventing the splitter grounding excessively. This effect under braking could be further augmented with either gravitationally load sensitive valves, altering the displacement of fluid front to rear. Or similarly, a valve directly controlled by brake pressure. The former G-load system already in legal use on the individual wheel dampers and the latter solution a common fitment to motorbikes in the eighties, often termed Anti-Dive.

Summary
With Rake being ever important to the cars aero set up, such linked systems are increasingly being investigated by the teams. Indeed one team has run such a solution since mid 2009 and at least two other teams (one at each end of the grid) ran them last year.

Mercedes W02 preseason side pod & exhaust update

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After a slow start to the 2011 campaign Mercedes GP brought along the long expected changes to the W02 at the last Barcelona test. We have already covered the front wing (http://scarbsf1.wordpress.com/2011/03/11/mercedes-w02-new-front-wing-analysis/). But more crucially was the revised sidepod and exhaust package. Mercedes have gone their own way with the design of the W02, with its short wheelbase set up and the resultingly bulbous mid section. Contrary to my expectations the new sidepod\exhaust package was not as unconventional as expected. Which still leaves some questions over some design choices on the car or the permanence of the solution shown in Barcelona.

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Firstly the new sidepods are formed of a completely new moulding, common to several other teams the sidepod bodywork is one piece and is not formed by add-on sections to the monocoque. Even though the general shape appears the same as the launch format, the overhead view shows the sidepod inlets are angled inboard slightly. Although the bigger visual change is the exhaust and cooling arrangement. Uniquely the exhausts are sited halfway along the sidepods, exiting where the sidepod is nearly at its widest and starts to taper in to the coke bottle shape. Unlike Red Bull and Ferrari Mercedes have not extended the exhaust towards the diffuser, instead the exhaust blows over a long length of open floor. A small vane redirects the flow inboard of the rear wheels and into a coved section that sends the exhaust flow under the diffuser to be more effective at creating downforce. To keep the bodywork safe from its close proximity the exhaust pipes numerous grilles are moulded into the sidepod. The rearmost of these are outside the exclusion zone for cooling outlets, but the larger removable grille appears to be at odds with the bodywork rules. Perhaps the low exhaust position (below the 100mm above the reference plane) allows the grille to be regarded as the opening for the exhaust. Equally these could have been precautionary fitments for overheating (which blighted the cars earlier tests) and might removed for the Australian race.
Having the exhaust so far forward does not make the exhaust act like Renaults Front-Exit-Exhaust, nor like Red Bulls ducted set up. The exhaust gas will lose energy as its merges with the freestream airflow before it reaches the diffuser. Its exactly this energy that teams want to exploit to drive more flow through the diffuser for more downforce. So why is the set up a less efficient solution? Potentially there are several reasons, last year Mercedes struggled with overheating bodywork, unable to get enough supply of the permitted Glass Ceramic Composite (GCC) material used to protect the phenolic composite of the cars floor and bodywork. When they ran their blown floor, the heat, simply melted and warped the bodywork. Its unlikely supply of the material is still an issue, but keeping the bodywork cool and the nature of the exhausts might be the problem.

All three Mercedes teams (McLaren, Mercedes GP and Force India) all had issues with sensitivity of the car when run with EBDs in 2010. McLaren found the cars balance changed significantly on and off throttle, while Mercedes found that the exhaust plume would touch differing parts of the bodywork in different sessions and even differed between cars. This suggests that the exhaust plume was less than predictable. Where-as CFD and wind tunnel tests use a simulation of the exhaust blowing, perhaps the knowledge of what the exhaust flow is actually like is missing. Strangely this seems to be a very Mercedes engine specific problem. Being too aggressive with the exhaust blowing and too specific with the heat shielding makes the car throttle-sensitive and prone to overheating bodywork. McLaren have more problems with their EBDs in pre-season testing and Force India have yet to truly shine, with an otherwise good looking design. If this is the case, then the teams either have to lose potential downforce by having to use a less aggressive EBD solution or suffer the sensitivity problem. Its hard to be clear how easy an unpredictable exhaust plume might be to solve, its not likely to be a solution teams and engine suppliers have had to look at before.

