The Rumpler Tropfenwagen ("Rumpler drop car", named after its shape) was a car developed by Austrian engineer Edmund Rumpler.

Rumpler, born in Vienna, was a designer of aircraft when on the 1921's Berlin car show he introduced the Tropfenwagen. It was to be the first streamlined car (beating the American Chrysler Airflow and Czech Tatra T77). The Rumpler had a Cw-value of only 0.28. The measuring, which was run at a Volkswagen windtunnel in 1979, astonished engineers; Volkswagen wouldn't beat the value until 1988 with the Passat The Fiat Balilla of the period, by contrast, was 0.60.

The car featured a Siemens and Halske-built 2,580 cc (157 cu in) overhead valve W6 engine, with three banks of paired cylinders, all working on a common crankshaft.Producing 36 hp (27 kW), it was mounted just ahead of the rear axle. The engine, transmission, and final drive were assembled together and installed as a unit. The rear swing axles were suspended by trailing leaf springs, while the front beam axle was suspended by leading leaf springs.

Able to seat four or five all the passengers were carried between the axles, for maximum comfort, while the driver was alone at the front, to maximize view. With the 1923 model, two tip-up seats were added.

Weighing nearly 3,000 lb (1,361 kg), the Tropfenwagen was nevertheless capable of 70 mph (110 km/h) on its mere 36 hp (27 kW). This performance got the attention of Benz & Cie.'s chief engineer, Hans Nibel. Nibel conceived the Tropfenwagen racers using the virtually unchanged Rumpler chassis. Poor sales and increasing losses led Benz to abandon the project. Later Auto Union racing cars resembled the Benz Tropfenwagen racers and were built in part by Rumpler engineers.

Rumpler made another attempt in 1924, the 4A106, which used a 50 hp (37 kW) 2,614 cc (159.5 cu in) inline 4-cylinder engine. This compelled a growth in wheelbase, with a consequent increase in seating to six or seven.

Although the car was very advanced for its time, it sold poorly—about 100 cars were built. Small problems at the start (cooling, steering), the appearance of the vehicle, and the absence of a luggage compartment hindered sales. Most were sold as taxis, where easy boarding and the high ceiling were advantages. The last cars were built in 1925.

The Tropfenwagen did become famous, thanks to the film "Metropolis", in which Rumplers found a burning end. It also inspired Mercedes-Benz 130H and 150H road cars.

Only two examples are known to survive, one in the Deutsches Museum's Verkehrszentrum in Munich and one in the Deutsches Technikmuseum Berlin.

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