Wankel

Wankel (pronounced wahng-kuh)

A type of rotary internal combustion engine, first produced 1961, named after its inventor, German engineer, Felix (aka Fritz) Wankel (1902-1988).

The Wankel engine is a type of internal combustion rotary engine, one of many based on the a rotary principle, the Wankel using an eccentric drive to convert pressure into rotating motion.  The design was conceived by German engineer Felix Wankel, an eccentric, though clearly gifted, self-taught engineer who was an early convert to National-Socialism (linked with a right-wing political movement in 1921) who joined the NSDAP (the National Socialist German Workers Party which would become the Nazi Party) the following year.  It’s important not to make too much of that, the party in its early days an aggregation of factions which were, literally more nationalist and socialist in character than anything like the racist and ultimately genocidal thing into which the Nazis evolved under Adolf Hitler (1889-1945; Führer (leader) and German head of government 1933-1945 & head of state 1934-1945). 

But an enthusiastic Nazi Wankel certainly was although that didn’t protect him from falling victim to the internecine squabbles which would beset the party to the very end, expelled from the party in 1932 after feuding with his Gauleiter (the regional party boss) who, after Hitler came to power in 1933, succeeded in having Wankel jailed although, under less unpleasant conditions that those tossed into concentration camps.  Indeed, while in prison, he was able to continue working on his rotary engine, a patent for which had been granted to him in 1929.

Felix Wankel admires a shaft.

Wankel though had friends in the party, one of whom approached the Führer, stressing the importance of the amateur engineer’s contribution to German industry and that proved enough to secure his release.  He worked on a variety of projects during the 1930s, some on contract for BMW but mostly for the military including on seals, something which years later would absorb much of his energy at that of many others.  Despite his efforts for the Reich, his attempts to rejoin the party were rebuffed but his friends did gain him the honorary rank of Obersturmbannführer (Lieutenant Colonel) in the Schutzstaffel (The SS (Security Squad or Section), originally Hitler's personal security detail which evolved into a vast party security apparatus and later a parallel army almost a million strong) although his career in the "black mist" wasn't long, Wankel expelled within two years.  The records were lost in the confusion of war so the reasons aren’t known but while it’s tempting to wonder just how ghastly one has to be to be thought too evil for the SS, given the lack of any subsequent punitive action against him, it’s likely he just lost out in another of the squabbles that were so common in the Nazi system, the structures of which actually encouraged internal conflict.

It didn’t stop the Nazi state funding his research including what he was then calling his “rotary motion engine” although progress was slow and slow for a reason, the fundamental flaw in the design not resolved until the 1950s when another engineer, less visionary but more practical, rectified the fault.  Wankel's rotating cul-de-sac was far from unique in wartime Germany, the interest of the regime in technical innovation and the gullibility of party officials drew cranks, con-men and inventors inspired and otherwise.  Among the projects which received interest and sometimes cash from the state was a “non-combustible” material called durofol (which would catch fire), a scheme to create liquid fuel from the roots of fir trees (which consumed three times as much energy as it produced), the production of alcohol from bakery fumes (apparently that one was quickly rejected), a “death ray” championed by notorious drunkard Reichsleiter Robert Ley (1890–1945; head of the German Labour Front 1933-1945), which turned out to be impossible to build or even test, a plan to turn the atmosphere into a conductive element using ionization (which at least has a theoretical basis even if impossible) and the mysterious “Gerloff miracle pistol”, the records for which were lost.  Compared to some of these, Wankel’s engine (which didn’t work) probably appeared quite promising.

Gleitkufenboot (skid boat).

Wankel had other projects too, one of which he would, like his engine, later revisit.  This was the Zischboot (Hiss boat), intended as a small, high-speed torpedo-boat for the navy, a kind of hydrofoil that used clusters of skis.  In the 1970s, Wankel would display a prototype (now called the Gleitkufenboot (skid boat)), powered by an impressively powerful Mercedes-Benz four rotor Wankel engine.  Wankel claimed not only was it impossible to capsize the boat but that it was unsinkable, a notable feature said to be borrowed from certain sea creatures, air-intake "nostrils" with flaps controlled by sensors to ensure no water could penetrate when driving through waves.

Wankel survived the war and suffered not greatly in the denazification process the allied occupation authorities ran to weed out the worst of the worst, his work as an engineer suggesting someone unpolitical and being expelled both from the party and the SS probably helpful in mitigation.  In that he was lucky; had the investigators dug deeper they would have discovered Nazi-era Wankel held some fairly unsavory views and had expressed them more than once.  In the new Germany, those opinions he either no longer held or kept to himself, in 1951 obtaining a position with NSU as a technical consultant.  NSU were interested in his rotary motion engine.      

