Sikorsky S-69

S-69/XH-59

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.

Development

Also known by the military designation XH-59, the S-69 was demonstrator for the Advancing Blade Concept (ABC).^[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.^[2] 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 XH-59A had high levels of vibration.^[4]

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.^[3]^[5]^[6] 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^[7] and 73-21942 is on display at the Army Aviation Museum, Fort Rucker, Alabama.^[8]

Design

The Advancing Blade Concept system consisted of two rigid, contra-rotating rotors (30 inches apart)^[9] 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.^[10]^[11] 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.^[12] 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]

Specifications (S-69)

Data from U.S. Army Aircraft Since 1947,^[13] Illustrated Encyclopedia,^[12] US Army Research Laboratory^[3]

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)
Loaded weight: 12,500 lb (5,700 kg) (with fuel)
Max. takeoff weight: 11,000 lb (5,000 kg) with turbojets (9,000 lb (4,100 kg) 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) (or 1,500 hp^[3])
Rotor: 2 three-bladed co-axial, with 30 inch separation
345 rotor rpm

Performance

Maximum speed: 322 mph, 518 km/h or 263 knots (303 mph; 487 km/h) with jets^[3] (184 mph, 296 km/h^[4] or 156 knots (180 mph; 289 km/h)^[3] 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^[3])
Rate of climb: 1200 ft/min at 140 kn^[3] (6 m/s at 259 km/h)

References

↑ Michael J Taylor: The Illustrated Encyclopedia of Helicopters, page 20. Exeter Books, New York, NY USA, 1984. ISBN 0-671-07149-1
↑ 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
1 2 3 4 5 6 7 8 9 10 11 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.
1 2 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. 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.
↑ Kocivar, Ben. "Turbofan-powered flying carpet" page 68, Popular Science, September 1982. Accessed: September 2014.
↑ Chandler, Jay. "Advanced rotor designs break conventional helicopter speed restrictions (page 1) " Page 2 Archived July 18, 2013, at the Wayback Machine. Page 3 Archived July 18, 2013, at the Wayback Machine.. ProPilotMag, September 2012. Accessed: 10 May 2014. Archive 1 Archive 2
↑ Jackson, Dave. "Coaxial - Sikorsky ~ S-69 (XH-59) ABC Archived November 6, 2014, at the Wayback Machine." Unicopter, 9 March 2012. Retrieved: 22 May 2015. Archived on 6 November 2014.
1 2 Apostolo, G. "Sikorsky S-69". The Illustrated Encyclopedia of Helicopters. Bonanza Books, 1984. ISBN 0-517-43935-2.
↑ Harding, Stephen (1997). U.S. Army Aircraft Since 1947. Atglen, PA, USA: Schiffer Publishing Ltd. p. 251. LCCN 96-69996.

External links

Wikimedia Commons has media related to Sikorsky S-69.

Global Security.org Sikorsky XH-59 page
Sikorsky X2
"X2 marks the spot for radical rotor designs" FlightGlobal
Leoni, Ray. The High Speed Helicopter – A New Beginning (Sikorsky)

Sikorsky aircraft

Fixed-wing aircraft (company designations)	S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12 S-13 S-14 S-15 S-16 S-17 S-18 S-19 S-20 S-21 S-22 S-23 S-24 S-25 S-26 S-27 S-28 S-29-A S-30 S-31 S-32 S-33 S-34 S-35 S-36 S-37 S-38 S-39 S-40 S-41 S-42 S-43 VS-44 S-45

Fixed-wing aircraft (military designations)	C-6 C-28 JRS JR2S PS RS XBLR-3 XPBS XSS XV-2

Helicopters (company designations)	VS-300 (S-46) S-47 S-48 S-49 S-51 S-52 S-53 S-54 S-55 S-56 S-57 S-58 S-59 S-60 S-61 S-61L/N S-61R S-62 S-63 S-64 S-65 S-66 S-67 S-68 S-69 S-70 S-71 S-72 S-73 S-74 S-75 S-76 S-80 S-92/H-92 S-97 S-300 S-333 S-434

Helicopters (military designations)	SH-3 HH-3E/F R-4 H-5 H-6 H-18 H-19 H-34 CH-37 XH-39 HH-52A CH-53 CH-53E CH-53K CH-54 HH-60G HH-60J MH-60R/S SH-60B/F SH-60J/K UH-60 VH-60 RAH-66 CH-124 CH-148

Experimental aircraft	Cypher Cypher II Firefly X2 XBLR-3 XV-2

United States helicopter designations, Army/Air Force and Tri-Service systems

Numerical sequence used by USAAC/USAAF/USAF 1941–present; US Army 1948–1956 and 1962–present; US Navy 1962–present

Main sequence
(1941–1962)

Prefix R-, 1941–1948	R-1 R-2 R-3 R-4 R-5 R-6 R-7 R-8 R-9 R-10 R-11 R-12 R-13 R-14 R-15 R-16

Prefix H-, 1948–1962	H-5 H-6 H-9 H-10 H-11 H-12 H-13/J H-15 H-16 H-17 H-18 H-19 H-20 H-21 H-22 H-23 H-24 H-25 H-26 H-27 H-28 H-29 H-30 H-31 H-32 H-33 H-34 H-35 H-36¹ H-37 H-38¹ H-39 H-40 H-41 H-42 H-43 H-44¹ H-45¹

Main joint sequence
(1962–present)

1962 redesignations	OH-13/UH-13J UH-19 CH-21 OH-23 UH-25 CH-34 CH-37 HH-43

New designations	CH-46/HH-46/UH-46 CH-47 UH-48 XH-49 QH-50 XH-51 HH-52 CH-53/HH-53/MH-53/CH-53E/CH-53K CH-54 TH-55 AH-56 TH-57 OH-58 XH-59 UH-60/SH-60/HH-60/HH-60J YUH-61 XCH-62 YAH-63 AH-64 HH-65 RAH-66 TH-67 MH-68 H-69¹ ARH-70 VH-71 UH-72 H-73 to H-89¹ MH-90 H-91¹ VH-92

1962 redesignations
reusing old numbers

¹ Not assigned

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