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Rudolf Uhlenhaut, the Mercedes-Benz tech brain



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Rudolf Uhlenhaut


Mercedes-Benz W154, chassis #14


Pflanzgarten, Nürburgring


July 1938


This picture shows a unique driver as he never took part in any competitions!

In 1936 Mercedes-Benz Grand Prix effort found itself in a crisis. While Auto Union and Bernd Rosemeyer swept the track with victory after victory, the Mercedes drivers, Rudi Caracciola, Luigi Fagioli, Louis Chiron, Manfred von Brauchitsch and Hermann Lang were struggling with reliability, engine and handling problems.

To face the challenge from the new cars of Auto Union and Alfa Romeo the Mercedes factory had, for the 1936 season, constructed a new 600bhp 5.6 litre V12 unit known as the DAB. To fit this heavy engine into the cars under the 750 kg limit demanded considerable changes to be done to the 1936 cars to save weight. The new car was built with no less than a 25 cm shorter wheelbase than the old ones. Other news included a transverse gearbox and a de Dion rear axle. The new car was in fact so small that the tall von Brauchitsch could not fit into it properly, a problem most associate only with modern F1 racing.

The finished DAB engine proved to be seriously overweight. Instead a 4.7 litre 450bhp variant of the old engine known as ME25 had to be built in a hurry. Increasing a 3.3 litre design to 4.7 litre proved to be too much. During the season it was found that the blocks and cylinders were too weak to handle the strain. Completely new blocks and cylinders were manufactured for the German Grand Prix. After that catastrophic race for the team, where the best Mercedes-Benz limped home in fifth position, it was clear that radical changes had to be done to the Mercedes sporting organization.

The organization used by Mercedes in 1936 had its roots before the First World War. It was in a time where the racing drivers were picked from those who were running in the cars for the experimental department. After the death of Hans Nibel in 1934 the central design office was managed by ex-driver Max Sailer. Under him Albert Heess and Otto Schilling were in charge of the engine designs and Max Wagner of the chassis designs. The actual construction, assembly and tests of the cars were handled by the experimental department led by Fritz Nallinger. Jacob Krauss managed the chassis construction and Otto Weber the engine assembly while George Scheerer, who was in charge of the dynamometer section, was responsible for the important engine testing.

By the years the communications between the experimental department and the sporting department led by Alfred Neubauer had begun to fail. The experimental department was totally dependable on the reports the often not too technical minded or talkative drivers were sending them. Therefore a new technical department between the design office and the racing team was created in 1936. Known as the Rennabteilung (racing department) it took over the assembly and testing of the racing cars from the experimental department. Placed in charge of the new department was a gifted young engineer named Rudolf Uhlenhaut.

Uhlenhaut had joined Mercedes Benz in 1931 after having graduated from the Munich University the same year. Until 1936 Uhlenhaut had only worked on passenger cars including a construction called 170V. Now the first task for the new department was to get the cars ready for the Swiss GP. Mercedes-Benz decided not to start at Coppa Acerbo and concentrate on testing instead.

On the 12th of August 1936 the Rennabteilung assembled at Nürburgring with one rebuilt 1935 car and two 1936 cars and with Caracciola and von Brauchitsch as drivers. Tests included running with different types of tyres and shock absorbers and even with a 60kg lead weight over the front suspension to get more front grip. After two days of testing the drivers left and Uhlenhaut took over the running himself.

Uhlenhaut had never tried a race car before, even if he had become used to test the passenger car constructions at high speed. However, Uhlenhaut soon settled in and proved to be an exceptionally gifted driver, who surely would have been a competitive racer had he (and especially his wife) wanted to. It has even been rumoured that Uhlenhaut once went faster than Fangio at the 'Ring during a test sometime in the mid 50s. Of course conditions change fast at the Nürburgring between test sessions and lap times aren't always comparable. However, just the fact that such a rumour exists shows Uhlenhaut's potential.

Soon Uhlenhaut found some fundamental errors in the 1936 cars. The toe-in changes caused by the old steering geometry were too big while the suspension movement was too short making the springs to bottom and the whole weak chassis to bend during braking. The experimental department had tried to solve the problems by using both hydraulic and friction dampers and harder and harder springs making the handling problems and a violent kickback to the steering wheel that the drivers used to complain about even worse. And at the rear the attachment point for the De Dion axle could bend as much as 7-10cm during braking. Because the suspension was so stiff the wheels couldn't follow the road. Once during Uhlenhaut's tests a wheel came off at high speed yet the car continued on three wheels as if nothing had happened.

After the Swiss GP had ended in a triple victory for Auto Union Uhlenhaut suggested that further participation in racing during 1936 was useless. So Mercedes-Benz retired from the season concentrating all their efforts on the 1937 car instead.

