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-42 span the oceans. The new design would need increased lifting capacity to carry enough fuel and 300 pounds of mail, but no passengers, for a 2,500 miles (4,023 kilometers) nonstop flight against a 30 mph (48 km/h) wind, at a higher cruising speed than the norm for similar flying boats at that time. Of the six companies tenders had been sent to, only Sikorsky and Martin provided submissions. Sikorsky offered the S-42. The other offer was the more ambitious Martin M-130. The new Sikorsky design, the S-42, had major aerodynamic improvements over the S-40. Igor Sikorsky said, "in its very