Mercedes CLK GTR Le Mans flights.

[helgi]

I'm interested in engineering side of motor racing. I'd like to know your opinion about that famous flights. It was certainly an aerodynamics fault. But could you tell me about that more specifically?
Thanks!

[ckiesz]

I am interested also. With a high power and low slung flat bottom, what keeps a car like mine from going airborne?
If you haven't already, check this out:
http://www.mulsannescorner.com/techarticle1.htm
Christian

[helgi]

Great! Thanks!

[helgi]

So,the problem was in suspension and aerodynamics. The place,where they "take off" is on the top of the hill. There must be some weight transfer. As the rear suspension was soft to help wheels trasfering huge torque to the ground, the nose for some moments appeared to be higher than the tail. The flat bottom began to produce lifting force and the car made its flight.
Is it right?

[Locost47]

The Mulsanne's Corner article is good, apart from quoting the 'equal transit time theory' for lift generation (which is emphatically incorrect), but there's a more thorough and technical investigation of what happened here:

http://www.sae.org/technical/papers/2000-01-0872

The summary of it is the same: flat floors ARE aerodynamic devices in themselves and are intrinsically far more sensitive to pitch angle and ground clearance variations than diffusers. Rules people think they're eliminating aerodynamics trickery by mandating them but all they're doing is forcing the engineers to use far more risky methods of achieving the necessary performance instead. Not good!

[AU N EGL]

Originally Posted by helgi

So,the problem was in suspension and aerodynamics. The place,where they "take off" is on the top of the hill. There must be some weight transfer. As the rear suspension was soft to help wheels trasfering huge torque to the ground, the nose for some moments appeared to be higher than the tail. The flat bottom began to produce lifting force and the car made its flight.
Is it right?

Not necessarily wt transfer but LIFT. The car was an very good wing shape, and when a little air gets under a wing, as in cresting that small rise, TAKE OFF.

also happened at Road Atlanta's back straight. Men the MB got behind another car, no down force on the nose, so the nose lifted slightly and air got underneath and TAKE OFF.

[helgi]

It becomes more and more interesting and complicated.
And what's wrong with weight transfer? I think, that the road section where that accidents took place has a changible relife. Photos in our magazines were of bad quality and I can not affirm the fact, but it seemed to be a top of the hill. So there must be some horisontal/vertical accelerations = weight tranfer relative to the axles. of course, I don't think that in a moment 1000 kilos went to the tail and the car did a wheelie. Maybe, CLK managed to get into the aerodynamic shadow of some car ahead. But it had to go in one-two meters behind - I don't think there were cars so close to it at that moment. The accident is a sum of different elements, and we can not know all the 'ingredients'.
As for risky methods - I agree. The fact - we can not usually notice 'bottlenecks' before tragedy has happened...

[helgi]

Just one more question. How great is that aerodynamic shadow effect? I mean, for what distance behind a GT car it has its influence? At 200 mph is it 2 or 5 meters of low pressure area? Thanks!

[AU N EGL]

Originally Posted by helgi

Just one more question. How great is that aerodynamic shadow effect? I mean, for what distance behind a GT car it has its influence? At 200 mph is it 2 or 5 meters of low pressure area? Thanks!

I dont know about 200 mph, but at 150 mph, I have felt a differnce at 50 feet behind another GT car. I notice the water temp go up right away, oil temp start to climb and the car is a bit unstable. So I never get right behind a car at speeds over 100. Just slightly off to the side, so the front of my car does get some air.

Or may be I am just not into NASCAR bump drafting at those speeds. EEK

[helgi]

Thanks a lot for the explanation!
There was Toyota ahead of CLR at the top of the hill. At the speed about 200 mph the influence can be noticed at 80-100 feet I think. It would be enough to disbalance the car.
So,there were many factors led to the crash - CLR aerodynamic,suspension-weight transfer, aerodynamic shadow.

[AU N EGL]

Originally Posted by helgi

Thanks a lot for the explanation!
There was Toyota ahead of CLR at the top of the hill. At the speed about 200 mph the influence can be noticed at 80-100 feet I think. It would be enough to disbalance the car.
So,there were many factors led to the crash - CLR aerodynamic,suspension-weight transfer, aerodynamic shadow.

To close? Watch this video at Road Atlanta. Looks about 2 meters behind the lead car it that much.

http://youtube.com/watch?v=XxpnqL8-0_w

[helgi]

But we can not say that there was only aerodynamic factor. It was a multifactor accident. I've started this topic because almost everyone at russian forums thinks it was aerodynamic. But,why that flights took place only at one or two places? If it was a car aerodynamic fault,why CLR hadn't taken off somewhere else? Or it competed few races to have an extra opportunity to fly? Of course, we'll never know the reasons-we have no data at all.

