Red Bull RB7 – Sidepods and Cooling

When the Red Bull RB7 was rolled out, it was clear the car was a neat development of the RB6, but was not an innovative car. As with well developed cars like this, its details are well thought through, a particular case is the sidepod design. If you look at the RB7s sidepods, from the radiators back they appear to slope away to nothing. This leaves the distinctive flat floor and open area ahead of the rear wheels. This creates an obvious aero gain, but how is cooling achieved with such a tight design?

Firstly the sidepod forms the main blockage to the rear wing and diffuser. We’ve seen several approaches this year to manage the airflow around the sidepods to the rear of the car. In each case the team are trying to get the best and most direct airflow to the top of the diffuser and beam wing. As the better flow these devices receive, the more downforce they produce and the less drag is required from a larger rear wing.

Since the 2009 aero rules sidepods are extremely limited in the openings they are allowed, so most of the flow has to exit between the rear wheels. Normally sidepods send the heated air from the radiators back through the tapered rear (known as the coke bottle, due to its shape). In a simple sidepod this means the coke bottle ends with an opening and the hot air passes out and over the diffuser. However this makes the tail of the coke bottle unduly wide, which creates a blockage between the rear wheels and blocks flow over the diffuser. Red Bull discovered with the RB5 that the radiator airflow can pass up towards the centre of the car and exit above the gearbox in a bulged opening. This keeps the tail of the coke bottle nice and narrow.

With the RB7 Red Bull have taken this a step further, there is no appreciable exits in the tail of the coke bottle, so nearly all the radiator airflow ends up passing through the bulged outlet. This means the coke bottle is the slimmest and simplest of all the cars on the grid. Clearly the huge floor area and exposed beam wing show how easily airflow can reach the rear of the car. The concession Red Bull has to make for this benefit is the increased blockage in front of the rear wing. But as they are aiming for downforce from the more efficient diffuser and beam wing, the rear wings effectiveness is not such a concern. Other teams have similar low swept coke bottle shapes, but each of them still exploits some cooling exit at the back of the sidepod. Given enough testing a fully enclosed sidepod with the central bulged outlet could be copied.

McLaren Roll Hoop and Cooling Arrangement

 

McLaren have adopted ideas from other teams with the cooling set up for their MP4-26. With the return of KERS, having to package all the hardware and its cooling requirements is a challenge. McLaren want to reduce the volume within the sidepods for aero benefit, so anything the team can do to resite cooling to other areas of the car will be an advantage. Thus the team have developed a car with three inlets around the roll hoop.

Typically all the cars coolers are fitted within the sidepod and fed by air from the sidepods inlet. An F1 car needs to cool the engines water and oil, as well as the gearbox oil and the hydraulic fluid. KERS places an additional load as the MGU and batteries each need to be cooled (via oil and water). With the 2010 move to no refuelling, the fuel tank had to be increased in size. The bigger fuel tanks robbed the sidepod of space and the recent emphasis on airflow to the diffuser\rear wing also creates a demand for smaller sidepods. Over recent years teams have fed the gearbox and hydraulics coolers above the gearbox and fed via different methods from the roll hoop. Typically this is either a dedicated inlet (as per the Williams FW32, Force India VJM03) or by splitting the main inlet snorkel above the drivers head (Ferrari F60-F10).

McLarens 2011 solution is to provide a dedicated feed for each of the different cooling requirements. The engines main coolers reside within the sidepod, fed by the “L” shaped inlets. These vent partly through the rear of the sidepod and partly through the bulge in the tail of the upper engine cover. Equally the engines induction system if fed by the snorkel formed by the roll hoop, which leads into the airbox above the engine.

McLaren MP4-26 airbox inlet flow

Then McLaren feed the gearbox cooler with an inlet moulded behind the roll hoop, this leads down to the cooler behind the airbox and vents via a dedicated tube out the back of the car.

McLaren MP4-26 gearbox cooler flow

Lastly the KERS system is mounted beneath the fuel tank as one component. The entire KERS is cooled by a dedicated cooler mounted behind the roll hoop and under the airbox snorkel. This gets fed from air passing just above the drivers helmet and under the snorkel. From straight ahead the coolers aluminium matrix can be seen through the hole. Heat rejected from the KERS cooler then vents out the back of the engine cover.

McLaren MP4-26 KERS cooling flow

With all of these inlets McLarens reduced sidepod shape, has lead to some compromises. Which is has been to adversely affect the airflow approaching the centre of the top rear wing. Equally inlets create drag and McLaren have two additional inlets to account for. I doubt the cooling set up is a major differentiator between teams. But the different approaches do create some welcome variances in appearance between the cars.

