McLaren: Suzuka upgrades and design overview

McLaren have proven to be Red Bulls nearest competitor for most of the season. While not quite having the same raw pace as the RB7, the MP4-26 is as fast on race day and arguably can be easier on its tyres. Having started with two bold concepts the “U” shapes sidepods and the mysterious “Octopus” exhaust, the design had to be compromised to ditch the complex exhaust and revert to a Red Bull style outer blown diffuser. Leaving McLaren with a large amount of space under the gearbox, that was supposed to package the exhaust. This left the car with a higher rear CofG without the benefits of the exhaust to offset it. So it’s been remarkable that McLaren have been able to morph the initial concept into a race winning, Red Bull baiting package.
The pace of development never slows, So McLaren arrived at Suzuka with a new diffuser detail and another iteration of its Silverstone short-chord rear wing.

Following a lot of the rest of the paddock , McLaren added a diffuser flap across the top edge of the diffuser exit. The flaps profile only being broken by a large gurney flap under the rear crash structure. As already discussed in the Red Bull Monza diffuser article (https://scarbsf1.wordpress.com/2011/09/22/red-bull-monza-diffuser-analysis/), this flap is an evolution of the trailing edge gurney, used to create lower pressure aft of the diffuser for more downforce. McLaren can run such a large central gurney flap as it sits in a 15cm window in the bodywork rules that allow taller bodywork. Its also beneficial as the raised rear crash structure (for the “octopus” exhaust) allows a good airflow to pass underneath it towards the gurney.

Again we saw McLaren run the short chord DRS rear wing, allowing the team to use the DRS more frequently during qualifying runs. This wing has already been detailed in the blog (https://scarbsf1.wordpress.com/2011/07/14/mclaren-new-drs-rear-wing/).

Further down the car, we can see the rear brake duct cascade. Rules allow 12cm of bodywork inboard of the rear wheels, there is no stipulation that these function as brake cooling ducts, so teams exploit this for ever larger stacks of aerofoil sections to gain downforce directly acting upon the wheels.
McLaren have also altered their exhaust system over recent races, switching from a simple oval profile tail pipes, for pipes that pinch-in to form a nozzle at their exit. Also the detailing around the floor area varies by track, with more or less floor being cutaway around the exhaust exit. This alters the amount of exhaust flow passing beneath the floor to suit differing ride heights. As one of the functions of the EBD is to act to seal the diffuser, often likened to a virtual skirt. The high energy exhaust gas, prevents other airflow entering the diffuser, thus maintaining downforce.
Its no surprise given the proximity of the brake ducts to the exhaust outlets, that the lower stack of brake duct aerofoils are heat protected. No doubt some of the exhausts energy is used to drive airflow under the ducts to create more downforce.

McLaren use a split cooling outlet set up, rather than Red Bull who tend to focus all the outlet area into the large bulged exit high up on the engine cover. McLaren’s main outlets are the exit to the sidepods coke bottle shape. With outlet area to the side of, and above the gearbox. This is aided by 3-slotted louvers on the flanks of the sidepods.

Lastly McLarens unique sidepod design is clear to understand from this angle. The “U” pods create a path for the airflow passing over the centre of the car, to reach the rear wing relative unobstructed. Typically airflow closer to the cars centreline is cleaner and has more energy. This is why designers tend to use this airflow to feed the sidepods for cooling purposes. What McLaren have done is to compromise on the cooling efficiency for greater rear wing performance. The small fin inside the channel is used to create a vortex to main the airflows energy and direction through the channel.

Analysis: McLarens Rear Wing Vapour Trails

Picture courtesy of F1Pulse

A feature of F1 for many years were the vapour trails spiralling off the rear wing tips. This phenomenon largely disappeared a few years ago, but was apparent once more on the rear wings of the McLarens at the recent damp race weekends. So what are these vapour trails and why do McLaren tend to create them more than other teams?

