1. Development

2. Design

3. Surviving aircraft

4. Specifications (S-69)

5. See also

6. References

7. External links

The Sikorsky S-69 (military designation XH-59) is 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

In late 1971, the Army Air Mobility Research and Development Laboratory, which later became a part of the Army Research Laboratory, awarded Sikorsky a contract for the development of the first prototype.{{cn|date=August 2018}} The S-69 was the 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 low-speed crash on August 24, 1973 due to unexpected rotor forces and insufficient control systems.^[2] The airframe was then converted into a wind tunnel testbed, 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, two auxiliary turbojets were added in March 1977. As a helicopter, the XH-59A demonstrated a maximum level speed of {{convert|156|kn|km/h mph|0}}, but with the auxiliary turbojets, it demonstrated a maximum level speed of {{convert|238|kn|km/h mph|0}} and eventually a speed of {{convert|263|kn|km/h mph|0}} in a shallow dive. At {{convert|180|kn|km/h mph|0}} level flight, it could enter a 1.4g bank turn with the rotor in autorotation, increasing rotor rpm.^[4] Airframe stress prevented rotor speed reduction and thus full flight envelope expansion.^[4] The XH-59A had high levels of vibration and fuel consumption.^[3][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 powerplants (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.^[4][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.

Design

The Advancing Blade Concept system consisted of two rigid, contra-rotating rotors (30 inches apart)^[7] 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.^[8][9] This system did not require a wing to be fitted for high speeds and to improve maneuverability,^[10] and also eliminated the need for an anti-torque rotor at the tail.^[15] 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.^[10]

Surviving aircraft

Airframe 73-21941 is in storage at the NASA Ames Research Center^[11] and 73-21942 is on display at the Army Aviation Museum, Fort Rucker, Alabama.^[12]

Specifications (S-69)

|plane or copter?=copter
|jet or prop?=both

|ref=U.S. Army Aircraft Since 1947,^[13] Illustrated Encyclopedia,^[14] US Army Research Laboratory^[10]

|crew= two
|capacity=
|length main= 40 ft 9 in
|length alt= 12.42 m
|span main= 36 ft 0 in
|span alt= 10.97 m
|height main= 13 ft 2 in
|height alt= 4.01 m
|area main=
|area alt=
|airfoil=
|empty weight main=
|empty weight alt=
|loaded weight main= {{convert|12500|lb|kg|abbr=on}}
|loaded weight alt= with fuel
|useful load main=
|useful load alt=
|max takeoff weight main= {{convert|11000|lb|kg|abbr=on}} with turbojets
|max takeoff weight alt= {{convert|9000|lb|kg|abbr=on}} without turbojets

|engine (jet)=Pratt & Whitney J60-P-3A
|type of jet=turbojet
|number of jets=2
|thrust main= 3,000 lbf
|thrust alt= 1.350 kN
|thrust original=
|afterburning thrust main=
|afterburning thrust alt=
|engine (prop)=Pratt & Whitney Canada PT6T-3 Turbo Twin Pac
|type of prop=turboshaft
|number of props=1
|power main= 1,825 hp (1,360 kW)
|power alt= or 1,500 hp^[10]
|power original=
|propeller or rotor?=rotor
|propellers=
|number of propellers per engine=
|propeller diameter main=
|propeller diameter alt=
|more general= Rotor: 2 three-bladed co-axial, with 30 inch separation
345 rotor rpm

|max speed main= 322 mph, 518 km/h{{Citation needed|date=March 2012}} or {{convert|263|kn|mph km/h}} with jets^[10]
|max speed alt= 184 mph, 296 km/h^[3] or {{convert|156|kn|mph km/h}}^[10] without jets
|cruise speed main= 109 knots
|cruise speed alt= 125 mph, 185 km/h
|never exceed speed main=
|never exceed speed alt=
|stall speed main=
|stall speed alt=
|range main=
|range alt=
|ceiling main= 15,000 ft, 4,570 m
|ceiling alt= {{convert|25,000|ft|m}} density altitude with jets^[10]
|climb rate main= 1200 ft/min at 140 kn^[10]
|climb rate alt= 6 m/s at 259 km/h
|loading main=
|loading alt=
|thrust/weight=
|power/mass main=
|power/mass alt=
|more performance=

|armament=
|avionics=
}}

See also

• Sikorsky X2
• Sikorsky S-97 Raider
• Sikorsky/Boeing SB-1 Defiant

• Sikorsky S-72

• List of helicopters

References

External links

• Global Security.org Sikorsky XH-59 page
• [https://web.archive.org/web/20080714064426/http://www.sikorsky.com/details/0,3036,CLI1_DIV69_ETI2088,00.html Sikorsky X2]
• "X2 marks the spot for radical rotor designs" FlightGlobal
• Leoni, Ray. The High Speed Helicopter – A New Beginning (Sikorsky)

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