Something noted on the cars over the opening race of the year was the presence of matt black aero components on the cars.  Not carbon fibre and not metal, the tell tale surface finish shows that teams are using parts manufactured in special resin produced in 3D printers via the technique of rapid prototyping. 

RP brake duct scoop as seen on a car at the 2010 Bahrain GP

For some years Stereo Lithography (SLS) has been used at the factories to make parts for wind tunnel models, casting moulds and mechanical mock ups.  SLS is the process of making a 3D part by solidifying a liquid or powdered resin, one a layer at a time.  Even though hundreds of layers are required to make a single component, the process is now  more commonly termed rapid prototyping (RP).  This creates a solid 3D part often made with with a distinctive orangey coloured resin.  By taking the data from the teams CAD systems, RP allows parts to created accurately rapidly and also to a chosen scale.  All without recourse to other machining or hand working.  While this technology is commonly seen at the factory, the results had not been seen out on track as the resins were incapable of withstanding the stresses of mechanical, aero or thermal loads.  Subsequent development of better materials has now allowed the teams to go from 3D CAD data direct to finished parts on the car.  This short cuts the existing process to make parts from patterns, moulds and finally the laying up of carbon fibre.  Reducing the lead time for a component from weeks to hours.  Additionally the ability of RP to replicate the exact shape and thickness of the part as it was designed allowed designers and production engineers to create even more complex surfaces and wall thicknesses not easily created with carbon lay ups. Details such as wall thickness tapering into sharp edges and corners.  As result a RP component can open avenues to designers not easily accessible with conventional manufacturing techniques.

Teams are increasingly using RP (rapid prototyping) materials on the race car itself.  Most commonly for the complex front brake duct scoops.  I picked up on this when Red Bull first used them in 2006.  In Bahrain 2010 several teams had the distinctive looking matt black ducts bolted to the front of their cars.  Although the duct is not a highly stressed part, it does have to meet the airflow head on and is placed relatively near the front brakes, so when the car is at rest the heat will soon pass through to the duct.  thus the component does suffer some stress and heat.  Red Bull using the Windform XT RP material (Windform.it) are able to engineer a duct  that copes with both the heat and loads seen by these components.  Windform XT is Carbon filled PA resin, which is not as strong as carbon fibre, so it does not suit all structural parts.  Previously the Red Bull used RP materials with an alumised coating to provide thermal protection, the more durable XT material alleviates the need for this secondary process, further enforcing the “rapid” element of RP.

More intricate vents have been bonded into the carbon fibre endplate

Lotus also appear to have used RP parts within their rear wing.  On the rear wing endplate the stack of louvers were not moulded into the carbon fibre, but rather made from RP material and bonded into the endplate.  This is the first evidence I’ve seen of RPM being bonded to a carbon part.  The benefit that the profiles and edges can be far sharper in RP than Carbon fibre.

http://www.3dsystems.com/appsolutions/casestudies/pdf/CS_Jordan_Motorsports.pdf

http://www.3dsystems.com/appsolutions/casestudies/pdf/CS_Minardi_Motorsports.pdf

http://www.3dsystems.com/appsolutions/casestudies/pdf/CS_RenaultF1.pdf

NOTE: Update on McLarens SnorkelRear wing here http://wp.me/sNdA9-235 

Renaults CFD shows how the flow passes around a multiple element rear wings

For an F1 car the rear wing creates around a third of the cars downforce.  But running at high speed the drag from the rear wing is tremendous.  Anything that reduces the drag of the rear wing will aid top speed.  If this can be done in a non linear way, that is; high downforcedrag at lower speeds increasing towards top speed and then less drag only at speeds where car is in a straight line and doesn’t need downforce, then laptimes will show an improvement.

A single element wing sees the flow separate (circle) at steep angles

As airflows over the surface of a wing it has a tendency to slow down and separate from the wing.  Particularly underneath the wing which runs at a lower pressure than the top surface.  This separation initially reduces efficiency by adding drag to the wing, before the airflow totally breaks up and the wing stalls.  When a wing stalls the wing loses most of its downforce and drag. 

