Improving aerodynamics with aftermarket parts

[the bruce]

Windkanal: Aerodynamische Balance

8 von 10 Punkten
    Fahrzeugstirnfläche (A): 2.170 m²
    Luftwiderstandsbeiwert (cw): 0.33
    Luftwiderstandsindex (cw × A): 0.71
    Vorderachse: 10 kg Auftrieb Hinterachse: 23 kg Auftrieb

Der mit auffälligem Powerdome auf der Motorhaube sowie angemessen ausgestellten Kotflügeln auf sich aufmerksam machende M3 tritt mit etwa demselben cw-Wert an wie die  bisher sportlichste M3-Variante, der CSL. Die Hilfsmittel zur Reduzierung des Auftriebs bei hohen Geschwindigkeiten sind dafür etwas dezenter ausgefallen. Der auf der Kante des  Kofferraumdeckels platzierte Gurney hilft, die ungewollte Wirkung des Fahrtwinds auf ein vernünftiges Maß zu reduzieren. Das Heck wird bei 200 km/h um lediglich 227 Newton entlastet. An der Vorderachse wurde ein noch geringerer Auftrieb, nämlich nur 102 Newton, registriert.

cd: 0.33
cd x A: 0.71

lift:

front: 10 kg
rear: 23 kg

[fuscobal]

Interesting to see how much lift can even super spot cars have. This is probably due to the fact that they want to keep the ground clearance as decent as possible for street use. Also, by protruding with an air-dam or splitter further away to the front wheels you have a bigger chance of hitting on a ramp !

[sub39h]

i read somewhere that the PQ34 cars had problems with drag due to air collecting in their engine bays. the TTs however had vented wheel arch liners to vent this air and improve the drag.

is this something that the PQ35 chassis cars are also afflicted with? OSIR do vented wings for the A3 8P that i've considered purchasing when i next go over to the USA but i'm wondering if it's actually worth the trouble/expense?

[the bruce]

Great read:

http://www.google.de/imgres?q=OEM+Underbody+Aero&hl=de&client=firefox-a&sa=X&rls=org.mozilla:de:official&biw=1366&bih=637&tbm=isch&prmd=imvnsfd&tbnid=fwiOnIhJWk8ikM:&imgrefurl=http://www.rx7club.com/showthread.php%3Ft%3D873466&docid=kL9oEOrXUkJBOM&imgurl=http://www.madpsi.net/Aero-kits/MadPSI/Rear%252520Diffuser/Madpsi%252520-%252520F430%252520Underbody.jpg&w=640&h=395&ei=15KcT4StN4fEsgaM-tlK&zoom=1&iact=rc&dur=441&sig=106977374515276114731&page=4&tbnh=112&tbnw=181&start=66&ndsp=24&ved=1t:429,r:18,s:66,i:255&tx=82&ty=43

[fuscobal]

Good read indeed. For our Golfs there aren't any options for a full underbody. Just took a look under the car several days ago and the cat + horisontal exhaust pipe are lower than the 2 horisontal flat sides so in order to install a full underbody wich can probably be made quite easy from flat panels, you have to lower the entire underbody by about 3cm. Then, for the rear diffuser, the rear muffler (resonator) stands in the way and is lower than the rear bumper (in my case at least). I've looked there and there is no space to move it upper so it has to be much flatter than already is to allow a diffuser to go under it. A better option is to simply remove it and stay with only the pipe but the noise will probably be too much for me !

[rex]

Fuscobal... I looked at the under carriage. If we just give up the rear muffler and possibly install another muffler in the center of the car we might just install a diffuser and not make so much noise...

[Richn83]

I think you can manage a couple of panels on the rear to cover the areas by the fuel filter and the first muffler for a start by using aluminium panels that aren't heat dependant you could improve the flow and another sheet could extend from this out between the rear suspension arms over the exhaust, it doesn't have to function as a diffuser it just has to smooth the flow to reduce the rear lift

If you can also create an amount of expansion by creating an angle to expand the air flow to reduce drag all the better and add some small ridges to control the lateral movement of the air then that is all the better I think it isn't that difficult rear fixing could also be metal strap fixed to the exhaust rear muffler.

[rex]

Guys.. why is the exhaust so long? Is there any reason why it shouldn't stop where the diffuser begins?

[the bruce]

Yes. Otherwise it would burn the diffusor.
There also may be some reasons dependent on the rules (RCN).

[Richn83]

Bruce your friends car in the picture does it have the standard fuel tank or a race version, just wondering if he has fitted that panel flush under the fuel tank.

You don't have more pictures of the whole underside?

[the bruce]

ATL Fuel Cell - keep in mind it's a diesel.

http://www.erft-racing.de/fahrzeug.php

http://www.erft-racing.de/galerie_bilder.php

Unfortunately I couln't fid any additonal pics that show the underside, but I guess the above pic
shows most you need to know.

 

[the bruce]

Looks like serious downforce: 

[mkviken]

Looks way too much for a FWD car. The drag must be terrible too!

[fuscobal]

Awesome pics Bruce. Do you know the chord and span of those wings ?

[rex]

Ha ha... I also saw the Scirocco Cup cars in last August.
The rear wing is not adjustable and the chord seems to be somewhere around 150 - 170.
Personally I do not like those rear wings.