Footnote:

Those little inlets inside the main ones are for cooling the electronics and hydraulics within the sidepods.  Most teams have inlets positioned just inside the main sidepod inlet.

Blade Roll Structures – Legality (Lotus & Force India)

Last year Mercedes GP surprised many with their blade style roll hoop. Rather than the rounded hoop with the engine air inlet snorkel formed in the centre, the structure was a single thin blade and the inlet split into two either side of the blade. There are several benefits to such a solution, the primary one being better airflow to the rear wing, but also weight and inlet tract length are likely secondary benefits.

Although meeting the various load and impact tests, many thought the set up was marginal on safety, primarily thought the narrow structure being likely to dig into soft surfaces such as gravel traps, reducing the effective height of the structure, with obvious consequences for the drivers head. When the new rules for 2011 were introduced, I immediately thought the regulation 15.2.4 intended to ban these structures, but the wording does not go as far as that. What the rule requires is that there is a minimum cross section for the structure. It transpires that the rules intent was not to outright ban these blades, but to ensure they had a reasonable cross section, to allay fears of a ‘digging in’ problem.

15.2.4 “The principal roll structure must have a minimum enclosed structural cross section of 10000mm², in vertical projection, across a horizontal plane 50mm below its highest point. The area thus established must not exceed 200mm in length or width and may not be less than 10000mm2 below this point.”

The rules mean when looking from above (vertical projection) a horizontal projection 50mm below the top of roll hoop must have a cross sectional area of 10000mm2. Which for a rectangular cross section, the blade would to be a minimum of 50mm wide, which isn’t too difficult to achieve. The effect of this rule is that the long very thin blade of the Mercedes is outlawed, but shorter and wider structures are still allowed.

Roll hoops have a series of load and impact tests to ensure they are strong enough to survive an accident. Historically a roll hoop has been a metal tubular fabrication, bolted\riveted to the top of the fuel tank area of the tub. As carbon fibre became the choice for monocoques teams started to simplify the roll hoops, making a point or blade structures moulded into the top of the tank. Gordon Murray’s BT53 is the first example I can recall. Over subsequent years, Arrows and Benetton have tried pointed hoops, but since the advent of normally aspirated engines the roll structure has also formed the inlet snorkel for the engine, making blades less desirable. Rules initially mandated a maximum cross section to prevent huge inlets seen in the seventies. These rules appear to have been dropped from the regulations and there have been few regulatory requirements for size and shape of the structure. Aside from the demand for a slot to pass a sling through, should the car need to be craned away. As Monocoques are now homologated, the structural shape of the roll hoop cannot be altered during the season. Mercedes achieved this last year, by homologating the blade and later adding non structural bodywork to form the inlet snorkel. This add-on section being later removed to expose the blade. The blade used to be visible inside the inlet snorkel, even at its launch. A point to note is that although the roll protection has to absorb massive loads to pass the crash tests, it is not in itself an initial part of the monocoque. The carbon fibre tub is made up of several major parts, the top and bottom of the main shape, bulkheads and cockpit surround. But the roll structure is a separate bonded on part. Laid up separately and attached at the later part of the monocoques completion.

This year Both Lotus and Force India have adopted blade style roll over protection, both adopting similar layouts albeit different structural solutions. Mike Gascoyne was clear that the benefit on aero was marginal, but he insisted the prime benefit is also CofG height. Lotus have engineered their structure from composites, this in itself is quite unique, as even conventional roll hoops are made of metal to create the slim undercut shapes to meet the impact\load tests. Albeit they are subsequently wrapped in carbon fibre, acting as both streamlining and structural reinforcement. As the blade shape is simpler, Lotus have been able to make the protection from carbon, this saving a weight and significantly removing weight from about the highest point on the car. Force India meanwhile went a similar route but their structure is a metal part, clad with carbon, although the weight comparison to the lotus is impossible, it would be fair to assume it is slightly heavier.

As Mercedes have moved away from this solution, it will remain to be seen if the blade will be a more permanent solution in F1 or just a passing fad.

Williams FW33 – Lowline gearbox

Williams said their new car would be aggressive, but at first look the FW33 seemed quite conventional.  Until the area above the gearbox is looked at.  In order to gain the maximum flow towards the lower beam wing, Williams have removed a large part of the gearbox case (as described in the below illustration shaded yellow) ,lowered the differential and reworked the rear suspension.

