In 1967, the small German automaker NSU introduced what would be its final and most ambitious product: the remarkable Ro80. It was NSU’s first and last luxury car, a sophisticated, highly aerodynamic sedan powered by a Wankel rotary engine. The Ro80 survived for 10 years, generating critical acclaim and controversy in roughly equal measure. In this installment of Ate Up With Motor, we take a closer look at the turbulent and sometimes troubled history of the 1967-1977 NSU Ro80.
NSU PLAYS THE LONG SHOT
NSU was founded in 1873 in the small town of Neckarsulm at the union of the Neckar and Sulm rivers in the German state of Baden-Württemberg. Like many early automakers, the company started off in a very different field, in this case sewing and knitting machines. (NSU was originally an acronym for Neckarsulm Strickmachinen Union, Neckarsulm Sewing Machine Co.) NSU started building motorcycles in 1901 and automobiles in 1905, followed a few years later by trucks.
Although the company produced some successful and rather sporty cars in the 1920s, the onset of the Depression led NSU to sell its automotive business to Fiat (which used the NSU-Fiat brand into the mid-1930s) and focus exclusively on motorcycles and motorbikes. It was not until the mid-1950s that NSU once again turned its attention to automobiles, introducing the NSU Prinz in 1957. While NSU had offered four- and six-cylinder cars back in the 1920s, the Prinz was a rear-engined mini-car powered by a decidedly motorcycle-like air-cooled, two-cylinder engine.
NSU introduced its first four-cylinder postwar car, the Prinz 1000, at the 1964 Frankfurt auto show, but managing director Gerd Stieler von Heydekampf had already set his sights on bigger game. The West German economy had improved markedly in recent years, and buyers were graduating from mopeds and tiny bubble cars to larger and more luxurious sedans. NSU’s market share was only modest as it was; if the company didn’t evolve, its future looked gloomy.
In late 1962, NSU commenced work on a new model known internally as Typ 80. As originally conceived, it was to be in the same class as the Ford Taunus P4. Design targets were an engine output of 80 PS (79 hp, 59 kW), a weight of 800 kg (1,765 lb), and a price of 8,000 DM — about $2,000 at the contemporary exchange rate. Like the Taunus, the Typ 80 would have monocoque construction and front-wheel-drive, developed by chief engineer Ewald Praxl. The new model’s styling, meanwhile, was the responsibility of in-house designer Claus Luthe, who had joined NSU in 1956 after stints at Fiat and the bus maker Spengler.
Luthe’s design, commenced in early 1963 and completed as a full-size model that September, was exceptionally clean and airy, with a large, six-light greenhouse that made the car look smaller than it actually was. Space utilization was excellent, but the Typ 80 was far less boxy than most contemporary German sedans, leading to (unfounded) rumors in later years that it was actually designed in Italy like NSU’s earlier, Bertone-styled Sport Prinz coupe. The Typ 80’s most impressive attributes were its aerodynamics; in the interests of maximizing fuel economy, low drag was an important part of the design brief. Subsequent wind tunnel tests at Stuttgart Polytechnic Institute revealed a drag coefficient of 0.355, outstanding for the era.
The full-size model, which was presented to NSU’s managing board in May 1964, was very close to the eventual production model in shape, but not dimensions. After considering the car’s likely cost, Von Heydekampf and the board selected a loftier target than the Taunus: the executive car market occupied by the likes of the Mercedes W110 (200/230) and BMW Neue Klasse sedans. To compete in that segment, the Typ 80 would be scaled up in size, weight, and price, eventually rising from 8,000 to more than 14,000 DM (about $3,500).
You’ll note that we haven’t yet said a word about the Typ 80’s most significant and unusual feature, its rotary engine. However, even with a completely conventional powertrain, the Typ 80 would have been a very ambitious step for NSU, analogous to Honda proceeding directly from the original 1972 Civic to the six-cylinder Legend. BMW, of course, had developed its Neue Klasse sedans after several years of focusing on motorcycles and mini-cars, but BMW had also built larger, more prestigious cars like the 502, 503, and 507 throughout the fifties and early sixties (albeit not in large numbers). By contrast, NSU hadn’t built anything like a luxury car in more than 30 years.