They are in fact more correctly termed ‘vortices’, they are created when the pressure differences are created at the wing tip. As you get high pressure above the wing, low pressure beneath and near ambient pressure to the side of the endplate. When these three flows meet, the higher pressure flow naturally moves towards the low pressure areas. This sets up a tumbling motion and a spiralling flow structure is created. As we know from the aerodynamicists use of vortices to shape and alter flow over other areas of the car, vortices are extremely high energy structures. But with them comes a lot of drag. These wing tip vortices rise upward and outward from the rear wing tips and eventually flatten out behind the car as their energy is dissipated in the free stream flow around the car.
The greater the pressure differential, the greater the vortex created, and this is generally seen better in damp conditions as the water in the air concentrates into the vortex to become visible as a vapour trail.

In years gone by, the site of vortices spiralling from wing tips was seen as a good thing, as the belief that the wing is working hard. To some extent this was correct, with a simple wing the fact that it can create visible vortices did prove the wing was highly loaded. However the drag that it created was less well understood. Since the early 2000’s teams have sought to reduce this pressure difference at the wing tip, in order to reduce drag. Several solutions have been tried to alleviate the pressure differences at the wingtip.

As F1 rear wing have such small aspect ratio’s, (width versus length), there’s little that can be done to reduce this high pressure created towards the endplate without sacrificing total downforce created by the wing. Teams have experimented with twisted wing profiles, reducing the angle of attack of the wing cross section nearer the endplate, to reduce the high pressure created above the flap. But this in turn reduces the downforce created by that section of wing. At tracks where lower downforce is required, teams will still ease the loading of the outer part of the wing, centering the pressure distribution in the middle of the wing.

The other option is to allow the whole span of the wing to be aggressively steep, but use other methods to reduce the pressure difference at the wing tip. Firstly teams such as BAR created a cut-out in the end plate ahead of the flap, this allowed some of the high pressure above the flap to bleed off outside the flap, negating the pressure difference and therefore the strength of the vortex. But this was a fairly blunt solution, so teams created the now-common louvers in the endplate.

This solution directs some of the high pressure air above the wing to the wing tip in a more elegant way. Renault, then latterly Honda and McLaren created a different approach by merging the flap into the endplate, this creates a small gap to direct the high pressure flow to the wing tip.

In the past two seasons reducing this effect has been negated somewhat by other means to reduce the rear wings drag. In 2010 the F-duct allowed the driver to reduce the rear wing downforce and therefore drag. In wet races in 2010 we saw the McLaren’s exit a turn, as speed built up the vortices would appear, then as the driver closed the cockpit control duct the rear wing stalled downforce\drag was instantly reduced. As the driver did this, the vortices also disappeared. This allowed us to see just how soon the F-duct was engaged out of turns.
With the F-duct banned and DRS allowed for 2011, teams are able to adjust the rear wing in qualifying and for overtaking in the race. Depending on the teams qualifying\race strategy, they have redesigned their rear wing to have a different flap size. A small flap, means that the DRS effect is larger, more downforce and drag are shed for more top speed. However the smaller flap means that the rear wing is limited in the downforce it can create, as the sot gap is further back on the wing and separation is likely with aggressive angles of attack. Most teams have followed a design path that errs on this level of DRS effect. As the wing tip is not loaded so highly, there are few vapour trails created.
McLaren however have been almost alone in creating a DRS wing with a large flap, this creates the opposite characteristics of a small flap wing. Less DRS effect is created, but the wing can create a larger amount of downforce when DRS is not activated. Thus their rear wing is steeper and more heavily loaded at the wing tips.

Its for this reason that McLaren tend to be the team in 2011 that create the vapour trails on damp days. McLaren do however have a small flap DRS wing in development. We can expect this to create less trails than their current if it gets to be run in the damp.

 

McLaren New DRS Rear Wing


McLaren have followed their own strategy on the DRS rear wing this season. In contrast to other teams McLaren have designed their wing for the best Non-DRS Performance, thus when deployed the DRs provides a more modest boost in speed. This Strategy appears to have been reviewed as their new rear wing tested at Silverstone shows.

Already being one of the fastest cars in a straight-line, McLaren perhaps haven’t needed to exploit DRs as much as other teams. Their current wing sports a large flap which due to its geometry flattens less when DTS is deployed. See DRS Geometry. But we have seen that McLaren can deploy their DRS less on Q-laps and despite their KERS and speed, sometimes struggle to pass other cars. SO their new wing exploits more conventional geometry with a shorter chord flap that flattens out more completed to maximise the drag reduction system.


