9 replies to this topic

[Ninja2]

Afternoon Everyone

Im working on a project for a road vehicle aerodynamics course, and was wondering if anyone could shed any light on why the Audi TTs rear wing is mounted so far back on the DTM car? Is it to try to get it into cleaner air and out of the wake of the body? The car also retains a small flip up rear spoiler - is this device used to direct air onto the rear wing, or is it a downforce generating spoiler in its own right?

If it is mounted back to try to get it out of the wake, why doesnt anyone do this?

Also, GT cars like the BMW V12 LMR also have a rear wing mounted almost behind the rear bodywork - its far back, and relatively low. Why is this? It almost seems to be out of the airstream of the car....

Thanks if anyone can shed any light on this mind boggling subject

Cb

[alexbiker]

I don't know for sure this is the answer, but two things spring to mind.

1. Further back means more force on the rear tires. If you consider the front wheels as a pivot, and the back tyres x mm from the front, having the rear wing x + 1000 mm back will effectively mean a leverage advantage increasing the force exerted on the rear tires (until the rear suspension compresses enough that load is removed from the front tires).

2. Yes, cleaner air.

Remember also that many aerodynamic implementations make no sense whatsoever outside the concept of techincal regulations - it may be that the rear wing must be in a certain posistion for homologation reasons.

Alex

[Antoine]

put an eye on the rear wing of the french ST car!
they are somethimes very interesting!

here a 406 peugeot

the Seat

my car with the old rear wing


For your question:
like that the rear wing of the Audi give an aero balance more on the rear for a same load!
but it could have clainer air too and use a little bit the aero depression of the extractor...

[kilcoo316]

I have no photos of, could someone please post some, or links. But it is worth considering that placing the wing behind the car may increase the effective angle of attack, as sometimes a standing vortex will attempt to generate behind the car (although on an Audi TT, I'm really not sure), that is why a estate often posts better Cd figures than a hatchback, the hatchback has two longitudinal vortexes off the rear pillars, whereas an estate has a standing vortex behind the car. Apparently the worst angle is around 30-35 degrees or so. What angle is the audi?

[mulsannemike]

The BMW LMR ran the wing in its low position to enhance the wing/diffuser interaction enhancing underbody produced downforce. The MG-Lola also uses this solution and while it seems to actually sacrifice maximum potential downforce for drag reduction then simply reducing flap angle in a high wing situation, ultimately it makes sense for the MG as it is in a horsepower deficit compared to the more powerful LMP900 cars so drag is more of the driving factor. Same too the ideaology behind the LMR as it was primarily aimed at running at Le Mans.

[Wingman]

Well, the Audi TT-R rearwing is a special construction - as the whole car generally is because it doesn't match the DTM rules. All involved manufacturers go with their cars in a windtunnel in winter and together decide on those rear wing positions in order to have similar downforce.

The road TT has some very weird aerodynamics in general with the original design being too critical on the rear at high speeds. The curvature of the roof resulted in too little downforce which in special conditions made inexperienced drivers lose the car in the Autobahn... As a consequence Audi introduced that small flip at the rear which cured that and Abt was allowed to use it in DTM as well. And the position of the rear wing takes that odd rear construction into account, too. In 2000, the Audi TT-R was designed much more similar to the road version and had a "normal" positioned rearwing... and was about 2 seconds off the pace...

[Wuzak]

Doen't the DTM Audi have a lengthened rear end, to help fit in with the regulations.

And it was my understanding that the rear wing profiles are standard across all the makes.

[Wingman]

Originally posted by Wuzak
Doen't the DTM Audi have a lengthened rear end, to help fit in with the regulations.

And it was my understanding that the rear wing profiles are standard across all the makes.

Yeah, the TT-R has a lengthened rear end. However, if I recall correctly, it was not introduced to make it fit in with the regulations. In 2000, they ran without that special rear end as the rules were that year. After that - and considering the different bases of the Merc CLK, Opel Astra ana Audi TT - the rules were changed for 2001 which allowed modifications like this. I think the Opel was also a bit longer than before though by far not as visible than what happened to the TT.

I also think the rear wing profiles are standard, however what gets adjusted is the position where this standard profile is placed relative to the car.

[Ninja2]

Thanks for the responses on the Audi TT question, Im starting to appreciate how all aerodynamic devices interact with each other in ways that arent obvious at first!


On another similar topic, what is the purpose of the dive planes on the front corners of various race cars? Some seem to indicate they are purely for downforce generation, and others suggest they are to direct air over/around the front wheel arches.

Thanks

Cb

[Rainer Nyberg]

Originally posted by Ninja2
On another similar topic, what is the purpose of the dive planes on the front corners of various race cars? Some seem to indicate they are purely for downforce generation, and others suggest they are to direct air over/around the front wheel arches.

Don't they in fact do both?