Background

The S-54 was an experimental model that was not intended for production. Its purpose was to explore the effects on performance and flying qualities of the Sikorsky single main rotor configuration modified with a small horizontal rotor mounted at the tail together with the conventional vertical tail rotor. Because this horizontal tail rotor produced lift which added to that of the main rotor, this configuration was called a sesqui-tandem design.

The S-54 was built by modifying a borrowed R-4B from the then US Army Air Force. It made its first flight on December 20, 1948 and was retired in early 1949 pafter accumulating 4 hours and 20 minutes flight time. The incentive to experiment with the horizontal tail rotor was founded in the results of a 1948 competition for a US Navy sponsored program for a search and rescue helicopter. In that competition, Sikorsky delivered its S-53 (XHJS-1) prototypes against a Piasecki tandem rotor prototype (XHJP-1) for a Navy flight test evaluation. That evaluation concluded that the Sikorsky design was deficient in its ability to retain good control and flying qualities after hoisting up rescuedersonnel to the cabin area that was located in front of the main rotor rotational axis.

The S-53 location of the engine directly below the main rotor forced the useable cabin volume to be in front of the rotor, which resulted in significant center-of-gravity excursions when payload was added or removed. This situation was a basic design flaw of the early, small Sikorsky models. Sikorsky designers sought to fix this flaw by installing the horizontal tail rotor on the S-54 as a means of providing a controllable pitching moment to offset the adverse pitching moments caused by the payload being away from the main rotor axis. This S-54 configuration was found to produce the desired result; however, it was overtaken by a better configuration embodied in the S-55 which first flew in late 1949. That new configuration, embodied in all subsequent models, moved the engine from below the main rotor and enabled Sikorsky to successfully enter and achieve a leadership position in the utility size helicopter market.

S-54 Details

The Sikorsky S-54 was a R-4B helicopter with the following experimental modifications:

• Powered by a Warner R550-3 engine
• Main Rotor Diameter: 38 ft, 3 blades
• One single-blade vertical ant-torque tail rotor, 5 ft diameter
• One 3-blade horizontal tail rotor for lift, 13 ft diameter