Along with the shorter flap other aspects of the wings design have changed, the slots on the endplate have been made even more shapely and the endplate merged into the flap. These slots have been a feature on F1 rear wings for nearly ten years. They aim to take some of the high pressure air above the wing and direct it out through the endplate at the wing tip. This reduces the pressure differences that create the vortices at the wing tip, these vortices often seen in damps condition create a large amount of drag, reducing them further aids top speed.

Although the slots are so curved it’s hard to detect, but the sections between these slots on upper part of the endplate are directly joined to the flap, thus the flap is remotely mounted, the loads pass through these three narrow section of endplate. This must be quite a structural feat. This design harks back to McLaren’s 2008-209 wings (see below) which mimicked the Renault practice of merging the endplate into the flap. Again the aim of this design was to manage the pressure differences at the wing tip for reduced drag.

McLaren: European GP wing movement

UPDATE: While I am still awaiting a response from McLaren, I have had a direct reply from Charlie Whiting, FIA Formula One Race Director, to my questions. He responds “The slight anomaly you refer to has been investigated and we have told the team improvements need to be made”. I also asked if this area is subject to any specific deflection tests or construction of the wing\pylon interface “there is no stated permissible deflection of the parts you’re referring to, we do of course have a blanket restriction on any bodywork moving but, in some cases, we define limits given that no bodywork can be designed infinitely rigid”. So it seems any movement there should not be evident at the British GP.

McLaren sported a new front wing at the European GP last. Although the endplates, main plane and cascades were all new, it was the way the wing mounted to the nosecones pylons that has caught attention. From the onboard Tv footage the wing can be seen to apparently and progressively separate from its mounting. However this movement is caused, it is likely to spark questions on flexible aerodynamics, although its clear the McLaren was passed as legal by the FIA scrutineers checks.

http://www.twitvid.com/NLDQ1 Video via Ian Doreto

As McLaren place their camera pods on the front wing pylons (the two vertical plates bonded to the nose cone) and also slightly behind them, the onboard footage presents a clear view of the side of the pylon and the wing below it.

Typically the construction of this area is relatively simple. The wings central section has a metal plate bonded to it, through which run threaded studs. These studs pass up inside corresponding holes in the pylons and are then fastened down with nuts. This makes the assembly rigid, with no freedom of movement. Teams fit a spacer shim into the gap, to ensure the wing sits at the correct static ride height when fitted to the car. Almost every team follows this basic design.

However from the onboard footage, it appears that the McLaren wing is hinging on the pylons allowing the wing to rotate backwards slightly. What can be seen is a gap incrementally opening up at speed towards the rear of the interface between wing and pylon (pictured above). Then as the car slows, the gap closes back up to nothing. I have seen two onboard shots of both the cars in the race and both appear to behave in a similar way (pictured below).


This would have the effect of flattening the front wings angle of attack at speed, decreasing downforce. Depending on the way the diffuser sheds downforce at speed, this would have the effect of inducing understeer, probably for the purpose of making the car more balanced and stable for the driver at high speed. The practice of flattening front wings has been seen before, historically it’s not been unusual to see a front wing flap flatten out at speed, as the compliant flap is subject to aero load.
By achieving a better aero balance at speed, this achieves a different effect to the Red Bull, which appears to droop the front wing into an anhedral shape at speed, this creates more downforce rather than shedding it. So Red Bull are seeking more performance, rather than managing the cars balance.

McLarens wing behaving in this way could be explained in several ways, perhaps as the result of a manufacturing fault, I will ask the team if they had any such problems with the new front wing in Valencia.

I have heard previously from several ex-designers and technical directors, that even in recent seasons teams have had springs in designed into this area. Designed in such a way, that a gap opens up by creating some compliance in the wing\pylon interface. Normally by having a sprung mount, the spring being preloaded to meet any FIA test, but above the FIA load the spring is able to move the wing in a controlled manner. This is of course a far easier way to control the wing than compliance designed into the carbon fibre lay up. The rules do not specifically state that such compliant mechanisms are banned, although a similar wording has been created for the T-Tray splitter mounting. Following the precedent of the Red Bull front wing, which also appears to move at speed, it seems that any movement of the wing is allowed as long as the wing passes the FIA deflection tests. Which is in turn contradicting the FIA demand for bodywork to be rigid and having no degree of freedom in relation to the body/chassis unit.

