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May/June 2008
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6.12.08

Another Thursday before Le Mans and another vague ACO press conference!  Man these guys don't like specifics!  We're again waiting until November for rules specifics but changes are on their way.  The ACO seems to be embracing downforce reduction as a method of solving the recent yaw induced aero issues.  According to the ACO via autosport.com, direclty from Daniel Poissenot, and this is in quotes, "We need to look at the performance of the cars. We want to reduce downforce, which in turn will reduce corner speeds. All aero devices on the bottom of the cars will be banned for 2009."  Not sure what to make of the italicized part.  Will the cars have no underfloor at all,  just exposed mechanical bits?  Will the diffuser section of the underfloor be removed?  Or is it simply the elimination of splitter turning vanes and the like and a possible limitation of the front diffuser?  Who knows at this rate...

But ultimately I don't agree with this direction, at least in regards to solving the yaw issues.  All the incidents this year have occurred on tracks where the cars are trimmed to their lowest downforce levels therefore it would seem to me to be an issue of sudden yaw at maximum speed while in the lowest downforce setup as that is the common thread to them all.  So to mandate even lower levels of downforce without doing anything about the amount of flat bottom area (and I don't advocate reducing the amount of underfloor area, just don't make so much of it flat!) seems to play right back into the hands of the many factors that cause these incidents to happen in the first place.  And with the cars carrying less downforce you end up with a more dangerous cars because after all, these incidents have all occurred in the braking zones right when you need downforce the most!  At very least we can say for certain the incidents haven't occured because the cars have been carrying too much downforce. 

But then ACO has two issues here, they want to slow the cars down in addition further reducing the yaw incidents.  Certainly these will be intertwined but I would have preffered language that spoke to one issue, and then the other if only because it reads as though the ACO's answer to the yaw incidents is to reduce downforce and I don't think that's there intention.  Fair enough that the ACO wants to slow the cars down, but this isn't a two birds one stone situation and specific research needs to be done that looks at the yaw incidents. 

On to other things, there was more talk about LMPEvo, but again nothing specific.  November.  Wait on it.  Again. 

LMP1 eligible GT1 engines get a capacity increase to 7.0 liters.

That's all for now...

6.2.08, updated

Marc Gene's Peugeot 908 suffered a rather big accident today at the Le Mans test in which the car became airborne as it entered the Porsche Curves.  See the video, as well as a compilation of other yaw and pitch induced aerodynamic flips on our youtube channel.

Here's something I wrote for Race Car Engineering with some thoughts/additions added today:

“There is not a problem until something unusual happens and than it seems there is too often a problem.  That is particularly a problem when high speeds are involved and of course here that is very often the case. It should certainly be looked at very carefully.”  That’s how Hugues de Chaunac assessed the events that led up to Stefan Ortelli’s rather horrific accident at the Monza Le Mans Series round.  Ortelli’s Courage-Oreca LC70 shot off the track in the braking zone for the first chicane and became airborne, narrowly missing Alan McNish’s Audi as the Oreca-Courage careened back onto the track and started a series of barrel rolls.  In addition to Ortelli’s accident, Rinaldo Capello’s Audi R10 nearly rolled over when the car became sideways while avoiding the Rollcentre Pescarolo on track.  The roll angle was so lurid that damage was inevitable and subsequent repairs cost the second Audi any shot at victory. 

As a result, many are asking this question, how is it that these types of incidents are still occurring given the 2004 LMP regulations were designed to address the issues of downforce loss at high yaw angles?  Indeed, but the 2002 FIA commissioned Piper study seems to have produced a vehicle who’s critical take off speed is much reduced, especially compared to the 2002 baseline.  But perhaps the "much reduced" should be emphasized?  With the hindsight of the Piper Report we can see, for example, at a 180 degree yaw angle the critical take off speed was increased to more than 500 km/h by the 2004 LMP regulations (this at a 4 degree roll and 55/45mm front/rear ride height).  That’s a substantial positive change given the old-rules-car would take off at 281 km/h when backwards and effectively the LMP2004 modifications have eliminated issues if a car is ever to get completely backwards.  But at angles exceeding 45 degrees the critical take off speed of the new rules car is still surprisingly low going from 282 km/h to a mere 192 km/h at 90 degrees.

The common factor in these most recent incidents seems to be low downforce and high speed as the accidents have occurred at circuits that require low drag/high speed (to put it into perspective, the top speeds at Monza are sufficient for a light aircraft to take off and fly!).  The Mazda-Lola Sebring incident is the lone standout.  The other common factor is that none of these incidents has occurred "insitu".  That is, other elements, namely the off track topography (grass, gravel traps, curbing), have come into play.  In all these cases the cars in question have been launched into yaw and roll angles that are impossible to escape from due to cresting curbing.  And as the cars careened off the track into the grass the tire-road friction component was eliminated therefore little speed reduction was occurring as the accidents unfolded.  And as these incidents are a relationship of yaw angle to speed, if you have a way to bleed off speed in a hurry (adding a massive drag component [tire friction or aerodynamic drag] forgetting about generating downforce or reducing lift for the moment) you're in better shape than if you didn't.