In fact Williams Design team have completely rethought the rear suspension and gear case. By going to a Pullrod set up, the rockers, torsion bars and dampers that normally occupy the space above the gearbox are sited low down at the side of the gearbox (see https://scarbsf1.wordpress.com/2010/10/10/red-bull-pull-rod-suspension-what-is-looks-like-how-it-benefits-aerodynamics/).  Without this hardware mounted so high up,  the area above the gearbox is just a void. So although it serves a structural purpose the stiffen the suspension mounting points.  If they can be sufficiently stiff, then this area can be removed. Thus with the Williams the air flows over the upper body and around the engine cover, the bodywork then curves in behind the engine and airbox in a sharp “V”.   There is then no structure to hinder the airflow, until the air passes around the rear wing support, which now doubles up as the top rear wishbone mounting.

To remove other elements in the air steam, Williams have removed the toe link from behind the driveshaft and replaced it with a “Z” link upper wishbone. The slim carbon fibre moulding acting as both suspension members.
Further lowering the rear end the differential is lowered as far as possible. The differential is driven from the cross shaft between the diff and the main gear cluster. The differential can effectively be at any angle pivoted around the centreline of the cross shaft. What Williams have done is to lower it as far as possible while still allowing the CV joints some consideration and the starter shaft to be accessed.  This does effectively make the gearbox slightly longer.

One fear from the outsiders point of view would be the structural efficiency of such a waisted design, especially the vertical spar, that supports the wishbones leg above the differential. Williams would either have to compromise weight or stiffness to make the design efficient. So despite the loss of a large proportion of the gear case, the gain may be offset by the penalty of added weight to make the remaining structure stiff enough.

This gearbox has been a long lead time project, Sam Michael told me the new case was planned as early as March last year and the hard worked CV joints and driveshafts are designed and made by Pankl. They have no worries about the set ups reliability, although the joints are installed with such an extreme angularity, that they would either rob power or reliability with a normal design joint.

So complex is this set up, it would be near impossible to copy during the season.  As this would require new rear crash structures which are now homologated.  Not to mention the lead time and cost involved in developing a new gearcase and driveshaft solution.

Toro Rosso STR06 – Double Floor

Scuderia Toro Rosso (STR) launched their car on the first day of the Valencia test. It’s significance has been somewhat lost amongst the fanfare of the front running teams cars and the innovation of the midfield runners. However the new STR06 deserves more attention, as it has some unique aerodynamic concepts that are drawing praise from other teams engineers. STR have been able to reduce the cooling and packaging demands placed on the sidepods. Thus with a smaller sidepod envelope, the team have revived an old concept from Ferrari, the double floor. This separates the sidepod from the flat floor of the car to improve airflow towards the rear. Pioneered by the Jean Claude Migeot while at Ferrari, the twin floor concept came about in 1992 for the teams F92A. Although not a success, mainly due to mechanical reasons, the car did exploit clever sidepods to improve flow over the diffuser.

Diffusers are limited in length and exit height, as such there is little that can be done with their internal geometry to create a greater volume for more expansion-ratio and hence more downforce. Teams realise that driving more airflow over the diffuser not only creates higher pressure above, but can also drive airflow within the diffuser with aids such as gurneys on the trailing edge of the diffuser opening. The problem is getting airflow with enough energy to pass over the diffuser. To reach the diffuser, the air has a tortuous journey. Starting with passing over the front wing, under the nose and raised chassis, then over the splitter and around the sidepods, before sweeping in between the rear wheels and through the rear suspension. We’ve seen other solutions aimed at improving this path, such as the extreme raised nose, tight coke bottle shape and recently the undercut sidepod. It is the sidepods that create the biggest obstacle to the airflow, sidepods span some 30-40cm beyond the sides of the chassis and in order to package large enough radiators they tend to need the full width across a significant height, making the sidepods effectively a rectangular block to the airflow. If you could remove some of this blockage, especially low down then the airflow can head unimpeded to the diffuser. This is exactly what Migeot did with the Ferrari F92A and Ascanelli has done with the STR06. The Toro Rosso’s sidepods curl in backwards towards the monocoque along their full length, this space is evidenced by the large area of flat floor beneath the sidepods. Air passes under the sidepods directly to the diffuser with little to sap energy from the airflow.
With any advantage comes compromises, as it is the case with the double floor. These compromises being the space available within the sidepod and centre of gravity height. Space within the sidepod is already taken up by extra wide fuel tanks and various electronic boxes, not to mention in STRs case the rounded sidepod profile which further robs space. STR must have somehow been able to package large enough radiators to meet the Ferrari engine and KERS heat rejection requirements. Indeed at the first test the team soon blocked up the sidepod openings with moulded panels to reduce the inlet size.
Centre of Gravity height is clearly compromised, as the sidepods sit some 10-15cm higher than normal, This weight needs to be offset with ballast placed low down in the car. The increased minimum weight limit this year (640kg) will help, but conversely running KERS will not help in this regard. As with many of this years concepts, the double floor can be copied. As it does not impact on the homologated monocoque, although the teams side impact crash structures may not be optimised for this sidepod shape. Just as with McLarens “L” shape sidepod, any switch to this format would be a major undertaking. Which would also only be possible if the engine can cope with the downsized radiators.

