They say a person’s character is shaped by their surroundings. And you might well say the same about automotive technology: The art of the engineer is shaped by the technical possibilities available. One of the major technical objectives over the course of the 20th century was to increase speed. In the 1920s and 1930s, for example, the automotive sector benefited from increasing road construction and a deepening knowledge of how wind resistance influences and limits the speed of vehicles.
In Germany, it was only in the 1920s that racing and test circuits were constructed whose layout and surface consistency made high speeds possible. The Avus circuit in Berlin, opened in 1921, was the first road in Europe intended exclusively for passenger cars, and in 1927 the spectacular Nürburgring race course was inaugurated. During this decade and the next it was aerodynamics – measures for overcoming wind resistance – that increasingly dictated maximum and constant speeds, and therefore the chances of victory. The aviation sector was also a significant source of innovation during this era, as aerodynamic design and advances in lightweight construction were necessary prerequisites for successful aircraft. And automotive engineers would benefit tremendously from this technological progress.
Speed and comfort
Mercedes-Benz was a dedicated and successful participant in the race for greater speed. Indeed, in the inaugural automobile race on the Nürburgring on June 19, 1927, the brand achieved a double victory with Rudolf Caracciola and Adolf Rosenberger driving the Mercedes-Benz Model S. Less than a decade later, the first grand era of the Silver Arrows showed how far the aerodynamic aspects of vehicle design had already come. Meanwhile, a unique automobile built by the special-vehicles department in Sindelfingen, Germany, in 1938 was likewise created to compete at the highest level. The purpose behind the development of the Streamliner was to produce a race car for the Berlin–Rome long-distance race scheduled for late summer of 1938. The desired attributes of this car were high constant speeds accompanied by a high level of long-distance comfort for the occupants – characteristics that describe modern luxury-class cars to this day.
One of the strongest horses in the stable was chosen as the basis for the long-distance contender: the Mercedes-Benz 540 K, Model W 29, produced from 1936, with its 5,401-cc eight-cylinder inline engine. Its constant output was 115 hp, and the selectable Roots blower (a kind of super-charger) made a peak output of 180 hp possible. The special-vehicles department in Sindelfingen designed and produced a special aluminium body in the quest for more speed. Its aerodynamic shape was a necessity for fast driving on highway stretches, and use of this lightweight material was also conducive to the desired level of performance. With this 540 K Streamliner, Mercedes-Benz temporarily reached a zenith in the design of aerodynamically efficient road vehicles.
The new “Model 500 with supercharger,” the W 29 known as the “Autobahn Courier,” had already been presented in March 1934 at the International Automobile and Motorcycle Show in Berlin, with a striking coupe body. The brochure described it as “a special version built for particularly high speeds.” Until the presentation of its successor, the 540 K, in Paris in October 1936, further one-off examples of the 500 K with streamlined bodies were produced, one of them for a customer in the Dutch East Indies, or present-day Indonesia. The special-vehicles department was also responsible for building these unique bodies, and they bore the coveted trademark “Sindelfingen coachwork.”
One of the major challenges for the Sindelfingen stylists – the term commonly used for designers at the time – working on the 500 K and 540 K models was the very tall radiator grille, which was to remain a distinctive feature of Mercedes-Benz models right up until the 1950s. Integrating this into a functional, visually appealing body was one of the feats they achieved outstandingly in the 540 K Streamliner of 1938. Present-day aerodynamics and design experts such as Professor Ralf J. F. Kieselbach emphasize that the body shape not only represented state-of-the-art aerodynamics at the time in every detail, but may well have had a strong influence on later developments. Professor Kieselbach points out that the front wings with integrated headlamps already anticipated the frontal appearance of the 300 SL of 1954, which was based on the 1952 race car. There is another parallel in the fact that the W 198 I Gullwing series likewise combined top performance with the comfort level of a roadgoing passenger car.
As it turned out, the 540 K Streamliner did not take part in the Berlin–Rome long-distance race for which it was intended. During the short development time available, it became clear that not all the desired attributes were achievable. At the same time, an alternative use for this one-off example presented itself: On December 23, 1937, the tire manufacturer Dunlop ordered a Mercedes-Benz 540 K from the Daimler-Benz sales subsidiary in Frankfurt/Main. The company wanted to use the high-performance car for tire testing, as the newly introduced autobahns allowing increasingly higher speeds made it necessary to produce innovative tire designs particularly for powerful, heavy and fast automobiles.
A high-performance car for testing tires.”
On the basis of the preparatory work already done, the special-vehicles department formed in 1932 and managed by engineer Hermann Ahrens produced the design specifications for the aluminium body of the Streamliner in February 1938. A model of the bodywork had already been tested in the wind tunnel – a method that first became available in the 1930s. Ahrens, who had already worked in the automotive industry, had come to the attention of Daimler-Benz as a designer who was able to combine function with visual appeal, and whose vehicle bodies had won numerous prizes.
The Streamliner was delivered to Dunlop in June 1938. A Dunlop brochure from the same year describes the test activities as follows: “Our experiments with a fast, supercharged car of streamlined design on the public motorways to study the performance of the tires at high continuous speeds are a special part of our test program. The vehicle is driven constantly with changes of driver, at a speed of around 170 km/h. Breaks are only taken to refuel and to change drivers.” The brief initial career of the 540 K Streamliner came to an abrupt end, however, with the outbreak of the Second World War, as civilian vehicle development ceased for all practical purposes.
The resurrection of this vehicle in early summer of 2014 was hardly less spectacular than its development history in 1938. Fragments of the car, which was disassembled after 1945, had already been found in the Mercedes-Benz Classic collection in 2007. After extensive research in the Mercedes-Benz Classic Archives and the unearthing of important design drawings, work on reconstructing the car commenced in 2011. In May 2014, the one-off example was presented to the public.
Wind-tunnel tests conducted at the plant in Untertürkheim – this was the first time that the Streamliner was aerodynamically evaluated following its construction – had previously shown an excellent drag coefficient of 0.36. This confirmed two things: first, the all-round efficiency of the 1938 design, and second, how perfectly Mercedes-Benz Classic had reconstructed the car over a period of almost three years. In mid-2014, driving tests were conducted on the test track in Papenburg. Shod with Dunlop tires and with the Roots supercharger in operation, the Streamliner achieved a top speed of 185.57 km/h – almost exactly the 185 km/h calculated by the engineers working under Hermann Ahrens in 1938.