3.15 Aerodynamic influence :
With the exception of the driver adjustable bodywork described in Article 3.18 (in addition to minimal parts solely associated with its actuation) and the ducts described in Article 11.4, any specific part of the car influencing its aerodynamic performance :
– must comply with the rules relating to bodywork ;
– must be rigidly secured to the entirely sprung part of the car (rigidly secured means not having any degree of freedom) ;
– must remain immobile in relation to the sprung part of the car.

McLaren rear end: Exhaust, cooling and suspension

 

A ScarbsF1 follower in the Melbourne pit lane sent me these exclusive pics. We can see the McLaren stripped in the garage. There’s a huge amount of detail to take in, The key details are the missing exhaust\ heat shielding, cooling ducts and suspension detail.

We can see the exhaust system is missing in the picture. However there’s a lot of grey heat shielding around the floor giving us some clue to where the flow is going. Notably at the side of the engine where the main exhausts will sit and beyond exit to the sidepod. I can also see heat shielding above the starter motor hole, which is a rounded profile further suggesting this will be subject to fast exhaust gas flow. There’s a curious bulge in the tail of the coke bottle shape. This would be next to the exhaust collector and unlikely to be a good place for sensors, so it’s a mystery why this shape is there.  So we can see potentially an exhaust route blowing out of the back of the sidepods, some of this flow passing under the gearbox to the starter motor hole.  This seems innocuous enough, as long as the gas finds its own way to these areas.  Continued rumours around the pitlane suggest bodywork is used to duct flow to these areas, which would be a contraversial solution.  Only when the car is fully built and scrutineered will we fully know what the solution is.

As already explained in this blog (https://scarbsf1.wordpress.com/2011/02/16/mclaren-roll-hoop-and-cooling-arrangement/) the roll hoop fulfils several function for engine air feed and cooling. We can see the main airbox, beneath it the KERS cooler and its exit duct wrapping around the airbox. At the rear of the airbox is the gearbox oil cooler. The oval exit duct for this cooler isn’t fitted in this picture.

Lastly the pullrod suspension can be seen, the rocker and some of the spring\damping set up is down low on the gearbox. A small detail is the shaft and rocker merging vertically from the gearbox, (beneath the silver pipe with blue connector). This might either be the heave damper or inerter, placed higher up for better access, or it might be the pre-load adjuster for the torsion bar (if torsion bars are fitted).

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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

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McLaren preseason rear end update

20110318-093655.jpg

McLarens pre season has been thwarted by unreliability and apparently aerodynamic problems. The team have run a succession of exhaust designs (at least 4 so far) and time has been spent mapping the cars aerodynamics with sensor arrays\flowviz. While the exhaust solution has yet to be finalised (I have a forthcoming post on this), The last days of the Barcelona test allowed the team to introduce some new parts around the back of the car and a new front wing.

20110318-093710.jpg

Their new rear wing sports vanes along its lower edge. These are legal as they sit in a small 5cm loophole zone in the bodywork regulations. This area has been exploited before by Red Bull on the RB5 and subsequently Toyota and Williams in 2009. Sauber also have much smaller solution on their current car. Having bodywork in this area effectively extends the diffuser sidewalls by some 30cm, which helps maximise the expansion ratio of the diffuser for more downforce. Such is the shape of the flow out of the diffuser, the bodywork needs to be vaned to allow the flow to expand. McLaren have formed four vanes into the allowable area. For the test, the rear-pointing exhausts were lined up with these vanes, thus the exhaust flow (red) will be routed by these vanes, accelerating flow inside the diffuser for even more downforce.

20110318-093727.jpg

McLarens problems also delayed the testing of their DRS (Drag Reduction System) adjustable rear wing. To feed the hydraulics to the actuator mounted inside the middle of the rear wing, the team have routed a non-structural pylon up from the gearbox to the wing. This houses the hydraulic cables & sensor wiring and does little to support the upper rear wing.

20110318-093737.jpg

With the weather warming a little during the relatively cold Spanish tests, the team were able to reduce the size of the engine hot air outlet for the last test. In the middle of this outlet is the oval gearbox oil \hydraulic cooler outlet. Leaving the rest of the outlet for general sidepod cooling



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