The rise and fall of rotary engine F elix Wankel originated the idea of rotary engine as early as the 1920s but full development was not started until 1954, when he persuaded NSU, a motorcycle manufacturer then, to fund the project.



In theory, the rotary engine has a lot of fascinating advantages. Firstly, the rotors spin in one direction, unlike pistons which change direction reciprocatingly, thus must be smoother and more energy efficient. Secondly, it uses fewer components – a twin-rotor Wankel engine compares favourably with a conventional 6-cylinder engine, and it saves considerable valve-gears and crankshaft components, thus it can be made smaller, lighter and simpler than piston engines. Thirdly, lacking valve-gear mechanisms and crankshaft leads to less vibration and noise.

NSU's rotary engine Dr. Wankel experimented his first rotary engine in NSU. It eliminated the imperfect eccentric movement of rotor by a revolving housing which was held by another housing. It was perfectly smooth, but too complicated to implement in an economical way. Therefore at last a more compromised design, with eccentric rotor and a single fixed housing was adopted. This is also the design that Mazda still uses today.

The first 498 cc single-rotor engine was introduced to the 1963 NSU Spider, a small roadster like Fiat 850 Spider. It was just a low-volume experimental project. Next step was to put the technology into a mass production car. The 1967 Ro 80 seemed to be a winner. It had all sorts of advanced technology and futuristic design to win European Car of the Year award, but its 115 hp twin-rotor engine was found to be unreliable soon. Rotor tip sealings worn out quickly, increasing fuel consumption, decreasing power, causing oil leak and breakdown. This cost NSU substantial money on warranty and established a bad reputation for Wankel engines. To a large extent, NSU’s financial trouble and eventual acquisition by Volkswagen was driven by the Wankel engine. It has never produced rotary engines since then. However, before that happened Wankel engine technology had already attracted the attention of the world. To raise development budget, NSU sold its license for United States to an aircraft engine maker called Curtiss-Wright, which then sub-licensed to General Motors, Ford and other car makers. GM's effort General Motors was the most eager player besides NSU and Mazda. It obtained worldwide license from NSU in 1970, then displayed two prototypes in 1973, i.e. Chevrolet Corvette 2-Rotor and Corvette 4-Rotor, both were mid-engined. Having invested a lot of money on rotary projects, GM estimated 80 percent of its production in 1980 would be powered by rotary engines. The real production car, Chevrolet Monza, was to be launched in 1974, but the plan was hit by the newly announced smog regulations for 1977, which was so strict that GM feared the rotary engine could have problems to comply with. Eventually, Monza appeared with conventional engines. The prospect of rotary programme became uncertain, and virtually dead when its supporter, Ed Cole, president of GM, retired in September 1974. Citroen, Mercedes and Nissan Citroen collaborated with NSU and created 2 rotary-engined cars, Ami 6 and GS Bimotor. Both were installed with NSU's engine. However, they were short-lived and limited in numbers. Mercedes was another giant European car maker to experiment Wankel engines. Mid-engined exotic concept car C111 stunned the world in the 1969 Frankfurt motor show. 3-rotor and 4-rotor version output 320 hp and 405 hp, respectively. But it did not come true. Nissan took a Wankel license in 1970 and created a prototype in 1972. It planned to produce a small sports car at the rate of 120,000 cars per year, but eventually cancelled after the 1973 oil crisis. Mazda - the only survivor Mazda, called Toyo Kogyo then, obtained the license from NSU in 1960. Originally it wanted to put NSU's engine directly to its vehicles, but after experienced delivery delay and disappointing vibration and fuel consumption, it designed its own Wankel engines from scratch. Why was Mazda so eager to develop this technology? Because in the 1960s the Japanese government wanted to merge car makers in order to enhance international competitiveness. To retain independence, Mazda believed developing a unique technology would help. Its first rotary-powered car, Cosmo, went into low-volume production in 1967. That was a 2-seat GT like the original Ford Thunderbird. Twin-rotor each displaced 491 cc, capable of pumping out 110 hp, later upgraded to 130 hp. It was a true 200 km/h grand tourer. 5 years of production totalled 1,519 units. Having experimented the technology, Mazda became confident to put Wankel engines into mass production. In 1968, it launched a 4-seat coupe called R100, which was derived from the mass-produced Familia sedan. Powered by 10A twin-rotor engine and output 100 hp. It was shipped to the USA in 1970 and became a hit. Mazda created a rotary boom there with more rotary cars – R130, RX-2 and RX-3, all were based on the R100. In 1971, Mazda produced the 200,000th rotary cars! The prospect was bright, and the company planned to produce 100% rotary cars by 1975. But the oil crisis changed that overnight. Since rotary engines were well-known for thirsty, sales in the US dropped by half in 1974 and did not recover to the 1973 level until RX-7 was launched. Wankel engines for econo cars became out of the plan, thus its application was limited to RX-7 in the following 20 years. The only exception was the 1992 Cosmo, which was a modern version of the original Cosmo powered by a 280 hp twin-turbo 3-rotor Wankel engine. Its sales was bounded in Japan.

In 2003, Mazda introduced the next generation Wankel engine called RENESIS (which meant Rotary Engine Genesis) on its new 4-seater coupe RX-8. While the previous rotary engines employed side intake ports and peripheral exhaust ports, the new one switched to side ports for both intake and exhaust. This lengthened the expansion stroke and enhanced thermal efficiency. It also enabled larger exhaust area, enhancing breathing and power output. Emission was also significantly improved by the design. The RX-8 achieved considerable sales success, if not matching the early RX-7 in the good old days. Nevertheless, as the world pursued green motoring harder and harder, its thirst of fuel became a big hurdle to sales. Following its end of life in 2012, Mazda's rotary engine production came to a stop.

