BMW flip

[vogelmann4]

My lit prof is making us do one more speech before the end of the term. He want's it on a technical subject, which is so broad its actually tough to pick a subject. Anyway I thought it would be cool to try and explain what happened to the BMW Lmp a couple of years ago at Road Atlanta. My prof is a sports car fan and I was standing on the bridge when it took off. I was wondering if any one a) has the video of the flip and b) if anyone knows were i can find a descriptive explanation of what happened. thanks.

[pplater]

Welcome to Ten-Tenths!

It was a Porsche at Road Atlanta in 1998. I'm no expert, but I don't recall a BMW flipping there.

Here's a video of the Porsche flip.
http://www.pocketrocket.ca/multimedi...sche_flip.mpeg

The Mercedes flip at Le Mans could be a better choice, as there's heaps better footage and tech. discussion of it.

Webber's flip (Photo halfway down the page0
http://www.motorracing.tv/html/mark_webber.asp

Dumbreck's flip (video)
http://www.jabberwocky.co.uk/lemans/1999/clr-flip.mpg

Webber's car became airborne during Thursday's practice session at Le Mans, somersaulting several times before coming to rest.

A new car was built in time for Saturday's race but on Webber's first lap out of the pits in the morning warm-up session, exactly the same thing happened again—this time in full view of TV cameras, drivers and spectators. Webber was again fortunate to escape unharmed but five hours into the race, his team-mate, Peter Dumbreck, experienced an identical flip and Mercedes withdrew its remaining car instantly. The rest of the year's programme was shelved and the cars were never raced again.

(http://en.wikipedia.org/wiki/Mark_Webber)

There's a technical explanation of it here:
http://www.mulsannescorner.com/techarticle1.htm

While at Mulsannes, have a look at trap speeds over the years, I.E the trend since 1999.

Hope I've been helpful.

[thebear]

Originally Posted by vogelmann4

My lit prof is making us do one more speech before the end of the term. He want's it on a technical subject, which is so broad its actually tough to pick a subject. Anyway I thought it would be cool to try and explain what happened to the BMW Lmp a couple of years ago at Road Atlanta. My prof is a sports car fan and I was standing on the bridge when it took off. I was wondering if any one a) has the video of the flip and b) if anyone knows were i can find a descriptive explanation of what happened. thanks.

I believe it was '99 or '00, Bill Auberlin (?) approaching the bridge had a wild ride to driver's right and ended up basically sitting on the ground holding the steering wheel while pices of car rained down from overhead.

[bryan]

It was Bill Auberlen in a BMW V12 LMR. He was drafting another car as they went over a rise at Road Atlanta between turns 8 and 9. As the track crested, the front end of his car lifted up and flipped over once completely due to the lack of downforce on the front end from the draft. It landed on the back left corner but ended up on all four wheels and skidded a little further with Auberlen unhurt.

I have a low quality clip of the speed channel broadcast showing the flip and some analysis of what happened, but I have nowhere to post it for downloading.

[Mad-Dog-mk2]

Wasn't he pulling out to pass a Viper and the Lola moved out subjecting the BMW to (very) dirty air as he crested the rise?
Basicly the Lola was a very high downforce car and most teams told their drivers not to follow closely behind it for reasons Mr Auberlin found out.
I think he was quoted as saying he knew he was in trouble when the visor on his helmet flipped open moments before the car went over.

[PascaLM]

Originally Posted by pplater

There's a technical explanation of it here:
http://www.mulsannescorner.com/techarticle1.htm

I'm afraid this is not the right explanation.

Even if the Mercedes profile looks like a wing, the surface of the upper shape is not wide enough to have the same aerodynamic force that a real airplane wing does. So, this doesn't explain why the Auberlen's BMW V12 LMR, which has not such a profile, took off. The Riley & Scott and the Panoz (pictures)are not fast enough to have the same problem.
Christophe Bouchut reported in the Le Mans Racing magazine : "...I did not appreciate their (Mercedes staff) behaviour after the Dumbreck accident.../...We were explained that he made a fault, I explained to them that they were wrong ! The reason of the problem is that we had few aerodynamic charge, in order to increase the maximum speed and to reduce the comsumption. And the suspension was to smooth because they wanted the car to hold the road through the suspension. Result : the car was bouncing with hops and the air was rushing under it. And when a car leaves the ground, you don't feel it !..."

