Part one: Driven to Write meets (and briefly drives) one of its heroes.
A commonly espoused orthodoxy warns us that close proximity to our idols can only lead to disappointment. Some go further, suggesting that the renunciation of hero worship is the mark of a mature mind. This being the case, I can categorically claim not to have attained it. But surely it is preferable to go down in flames than regret never making the attempt?
Which is by way of introduction to one of automotive’s great Icarian narratives. A car which embodies beauty, craft, intelligence and bitter reversal. From a very young age, I have been infatuated with NSU’s Ro80. I know, with my reputation and everything, but true nonetheless. Up to now however, I’ve known my place – firmly on the sidelines, nose pressed to the glass. But today that changes.
For this I have Steve Randle to thank. The engineer and serial collector of automotive’s braver and more compelling experiments owns this rather splendid and beautifully preserved example of a car history deems to have brought the Neckarsulm car maker to its knees. A 1973 second-series single plug Ro80, Randle tells me, “It’s been an itch that needed to be scratched for many years. That and the Citroen SM were pivotal in drawing me into engineering.”
A similar tale of hero-worship perhaps, albeit unlike mine, one that has been consummated. So what first drew him to the car? “I can’t recall whether it was the appearance or the engineering – I suspect it was the way it looked. From an early age I was fascinated by the geometric elegance of the Wankel though. Poppet valve four strokes just seemed (and still do) hopelessly crude and overcomplicated by comparison.”
Looking back some fifty years, the latter-end of the 1960’s seems a halcyon period of unfettered creativity and lambent optimism. We were travelling further and faster than before and were doing so in vehicles of such sophistication and comfort that were unimaginable even a decade before. The future truly appeared as boundless as those unlimited German Autobahns.
Of three landmark car designs from this period, Claus Luthe’s Ro80 would prove the most lasting testament. In fact, over the intervening half century the NSU has become something of a victim to its modernity, simply because it really hasn’t dated at all. Indeed, apart from matters of detail design and materials, it’s rather difficult to see where any tangible progress in car design has since taken place.
Regardless of one’s opinion as to who was ultimately responsible for its shape, the Ro80’s significance lies in how it manages to combine science and aesthetics in a manner that really hasn’t been surpassed. While contemporary big Citroens offered a somewhat binary visual proposition, the NSU presented a considerably less uncompromising (if bracingly modernist) face to the world.
But not only was the styling and aerodynamics ahead of its time, as Randle outlines. “There were other features on the Ro80 that were influential – its ATE brakes were quickly adopted by Audi, not to mention its packaging. And while the suspension wasn’t ground breaking, it was really well done. The careful approach to aerodynamic drag and wind noise can clearly be seen in the detail and profile of the Audi 100 of 1982. Many cars mimic the Ro80’s layout today.”
Suspension was by McPherson struts / coil springs and lower wishbones at the front, while at the rear, semi-trailing arms and coil springs kept matters in hand. Brakes were discs all round, the fronts mounted inboard to reduce unsprung weight. In fact, looking under the Ro80’s bonnet, one is struck not only by the power unit’s compactness, but the possibility that Dr. Rudolph Hruska took a very thorough poke around before he began work on the Alfasud programme, which incidentally was initiated around 1967.
In most histories, the Ro80’s design elicits most of the acclaim, but NSU’s engineers under chief engineer Ewald Praxl and technical director, Walter Froede (who doubtlessly received all the opprobrium when things went south) deserve immense credit as well.
My first sight of Steve’s Ro80 is in profile as it slowly glides into view, a graceful sky blue apparition amongst the monochrome moderns. Gleaming in the mid-August sunshine, I take in a shape I haven’t viewed properly in decades. It’s a stunner. The histories state that various fastback body styles were experimented with by Luthe and his NSU stylists, but were rejected in favour of the now familiar three volume silhouette, albeit one which featured for the time, a radically high bootline, dictated by wind tunnel experimentation.
