Discussion - is there a design issue with LMP

[Mal]

There is a really interesting debate going on the the Monza thread about LMP design in the light of the three airborne incidents at Monza.

I think this needs its own thread as it is relavent to all prototypes in all series.

The 3 incident raise the following questions:

1) Is there a design issue leading to the cars becoming airborne when travelling sideways at high spead
2) If so how can it be solved - if at all
3) Is there not an issue at because in two of the three incidents the aerodynamics returned the car to the ground the right way

[Dario911]

You can find an excellent explanation about this argoument on the www.mulsannescorner.com
Here you can find a great discussion about LMP aerodynamic.

[gwyllion]

Indeed http://www.mulsannescorner.com/aco2004.html explains the reasoning behind LMP1/2 aero rules.

[zac510]

I think there is an issue because the car can't decelerate as quickly as it could if it were on the ground (ie brakes could be used).
But I'm still trying to work out whether it is something that has become worse as a result or a design trend or rule change, or whether it is just merely the nature of the beast, like trying to keep an open wheeler's wheels attached to the chassis.

[johntt]

I'd say that the incidents at Monza were freak accidents which happened to fall on the same weekend. Its one of those things that you can't legislate to prevent, like open-wheel cars catching wheels and getting airbourne.

[The Badger]

I suppose you could get back into ground effect , but that would not help when the car ends up at an attitude it wasnt supposed to be in .....

They use a lanyard system to keep the wheel attached to the chassis in the event of an accident , in F1 , or did use it ?

Maybe the angle of the undertray , when faced into the airflow generates too much lift ? A flatter bottom would not have such an angle , and maybe not generate as much lift . But im just guessing ?

Wheres Mulsanne Mike when ya need him ?

[PorscheFanNo1]

Originally Posted by The Badger

Maybe the angle of the undertray , when faced into the airflow generates too much lift ? A flatter bottom would not have such an angle , and maybe not generate as much lift . But im just guessing ?

Yeah, youre guessing :P

The undertray of modern LMP cars generates downforce when at an angle (going sideways). With a flat bottom the undertray dont generate any downforce, but the air going over the car will generate lift, so it will take off. The downfroce from the undertray of moderns LMP cars when going sideways should be more then the lift created byt he air going over the car, so it should stan on the ground. But as seen when the cars get a little help from the grass it can still take off.

[vorsprung]

Originally Posted by The Badger

Maybe the angle of the undertray , when faced into the airflow generates too much lift ? A flatter bottom would not have such an angle , and maybe not generate as much lift . But im just guessing ?

Wheres Mulsanne Mike when ya need him ?

Mike posted something on ALMS forum. He thought that the cars did pretty well and an old flat bottom car would've flown much further and higher. But he also thinks that there should be a follow up to Piper's '02 study of the aerodynamics at some point.

Originally Posted by PorscheFanNo1

The undertray of modern LMP cars generates downforce when at an angle (going sideways). With a flat bottom the undertray dont generate any downforce, but the air going over the car will generate lift, so it will take off. The downfroce from the undertray of moderns LMP cars when going sideways should be more then the lift created byt he air going over the car, so it should stan on the ground. But as seen when the cars get a little help from the grass it can still take off.

According to Piper's study the take off speed for current rules car (chamfered floor, big wing endplates) going sideways is 500km/h. The test were done in a 40% rolling road windtunnel.

[MulsanneMike]

Originally Posted by PorscheFanNo1

Yeah, youre guessing :P

The undertray of modern LMP cars generates downforce when at an angle (going sideways). With a flat bottom the undertray dont generate any downforce, but the air going over the car will generate lift, so it will take off. The downfroce from the undertray of moderns LMP cars when going sideways should be more then the lift created byt he air going over the car, so it should stan on the ground. But as seen when the cars get a little help from the grass it can still take off.

Actually both generate downforce in yaw. But as that yaw angle passes a certain angle the downforce drops and eventually will turn to lift (at around 35 degrees of yaw for a pre-'04 reg car, around 70 for a LMP'04 reg car) , especially if the car's roll isn't 0 degrees (add just a few degrees of roll into the windward side of the yaw and things change rather drastically). And the one thing that is missing in both Ortelli's and Capello's accident is tarmac induced friction (from the tire-road relationship) that would have further reduced the speed.

[rcarr]

Bring back the aerodynamically ultra sticky high winged cars of the early 90s!

[dazbaz_99]

From the footage I have seen from all 3 accidents from the weekend at Monza, it would appear to me that the aero of the LMP's is not to blame for them lifting.

Jamie Campbell Walters appeared to be caused by hitting the Rumble Strip at high speed?

Capello's incident I have only seen from the in-car camera, but it looked like his car didnt lift up until it had hit the armco once or twice, so surely this was a factor in unsettling the car.

Ortelli's flip was aided by digging into the grass.

Are we not jumping the gun a bit in suggesting the LMP regs are to blame?

[ss_collins]

This will be discussed on midweek motorsport tonight on Radio Le Mans

[duke_toaster]

Originally Posted by The Badger

They use a lanyard system to keep the wheel attached to the chassis in the event of an accident , in F1 , or did use it ?

F1 still has wheel tethers, I'm not sure if any other series use them, but they are sensible (but mainly for spectator safety reasons). They came in in the late 90s IIRC.

[zac510]

dazbaz, you should watch the videos again (they're all on youtube).

