Mercedes: Downwashed-Exhaust Sidepod

After 13 races of the 2012 F1 season, Mercedes AMG have finally followed the trend of side exiting exhausts to blow the diffuser area. After low placed exhausts were banned for 2012, each of the top teams found methods to coerce the exhaust plume back down from the higher tailpipe. Notably Lotus and Mercedes did not follow this route, although at the Young driver test at Magny Cours, Mercedes were seen testing the McLaren style of sidepod.

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Monza: Rear End Analysis

One of the most insightful views of an F1 car is from the rear. From this angle we can easily assess the amount of rear wing, cooling, exhaust position\effect, suspension geometry and important elements of aero\diffuser design. At Monza this weekend XPB images kindly allowed us to show these images, which clearly show different elements of some of the cars running this weekend.

Ferrari


The F2012 has followed its own aero philosophy, so it looks different to many other cars from the rear. For Monza specifically we can see the low drag rear wing, much shallower than the usual rear wing and with the “V” cut outs on the trailing edge. Also for Monza Ferrari cut down the beam wing, the small amount of drag the beam wing creates is reduced by slimming the outer spans of the wing, to reduce the tip vortices.
Ferrari’s sidepods are laid out differently to other cars, most of the cooling outlet area is on the flanks of the sidepods, through the Acer ducts and in the area of the tail of the coke bottle shape. So when we look at the car from the rear, the central tail funnel cooling exit is not present. This design may hinder flow in the coke bottle area, but does leave far more airflow to reach the rear wing. Additionally several cooling vents are made in the narrow bodywork around the gearbox.
Around the diffuser Ferrari have gone further than other teams, with the aero parts around the perimeter. Teams often fit gurney flaps or flaps at the diffusers trailing edge to lower the pressure behind the diffuser and encourage more air to pass through the diffuser for more downforce. In Ferrari’s case the diffuser now sports two flaps above the diffuser, one lower down and the larger one above. This larger one is clearly visible, the lower one is mainly visible through the arched shaping. Having a two element design to this flap means it can be angled more aggressively to have a greater aero effect.


Along with trailing edge the flap the tall flap formed under the crash structure has also gained a two element design. Evident in this picture is the starter motor hole, the end of the shaft that the starter motor engages with is clearly visible through it, but although the starter motor shaft is round the resulting hole is far from circular. Teams exploit the ruling for this opening, by making the hole a blow slot to improve airflow through the middle of the diffuser. Rules dictate only one hole must be used and of a maximum surface area. In Ferrari’s case their two holes are joined by a small slit to make them effectively one hole. Most teams exploit this area in one form or another.

Lotus


In comparison to the Ferrari the Lotus is a more conventional shape with the sidepods, although the exhaust position is evidently different. As Lotus are one of the most successful teams to race this year without a downwashed exhaust solution blowing the diffuser. In the case of Lotus the exhaust blows into the duct formed by the rear wing. Cooling for the E20 is largely exited through the middle tail funnel.
For Monza this wing is very small indeed, the reduced drag helping the Renault powered Lotus reach higher top speeds on the long straights of Monza. Unlike other cars described here, the Lotus beam wing is not waisted away and also retains the taller flap exploiting free bodywork zone the middle 15cm of wing span. Also interesting to note with the tidy rear end of the Lotus is the extreme convergence of the wishbones where they meet the gearbox.


There are two distinct features on the E20 diffuser exit; the side exits and the trailing edge flap. Lotus expands the diffuser not only upwards but also outwards, such that the diffusers exit passes sideways out of the maximum 1000mm width allowed for the diffuser. This increases the diffusers expansion ratio, for more downforce, the trick being keeping the airflow attached to the aggressively shaped diffuser walls. Above the trailing edge Lotus fit a flap in-between the rear wing endplates.

McLaren


McLaren is very similar to Lotus with the conventional sidepod and cooling arrangements, of course McLaren exploit different exhaust positions, with the side exiting exhaust being downwashed to blow the side of the diffuser. The central cooling funnel has been augmented by two small outlets near the cockpit. These sit just inside the free area for sidepod bodywork, any further outboard and they would be subject to the strict rules on openings and curvature in the sidepod bodywork.


McLaren run a low incidence Monza spec wing, but this is not as slim as some other teams. Likewise their beam wing is slightly revised with the outer tips eased off to reduce drag they create. Below this the diffusers trailing edge is treated to a flap around most of its perimeter and inside the diffuser large single opening for the starter motor is apparent.

