An installation with history
- In 1939 one of the first installations for measuring full-scale vehicles
- Building and original conceptual design remain intact and in use
- Embedded in the development activities of Daimler AG
Building on experiences gleaned from aeronautical engineering, aerodynamics played a growing role at the beginning of the 1920s in the worlds of technology and vehicle manufacturing: in the ensuing two decades, countless aerodynamically optimised prototypes and race cars attracted a great deal of public attention. Edmund Rumpler’s “Tropfenwagen” (“teardrop car”), which debuted in September 1921 at the first Motor Show to be held in Berlin since the First World War, was a real sensation. It was the catalyst for the development of other aerodynamically optimised vehicles. These were built by such renowned researchers and engineers as August Everling, Wunibald Kamm, Reinhard Freiherr von Koenig-Fachsenfeld, Paul Jaray, and Karl Schlör.
The emergence of the wind tunnel at the Mercedes-Benz plant in Untertürkheim is closely linked with this trend. It goes back to Wunibald Kamm’s activity at the Technische Hochschule (TH) Stuttgart (technical university).
The graduated engineer Dr.-Ing. Wunibald Kamm worked in vehicle development at Daimler-Motoren-Gesellschaft (DMG) from 1922 to 1925. Following stints at the Schwäbische Hüttenwerke (SHW) in Aalen and the Deutsche Versuchsanstalt für Luftfahrt (DVL) in Berlin-Adlershof, he became Professor and Chair of the Technische Hochschule Stuttgart and on 15 July 1930 founded the Forschungsinstitut für Kraftfahrwesen und Flugmotoren an der Technischen Hochschule Stuttgart (FKFS) as a non-profit foundation at the technical university, in which the state of Württemberg with the Württemberg Ministry of Culture and Ministry of Economics, the City of Stuttgart, the Verband Württembergischer Metallindustrieller, the Reichsverband der Automobilindustrie, and subsequently the Reichsverkehrs- und das Reichsluftfahrtministerium (RLM) were involved.
In the period that followed, the names and statutes underwent some changes: FKFS came to stand for Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart, with the word “Flugzeugmotoren” (aeroplane engines) being replaced by “Fahrzeugmotoren” (vehicle engines). Today the institute is an independent foundation under public law in Stuttgart and is partnered with the University of Stuttgart through contracts; it receives no public funding.
It all began in 1934 with a small wind tunnel
When it was founded in 1930, the institute was located in front of the Untertürkheim plant owned by the then Daimler-Benz AG when approached from the direction of Bad Cannstatt. The plant and the institute were separated at the time by a railway embankment which no longer exists today. In the tax year 1934, a small wind tunnel with a jet diameter of 70 centimetres was installed to conduct tests on vehicle models. In addition, starting in 1935, aerodynamic resistance tests began to be carried out in the small wind tunnel and with coast-down tests using normal-sized vehicles. In the year that followed, a water-flow tunnel was built for aerodynamic resistance measurements on vehicle models.
A wind tunnel for full-scale vehicles came into existence between 1939 and 1943. Kamm recognised that with model wind tunnels, the full complexity of vehicle aerodynamics could not be measured and that research facilities for full-size vehicles was indispensable. The wind tunnel created by Kamm was a system based on the “Göttingen design” with horizontal air ducting, one closed measurement section and one measurement section three-quarters open, and 125 metres long. The air jet cross-section was 32.6 square metres and the measurement section was 10 metres long.
Although the institute was destroyed in 1944 and 1945 by air raids on the Untertürkheim plant, the wind tunnel survived, though heavily damaged. Immediately following the liberation by the French, the institute’s new director, Prof. Paul Riekert, saved the wind tunnel, which was actually slated to be dismantled, by filling it so full of vehicles and instruments that he was able to present it to the Occupation Authority as a warehouse for the institute.
By 1950, the test site at the technical university was a focus of deliberations for Dr. Wilhelm Haspel, Managing Director of the then Daimler-Benz AG. During a meeting of the Board of Management on 10 May 1950, he voiced his opinion that if any property purchases were made, the test site at the technical university should be considered first and foremost, since it already housed test beds and the wind tunnel.
Property and wind tunnel under Daimler-Benz ownership
In 1954, the company acquired from the City of Stuttgart lots on the other side of the railway embankment, on which Mercedes-Benz commercial-vehicle testing is located today, and also where the FKFS wind tunnel is found. At the same time, the FKFS was now again able to take over operations of the wind tunnel after the Second World War. From 1960 onwards, vehicle development at Mercedes-Benz began using more and more of the wind tunnel’s capacity, increasing to 40 per cent of capacity in 1970.
The wind tunnel was then acquired by Daimler-Benz AG in 1970. The FKFS retained administrative authority until 1974. The company then began a renovation project costing 8 million Deutsche mark and the modernisation of the complete installation, which took nearly two years to complete. In April 1976, the Engineering Department at Mercedes-Benz began operating the installation, now with four times more capacity.
As part of the capacity increase, a wind tunnel weighbridge, a multi-point pressure system, and a roller-type performance test rig were installed. Built into a rotating base plate, the wind tunnel weighbridge replaced the suspended balance used previously, with which the vehicle was suspended by four steel cables in an H-shaped frame, and the four steel cables were suspended by the lifting scales in the turntable. With the underfloor weighbridge now installed, the vehicle was placed on four contact plates which were fitted level in the floor of the rotating measuring plate. The contact plates were located on four individual lift scales which were used to measure the lift forces. The rotating measuring plate made it possible to simulate and measure the effects of crosswind.
In the mid-1980s, the wind tunnel was again modernised with a view to speeding up procedures and attaining more precise measurements with the wind tunnel. Thus for example a traversing system was fitted, which enabled quick and precise contour measurement, flow measurement, and front surface area measurement. For the contour measurement, which until then had been carried out using templates, photos, and measurement with measuring sticks, the contour was now measured for greater precision in coordinates with a so-called optocator (an optical-electronic diode-light laser indicator). Instead of using manually positioned probes, the flow measurement now took place with probes which automatically moved along a measuring point grid. Whereas before the measurement of the front surface area took four hours to complete with a laser procedure, it now only required between half an hour and one hour thanks to edge tracking. A further advantage was the capability of measuring full-scale commercial vehicles.
Alongside aerodynamic studies, the wind tunnel could also be used for other jobs, such as contamination measurements and measurements of the wiping precision of windscreen wipers in the high-speed range, temperature measurements at the radiator, and brakes and tests of the passenger-compartment ventilation.
Measurement installations and technical data for the wind tunnel at the Mercedes-Benz plant in Untertürkheim:
- Wind tunnel weighbridge
- Multi-point pressure system
- Roller-type performance test rig
- Traversing system
- Data acquisition system
- Length of the measurement section: 10 metres
- Length of the tunnel axis: 125 metres
- Air jet cross-section: 32.6 square metres
- Maximum flow cross-section: 120 square metres
- Maximum blowing speed: 250 km/h
- Maximum power input: 5,000 kW
- Blower diameter: 8.5 metres
- Turntable diameter: 12 metres
- Swivelling range of the turntable: 180 degrees
- Maximum axle load: 10 tonnes
- Contraction ratio prechamber/air jet: 3.6