Advanced measuring device and modern methods.

The centerpiece of the 19-metre-long measuring section of the wind tunnel is the approximately 90-ton treadmill-balance system with turntable. The new wind tunnel has a five-belt system to simulate the road: a small treadmill runs under each wheel and a nine-metre-long and over one-metre-wide centre treadmill runs between the wheels. All five belts run synchronously with the wind and thus represent exactly the same conditions as on the road up to 265 km/h. The 24-ton scale on which the vehicles are mounted is extremely sensitive and measures to the nearest gram. Even the supply lines of the cables must be laid in such a way that they do not introduce any disruptive forces into the system. The values measured with the help of the aerodynamic balance serve as the basis for determining the coefficients for air resistance force, lateral force, and lift force per axle as well as pitch, roll, and yaw moment.

The traversing system enables the engineers to position various aerodynamic probes or microphones around the measuring object with very high accuracy in order to be able to carry out pressure, acoustic, and speed measurements precisely. The system in the Sindelfingen wind tunnel has seven axes and can thus cover a measuring volume of 19 x 14 x 5 metres. The weight of this system is 26 tons, because even at maximum wind speed, the measuring probes must be held exactly and without vibrations in their position.

The centrepiece of the measuring section of the wind tunnel is the approximately 90-ton (198,416 lbs) five-belt system, which perfectly replicates road conditions. Thanks to the integrated turntable with a diameter of twelve metres, the vehicles to be measured can be rotated at any angle and, for example, crosswinds can be simulated realistically.

The “Large Wind Tunnel” of the then Daimler AG in the Stuttgart-Untertürkheim plant was the world's first to be specially designed to investigate the aerodynamic properties of motor vehicles. Construction work began in 1939, driven by the legendary aerodynamics pioneer Wunibald Kamm. The first documented measurement took place on 5 February 1943. Due to the war, it was not until 1954 that the wind tunnel was the first in the world to be used regularly for measurements on original-size cars.

Always brought up to the latest technical standards, the wind tunnel in Untertürkheim is still indispensable for Mercedes Benz development, especially for contamination studies and windshield wiper tests. The aerodynamicists also still test there whether the camouflage of test vehicles is high-speed resistant. And the “Large Wind Tunnel” is not just called that: many commercial vehicles from Mercedes Benz also get their fine-tuning there.

In addition to the aerodynamic work on vehicles, the wind tunnel is sometimes also used for non-automotive tests: Whether television is filming sequences here for a report on hurricanes, sleds are being optimised for bobsleighing or ice skaters are improving their posture - anyone who fights with or against the wind will find an ally in Untertürkheim. One of the very special challenges was the aerodynamic investigation of the revolutionary tent roof of the Munich Olympic Stadium.

Mercedes Benz also operates two climate wind tunnels in Sindelfingen that move weather events indoors. The climate wind tunnels allow engineers to optimise newly developed vehicles or components for all weather conditions at an early stage. For subsequent real-world testing on roads in arctic cold and scorching desert heat, only prototypes that have already proven a high degree of maturity under the most adverse climatic influences are now launched.

One of the two climate wind tunnels is designed as a cold channel with a temperature range of minus 40 to plus 40 degrees Celsius. In the warm channel, a temperature range of minus 10 to plus 60 degrees Celsius is available. Both channels have an integrated two-axle roller dynamometer and allow speeds of up to 265 km/h - enough reserves to put even sports cars on the test bench.

A special microphone array helps with noise measurement in the acoustic wind tunnel. The extensive measurements in the interior are also referred to as “acoustic holography”. Mercedes Benz uses 64 double microphones (hand array) that can locate problem areas in the low-frequency range. Including the devices for the measurements outside, almost 500 microphones are used.

Flow measuring dummies, artificial heads and near-field microphones are used in aerodynamic and aeroacoustic development. “Tanja” is such a measuring dummy: Mercedes Benz uses ‘her’ to analyse drafts in convertibles and roadsters. More than a dozen sensors on the head, neck and arms measure the flow velocities of the airstream in the interior. “Tanja” takes care of every seat. On the front seats, ‘she’ acts as a 75 percent man, in the back as a 50 percent man. At the front, the test dummy is placed so that it is larger than 75 percent of all men. At the rear, the seating position corresponds to that of an average man.