We doubt you have ever heard of them, but in the early days of World War 1 Rumpler was known to millions. The Rumpler Taube monoplane, with its swept-back wings and triangular tailplane epitomised German military air power. One sight of its sinister silhouette was enough to make any allied civilian run for shelter.
Dr Edmund Rumpler
Forbidden to continue with his aeronautical work after the armistice, Dr Edmund Rumpler decided to apply the lessons he had learned from aircraft engineering to the development of a revolutionary type of motorcar. He was, after all, a car engineer by training. Born in Bohemia in the Austro-Hungarian empire, Rumpler had been associated in the production of the first Nesseldorf car, the flat-twin Prasident, in 1897, along with another engineer who was to receive a wider fame, Hans Ledwinka.
Rumpler later moved to Daimler, and then joined Adler in 1903, where he developed the first German engine to be built in unit with its gearbox and also produced and patented a form of swing-axle independent rear suspension. He left Adler for aeronautics as early as 1907, and returned to car manufacture in 1921, causing a sensation at that year's Berlin Motor Show with a vehicle unlike any seen before.
Built in Rumpler's little factory in Berlin, the Tropfenwaagen (Teardrop Car) was completely unconventional. In plan it looked like a fish, with a rounded forward end and a long tapering tail, for maximum efficiency of air penetration. Horizontal mud wings were mounted above the disc wheels to protect the body sides from splashing without setting up any forward resistance.
Even the rigid steel chassis frame was contoured and faired so that it did not impede airflow, and closed Tropfenwagens had curved window glass moulded to the body outline, too. The driver sat well forward, in a solitary central seat, for optimum visibility, and all seats were carried between the axles for maximum riding comfort. Long cantilever springs carried a beam axle at the front, swing axles at the rear.
Siemens and Halske
But apart from all this, the Rumpler had an entirely new type of power unit. Mounted at the rear, and built in unit with the gearbox and final drive, the engine was a six-cylinder four stroke with its cylinders set in arrowhead configuration in three banks of two. Specially built by Siemens and Halske, it had a swept volume of 2580 cc, overhead valves closed by leaf springs and alloy pistons. Power output was claimed as 36 bhp at 2000 rpm.
These drawings give some indication of the mechanical layout of the original Tropfenwagen of 1921; the engine was placed in the rear and built in unit with the gearbox and the final drive.
The multi-plate steel clutch ran in oil, and the entire engine/transmission unit was exceptionally short to aid weight distribution. Scaling virtually 3000 lb, the Tropfenwagen was capable of reaching 70 mph, thanks to its clean contours: and it was the speed potential of the Rumpler which led the Benz company to take an interest in the project. Their eventual aim was to develop a production Rumpler-Benz; but they decided to prove the design by producing a series of racers.
Under the leadership of Hans Nibel, the Benz engineers built a sleek cigar-shaped racer whose appearance uncannily presaged that of the rear-engined Auto-Union of a decade later (of course, that project involved several former Rumpler engineers). The Rumpler chassis was used almost unchanged, though Benz developed their own six-cylinder racing engine of 1991 cc with twin shaft-driven overhead camshafts, alloy pistons and roller-bearing crankshaft; four-wheel cable operated brakes
were fitted, those at the rear being mounted inboard to reduce unsprung weight. Even the radiator
was streamlined, contained in a fan-shaped fairing behind the driver's head, with a bullet-shaped headed tank in polished metal.
The Tropfenrennwagen - Racing Teardrop
Developing 80 bhp at 4500 rpm the engine could propel the Tropfenrennwagen ('Racing Teardrop') at 100 mph. On its maiden outing, the new racer seemed destined for great success, for in the 1923 Italian Grand Prix
three Tropfenrennwagen were entered, driven by Homer, Minoia and Walb: Walb retired early, but the other two drivers finished fourth and fifth, no mean achievement for a totally untried design of such radical concept. But that, apart from a few victories in minor races and hill-climbs, was the sum total of the Tropfenrenn-wagen's achievements.
Benz also built some road-equipped sports cars to Rumpler's designs; but they were now drifting into the period of poor sales and financial crisis that led to the merger with Mercedes in the mid-twenties, and the 3 million mark development cost of the Rumpler-Benz models was becoming an embarrassment. So the project was dropped, leaving only a few road tests which spoke admiringly of light, positive steering
and impeccable road-holding at 90 mph and over.
The Tropfenwagen 4A-106
On his own again, Edmund Rumpler announced a new Tropfenwagen in 1924. Designated the 4A 106, this had a conventional four-cylinder-in-line engine of 2614cc developing 50 bhp at 2400. Overall design was otherwise little changed apart from a longer wheelbase to accommodate the new power unit (which gave the incidental benefit of increasing passenger capacity from 4/5 to 6/7. Top speed was around 75 mph, but it was said that the increase in wheelbase had upset the roadholding. Sales continued to be minimal, and in 1925 Rumpler modified the design to give somewhat more generally acceptable lines, with 'proper' mudguards and running boards.
This did not help sell the Rumpler, and in 1926 Dr Rumpler began work on a new front-engined design. As square-cut as its predecessor was streamlined, the Rumpler Ru-6A-104 was nevertheless still an advanced, unconventional vehicle. It used the in-line four-cylinder engine of its predecessor turned round to give front-wheel drive and independent front suspension by swing axles and quadruple quarter-elliptic springing; rear axles were independently sprung, too, though only a pair of quarter-eliptic was used here. A light Z-beam chassis was employed, and there were four-wheel mechanical brakes: but this model never reached production, it was a victim of the increasingly confused German financial situation and of its own unorthodoxy.