Red Bull


The unique shape of the RB8 is apparent in this image, the sidepods blend into the gearbox and rear structure freeing up airflow to the diffuser and beam wing. This is possible because so much cooling flow is ducted out of the central tail funnel. Although for the heat of Monza extra openings are created in the lower flanks of the sidepod. Drag reduction is aided by the beam wing being shorn of its central peak. Resulting in a “V” shape dip in the beam wing. Below the tail light a small electronic device with cabling emerging from it is visible. This is the back up timing transponder. The primary transponder to signal to the timing system sits under the nose of the car. Being mounted in the position, the transponder is exposed to potential damage, so teams fit covers over the device to protect it.

Timing transponder position as described in the Appendix to the FIA Technical Regulations

The exhaust position is clear in this image, the exhaust outlets despite pointing upwards, is actually diverted downwards by the downwash over the sidepods and the coanda effect of the sloping tail of the sidepods. These effects deliver the exhaust gas to the edge of the diffuser for a greater sealing effect. This sealing effect is critical as the Red Bull runs the car with a high rake angle, which is a low front ride height compared to the rear ride height. We can see the edge of the diffuser is nearly as high as the rear wheel rim; this rim is about 15cm high, so with the 5cm under floor step the rear ride height must be near 10cm.


Similar to other diffusers, the RB8 also sports an arched diffuser with a trailing edge flap. However, Red Bull curves the flap downwards over the arched sections, this results in a small flat edge on the flap above the arch. Due to the way the carbon fibre is finished around these flats, they appear like openings from some angles and have been mistaken for blown outlets. Lastly Red Bull continues to use extended rear wing end plates that form vanes behind the diffuser. While other teams have used this design, they have raised the bottom of the vanes to only sit in the wake coming over the top of the diffuser, not coming out from under it.

Williams


Aside from their waisted gearbox creating nothing but open space ahead of the beam wing, Williams follow many of the principles seen on the other cars in this article. The rear suspension geometry can be clearly seen with the near horizontal top wishbone and far less convergence in the top\bottom wishbones compared the Lotus. While the steep angle of the driveshaft’s shows just how low the differential is placed. In this picture the lack of cooling outlets on the Williams is apparent and very different to the Red bull & Lotus who run the same Renault engine.


For Monza the beam wing has been dramatically slimed down to reduce drag on the straights. While the diffuser sports a trailing edge flap and tall curved vertical gurney under the rear crash structure. Like many teams William paint the cover of the rear timing transponder in fluorescent paint to make is clear to the rear Jack man to avoid it during hurried race pitstop.

Lotus: DRS Device Analysis

For three races now, Lotus have had a prototype ‘drag reduction device’ fitted to the cars rear wing. This is a system of ducts and is not linked to the normal DRS that moves the rear wing flap. Mysteriously described by Lotus as the ‘prototype device’, most people in the paddock are still calling it DDRS (Double DRS), as although its not part of the DRS, its aim is to reduce drag on the straight for more top speed.
The Lotus device can be recognized by the cars sporting two roll hoop inlets and ductwork exiting the engine cover between the upper and lower rear wings. This was first tested In Friday free practice in Hungary and again in Germany, albeit only on Raikkonen’s car. For the Belgium GP, the system has been applied to both cars, but the wet Friday practice session means the team have elected not to run the device for Qualifying or the Race.

The device came about from the Lotus request for clarification on Mercedes DDRS, which is linked to the rear wings DRS to stall the front wing. This system was controversial as switchable drag reduction systems were effectively banned after the F-Ducts of 2010. However the rules to counter this were largely worded to reduce the stalling slots in the rear wing and the driver interaction in turning the system on or off. The Mercedes system sidestepped these rules by having the stalling slot in the front wing and the system switch by the DRS opening (an allowable moveable aero device). When in Bahrain the FIA gave clearance for other drag reduction systems, whether linked to DRS or not, Lotus announced they would take advantage of the clarification and develop their own device.
Unlike Mercedes whose system stalls the front wing to balance the aero when the DRS rear wing is used in qualifying (and the race); The Lotus system is passive and not linked to an external switch. Instead the system uses increasing airspeed to send more flow to slots under the wing to stall the airflow and reduce drag (and downforce). Having the passive system means that the Lotus device can be used to stall the wing above a certain speed on every lap, meaning the small c5-8kmh speed advantage is available on every straight and fast corner. With the system being tuned to airspeed, the wing can be designed to stall at speeds high enough to allow fast corners to be taken with the rear wing stalled. At these speeds the diffuser provides enough downforce for cornering and the rear wing in not required for aero load. Typically teams will want this stalling to occur at speeds of over 250kmh.

