|Sikorsky X2 Demonstrator|
|Role||Experimental compound helicopter|
|Manufacturer||Sikorsky Aircraft / Schweizer Aircraft|
|First flight||27 August 2008|
|Retired||14 July 2011|
|Developed into||Sikorsky S-97 Raider|
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 aircraft; and the RAH-66 Comanche developed expertise in composite rotors and advanced transmission design.
Other features include slowed "de-swirling" rigid rotors two feet apart, active force counter-vibration inspired by the Black Hawk, 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. The fly-by-wire system is provided by Honeywell, the rotor by Eagle Aviation Technologies, anti-vibration technology from Moog Inc, 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.
The X2 first flew on 27 August 2008 from Schweizer Aircraft, a division of Sikorsky Aircraft Corporation's facility at Horseheads, New York. The flight lasted 30 minutes. 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 225 knots (259 mph; 417 km/h) during flight testing in West Palm Beach Florida, unofficially surpassing the current FAI rotorcraft world speed record of 216 knots (249 mph; 400 km/h) set by a modified Westland Lynx in 1986.
On 15 September 2010, test pilot Kevin Bredenbeck achieved Sikorsky's design goal for the X2 when he flew it at a speed of 250 knots (290 mph; 460 km/h) in level flight, an unofficial speed record for a helicopter. The demonstrator then reached a new record speed of 260 knots (300 mph; 480 km/h) in a shallow 2˚ to 3˚ dive, which was just short of the 303 mph achieved by the Sikorsky S-69 technology demonstrator helicopter. 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 RPM to keep tip speed below Mach 0.9, the rotor disc is slightly nose-up, and the lift-to-drag ratio is about twice that of a conventional helicopter. Hands-off flying was also successfully performed during flight tests.
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 in October 2016 and is on display in the Steven F. Udvar-Hazy Center in Chantilly, Virginia.
The Sikorsky Aircraft Corporation and the X2 Technology Demonstrator Team was awarded the 2010 Robert J. Collier Trophy by the National Aeronautic Association "...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).
Data from Flug-Revue NOTE: No other specifications have been released by Sikorsky.
- Crew: Two
- Aspect ratio: 9.5
- Empty weight: 5,300 lb (2,404 kg) 
- Gross weight: 6,000 lb (2,722 kg) 
- Max takeoff weight: 5,300 lb (2,404 kg) –6,000 lb (2,700 kg)
- Powerplant: 1 × LHTEC T800-LHT-801 turboshaft, 1,800 shp (1,300 kW)
- Main rotor diameter: 2× 26 ft 5 in (8.05 m)
- Main rotor area: 548 sq ft (50.9 m2) contra-rotating four-bladed coaxial.
- Propellers: 6-bladed pusher
- Maximum speed: 290 mph (460 km/h, 250 kn) 
- Range: 35 mi (56 km, 30 nmi)
- Wing loading: 0.44 lb/sq ft (2.1 kg/m2)
- Power/mass: 3.66 hp/lb
Aircraft of comparable role, configuration, and era
- Eurocopter X3
- Kamov Ka-50
- Kamov Ka-92
- Lockheed AH-56 Cheyenne
- Mil Mi-X1
- Piasecki X-49
- Carter Personal Air Vehicle
- Trimble, Stephen. "Sikorsky's X2 speedster completes first flight". Flightglobal.com, 27 August 2008.
- Goodier, Rob (September 20, 2010). "Inside Sikorsky's Speed-Record-Breaking Helicopter Technology". Popular Mechanics. Retrieved 22 September 2010.
- Thomas Lawrence and David Jenney (31 Aug 2010). "The Fastest Helicopter on Earth". IEEE Spectrum. Archived from the original on 30 January 2017. Retrieved 1 August 2017.
the helicopter vibrated so much at these higher speeds that its pilots struggled to control it .. The heavy and fuel-hungry jets pushed the aircraft to high speedCS1 maint: uses authors parameter (link)
- XH-59A / X2 comparison IEEE
- Sikorsky to Build and Test X2 Technology Demonstrator Helicopter Archived July 14, 2008, at the Wayback Machine. Sikorsky
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- First Flight Of Sikorsky X2 Demonstrator, Archived March 7, 2012, at the Wayback Machine Aviation Week & Space Technology, 27 August 2008. Accessed: 9 March 2012. Archived on 7 March 2012.
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- US 20150125299 "Counter-rotating Rotor System With Stationary Standpipe" PDF
- Trimble, Stephen. Sikorsky unveils mock-up X2 armed scout. Flightglobal.com, 4 May 2009.