A single element wing will then stall, as the flow breaks up under the wing

The steeper a wings angle, the greater chance of separation.  To combat this aerodynamicists need to speed up the flow near the wings surface, to do this they split the wing into separate elements, this creates a slot.  Which sends high pressure air from above the wing through the slot, which then speeds the local flow underneath the wing.  The more slots the steeper the wing can run. 

With a two element wing, flow passes through the slot to prevent seperation

In the nineties teams were unlimited in the number of elements they could use.  Slowly the rulemakers sought to reduce the wings potential for downforce and reduced the number of elements (defined as ‘closed sections’ within the rules), initially to four then three and currently two.  Modern rear wings are made up to two elements, a main plane (the forward section of wing) and a flap (which sits behind it).  Thus the wing is intended only to have a single slot and hence only one place to speed up the flow under the wing.  However the rules are typically vague, thus a small 15cm section in the middle of the wing is exempt from this rule, teams have been adding a slot in this area for several years now.  This slot is the same dimension on the front as it is on the back of the wing, so there has been no issues of legality within the rules, most team run a wing of this configuration.

Last year BMW Sauber and McLaren ran wings with the narrow 15cm opening on the front of the wing, but this inlet diverged to make a slot the full width of the rear wing (normally within the main plane).  This slot was aligned to send its airflow at an acute angle, roughly inline with the general flow over the wing.  Again this was deemed legal as the slot made the wing profile an ‘open section’ only in the middle of the wing, where as the outers spans remained a ‘closed section’ albeit one with a “U” shape.  With this design the slot could allow the entire wing to be steeper and not just the geometry in the middle 15cm of the wing.  This year Williams have joined the group running these sorts of wings.

With a blown wing, the extra inletoutlet creates a legal second slot

Again previously teams have sought to use the wing stalling to gain top speed (from the reduced drag).  By flexing the wings at higher speed, the wings move to create smaller slot gaps and this leads to the wings stalling.  The FIA has acted with both load tests and in the past few year slot gap separators to prevent this practice.  Slot gap separators are now mandated for the rear wing, and appear a plate fitted around the profile of the two wing elements to prevent them moving.

The McLaren 2010 wing uses a slot in the flap (not the main plane), this time fed by the shark fin and an opening above the drivers head.  If the teams’ protests about its legality are true, then the issue is that McLaren are using the slot to stall the wing. 

A slot in the flap could break up the airflow and allow the wing to stall

This could be possible in several ways; one could be having the slot orientated differently to the airflow over the wing, if it were at nearer right angles to the flow it could blow hard enough to disrupt the airflow enough to stall the wing.  Another solution might be that the slot blows at lower speed maintaining a clean airflow over the wing, then at higher speed the slot chokes with the greater airflow trying to pass through it, the slot no longer blowing stalls the wing.

These approaches would have to be tuned to have no effect at speeds lower than the top speed on the straight, thus the wing would provide normal downforce until near top speed.  Then near top speed the flow through the slot would start disrupt the wings flow and stall the wing.  The difficulty in getting this tuning to work is what’s given rise to the rumour about the driver operated snorkel duct on the McLaren.

Mercedes: the beam wing is exposed and sits above the crash structure, allied to a small supplementary wingletRenault: the Beam wing is mounted to the central pylon, that also supports the top rear wing

An increasingly common feature this year has been the choice of an exposed beam wing design. The beam wing is the single element wing that sits below the rear top wing. Normally this wing runs the full span of the allowable 800mm rear wing width, but often is split into two by the rear crash structure. In the rules the location of both the crash structure and beam wing are relatively fixed, the wing needs to sit between 300-400mm high and only sport one element, while the crash structure needs to be no higher than 400mm. Along the centre line of the car clearly they vie for the same space.

The beam wing acts both as a wing in its own right, as a device that turns the airflow upwards improving the scavenging from the diffuser and the flow under the top rear wing. Recently, the increasing use of pylons to take the loads from the top rear wing into the chassis (via the top of the gearbox case) means that the structural demands of the beam wing are reduced, as it no longer has transfer the loads from the top Rear wing via the endplates into the chassis. If you ever get to pick up a structural beam wing you;d be surprised at just how heavy it is. Certainly not the piece of feather weight F1 bodywork you’d expect.