Construction

lOTUS_ddrs_assy

The system is formed of two roll hoop inlets feeding a fluid switch, and then two ducts tee off, one to exit nuetrally and one “L” shape duct to blow the rear wing. The inlets are clearly visible either side of, and slightly behind the roll hoop inlet, they are reminiscent of the 2010 F-Duct, although they are permanently bonded to the roll hoop structure, so even when the car is running without the device, they are still in place. These inlets form ducts that pass up and over the airbox snorkel to merge into a single duct that then passes down to the fluid switch above airbox. Indeed the pictures from Spa show that part of this duct is bonded to the airbox before a tail section of duct is bolted to it. This is where the other conenctions to the fluid switch is hidden; as we can see the fluid switch splits into two exit above the airbox, with one exit above the other. The outlets are formed by machined metal flanges, to ensure that the connection to the subsequent duct work is air tight.

lOTUS_ddrs_stalled
The neutral duct exits over the centre of the beam wing, a small Y75 winglet (monkey seat) is formed around the exit to reduce pressure at its trailing edge. Visible inside the exit of this duct is a smaller duct exiting within, so the apparently large cross section central duct may be a double walled structure housing two exit ducts.
With the neutral duct’s outlet blowing over a revised beam wing, it’s possible that the effect of the Device when not stalling the rear wing is to aid the upwashed airflow coming up under the centre of the car, to create downforce. Albeit this would be an inefficient way to create downforce, it is probably a way for the system to contribute to laptime when the upper rear wing is not stalled.
Teed off from the from the fluid switch duct is the “L” duct, this is far smaller in cross section than the central duct, and would offer a lot of resistance to airflow, most likely to encourage airflow at lower speeds to pass into the neutral ducts exit, rather than up to the rear wing
The “L” shaped duct has the 90 degree bend, not for aero reasons, but as a workaround to the zone ahead of the rear wing not being allowed to have bodywork. This was part of the 2010 F-Duct ban on bodywork (shark fins and F-Ducts) reaching the rear wing.
Other than the join of the “L” duct to the underside of rear wing’s main plane, the top rear wing and endplates appear to be the same as the non-device set up. The “L” duct meets the wing, but does not blow into it. Unlike the 2010 F-Ducts the stalling slot is not a lateral slot across the wings span, but instead four small vertical slots in the “L” duct, these blow sideways where the “L” duct meets the wings underside. Being part of the “L” duct and in the middle 15cm of wing, they are exempt from the minimum radius rule that was introduced to ban F-Ducts.
It’s clear the system has had to be compromised to fit into the post F-Duct rules, but in every sense is meets the regulations and would be hard to declare illegal without a new clarification of the rules being issued by the FIA.

How does it work?
There are two aero effects being used with this device, the method to ‘switch’ the blown effect on above certain speeds and the effect to stall the rear wing.

When Neutral, flow passes through the switch to the exit by the beam wing

When Neutral, flow passes through the switch to the exit by the beam wing

The ‘Switch’ effect, as previously described is passive, with no moving parts or external interaction. There is clearly something clever going on with the ductwork inside roll hoop inlets to the fluid switch. Its not clear if this fluid switch is somehow linked to the engines airbox and the pressures created within. But I increasingly suspect hat engine airbox pressure provides the “switch effect” to the fluid switch. Perhaps at higher speeds and with full throttle the pressure difference inside the airbox sets off the fluid switch to alter the flow from the neutral to the “L” duct.  Technically this is legal, but other teams might take a different view off this if indeed that is the case.

When the airspeed\airbox pressure change at high speed, the switch 'trips' to send the flow to the "L" duct to stall the wing

When the airspeed\airbox pressure change at high speed, the switch ‘trips’ to send the flow to the “L” duct to stall the wing

As speed or airbox pressure increases the flow passes into the fluid switch, to change the flow from neutral to stalling.  Without seeing the remaining ductwork, this is purely speculation, but the system appears to more complex than simply increasing air pressure in the duct eventually leading to stalling at higher speed.

