Five more weeks until the Le Mans 24 Hours celebrates its 90th anniversary. Over the period of 14 years, Audi has won this classic race eleven times and in doing so has consistently been delivering top performances in aerodynamics as well. They are a major reason for excellent lap times being achieved again and again despite the reductions of engine output due to the regulations.
A look at Audi’s first sports prototype is quite revealing, as the
concept of the Audi R8R from 1999 clearly differed from the current R18
e-tron quattro – not only because the first race car had an open cockpit
as opposed to the closed one of the current car.
On the road from the past to the present, not a single aspect of aerodynamics has remained untouched:
- The radiators of the R8R engine still laid flat at the front end. The warm exit air escaped from the hood in front of the cockpit opening and partially flowed across the top of the cockpit and to the right and left. To optimise airflow to the rear end, including the rear wing, Audi has been integrating the radiators and intercoolers into the sidepods as of the Audi R8 (2000). This clearly improved the airflow.
- The introduction of diesel direct injection in the Audi R10 TDI in the 2006 season, due to the different combustion process, increased the cooling requirements by around 30 percent. Furthermore, the Audi R18 e-tron quattro, which has been fielded since 2012, has a low-temperature circuit for cooling the hybrid system – which poses an additional challenge. Still, no other Audi LMP sports car has ever been as aerodynamically efficient as the R18 e-tron quattro.
- With the innovative micro-tube radiator, Audi managed to make a major step ahead. The conventional aluminum louver-finned radiator that creates high aerodynamic drag is now a thing of the past. The coolant in the R18 e-tron quattro flows through a system made up of more than 11,000 small tubes per radiator, and the radiators no longer require fins. These radiators can be freely configured. With the same radiator size, the pressure drop of the airflow can be reduced by more than 25 percent. Alternatively, with pressure conditions remaining the same, the size of the radiator can be reduced accordingly.
- With respect to the ratio between downforce and aerodynamic drag, Audi has continually optimised the LMP sports cars. This ratio expresses how much the aerodynamicists have improved the race car’s downforce without a corresponding increase of aerodynamic drag.
- Audi achieved these advances despite the fact that the regulations have increasingly restricted the latitude for the aerodynamicists. For example, when the project was launched in 1999, the rear wing was allowed to fill a maximum volume of 2,000 mm (width) x 400 mm (length) x 150 mm (height). Today, these dimensions have been reduced to 1,600 x 250 x 150 mm. Through a large number of individual solutions, such as the rear wing suspended from the top (in use since the Audi R15 TDI in 2009), Audi has compensated for a major part of the lost downforce. It allows significantly improved airflow to the wing. This principle was subsequently used by many others too.
- The specifications for the underfloor were significantly modified as
well. As of the Audi R10 TDI (2006), the specifications have been
requiring a seven-degree increase of the profile cross-section toward
the sides and a central wooden board being mounted underneath the
chassis. Despite such
limitations, a modern LMP sports car achieves downforce levels that would theoretically allow it to run on the ceiling of a tunnel without falling down. - The distribution of the aerodynamic loads on a sports car, for instance, harbours surprising elements, such as the front diffusor together with the rear wing generating half of the downforce, as does the underfloor with the rear diffusor. This downforce is counteracted by the inevitable lift that is generated by the airflow around the cockpit and above the body. It equates to around a fourth of the downforce value.
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