Wolfgang Appel - On The Audi R10

The Audi R10 will make its race debut in this weekend’s Sebring 12 Hours. Alan Lis spoke with Audi Sport’s head of chassis design Wolfgang Appel (below right) about the project.

Did the start of design work on the chassis have to wait for a decision on which engine configuration would be used?
“We started work on a chassis for a car with a gasoline engine when we made the first sketches for the R10. In the spring of 2004 it was decided to use a diesel engine. The R8 was a successful gasoline engined car so at the beginning of the R10 project we planned a V8 gasoline engine car.”

The decision to use a diesel V12 in place of a gasoline V8 must have meant big changes in the design. Did you have to start again?
“It’s impossible to fit a V12 engine in the space for a V8 in a well made racecar, so it was a complete redesign.”

The V12 diesel engine is longer and heavier than the V8 engine. Given a free choice what engine would you prefer?
“From the viewpoint of the chassis design and aerodynamics you would always go for the smallest engine package – a V6 or maybe something even smaller. Of course that was not an option when it became clear that we would be using a diesel engine. In the end I was not really happy with a V12 engine but to make the diesel step – and it really is a step, to build a racecar to completely design to use a diesel engine – the only option was to go with a V12. It was the best solution from the engine side. So I accepted it.

When was the chassis design completed and when was the first monocoque finished?
“Like any racing project we kept working in the wind tunnel for as long as we were able to and the design was changing because of that. The first monocoque was ready at Audi Sport in the middle of November 2005 and to do that, development of the chassis design would have stopped one or two months before.”

What were the effects of the aerodynamic rule changes like the stepped underside and the twin roll hoops on your work?
“I was not very happy about having to accommodate two roll hoops on the car but they were part of new safety regulations on which we worked very closely with the ACO and it’s the same for every competitor. For the R10 we decided to make the two roll hoops very sharp and small and make no hole in the structure. They affect the rear aerodynamics to some degree but not as much as we were expecting. In the end we lost less downforce than we thought we would. Under the new rules the rear diffuser is bigger and there is more downforce generated under the car than on the R8, which compensated for the loss with the roll hoops.

Was there a change in the aerodynamic balance compared to the R8?
“Not really. With the new regulations the ACO’s intention was really to cut overall downforce by about 15% and increase drag by 10%. From our side we worked to be as close to the R8 in terms of downforce, drag and balance as we could be.”

Is the longer wheelbase of the R10 purely to accommodate the longer engine?
“Not only that it also affects the aerodynamics of the new car. We also changed the size of the front tyres.”

Why did you do that?
“It has to do with the balance of the car. You have to balance it on the weight distribution, on the aero distribution and on tyre wear.”

What are the ‘new technologies’ used in the monocoque?
“The materials are the same as those used in Formula One, high strength carbon fibre and Kevlar. What is new for us is that the monocoque is a single piece. Previously the monocoques were built in many pieces, which were bonded together to build the main chassis structure. Also new for us on the R10 is that most of the outer skin of the monocoque is also the outer skin of the bodywork. On the R8 we had a full set of body panels to cover the complete car.

Which parts of the R10 are add-on panels?
“There is a front body section incorporating the front wheel arches which attaches to the bulkhead at the front of the footbox. This is a crash cone that is mounted onto the front of the monocoque by pins, like on a Formula One car. Moulded into the sides of this cone are the legs that support the front wheel housings. Above that split line where the cone is attached to the monocoque is a hatch that gives access to the front suspension rockers and dampers.
“The ducting for the side mounted coolers are very stiff parts that are part of the monocoque and there are only sidepod covers and then there is a conventional tail section that covers the engine.”

Was the use of fewer body panels necessary to save weight to compensate for the heavier engine?
“Absolutely, we did everything we could to save weight and to be within the minimum weight limit. The V12 engine is bigger and heavier than a V8 so we had to do this. Having fewer body panels means that you save a lot of weight but on the other hand that means that you have to fix the aerodynamic shape of the car and if you want to change something you will be changing structural parts of the car which is a disadvantage.