Perhaps the aspect which gives the car such a contemporary resonance is its stance. Wide tracked, low nosed with a four-square wheel at each corner appearance, the Ro80 looks poised and purposeful on its attractive optional alloy wheels. Another rejected proposal was for the entire roof panel to be coated in the same stainless steel finish which enlivens the glasshouse, which while striking, would likely have played hell on bright days like today. But it’s the NSU’s wonderfully realised mix of confidence, studied scientific rectitude and impeccable build that lends the Ro its timeless appeal – the engineer’s car that went to the ball.
Open the door and the evocative aroma of polyvinyl, fabric and fifty year old insulation assails the senses – the heady scent of the ’70s. Second impression: There’s so much space inside. Flat floors, an empty void beneath the businesslike dash, just the spindly gear selector in lone attention between the seats. One gets a strong impression that any visual flamboyance was hard won.
Luthe’s team is believed to have mocked up a more stylish looking dashboard arrangement which was rejected by NSU management. It doesn’t matter, this one is fine. It’s solid, stark looking but very well finished, as is everything else in here. The vast glass area, the lack of intrusive door trims and bulky consoles lends the interior a tremendous sense of openness, but is the first really tangible evidence of the car’s age.
Rotary fun fact (1) : the Ro80’s engine isn’t strictly speaking a Wankel. Apparently, NSU engineers under Walter Froede discovered once they began working with inventor, consultant, (and thoroughly unpleasant individual) Dr. Felix Wankel during the late 1950’s, that his concept design was totally unsuited for road car use. Froede had his engineering team develop their own in-house rotary design on Wankel principles, one which differed quite markedly in detail, leading to bitter disputes with the concept’s originator over his work being adulterated.
This engine, dubbed Kreiskolbenmotor or KKM at Neckarsulm, was far from perfect out of the box either, early examples being plagued with maladies, some of which like excessive fuel and oil consumption, a lack of low-end torque and difficulties with the rotor tip / apex seals, would dog the power unit throughout its life. But having convinced the NSU board of its merits and with the prospect of lucrative royalties from rival manufacturers, both Wankel himself and NSU’s cash-strapped management backed Froede’s KKM powerplant.
Rotary fun fact (2) : Steve informs me that “low sulphated ash oils work well in Ro80 motors. The same oils are favoured by Detroit Diesel 2-strokes”.
It was those Apex seals that proved the early Ro80’s undoing. Firstly because NSU engineers miscalculated as to the type of usage customers would expose their cars to. Having devoted the bulk of the car’s development on high-speed simulations, customers found that excessive short trips when the engines were cold would lead to problems. Also, the Wankel was intended to spin at high revolutions. Owners needed to reset their driving style to get the best from the power unit, but those who slogged the car in the upper ratios rapidly saw the costly error of their ways.
So a combination of lack of foresight, naiveté and the unintended consequences of being first in the field led to NSU’s rotary developing a reputation for fragility that hobbled the Ro80, even before the 1973 fuel crisis skewered it completely. Nevertheless, NSU persevered and by the close of production in 1977, the bulk of the engine’s weaknesses had been addressed. After falling into the arms of Audi in 1969, development continued, with a triple rotor version of Ingolstadt’s 1976 C2 model said to have been well advanced before being axed by a certain Ferdinand Piëch, quite late in proceedings.
Meanwhile in Hiroshima, Mazda kept the rotary flame alive for decades more, expunging the fragility, but issues of consumption and emissions increasingly saw its case undermined. Could the Wankel have a future I wondered? Randle seems to think so.
“It may well with other fuels. I’m not sure that with petrol it’s likely. I’d be delighted if Mazda or Audi gave it another go. As a range extender, it makes more sense, as it can always be run in its sweet spot, at higher rpm and it’s so refined that doing so isn’t at odds with the electric vehicle experience. It does prefer LPG and CNG where the combustion chamber surface area is less of an issue. Same with hydrogen. Modern materials would help. There is a guy in Neckarsulm who offers ceramic tip seals that last forever, and so does the chamber surface.”
Postscript: Recent noises from Hiroshima appear to suggest Mazda may indeed reintroduce the rotary powerplant for use in a forthcoming hybrid model.
See part two.
Data source: Ate Up With Motor / RO80.nl
Authors note: The spelling of Walter Froede’s name has been amended within the text owing to an error in the original piece. [20/09/17 12.08 PM]
Driven To Write 
The name of NSU’s then technical director is actually written Froede, no Umlaut there.
