Le Mans 24 hours 2008

[vyselegend]

Actually all the stuff I've read on the subject underline a general aero problem with current P1 cars, not specifically the Peugeot. It seems that whenever a P1 car slide at speed, it will generate lift, while it's wings can't make downforce at such angles (I remember reading the phenomena starts when the car is at a 60° angle and reach it's summum while perpendicular to the track, but I can't find this article back).

The commonly incriminated area of the rules is the implementation of the raised sides (aiming at limiting ground effect), alowing for lots of air to engulf between the ground and the flat floor as soon as the car takes more than 60° angle from the track, at speed around 250 + km/h it will start flying.

[WhiteBlue]

whatever it is they should make a design study and have accident rcorders on the car to find out what happens. sooner or later someone will get seriously hurt.

LeMans is dangerous enough with the different level of speeds the cars have and different driver professionality. they do not need an unsafe regulation on top.

I do like the LMP1 fight between Peugeot and Audi though. Are they on different Michelin tyres?

[donskar]

RE:

Actually all the stuff I've read on the subject underline a general aero problem with current P1 cars, not specifically the Peugeot. It seems that whenever a P1 car slide at speed, it will generate lift, while it's wings can't make downforce at such angles

Reminds me of the flying Group 7 cars in the early days of Can-Am. Very scary.

I wonder if there's a simple solution like the airbrake/flap used on the roof of NASCAR machines.

[zac510]

Make sure you are comparing like with like.

The Mercedes accident was pitch induced.

This Peugeot indicent was yaw induced, however there were a few other yaw-induced flights at Monza last month. vyselegend is speaking about this in his post above.

I don't think it's a design fault per se, it's simply the nature of a prototype car with a large floor, be Nascar, Gp7, etc...

[Saribro]

There's some interesting thoughts about the matter here: http://www.mulsannescorner.com/newsmay08.html

In the end though, you'll always be looking at a 2m by 4m nearly flat surface, once it's up, it's gonna fly.

[vyselegend]

I do like the LMP1 fight between Peugeot and Audi though. Are they on different Michelin tyres?

No, they're on the sames 2008 compounds. Audi seems to be a tad better with them at the moment in terms of consistency (particulary obvious at Spa when they doubled stints while Villeneuve struggled on similar conditions with the 908), but it might be because they're nearly 1.5 sec a lap slower than the Pug (on traditional tracks), thus pushing less on the rubber.

There's some interesting thoughts about the matter here: http://www.mulsannescorner.com/newsmay08.html

In the end though, you'll always be looking at a 2m by 4m nearly flat surface, once it's up, it's gonna fly.

Very interresting article! It reminds me the one I read was probably this one from Mulsanne Mike on RCE. (which means I was wrong on the 60° yaw figure, but it reach it's worst at 90° indeed). He explains well why the NASCAR flap idea isn't easy to adapt. I think the text deserves to be copied here. I highlighted a phrase that could have been wrote by Ciro , but would make all the LM fans (who find the track has already been transformed too much) become sick:

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!

[WhiteBlue]

so the basic problem is a lack of downforce at yaw angles exceeding 45 degees. It appears as if the changes of regulations following the Porsche and Merc flying shows were not getting at the core of the issue.

[youtube]http://www.youtube.com/watch?v=rQbgSe9S54I[/youtube]
[youtube]http://www.youtube.com/watch?v=j5juuI_- ... re=related[/youtube]

They should consider an F1 style front wing with a more reliable down force perhaps with auto adjustment triggered by attitude sensors. The sensors would be cheap to do. Every I-phone has such a device.

Perhaps Audi has more front downforce? What do the CFD specialists think? If that is the case it may make the Peugots quicker due to less drag but will it make them easy to drive through a 24h race? a potential scenario is pole and initial race lead followed by shunts in the night.

[zac510]

so the basic problem is a lack of downforce at yaw angles exceeding 45 degees. It appears as if the changes of regulations following the Porsche and Merc flying shows were not getting at the core of the issue.

I suggest you go and look up the definition of 'yaw' then.

Then do the same for 'pitch'.

[WhiteBlue]

so the basic problem is a lack of downforce at yaw angles exceeding 45 degees. It appears as if the changes of regulations following the Porsche and Merc flying shows were not getting at the core of the issue.

I suggest you go and look up the definition of 'yaw' then.

Then do the same for 'pitch'.

I am aware what yaw and pitch means.



I just think that they did not get to the root of the problem which is a lack of downforce on the front. only now it doesn't happen on a straight line anymore. it still happens at larger yaw angles. unforetunately motorsport involves slides that routinely result in yaw angles greater than zero. so the rules should take that into consideration.

[vyselegend]

Yes, those are two different problems (although both are results of the aerodynamical concepts induced by the respective sets of rules). The "take off" phenomena endured by those Mercs and Porsches (related to pitch sensitivity as zac stressed, happening in conditions of slipstreaming while going uphill) has been tracked out and corrected by the new LMP ruling.

