Service Bay
The rotary engine was meant to be the future but half a century after the first full production rotary car appeared, it looks like it’s been consigned to history.
Inside the Wankel rotary engine and a look at some of the interesting cars this alternative technology powered.
It’s an often-heard comment in the classic car world that modern cars are increasingly similar both in their appearance and engineering. Gone are the wacky ideas of the ’70s and ’80s and in are high-efficiency, low-emissions engines of increasingly smaller capacity and with the last RX-8 leaving the Mazda production lines in 2012 yet another automotive curiosity disappeared in the shape of the rotary engine.
The ever-present difficult in meeting emissions and fuel consumption targets with the rotary engine are to blame, although Mazda continues to develop the design and it’s still rumoured to be preparing a return.
It’s Mazda which has done more than most to develop Dr Felix Wankel’s engine, although the original pioneer was the German firm NSU, which ironically ended up as part of the Audi empire after the warranty costs of the rotary-powered Ro80 nearly bankrupted it.
The story begins with the inventor of the design, Dr Felix Wankel who had been inspired from a young age by the desire to create an engine without the usual reciprocating parts and who in 1924 established a small lab to develop the idea. During WW2 he continued his work in collaboration with the German aviation ministry and when peace returned, resumed developing the commercial possiblities of the rotary – both as an engine and as a compressor.
One firm showing early interest was the German motorcycle maker NSU which initially used Wankel’s design as a supercharger on its motorbike engines, managing to extract nearly 120mph from a singlecylinder 50cc engine.
In 1957 NSU constructed its first engine, the DKM, using the rotary principle, but the need for the troichidal housing to rotate made it less than practical. Redevelopment saw this turned into the KKM with a fixed housing and rotating, er, rotor and it’s this concept which formed the basis of future development.
When NSU officially announced that it had made the rotary engine a practical reality, some 100 firms lined up to request patents, 34 of them Japanese.
Mazda president Tsuneji Matsuda was at the head of the queue and signed a formal contract with NSU in 1961, the firm establishing its own rotary engine department in 1963.
The rotary engine was far from perfect though and a major problem still required solving in the shape of the ‘chatter marks’ left on the housing by the seals of the rotor tips which were rotating at 7000rpm. it was
Mazda which cured the issue by recognising that the issue was caused by the seal material vibrating at its inherent natural frequency and drilling a small 2.5mm horizontal hole in the seal cured the issue. This only left the problem of excessive white smoke caused by oil leaking past the apex seals into the combustion chamber.
A specially designed oil seal solved that problem and Mazda was able to experiment with differing combinations of single, double, triple and even four-rotor designs. The single rotor engine was found to be smooth at higher speeds but to vibrate at lower speeds, while the twin and triple rotor designs were as smooth as the concept promised.
By 1964 the engine was at the driving prototype stage, with the 399cc single-rotor L8A installed in a prototype of the Cosmo Sport, followed by the twin-rotor 491cc 3820.
It was this which evolved into the production version Type L10A design which was put through durability testing in the Cosmo Sport – a car designed specifically for the revolutionary new powerplant.
At the same time, NSU was one step ahead and launched the first productionready rotary powerplant in its NSU Spider in 1964, running a single-rotor 498cc engine
rated at 5bhp. Like the Cosmo, the Spider was produced as a showcase for the new engine, although it was heavily based on the Prinz saloon.
The Cosmo went on public sale in May 1967, featuring a 110bhp Type 10A 491cc engine running pyro-graphite apex tip seals, a four-barrel carburettor and a twin-spark ignition.
The same year saw NSU launch its second rotary-powered car, the Ro80 which was a much bigger and altogether more innovative car than the Spider, powered by a twin-rotor, 113bhp engine.
In 1970 the rotary engine was exported to the USA in the Mazda R100, complete with a thermal reactor in the exhaust system to burn off the hydrocarbon emissions
The rotary was still a thirsty beast though, which is why Mazda worked hard on reducing its fuel consumption with a 40 per cent improvement as its ultimate goal. This was eventually achieved with the RX-7 launched in 1978, which made the rotary a practical option thanks largely to the adoption of a six-port intake using three ports for each chamber.
By then of course, NSU’s own rotary adventure was well and truly over, with the Ro80 leaving production in 1977.
This was a great shame but in reality NSU had rushed the engine into production before sufficient testing and early cars suffered problems with rotor sealing which did lasting damage to its reputation. By 1970 it’s reckoned that NSU had actually solved the problems but it was too late and warranty costs continued to spiral.
The generous two-year engine warranty and the negative publicity was just too much for the tiny NSU firm which was swallowed up by Audi in 1969 just as a triple-rotor version was being developed. In fact, the revenues from licensing Wankel designs had been supporting the company for a while.
Intriguingly, hard-driven cars survived much better than those used on short trips, but many Ro80s ended their days parked up after the engine compression eventually dwindled to almost nothing and the car would no longer start. The few luckier examples with broken engines were converted to the Ford V4 which was one of the few engines compact enough to fit in the same space but the rough Ford motor was an ignoble end to the rotary dream.
In 1982, the Cosmo RE Turbo was unveiled in Japan which was the first rotary engine equiped with a turbocharger. Bigger news came in 1990 with the domesticmarket Eunos Cosmo which employed the first triple-rotor production engine in the shape of the 20B-REW. This was later given sequential turbochargers and the result was an amazingly smooth yet powerful engine which was installed in the third generation RX-7, known as the Efini. The twin-turbo 13B-REW engine was rated at 280bhp.
Mazda offered the rotary in a great many of its domestic-market and US-bound vehicles including the Rotary Pickup and the Roadpacer coach, but for Europe the engine was offered in just the RX-3, RX-7 and then the RX-8 from 2003 which used the ‘RENESIS’ development of the engine featuring detail improvements which made it good for 250bhp in normally-aspirated form.
Does the rotary have a future? Mazda still maintains a development team working on the idea and the most recent developments have surrounded hydrogen-powered rotaries. There may well be life in Wankel’s idea yet.