The W125 was constructed according to the lessons learned in 1936. It was a car with long wheelbase but reduced polar moment of inertia. The frame was much stiffer and the front suspension was new with more spring travel and much softer springs than on the earlier Mercedes race cars. The car had hydraulic dampers only (it took some time for Uhlenhaut to convince the drivers that the friction dampers were unnecessary). The gearbox was changed to a constant mesh type bettering the reliability considerably. During the season George Scheerer developed a new suction-type supercharger that proved superior to its precursor.

The W125 proved to be winner, Caracciola being victorious at the German, Swiss Italian and Hungarian GPs to give him his second European Championship while Lang won at Tripoli and von Brauchitsch at Monaco.

For 1938 the new 3-litre formula brought new challenges to the racing department. The new suspension developed by Uhlenhaut's team had proved its value. The only change done to the new car was that now the hydraulic rear dampers could be controlled from the cockpit during the race. Now it was time to concentrate on the engine and the weight distribution instead. Lots of tests were done during the next two seasons with two-stage supercharging and direct fuel injection, the first eventually seen on the racing cars, while the latter had to wait until 1954. The 1938 V12 engine with its double overhead camshafts was in fact prepared for fuel injection but at the end carburettors were used.

The double carburettors incorporated all the experience gained by the DAB engine during record attempts. They featured the most advanced pre-war GP system with automatic venturi valves and an "extra" carburettor (known as the Zusatzvergaser) coming on at high rpm's. The engine was placed offset in an angle so that the propeller shaft passed to the left of the driver seat, making it possible to build the car very low with a low center of gravity. That enabled even softer suspension, a further development of Uhlenhaut's ideas.

The new engine proved to be extremely heavy on both fuel and oil. As fuel was used to cool the high revving engine the fuel consumption went up to 1.2 - 1.5 litre/km (1.6 - 2.0 mpg). That meant that special consideration had to be made about the tank location and a lot of tests with different tank combinations were made during the 1938 season.

After a troublesome Pau the W154 was to dominate the 1938 season with 6 victories, 6 second positions and 5 third positions from 9 starts and Caracciola claimed his third European Championship. For those 9 races 14 cars and 19 engines were produced, which shows that Mercedes-Benz saved no efforts to achieve success. Uhlenhaut himself said that he was on a non-limit budget and that he himself had no idea of how much they spent.

During all this time Uhlenhaut was closely involved with the development of the cars, testing the cars himself both at Nürburgring and when following the team around the world. The car in the picture is chassis #14. While the normal cars had a 42-litre saddle tank over the driver's legs plus a 242-litre rear tank, chassis #14, known in the literature as the "experimental car", had a new tank combination with a 227 litre saddle tank and a 170 litre rear tank in an effort by Uhlenhaut to optimize the weight on the rear wheels. Probably it was the same chassis that was built less rigid than the other ones making it weigh 13 kg less. The car also featured two unique air scoops. The team was working hard on the engine cooling throughout the season and tried different radiator constructions and ethylene glycol-water mixtures.

Both Uhlenhaut and the drivers tested the car at the 'Ring and while Lang and von Brauchitsch did not like the car as it tended to break away suddenly, Caracciola was quite positive as it was a low momentum car that needed finesse rather than force to handle. Chassis #14 was used as a T-car during the German GP and also at Coppa Ciano where Caracciola raced the car after having an engine failure in his own car during practice. Caracciola liked the car so much that he raced it also in the Swiss GP which he won. Before that race the car got a new radiator design with two small openings each side of the main radiator.

In 1939 the team used a more streamlined variant of the W154. The season wasn't without its problems, a series of material failures, trouble with the advanced carburettor and two stage-supercharging gave the racing department their fair share of work.

Of the drivers Uhlenhaut, who was British-born and multilingual, became good friends with Dick Seaman, the engineer especially appreciating the British driver's honesty and ability to give technical feedback.

After the war Uhlenhaut worked on the Mercedes 300 Sedan before the factory was again ready for racing. Uhlenhaut then worked hard on the development of the W194 alias Mercedes-Benz 300 SL "Gullwing", the W196 F1 car and the W196S alias 300 SLR sports car. Uhlenhaut himself used to drive the unique 300SLR Coupe with a top speed of 284 km/h, the ultimate dream car for the enthusiast?

Before the war it was expected that the drivers raced their cars as they were set up by the technicians when arriving at the race tracks. Practice sessions were for learning the tracks, not for car setup. Thus Uhlenhaut did not only much of the work modern test drivers have to do but also the setup work now expected from the GP drivers during Friday practice. Therefore his enormous contribution to the success of the Mercedes-Benz racing team cannot be denied.