posted on March 19, 2013 23:30
Nerd's Eye View: Going Endurance Racing With Raeder Motorsports' Audi TT RS at the Nurburgring
By Khiem Dinh
Khiem Dinh is an engineer for Honeywell Turbo Technologies at the time of this writing. All statements and opinions expressed by Khiem Dinh are solely those of Khiem Dinh and not reflective of Honeywell Turbo Technologies.
This Audi TT RS is campaigned in the VLN Endurance Championship race series run exclusively at the Nurburgring. As this car is based off the production Audi TTRS, somewhat unique challenges had to be overcome to create a vehicle that kicks ass and takes other cars’ bier money (beer for you non-German speaking folks). Follow along to see what makes this car go uber fast.
When the current generation Audi TT was released in 2008, it marked a significant change in design. The chassis is based on Audi's Aluminum Space Frame (ASF) principle with the goal of drastically reducing weight. Reducing weight is a great thing. However, you can't weld a steel cage to an aluminum chassis presenting a challenge that will be common on many newer high performance vehicles (such as the new C7 Stingray Corvette and Aston Martin Vanquish). Audi is also known for their Quattro all-wheel drive system which allowed them to demolish the competition in rally car racing back in the day. However, to make Quattro fit, the engines in Audis are often pushed quite far forward giving a front heavy weight bias. We will see how these two fundamental characteristics of the car influence the build. Of course, we’ll explore all the other cool stuff too (figuratively and literally).
|For endurance racing, you need a lot of cooling and lights for running when the sun goes down. Lights present an interesting cooling problem. They generate a fair amount of heat which gets dumped into the radiator plus the lights block airflow to the radiator. So a bit larger than normal radiator is probably needed. As for the big bumper duct, it has three hoses attached to it.
|Another view of the front end, just because. And it looks like the car ate one of the mechanics. Oh yeah, check out the intricate hood. More on that later.
|One hose from the duct goes up into the engine bay and the other two feed the front brakes. Also check out how the splitter is solidly mounted to the front steel bar.
|I'm guessing those two hoses are required to feed cooling air to the front brakes because this Audi is setup in FWD configuration. I think the front upright has to be made larger to account for the driveshaft as compared to a typical front upright on a RWD car that doesn't have a driveshaft going through it. There doesn't appear to be much gap between the upright and center part of the rotor where you want to feed cooling air, so that's my guess as to requiring two hoses. On a side note, that's a custom fabricated lower control arm. You can also see the louvers in upper surface of the fenders and the diffuser built into the under tray to aid frontend downforce.
Wednesday, March 20, 2013 12:42 AM
The rear diffuser doesn't create a low pressure zone (or downforce) in the actual diffuser, it helps evacuate air and create higher velocity before it. Depending on the design of the flat bottom, the underbody could be creating more downforce from as far forward as the front tires on a focused point, though more likely a larger, a more general low pressure zone underneath the whole of the cabin.
Also, rather than moving the wing rearward to create more understeer, my best guess is they are using the low pressure zone created under the rear wing to improve rear diffuser efficiency. The low pressure pulls more air through the diffuser, creating higher velocity farther forward under the vehicle. Because of this, setting the rear wing more aggressively might actually increase front downforce as well as rear.
Wednesday, March 20, 2013 1:39 AM
Dan, correct on the diffuser operation. I'll go back and edit it a bit.
But, I disagree on the wing placement. I think the rear wing is mounted too far back and too high to have significant affect on the diffuser performance. Compared to the wing placement on the new BMW Z4, Aston Martin, and Corvette, this Audi has the rear wing waaaay off the back. The Z4, Aston, and Vette basically have the wings mounted on the rear decklid; the trailing edge of their wings basically lines up with the rear of the car. On this Audi, the leading edge of the wing is about in line with the rear. So basically it's sitting a full cord length further back than on the other cars which are all front engine, RWD.
What are you still doing up anyways? Go to sleep!
Wednesday, March 20, 2013 8:57 AM
Haha, I should have been sleeping, work is fun this morning!
You very well could be right, this is where I wish I had more experience. When looking at the Aston Martin, the wing looks too far forward. The curve of the bottom of the wing tends to be the area of peak low pressure, not the trailing edge. In my mind, I'd want the curve to be slightly rearward of the diffuser, not the trailing edge. I do agree though, lower would probably work a lot better if that is indeed their intent.
Wednesday, March 20, 2013 9:06 AM
Hey Khiem, its been a few months... lol. Looks like all is well ;)
Anyway, I think the position of the rear wing has more to do with getting the best free stream to it considering the shape of the rear of the car. Given the position, I'm with Khiem, I doubt there is much communication between the wing and the diffuser. I will say I'm a bit surprised there is no "gurney flap" or spoiler type device on the bottom of the hatch under the wing. But it may be against the rules (not sure the ruleset) or it could reduce the efficiency of the wing enough to not be a benefit overall by increasing the air pressure under the wing too much.
Wednesday, March 20, 2013 9:31 AM
@Rara... hey, I know you! Ha :) Yeah.... I managed to not get sucked into the blackhole over here.... phew!
Wednesday, March 20, 2013 10:42 AM
Khiem - To us German speaking folk, we won't recognize your spelling because it's spelled Bier. An "ie" group of letters is pronounced "e" while "ei" is pronounced "i". Enough about German lessons! I do believe that rear wing has probably been carefully calculated to balance the front diffuser at race speeds for maximum down force, assuming I remember some of my aerodynamic principles ?
Wednesday, March 20, 2013 11:01 AM
Gosh darnit, typo, I swear ;) I fixed it though.
Wednesday, March 20, 2013 12:22 PM
This is a really interesting car. Removing the Haldex to make it FWD seems counter-intuitive at first glance. Thanks for a great article detailing some of the unique aspects of this chassis for motorsport. It is articles such as this which make MotoIQ one of my favorite automotive sites.
Wednesday, March 20, 2013 1:00 PM
Actually they alternate between FWD and AWD throughout the season depending on the race/class they are competing in... I was fortunate enough to get a ride around the Ring in this car during a practice session and it was fucking retarded fast! With a little rain on the track and Jürgen Wohlfarth (Klaus Wolfarth's (KW) brother) at the wheel we were overtaking the faster class porsche/ferarri/aston martin's with ease! Probably the most awesome thing i've ever gotten to do--I almost pee'd :)
Wednesday, March 20, 2013 3:43 PM
Where is the intercooler on this car? It appears that only the radiator is visible thru the large central duct at the front.
Wednesday, March 20, 2013 9:57 PM
@marck_c, it appears they are still using the stock intercooler. In the second picture with the car eating the mechanic, the intercooler should be in the lowest opening and set behind the radiator a bit (you can see that in the first picture taken at an angle to the frontend). The air partition that creates the smiley face looks to separate the airflow between the radiator and intercooler. If you look very carefully, the radiator and intercooler have different spacing of the tubes. This race car is only making around 370-380hp where the stock car is rated at 360. All that gain is probably from the exhaust, so the stock intercooler should be perfectly adequate. Of course, with it being stock, it has gone through all of Audi's durability testing and qualification process which should make it reliable. Perfect for endurance racing.
Friday, March 22, 2013 12:27 AM
The large blue brake pads are ENDLESS. ENDLESS have a relationship with the Audi Sport Customer racing. I'm picking either MA45B or YZ080 compounds!
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