1957 NSU Prinz.

NSU (the name an abbreviation of "Neckarsulm", the city in which the factory was located) began in 1873 as a knitting machine manufacturer which in 1886 branched out into the production of bicycles and so successful did this prove that by 1892, the knitting machines were abandoned, the factory converted wholly to the building of bicycles.  The first NSU motorcycles appeared in 1901 and were both popular and profitable, encouraging the company in 1905 to enter the potentially even more lucrative market for cars.  Between then and the end of World War II (1939-1945), there were ups and downs but NSU survived and, in December 1946, resumed building bicycles and motorcycles, commercial vehicle production starting in 1949.  These efforts proved successful and the company, by now a significant beneficiary of Wirtschaftswunder (the post-war German "economic miracle"), was by the mid-1950s the world’s largest maker of motorcycles and profitable enough for car production to resume in 1957.     

1958 NSU Prinz Sport.

The car was modest enough, tiny and powered by a 600 cm³ (37 cubic inch) air-cooled twin cylinder powerplant which was essentially two motorcycle engines joined by a common crankcase.  As was fashionable in small European cars of the era, the engine was at the rear, something which would prove a cul-de-sac, most manufacturers outside the Warsaw Pact soon convinced to abandon the idea.  That disenchantment actually extended to Porsche which had the 911’s replacement in production by the mid-1970s, only to find out just about every soul left on the planet who still thought rear-engined cars a fine idea were Porsche 911 buyers who insisted nothing else would do.  The customer being always right, the 911 survives to this day and that a rear-engined machine can be as well-behaved as 911s now are will be no surprise to those familiar with modern electronics but Porsche, remarkably, had engineered a high degree of predictability into its behavior even before computers were robust and fast enough to do the job.  In 1958, NSU didn’t face the same issues of high-speed handling, the new Prinz (Prince) having but 20 bhp (15 kW).  It was wholly utilitarian but suited to the times and sold well, national success (and growing incomes) meaning within a year, the idea of a more profitable up-market version became attractive.  Although little more than an Italian-styled body atop the existing underpinnings and never a huge seller, the Prinz Sport remained in production for a decade and its lightweight and slippery shape made possible an impressive top speed of 75 mph (120 km/h).  By 1968 over twenty-thousand had been built and it was the Prinz Sport NSU used as the basis for the world’s first Wankel-engined car.

The rotary engine, light, powerful and with few moving parts had interested NSU which saw the potential for motorcycles but they also quickly identified the fundamental flaw in the design which Wankel had never resolved: both rotor and rotor housing rotated, each on different axes, creating an assembly almost impossible to keep in balance as well as necessitating an additional housing.  While Wankel proceeded along his path, publicized by NSU in 1954, another NSU engineer, Hanns Dieter Paschke (1920-1999), unbeknown to Wankel, was developing his own version (KKM 57), displayed in 1957 as the DKM 54 at the NSU Research & Development Department in Versuchsabteilung.  Before long, the concept would be refined in that the single housing became static and only the rotor rotated, Wankel’s original vision intriguing but perhaps, even now, impossible to build as a practical working device and NSU devoted some years to making their version exactly that.  In 1964, it was released to the public.

1967 NSU Spider.

In 1964, the Western world was not so laden with rules and restrictions (for good and bad) and it was possible to sell for use on the public highways what were essentially prototypes in development and that the NSU Spider certainly was.  It was also a seen by NSU as an advertisement on wheels, a showcase not only for their upcoming models but also to encourage other manufacturers to buy licenses to produce their own Wankels, an option that would be exercised by many, including Alfa Romeo, Curtiss-Wright, General Motors, Daimler-Benz, Rolls-Royce and Mazda.  For whatever reason, BMW, Felix Wankel's Nazi-era employer, declined.  Citroën, an outfit with a reputation for the quirky, were enthusiastic enough to set up with NSU a Swiss co-venture to pursue the technology.  More than most, the French would come to rue the day they ever heard Wankel’s name.

Skoda (rear) engine bays, the conventional (piston) engine (left) vs the single-rotor Wankel (right).

Although the project never progressed beyond the prototype stage, the Czech manufacturer Skoda was apparently the first to have running vehicles with a rotary engine installed (a complete engine said to have been running as early as 1961) but in 1964, the NSU Spider was the first to go on sale.  It used a single-rotor, water-cooled engine and was easily distinguishable from the Prinz Sport because it was a soft top cabriolet, apart from which it was substantially the same car with only detail differences in styling and specification except it was offered only in red or white.  One other change was definitely apparent however, power had jumped to a heady 50 bhp (37 kW) at a surprisingly low 5,500 rpm, enough to propel the Spider to close to 100 mph (160 km/h) for anyone on the autobahn prepared to push the little machine to the limit.  Never expected to be a big seller, fewer than 2500 were built between 1964-1967, its purpose more to whet the public appetite for what NSU intended to be their entry into the burgeoning middle-class mass market.  Additionally, though not at the time discussed, the Spider’s engine, while at a stage of development beyond being a prototype, was not ready for release to a public using it in a wide variety of ways in different climates in different countries.  The Spider’s customers unwittingly were also NSU’s development test team, something which later in the century would become a handy business model for many software companies.

