Rotary motion
In the early ’60s the rotary engine looked like it could well be the shape of the future – think today’s hybrid designs – and few makers wanted to risk being left out in the cold. One of the biggest joint ventures was the Comotor concern, created by NSU and Citroën purely to develop and manufacture rotary engines. The first product of the operation was the rotary-powered Citröen GS Birotor which was sent out on extended test with favoured customers until rising fuel prices put an end to the project, with most of the cars subsequently destroyed.
Other uses involved the Sachs rotarypowered lawnmower (no, really!) and various ultralight aircraft and marine engines, with the main commercial use for the Wankel concept being fluid pumps. Meanwhile, Norton was an enthusiastic user of the rotary in its bikes, notably the Commander and the police special Interpol.
How it works
So much for the history, but how does the rotary actually function? Well as you’d expect it goes round and round instead of up and down but the details are harder to get your brain around. A single-rotor engine essentially contains just three components: a housing, a rotor and an offset shaft which is the equivalent of what we know as a crankshaft. The troichidal (that’s its shape) rotor is fixed to the stationary housing via a ring gear around which it rotates, turning the eccentric shaft which transfers the motion to the wheels. The actual business of sucking in petrol and burning it is the same suck-squeeze-bangblow affair as in a conventional engine, with the mixture sucked in and exhausted through openings in the housing which are opened and covered as the rotor passes.
The tricky thing with a rotary is sealing the rotor itself against the housing to keep the combustion where you want it. Think about it: a piston ring is a nice round shape whereas there are some awkward corners inside a Wankel housing.
NSU just hadn’t got it right and the Ro80 would wear out rotor seals in as little as 20,000 miles, especially if the cars were used for frequent short journeys. The other bugbears of the rotary are poor fuel consumption – which even Mazda hasn’t been able to solve completely – and poor emissions, which electronic controls have largely got covered.
Ironically, by the ’80s metallurgists had made the rotor seals work properly but the damage had been done and it was left to Mazda to develop the rotary car engine.