Motorenfabrik Oberursel

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Motorenfabrik Oberursel A.G. was a German manufacturer of automobile, locomotive and aircraft engines. During World War I they supplied a major 100 hp-class rotary engine that was used in a number of early-war fighter aircraft designs. In 1921 the company merged with Deutz AG, and then again in 1930 with Humboldt-Deutz Motoren, and finally in 1938 with Klöcknerwerke AG. From this point on they were known as the Klöckner-Humboldt-Deutz Oberursel factory, known primarily for their locomotive engines. Today they are part of Rolls-Royce plc, and produce one family of their jet engines.

The company started when Willy Seck invented a new gasoline fuel injection system and produced a small one-cylinder stationary engine of about 4 hp he called the Gnom. The next year he started Willy Seck & Co. to sell the design, which became famous around the world. The engine was improved to achieve more power, but in 1897 the shareholders refused to allow Seck to develop a Gnom-powered car and he left the company. The company was reorganized as Motorenfabrik Oberursel the next year, and by 1900 had built 2000 engines.

The same year the company granted a licensed to produce the Gnom in France to the Seguin brothers in Lyon. Selling it under the French name Gnome, the engine became so successful they renamed their company to the same name. In 1908 they developed a rotary version of the basic Gnome system as the Gnome Delta aircraft engine, and from there a series of larger versions of the same basic design. The new Gnome engines were wildly successful, powering many of the early record breaking aircraft.

Oberursel eventually took out a license on the design in 1913, and the similar Le Rhône 9C at the same time. They produced both, the Gnomes as the U-series, and the Le Rhônes as the UR-series. When the war started the next year, the Oberursel U.I of 100 hp, a clone of the Gnôme Monosoupape 100 hp rotary, had the best power-to-weight ratio of any German engine. It went on to power most of the early German fighters, such as the Fokker and Pfalz E-series monoplanes.

Oberursel also built a copy of Gnome's 14-cylinder two-row rotary. This 160 hp (120 kW) engine, designated U.III in Germany, was difficult to build and quickly wore out in service. It was used on the Fokker E.IV and D.III designs.

The 110 hp Oberursel UR.II, the clone of the Le Rhône 9J of the same power output, was the next major success. Fokker bought the company in 1916 in order to guarantee supplies of the UR.II. This acquisition proved advantageous because Fokker was partial to rotary powered designs, and because supplies of the Mercedes D.III engine were limited. The UR.II was used in the Fokker Dr.I and Fokker D.VI.

By 1917, the UR.II had been rendered obsolete by its relatively low power and poor performance at altitude. An 11-cylinder development, the UR.III, was not used operationally. Indeed, by 1918, rotary engines had largely fallen from favor with the Idflieg and with pilots. The lack of castor oil and the poor quality of the mineral oil substitute "Voltol" severely reduced engine life and reliability. Nevertheless, in the summer of 1918, the UR.II was intalled in the Fokker D.VIII. The light weight and aerodynamic cleanliness of the D.VIII allowed it to achieve excellent performance even with the outdated UR.II.

After the war the company was purchased in 1921 by Gasmotorenfabrik Deutz, another gasoline engine manufacturer, who moved their two-stroke diesel manufacturing to the Oberursel factories. In 1930 they merged with Humboldt-Deutz, but with only one product line. The factory was eventually closed in 1932 during the Great Depression, reopening in 1934 for small-scale production.

In 1940 all diesel research was relocated to Oberursel, where Dr. Ing. Adolf Schnürle led the development of much larger and more advanced engines for aircraft use. This led to the Klöckner-Humboldt-Deutz DZ 700 8-cylinder radial engine, the DZ 710 16-cylinder boxer engine, and the DZ 720 32-cylinder H-block made from twinned 710's. None of these designs reached operational use by the end of the war, when the factory was occupied by US troops. For a short period in 1946 the factories were used as a tank repair depot.

In 1956 the factories were returned to Klöckner-Humboldt-Deutz, and from then on have been used primarily for gas turbine development and production. For the next twenty years they produced a variety of designs, typically under license from other companies. In 1980 they were renamed KHD-Luftfahrttechnik.

In 1990 the company was sold to what was then BMW Rolls-Royce. The new owners decided to use the Oberursel plants to produce an entirely modern engine for the "small end" of the aviation market, and started development of the BR700 family in 1991. The engines have since gone on to power a number of aircraft from Bombardier, Gulfstream and the Boeing 717.