Given the specifications of the Wankel NSU would produce in the future, it may that the Spider’s single rotor powerplant wasn’t an ideal a test bed for the customers to debug but problems in design and the choice of materials were identified and, where possible, within the limits of metallurgy and the realities of economics the lessons learned were applied.  Nor was the Spider’s specification static, the experiences of the customers applied to improve not only longevity but also power, the later cars enjoying a slight increase in capacity, output now 54 bhp (40 kW) at 6,000 rpm, 4 bhp perhaps not impressing all but it was close to 10% more and although the factory didn’t claim any increase in attainable speed, the most recent Spider owners presumably got there a little more quickly.

1967 NSU Ro 80 (1967-1977).

If the spider had generated interest, the NSU Ro 80, released in 1967, was a sensation.  Even without the novelty of the rotary engine (without which all concede it would doubtless have been a success), it would have made quite an impact.  The body, which does not look out of place even in the twenty-first century, was a modernist masterpiece, trendsetting in a way the 1955 Citroën DS (often called the déesse (literally "goddess")) was just too extreme to be yet more aerodynamically efficient, the Ro 80’s drag coefficient (CD) of .354 just a fraction better than the French car’s .359.  Beneath the skin, the futurist vision continued, the efficient front-wheel-drive packaging in the vanguard of adoption by larger vehicles, four wheel disk brakes (inboard at the front), a semi-automatic transmission, power-assisted rack and pinion steering and all independent suspension.  Reviews upon release were sometimes ecstatic, the only criticism from some who found the interior austere but it was era in which only the most expensive German cars were fitted-out with much beyond the starkly functional; NSU’s designers looked to Le Corbusier and Gropius, not the Jaguar Mark X.

The Ro 80 won the 1968 European Car of the Year award and buyers seemed as impressed as the many journalists who voted NSU.  Out on the autobahns, the twin-rotor engine was a smooth, quiet and a delight to use, the slippery shape meaning the 113 bhp (85 KW) it generated from a comparatively small 995 cm³ (61 cubic inch) displacement allowed it to match the speed of cars with even three times the capacity, the turbine-like feel encouraging a disregard for the 6500 rpm redline which it seemed to exceed without complaint.  The honeymoon didn’t last.  Critics began to notice it was good to match larger six cylinder cars in performance but it came at the cost of a thirst many V8 owners didn’t suffer.  Nor was the Ro 80, so at home cruising at 100 mph (160 km/h) on the autobahn, quite as happy in the stop-start urban conditions where the modern German motorist was now spending much time, some finding the previously admired semi-automatic transmission clumsy to use, the experience jerky.  The Wankel engine didn't deliver much much low-speed torque and drivers had to adjust their technique; those used to the more effortless performance of the 2-3 litre engines most often found in this class of car found negotiating their commute through a succession of red traffic-lights harder work than before.    

Nothing is perfect and such was the appreciation of the Ro 80’s virtues these drawbacks may have been overlooked or at least endured but what couldn’t be forgiven was that the Wankel engines were frequently, numerously, rapidly and expensively failing and, being within the warranty period, it was NSU which bore the cost to repair or replace.  That was bad enough but the car was quickly gaining a reputation for unreliability and sales were falling, exacerbating the financial strain NSU was suffering from all the warranty claims.  Nor was the once profitable motorcycle business there to subsidise the four-wheel venture, production having ended in 1968 to allow the company to focus on the Ro 80.  The problems hadn’t been wholly unexpected, just underestimated; NSU’s engineers had warned the board the engine wasn’t yet ready for production and needed at least months more durability testing and development but, perhaps remembering the relatively smooth introduction of the Spider, and certainly seeking cash-flow, approval was given for a debut in 1967.

It wasn’t difficult to work out where the problems lay which was mostly in the high wear of the apex seals and consequent damage to the rotor housing.  Essentially, the seal failure destroyed the engine, necessitating a replacement and it was not uncommon for replacement engines also to fail and require replacement, again under warranty.  For a small company with limited resources, it was unsustainable and NSU was soon unviable, the takeover by Volkswagen in 1969 said to be a "merger with Audi" only an attempt to glue a veneer of corporate respectability on what was the takeover of a distressed competitor.  It was unfortunate.  In just about every way except the flawed engine, the Ro 80 was years ahead of its time and deserved to succeed.

1967 Mazda Cosmo.

The issue was the engine at that stage of its development given the metallurgy of the time rather than NSU because Mazda, which had in 1961 purchased a licence to produce the Wankel, were suffering the same problems in the Cosmo sports car, introduced also in 1967.  The Cosmo however, was a low-volume model and Mazda had other, profitable ranges on sale and so could absorb the cost of fixing failed Cosmos.  Mazda did seem to learn from the NSU experience however.  When they put the Wankel into volume production, the vehicles initially were offered either as a rotary or with a conventional piston engine, an approach which seemed promising but such was the fragility of the Wankel, even that had to be abandoned.  Mazda, after putting Wankels even into small trucks and busses, realised that for consumer vehicles, it was a niche product and restricted it to specialist sports cars.  The problems didn’t go away, but, for a while, they became manageable.