WRT the F1 wheels, I used that analogy because it was similar to the point I was making that if the wheels are in the air then the car can't slow down as rapidly as if it were on tarmac. Similarly if an F1 car has had wheels knocked off by a driver then the brakes will no longer have much effect.

[canam]

Originally Posted by vorsprung

According to Piper's study the take off speed for current rules car (chamfered floor, big wing endplates) going sideways is 500km/h. The test were done in a 40% rolling road windtunnel.

...then JCW was going at one heck of a speed! The Creation appeared to go airborne when it went largely sideways.

[MulsanneMike]

Originally Posted by canam

...then JCW was going at one heck of a speed! The Creation appeared to go airborne when it went largely sideways.

Note the yaw dynamics are drastically different from 1 degree to 90 to 180. The peak lifting forces are occuring in the 90 range and diminish at 180. So the lift you'll see at say 90 is potentially much higher, hence the difference in the critical take off speed of 500 km/h for 180 degrees vs. some 282 at 90 (don't quote me on the 90 figure, thinking off the top of my head as I don't have my notes with me at work). And again, these numbers are all dependant on how much roll is in the car and its ride height. The numbers quoted above are for 4 degrees of roll and a 55/45 ride height (ie slightly nose up).

[MulsanneMike]

Originally Posted by dazbaz_99

Are we not jumping the gun a bit in suggesting the LMP regs are to blame?

Yes, I most certainly think we are. Though I think that more study should be done at some point. If the Ortelli and Capello cars had been old-rules cars then the situation would have been very ugly. As it was Ortelli has a broken ankle and one hell of a story (one I'd bet he'd rather not repeat live).

[The Badger]

Originally Posted by PorscheFanNo1

Yeah, youre guessing :P

Yeah ..... sounds like your guessing too !!!

Quote from Mulsannemike : But as that yaw angle passes a certain angle the downforce drops and eventually will turn to lift (at around 35 degrees of yaw for a pre-'04 reg car, around 70 for a LMP'04 reg car) , especially if the car's roll isn't 0 degrees (add just a few degrees of roll into the windward side of the yaw and things change rather drastically).

[Mal]

I was not trying to blame the LMP regs for anything, but I was trying to prompt a discussion on it in the light of the weekends incidents and get some input from people on this site who have far more knowledge on the subject then I do.

Incidentily didn't Ben Devlin's Mazda lift in the same way at Sebring?

[jonm2]

ben delvin's crash was odd, it seemed as if the bodywork, which was knocked loose, lifted the car off the ground.

[brielga]

Originally Posted by dazbaz_99

Capello's incident I have only seen from the in-car camera, but it looked like his car didnt lift up until it had hit the armco once or twice, so surely this was a factor in unsettling the car.

Dindo also "clipped" the Rollcentre Pesca as he moved to the right (you can see the clear change of direction in the video). This clearly contributed to the take-off. I could ask Vanina for more details since she was driving the Pesca but I think that one is clear, Dindo pulled a similar one on one of the Lizards at Sebring but a GT car has a different shape clearly which won't tilt the Audi sideways.... On the JCW one clearly the car lifts from the kerbstone hit and then gets sideways increasing the lift but almost immediately gets back on the ground. The Ortelli one is also one where the car lifts after getting sideways and the grass does not reduce speed as e.g. a gravel trap would do (even if that could have other negative effects as well). At that speed as well, losing all the downforce on that very fast sector increases the force of the lift causing that undesired effect. I think the strength and safety of the car is commendable and Stéphane was lucky to land with the bottom end on the car on the barrier. I stand to be corrected in all cases clearly but imho it had some similarities to Villeneuve's fatal accident at Zolder even when that one was caused by rotation differential in the touching wheels (Vielleneuve's front and Mass' rear) and the amplified lift cause by the wing car shape.

[deggis]

Ralf Jüttner's opinion:
http://www.gt-eins.at/cms/index.php?...=2588&Itemid=1

Google translator didn't work so well but here's a summary from a nother forum and this is pretty much all he said:

He thinks the 2004 regulations work very well still today. The huge ride heigth looks very ugly to him if you see the cars side, but it led to a dramatic reduction of the risk getting air underneath.
With the old LMP900 regs those cars would've been flying very high, higher than people could look.
For him, ACO has done a good job, but you can't take away the 10m² underbody, so if it goes sideways and probably over bumpy grass a car will still fly at those speeds.

[RaiseYourFist]

Would side skirts help in not getting so much air under the underbody when its going sideways? I doubt we will ever see them again but if it was for safety reasons they could potentially think about it.

[The Badger]

Wouldnt that be ground effect ..... to some degree ?

[GTfour]

Ofcourse there's a solution to this problem! Limit the cars topspeed to about 200km/h or 120 mph,minimum weight of about 1500 kilos and we'd be rid of this problem...

Let's face it,speeds of 200 mph will cause a car to go flying when it goes sideways. DUH!
All is being done to keep them glued to the tarmac by using downforce and groundeffect,but it is logic they'll go flying when that balance is being disturbed!
Hell,a 747 gets airborne at around 260 kph,so unless we'll bring down the speed of our beloved cars to ludicrious low's,we'll forever battle this problem.

It's a part of racing. One know's when one goes blasting of at speeds of 150mph+,that there's a risk! And let's face it,that's part of the attraction of the whole thing,the risk of it all.

We could ofcourse make reallife Scalectirx tracks,were the car's would be secured to the tracks and they'd never ever leave the track and crash...