The Sikorsky X2 is an experimental high-speed

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 attributes ...

with

coaxial rotors Coaxial rotors or coax rotors are a pair of helicopter rotors mounted one above the other on concentric shafts, with the same axis of rotation, but turning in opposite directions ( contra-rotating). This rotor configuration is a feature of helicop ...

, 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 ...

, that made its first flight in 2008 and was officially retired in 2011.

Design and development

Sikorsky developed the X2 helicopter on a $50 million budget. The design includes expertise gathered from several earlier design projects. The S-69/XH-59A Advancing Blade Concept Demonstrator had shown that high speed was possible with a coaxial helicopter with auxiliary propulsion supplied using two jet engines, but that vibration and fuel consumption was excessive; the Cypher UAV expanded the company's knowledge of the unique aspects of coaxial flight control laws with a

fly-by-wire Fly-by-wire (FBW) is a system that replaces the conventional manual flight controls of an aircraft with an electronic interface. The movements of flight controls are converted to electronic signals transmitted by wires, and flight control ...

aircraft; and the RAH-66 Comanche developed expertise in composite rotors and advanced transmission design.Sikorsky to Build and Test X2 Technology Demonstrator Helicopter
. '' Sikorsky'' Other features include slowedFirst Flight Of Sikorsky X2 Demonstrator
''

Aviation Week & Space Technology ''Aviation Week & Space Technology'', often abbreviated ''Aviation Week'' or ''AW&ST'', is the flagship magazine of the Aviation Week Network. The weekly magazine is available in print and online, reporting on the aerospace, defense and aviatio ...

'', 27 August 2008. Accessed: 9 March 2012
Archived
on 7 March 2012. "de-swirling"

rigid rotor In rotordynamics, the rigid rotor is a mechanical model of rotating systems. An arbitrary rigid rotor is a 3-dimensional rigid object, such as a top. To orient such an object in space requires three angles, known as Euler angles. A special ri ...

s two feet apart, active force counter-vibration inspired by the

Black Hawk Black Hawk and Blackhawk may refer to: Animals * Black Hawk (horse), a Morgan horse that lived from 1833 to 1856 * Common black hawk, ''Buteogallus anthracinus'' * Cuban black hawk, ''Buteogallus gundlachii'' * Great black hawk, ''Buteogallus urub ...

,X2 marks the spot for radical rotor designs
''

Flightglobal.com FlightGlobal is an online news and information website which covers the aviation and aerospace industries. The website was established in February 2006 as the website of ''Flight International'' magazine, ''Airline Business'', ''ACAS'', ''Air ...

'', 12 June 2007. and using most of the power in forward flight for the pusher propeller rather than the rotor. Unusually for helicopters, the power required for high speed is more than the hover power. The pilot controls the independent propeller power with a thumb wheel on the collective. Test flights and flight simulations were combined to improve test procedure.Wilson, J.R.
Defense Interview: Mark Miller
''Defense Media Network'', 9 September 2011. Accessed: 4 October 2014
Archived
on 2 November 2012. The fly-by-wire system is provided by

Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...

, the rotor by Eagle Aviation Technologies, anti-vibration technology from

Moog Inc Moog ( ) is an American-based designer and manufacturer of electric, electro-hydraulic and hydraulic motion, controls and systems for applications in aerospace, defense, industrial and medical devices. The company operates under four segments: a ...

, and propeller by Aero Composites. The rotor hub can have 10-20 times the drag of the blade. Sikorsky intended to test hub fairings to reduce drag by 40%, and test flew fairings on the hubs themselves but not the central hub fairing ("aero sail") in between the hubs. Sikorsky has since patented a "Standpipe" (fixed tube between rotating rotor axes) suitable for a central hub fairing. On 4 May 2009, Sikorsky unveiled a mockup of a Light Tactical Helicopter derivative of the X2, and unveiled a prototype in October 2014.Warwick, Graham.
Sikorsky Talks To Customers About Potential Raider Applications
''

'', 6 October 2014. Accessed: 3 October 2014
PhotosArchived
on 3 October 2014 In June 2014, Sikorsky/Boeing submitted the SB-1 Defiant helicopter design for the Future Vertical Lift program based on the X2 principle,Majumdar, Dave.
Sikorsky and Boeing Team Submit New Army Helicopter Design
- News.USNI.org, 17 June 2014. Accessed: 19 June 2014
Archive
/ref> which was approved by the Army in October.

Operational history

The X2 first flew on 27 August 2008 from Schweizer Aircraft, a division of Sikorsky Aircraft Corporation's facility at

Horseheads, New York Horseheads is a town in Chemung County, New York, United States. The population was 19,412 at the 2020 census. The name of the town is derived from the number of bleached horses' skulls once found there. Horseheads is north of the city of Elmira ...

. The flight lasted 30 minutes.Trimble, Stephen
"Sikorsky's X2 speedster completes first flight"
Flightglobal.com, 27 August 2008. This began a four-phase flight test program, to culminate with reaching a planned 250-knot top speed. The X2 completed flights with its propeller fully engaged in July 2009. Sikorsky completed phase three of the testing with the X2 reaching 181 knots in test flight in late May 2010. On 26 July 2010, Sikorsky announced that the X2 exceeded during flight testing in West Palm Beach Florida, unofficially surpassing the current FAI

rotorcraft A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The Internat ...

world speed record of set by a modified

Westland Lynx The Westland Lynx is a British multi-purpose twin-engined military helicopter designed and built by Westland Helicopters at its factory in Yeovil. Originally intended as a utility craft for both civil and naval usage, military interest led t ...

in 1986.Rotorcraft Absolute: Speed over a straight 15/25 km course
".