[AU N EGL]

Originally Posted by helgi

Or it competed few races to have an extra opportunity to fly? Of course, we'll never know the reasons-we have no data at all.

IIRC after the three flights ( two at Le Mans, and one at Road Atlanta) MB pulled the car from races and ended their racing involvment.

[diabloA1]

Hi! I just joined this forum.

Perhaps it is worth noting that the topic title is inaccurate. The car in question wasn't CLK-GTR but rather the CLR-LM

[Aysedasi]

Originally Posted by AU N EGL

IIRC after the three flights ( two at Le Mans, and one at Road Atlanta) MB pulled the car from races and ended their racing involvment.

An embarrassing time for Merc, particularly after the lame performance at LM the year before.

[Mal]

Originally Posted by AU N EGL

IIRC after the three flights ( two at Le Mans, and one at Road Atlanta) MB pulled the car from races and ended their racing involvment.

The Road Atlanta flights was the GT1 Porsche was it not - Yannick Dalmas at the wheel

[Aysedasi]

Yep, that's true. Were there only two flights at LM? I somehow have it in my head that three were three......? Three incidents, anyway......

[Notso Swift]

Long time ago so memory may not be 100% but I thought it was 2 with Webber, after the second they (Norbet) were blaming him (in the press as well) as he was the only one with the issue to which Webber said you can go F yourself, it is the car, they dropped him from the race as a result.
During the race itself the third one went with another driver, can't remember, Dumfries maybe.
Later they worked out that Webber was going harder at that point behind other cars, in other words he had the problem first because he had more brave pills

[helgi]

Excuse me,I don't want to start a new thread,and maybe it's discussing somewhere else,but that flying prototypes (now LMP2 already) were moving sideways before they began to lift. Is the reason in huge speeds? Don't you think designers are 'doing some chemistry' (I mean, concocting) with that 'flat' bottom. The car can not become seven seconds faster in a year only because of more power,better suspension or simple usual aerodynamics evolution. Maybe,one or two seconds,but not seven seconds a year.Well,the track was reconstructed,I've heard.But nevertheless it's very-very strange and alerting.

[Mike_Wooshy]

Originally Posted by Notso Swift

Long time ago so memory may not be 100% but I thought it was 2 with Webber, after the second they (Norbet) were blaming him (in the press as well) as he was the only one with the issue to which Webber said you can go F yourself, it is the car, they dropped him from the race as a result.
During the race itself the third one went with another driver, can't remember, Dumfries maybe.
Later they worked out that Webber was going harder at that point behind other cars, in other words he had the problem first because he had more brave pills

Peter Dumbreck was the third flip.

[JAG]

Originally Posted by helgi

Excuse me,I don't want to start a new thread,and maybe it's discussing somewhere else,but that flying prototypes (now LMP2 already) were moving sideways before they began to lift. Is the reason in huge speeds? Don't you think designers are 'doing some chemistry' (I mean, concocting) with that 'flat' bottom. The car can not become seven seconds faster in a year only because of more power,better suspension or simple usual aerodynamics evolution. Maybe,one or two seconds,but not seven seconds a year.Well,the track was reconstructed,I've heard.But nevertheless it's very-very strange and alerting.

2 seconds at a regular circuit can, in an exceptional year, easily become 7 seconds on the long Le Mans circuit.

Last years pole time was also set in the dark, as it was raining for most of the qualifying sessions.

[rcarr]

Originally Posted by Aysedasi

An embarrassing time for Merc, particularly after the lame performance at LM the year before.

The 98 CLK-GTR LMs didn't have a "lame" performance, they were leading the majority of the time they were on circuit, their oil pump belt broke, a fault that could happen to any car at any time during the race.

[Rubinho]

Originally Posted by helgi

...that flying prototypes (now LMP2 already) were moving sideways before they began to lift. Is the reason in huge speeds? Don't you think designers are 'doing some chemistry' (I mean, concocting) with that 'flat' bottom.

Angle of roll, pitch and yaw drastically affect the critical take-off speed of prototypes. As can be read in more detail in the most recent Racecar Engineering (V18N7) cars designed to the new 2004 regs can have take-off speeds of 192kph to 282kph at yaw angles from 90-45 degrees. Any sort of tyre or suspension failure could cause one of these cars to reach fairly wild angles and take off.