Sikorsky Aircraft and it became a part of [[United Aircraft and Transport Corporation]] (now [[United Technologies Corporation]]) in July of that year. [[File:Sikorsky Aircraft Corporation ad Model S-42 Clipper Flying Boat 1937.jpg|thumb|left|upright|Advertisement for [[Sikorsky S-42]] Clipper flying boat from 1937]] In the United States, Igor Sikorsky originally concentrated on the development of multi-engined landplanes and then amphibious aircraft. In the late 1930s, sales declined and United Aircraft merged his division with [[Vought Aircraft]]. He then began work on developing a practical helicopter. After first flying the [[VS-300]] he developed the [[Sikorsky R-4]], the first stable, single-rotor, fully controllable [[helicopter]] to enter full-scale
Sikorsky S-9 Sikorsky S-9 The Sikorsky S-9 "Kruglyj" (Rounded One) was a Russian single engine prototype aircraft completed in the spring of 1913 by the Russian Baltic Railroad Car Works while Igor Sikorsky was the chief engineer of the aircraft manufacturing division. The S-9 was a three-seat mid-wing monoplane with constant-chord wire-braced wings originally powered by a Gnome air-cooled rotary engine rated at . It was the first monocoque monoplane built in Russia and the cylindrical tapered fuselage was constructed of plywood 5 mm thick in the forward section and 3mm thick aft. Construction was completed in the spring of 1913. Upon