- S-97 Rollout video Sikorsky
- Parsons, Dan (2 October 2014), "Sikorsky rolls-out high-speed Raider rotorcraft", Flightglobal, Reed Business Information, retrieved 3 October 2014
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- "Rotorcraft Absolute: Speed over a straight 15/25 km course Archived 2013-12-03 at the Wayback Machine". Fédération Aéronautique Internationale (FAI). Note search under E-1 Helicopters and "Speed over a straight 15/25 km course". Accessed: 26 April 2014.
- "X2 Technology Demonstrator Achieves 225 Knots, Sets New Top Speed for Helicopter - Target Milestone of 250 Knots Looms in Q3 2010". UTC.com, 15 June 2015.
- Croft, John (September 15, 2010). "Sikorsky X2 hits 250kt goal". Flight International. Retrieved 2010-09-16.
- Sikorsky's X2 Chases World Speed Record
- "Sikorsky X2 Technology Demonstrator Achieves 250-Knot Speed Milestone". sikorsky.com. 15 September 2010. Retrieved 23 September 2010.
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- Robb, Raymond L. Hybrid Helicopters: Compounding the Quest for Speed[permanent dead link] p49, Vertiflite, Summer 2006. Quote: "Ultimately, the XH-59A achieved an incredible 303 mph"
- Datta, Anubhav et al. Experimental Investigation and Fundamental Understanding of a Slowed UH-60A Rotor at High Advance Ratios, page 2. NASA, 2011. Accessed: April 2014.
- Jackson, Dave. "Coaxial - Sikorsky ~ X2 TD" Unicopter, 18 September 2010. Accessed: April 2014. Archived on 13 September 2013.
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- Paur, Jason (15 July 2010). "Sikorsky's Record-Setting Helicopter Retires". WIRED. Retrieved 15 July 2011.
- "Sikorsky X2 rotorcraft prototype makes final flight after proving technology for S-97 scout/attack helicopter". www.militaryaerospace.com. 17 July 2011.
- "Award-Winning X2 Technology Demonstrator Takes its Final Flight - Program paved the way for upcoming S-97 Raider helicopter", Sikorsky Aircraft Corp., 14 July 2011.
- Connor, Roger (25 October 2016). "Sikorsky X2 Helicopter Reaching New Speeds". National Air and Space Museum. Archived from the original on 16 May 2020. Retrieved 5 December 2016.
Weight, empty: 2,404 kg (5,300 lb)
- "Sikorsky X2 joins Smithsonian collection". Helicopter Association International. Helicopter Association International. 28 October 2016. Retrieved 5 December 2016.
- Warwick, Graham. "Sikorsky's X2 - Collier Win, Commercial Next?" Aviation Week, Mar 16, 2011. Accessed: March 8, 2014. Archive Archived March 9, 2014, at the Wayback Machine
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- "Howard Hughes Award", American Helicopter Society
- Johnson, Wayne (January 18–20, 2012). "Design and Performance of Lift-Offset Rotorcraft for Short-Haul Missions" (PDF). NASA. p. 4.
nominal gross weight of 5950 lb.
- Drew, James (2016-02-19). "ANALYSIS: Sikorsky seeks next leap in rotorcraft technology". Flight Global. Archived from the original on 30 August 2020.
We started with [the] X2 technology demonstrator at about 6,000lbs (2.7t) gross weight.
- Walsh, D (January 2011). "High airspeed testing of the Sikorsky X2 Technology™ demonstrator".
- Tomkins, Richard. "Sikorsky powers on S-97 avionics" United Press International, 17 June 2014. Accessed: 19 June 2014. Archived on 18 June 2014.
- Note: this is the disc area of one rotor set, not the effective area of the whole coaxial rotors set.
|Wikimedia Commons has media related to Sikorsky X2.|
|Official Sikorsky X2 videos|
|on YouTube, mitigating dissymmetry of lift and air compressibility near rotor blade tip|
|on YouTube in 2010|
|on YouTube, pilot and staff commentary|
- Sikorsky X2 company page Archive from 2009
- Sikorsky X2 (proposed) on unicopter.com (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
- "Hyper Helos: Prototypes coming off the drawing board and into the race", Flight International, 3 July 2008
- "Swamp Pirates", Aircraft Owners and Pilots Association, October 1, 2011
- Sikorsky X-2 at the Stuart Air Show, Nov 11, 2011