20110318-094617.jpg

Elsewhere on the sidepods the cars pod vanes have been enlarged from the truncated versions seen in the cars early tests. Why the team would be run stunted versions of long standing designs is again part of the confusion around the W02 debut. The pod vane features an unusual outwards bulged lower section. This mimics the shape of the short launch spec vane. I presume this is mated to the sidepods undercut to feed more flow around the sidepod and over the diffuser. Along with the new undercut the car sports new serrated bargeboards and the complex shaped under nose vanes from late last year have been revised with the more common nose cone mounted vanes.

One last unsolved conundrum is the side impact protection on the sidepods. Normally teams pass the side impact tests with two pairs of crash beams, one upper pair above the sidepod inlet and a lower pair in line with the floor. Each of these pairs are formed of one larger carbon beam and a smaller one to spread the load over a wider area of the chassis. Rules demand these parts are not exposed to the exterior airflow and must be covered by bodywork. These structures are quite heavy and unavoidably raise the cars Centre of Gravity (CofG). This years car sports something appearing very much like a side impact structure passing horizontally across the middle of the sidepod inlet. This would be beneficial as the weight is that much lower down and better for a low CofG, a high CofG was a problem that afflicted the 2010 W02. Meanwhile at floor level the structure is unusually slim, which is better for aerodynamics.
But this mid placed structure appears to be in contravention of the rules as its exposed to the airflow. The FIA have started to be stricter with teams interpretation of these structures, so its hard to understand why this set up has been accepted. Possibly the structure is covered by vestigial bodywork to bypass the rules, but this detail did again promote some of my ideas that the sidepods were to be more unconventional. If allowed this year, we can expect the FIA to stamp out this set up for future years. Of course teams cannot copy this, as crash structures are homologated for the year, and cannot be changed.



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Mercedes W02 – New front wing analysis

After three tests Mercedes produced their updated front wing at Barcelona today.  Elements of this wing have been seen on the Launch specification wing, such as the extra slot made in the main plane.  The wing (main plain and flap) itself is largely similar to the launch spec wing, while the endplate and cascades have been changed.  Mercedes front wing design harks back to the Brawn BGP001 of 2009.  The BGP001 pioneered the idea of the endplate-less wing.  With the wider wings for that season sitting as far out as the width of the tyres, the contemporary endplates before that time, no longer worked to direct  flow inside the front wheel.  Brawns aerodynamicists reshaped the wing to best redirect flow around the front wheel and effectively removed the vertical endplate and replaced it with vanes. These vanes are there to both redirect airflow and to meet the minimum bodywork rules.  To aid downforce in the area inboard of the front tyres, Brawns designers added a free standing winglet, known as a cascade.  Through out 2009 and 2010 Brawn\Mercedes developed the wing, but retained the two element layout.  The new wing retains all of these features to some extent.

Mercedes W02 launch spec front wing

The free standing cascade has been retained, but this is now aided by a small additional winglet inboard of the main winglet.  The split between the two winglets is inline with the inner face of the front tyre. This is not coincidence, as the two winglets seek to create tip vortices trailing both inside and outside the front wheel to set up  the airflow structures dividing either side of the front wheel.

Detail changes to the endplate include a small cut out in the trailing edge and a complex leading edge.  The raised section of footplate (the horizontal outboard section of endplate) cleverly features a tiny vane inside.  this vane curves outwards and was a feature of Mercedes 2010 wing.

Mercedes have not gone as far as a full three element wing, across its full width.  Instead they have divided the wing into three sections across its width.  Near the endplate, the wings leading edge rises, this reduces the angle of attack and amount of load this area of the wing creates.  This is because the area in front of the tyre is not a good location for creating downforce, as the tyre sits directly downstream of the wing.  The inner span of the wing nearest the cars centreline is also much reduced in chord length and angle of attack, again downforce does not want to be created here, as the wake will upset airflow over the middle of the car.  Thus the middle of the wing span, which sits both away from the tyre and the centre of the car, is the area where most load is created on the wing.  We can see this section has both the greatest flap size and angle of attack.  To keep the airflow attached to the wing with its more aggressive geometry, Mercedes have moulded a slot into the main plane.  Higher pressure air above the wing enters the slots and helps keep the flow attached to the wings underside.  This section of wing is therefore a termed a three element (two slot) wing.  This creates downforce where its most efficient to do so, maximising downforce for the minimum drag and downstream disruption.



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