For many years the shape and position of the cars suspension elements have been an important factor in the cars aerodynamics. For 2013, almost every team have taken the same approach pioneered by Red Bull in 2012, by raising the rear lower wishbone. In doing this the teams have also oversized the wishbone’s cross section to enclose the driveshaft. It transpires that there are two gains from this practice, primarily improving flow over the diffuser and secondarily reducing the aerodynamic effect of the spinning driveshaft.

Rear Suspension layout

Conventional Rear suspension is formed of wishbones, a driveshaft and a trackrod.

On all F1 cars the rear suspension layout uses effectively the same elements; there are two wishbones, one upper and one lower. Then there’s the track rod and the driveshaft. For the purposes of this discussion the use of either pull or pushrod rear suspension is irrelevant.
To obtain the ideal rear geometry the wishbones are more conventionally placed than they are at the front of the car. Rear suspension movement is far greater at the rear of the car than at the front, thus the geometry is more important. Teams will have longer wishbones due to the narrower gearbox (compared the front of the monocoque) and often employ spherical bearings, rather than flexures due to the greater angular movement of the joints. Lastly anti-squat geometry is employed to prevent the rear sitting down under acceleration.

The lower wishbone is mounted very close to the diffuser

The wishbones are spaced apart vertical to reduce the loads on the wishbones. Thus the Rear Top Wish Bone (RTWB) is mounted near the top of the gearbox case, while the Rear Lower Wish Bone (RLWB) tends to be mounted lower. Its rear leg mounting to the cover for the gearbox cross shaft, which is positioned about 140mm above the floor of the car. In this position, the lower wishbone is very close to the upper surface of the diffuser, which is 125mm above the floor. As teams are driving ever more flow over the diffuser, to activate the trailing flap or gurney to increase the pressure difference at the diffusers trailing edge.

With the top wishbone removed, the exposed driveshaft and trackrod can be seen

Additionally the driveshaft is exposed; rules prohibit fairings specifically used for covering the driveshaft. As the driveshaft spins in the open air stream, there is an unwanted aerodynamic disruption, known as the Magnus effect.

Raised rear wishbones.

Over recent years teams have been raised the rear wishbones for aerodynamic effect, often the RTWB is raised to position itself in front of the beam wing for a slight cascade effect, but until Red Bull’s recent design the lower wishbone remained mounted quite low on the gearbox.
Red Bull’s RB8 2012 design raised the RLWB higher up inline with the driveshaft. The rear leg of the wishbone gained a far larger cross section and this structural part of the wishbone enclosed the driveshaft and rear track rod. This approach is legal as it’s the structural wishbone covering the driveshaft and not a aerodynamic fairing. In conjunction with this, the RTWB was raised as well. This raising of the upper element was required to maintain the vertical space between the wishbones to reduce the load on the elements.

Mclaren’s 2013 Raise wishbone set up, note the upper wishbone mount being inboard and above of the wheel rim

In raising the RTWB its mounting to the upright now conflicted with the space available inside the rear wheel. Thus the outer mounting had to be moved inboard and upwards to maintain a reasonable geometry. This explains why we see the uprights extending into area normally reserved for brake ducts. Rules limit the area allowed for the upright to extend inboard and upwards of the front wheel. Team such as McLaren are now also shaping these areas into aerofoil sections for further aerodynamic benefit.

With the raised wishbones, the space above the diffuser is apparent as is the top wishbone mounting being above the wheel rim

The aerodynamic benefit of the raised wishbone set up, is the RLWB is now spaced further from the diffuser and thus greater flow can reach the trailing edge of the diffuser.

With the top wishbone removed the oversized lower wishbone can be seen to enclose the driveshaft and trackrod

The method of fairing-in the driveshaft and track rod helps reduce the blockage, further aiding flow over the diffuser while I am told that the reduction in turbulence from the Magnus effect on the driveshaft is a useful but secondary benefit.

Following on from the under nose slot of two years ago and the letterbox slot of last year, this years Red bull continues to explore aero solutions around the nose box.  However with revised nose rules this year, it’s an idea from Sauber that found its way onto Newey’s drawing board.  Now letterbox opening faces backwards and is joined to the slot below the nose with a duct, to overcome aerodynamics issues presented by the nose box.

Last year I explained that Red Bulls letterbox opening was largely to overcome the issues of the stepped nose.  Sauber also had a ducted solution aimed at the same issues which also resolves some of the airflow problems under the nose.  This year’s Ferrari 2013 nose slot has also been explained here.

A short modesty fairing, removes the 2012 slot but keeps the lower slot (arrowed)

In an attempt to keep the nose box cross section as small as possible and according to Newey to save weight, Red Bull haven’t adopted a full modesty fairing, instead the stepped nose is smoothed with a small fairing.  This modesty fairing removes the letterbox opening use last year.  But the high pressure generated under the nose and increasing boundary layer remain an issue, as does keeping the airflow attached over the step.  So the car keeps last years under-nose slot, but rather than exiting into the monocoque to cool the electronics, the slot now feeds a duct that curves up in an “S” shape to exit rearwards in the scalloped top of the monocoque.

