Gavin Green:

Meanwhile, the sight of the delicious Jaguar C-X75 thundering through the streets of Rome in the Bond movie Spectre reminded me of the early days of that stillborn concept car, when it was powered by twin micro gas turbines. The good people at Bladon Jets continue developing their promising engines, and production versions are one day likely.
 But let us return to the rotary. The brainchild of former Hitler Youth leader Felix Wankel, the rotary has many advantages over a conventional petrol unit, including one-third the weight and size. As there are no reciprocating parts or a valvetrain, it is smoother and quieter. NSU, precursor of Audi, gave the world the first production rotary car, the two-seat Spider of 1964. Later came the Ro80, the most avant-garde sports saloon of the ’60s. In 1967, Mazda gave us the rotary-powered Cosmo, the first futuristic Japanese sports car.
 The Ro80 and Cosmo had much in common, including delectable looks. A smaller engine gives designers greater styling freedom, as well as the potential for better packaging. (And great packaging is the hallmark of superior car design.)
 Alas, there were bugbears with the only fundamentally new car engine to emerge, with any success, in the 20th century. First, was reliability. This was a problem those clever Japanese at Mazda apparently solved, as evinced by its rotary-powered victory at Le Mans in 1991. The second problem was the rotary’s poor fuel economy, due to seal leakages and inferior thermal efficiency. That a lighter and smaller engine should be less economical was a cruel irony; eventually even those rotary stalwarts at Mazda abandoned their free-revving progeny.
 Now, the rotary is on the verge of a comeback. Mazda and Audi, unsurprisingly, are leading the resurrection. Back in 2010, Audi showed one of its many electric concept cars, the A1 E-tron, which used a little single-rotor engine – less than 10in x 10in – as an on-board range-extending generator. The rotary may be a gas-guzzler as the primary power source, as revs rise and fall, and loads vary. But at constant and optimal rpm, such as experienced by a range-extending generator, it is ideal.