Aerodynamics in the R18 e-tron quattro That a car has to be aerodynamic is a fact that applies to both motorsport and series-production vehicles – after all, the air is a source of Scan the QR code and experience the highlights of Le Mans 2013. extreme resistance. Nevertheless, engineers face very different parameters in the two disciplines. The fascination of form is accompanied by concrete and highly differentiated demands for everyday and racing applications. AIR TIME

154 Encounter Technology 159 Encounter Technology The Calm of the Victor The R18 e-tron quattro has secured its place in Audi’s – as it looked when it crossed the line, complete with battle scars. With two Le Mans victories in succession, the LMP1 prototype has written motorsport history. It is still competing in the World Endurance Championship, but will reach the end of its career at the close of the season. Text Alexander von Wegner Large volume The original dimensions for the width, length and height of the rear spoiler 2,000 × 400 × 150 mm

Considerably smaller The cd figure is one that every car driver The current maximum measurements for the spoiler Audi went one step further with the R15 TDI, which has surely heard of. It represents the co- set a new distance record at Le Mans in 2010. “The extremely efficient of drag generated by a body and is measured in the wind high nose enabled us to guide the air along the underbody with tunnel. Multiplied by the frontal area, it delivers the resistance 1,600 × 250 × 150 mm very little turbulence. That helps with the ground effect, i.e. the index of a car. The aim of the engineers is to optimize this figure. suction generated by the underbody,” says the expert. In motorsport, too, the airflow around a car should be as effi- 2006 But improvements aren’t always forthcoming. The cient as possible. The frontal area, however, plays a secondary aerodynamicists have repeatedly had to accept restrictions. role. Far more important is downforce – the force that pushes Audi With the introduction of diesel direct injection in the Audi R10 the car onto the track and thus permits higher cornering speeds. R10 TDI TDI in the 2006 season, the cooling requirement increased by Aerodynamicists are working continuously on the optimization around 30 percent as a consequence of the different combustion of first-class race cars like the e-tron quattro, with which process. The R18 e-tron quattro, introduced in 2012, also has a the brand celebrated its twelfth Le Mans victory. The aim of the low-temperature circuit for cooling the hybrid system – present- engineers is to generate more downforce without increasing ing a further challenge. Nevertheless, no Audi LMP drag – through new ideas for spoilers, bodyshell, underbody or has ever been as aerodynamically efficient as the current hybrid the diffusers front and rear. sports car. The scale of the development steps is apparent when French Revolution – the 2006 season saw a Again and again, existing freedoms are also limited you take a look at the first and the most recent Audi sport pro- diesel sports car win the by the regulations. When the project began in 1999, the rear for the very first time. The Audi R10 TDI totypes. The aerodynamic concepts could hardly be more differ- spoiler was permitted a maximum volume of 2,000 mm (width) with its was designed from scratch. ent. The open from 1999 compared with the closed × 400 mm (length) × 150 mm (height). Today, the figures are R18 e-tron quattro – they have absolutely nothing in common. just 1,600 × 250 × 150 mm. Audi has managed to reclaim a large At the start of the LMP project, Fondmetal Techno- proportion of the downforce lost with a host of individual solu- logies was Audi’s aerodynamic partner. The engineers carried tions such as the suspended rear spoiler introduced on the R15 out airflow testing in Italy with a 40-percent scale model. At the in 2009, which enables significantly better airflow around the time, models of this kind had made from carbon fiber that spoiler. By comparison, downforce drops considerably if the were fixed from the outside. “The state-of-the-art is complete- spoiler supports are mounted beneath the wing. The new fasten- ly different today,” explains Axel Löffler, who was responsible 2010 ing principle spawned a large number of imitators. for aerodynamics for many years as Head of /Bodywork The stipulations for the underbody have also Engineering. Jan Monchaux took over this role in 2013. “We now Audi changed enormously. Since the Audi R10 TDI (2006), the profile work with 60-percent models. Thanks to the rubber tires of R15 TDI cross section has to rise to the flanks at an angle of seven de- today, we are able to simulate the airflow around the model far grees, while a central wooden panel beneath the chassis is now more realistically. A movable floor in the wind tunnel likewise part of the regulations. Since 2012, the rules also call for con- helps achieve more exact measurements. We are also able to 1999 spicuous openings above the wheels, as well as a fin on the back fit the models with fully replicated, moving suspension compo- of the race car. These are intended to prevent a car from lifting nents.” Audi R8R off if it turns side-on at high speed, allowing the airflow to hit it The fundamental aerodynamic concept between the from the side. Under normal, head-on driving conditions, of individual generations of the LMP race cars from and New record – the Audi R15 TDI with its radically course, these openings don’t benefit the aerodynamics at all, in has developed considerably over the years. In the changed aerodynamics, the V10 TDI engine fact restricting clean airflow across the top of the body. R8R from 1999, the engine radiator still lay flat in the front end. and innovations such as its lithium-ion battery Despite this kind of restriction, a modern LMP sports The warm air escaped through the hood in front of the cockpit broke a 39-year distance record at Le Mans. car achieves a huge amount of downforce. Theoretically, it could opening, flowing in part over the cockpit, as well as to the left drive at high speed along the roof of a tunnel without falling. and right. In order to achieve better airflow around the rear end The aerodynamic loads at play here prove very insightful. The and its spoiler, Audi integrated water and charge air coolers into First outing – Audi began a new era in motor- front diffuser and the rear spoiler together generate half of the the side boxes of the next to the cockpit as of the year sport with its 1999 Le Mans debut. The R8R was downforce, while the underbody and the rear diffuser account the brand’s first LMP racing car. 2000. “This significantly improves airflow,” continues Löffler. for the other half. This downforce works against an unavoidable “And it gave us new latitude at the front end. We were able to lift generated by the airflow around the cockpit and over the direct the air from the front diffuser far more cleanly.” bodyshell. It equates to roughly a quarter of the downforce pro- 2000 duced. Audi R8

