Concept Car of the Week: Mercedes-Benz C111, C111-II and C111-IID

In 1962, Mercedes-Benz launched a research program to investigate the development of the Wankel rotary engine and its potential both on the road and track. While the early mule wasn't a looker, the prototype's design continued to evolve until a public unveiling of the C111-I concept, designed by Bruno Sacco, at the 1969 Frankfurt motor show.

The coupé may have looked like the systematic further development of the Sport Light models from the ‘50s with its gullwing doors, but it wasn't a design study for a new SL. Despite its complete interior and cargo space, it served as an experimental car.

The body, made of glass-fiber reinforced plastic, was extremely light and offered new opportunities in design and manufacturing impossible in sheet metal. It was bonded to a steel frame/chassis and finished in "weissherbst" orange. The C111-I's three-rotor Wankel engine delivered 280bhp, which pushed the car up to 260km/h.

The following year, Mercedes presented the next evolution, the C111-II, which enjoyed a discreet but successful facelift recognizable by its two black vents on the hood and round tail lamps. This time, the engineers tested a four-rotor engine producing up to 350bhp and a top speed of 300km/h. It could accelerate from 0 to 100km/h in a very impressive 4.8 seconds.

It might sound like a success for Mercedes except for a few (major) flaws. Dr. Kurt Obländer, head of engine testing in the C111 project, explains: "We were able to solve the difficult problems in engine cooling and engine mechanics by technical means. But the main problem of the concept, its low thermodynamic degree of efficiency, remained. Due to the elongated – and not exactly compact – combustion chambers, fuel economy was poor, resulting in high fuel consumption and unacceptably high pollutant emissions. These drawbacks were inherent in the design principle."

The 1973 oil crisis put the final nail in the coffin for a Mercedes powered by a rotary engine, but by 1976 the unstoppable team of engineers bounced back. They dropped a 190bhp turbocharged five-cylinder 3.0L diesel engine in the C111-II, now called the C111-IID. During a 60-hour run on the Nardo test track, it broke no less than 16 records, averaging a speed of 252km/h (160mph) over 10,000 miles.

Designer Bruno Sacco

C111-I

First seen Frankfurt motor show 1969
Length 4,200mm
Height 1,125mm
Width 1,800mm
Wheelbase 2,620mm
Weight 1,100kg
Engine Three-rotor Wankel engine, 1800cc, 280bhp

C111-II

First seen Geneva motor show 1970
Length 4,440mm
Height 1,120mm
Width 1,625mm
Wheelbase 2,620mm
Engine Four-rotor Wankel engine, 350bhp

C111-IID

Engine Five cylinder, 3.0 liter, turbocharged, 190bhp

Your author, Flavien Dachet, is a UK-based, French-born car designer. You may know him as the purveyor of KarzNshit, a photo blog that if isn't already in your bookmarks, certainly should be.

By Flavien Dachet