Mazda RX-7 (the Porsche 924-928 inspired second generation (1985-1992) model) in Lindsay Lohan's music video clip First (2005).

The Cosmo's spiritual replacement was the RX7, a two door coupé (there was a short run of roadsters in the second generation) built over three generations between 1978-2002.  With over 800,000 produced, it's probably still the machine most identify with the Wankel engine and was the car which came closest to gaining the mainstream acceptance which had eluded earlier models such as the RX-2 (Capella), RX-3 (Savanna) & RX-4 (Luce), probably because reliability had significantly improved and those buying relatively expensive sports cars were more tolerant of the higher fuel bill and in fairness, much of the competition offering similar performance returned fuel consumption which was little different.  It was replaced by the RX-8 which proved (thus far), the swansong for the Mazda rotary on the streets.     

1972 NSU Prinz 1200 TT.

Remarkably, Audi-NSU, although axing the outdated rear-engined Prinz range, maintained the troublesome Ro 80 in production and despite its thirst it survived even the first oil crisis which killed off so many others.  Although most of the old NSU manufacturing capacity had long been given over to the Audi production line, it wasn’t until 1977 the last Ro 80 was built, the decade’s total production of 37,000-odd a disappointment for a car expected to ship more than that every year.

Despite NSU’s takeover in 1969 in the wake of the problem, even in the early 1970s, many major manufacturers were still convinced the Wankel's many advantages would render the piston engine obsolete and embarked on large, and expensive, development programs.  In this they were encouraged by the legendary optimism and confidence of engineers who so often think any engineering problem can be solved with enough time and money.  However the problems, seal wear, emissions and high fuel consumption proved insoluble and the projects which hadn’t been abandoned didn’t survive the first oil crisis.  Apart from the odd small-volume independent, only Mazda persisted. 

Notable Wankel Moments

1974 Mazda Rotary Parkway 26 Minibus (1974-1976).

The Mazda Cosmo was shown only weeks after the NSU Spider. Twice the capacity of the NSU, it was much more ambitious and though also troubled, its low volume meant the rectification was manageable.  Only Mazda has produced Wankel engines in large quantities and they've offered the power-plant in sports cars, racing cars, sedans, coupés, station wagons, pick-up trucks & buses, the last two perhaps a curious place to put an engine not noted for its prodigious torque.  Others, with varying degrees of success, have put them in automobiles, motorcycles, racing cars, aircraft, go-karts, jet skis, snowmobiles, chain saws, and auxiliary power units.

1976 Mazda RX-5.

Even Mazda, which has at least partially solved most of the problems, currently don't have a Wankel in production; the last, used in the RX-8, unable to meet the latest EU pollution standards.  Despite this, Mazda claim to be committed to the Wankel and the factory say development is continuing, in 2016 showing the RX-Vision, hinting it could be on sale as early as 2020.  The COVID-19 pandemic put that at least on hold and concerns about CO₂ emissions may mean the Wankel's historic automotive moment, which lingered for so long, may finally have passed so whether Mazda really solved the problem of toxicity may never be known. 

1975 HJ Mazda Roadpacer (HJ & HX, 1975-1977).

Even Holden fans, as one-eyed as any, don’t have fond memories of the HJ Premier.  Usually, all they’ll say is its face-lifted replacement, the HX, was worse.  Its engines strangled by the crude plumbing used in the era to reduce emissions, driving an HX wasn’t a rewarding experience so there might have been hope Mazda’s curious decision to use the HJ (and later the HX) Premier as their top-of-the range executive car, complete with a smooth two-rotor Wankel, might have transformed the thing.  That it did but the peaky, high-revving rotary was wholly unsuited to a relatively large, heavy car.  Despite producing less power and torque than even the anemic 202 cubic inch (3.3 litre) Holden straight-six it replaced, so hard did it have to work to shift the weight that fuel consumption was worse than when Holden fitted their hardly economical 308 cubic inch (5.0 litre) V8 for the home market.  Available only in Japan and sold officially between 1975-1977, fewer than eight-hundred were built, the company able to off-load the last of the HXs only in early 1980.  The only thing to which Mazda attached its name not mentioned in their corporate history, it's the skeleton in the Mazda closet but does have one place in history, the footnote of being the only car built by General Motors (GM) ever sold with a Wankel engine.

Mercedes-Benz C-111 (1968-1970 (Wankel versions)).

Although the C-111 would have a second career in the late 1970s in a series of 5-cylinder diesel and V8 petrol engined cars used to set long-distance speed & endurance records, it's best remembered in its original incarnation as the lurid-colored ("safety-orange" according to the factory) three and four-rotor Wankel-engined gullwing coupés, sixteen of which were built.  The original was a pure test-bed and looked like a failed high-school project but the second and third versions were both finished to production-car standards with typically high-quality German workmanship.  Although from the school of functional brutalism rather than the lovely things they might have been had styling been out-sourced to the Italians, the gullwings attracted much attention and soon cheques were enclosed in letters mailed to Stuttgart asking for one.  The cheques were returned; apparently there had never been plans for production even had the Wankel venture proved a success.  The C-111 was fast, the four-rotor version said to reach over 300 km/h (190 mph), faster than any production vehicle then available.

