The new Mercedes-Benz E-Class Cabriolet - TecDay Aerodynamic 2009 - PART X


Stuttgart, Germany, Dec 15, 2009

Under the microscope: the "large wind tunnel" in Untertürkheim

From the Kamm rear to AIRCAP®

The wind has been blowing here for some time: Daimler AG's "large wind tunnel" at its parent plant in Stuttgart-Untertürkheim was the first in the world to be designed specifically for analysing the aerodynamic properties of motor vehicles. The building work began in 1940, inspired by the legendary aerodynamics pioneer Wunibald Kamm (1893 - 1966), first Professor of Motor Vehicles at Stuttgart's Technical University and founder of the private and non-profit-making Research Institute for Motor Vehicles and Vehicle Engines in Stuttgart (FKFS) in 1930. The "K-Wagen" developed by Kamm between 1938 and 1941 was the prototype for an aerodynamically innovative passenger car. And the name "Kamm rear" is still used today to describe the sharp spoiler lip at the tail end.

Because of the war, it was not until 1954 that the wind tunnel became the first in the world to be used for measurements on original-size passenger cars. Since then, it has played a key role in developing the aerodynamic efficiency of the car – especially models bearing the Mercedes star. But not exclusively: up until the 1970s, the wind tunnel was operated by FKFS and was therefore available for independent research as well as being open to other manufacturers. Daimler, the current owner, was one of the most frequent tenants – much like at the new FKFS wind tunnel at the university site in Stuttgart-Vaihingen, which went into operation in 1988.

Yet the wind tunnel in Untertürkheim, which has been repeatedly further
developed to ensure that it remains state-of-the-art, is still indispensable for the Mercedes-Benz developers. Not just for optimising aerodynamic design, but also for dirt analyses, windscreen wiper trials and cabriolet comfort tests. Furthermore, the "large wind tunnel" more than lives up to its name, for it is here that the Mercedes-Benz commercial vehicles are also honed to perfection.

As well as hosting these tests, the facility is also often used for completely unrelated activities: ZDF, Germany's second TV channel, has shot film sequences for a hurricane report here; bobsleighs are optimised here; and speed skaters perfect their technique here. In short, anyone who has to work with or against the wind is welcome in Untertürkheim. Another major challenge overcome here was the aerodynamic testing of the revolutionary roof for Munich's Olympic Stadium.

Technically speaking, this is a "Göttingen-type" wind tunnel: downstream of the test section, the air is sucked into a funnel by a fan. From here, it flows back to the air nozzle upstream of the test section via a duct. This design makes it easy to control the physical properties of the air in the duct. By way of example, the entire duct and the test section can be highly pressurised or cooled down, thus improving efficiency compared to the "Eiffel-type" wind tunnel, since the kinetic energy of the air flowing out of the test section is reused.

The technical data for the "large wind tunnel" in Untertürkheim:
Maximum wind speed - 250 km/h
Air nozzle cross-sectional area - 32 m²
Test section length - 12 m
Turntable range of movement - +/- 180°
Maximum axle load - 10 t
Maximum output - 5000 kW

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