[billnchristy]

http://www.motorsport.com/news/artic...FS=ALMS-LEMANS
article about Auberlin after the accident, his account.

[brielga]

Originally Posted by PascaLM

I'm afraid this is not the right explanation.
Christophe Bouchut reported in the Le Mans Racing magazine : "...I did not appreciate their (Mercedes staff) behaviour after the Dumbreck accident.../...We were explained that he made a fault, I explained to them that they were wrong ! The reason of the problem is that we had few aerodynamic charge, in order to increase the maximum speed and to reduce the comsumption. And the suspension was to smooth because they wanted the car to hold the road through the suspension. Result : the car was bouncing with hops and the air was rushing under it. And when a car leaves the ground, you don't feel it !..."

I have always wondered about the responsibility taken in those "flights". Of course I understand all the discussion about the risk taking by driving a racing car, etc., etc. but what I do not understand is that they sent the drivers out AGAIN after Dumbreck's shunt. Which fault could he possibly have made? Was he pulling the steering wheel upwards? What would have happened if Webber had had more serious consequences (or died) during his warm-up accident?? Well, I think the answer is that marketing is king.....They had to get those Mercs out there whatever the consequences. Only a 2nd shunt had them change their minds.

[Mal]

Dumbrecks was the third and last shunt. The first two were wiith Mark Webber in practice and the rushed through aerodynamic winglets to the front that were supposed to solve the problem.

Immediately after Dumbrecks shunt they withdrew from the race.

[brielga]

Originally Posted by Mal

Dumbrecks was the third and last shunt. The first two were wiith Mark Webber in practice and the rushed through aerodynamic winglets to the front that were supposed to solve the problem.

Immediately after Dumbrecks shunt they withdrew from the race.

Thanks Mal, I guess I got mixed up in the order of events ...

[PascaLM]

Originally Posted by brielga

...Only a 2nd shunt had them change their minds.

I agree. I bet that aerodynamics is the experimentation field that brought the most dangerous accidents in motor racing. And it seems that it's still not mastered even in 2005 and despite the computerised simulations.

[pirenzo]

Yes, probably, as aerodynamics is an experimental science as it is.
The computer models used are only based on experience.

I was talking to my maths teacher not long after the christmas holidays about universities, and he got onto how he'd done one of his PhD's in fluid dynamics, he was saying the problem is because it is so difficult to produce a mathematical model of exactly what a fluid is, the best you can get after hours of mind-bogglingly complicated maths is nothing more than an educated guess as to what's going on.

So its not surprising nobody is really sure about what caused any of the incidents.
The 'wing' shape of the cars is a fairly plausible explaination, given the other wierd things it causes, I think somewhere in that Mulsanne's Corner article is a picture of the Audi R8C which has had its rear bodywork 'sucked' off by the airflow.

[jhansen]

I have video clips of the Dalmas shunt from Petit Le Mans '98, the Dumbrek shunt from Le Mans '99 and the Auberlen shunt from Petit Le Mans '00. I wont claim to be an expert. But the common thread in all three of those video clips is traffic/drafting/dirty air.

Remember, the Mercedes CLR ran a ton of testing miles without flipping. However, it ran all of those testing miles without the turbulent air from other cars affecting it.

[Fab]

Originally Posted by Mal

Dumbrecks was the third and last shunt. Immediately after Dumbrecks shunt they withdrew from the race.

My worst memory at LM... there has been a "OOOOOOOO" in the crowd when we saw that on the big screens, and then the red flag... we were stun and stuck to the screens... what a relief when we had good news from Dumbreck...

[Fab]

Did Michele Alboreto take off for his accident ? I saw a terrible wreckage of the Gulf Audi on a PK Sport video too, involving a Courage Pescarolo (2001, I think)...