One reason for the engine’s bad image was that NSU ordered their dealers to replace the engines whenever they found a problem they could not solve. The engines were sent back to NSU for a thorough analysis, which in most cases showed no more than trouble with the unique surface gap spark plugs. Many of these engines were used as spare parts without any repair work done on them.
A former schoolmate’s father always drove around in Ro80s. When the news came out that NSU would stop production he quickly bought another three of them.
He told me he could not drive anything else.
That reminds me of a thought excercise: what would it take to buy, say, five exact same examples of your favourite car (from new) and use each for a decade. In my case: £22,000 for five XMs. I’d be on the third car, with or two years before unwrapping car 4. The cost would be considerable: five cars plus storage and maintenance. What happens to a little used car over four decades? It’s a millionaire’s scenario.
Problem would be the cars’ storage.
Two years ago I helped to unwrap a brand new and professionally stored (e.g. Castrol Storage Oil everywhere) Triumph T140 from 1979. The bike had to be rebuilt using new rubber parts, oil seals, bearings and so on.
The original intention of the guy with the four Ro80s was to have them professionally restored after a couple of years and to use them alternatingly.
One point for the story above: AFAIK there was no triple rotor engine under development at Audi (as going beyond two rotors makes a Wankel engine extremely complicated to manufacture). For the Audi 100 C2/Type 43 they had an engine under development with 2 x 750cc swept volume, delivering 170 hp. There were a couple of prototypes with this engine for exclusive use by Audi managers, who reportedly liked them a lot because the cars were really fast and comfortable. Remember that this was before the arrival of the horrible turbo five cylinder engines.
What happened to the bearings in the interim?
So, my five hypothetical XMs would really be unused bodies and interiors; the moving parts would need recommissioning. I’d also need crates of parts – some of which might perish too.
There’s a fellow in Citroen circles who has a box fresh DS. It is stored on blocks, doors open and the service schedule followed. I wonder why.
The main bearings were inp perfect condition thanks to Castrol and kicking it over once a month. The wheel bearings were shot because the grease had dried up, allowing water in and corrosion had destroyed the races. There were also things like the seat foam which was completely dried up and fell out at first opportunity.
I could imagine that some of the finer parts in the Hydropneumatic system like the height correctors or the membranes in the suspension spheres wouldn’t like being stored for so long
Dave, many thanks for your corrections. I have amended accordingly. The more powerful KKM 871 engine was stated in some accounts to be a triple rotor, but I think you’re probably correct in stating it was a twin. The RO80.nl account contains a photo of an Audi C2 thus equipped. It is believed this engine was to have gone into late model RO80’s, which had revised gear ratios to accommodate it, but it never happened.
I am not an engineer, although I have a passing interest in engineering. I understand the basic principle of how the rotary Wankel engine works. In layman’s terms, why is it not fuel efficient?
I’m sure some of our more learned readers can provide a more comprehensive answer, but from the reading I’ve done, it appears the rotary isn’t as thermally efficient as a poppet valve engine. From a thermal efficiency perspective, the 995 cc NSU ‘wankel’ was said to be rated as equivalent to a poppet valve engine of close to three litres capacity. Furthermore, owing to the chamber design, unburnt fuel tended to cling to the rotor surfaces and was evicted unburned via the exhaust. I think later developments helped mitigate this, but fuel economy has always been a rotary bugbear, as indeed was hydrocarbon emissions.
A Wankel combustion chamber has a very unhappy ratio of surface to volume. Therefore a lot of thermal energy created in the combustion process gets lost by heating the metal surfaces instead of creating motive power for the rotor. A Wankel rotor gets extremely hot and cooling it is a major engineering challenge in a Wankel (it would have been interesting to see how Audi solved this problem with their A1 e-tron show car. This had a Wankel driven range extender with a rotor welded up from stainless steel pressings).
