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Sikorsky S-66

S-67In 1964 Sikorsky submitted the S-66 project to the US Army for the Advanced Aerial Fire Support System (AAFSS) requirement, which called for an aircraft with a maximum speed of approximately 418 km/h and ten minutes' hovering capability. The S-66 looked very much like the Lockheed AH-56A Cheyenne (which won the contest), but had a Rotorprop tail rotor which could rotate its axis through 90 to act both as a conventional anti-torque rotor in horizontal flight and as a pusher propeller, thereby transforming the S-66 into a compound aircraft in cruising flight.

Successful flight testing of a thrust-producing system termed a Rotoprop, a combination tail rotor-propeller similar to that proposed for the S-66 high-speed compound helicopter being designed for the Army Advanced Aerial Fire Support System (AAFSS),was reported in July. Lee S. Johnson, president of Sikorsky Division, United Aircraft Corp., announced the system as a "major technical advanced in the propulsion and control of vertical takeoff andlanding aircraft."

The Rotoprop used in the initial ttight tests was a standard helicopter tail rotor adapted to prove the Rotoprop principle. In helicopter flight, the Rotoprop provides side thrust to counter mainrotor torque and to give directional control. In high-speed flight, it provides forward thrust by turning 90 degrees aft and serving as a propeller, while directional control is supplied by a conventionmal rudder.

The Sikorsky test pilots described the test ftight transition from the tailrotor to the pusher propeller as "very smooth - no problem at all." Sikosky engineers said the Rotoprop, in addition to the advantage of simplicity of design and efficient operation, offered significant weight and cost reduction. The Rotoprop was represented as conserving power at both high and low speeds to provide improved agility, acceleration and deceleration - all essential to the AAFSS mission. Sikorsky was one of two companies participating in the project definition phaseof the Army program.

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Page last modified: 16-02-2014 18:28:12 ZULU