Herr Wankel’s personal R107 (350 SL) fitted with 4 Mercedes-Benz Rotor Wankel (KE-413).

Less conspicuously than the C-111s in lurid safety orange were the roadsters which Mercedes-Benz used as Wankel test-beds.  The first used the W113 (1963-1971) platform, remembered now as the first “pagoda” and while it would never have been suitable as a production car, it apparently wasn’t as unbalanced as the sole W113 fitted with the 6.3 litre (386 cubic inch) M-100 V8 used in the big 600 Grossers and the 300 SEL 6.3 which the test drivers described as "exciting but unstable".  Still, the Wankel W113 proved quite a bit faster than the 280 SL and as a proof of concept was judged a success.  The W113 though had never been intended to use anything but a straight-six whereas the successor W107 (1971-1989) was designed from the start with an engine bay and transmission tunnel which would accommodate either a V8 or the Wankel with its high central power take-off.  The W113 had used a three rotor unit (M 50 F) but R107 had four (KE-413) and delivered considerably more power than the 3.5 litre (215 cubic inch) & 4.5 litre (275) V8s used in the production models and not until the adoption of 5.0 (305) & 5.5 (339) V8s in the 1980s would the performance be matched.

Four rotor Wankel engine (KE-413, left) and the unit installed in Herr Wankel’s 350 SL.

Yet however successful the proof of concept may have been, the early skepticism mentioned by the combustion chamber specialists was vindicated because as they pointed out the chamber was "...the central feature of the combustion engine.  The priority is to produce an optimum design so as to achieve the most favorable thermodynamic efficiency."  By that they meant "...as complete combustion of the fuel as possible” and not only was this not happening with the Wankel, their point was that fundamental aspects of the design meant it could not happen, something which manifested in high fuel consumption and difficulties in meeting the exhaust emission standards due to all the non-combusted hydrocarbons.  Modest in their demands in the early 1970s, the US regulators had already provided a decade-long roadmap which would make the rules so onerous there was then no realistic prospect the Wankel could ever be made to comply.  The engineers were confident they could produce a smooth, reliable and powerful Wankel, albeit a thirsty one, but knew they could never make it clean.  All of the factory’s W113 & R107 test-beds were scrapped when the project was cancelled but Felix Wankel’s personal R107 SL survives.  He obtained a four rotor unit from Mercedes-Benz, had it installed by technicians at his institute and in 1979, the trade journal Auto Motor und Sport published their road-test of the unique machine, reporting a 0-200 km/h (120 mph) time of 25.9 seconds and a top speed of 242 km/h (150 mph).

Citroën GS (GX) Birotor (1973-1975), Frankfurt Motor Show, August 1973.

Sometimes one gets lucky, sometimes not.  In the US, Ford introduced the new, small and economical Mustang II a few weeks before the first oil shock in 1973 and had a big hit (something sometimes forgotten by those who so decry the Mustang II and condemn it a failure).  In Australia, about the same time, Leyland announced the big new P76, a selling point its V8 engine.  The P76 wasn’t without faults and may anyway have failed but the timing didn’t help and it didn’t last long, shortly taking with it whatever remained of Leyland Australia.  In France, in October 1973, the very month in which events in the Middle East triggered the first oil shock, Citroën's thirsty GS Birotor went on sale.  Shown at the Frankfurt Motor Show in August, the reception had been generally positive, most complaints being about the aesthetic; all the Birotors appeared to be painted in shades of brown, a color which seemed to stalk the 1970s.

Mechanically though, even before going on sale, some with high hopes for the Wankel were disappointed, the Birotor not realising the promise of smaller, lighter packages.  Despite the compact size, the engine would fit in the GS’s engine bay only transversely so Citroën’s signature inboard disk brakes couldn't be used for the first time since the pre-war Traction Avant. That necessitated a different subframe, a wider track, and bigger wheel arches than the standard GS.  Combined with other detail differences, it bulked the rotary-powered GS up to 690 lb (290 kg) more than the standard GS, compelling the addition of anti-roll bars to reduce the increased propensity towards body roll.  Another mechanical aspect not much discussed at the time was the Wankel's high exhaust emissions.  In one of many possible illustrations of how the politics of the matter has changed, it was a time when the exhaust pollution rules imposed by the United States appalled Europeans because of the way they made the detoxed cars behave.  Not wishing to sacrifice power, in Europe, drivers for years enjoyed un-emasculated engines and accepted the higher emission of CO₂ and other pollutants as part of life.  Widespread interest in climate change, then the concern of a handful of specialists looking at what was called the "greenhouse effect", was a generation away.  Despite cubic money being spent, it was one aspect of the Wankel that was never fixed and was the final nail in the coffin of Mazda's RX8.    

