The Sikorsky S-69 (military designation XH-59) is an American experimental co-axial

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struct ...

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

developed by

Sikorsky Aircraft Sikorsky Aircraft is an American aircraft manufacturer based in Stratford, Connecticut. It was established by aviation pioneer Igor Sikorsky in 1923 and was among the first companies to manufacture helicopters for civilian and military use. Pre ...

as the demonstrator of the Advancing Blade Concept (ABC) under

United States Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...

and

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

funding.

Development

In late 1971, the Army Air Mobility Research and Development Laboratory, which later became a part of the

Army Research Laboratory The U.S. Army Combat Capabilities Development Command Army Research Laboratory (DEVCOM ARL) is the U.S. Army's foundational research laboratory. ARL is headquartered at the Adelphi Laboratory Center (ALC) in Adelphi, Maryland. Its largest singl ...

, awarded Sikorsky a contract for the development of the first prototype. The S-69 was the demonstrator for the Advancing Blade Concept (ABC).Michael J Taylor: ''The Illustrated Encyclopedia of Helicopters'', page 20. Exeter Books, New York, 1984. 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. 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. 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 , 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 1.4 g bank turn with the rotor in

autorotation Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Igor ...

, increasing rotor rpm. Airframe stress prevented rotor speed reduction and thus full flight envelope expansion. The XH-59A had high levels of vibration and fuel consumption.Robb, Raymond L
Hybrid Helicopters: Compounding the Quest for Speed
p. 48, ''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 powerplants (two

GE T700 The General Electric T700 and CT7 are a family of turboshaft and turboprop engines in the class. Design and development In 1967, General Electric began work on a new turboshaft engine demonstrator designated the "GE12" in response to US Army i ...

s), 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 The Sikorsky X2 is an experimental high-speed compound helicopter with coaxial rotors, developed by Sikorsky Aircraft, that made its first flight in 2008 and was officially retired in 2011. Design and development Sikorsky developed the X2 heli ...

and

Sikorsky S-97 Raider The Sikorsky S-97 Raider is a high-speed scout and attack compound helicopter based on the Advancing Blade Concept (ABC) with a coaxial rotor system under development by Sikorsky Aircraft. Sikorsky planned to offer it for the United States ...

, from 2007.

Design

The Advancing Blade Concept system consisted of two rigid, contra-rotating rotors (30 inches apart) 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.Chandler, Jay.
Advanced rotor designs break conventional helicopter speed restrictions (page 1)

. ''ProPilotMag'', September 2012. Accessed: 10 May 2014

/ref>Jackson, Dave.

" ''Unicopter'', 9 March 2012. Retrieved: 22 May 2015

on 6 November 2014. This system did not require a wing to be fitted for high speeds and to improve maneuverability,J. Rudell et al
Advancing Blade Concept (ABC) Technology Demonstrator report: USAAVRADCOM-tr-81-D-5
''

United States Army Research Laboratory The U.S. Army Combat Capabilities Development Command Army Research Laboratory (DEVCOM ARL) is the U.S. Army's foundational research laboratory. ARL is headquartered at the Adelphi Laboratory Center (ALC) in Adelphi, Maryland. Its largest singl ...

'', April 1981. Size: 11 MB. Accessed: 10 March 2012. 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 A short takeoff and landing (STOL) aircraft is a conventional fixed-wing aircraft that has short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on airstrips with harsh condition ...

for safety reasons.

Surviving aircraft

Airframe 73-21941 is in storage at the NASA Ames Research Center and 73-21942 is on display at the Army Aviation Museum, Fort Rucker, Alabama.Baugher, Joe
"1972 USAF Serial Numbers."
Retrieved: June 8, 2011.

Specifications (S-69)

References

External links

* Leoni, Ray
The High Speed Helicopter – A New Beginning
(Sikorsky) {{Gyrodyne Coaxial rotor helicopters United States military helicopters 1970s United States experimental aircraft 1970s United States helicopters Experimental helicopters S-069 Twin-turbine helicopters Twinjets Jet-propelled helicopters Aircraft first flown in 1973