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Sikorsky S-69

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Title: Sikorsky S-69  
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Sikorsky S-69

Sikorsky S-69/XH-59A with auxiliary turbojets
Role Experimental compound helicopter
National origin United States of America
Manufacturer Sikorsky Aircraft
First flight July 26, 1973
Retired 1981
Primary users NASA
United States Army
Number built 2

The Sikorsky S-69 was an experimental co-axial compound helicopter developed by Sikorsky Aircraft 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).[1] This Advancing Blade Concept system consisted of two rigid, contra-rotating rotors (30 inches apart)[2] 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 require a wing to be fitted for high speeds and to improve maneuverability,[3] and also eliminated the need for an anti-torque rotor at the tail.[4] Forward thrust was provided by two turbojets, which allowed the main rotor to only be required to provide lift. It was found to have good hover stability against crosswind and tailwind. With jets installed, it lacked power to hover out of ground effect and used short take-off and landing for safety reasons.[3]

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 feet full-scale wind tunnel in 1979.[5] 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 156 knots (289 km/h; 180 mph), but with the auxiliary turbojets, it demonstrated a maximum level speed of 238 knots (441 km/h; 274 mph) and eventually a speed of 263 knots (487 km/h; 303 mph) in a shallow dive. At 180 knots (333 km/h; 207 mph) level flight, it could enter a 1.4g bank turn with the rotor in autorotation, increasing rotor rpm.[3] Airframe stress prevented rotor speed reduction and thus full flight envelope expansion.[3]

The 106-hour 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 as Sikorsky refused to share costs. The XH-59A had high levels of vibration.[3][6][7][8]

Airframe 73-21941 is in storage at the NASA Ames Research Center[9] and 73-21942 is on display at the Army Aviation Museum, Fort Rucker, Alabama.[10]

Specifications (S-69)

Data from U.S. Army Aircraft Since 1947,[11] Illustrated Encyclopedia,[4] US Army Research Laboratory[3]

General characteristics


See also

Related development
Related lists


  1. ^ Michael J Taylor: The Illustrated Encyclopedia of Helicopters, page 20. Exeter Books, New York, NY USA, 1984. ISBN 0-671-07149-1
  2. ^ Kocivar, Ben. "Turbofan-powered flying carpet" page 68, Popular Science, September 1982. Accessed: September 2014.
  3. ^ a b c d e f g h i j k J. Rudell et al. Advancing Blade Concept (ABC) Technology Demonstrator report: USAAVRADCOM-tr-81-D-5, United States Army Research Laboratory, April 1981. Size: 11 MB. Accessed: 10 March 2012.
  4. ^ a b Apostolo, G. "Sikorsky S-69". The Illustrated Encyclopedia of Helicopters. Bonanza Books, 1984. ISBN 0-517-43935-2.
  5. ^ Felker, Fort III. NASA NASA-TM-81329, USAAVRADCOM-TR-81-A-27 Performance and loads data from a wind tunnel test of a full-scale, coaxial, hingeless rotor helicopter.
  6. ^ a b Robb, Raymond L. Hybrid Helicopters: Compounding the Quest for Speed p48, Vertiflite, Summer 2006.
  7. ^ Goodier, Rob (September 20, 2010). "Inside Sikorsky's Speed-Record-Breaking Helicopter Technology".  
  8. ^ Croft, John. Hyper Helos: Prototypes coming off the drawing board and into the race, 3 July 2008. Accessed: 9 March 2012.
  9. ^ Bagai, Ashish. "Sikorsky XH-59A ABC (S-69).", March 29, 2011. Retrieved: June 8, 2011.
  10. ^ Baugher, Joe. "1972 USAF Serial Numbers." Retrieved: June 8, 2011.
  11. ^ Harding, Stephen (1997). U.S. Army Aircraft Since 1947. Atglen, PA, USA: Schiffer Publishing Ltd. p. 251.  

External links

  • Global Sikorsky XH-59 page
  • Sikorsky X2
  • "X2 marks the spot for radical rotor designs" FlightGlobal
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