The compression ratio in a Wankel is more or less fixed at 9 to 1 because it is dictated by the internal geometry of the rotor and trochoid. This makes it impossible to get compression ratios necessary for high thermal efficiency. That’s why they started with four sided rotors to create Diesel wankels…
The Wankel combustion chamber has a very unfavourable form. It is shallow, oblong and when looked from the side resembles a horizontal “B”, effectively parting it in two combustion areas. It also constantly changes its form because of the rotor’s movement. This more or less prevents creation of swirl in the mixture, which would be necessary to get a fast ignition phase and thorough combustion (look at a modern piston engine with pentroof combustion chamber and wide squish band for efficient burning of the mixture. An indicator is the amount of ignition advance, which is very small in modern engines because combustion is happening extremely fast). Combustion quality in a Wankel is very bad and leads to enormous amounts of unburnt hydrocarbons and carbon monoxide in the exhaust fumes (always indicators to bad combustion quality). The Wankel exhaust gases are extremely hot because so much thermal energy is lost through the exhaust instead of being put to use inside the engine.
Wankel combustion quality because of this is extremely bad. Under partial load, combustion is very incomplete, creating a nucleus of increasingly rich mixture in the trailing part of the “B” shaped combustion chamber. This leads to uneven running when this nucleus eventually burns, creating a similar effect as in a two stroke engine which on the overrun starts to “four stroke”. This uneven running characteristics were the reason why NSU had to fit a torque converter to the Ro80 to filter out this unevenness. To avoid this Mercedes fitted the C111 Wankel engine with direct injection and Mazda used the side inlet instead of the circumferential inlet preferred by NSU because this makes it easier to prevent this running condition (at the cost of power delivery). Norton Commander F1 Wankel motorcycles retrofitted with digital ignition had very unusual ignition timing to make the Wankel more usable on two wheels. Ignition was extremely retarded during engine start to make the engine start reliably, as soon as the engine was running the timing was advanced extremely to avoid forming of a rich nucleus and with increasing load the ignition was retarded again to create more power.
Thanks Eóin, that explanation made sense.
The much-derided piston engine has one major advantage, an almost unchangeable combustion chamber during combustion. For 15 degrees either side of top dead centre, due to geometry the piston moves very little up and down in the cylinder, giving almost constant volume conditions. This allows combustion chamber shapes to be modelled fairly accurately, although all sorts of eccentric inventors have come up with things that ruin the basic premise.
The rotary’s combustion chamber is far from this almost ideal situation. Constant rotational speed means the combustion chamber is constantly on the move being in the rotor, and you’ll never get the thermal efficiency out of it compared to a piston engine.
Once gas turbines got decent compressor stages of both high efficiency and pressure ratio, they could be persuaded to deliver decent thermal efficiency as well because they have unchanging combustion chambers. Aerodynamics tend to limit it to a small rpm range for best efficiency. Large gas turbines are used to efficiently generate electricity to fill in sudden demand on the system, because they can be ramped up from a cold start to synchronous rpm very rapidly indeed and produce prodigious amounts of power from a small size.
However, only the piston engine can be fiddled and farted around with, like using independently intake and exhaust variable cam timing and variable lift, variable fuel injection strategies, now variable compression ratios as per Nissan, variable super/turbocharging pressure, etc. to change operating conditions on the fly. The rotary is a bit of a one-trick pony, although with a lot of trouble some of the variables the piston engine can easily implement can be applied, leaving only the far from optimum moving combustion chamber shape to ruin things – probably not worth the effort.
The new Toyota “Dynamic Force” petrol 2.5 litre 4 cylinder makes it to 40% efficiency (41% on the pure Atkinson cycle version used in hybrids), about the same as your average electricity thermal power plant. There’s life in the old dog yet. If diesels didn’t spew so much nasty NOx due to even higher combustion temperatures which have to be artificially reduced, then it could probably be the engine of choice – as it stands it looks like a bit of a dead end, despite all the hand-clapping in Germany. And yet Toyota makes an emissions compliant 2.8 litre four that gets 44% efficiency. Europe needs to watch out for Japanese engine tech – that Brudack cycle VW petrol engine is a loser compared to what Honda churns out in Direct Injection turbo units.
Oh yes, the Ro80. Nice car in the modern idiom, the real trendsetter for the future in terms of suspension design for a FWD car. Not much change to this day except variations in rear suspenson from cheap torsion beams to multilink setups. Rational.