Fédération Aéronautique Internationale The (; FAI; en, World Air Sports Federation) is the world governing body for air sports, and also stewards definitions regarding human spaceflight. It was founded on 14 October 1905, and is headquartered in Lausanne, Switzerland. It maintain ...

(FAI). Note search under E-1 Helicopters and "Speed over a straight 15/25 km course". Accessed: 26 April 2014. On 15 September 2010, test pilot Kevin Bredenbeck achieved Sikorsky's design goal for the X2 when he flew it at a speed of in level flight, an unofficial speed record for a helicopter. The demonstrator then reached a new record speed of in a shallow 2˚ to 3˚ dive, which was just short of the 303 mph achieved by the

Sikorsky S-69 The Sikorsky S-69 (military designation XH-59) is an American experimental co-axial compound helicopter developed by Sikorsky Aircraft as the demonstrator of the Advancing Blade Concept (ABC) under United States Army and NASA funding. Developm ...

technology demonstrator helicopter.Robb, Raymond L
Hybrid Helicopters: Compounding the Quest for Speed
p49, ''Vertiflite'', Summer 2006. Quote: "Ultimately, the XH-59A achieved an incredible 303 mph" Sikorsky states that the X2 has the same noise level at 200 knots that a regular helicopter has at 100 knots. Above 200 knots, the rotor speed is reduced from 446 to 360 RPMDatta, Anubhav et al.
Experimental Investigation and Fundamental Understanding of a Slowed UH-60A Rotor at High Advance Ratios
', page 2. ''

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, succeedin ...

'', 2011. Accessed: April 2014.Jackson, Dave.
Coaxial - Sikorsky ~ X2 TD
''Unicopter'', 18 September 2010. Accessed: April 2014

on 13 September 2013. to keep tip speed below Mach 0.9, the rotor disc is slightly nose-up, and the

lift-to-drag ratio In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficiency under gi ...

is about twice that of a conventional helicopter. Hands-off flying was also successfully performed during flight tests.D. Walsh, S. Weiner, K. Arifian, T. Lawrence, M. Wilson, T. Millott and R. Blackwell.
High Airspeed Testing of the Sikorsky X2 Technology Demonstrator
'' Sikorsky'', May 4, 2011. Accessed: October 5, 2013. On 14 July 2011, the X2 completed its final flight and was officially retired after accumulating 22 hours over 23 test flights. With the end of development, the X2 will be followed by its first application, the S-97 Raider high-speed scout and attack helicopter. It was donated to the

National Air and Space Museum The National Air and Space Museum of the Smithsonian Institution, also called the Air and Space Museum, is a museum in Washington, D.C., in the United States. Established in 1946 as the National Air Museum, it opened its main building on the N ...

in October 2016 and is on display in the

Steven F. Udvar-Hazy Center The Steven F. Udvar-Hazy Center, also called the Udvar-Hazy Center, is the Smithsonian National Air and Space Museum (NASM)'s annex at Washington Dulles International Airport in the Chantilly area of Fairfax County, Virginia. It holds numerous ...

Chantilly, Virginia Chantilly is a census-designated place (CDP) in western Fairfax County, Virginia, Fairfax County, Virginia. The population was 24,301 as of the 2020 census. Chantilly is named after an early-19th-century mansion and farm, which in turn took the ...

Awards

The Sikorsky Aircraft Corporation and the X2 Technology Demonstrator Team was awarded the 2010 Robert J. Collier Trophy by the

National Aeronautic Association The National Aeronautic Association of the United States (NAA) is a non-profit 501(c)(3) organization and a founding member of the Fédération Aéronautique Internationale (FAI). Founded in 1905, it is the oldest national aviation club in the Uni ...

"...For demonstrating a revolutionary 250 knot helicopter, which marks a proven departure point for the future development of helicopters by greatly increasing their speed, maneuverability and utility." For 2011, the X2 team received the Howard Hughes Award (

American Helicopter Society American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

).Howard Hughes Award
, ''

Specifications

References

External links

Sikorsky X2 company page
Archive from 2009
/small>

(patent list at the bottom)
"Sikorsky Calls X2 Shape of the Future", Aviation Week, 25 February 2008

"Sikorsky X2 In Blades-On Ground Tests", Aviation Week, 21 May 2008

* ttp://www.aopa.org/News-and-Video/All-News/2011/October/1/Swamp-Pirates.aspx "Swamp Pirates" ''

Aircraft Owners and Pilots Association The Aircraft Owners and Pilots Association (AOPA) is a Frederick, Maryland-based American non-profit political organization that advocates for general aviation. AOPA's membership consists mainly of general aviation pilots in the United States ...

'', October 1, 2011
Sikorsky X-2 at the Stuart Air Show, Nov 11, 2011
{{Sikorsky Aircraft Compound helicopters Coaxial rotor helicopters Experimental helicopters Slowed rotor 2000s United States experimental aircraft 2000s United States helicopters Pusher aircraft Aircraft first flown in 2008