Sikorsky S-69

History

The road to today's Sikorsky S-97 "Raider" compound helicopter program was developed through developments such as the experimentally oriented "S-69" model. For decades, rotorcraft have tried to squeeze every ounce of speed and performance out of helicopter systems, but have been limited by traditional engine and blade configurations.

Compound helicopters are designed to provide the same system with the benefits of an improved main blade layout or the addition of a stern thruster/propulsion unit to provide jet-like airframe performance while maintaining the vertical take-off and landing (VTOL) capabilities that helicopters possess. The modern S-97 embodies this, as does the S-69 of the early 1970s.

The S-69 is funded by the U.S. Army and NASA through the Propel Blade Concept (or "ABC") program.

Due to the military's involvement in the program, the S-69 was also recognized under the military designation "XH-59", and two airworthy prototypes were eventually built for the program, the first of which flew on July 26, 1973.

The aircraft employs a dual main rotor mast arrangement with one main rotor system on top of the other ("coaxial counter-rotation"). There is no anti-torque rotor mounted aft as the two counter-rotating main blade units counteract the naturally occurring torque forces.

Rotors of rigid design are mounted on the slender fuselage, and two engine nacelles are located on the outboard sides of the fuselage. As usual, the cockpit is overhead, with side-by-side seating for the two crew members.

The rear wing features separate vertical fins set on an upturned horizontal plane. The landing gear is retractable.

The structural dimensions of the aircraft include an overall length of 40.8 feet, a diameter of 36 feet (including main rotor), and a height of 13.2 feet. Loaded weight is 12,500 lbs.

A total of three engines were installed on the S-69: 2 x Pratt & Whitney J60-P-3A turbojets, each providing 3,000 pounds of thrust, and 1 x Pratt and Whitney Canada (PWC) PT6T-3 "Turbo Twin-Pac" turboshaft 1,825 hp engine. Performance specs show a top speed of 322 mph and a cruising speed of nearly 125 mph.

Service is capped at 15,000 feet with a climb rate of 1,200 feet per minute.

The first prototype only lasted until August 24, 1973, when it crashed during a test flight. From 1979, this example was rebuilt for wind tunnel testing. The second prototype was launched on July 21, 1975, but without an outboard engine.

After successfully passing the early test phase, the aircraft completed full engine assembly in March 1977. The airframe recorded a top speed of over 300 miles per hour on a single dive.

Active testing of the S-69 continued until 1981, when the XH-59 withdrew from further work after approximately 106 hours in the air. It was found to run out of fuel quickly and the airframe vibrated violently in certain flight envelopes. There were plans to rebuild the XH-59 prototype with a new GE T700 turboshaft engine, a ducted "thrust" propeller unit in the stern, and an all-new main rotor like the "XH-59B", but Sikorsky was not keen to fund the project, nor part. The work on the S-69 wasn't entirely in vain, as the company's "X2" first flew on August 27, 2008, continuing the tradition of Sikorsky's experimental compound helicopter that eventually gave rise to today's S-97 Predator.

U.S. Army researched.

Specification

Basic

Production

Roles

Dimensions

Weight

Performance

Performance

Armor

Changes