Mercedes: Drag Reduction Device

Amidst the other updates and wet weather at the Belgian Grand Prix, one small detail that I tweeted about  went largely unnoticed by the main stream press, Mercedes AMG ran a Lotus-style Drag Reduction Device. The additional ductwork emerging from the engine cover routed up to the rear wing and back to beam wing, apes the Lotus device. This device was run again in the Young Driver Test (YDT) this week and closer images show the device departs from the Lotus design in the way it blows the rear wing to stall the airflow.
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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.

Renault: European GP Alternator Failures

At the European GP in Valencia we saw the unusual circumstance of two ‘leading’ cars both retire within a few laps of each with a related fault. It was confirmed by Renault that there were alternator failures on the Renault Engines of Vettel’s Red Bull and Grosjean’s Lotus. Typically the alternator in a Modern F1 car is unseen and causes almost no issues, so this is an opportunity to look at this component and the failures in Valencia.

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Lotus E20: Overview and Development

Compared to the other leading teams the Lotus appears to be quite conservative car. However performances in testing and the in particular at the Bahrain GP show the cars looks belie its pace.

E20 Overview


Unlike its rivals there isn’t a stand out feature or innovation that’s obvious on the E20. Development from the Renault R31 with its ill fated front exit exhausts (FEE) has been iterative and logical. Unlike its forebear the E20 features a simple exhaust set up, blowing over the tail of the engine for apparently less aero effect than other team’s downwashed sidepodexhaust solutions.

Indeed the sidepods are largely conventional, the peak above and below the sidepod inlet are similar to the R31, only the vane atop the sidepod front is unusual. Within the sidepods the team have spent time with internal airflow management, the left sidepod houses a large single water radiator, the left sidepod has a split cooler set up, which appears to keep the coolers mounted clear of the floor with electronics houses below. Perhaps for the KERS power control hardware. This high mounted radiator set up reminiscent of the packaging for the FEE and also similar to McLarens 2012 cooler package.

The nose is a straightforward interpretation of the 2012 regs, with the rounded undernose profile similar to 2011. Only the presence of a slot under the nose is a distinctive feature, this smiley face shaped slot is created under the nosecone and passes through the front bulkhead into the chassis. Presumably for cooling the driver or the steering rack mounted low on the front bulkhead. One interesting point on the front of the car is the unusual hump arrangement on the top of the chassis. The usual bumps used to clear the rockers and other front suspension linkages are asymmetric. With a larger bulge on the left and a smaller one to the right. This suggests something is unusual about the suspension, Renault were known for the innovation in this area with front to rear interlinked suspension, the reactive ride height system and also running with a roll damper in place of side dampers. I suspect the bulge is to neatly incorporate the asymmetric rocker arms needed for a roll damper and hence the car runs without left and right dampers. However the front of the bulkhead is so heavily packaged with other hardware it’s impossible to see the springdamping elements inside. Externally we can see that the torsion bar mounts allow for free rotation and even feature a rotary sensor to measure their movement. This shows that the torsion bars are not grounded to the chassis instead react against each other. This negates their spring effect in roll, so all roll stiffness is provided by the anti roll bar. This approach has been common on other cars for a few years.
The anti roll bar is mounted higher in relation to the front bulkhead compared to last year, equally the link between the torsions has been moved inside the chassis, rather than the external bracing strut seen on last year’s car.


At the rear, the gearbox shows no evidence of side dampers either, although these could be packaged inside the casing so also not visible externally. Its possible Lotus have made a step in suspension design, which makes the best use of the tyres or control of the aero platform better.
Lotus are another team to adopt OZ wheels with integral fairings added to the front rims.


At the rear, a lot has been made of the laterally diverging diffuser. All teams start the diffuser far narrower than the 1000mm allowed between the rear wheels, and then diverge the diffuser (in plan view) outwards towards the limit of the allowable area. This effectively limits the expansion that can be achieved within the regulatory diffuser volume. Lotus has effectively diverged the diffuser to the 1000mm limit far earlier, with the outermost channels effectively exiting out of the side of the diffuser. This potentially gains more theoretical volume for the diffuser, but also creates a far more aggressive sidewall to the diffuser, risking flow separation and the diffuser sidewall is shorter more open and hence may leak more. Other teams have followed this path in the past, so the potential benefit is there assuming the drawbacks of the geometry can be overcome.

Developments
Pre season
As one of the cars shown at the launch was a R31 rebranded and reworked to look like the E20, initial observations were hard to make. The car that commenced testing was the E20.
The first test went outwardly successfully, but problem on the first runs of the second chassis being tested at the Barcelona test showed problems with the monocoque. Subsequent checks on the first monocoque tested in Jerez, revealed the same structural problem. The tub was failing where rear leg of the top wishbone mounts. The team skipped the test to add 1kg of reinforcement to the cars.


As soon as the car recommenced testing it started to gain revisions to the floor and front wing. This included a re-profiled splitter along with its side vanes, as well as a new iteration of the front wing. The initial wing with its “R” shaped vanes and cascade winglet were nearly parallel to the cars centreline, the updated wing changed these into a more curved outswept shape. Notably the front wing pylons also house the FIA camera pods, these being mounted between the pylons and siamesed into an aerofoil shape behind the neutral centre section, to negate the lift created by this profile.

ChinaBahrain update


A new aero package was prepared for China, but the team found testing inconclusive with the variable track conditions. The package was run again in practice for the Bahrain GP and adopted for both cars from qualifying onwards. The package included a revised rear wing, with new endplates sporting a squared-off lower section and mated to the diffuser with a larger vane. The floor was also revised, although the concept was largely carried over, so the changes are in the detail geometry and not the overall shape.
At the front the wing was altered for a completely new version. At first the wings appear similar aside from the vane treatment on the endplates, but the main planes leading edge dips downs more suddenly at the on with the neutral centre section, while the flaps join the same area without the coved section on the old wing. At the wing tips, the flaps fold down to form the endplate as is common in current F1, the upper flap gaining a small extra slot to aid flow through the steepest section of wing. With this endplate-less set up, the minimum surface area regulation is met by two vanes added to the footplate. These being somewhat reminiscent of Toro Rosso’s vaned set up. It’s hard to speculate on how the new package gains lap time or bring a difference in aero efficiency over the old set up.

The new package was worth a couple of tenths according to the team and the back to back tests in free practice proved its worth over the older aero package. As with the rest of the car it’s hard to pin point where the lap time comes from, For Lotus the conventional approach and iterative detail development has brought dividends over a more aggressive approach.
One wonders how much more potential there is within the car should adopt the sidepodexhaust or DRS solutions of its rivals. If the team can successfully introduce these performance upgrades and continue to understand the tyres requirements, then there is scope for them to remain in the hunt for strong results throughout the year.