And this is where the NASCAR roof flap solution comes up, though ultimately this solution is vastly more complicated for road racing cars as they tend to turn left and right.  How do you devise a system that is so sensitive to note when a slid is just a slid versus truly getting it all wrong?  The situation is further complicated by the fact that stock cars tend to be at their worst when facing backwards, they are generating more lift than car weight at yaw angles of 180 degrees.  So the roof flaps are designed to deploy in that worse case situation.  But LMPs, as they pass 45 degrees of yaw, are already in the danger zone of lift off.  And then how do you homogenize it so that it will fit onto every car given that every chassis design is different?  Of course this also overlooks specifics in where do you mount the flaps?  Understand the yaw induced flips are a essentially case of getting aero balance all wrong (one end's generating lift, the other still generating downforce).  The Piper study showed that on the old-rules car, front downforce fell off at yaw angles above 20 degrees but that rear downforce actually increases approaching 10 degrees.  But with the LMP2004 regulations, downforce loss to yaw is much more gradual and the car maintains some 60% of it's straight line downforce at 30 degrees of yaw.   But if you place flaps in one area of the car (towards the rear for instance), they might only help in some incidents and hurt in others.  So the flap solution, while seemingly obvious, is indeed not an easy one.

The easier solution could very well lie in looking at track design and eliminating grass verges as well as gravel traps, and reducing the heights of curbing. 

In conclusion, I'm certainly not advocating that nothing be done.  But it isn't a situation where the solutions are easy.  All modifications to the chassis regulations need to be done with study.  Simply reducing the size of the rear wings or front splitters, as some advocate, will only further complicate things (and reduce efficiency while reducing drag--so you then have a car with a higher terminal velocity yet even less downforce!).  Solutions that look at major alterations to the cars need to be made in concert with the data derived from the Piper report.  Hacking willy nilly isn't a scientific way to go about this and could (dare I say will) lead to further muddying the waters.  But ultimately it is up to the ACO to tread in a premeditated fashion and certainly (thankfully!) not up to forum monkeys!

5.25.08

At the Spa Le Mans Series event a few weekends ago the Audis were running in a slightly revised aerodynamic spec which consisted of a simple add-on "wing" mounted between the rear fenders at the very trailing edge of the engine cover. 

Having a closer look at the wing and it appears to be a simple parallel extrusion in cross section without a differing top and bottom chord line (ie, it appears to be "constant thickness" and therefore not a wing as the ACO defines it, but lacking any other wording we'll call it a wing here out for clarity sake, I mean what else are we going to call it?).  Overall it seems rather crude in execution and is very simplistic. 
Perhaps the most telling feature of this device's function are the related cutouts in the trailing edge of the rear bodywork which allows the low pressure zone that is generated by this wing to potentially "see" the trailing edge of the tunnels.  And given the proximity, there's potential for some (minor) positive interaction with the underfloor. 

In general, the new wing would appear to allow a reduction in angle of the primary rear wing flap for less drag but similar levels of downforce, and quotes by Audi's Ralf Jüttner backs this up.

So if we agree that this new aero device isn't a wing and doesn't fall under that definition, does that mean it's a free-for-all for such non-defineable devices?  Well not so fast.  A cursory read of the regulations one comes across article 3.6.2, which addresses where aero devices can go and in what numbers:
 
3.6.2 - No aerodynamic element can be added on the bodywork apart from :

- Two aerodynamic elements maximum at the front of the front fenders provided that :

• They do not obstruct the driver's view
• They do not mask the headlights ;
• They are not situated more than 600 mm above the reference surface ;
• They are approved by the manufacturer and the ACO (homologation form of the car).


- One “Gurney” at the rear of the bodywork.
- The rear wing described below.

So it seems rather clear that said add-on device isn't, a.) an element attached to the front fender, b.) a rear body gurney (the cars still had the standard trailing edge gurney being run in conjunction with the new device), or c.) a rear wing.  So naturally there are questions as to how Audi defined this aero device and then to what standard the ACO accepted it.

Now a more clever interpretation might mean running a long chord (300 mm) single element wing in the traditional position and using the flap in this lower position.  The regulations simply state that the rear wing can consist of two elements that must fit in a box 300 mm x 150 mm.  It doesn't state that those elements must be in the same box nor does it specify the exacting vertical separation maximum between the two.  The argument will be the separation can be no more than 150 mm, but as far as I'm concerned that only defines the legality box the wing as a element must fit in.  So defined individually both wing elements must fit in said box, but the regulation doesn't state they both must fit in the box at the same time, therefore allowing you the freedom of vertically seperating the double elements of the rear wing as you see fit.  Patent pending. 

But clearly what Audi has done isn't along these lines as their rear wing as seen at Spa is using the traditional main plane and flap arrangement negating this new add on element as the second of the two elements.

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©Copyright 2008, Michael J. Fuller