Analysis: Sauber C31

Car: Sauber – Ferrari C31
Concept
On first sight the Sauber appears to be a well developed conventional package. Indeed in most areas the Sauber appears unremarkable, but this belies the wealth of small details around the car. In particular the cars aerodynamics make it quite progressive in comparison to its midfield rivals.
Also setting Sauber apart from almost every other team is its technical Structure. After the team had transitioned from BMW back to Sauber, long time technical director Willi Rampf retired and James key joined the team from Force India. However Key departed the team on the eve of the cars launch this year and its Sauber’s intention to continue without this central role. Instead the Heads of Department will work together to manage the technical side of the team. The two key people involved in this are Chief Designer Matt Morris and Head of Aero Willem Toet. This is certainly a unique arrangement, while I can imagine this working short term as the people involved are so experienced. They will be able to manage tactical decisions, but part of the technical directors role is set out the strategy and plan for the team in the years ahead. This is harder as the budget and resources need to be apportioned centrally to each department. Hopefully the team will resolve the management structure before they lose direction.

Nose

Sauber’s interpretation of the 2012 nose is unique; the team have followed the low nose and high chassis route, but like Red Bull have sought to offset the problems of keeping the airflow attached over the step in the nose. The removable nose cone has a rectangular cross section, while the front bulkhead has a slight “V” section. Where these two sections meet there is a corresponding gap behind the nose cone formed by the concave surface on the top of the chassis.

The rear facing nose slot is clearly visible here in a photo taken by Aero Student Sriram Chandra

Many observers immediately likened this to the Ferrari 2008 nose hole, but such a solution would be illegal with the post 2009 nose rules, that demand the ‘nose’ is an open section, not to mention the neutral centre front wing section would not make much use of such a nose hole.

A duct passes from below the nose to point rearwards and blow over the top of the chassis

I believe the step is a rear facing blown slot, to help the airflow attach to the flat chassis top. Inside the nose cone, there is a duct that takes high pressure from a slot underneath the nose and passes it up to the rear facing slot.

This creates a shear layer between the flow over the nose and that formed above the chassis. With this set up, the nose and chassis can be nearer horizontal and squarer in section, without the issue of flow separation; this allows the maximum amount of space beneath the raised chassis for airflow to reach the turning vanes and the underfloors lower leading edge.

This image shows the duct work inside the nose, captured by Aero Student Sriram Chandra - Copyright

In doing this Sauber have been very clever with their reading of the rules. The nose must be formed of an open section, and then the only openings in that are for the driver cooling hole, which must be for the primary purpose of cooling the driver. Sauber’s nose cone can be considered an open section; as the lower inlet slot and the upper outlet slot are both formed in the plane between the nose and chassis, thus the nose has no extra holes and is legal.
Curiously the normal driver cooling hole has not been present on the car during testing.
The nose cone itself follows Sauber 2011 pattern in that the nose is very long and features a high and wide nose tip. Flow spilling of the noses top surface is controlled by a small fin running horizontally along the nose. This aligns with the front upper wishbone. With the noses upper surface being flat, the underside slopes down quite steeply aft of the front wing mounting pylons. This set up collects a lot of air beneath the nose tip and directs it towards the under nose vane set up. These are pair of curved vanes, each split into two sections, mounted below the front suspension. Coincidentally a design path Red Bull followed in the middle of last year

Front wing
Aside from the need to meet the doubling of the wing deflection test, the front wing appears to be based around the late 2011 spec front wing.  Sauber 2011 front wing

Roll hoop

Although it may not appear so at first glance, the Sauber roll hoop is heavily undercut. The inlet snorkel is flanked by four supports; these are part of the metal inner roll hoop structure. The snorkel does not merge with the chassis until the rear pair of these supports, making over half of the roll structures length undercut. This aids airflow over the top body and to the rear wing.

Sidepods\Cooling

Traditionally Sauber have gone for quite extreme shaped sidepods, this year the undercut does not appear as large, as the inlets are now much smaller. The “P” shaped inlets being very small and mounted inboard, leaving a large between them and the sidepod vanes. The sidepods then sweep in and downwards, with their lower edges tapering out towards the floor. As is common this year cooling is managed by the radiators directing their outflow towards the cars centre and then around the aerodynamically shaped heat shields around the engine, to exit out the back of the engine cover. In Sauber’s case, there are two main exit areas. Firstly pair of tall vents at the tail of the sidepod and then a tail funnel. Although this is not a Red Bull style oval tail funnel, but instead a pair of vertical slots in the rear most section of the engine cover. Albeit an oversized Red Bull style funnel was tried in testing, presumably for the upcoming hot weather races.