So if you make changes to the aerodynamic shape of the R10 you may need to re-do the crash tests?
“Yes, in fact we would have to build a new car to make aero changes…”

Let’s hope you got it right….
“Yes, I hope it’s good enough!”

The R10 has torsion bar front and rear suspension. Is this for packaging reasons?
“For packaging and also for less friction in the dampers. With torsion bars you can pretty much eliminate side forces in the dampers and reduce friction that way.”

How many dampers are used at each end of the car?
We have three dampers at the front and three at the rear.

What have been the effects of having to accommodate a heaver power train? Has the front:rear weight distribution changed?
“A little bit. The centre of gravity is nearly at the end of the monocoque so with the new wheelbase we have ended up with a proper weight distribution that is not far from ideal. That was another reason for the longer wheelbase.”

Has the weight saved by deleting body panels allowed you to shift weight, as ballast, forwards to counterbalance the added weight of the engine?
“Yes, to a small degree…”

Was the increase of the LMP1 minimum weight limit by 25 kilogrammes a help to the R10?
“For the R10 project of course it was a good thing but I would say that it would have been possible to reach the old 900 kilogramme limit with the new car. The extra 25 kilogrammes is a help to us because it allows us more room to play with weight distribution.
“On the other hand I am not happy that there is now a rule that says that air conditioning is necessary for closed cars. I think a better solution would be to limit the temperature and to allow the technicians to do what they want to reach that temperature. I don’t think there is a need for air conditioning. In the DTM we did a lot work in investigating how to cool the driving compartment. It is possible to do it properly without using air conditioning.”

Is the R10 gearbox lighter than the R8 gearbox?
“That’s correct, but of course the R8 gearbox was originally designed in 1998 so that we could race with it in 1999. In the meantime we have gained a lot more experience, which has gone into the design of the R10 gearbox.
“For the new gearbox we have used different materials and technologies and have ended up with a lighter gearbox despite having to handle more torque.”

What are the differences between the R8 and R10 gearboxes?
“We switched to an aluminium casing for the R10 gearbox, the R8 gearbox had a magnesium casing. For the R10 project our aim was to go to a very stiff aluminium casing because of the extra torque but to avoid adding weight we have used thin wall aluminium casting techniques. An unusual side effect of that is that it’s a really loud gearbox. When the car is idling the noise from the transmission sounds terrible!”

To cope with the torque you have larger stronger gears and shafts in the gearbox?
“I don’t want to say too much about the gearbox because it’s one of the key points of the diesel car technology. It was not easy to reach the weight but from all the endurance testing that we have done on the test bench the new design seems to work very well.”

How has the Megaline pneumatic gearshift system changed to handle more torque?
“One of the main changes was devising a new strategy for the power cut because there is no ignition system on a diesel engine. We had to learn a lot about this working with Megaline.”

The clutch is ceramic?
“That’s right. A normal small diameter carbon clutch would not handle the torque.”

With the wider torque band of the diesel engine were you able to design the gearbox with fewer gears?
“We have designed to the R10 gearbox to use five speeds instead of the six gears of the R8 gearbox.”

How does using a diesel engine affect the provisions you must make for cooling?
“The turbocharging system for the diesel engine uses more boost pressure than for the R8 so we have to handle higher temperatures. So we had to change the cooling concept and use bigger water coolers than we used on the R8.”

This accounts for the larger apertures in the body to feed air to the coolers?
“Yes we used the Bentley idea of flowing air through the front suspension to water radiators and intercoolers.”

Is the engine still a stressed chassis member?
“Yes, as in the R8 the engine is fully stressed.”

If the engine is a stronger structure because of the internal pressures it must withstand as a diesel power unit does this make the overall chassis stiffness of the R10 greater than that of the R8?
“In principle that is probably correct but of course there are four more cylinders in the engine which makes the car longer so I think we’ve ended up with the same stiffness as the R8.”

Alan Lis is the associate editor of Race Tech magazine and this interview was part of the research for an in-depth article on the Audi R10 that was published in the February 2006 issue of Race Tech (www.racetechmag.com).