Outright winner – the Audi R8 with considerably modified aerodynamics and a host of new details made its debut in the 2000 season. By 2005, it had won the 24 Hours of Le Mans five times.

160 Encounter Technology 161 Encounter Technology The Beauty of Function The race car aesthetics are particularly apparent at the front of the Audi R18 e-tron quattro – here, the front right wheel arch. Slender CFRP sections guide the air, while the large splitter generates downforce at the front axle. Solutions like this are also attractive for Audi’s series-production design.

162 Encounter Technology 163 Encounter Technology With more than 650 hp 2013 In 2006, the Audi R10 TDI at Le Mans achieved a lap time of Audi 3:31.211 min R18 e-tron quattro

Just 490 hp “The regulations have progressively limited our free- The current Audi R18 e-tron quattro circled the track in dom quite considerably,” sums up Axel Löffler. “Before, we were able to implement the desired configurations for fast tracks like Le Mans and for slow road circuits in the American Le Mans 3:22.746 min Series with a single bodyshell variant. The narrow scope now forces us to optimize a car for one set of requirements only, which is why we produced a variant of the R18 e-tron quattro with a longer rear end specifically for Le Mans 2013.” The longer rear end is just the most visible change. The entire aerodynamics of the hybrid sports car were changed for Le Mans 2013 in order to accommodate the specific require- Better in the long run – the Audi R18 e-tron quattro that ments. The extreme nature of the conditions can be illustrated won the 24 Hours of Le Mans in 2013 had an aerodynamically in numbers – this year, Audi works driver André Lotterer drove optimized bodyshell with a long rear end. the fastest lap at the 24-hour race at Le Sarthe, reaching in the process an average speed of 242 km/h. This kind of speed is possible on no other track in the FIA World Endurance Cham- pionship (WEC). The engineers repeatedly find ways to improve aero- dynamic efficiency, i.e. the relationship of downforce to drag. This quotient expresses how much the aerodynamicists have improved the downforce of the race car without increasing drag by the same degree. Since 1999, Audi has increased the aero- dynamic efficiency of its LMP sports cars by around 65 percent. “The extent of this aerodynamic progress is evi- dent in the lap times,” emphasizes Audi’s motorsport boss Dr. Wolfgang Ullrich. “Naturally there are a great many other influ- 2011 Le Mans Development steps – CFD calculations prove encing factors – drive, tires, chassis, ultra-lightweight design that the suspended rear spoiler first used and weight distribution. Just as a comparison, the fastest lap at Audi New Rules for 2014 in 2009 (above) was considerably more efficient. Le Mans in 2006 was 3:31.211 minutes. The R10 TDI had 12 R18 ultra The extra winglets were added to the rear cylinders, a displacement of 5.5 liters and, with more than 480 spoiler in 2013 (right). kW (650 hp), was our most powerful LMP sports car. This year, the best lap time was 3:22.746 minutes. Our cars were more than eight seconds faster. The V6 TDI engine in the Audi R18 e-tron quattro, however, was allowed a maximum displacement As of 2014, a completely new conceptual approach ap- of just 3.7 liters and had an output of around 360 kW (490 hp). plies in the world of LMP sports cars. For the first time, the focus is A substantial part of this progress is attributable to optimized Ready for the future – the closed Audi R18 no longer on the restriction of power output. Instead, the regula- aerodynamics.” ultra sports car has been delivering considerably tions define race cars entirely on the basis of efficiency. Displace- improved aerodynamic efficiency since 2011. ment, number of cylinders, the permitted volume of intake air and fundamental aspects of forced induction have been largely opened up. The limitation is now on the available amount of energy per lap, 2012 which is down by up to 30 percent. In addition, the registered ve- hicle manufacturers must opt for one of four classes permitting Audi varying degrees of recuperated energy. The maximum amount of R18 e-tron recovered energy that can be used in any one lap is now 8 mega- quattro joules, up from the previous Le Mans figure of 3.5 megajoules. Works race cars must use at least one and up to a max- imum of two hybrid systems. The winner is the one who builds the most efficient car and travels the farthest with the pre-defined amount of energy in a given time, i.e. drives the fastest. LMP1 pro- totypes like the Audi R18 e-tron quattro will also look significantly Quantum leap – the R18 e-tron quattro continues different next year. Much narrower wheels and an overall width the aerodynamic ideas of the previous year. The reduced by 100 millimeters will give the top race car class in Le revolution was in the hybrid drive, with the front Mans and the FIA World Endurance Championship a very different axle powered temporarily by electricity. appearance.

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