The lower slot feeds the “S” duct, as witht he Ferrari F138 lower slot, this relieves the pressure and boundary layer building up below the nose.  The duct then exits rearwards over the chassis.  As with Saubers solution last year, this helps keep the flow attached behind the stepped nose.

The “S” duct sends flow from below to over the nose

Although I’ve drawn the ductwork separately, the “S” duct is actually bonded into the nose box and isn’t removable.  No doubt we will get some pictures of the reverse face of the nose box once the season begins, to see the ductworks full details.

The V-Shape to the chassis creates the rear facing slot (arrowed)

Packaging the duct requires some repackaging around the front of the bulkhead.  The bulkhead features a rounded indentation at the bottom to help turn the air fed through the lower slot through 90-degrees and then the anti roll bar and brake fluid reservoirs are packaged into the top half of the bulkhead and flanked by carbon fibre mouldings that follow the shape of the duct.

Red Bull have always kept a slight V-shape to the cross section to the front of the monocoque, this keeps the blockage in between the wheels to a minimum and aids the lower wishbone geometry.  The resulting valley in the top of the chassis allows the flow out of the nose duct to exit.

What’s interesting about the new nose layout is that the 2012 RB8 lower slots purpose to cool the electronics and the upper slots purpose to cool the driver are no longer catered for.  This further underlines the slots purposes were for external airflow and not primarily for cooling or other internal purpose.  It’s likely that the nose will gain a conventional driver cooling hole in its tip for hot races.

In the latter part of testing at Jerez the Ferrari F138 appeared with a slot under the nose cone.  In adopting a nose slot, Ferrari have followed other teams’ recent developments in this area.  Contrary to much rumouring the slot is a relatively simple aerodynamic solution to improve the air flow under the raised section of chassis.

Nose box aero issues

The nose and the raised section of chassis it attaches to creates several issues for the aerodynamicists.  Firstly the nose box forms a blockage in between the front wheels and reduces the flow that can pass in the gap between the wheels.  Secondly the very high nose\bulkhead designs that are almost universal this year create a high pressure region under the nose\chassis that is effectively creating lift, thus working against the downforce.

Boundary layer (yellow) builds up as flow passes under the nose

Lastly the nose and chassis present some of the longest flattest sections of bodywork on the car (floor excepted) and thus a boundary layer builds up along these surfaces and can create issues with separating flow. A boundary layer is the airflow that is effectively stuck to the car; whereas the main flow is passing over the car.  As the bodywork surface continues more airflow sticks and the boundary gets thicker.  As the boundary later is not moving (relative to the car) it is providing no aerodynamic benefit and simply causes flow separation and aero issues downstream.  It appears the nose slot is a solution to resolve these issues, which one of these creates the greater problem for the cars performance, is debatable, but a small aero gain can be had by easing this issues.

Nose slots

The RB7′s slot\duct is formed by the layers of bodywork under the chassis

As long as two seasons ago, Red Bull also exploited a slot under their nose, its design was more discrete and even when the letter box slot at the top of their nose last year was introduced, the under nose slot largely went unnoticed.  Thus the RB7 had a slot created at the intersection between the chassis and nose box.  Rather than a slot being formed in the nose box shape, the slot was formed by a layer of bodywork being added below the chassis.  The small duct formed by this panel lead back to the front axle line, where it entered a small recess moulded inside the monocoque.  This recess was about the size of large paperback book and sported exit vents into the footwell area of the monocoque.  I suspect this area housed the FIA timing transponder, but probably not much else, due to its small size.  The cooling effect was probably of some benefit, although other teams do not see the need for specifically cooling the transponder.

The under nose slot reduces boundary and pressure, by venting into the cockpit

In fact the benefit of the slot was the effect on the cars external airflow.  As air passes under the nose, pressure and a boundary layer would start to build up.  The airflow would then be split by the slot\duct airflow adjacent to the noses surface, air would enter the duct, skimming off the boundary layer in the, process.  As the duct is also divergent it would reduce the air pressure under the nose at its entry, by the high pressure region venting into the slot.  The off body airflow, that is the moving stream of air a few millimetres away from the bodywork and thus clear of the boundary layer, would pass over the slot and the reattach to the under surface of the raised chassis.  This flow is moving faster and is at a lower pressure than the flow closely attached to the nose cone.  Thus this flow will have more energy to work on aero devices downstream.  By splitting the boundary layer and off-body flows at the slot, the preceding nose cone can be shallower, thus reducing the blockage it creates between the front wheels.  This simple slot effectively negates the three negative aero effects presented by the nose box.

F138 Solution

Ferrari solution is very similar to Red Bulls slot, but the slot is formed in the nose box itself.  Legally the slot might be far forward enough to be considered the driver cooling slot, if so it will be restricted in inlet size.  Or if the slot is behind the FIA defined A-A bulkhead line, then it will not be considered part of the nose box and has total freedom on inlet size.

The slot is mated to a corresponding opening in the monocoque, this appears to feed into the footwell area, I doubt that its purpose is to be ducted for aero effect elsewhere on the car (i.e. DRS) or cool anything that isn’t already inside the cockpit (i.e. KERS).  The air most likely cools the driver from the ambient heat and the heat created by the power steering rack and electronics boxes.

This is a simple and effective solution, as the front bulkhead on the monocoque needs the slot made into it; it’s not something that can be easily copied in 2013.