But since 2009 when Toyota realised that the beam wing needn’t be compromised by the crash structure and shaped the structure to pass under the wing, allowing its more potent underside to be fully exposed to the airflow. In some respects Red bull followed this philosophy too, albeit the beam wing mounting was still a relatively obstructive section mounded into the crash structure. This year several teams have chosen to shape the crash structure to expose the beam wing. Although this does necessitate a more complicated shape which in turn affects the structures efficiency, in terms of meeting the crash test and adding extra weight.

In Renaults case the wing is supported by the same central strut that supports the rear wing, other teams use smaller mounts beneath the beam wing. Lastly Virgin took a cue from their Acura LMP car and used a swan neck mount that despite the tortuous load path, does provide less obstruction to the underside of the wing.

Wheelbase is a factor of: seating position, fuel tank, engine and gearbox length

A huge amount of fan attention has been focussed on wheelbase this year.  Even in recent years some teams’ preference for longer wheelbases has driven a lot of assumptions.  A typical F1 car is over three metres long; this length is largely dictated by the need to package the driver, fuel tank, engine and gearbox along the centreline of the car.  With engines being fairly fixed in length, fuel tanks needing to be sight centrally for weight distribution reasons, it settles down to fuel tank length, gearbox length and how far back from the front axle line the driver sits to determine the wheelbase.

Wheelbase length is often seen primarily as a factor in how the car suits fast or slow turns.  The common assumption that shorter cars go better around slow tight bends and longer cars go best in longer fast turns.  This proves to be largely false, the difference in the longest to shortest cars is only a few percent, certainly not enough to substantially change the cars ability to corner around the hairpin at Monaco.  Indeed Monaco proves to be no litmus test for wheelbases as longer cars have frequently won there.  I am told that wheelbase changes by a few percent, affect lap times in just thousandths of a second.

If wheelbase is not a factor in agility, then why is it so important and closely guarded? There’s two main reasons: weight distribution and aerodynamics.  As the components that decide the wheelbase are also the major masses in the car (driver ~65kg, engine 100Kg, gearbox ~40kg) by placing these strategically along the wheelbase a more forward or rearward weight bias can be achieved.  This is critical as it decides how well the tyres are worked.  Tyre are the biggest area for potential lap time improvement, even more so than aero, however far harder to achieve.  Teams have run up to 49% weight over the front axle in 2009, the cars layout will have a major impact on how much weight gets placed in the right place, without too much ballast being needed to meet the desired distribution.  For a more forwards weight bias you want the major masses moved forward, thus the drivers feet closer (but not allowed in front of) the front axle, longer gearboxes to space the heavy engine and gearbox from the rear axle.  In moving these masses sometimes wheelbases have to be altered to get the components in the right place.

Then there’s aerodynamics, probably more important than layout as tenths gained from aero are easier to reap than with tyre usage. Teams will want to create space for the airflow to twist and turn in order to get the downforce figures the designers are chasing. Often this has lead to long wheelbases as the designers want space between the front wheels and sidepods for bigger bargeboards, or space between the engine and rear wheels for a slimmer coke bottle shape. Ferrari has probably been the team happiest to stretch wheelbase for aerodynamic benefit. This year BMW Saubers Willi Rampf told me the cars wheelbase was purely a function of the cars aerodynamics.

But, if long wheelbase is an aero benefit and has no loss in agility, then why doesn’t everyone go for longer wheelbases. Well, the offset of along car is weight. By definition a longer car has more structure and hence will be heavier to achieve the same stiffness as a shorter car. Teams with restricted resources may not be able to afford the resources to design ever lighter structures from more expensive materials, this perhaps backs up the reason Ferrari go for longer wheelbases, they can afford the expensive carbon gearboxes and months of detail design work to make a longer car as light and stiff as a shorter one.