Moving the project so far upmarket would have been a gamble no matter what, but what elevated it from bold marketing move to Citroën-like cliff-diving audacity was the Typ 80’s intended engine, NSU’s greatest and riskiest asset: the brainchild of inventor Felix Wankel.
We talked about the development and workings of the Wankel rotary engine in last year’s article on the early Mazda rotaries, but here is a recap for those joining us late.
Inventor Felix Wankel conceived the rotary engine while still a teenager and began filing patents on such engine designs in the 1930s, but his work on the rotary was interrupted by other projects and by the war. In 1936, Wankel joined the Deutschen Versuchsanstalt Für Luftfahrt (German Experimental Institute for Aviation), designing rotary valves for Daimler-Benz’s DB601, a 33.4-liter (2,020 cu. in.) V-12 for military aircraft, and later the Junkers KM8 torpedo engine. After the German surrender, Wankel spent time in prison for his military work, but he was released in 1946 and eventually allowed to return to practical research, establishing a new shop in Lindau, Bavaria.
Shortly afterward, Wankel’s old acquaintance Wilhelm Keppler arranged an introduction to Victor Frankenberger, NSU’s technical director, and NSU research chief Walter Fröde. On Fröde’s recommendation, NSU signed a consulting agreement with Wankel, first to apply Wankel’s rotary valve concept to motorcycle engines and subsequently to develop a unique rotary supercharger.
Throughout his consulting work, Wankel tried repeatedly to convince Von Heydekampf and the NSU board to fund the development of a rotary engine. However, NSU was far from over-capitalized, so it took three years and a great deal of cajoling before the board finally agreed.
Almost as soon as Wankel’s first DKM 54 (DKM for Drehkohlbenmotor, “Rotary Piston Engine”) prototype was running, Fröde concluded that it was hopelessly impractical for anything except perhaps stationary applications. Fröde and his staff in Neckarsulm soon developed an alternative design, the KKM (Kreiskolbenmotor, roughly “Circuit Piston Engine”), which first ran on a test stand in 1958. Unlike Wankel’s DKM, in which both the rotor and the housing rotated around a stationary shaft, the KKM used a trochoidal rotor (shaped something like a three-lobed peanut) that traced a mathematically complex path along a cocoon-shaped stationary housing. (See the animation on the next page.)
Wankel considered the KKM a bastardization of his concept and Fröde’s design did sacrifice a measure of the DKM’s smoothness and exceptional rev potential, but the KKM was unarguably more useful. With much of NSU’s limited capital tied up in the launch of the Prinz, the entire project was hanging by a thread and the board was definitely not willing to foot the bill for two engines, so Fröde finally convinced Wankel to accept the KKM. (It probably helped that the deal Wankel’s business partner Ernst Hutzenlaub struck with NSU later that year ensured that Wankel would share in the patent royalties either way. In fact, Wankel and Hutzenlaub received a substantial cut — initially 40% — of NSU’s rotary engine revenues, paid through a holding company called Wankel GmbH.)
Although NSU began selling patent licenses almost immediately, beginning that fall with a deal with the aviation company Curtiss-Wright, the KKM had a long way to go before it would be a viable production engine. Fuel and oil consumption were inherently high, low-end torque was poor, and early engines suffered a host of serious maladies, including excessive exhaust smoke, seized bearings, heat-induced cracks around the spark plugs, and scored rotor housings (the infamous “chatter marks” that would also plague Toyo Kogyo’s development efforts). Probably the greatest challenge was the apex seals at the rotor tips, which were responsible for maintaining compression and preventing exhaust gases from mixing with the intake charge. Developing workable apex seals would be a major test for every user of the Wankel KKM design, including NSU itself.