Known also as the GZ, the Birotor replaced the noisy but robust and economical air-cooled flat four used in the GS on which it was based and cost about 70% more.  The Wankel engine was the first fruit of the NSU-Citroën joint venture and, being of small capacity, attracted lower taxes than a similar piston-engined car.  However, it suffered the problems endemic to the Wankel: ruinously high fuel consumption and chronic unreliability caused by wear of the rotor seals and the damage this caused to the housing walls.  Citroën had looked at the Ro 80's issues and had included an additional oil pump to improve seal lubrication but the problems persisted.  Internal documents later revealed that just as at NSU half a decade earlier, there were those within Citroën who understood, long before the release, that a disaster was impending but a combination of corporate inertia, an unwillingness to admit failure and a number of contractual obligations meant the Birotor went on sale.  Within months the extent of the problem was realized.  Although only a few hundred had found buyers, broken ones were being towed to dealers around the country and owners were irate.  Early in 1975, Citroën dropped the model, offering to buy back all the 847 made, running or not, customers given a full-refund.  Most agreed and Citroen scrapped every one they could, hoping everyone would forget they ever existed.  A remarkable third of owners declined the offer and many survived in private hands; among Citroën aficionados they’re a collector’s item though probably more displayed as a curiosity than driven.

A twelve-rotor motor intended for marine applications.

The low weight, compact profile, small number of moving parts and very high specific output of the Wankel has always attracted engineers.  The Wankel turned out to be well suited to applications where it could be maintained at a constant speed for long periods, the problem of unburnt fuel in the exhaust substantially resolved, improving emissions and fuel consumption.  Wankels lose efficiency dramatically when they are revved up and down as they are in the normal use of a passenger car but in boats and aircraft where engine speed tends to be constant for long periods, they can work well.  In airframes especially, where weight is so critical, the inherent advantage of the vastly superior power to weight ratio can be compelling.

1989 Norton 588.

One of the many companies to purchase a licence from NSU was English motorcycle manufacturer BSA (British Small Arms) and this became the property of Norton when it absorbed BSA in 1973.  Norton’s troubled history in the 1970s had little to do with the Wankel but after bankruptcy, it was revived on more than one occasion and during one of those escapades, it made almost a thousand Wankel motorcycles.  Other manufacturers dabbled with Wankels and Suzuki actually made some 6000 RE5s between 1974-1976 but the best of the breed were thought to be the Nortons, even though they were admitted to be early in the development cycle.  The Wankel was a more reliable thing by the time the Nortons were made but they suffered the underlying problem of all road-going applications: the advantages just weren’t enough to outweigh the drawbacks, added to which, piston engines continued to improve.  Norton allowed the project to die but did use the Wankel technology to develop a line of UAV (unmanned aerial vehicles, sometimes called drones) engines that proved successful; weighing only 22 lb (8.2 KG) yet producing 38 bhp (28 kw) they proved ideal for the task.

1972 Chevrolet Corvette XP-895 Prototype.

In 1972, spooked a bit by the news Ford would be offering the mid-engined De Tomaso Pantera through Lincoln-Mercury dealers, to steal a bit of the thunder, Chevrolet dusted-off and displayed a mid-engined Corvette prototype, production of which had been cancelled because of the cost.  It was shown again in 1973, this time with a four-rotor version of the Wankel GM had been developing in a number of configurations.  After the Wankel project was aborted, there were plans to use the body with a V8 to replace the existing Corvette, a release penciled in for 1980 but again, costs and concerns about sales potential aborted the idea.  It meant the already long-serving Corvette stayed in the line for fifteen years, not replaced until 1983 and not until well into the next century was a mid-engined version released.

Resin

Resin (pronounced rez-in)

(1) Any of a group of non-volatile solid or semisolid organic substances & compounds (that consist of amorphous mixtures of carboxylic acids), obtained directly from certain plants as exudations of such as copal, rosin & amber (or prepared by polymerization of simple molecules) and used typically in pharmaceuticals, plastic production, lacquers, adhesives and varnishes.

(2) A substance of this type obtained from certain pine trees (also called rosin).

(3) To treat, rub or coat with resin.

(4) A precipitate formed by the addition of water to certain tinctures.

(5) Any of various artificial substances, such as polyurethane, that possess similar properties to natural resins and used in the production of plastics; any synthetic compound with similar properties.

1350–1400: From the Middle English resyn & resyne (hardened secretions of various plants), from the Old French resine (gum, resin), from the Latin rēsīna (resin), from the Ancient Greek rhētī́nē (resin of the pine tree), both probably from a non-Indo-European language.  In chemistry, the word came to be applied to synthetic products by after 1883.  The verb resinate (impregnate with resin) dated from 1756.  The adjective resinous (of the nature of, pertaining to, or obtained from resin) is documented since the 1640s, from the Latin resinosus; the earlier adjective was resiny (having a character or quality like resin), noted since the 1570s.  The related (and now rare) noun rosin (distillate of turpentine (especially when in a solid state and employed for ordinary purposes)) dates from the late thirteenth century and was from the Old French raisine & rousine, both variants of résine; it was used as a verb after the mid-fifteenth century.  The later adjectives resiniferous & resinless appear never to have been used except in chemistry or technical literature in relevant industries, the more common forms in general use being resin-like or resinous.  Because the word resin covers a wide field of substances, it usually appears in modified form (acaroid resin, acrylic resin, epoxy resin, phenolic resin, polyresin, polyvinyl resin et al).  The present participle is resining and the past participle resined.  Resin, resinousness & resinite are nouns, resinously is an adverb and resinify is a verb; the noun plural is resins.

