|Sikorsky S-69/XH-59A with auxiliary turbojets|
|First flight||July 26, 1973|
United States Army
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 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. 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.
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. 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 miles per hour (296 km/h; 160 kn), but with the auxiliary turbojets, it demonstrated a maximum level speed of 238 knots (274 mph; 441 km/h) and eventually a speed of 303 miles per hour (488 km/h; 263 kn). At 180 knots 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 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.
- 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)
- Loaded weight: 12,500 lb (with fuel)
- Max. takeoff weight: 11,000 lb with turbojets (9,000 lb without turbojets)
- 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) (or 1,500 hp)
- Rotor: 2 three-bladed co-axial, with 30 inch separation
- Maximum speed: 322 mph, 518 km/h or 263 knots (303 mph; 487 km/h) with jets (184 mph, 296 km/h or 156 knots (180 mph; 289 km/h) without jets)
- Cruise speed: 109 knots (125 mph, 185 km/h)
- Service ceiling: 15,000 ft, 4,570 m (25,000 feet (7,600 m) density altitude with jets)
- Rate of climb: 1200 ft/min at 140 kn ()
- Sikorsky X2
- List of helicopters
- Michael J Taylor: The Illustrated Encyclopedia of Helicopters, page 20. Exeter Books, New York, NY USA, 1984. ISBN 0-671-07149-1
- 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.
- Apostolo, G. "Sikorsky S-69". The Illustrated Encyclopedia of Helicopters. Bonanza Books, 1984. ISBN 0-517-43935-2.
- 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
- Robb, Raymond L. Hybrid Helicopters: Compounding the Quest for Speed p48, Vertiflite, Summer 2006.
- Goodier, Rob (September 20, 2010). "Inside Sikorsky's Speed-Record-Breaking Helicopter Technology". Popular Mechanics. http://www.popularmechanics.com/technology/aviation/news/inside-sikorskys-record-breaking-helicopter-tech?click=pm_news. Retrieved 22 September 2010.
- Croft, John. Hyper Helos: Prototypes coming off the drawing board and into the race, Flightglobal.com 3 July 2008. Accessed: 9 March 2012.
- Bagai, Ashish. "Sikorsky XH-59A ABC (S-69)." airliners.net, March 29, 2011. Retrieved: June 8, 2011.
- Baugher, Joe. "1972 USAF Serial Numbers." Retrieved: June 8, 2011.
- Harding, Stephen (1997). U.S. Army Aircraft Since 1947. Atglen, PA, USA: Schiffer Publishing Ltd.. p. 251. ISBN 96-69996.
|Wikimedia Commons has media related to Sikorsky S-69.|
- Global Security.org Sikorsky XH-59 page
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- "X2 marks the spot for radical rotor designs" FlightGlobal
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