Sikorsky XH-39

The Sikorsky XH-39, company designation S-59, was developed by Sikorsky Aircraft in 1954 and was the United States Army first turbine-powered helicopter. It was a four-seat machine derived from the piston-powered S-52 (H-18) with the same layout but retractable landing gear, a modified tail rotor and a four-blade main rotor, and it was powered by a single Continental XT51-T-3 turboshaft of 400 shaft horsepower. Two YH-18A airframes were converted into XH-39s. On 26 August 1954 it set a world helicopter speed record of 156 miles per hour, and in October of that year an unofficial altitude record of 24,500 feet. The Army rejected it in favour of the Bell UH-1 Iroquois, and the surviving S-59 demonstrator is displayed at the New England Air Museum.