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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. ==Development== Also known by the military designation XH-59, the S-69 was demonstrator for the Advancing Blade Concept (ABC).〔Michael J Taylor: ''The Illustrated Encyclopedia of Helicopters'', page 20. Exeter Books, New York, NY USA, 1984. ISBN 0-671-07149-1〕 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.〔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. http://hdl.handle.net/2060/19820004167〕 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 , but with the auxiliary turbojets, it demonstrated a maximum level speed of and eventually a speed of in a shallow dive. At level flight, it could enter a 1.4g bank turn with the rotor in autorotation, increasing rotor rpm.〔 Airframe stress prevented rotor speed reduction and thus full flight envelope expansion.〔 The XH-59A had high levels of vibration.〔Robb, Raymond L. (Hybrid Helicopters: Compounding the Quest for Speed ) p48, ''Vertiflite'', Summer 2006.〕 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 pay a share of the costs.〔〔Croft, John. (Hyper Helos: Prototypes coming off the drawing board and into the race ), ''Flightglobal.com'' 3 July 2008. Accessed: 9 March 2012.〕 Sikorsky and its partners funded the development of the next helicopters using the Advancing Blade Concept; the Sikorsky X2 and Sikorsky S-97 Raider after 2007. Airframe 73-21941 is in storage at the NASA Ames Research Center〔Bagai, Ashish. ("Sikorsky XH-59A ABC (S-69)." ) ''airliners.net,'' March 29, 2011. Retrieved: June 8, 2011.〕 and 73-21942 is on display at the Army Aviation Museum, Fort Rucker, Alabama.〔Baugher, Joe. ("1972 USAF Serial Numbers." ) Retrieved: June 8, 2011.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sikorsky S-69」の詳細全文を読む スポンサード リンク
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