Resin wheels

1972 Citroën SM with Michelin RR wheels. 

Although sometimes referred to as being made from “carbon fibre”, materials engineers insist the optional wheels offered on the Citroën SM must be described as “synthetic resin reinforced with long-strand carbon fibre”.  Notable as the first composite road wheel offered for public sale, they were developed by Michelin, the tyre-maker which since 1934 had been Citroën’s parent corporation and the innovation was an appropriate accessory for the SM which, upon release in 1971, was immediately recognized as among the most intricate and intriguing cars in the world.  A descendant of the DS which in 1955 had been even more of a sensation than the SM, it took Citroën not only up-market but into a niche the SM had created, nothing quite like it previously existing, the combination of a large (in European terms), front-wheel-drive (FWD) luxury coupé with hydro-pneumatic suspension, self-centreing (Vari-Power steering), high-pressure braking and a four-cam V6 engine, unique in the world.  The engine had been developed by Maserati, one of Citroën’s recent acquisitions and the name acknowledged the Italian debt, SM standing for Systemé Maserati.  Although, given the size and weight of the SM, the V6 was of modest displacement (initially 2.7 litres (163 cubic inch) and power was limited compared to the competition (181 HP (133 kW)), such was the slipperiness of the body that in terms of top speed, it was at least a match for most.

Michelin RR wheel.

However, lacking the high-performance pedigree enjoy by some of that competition, a rallying campaign had been planned as a promotional tool.  Although obviously unsuited to circuit racing, the big, heavy SM didn’t immediately commend itself as a rally car, early tests indicated some potential but there was a need radically to reduce weight.  One obvious candidate was the steel wheels but attempts to use lightweight aluminum units proved abortive, cracking encountered when tested under rally conditions.  Michelin immediately offered to develop glass-fibre reinforced resin wheels, the company familiar with the material which had proved durable when tested under extreme loads.  Called the Michelin RR (roues resin (resin wheel)), the new wheels were created as a one-piece mold, made entirely of resin except for some embedded steel reinforcements at the stud holes to distribute the stresses.  At around 9.4 lb (4¼ kg) apiece, they were less than half the weight of a steel wheel and in testing proved as strong and reliable as Michelin had promised.  Thus satisfied, Citroën went rallying.

Citroën SM, Morocco Rally, 1971.

The improbable rally car proved a success, winning first time out in the 1971 Morocco Rally and further success followed.  Strangely, the 1970s proved an era of heavy cruisers doing well in the sport, Mercedes-Benz winning events with their 450SLC 5.0 which was both the first V8 and the first car with an automatic transmission to win a European rally.  Stranger still, Ford in Australia re-purposed one of the Falcon GTHO Phase IV race cars which had become redundant when the programme was cancelled in 1972 and the thing proved surprisingly competitive during the brief periods it was mobile, the lack of suitable tyres meaning the sidewalls repeatedly failed.  However, the SM, GTHO & SLC proved a quixotic tilt and the sport went a different direction.  On the SM however, the resin wheels had proved their durability, not one failing during the whole campaign and encouraged by customer requests, Citroën in 1972 offered the wheels as a factory option although only in Europe; apparently the thought of asking the US federal safety regulators to approve plastic wheels (as they’d already been dubbed by the motoring press) seemed so absurd to the French they never bothered to submit an application.

Reproduction RR in aluminum. 

Michelin ceased to make the RR when SM production ended in 1975 but did provide another batch for sale in the mid 1980s and this was said to be a new production run rather than unsold stock.  A cult accessory for a cult car, perfect examples now sell for around US$2000 each which does sound expensive but, given what it can cost to restore (or even maintain) a SM, it’s not a significant sum and, unlike much of the rest of the machine, the RRs are at least trouble-free.  Michelin are not said to be contemplating resuming production but another company has produced visually identical wheels made from aluminum; these only slightly heavier.  Despite the success and the fifty-year history of robustness, Citroën didn’t persist and the rest of the industry never adopted the resin wheel.  The reason was two-fold: (1) Even if economies of scale operated to lower the unit cost, the technology was always going to be more expensive than using aluminum and advances in alloys meant the metal units can provide similar strength with only a slight weight penalty and (2) the resin was always susceptible to high temperatures, something not encountered on the SM which used inboard brakes.  Most cars however don’t use inboard brakes and as Ford found when testing resin wheels during Lincoln's downsizing programme in the mid-1970s, although the weight reduction was impressive, almost the same was possible with aluminum at much lower cost and the problems caused by heat-soak from the brakes were insoluble.  So it proved until the late 1980s when, with the development of new, heat-resistant materials, reinforced resin wheels were made available on the limited-production Dodge Shelby CSX (1989).