[pirenzo]

Yes, but Michele's accident was due to a deflating rear tyre wasn't it? That made the back end drop slightly exposing the underside of the nose to the air stream and flipping the car over the barrier. It would have been quick at least

[PascaLM]

Originally Posted by jhansen

I have video clips of the Dalmas shunt from Petit Le Mans '98, the Dumbrek shunt from Le Mans '99 and the Auberlen shunt from Petit Le Mans '00. I wont claim to be an expert. But the common thread in all three of those video clips is traffic/drafting/dirty air.

Remember, the Mercedes CLR ran a ton of testing miles without flipping. However, it ran all of those testing miles without the turbulent air from other cars affecting it.

Yes, it's a main cause of this kind of accidents. But sometimes it happens without any air perturbation (Pescarolo's Matra in 1968).
Mercedes did not discover early enough the problem because the high speed tests were made at Fontana, on a banking.

[racer11]

Originally Posted by jhansen
I have video clips of the Dalmas shunt from Petit Le Mans '98, the Dumbrek shunt from Le Mans '99 and the Auberlen shunt from Petit Le Mans '00. I wont claim to be an expert. But the common thread in all three of those video clips is traffic/drafting/dirty air.

where did you get the video of Auberlens flip from?

[jhansen]

I honestly cannot remember, pretty sure it was from one of the forums.

[XJR14/WSC95]

Having viewed all three accidents I fell that the common link is a drafting behind a car and coming over a rise at the same time. I think Both the Road Atlanta incidents happened at the same part of the track. With a combination of drafting over a rise, and a large amount of turbulent air getting under the cars flat bottom. And once it goes there’s no coming back. I am no expert but from watching the 99 Le Mans review I fell the fundamental floor with the CLR was its suspension. It would bounce furiously as it came into slow corners and run over bumps. Perhaps a combination of drafting in dirty air over rises on a bumpy track was the CLR’s cillies heal. I think it was a mistake to carry out so much testing on a very smooth banking to get the car ready to race on a very bumpy road course.

[Dunlop Corner]

I don't beleive this problem only exists on closed cars. I remember Tom Kristensen almost did a "Dumbreck" in pre-qualifying with the BMW in 98. We managed to brake in the last possible moment, preventing the entire car taking off. But his front wheels where of the ground some 50-60 meters i beleive!

[Spiteful]

Originally Posted by Dunlop Corner

But his front wheels where of the ground some 50-60 meters i beleive!

Was the car still attached to the front wheels at that instance?
I assume you were going for centimeters there

A sleek coupé roof would probably generate more lift, but thats not the real problem. IMO the old flat bottom rules meant that the aerodynamics of the cars were too easily upset. It wasn't a problem most of the time, but when drafting, crests, bad aero- and suspension setups... came together, cars would become unstable, airflow underneath the car disrupted, the body producing lift or too little downforce and that big wing levering the nose up. I think the new regs with the higher noses, shorter rear overhangs, flat bottom ending before the rear wheels and side intakes (chamfered floor) have made this less of a problem, although they weren't meant to adress blow-over problems. Mercedes have obviously made big mistakes in their testing programme and during LM '99, but I think blow-over accidents were (are) an inherent flaw of this type of car.

[Spiteful]

And I'm not crpping out of my mouth either:
http://www.mulsannescorner.com/aco2004.html

[rustyfan]

Originally Posted by Fab

Did Michele Alboreto take off for his accident ?

Alboreto got airborne and flipped out of the test-oval, yeah, landing upsidedown which tore off the rollbar, which in turn killed him instantly.

That, and Jeff Clinton's fatal Grand-Am flip at Homestead, is one of the main reasons I really, really, really dislike open-cockpit prototypes these days. There is no doubt in my mind that Alboreto - and Clinton - would have alive today had he been in a closed-cockpit car (illustrated by Eric van de Poele's huge test crash in 2002, where he flipped the Bentley at Paul Ricard, which he walked away from).

[Dauntless]

Originally Posted by Spiteful

Was the car still attached to the front wheels at that instance?
I assume you were going for centimeters there.

No, what he meant was that the car rolled down the track for some 50-60 meters with the front tires several centimeters in the air. The car almost flipped over backwards, but didn't quite have enough energy, and eventually recovered.