Exhaust

By having point upwards at no less than ten degrees the Sauber exhaust plume should look like this

The launch specification sidepod was soon replaced with a design aimed at a more beneficial use of the exhaust gasses. The sidepods sported a top surface that sweeps down over the exhaust outlets and merges with the floor.

But the Sauber sidepod shape creates a downwash (yellow) over the exhaust outlet

This creates a downwash effect over the exhaust outlets and the merging of the exhaust outlet to the sidepod surface induces a coanda effect to make the exhaust flow downwards, despite the upward angle of the exhaust outlet.

there's a host of detail in this photo by Sriram Chandra, its clear the flow from the exhaust, aided by the fence on the floor is directed to the side of the diffuser. Note the cooling slots and the aerofoil section ahead of the tyre.

This exhaust flow is aimed at the floor between the rear wheels and the diffuser, to achieve the same but less powerful effect of the 2011 blown diffuser.

The resulting effect is the exhaust is redirected towards the floor

To aid the downwash effect created by the sidepods shape, the team have added a new vane, placed laterally across the sidepod. This turns the airflows downwards to increase the pressure over the exhaust jet, which will help it to be redirected towards the floor.

These vanes over the sidepods help create a stronger downwash effect. COPYRIGHT OctanePhotos.co.uk

This vane is similar to the pod wings that first appeared on the Jordan cars on Hungary 2004. Under the post 2009 aero rules this bodywork is legal because it sits 450mm forward of the rear of the cockpit template. Bodywork this far forward is exempt from the same restrictions the main sidepods must conform to.

Rear suspension

Note the arched beam wing mount over the gearbox. COPYRIGHT OctanePhotos.co.uk

Sauber use the Ferrari gearbox, but their aerodynamic packaging of the bodywork around the gearbox, make the gear case is more visible. It’s possible to see how Ferrari have followed Williams practice to lower the top of the case to a point below the top wishbone mounting. This wishbone mounts to pylons projecting up from the gear case. This repackaging was partly possible through the repositioning of the springs\dampers to low down on the gearbox with the use of pull rod activation. The rear of the upper wishbone mountings also forms a mounting for the beam wing; this large structure emerges from the gearbox and hooks around to mount the top of the beam wing. This looks like a duct, but it’s hard to see how flow could be effectively ducted to the top of the gearbox and then out of the beam wing. Although the rules do have a loophole that allows a small 15cm slot in the middle of the wing, which might help the airflow up out of the centre of the diffuser. But, in my opinion this isn’t a duct, as there’s no evidence of the outlet in the beam wing.

Diffuser\rear impact structure

Diffuser and cooling detail. COPYRIGHT: OctancePhotos.co.uk

As seems to be the trend this year, the rear impact structure curves in between the diffuser and beam wing, this allows a clear flow of air to both devices. In Sauber’s case the impact structure is very slim, although the tail lamp section has add-on bodywork to make it much larger and rounder than the rest of the structure.
The diffuser is a straightforward interpretation of the rules. The boat tail section of diffuser is exposed below the crash structure; this allows the downwash airflow over the sidepods to enter the specially shaped starter motor hole and also to pass upwards over the large curved flap in the centre of the diffuser. Either side of this flap, the trailing edge of the diffuser, between the rear wing mounts, sports a smaller aerofoil section flap. All of these trailing edge devices help to reduce pressure behind the diffuser, this helps draw more flow through the diffuser for more downforce. Unlike last year the current rear wing endplates do not extend behind the diffuser to form vanes effectively extending the diffuser lengthwise.

Features
In order to package the very narrow sidepod fronts the car sports a single Side impact spar mounted in the upper front volume of the sidepod. Typically teams use two spars here, one smaller leading spar and a larger spar trailing that. Impressively Sauber seem to be able to get the crash protection and the aerodynamics shape from a single stout spar.

Saubers side impact protection - Picture via Auto Motor und Sport

Having used a unique hollow spoke wheel from OZ for several seasons, this year’s wheels are a revised version, going from five spokes to seven and the wheel incorporate fixings for the rim fairings.

Powertrain
Sauber continue to use the Ferrari powertrain, this consists of the Engine, KERS and gearbox.

A small introduction to Sriram Chandra:
Sriram contacted me with pictures and information, he’d independantly gathered at the Barcelona test. Amongst these was the first explanation of how the Sauber nose duct works.
Sriram is from India, where he completed his undergraduate degree in Electronics, but he realized he really wanted to specialize in Aerodynamics and especially F1. So he has moved to Europe and has since completed a Master’s degree in Aerospace engineering from ENSAE, Toulouse, France. He did his final internship in the Future Projects Office designing aerodynamic and fuel efficient aircraft.
Until he finds a break in F1, he is working in Toulouse for Altran, focusing on the Handling qualities of the A320 aircraft.