The Sikorsky S58 was one of the most successful piston powered mid size helicopters built.
Sikorsky developed the S58 in response to a US Navy requirement for an anti submarine warfare helicopter. What resulted was the S58, which features a single Wright R1820 radial piston engine mounted in the nose, one of the largest fuselages to be designed for a single piston powered helo and a raised flightdeck. As the XHSS1 the S58 flew for the first time on March 8 1954.
Large numbers of S58s were subsequently built to serve with the US Navy in anti submarine warfare roles as the SH34G and SH34J Seabat, and in utility roles with the US Marines as the UH34D Seahorse. The US Army operated large numbers as the CH34 Choctaw while many other allied countries operated the S58 in various military roles. The UK for example licence built a turboprop development called the Wessex, some of which saw civil service.
Modest numbers of piston powered S58s saw civil service with most were delivered to customers within the USA. The S58 offered a very large fuselage and lifting capacity, but its piston engine made it expensive to operate.
In 1970 Sikorsky announced it was developing a turboprop conversion package for the S58. Turboprop powered S58s are designated the S58T and were initially powered by a 1340kW (1800shp) Pratt & Whitney PT6T3, later aircraft a 1400kW (1875shp) PT6T6. The first S58T conversion flew for the first time on August 19 1970. Sikorsky set up a production line to convert customer S58s, offered kits for S58 operators to perform the conversion and purchased used S58s, converted them to turbine power and offered them for resale. Small numbers remain in commercial service.
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