True carbon fibre wheels have had a little more success, although only at the top-end of the market, Koenigsegg in 2013 manufacturing carbon fibre single-piece wheels which it offered as a US$40,000 option; a number which needs to be considered in the context of the US$2 million price tag for one of their cars.  Porsche, Mercedes-Benz, Ferrari and Ford have all flirted with carbon fibre wheels and some manufactures are interested in the possibilities offered by hybrid designs which use aluminum for some components and carbon fibre for others, an idea familiar from earlier steel/aluminum combinations.  Regulatory authorities are apparently still pondering things.

The SM V8

1974 prototype Citroën SM with 4.0 V8.

Ambitious as it was, circumstances combined in a curious way that might have made the SM more remarkable still.  By 1973, sales of the SM, after an encouraging start had for two years been in decline, a reputation for unreliability already tarnishing its reputation but the first oil shock dealt what appeared to be a fatal blow; from selling almost 5000 in 1971, by 1974 production numbered not even 300.  The market for fast, thirsty cars had shrunk and most of the trans-Atlantic hybrids (combining elegant European coachwork with large, powerful and cheap US V8s) which had for more than a decade done good business as alternative to the highly strung British and Italian thoroughbreds had been driven extinct.  Counter-intuitively, Citroën’s solution was to develop an even thirstier V8 SM.  It actually made some sense because, in an attempt to amortize costs, the SM’s platform had been used as the basis for the new Maserati Quattroporte but, bigger and heavier still, performance was sub-standard and the theory was a V8 version would transform both and appeal to the US market, then the hope of many struggling manufacturers.

Recreation of 1974 Citroën SM V8 prototype.

Citroën didn’t have a V8; Maserati did but it was big and heavy, a relic with origins in 1950s sports car racing and while its (never wholly tamed) raucous qualities suited the character of the sports cars and saloons Maserati offered in the 1960s, it couldn’t be used in something like the SM.  However, the SM’s V6 was a 90^o unit and thus inherently better suited to an eight-cylinder configuration.  In 1974 therefore, a four litre (244 cubic inch) V8 based on the V6 (by then 3.0 litres (181 cubic inch)) was quickly built and installed in an SM which was subjected to the usual battery of tests over a reported 20,000 km (12,000 miles) during which it was said to have performed faultlessly.  Bankruptcy (to which the SM, along with some of the company's other ventures, notably the Wankel programme, contributed) however was the death knell for both the SM and the V8, the prototype car scrapped while the unique engine was removed and stored, later used to create a replica of the 1974 test mule.

Citroën Traction Avant 22, Paris Motor Show 1934.

It was a shame because, despite being most associated with the US, it was the French engineer Léon Levavasseur (1863–1922) who in 1904 created the first V8 engine and at the 1934 Paris Motor Show, Citroën displayed their “22”, a variation of their Traction Avant model but fitted with a 3.8 litre (233 cubic inch) V8, created essentially by joining on a common crankcase two of their 1.9 litre (117 cubic inch) four-cylinder units.  When presented at the show, several models were displayed and the promotional material confirmed the 22 would be available with an extensive choice of coachwork including a saloon, an elongated limousine, a cabriolet and a coupé.  Bankruptcy however halted the project and Michelin, having just taken control, insisted the company concentrate on the best-selling, most profitable lines.  A reputed two dozen-odd 22s were built before the Michelin Man dropped his axe and although all passed into private hands, none appears to have survived the war although there have always been rumors one remains hidden somewhere in the Far-East, a survivor of the colonial presence in Indo-China.

1967 Cadillac Eldorado, which proved the big, FWD coupé could still be done.

Evidence does however suggest a V8 SM would likely have been a failure, just compounding the existing error on an even grander scale.  It’s true that Oldsmobile and Cadillac had offered big FWD coupés with great success since the mid 1960s (the Cadillac at one point fitted with a 500 cubic inch (8.2 litre) V8 rated at 400 HP (300 kW)) but they were very different machines to the SM and appealed to a different market.  Probably the first car to explore what demand might have existed for a V8 SM was the hardly successful 1986 Lancia Thema 8·32 which used the Ferrari 2.9 litre (179 cubic inch) V8 in a FWD platform.  It was about a daft an idea as it sounds.  Even had the V8 SM been all-wheel-drive (AWD) it would probably still have been a failure but it would now be remembered as a revolution ahead of its time.  As it is, the whole SM story is just another cul-de-sac, albeit one which has become a (mostly) fondly-regarded cult.

Lindsay Lohan in Tsubi Scooter Jeans, Andrea Brueckner Saddle Bag, L.A.M.B. Lambstooth Sweater, Manolo Blahnik Butterfly Sandals & Louis Vuitton Inclusion Resin Bangle, Los Angeles, April 2005.