Other details on the STR06 were the ducted exhaust outlets. On the cars initial runs the exhausts exited low and along the floor, contained within box like covers and blowing through long rectangular outlets. In later tests the car was tried with conventional periscope style exhausts, protruding through the upper part of the sidepod exit.

At the rear, the diffuser in interesting, STR have created a slotted gurney flap, air passes under and over the gurney for a greater effect in drawing air from within the sidepod. Perhaps a sign of the more powerful airflow now reaching the top of the diffuser. They have also exploited the middle 15cm behind the diffuser, this area does allow extra channels to be created, so STR have added a simple “U shaped diffuser trailing the main underbody.

Virgin MVR-02 – Exhaust Positioning

As the round of 2011 car launches nears it end, Virgin were the next team to unveil their new car today. Outwardly the MVR-02 is a simple evolution of the VR01, with every detail improved upon and developments that weren’t readied for last year have been applied (namely the EBD). In order to improve from last years reliability problems the cars hydraulic system has been subject to a lot of development and simulation. However this years must-have aid, KERS, is absent from the car.
One detail of note on the car was the exhaust system. Already the buzz word at every launch, the exhaust mates the simpler diffuser to help produce downforce. In Virgins case they have extended the exhausts to blow over the diffuser. Nick Wirth did confirm a Renault style front exit was simulated, but the more conventional approach has been adopted on the launch car at least.

Slim tapered sidepods allow the low-line exhaust the leave at the exit of the coke bottle shape and extend into the boat-tail formed by the underbody step. This is similar to Saubers idea, but instead Virgins exhausts diverge and blow over the mid part of the diffuser. To aid their airflow, fairings have been added the top of the diffuser; these direct the airflow onto a specific region of the diffuser, just above the inner pair of fences. These fences sit 50cm apart and thus can reach down to the reference plane, some 5cm below the floor of the sidepods. Blowing above these fences would pull air from the underfloor and also from along the underbodies step.

However the other design aspects of the MVR-02 suggest the exhaust outlets might be shifted once the car runs. Firstly the car has a well-shaped and detailed starter hole and secondly the inner face of the wings endplates are coated with heat shielding. Neither of these areas would directly benefit from the current exhaust positioning. So either Virgin will move the inlets inwards to blow partly through the starter hole or move the exits outwards to blow along side the wing endplates. As with most teams the exhaust positions will change and may even form a circuit specific set up, some exhaust exits being used for high downforce tracks and other for lower drag tracks.

McLaren MP4-26 – “L” shaped sidepods

Airflow passes over the sidepod to the beam wing (yellow), while an undercut still directs flow the sidepod

With a lot of expectation around McLarens new car, the newly unveiled MP4-26 did indeed surprise with its sidepods. Termed “U” shaped by Technical Director Paddy Lowe, as the two “L” shaped individual inlets together form a “U”. As with other design elements on the McLaren these are almost directly opposite to what the rest of the grid is doing.

What the team have done is to shift the inlet for the radiators at the front of the sidepod as far outboard as possible, to allow a freer flow of air to the rear beam wing (the lower element between the tail lamp and the top rear wing). Typically teams place the inlet for the radiators as close inboard a possible, as this airflow is the cleanest and with the most energy. This allows the sidepods to cool efficiently and hence have smaller inlets for less drag. By placing them outboard the vertical inlet catches the turbulent airflow from the front wheel wakes. Its this messy airflow teams try to keep away from the car with the pod fins. While McLaren may have to have a slightly larger inlet to cope with the poorer airflow, the benefit is that the better airflow closer the centre of the car can now be directed at the beam wing. With the double diffuser banned, a larger proportion of rear downforce will have to come the from the rear wing.

Also by creating this shape inlet it means McLaren cannot have the deep undercuts in the sidepods, which other teams use to direct the airflow around the sidepod and over the diffuser. McLaren have still managed to keep an undercut, but this is much smaller and lower, at about the same as the bottom of the raised nose.

Packaging radiators and ducting into this shape is far more complex than a simple inlet. The radiators themselves have a stepped upper edge, the protruding section reaching up inside the higher “L” shape section of sidepod. This makes the duct that directs air from the inlet to the radiator much simpler.

It remains to be seen if this set up works better than conventional undercut sidepods for creating rear downforce. Others team would be able to recreate the McLaren “L” shaped sidepod inlets. Although it would require a significant change the radiators and bodywork, making it a major package upgrade and not a quick test. For those teams that have not already tried this idea in the past, they will certainly being giving it some simulation time over the next few weeks.