Wankel versus Otto

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It must, I imagine, occur to most of us at some time that the Otto cycle (no, not a bicycle, the fourstroke engine we are content to sit behind) is very crude. The pistons rush up and down, stopping and restarting with every rotation of the crankshaft, the gas is sealed from escaping past them by gapped gas rings, the poppet valves dance up and down to bang onto their slender seats, and ignition parts still look Iike things taken from an early wireless set. Thank goodness for Dr Diesel… But as the Otto principle works and goes on working, we do not care. Like Panhard’s first sliding-cog gearbox, it may be crude, but it allows us to march…

It was so much more apparent in the days of single-cylinder motorcycles. Then the engines gave audible evidence of the Otto workings the suck, compress, expand (bang!) and exhaust functions. But as you drive your modern car, how often does any of this occur to you? How many of you know about the grinding-in of valves, the little tins of paste we once used, coarse one end, fine at the other, and the wrist-punishing chore of correctly preparing valves to mate with their seats, as you rotated them back and forth with a light spring under them? How frequently we did this, and slightly polished the valve ports while decarbonising the cylinder head, in the pathetic hope of getting more power.

All of which makes it opportune, I hope, to recall the Wankel rotary engine. A sort of turbine, it removed the crudities of the Otto concept. A petrol power unit sans pistons, con rods, or valves… Just the job surely? Space does not allow for describing Wankel development. Suffice it to say that Audi-NSU of Neckarsulm in Germany had production cars with such power in their catalogues by the ’60s. The problem of calculating size in cc For tax or competition purposes was overcome, and NSU gave us a simple rotating plastic cut out to explain how it functioned.

In 1965 I was able to drive an NSU Wankel Spider, which excitingly turbined an estimated 500cc propellant to a claimed power of 50bhp. Despite this it gave 52mpg and was an excellent little fun car. As it was German I took it to Cuffley to see the memorial to the crew of Zeppelin L21 shot down by Leefe Robinson’s BE2c in September 1916. I did not have to use the spare sparking plug (the Spider had but one), but oil consumption may have been thought heavy, at around 1000mpg; but remember, this was nearly 35 years ago, when many cars were lubricant scoffers.

In appearance a bit ugly but eager-looking, a top speed of just about a genuine 100mph was pretty good for the equivalent to a 1-litre piston car, but the handling was not really up to the performance. However, four years later I was able to try the NSU Ro80 saloon with twin Wankel power. It was an advanced car even apart from its rotary engine, a front-drive saloon with independent suspension, disc brakes, power steering and, notable then, an alternator. I would not have minded owning one had I not had to pay its too-high price. The Ro80 combined comfort with effortless cruising from the smoothly-spinning power unit and safe, fast cornering abilities.

No car is perfect, and the NSU Ro80 had an automatic clutch, giving it so-called `Sportamatic’ two-pedal control, with which I was not enamoured, and the price was too high compared to other 2-litre saloons with which it had to be classed. Also petrol thirst was heavy (19.3mpg, but of low octane fuel) and oil was quickly consumed. But you could forgive this after experiencing that unique smooth flow of power right up the rev range. It really seemed as all the failures had been overcome. But very soon NSU had abandoned the Wankel engine; apparently even VW and Mercedes-Benz could not make effective rotor seals for it. Yet NSU apparently managed to find some 12,000 customers for the rather tantalisingly nice Ro80 in its first 12 months.

But today, though Mazda makes small numbers of the fast and powerful RX-7 with rotary power, the Wankel concept is almost a dodo. It looks as if the majority of us will indeed have to continue with reciprocation and dancing valves as motorists have done for over 100 years!

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