The new phenomena has been pointed out during the study Mulsanne Mike is talking about (what was the model tested in windtunnel btw?). It is linked to the aerodynamic behavior of the car under yaw.

I think this is the backside of the rules trying to prevent teams to use too much ground effect. If there were skirts on the side of the cars there wouldn't be such a posibility for air to infiltrate under the car laterally and push it up like that. Then again, how fast would these monsters go with massive ground effect, I don't even dare to think of it. As Mike said, it's not a problem for us "forum monkeys" to solve...

I just think that they did not get to the root of the problem which is a lack of downforce on the front. only now it doesn't happen on a straight line anymore. it still happens at larger yaw angles. unforetunately motorsport involves slides that routinely result in yaw angles greater than zero. so the rules should take that into consideration.

That's where I disagree, I don't think it is related to a lack of front downforce, nor the inability of the front splitter to produce downforce in pronounced yaw angles. The formula 1's front wing probably isn't more efficient under such degree of yaw (remember we're talking about the cars being nearly perpendicular to the track), the difference is just that the P1 flat floor is offering a far bigger surface than the F1 one. As Saribro pointed out: "In the end though, you'll always be looking at a 2m by 4m nearly flat surface, once it's up, it's gonna fly."

That's why I'm thinking more about preventing the (upstreaming) air to get under the car from the side, pointing the responsability toward the raised floor...

[zac510]

hehe OK WhiteBlue, I get a bit sensitive over this stuff

Go to the Mulsanne's Corner page and you will see a link to his youtube channel in which videos of all the rollovers, including one in 1981 and one in 1989 which were almost identical.

[WhiteBlue]

I just think that they did not get to the root of the problem which is a lack of downforce on the front. only now it doesn't happen on a straight line anymore. it still happens at larger yaw angles. unforetunately motorsport involves slides that routinely result in yaw angles greater than zero. so the rules should take that into consideration.

That's where I disagree, I don't think it is related to a lack of front downforce, nor the inability of the front splitter to produce downforce in pronounced yaw angles. The formula 1's front wing probably isn't more efficient under such degree of yaw (remember we're talking about the cars being nearly perpendicular to the track), the difference is just that the P1 flat floor is offering a far bigger surface than the F1 one. As Saribro pointed out: "In the end though, you'll always be looking at a 2m by 4m nearly flat surface, once it's up, it's gonna fly."

That's why I'm thinking more about preventing the (upstreaming) air to get under the car from the side, pointing the responsability toward the raised floor...

I believe that the total size of the F1 floor versus the P1 floor isn't quite so different. consider that F1 even have a stepped floor and you see that the air should go sideways under the car much easier than it does under a P1. the difference may be the lack of a floor around the nose which cannot produce lift while the front wing always produces downforce unless at extreme pitch angles. all the more reason to impose a definite downforce as much forward as possible.

[dumrick]

LMP floors are also stepped, in amount of being raked sideways. You can get an overview of the underfloor rules here: http://www.mulsannescorner.com/aco2004.html

You can see that the studies seem to have adressed forward, backward and lateral motion induced lift. Also, it's curious to observe that both the Creation (in practice)...
[youtube]http://www.youtube.com/watch?v=dnLBf6N3xPA[/youtube]
...the Audi...
[youtube]http://www.youtube.com/watch?v=OAP2FJns0M0[/youtube]
...and the Courage-Oreca...
[youtube]http://www.youtube.com/watch?v=52wUHuZ7fqI[/youtube]
...at Monza only lifted at an angle between 90 and 180º (although track surface effect cannot be ignored, as Mike Fuller mentions). Can anybody perceive at which yaw angle the Peugeot has lifted?
[youtube]http://www.youtube.com/watch?v=gSsorp6F36s[/youtube]
It's attitude coming into view in the right hander is consistent with a spin and going to the grass at around or slightly above 90º.

My contribution for narrowing down this discussion, anyway...

[RacingManiac]

shunt or not, the fastest 908 went 3:22.2, which is 4 sec faster than the test day last year.....and 4 sec faster than anyone else(and Audi) managed this year thus far.....and this is back in the range(compensated for track changes too) of the 3.5 liter car can manage in early 90s.....when the car weighs 750kg powered by F1 engine with ground effect tunnels big enough to park a trailer inside....

Mulsanne's corner also features some of the only photos I've seen for Peugeot under the engine cover, including an intriguing rear suspension packaging....

[WhiteBlue]

Dumrick, good sources and good points you are making. The >90° yaw angle suggests indeed that they did not go off due to lack of front downforce. could the rear wing and diffusor be generating lift in that situation? probably but it still would not explain why the cars also lift at 90° sideways. To me it suggests that the theory with the profiled cross section is somewhat flawed. I'm out of options to say what could be done except do more research and apply that. the first video was clearly showing the car going off and tank slapping prior to lifting at perhaps 120° yaw angle. in totally different safety context I noticed that they actually had TecPro FIA approved crash barriers which seemed to have worked well.