1909 saw radial engine forms rise to significance. The air-cooled Anzani 3-cylinder semi-radial or fan engine of 1909 (also built in a true, 120° cylinder angle radial form) developed only 25 hp (16 kW) but was much lighter than the liquid-cooled Antoinette, and was chosen by Louis Blériot for his cross-Channel flight. A major advance came with the introduction of the Seguin brothers' Gnome Omega seven-cylinder, air-cooled rotary engine, exhibited at the Paris Aero Salon 1n 1908 and first fitted to an aircraft in 1909. This radial-configuration engine was constructed in such a way that the entire crankcase and cylinder assembly rotated around a stationary crankshaft, itself fastened securely through the engine's rear attachment to the airframe, ensuring an adequate flow of cooling air over the cylinders even when the aircraft was not moving. Although this type had been introduced as long ago as 1887 by Lawrence Hargrave and built two years later by Hargrave for compressed-air power—with an experimental five-cylinder internal combustion rotary engine used by French inventor Félix Millet that same year to power an early motorcycle design — improvements made to the Seguin brothers' Gnome series of engine designs created a robust, relatively reliable and lightweight design which revolutionised aviation and would see continuous development over the next ten years. Fuel was introduced into each cylinder direct from the crankcase meaning that only an exhaust valve was required. Producing 37 kW (50 hp) for a dry weight of 75 kg (165 lb), this engine soon became one of the most widely used powerplants; the company went on to produce a number of similar engines producing more power, first by increasing the engine capacity and also by producing two-row variants. The larger and more powerful nine-cylinder. French-made Le Rhone 9C 80 hp rotary was introduced in 1913 and was widely adopted for military use. Inline and vee types remained popular, with the German company Mercedes producing first a small number of water-cooled inline four-cylinder engines, then a series of water-cooled six-cylinder models. In 1913 they introduced the highly successful range of 75 kW (100 hp) to 120 kW (160 hp), SOHC-valvetrain design engines: the D.I to D.III series. Another area of advance was the development of specialist manufacturers of propellers. Although the Wright Brothers had developed their own highly efficient propellers and Hiram Maxim had also carried out research on propeller design, much of this work was unknown,