Sikorsky S-69

S-69/XH-59
Sikorsky S-69/XH-59A with auxiliary turbojets
Role	Experimental helicopter
Manufacturer	Sikorsky Aircraft
First flight	July 26, 1973
Primary users	NASA United States Army
Number built	2

The Sikorsky S-69 was an experimental compound co-axial helicopter developed as the demonstrator of the Advancing Blade Concept (ABC) under US Army and NASA funding.

Design and development

Also known by the military designation XH-59, the S-69 was demonstrator for the Advancing Blade Concept (ABC). This Advancing Blade Concept system consisted of two rigid, contra-rotating rotors which made use of the aerodynamic lift of the advancing blades. At high speeds, the retreating blades were offloaded, as most of the load was supported by the advancing blades of both rotors and the penalty due to stall of the retreating blade was thus eliminated. This system did not even require a wing to be fitted for high speeds and to improve maneuverability, and also eliminated the need for an anti-torque rotor at the tail. Forward thrust was provided by two turbojets, which allowed the main rotor to only be required to provide lift.

The first S-69 built (73-21941) first flew on July 26, 1973. However, it was badly damaged in a crash on August 24, 1973. The airframe was then converted into a wind tunnel test article, which was tested in the NASA Ames Research Center 40x80 full-scale wind tunnel in 1979. A second airframe was completed (73-21942) which first flew on July 21, 1975. After initial testing as a pure helicopter, the auxiliary turbojets were added in March 1977. As a helicopter, the XH-59A demonstrated a maximum level speed of 184 mph, but with the auxiliary turbojets, it demonstrated a maximum level speed of 303 mph. The test program for the XH-59A ended in 1981. In 1982 it was proposed that the XH-59A be converted to the XH-59B configuration with advanced rotors, new powerplant (two GE T700s), and a ducted pusher propeller at the tail. This proposed program did not proceed.

Airframe 73-21941 is in storage at the NASA Ames Research Center and 73-21942 is on display at the Army Aviation Museum, Fort Rucker, Alabama.

Specifications (S-69)

Data from U.S. Army Aircraft Since 1947, Illustrated Encyclopedia

General characteristics

• Crew: 2
• Length: 40 ft 9 in (12.42 m)
• Rotor diameter: 36 ft 0 in (10.97 m)
• Height: 13 ft 2 in (4.01 m)
• Max. takeoff weight: 11,000 lb with turbojets (9,000 lb without turbojets)
• Powerplant:
  • 2 × Pratt & Whitney J60-P-3A turbojet, 3,000 lbf (1.350 kN) each
  • 1 × Pratt & Whitney Canada PT6T-3 Turbo Twin Pac turboshaft, 1,825 hp (1,360 kW)
• Rotor: 2 three-bladed co-axial

Performance

• Maximum speed: 322 mph, 518 km/h (184 mph, 296 km/h)
• Cruise speed: 109 knots (125 mph, 185 km/h)
• Service ceiling: 15,000 ft (4,570 m)

See also

Related development

• Sikorsky X2
  

Related lists

• List of helicopters
  

External links

• Sikorsky S-69
• Global Security.org Sikorsky XH-59 page
• Sikorsky X2
• "X2 marks the spot for radical rotor designs" FlightGlobal