Concept
The Sikorsky CH-54 Tarhe is an American twin-engine heavy-lift helicopter designed by Sikorsky Aircraft for the United States Army. It is named after Tarhe, an 18th-century chief of the Wyandot Indian tribe whose nickname was "The Crane". The civil version is the Sikorsky S-64 Skycrane. Work on what would become the CH-54 can be traced back to Sikorsky's earlier activities with "sky-crane" helicopters, particularly the piston-engined Sikorsky S-60 of the late 1950s. Following the end of the Korean War, the United States Army sought to procure a successor to the Sikorsky CH-37 Mojave, an early piston-engined heavily lift helicopter; being aware of this need, Sikorsky were keen to fulfil it. The company was already working on the Sikorsky S-64 Skycrane, a civil-orientated heavy lift rotorcraft that was designed specifically for the purpose of carrying large payloads externally; the development of a military-configured derivative was viewed as a natural option. While Sikorsky were quick to recognise the advantages of adopting turboshaft propulsion, there were no suitable engines of that type initially available, thus it had to work with the American engine manufacturer Pratt and Whitney to modify their JT12 turbojet to produce one. One innovative feature for any helicopter of the era was the incorporation of an automatic flight control system, effectively a fly-by-wire arrangement. This feature enabled the aft-facing crew member to control the rotorcraft's pitch, roll, and yaw with 10% control authority, along with an altitude-hold function; it was also praised for being relatively easy to fly under instrument flight rules (IFR). Considerable attention was paid to the fuselage's design, particularly to minimising weight and maintenance requirements. The landing gear was designed to kneel to make loading easier as well as to ease operations from sloped surfaces.
