The exciting adventure of the Mercedes C 111

Madrid

Updated:06/02/2021 01:09h

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In the 1950s, a German engineer from the Black Forest works on his flagship project. His name is Félix Wankel and his idea is a revolutionary engine in which conventional pistons give way to one or more rotating elements. Its triangular “piston” with slightly convex sides rotates in an orbital motion within a special chamber by means of a combination of gears and an internal eccentric shaft, so that the free volume between the faces of the rotor and the chamber varies with the turn. Due to the reduction of moving parts, this solution has a number of theoretical advantages: balance, compactness, simplicity and reliability.

Felix Wankel offers his idea to NSU, a motorcycle manufacturer that is going to go all-wheel drive. After three years on the test bench, in 1960 the Wankel engine was officially presented. And in 1963 the NSU Spider Wankel was the first car to be sold with this type of engine. This brand will present in 1967 a second model with a rotary engine, the original Ro 80, of which 37,398 units will be manufactured until 1977.

In Japan, Mazda is the one that gets the Wankel engine manufacturing patent. In April 1960, he created the Engine Research Department, entrusted to Kenichi Yamamoto, an ardent defender of this type of engine. In 1964 the Cosmo, the first rotary-engine Mazda, was introduced, and in 1991 the Hiroshima brand made history by imposing a four-rotor engine at the 24 Hours of Le Mans.

In France, Citroën reaches an agreement with NSU and starts a joint venture, called Comotor, to manufacture the Wankel-type drivetrain. Two hundred and seventy M35s are assembled, a coupe derived from the Ami 8 with a rotary engine, which serves as a test bed in the hands of loyal Citroën customers. And in October 1973 they presented the Citroën GS Birotor of which only 874 units were made: the oil shock ends the project.

The Stuttgart project

In the sixties Mercedes wanted to bring back the idea of ​​a sports coupe in the style of the 300 SL Seagull Wings of the previous decade. It is not a question of returning to competition (absent since the Le Mans tragedy in 1955), but of having a prestigious sports car, with more character than the 280 SL Pagoda. The engineer Hans Leibold’s team got to work in 1967. The idea is that it be a showcase of the most advanced technology of the moment and that at the same time it can be used on the open road.

It has nothing to do with the SL of the fifties. It adopts a platform in which the security tanks are located under the threshold of the doors (to lower the center of gravity), the suspensions are those of the new W107 (SL / SLC) and in terms of mechanics the solution adopted cannot be Most revolutionary: a rotary engine with three rotors (600 cc each) located in the rear central part. Powered by a Bosch injection, it offers a power between 280 and 300 DIN HP: 150 HP per liter, something exceptional at the time. The first rolling prototype begins its tests with Rudolf Uhlenhaut at the wheel. An engineer, he has been in charge of the Mercedes competition team in the interwar period (he is responsible for the development of the Mercedes W 125 dominating the 1937 Grand Prix), or the 1952 competition W194. Uhlenhaut was not only a brilliant engineer but an exceptional driver (faster than Fangio himself, at Nurbrurgring) but who never wanted to race.

Tests and problems

This first prototype rolls in April 1969 on the manufacturer’s track in Untertürcheim, with a rough and provisional bodywork. Meanwhile, Karl Wilfert’s team, in charge of body development, together with Friedrich Geiger, in charge of style, work on the exterior shapes. Already a body with defined lines, due to Bruno Sacco, appears painted white during the tests carried out at the Hockenheim circuit. Another four prototypes are subjected to intensive testing. And in September the C 111 is presented to the public at the Frankfurt Motor Show.

The C 111 adopted the Seagull Wing door opening, a tribute to the SL of the 50s

In the tests carried out, the technicians have found that the Wankel has a problem: it offers very low torque at low revs and must be kept between 5000 and 6500 to take advantage of the 30 mkg available. Thus, the prototype, apart from being very noisy, is difficult to drive and its accelerations are inferior to the sacred monsters of the time: the Ferrari Daytona and the Lamborghini Miura.

