Mercedes C-111 & Felix Wankel

Cars

In the heady, creatively inspired days of the end of the 1960s, the whole world appeared ready to go rotary.

At the Frankfurt Motor Show of 1969 the Mercedes Benz C111 was one of the most spectacular manifestations of the much vaunted rotary revolution.

But that future never came true (at least not in this dimension). So what was the revolutionary rotary and what happened to it?

c111-engine-cut A thing of engineering beauty

The man who invented the rotary engine was Felix Wankel, a brilliant but fascist German autodidact born in 1902. Losing his father in WW1, he couldn’t afford to go to university but was a naturally gifted engineer who learnt his trade in tooling shops whilst hanging out with the Hitler Youth and other unsavoury characters. He had conceived this new type of engine as early as 1924 – and before he died in 1988 he would see it used in cars, chainsaws and even aeroplanes.

Wankel’s political leanings saw him rise high in the National Socialist party – but having fallen out with Nazi hierarchy when Hitler assumed power in 1933, he went on to design engine components for the military during the Second World War. In the early fifties he began developing the early versions of the rotary engine itself for small engineering firms in the reconstructing German state.

c111-frame
The C-111 frame in progress

Wankel’s design used a rotating triangle inside an epitrochoidal (oval) housing to convert pressure into rotating movement without pistons. The output shaft, being driven at three times the rotor speed, produced a firing cycle that a piston engine would require two cylinders to achieve, making the rotary a very compact engine.

As it was always moving in the same direction the rotor caused minimal vibration – at least when compared to the start-stop- back-forth motion of the piston engine. In short the Wankel had less parts, was smoother and more compact – and could deliver a higher power-to-weight ratio than the piston engines of its day.

There’s a great explanatory video below. Turn off the sound unless you like cheesy Euro techno.

However the only mainstream car manufacturer to stick with the Wankel was Mazda and that decision arguably nearly broke the company. Why?

The engine did have some problems. Although it had less moving parts, those it did have were complex and expensive to make, requiring major retooling by a manufacturer. Also the compression chambers in Rotary engines were notoriously hard to seal and the early versions burnt a lot of fuel, had a tendency to smoke and were generally higher on emissions than equivalent piston engines.

c111-engine-4discs Compact and efficient – but not economically viable for Benz

The wrinkles in the Rotary dream would eventually be ironed out – but by 1973 the oil crisis and ongoing tooling problems meant that, there wasn’t the political or economic will to press on with the new engine. At least within Mercedes-Benz.

C111 test models would use diesel engines and the rotary largely faded from the mainstream. Perhaps if Mercedes had stuck with the rotary we could be living in a counterfactual reality.

Perhaps we’d all be subscribers to rotaryheads.com

Words: Neil Siner

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