When most people think of rotary engines, they think of Mazda’s RX series or the NSU Ro80 both with engines based on Felix Wankel’s design.
However, the rotary engine has been around in different forms for at least 120 years. It was first used in aircraft until superseded by the radial engine. Early rotaries were the complete opposite of current car engines. In these rotaries, the crankshaft was static with the cylinder block rotating around it.
There were many builders of rotaries prior to the First World War and one of them was Lawrence Hargraves. If you are living in New South Wales you will recognise that name – the bridge in the Royal National Park near Wollongong is named after him. He was a pioneer of early aeronautics.
Rotaries were also found in early cars and even motorcycles – the German Megola had a 640cc engine inside the front wheel!
With the radial engine taking over in aircraft due to their better torque delivery, the early rotary designs died off, then during the 1950s, Felix Wankel a German engineer developed a rotary engine with a 4-stroke oval shaped housing and a triangular rotor connected to the crankshaft. He initially licensed it to Curtiss-Wright, an aircraft engine manufacturer and also to Norton, a British motorcycle company, but his best-known licensees were NSU – who he worked for – and Mazda.
Essentially the triangular rotor sucks in the fuel/air mix and drags it through a cycle where it is compressed, ignited and pushed out to the exhaust. The Wankel rotary engine is much more efficient in delivering power, not only does the crankshaft rotate three times for each rotor cycle but the power stage of the cycle is much more efficient – it is surprising that in today’s fuel conscious times, the rotary hasn’t become more popular as engine technology is developed further to provide better fuel economy.
This big issue with Wankel’s rotary was initially the seals between the rotor and housing. This was fixed by using a harder material than piston rings but they typically use a little more oil than a normal engine due to the configuration.
The NSU Ro80, which won the 1967 Car of Year Award, wasn’t a commercially successful model, however like the RX series is probably one of the best known examples of a rotary powered vehicle. NSU had developed an earlier rotary model called the Wankelspider, then followed by the Prinz 1000 and TT models using a 2 rotor design. The original Prinz had started life with an NSU motorcycle engine of 600cc and later versions returned to a conventional OHV motor. With the failure of the company, thanks in part to the ongoing development costs of the Wankel rotary, they were acquired by VW and they were rolled into the Auto-Union company along with a resurrected Audi to form Audi NSU Auto-Union AG. So, now you know where the Audi TT name came from!
The other and more well-known licensee was Mazda who have developed a range of cars known as RX and they have even successfully raced Wankel rotary engine cars. The most popular road car has to be the RX-7, which had three generations, although their first rotary car came out the same year as the NSU.
What does the future hold for rotaries? The current Mazda engine is the 13B Renesis as seen in the RX-8, essentially a 1.3 litre motor – 2 rotors of 650cc each. Mazda are developing an engine dubbed the 16x, which will be the equivalent of a 1.6 litre – 2 x 800cc, and there is a rumour they are developing a 3 rotor engine. The 16x is apparently lighter than the 13B due to the use of lightweight materials. Mazda are also looking at hydrogen based rotary too as part of a plan to use fuels other than petrol.
Reg Technologies, a Canadian company have taken the Wankel design, lightened it and found a way to provide more power using less fuel. The RadMax engine uses a set of vanes on the rotor to make sure that each cycle of the rotor has more ignition points. It also uses a very high compression rating to cope with multiple styles of fuel. Have a look at radmaxtech.com.
For motorcycles, the Norton Classic, Hercules (Sachs/DKW) and the Suzuki RE5 all had rotary engines.