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The Sikorsky S-72 was an experimental
Sikorsky Aircraft Sikorsky Aircraft is an American aircraft manufacturer based in Stratford, Connecticut. It was established by the Russian-American aviation pioneer Igor Sikorsky in 1923, and was among the first companies to manufacture helicopters for civilian ...
compound 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 attribut ...
developed as the Rotor Systems Research Aircraft (RSRA) for the
National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the United States's civil space program, aeronautics research and space research. Established in 1958, it su ...
(NASA) and the
United States Army The United States Army (USA) is the primary Land warfare, land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of th ...
. The RSRA was a
testbed A testbed (also spelled test bed) is a platform for conducting rigorous, transparent, and replicable testing of scientific theories, computing tools, and new technologies. The term is used across many disciplines to describe experimental research ...
for rotor and propulsion systems for high-speed.


Design and development


RSRA

Sikorsky and Bell Helicopters competed for the RSRA contract. Bell's preferred proposal was the "Bell 646A" with rotors based on the Bell 240 UTTAS; the alternative was the smaller "Bell 646B" based on the Bell 309 KingCobra. Sikorsky proposed either a new aircraft or a modified
Sikorsky S-67 Blackhawk The Sikorsky S-67 Blackhawk was a private-venture, prototype attack helicopter built in 1970 with Sikorsky Aircraft research and development (R&D) funds. A tandem, two-seat aircraft designed around the dynamic drive and rotor systems of the Siko ...
with the rotor and gearbox from the
Sikorsky S-61 The Sikorsky S-61L and S-61N are civil variants of the Sikorsky SH-3 Sea King, SH-3 Sea King military helicopter. They were developed and produced by the American helicopter manufacturer Sikorsky Aircraft. The commercial version of the Sea King ...
. Sikorsky won the contract for two aircraft in January 1974. The modified S-67 became the S-72. The S-72 could be fitted with wings and
General Electric TF34 The General Electric TF34 is an American military turbofan engine used on the A-10 Thunderbolt II, S-3 Viking and RQ-170 Sentinel. Design and development Developed by GE Aircraft Engines during the late 1960s, the original engine comprises a ...
turbofan A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a combination of references to the preceding generation engine technology of the turbojet and the add ...
s to allow compound helicopter configurations to be experimentally investigated at speeds up to . In addition, it could fly as a fixed-wing aircraft without a main rotor. Unique among helicopters of its time, it was fitted with a crew emergency extraction system. This system, when activated, fired explosive bolts that severed the main rotor blades, escape panels were blown off the roof of the aircraft. The crew was then extracted using rockets, rather than by a traditional
ejection seat In aircraft, an ejection seat or ejector seat is a system designed to rescue the aircraft pilot, pilot or other aircrew, crew of an aircraft (usually military) in an emergency. In most designs, the seat is propelled out of the aircraft by an exp ...
as on fixed-wing aircraft. The RSRA was a pure research aircraft developed to fill the void between design analysis, wind tunnel testing, and flight results of rotor aircraft. The joint NASA/Army project began in December 1970, first flight on October 12, 1976, with the first of two aircraft arriving from Sikorsky to NASA on February 11, 1979. One notable test performed with the RSRA was the use of the main and tail rotor load measurement system to determine the vertical drag of the airframe. In 1981, NASA and the US Army solicited proposals for fitting a four-bladed main rotor to the RSRA. Sikorsky proposed fitting a UH-60A main rotor to the RSRA in their proposal, while Hughes Helicopters proposed fitting a YAH-64A main rotor, and Boeing Vertol proposed fitting a YUH-61A or BV-347 main rotor. In the end, this program did not proceed.


The X-Wing

The X-Wing Circulation Control Rotor Concept was developed in the mid-1970s by the
David W. Taylor Naval Ship Research and Development Center The Carderock Division of the Naval Surface Warfare Center is one of eight Naval Sea Systems Command (NAVSEA) Surface Warfare Centers. The headquarters, located in Carderock, Maryland, includes the historic David Taylor Model Basin. The divisi ...
under
DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adva ...
funding. In October 1976,
Lockheed Corporation The Lockheed Corporation was an American aerospace manufacturer. Lockheed was founded in 1926 and merged in 1995 with Martin Marietta to form Lockheed Martin. Its founder, Allan Lockheed, had earlier founded the similarly named but otherwise-u ...
won a DARPA contract to develop a large-scale rotor to test the concept. The X-Wing was conceived to complement rather than replace helicopters and fixed-wing aircraft. The X-Wing was intended to be used in roles such as air-to-air and air-to-ground operations, as well as airborne early warning, search and rescue and anti-submarine warfare. These roles could take advantage of the aircraft's ability to hover and maneuver at low speeds and to cruise at high speeds. Intended to take off vertically like a helicopter, the craft's rigid rotors could be stopped in mid-flight to act as X-shaped wings to provide additional lift during forward flight, as well as having more conventional wings. Instead of controlling lift by altering the angle of attack of its blades as more conventional helicopters do, the craft used compressed air fed from the engines and expelled from its blades to generate a virtual wing surface, similar to
blown flap Blown flaps, blown wing or jet flaps are powered aerodynamic high-lift devices used on the wings of certain aircraft to improve their low-speed flight characteristics. They use air blown through nozzles to shape the airflow over the rear edge of ...
s on a conventional platform. Computerized valves made sure the compressed air came from the correct edge of the rotor, the correct edge changing as the rotor rotated. In late 1983, Sikorsky received a contract to modify one S-72 RSRA into a demonstration testbed for the X-Wing rotor system. The modified airframe was rolled out in 1986. While many of the aircraft's technical issues had been resolved, with plans for it to begin flight tests with the rotor/wing system, it never flew. Budgetary requirements led to the program being canceled in 1988.Art Linden, Ken Rosen and Andy Whyt
X-Wing
''Sikorsky Historical Archives'', March 2013


Specifications (S-72)


See also


References


Citations


Sources

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External links


Sikorsky S-72 Rotor Systems Research Aircraft (RSRA) on Sikorsky Archives

Sikorsky X-Wing on Sikorsky Archives



S-72 on helis.com
{{Sikorsky S-61 family Experimental helicopters S-072 Stoppable rotor helicopters 1980s United States experimental aircraft 1980s United States helicopters VTOL aircraft Twin-turbine helicopters Compound helicopters Twinjets Aircraft first flown in 1976