Sideways blowing slots in the “L” duct create the stalling effect

Then the stalling effect is created by the two pairs of slots in the last section of “L” duct, these are blowing sideways across the wing, the effect sets up a delta shaped pair of vortices that turn the laminar airflow passing under the wing into turbulent flow. This would stall a large section of the wings airflow, reducing downforce and with it the drag induced by the highly loaded wing. We can see evidence of this effect from Hungary when one of the practice runs used flowviz paint the distinctive “V” shaped area of stalled flow emanating from the slots could clearly be seen (these pcitures are posted on the F1Technical.net forum). The stalled flow only appears to cover about half of the wings underside, the limitation of the vertical slots rather than a wider slot as used in 2010 being the restriction.

Summary
We’ve seen Mercedes trial a similar device on their car at Spa, with other teams rumoured to have a system ready to test subject to conditions in Spa and its benefit at Monza. The gain of the system is small, but anything that improves aero efficiency will be useful, whether to allow a higher top speed for a given downforce level, or vice versa, a gain in downforce level for a given top speed. The gain is likely to worth no more than a tenth per lap and limited in use for circuits will shorter straights and lacking fast corners.
One issue facing the FIA and other teams is that the Mercedes DDRS solution will be banned in 2013, via wording to prevent secondary use of the DRS opening. But being passive, the Lotus system does not employ this solution to stall the wing. As it stand the Lotus will be legal for 2013, but the FIA are likely to find some wording to also outlaw this method of drag reduction.

Analysis: Scoop-less brake ducts


For a few years now, teams have been extending the inner face of their brake ducts to reach forward towards the tyres forward edge. Up until recently teams placed the protruding vane as close to the tyre as possible, but latest solution offsets the vane from the tyres sidewall to allow airflow to pass in-between the tyre and vane. An inlet formed in the brake drum duct catches some of this air and redirects it towards the brakes for cooling. This year Williams went even further and removed the usual brake cooling scoop and have the brakes entirely cooled by an inlet between the tyre and vane.

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Marussia: Exhaust/Sidepod Development

Marussia have not introduced any large upgrades so far this season. In season development being just small iterations of front wing and cascade design. For Silverstone the team have produced what Team Principal John booth called “our first proper wind-tunnel generated upgrade”. This being a reference to the new Technical team’s focus away from CFD only development. Booth also identified the upgrades as consisting of “new rear wing, exhausts, floor and side pods”.

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McLaren: Adjustable Front Brake Ducts

This year McLaren have had the option to alter rear brake cooling during the pit stops in a race. As a result they can vary brake temperatures and potentially alter tyre temperature slightly. This latter effect being possible from the heat conducting from the red hot brake discs through the wheel and into the tyre. This system has been used at various races and each driver appears to have preference when to use it. This system has been especially useful this year, as the tyres dropping below their operating temperature window will see grip their levels fall dramatically. At the British GP one of the mechanical updates McLaren have brought, is the front brakes now also have this adjustability.

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F1 Jack Technology

For years the F1 quick lift jack was a simple humble tool used around the garage and at pit stops. Since pit stops have become an ever greater part of the team’s performance during the race, the jack has come in for increasing levels of development. As powered jacks are no longer allowed, teams rely on a hefty pull from a mechanic to lift the car and gravity to return the car to the ground. Improving this process has lead to most teams adopting a similar quick-release swivel jack. At first a complicated looking piece of kit, the jack is still a simple device when reduced to its component parts.

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Red Bull: Ducted Sidepod and Blown Starter Hole

Red Bull have raced two major iterations of sidepod and exhaust this season, at Valencia they introduced their third. This iteration brought the re-introduction of the bridgetunnel concept first used with their V2 sidepod. These sidepods not only sport a single tunnel, but the inlet is split to feed two different flows inside the bodywork. Initially mistaken as a double floor or double diffuser, This V3 sidepod sees a return to the duct blown starter motor hole raced in 2011.

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InDetail: Caterham CT01

Caterham have been slowly working their way clear of Marussia and HRT to close-in on Q2 sessions and the Toro Rosso’s in the race. This year the CT-01 is a clean sheet design and exploits a Renault engine with a Red Bull gearbox and KERS.

I’ve been lucky to have been given permission from Ionut Pascut to post these detail pictures taken at Monaco, to allow us to look at the detail of the 2012 Caterham.

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