The second version

This leads to the development of the C 111 II. The fundamental change is that it incorporates one more rotor (four in total) and gives 350 hp at 7000 rpm, with a maximum torque of 40 mkg at 4000 rpm. The total displacement of 2400 cc is equivalent to that of a 5-liter engine with classic pistons. The car goes from 0 to 100 km / h in 4.9 seconds, exceeds 300 km / h and it is also easier and more pleasant to drive due to the better response of the engine in low conditions.

The 1970 C 111 II already incorporates a four-rotor engine.
The 1970 C 111 II already incorporates a four-rotor engine.

The higher performance requires working on reinforced running gear, it is equipped with a self-locking bridge and four ventilated brake discs. A lot of work is also being done on the aerodynamics of the car and on improving visibility. Thus the bodywork presents many changes, highlighting the double air outlet in the front hood or, in the back, the lower engine hood and the double arches (which will later be seen in the Maserati Merak) on the sides of it. Seen in profile, the glazed surface of the doors is greater.

The C 111 II is presented at the 1970 Geneva Motor Show. The response from the public is very good and there are customers willing to sign a check at the stand itself. But the car still has a long development process for which ten units have been built.

As the test kilometers accumulate, the engine shows quite a few problems with the tightness of the rotors and lack of reliability. Adaptation to US anti-pollution regulations adds to this picture. The set-up takes longer and the expected commercialization does not arrive.

The 1973 oil shock

As if that were not enough, the consumption of the rotary engine is high and the oil crisis that broke out after the Six Day War, in September 1973, is the highlight of the project of the Stuttgart firm.

The oil shock shocks the automotive world. Cutting back is an obsessive need. The eyes move towards the diesel engine, until then mainly destined for industrial, commercial vehicles or taxis, as a new alternative for private use passenger cars. But to achieve this goal you have to offer more dynamic, more attractive diesels. Thus began a technological and image career.

The star brand already has a range of diesel passenger cars appreciated by professional drivers convinced by their low consumption and resistance to the passage of kilometers. And to expand this clientele, it presents the 240 D saloon, from the W 114 series, with a three-liter, five-cylinder diesel block. Its 80 DIN CV at 4,000 rpm allow better recoveries and, above all, a top speed of 150 km / h. This block is very robust and Sindelfingen technicians decided to incorporate a turbo.

Second opportunity

It is necessary to make the user discover these versions as a real alternative for benefits to those of gasoline, but saving liters and money. Therefore, a new image must be promoted. The competition does not seem to be a better framework and then an idea arises: the records.

And this is how the C 111 opens a second chance. The engineers take one of the units of the finished project. In the small space in which the rotary engine was accommodated, it is no problem to fit the compact five-cylinder diesel from Mercedes. The capacity of the tanks is expanded to reach seventy liters each. A huge Garret turbo is adapted to the engine and the C 111 II D is thus pushed by the 190 CV DIN that offers 4,200 rpm is diesel mechanics.

The C 111 D with the team that broke a series of records with diesel engine
The C 111 D with the team that broke a series of records with diesel engine

And the whole team goes in June 1976 to the Italian circuit of Nardo where it turns lap after lap for 64 hours and exceeds 250 km / h. The image operation has worked but the engineers are convinced that reducing weight and improving aerodynamics can go faster.

The result will be the spectacular C 111 III D, with a body with a characteristic airplane wing profile, with faired wheels and a huge central spoiler: its Cx is only 0.18. And it is this car that is launched on April 28, 1978 on the asphalt of the Nardo track. At the wheel are Paul Frere, Rico Steinmann, Hans Liebold and Guido Moch. The car rotates producing a huge noise both rolling and engine. And, among other records, it covers a thousand kilometers at an average of no less than 318.308 km / h, with a stopped start.

And the C 111, version IV, will still return to Nardo, now with a V8 gasoline engine of 4.8 liters and 500 hp with which it makes the fast lap of the circuit at an average of 403.978 km / h. Hans Liebold at his wheel will thus sign in gold letters the end of his project that, even acknowledging its problems, can only be defined as exciting.

The C 111 IV would make a fast lap around the Nardo circuit at an average of 403.9 km / h
The C 111 IV would make a fast lap around the Nardo circuit at an average of 403.9 km / h

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