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Sikorsky X2

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First flight

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Number built

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Program cost

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Developed into

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The Sikorsky X2 is an experimental high-speed compound helicopter with coaxial rotors developed by Sikorsky Aircraft.

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, but that vibration was excessive;[3] 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.[4][5] Other features include slowed[6] "de-swirling"[7] rigid rotors 2 feet apart, active force counter-vibration inspired by the Black Hawk,[8] and using most of the power in forward flight for the pusher propeller rather than the rotor.[3] Test flights and flight simulations were combined to improve test procedure.[9][10] 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.[11] The rotor hub can have 10-20 times the drag of the blade.[12] Sikorsky intended to test hub fairings to reduce drag by 40%,[13] and test flew fairings on the hubs themselves but not the central hub fairing ("aero sail") inbetween the hubs.[14] Sikorsky has since patented a "Standpipe" (fixed tube between rotating rotor axes) suitable for a central hub fairing.[15]

On 4 May 2009, Sikorsky unveiled a mock-up of a Light Tactical Helicopter derivative of the X2,[16] and unveiled a prototype in October 2014.[17][18][19]

In June 2014, Sikorsky/Boeing submitted the SB>1 Defiant helicopter design for the Future Vertical Lift program based on the X2 principle,[20][21] which was approved by the Army in October.[22]

Operational history

The X2 first flew on 27 August 2008 from Schweizer Aircraft's (a division of Sikorsky Aircraft Corporation) facility at Horseheads, New York. The flight lasted 30 minutes.[1] This began a 4-phase flight test program, to culminate with reaching a planned 250-knot top speed.[23] The X2 completed flights with its propeller fully engaged in July 2009.[24] Sikorsky completed phase 3 of the testing with the X2 hitting 181 knots in test flight in late May 2010.[25]

On 26 July 2010, Sikorsky announced that the X2 exceeded Script error: No such module "convert". during flight testing in West Palm Beach Florida, unofficially surpassing the current FAI rotorcraft world speed record of Script error: No such module "convert". set by a modified Westland Lynx in 1986.[26] The X2 flight was purposefully made 37 years to the date of the S-69's first flight.[27]

On 15 September 2010, test pilot Kevin Bredenbeck achieved Sikorsky's design goal for the X2 when he flew it at a speed of Script error: No such module "convert". in level flight,[28][29] an unofficial speed record for a helicopter[3][30] until surpassed by the Eurocopter X3 in 2013.[31] The demonstrator also reached a speed of Script error: No such module "convert". in a shallow 2˚ to 3˚ dive,[32] slightly less than the 303 mph of the XH-59A.[33] 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[34][35] to keep tip speed below Mach 0.9, the rotor disc is slightly nose-up, and Lift-to-drag ratio is about twice that of a conventional helicopter. Hands-off flying was sometimes performed.[36]

On 14 July 2011, the X2 completed its final flight and was officially retired after accumulating 22 hours over 23 test flights.[37] With the end of development, the X2 will be followed by its first application, the S-97 Raider high-speed scout and attack helicopter.[38]


The Sikorsky Aircraft Corporation and the X2 Technology Demonstrator Team was awarded the 2010 Robert J. Collier Trophy by the National Aeronautic Association[39][40] "...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).[41]


Data from Flug-Revue[11] NOTE: No other specifications have been released by Sikorsky.

General characteristics
  • Crew: 2
  • Length: not available ()
  • Rotor diameter: 26.4 ft[35] (8.05 m)
  • Height: not available ()
  • Disc area: 548 ft²[35][42] (50.9 m²)
  • Empty weight: lb (kg)
  • Max. takeoff weight: 5,300[35] - 6,000 lb[43] (or 3,600 kg[11])
  • Powerplant: 1 × LHTEC T800-LHT-801 turboshaft, 1300–1800 shp (1000–1340 kW)
  • Propellers: 1 six-bladed pusher-type propeller
  • Rotor configuration: 2 four-bladed co-axial


See also

Related development
Aircraft of comparable role, configuration and era

Related lists


  1. ^ a b Trimble, Stephen. "Sikorsky's X2 speedster completes first flight"., 27 August 2008.
  2. ^ Warwick, Graham (22 May 2015). "Sikorsky Conducts First Flight Of S-97 Helo". Aviation Week & Space Technology. Retrieved 25 May 2015. 
  3. ^ a b c Goodier, Rob (September 20, 2010). "Inside Sikorsky's Speed-Record-Breaking Helicopter Technology". Popular Mechanics. Retrieved 22 September 2010. 
  4. ^ Sikorsky to Build and Test X2 Technology Demonstrator Helicopter. Sikorsky
  5. ^ Trimble, Stephen (26 July 2010). "Sikorsky X2 sets unofficial helicopter speed record". FlightGlobal. Reed Business Information. Retrieved 29 July 2010. 
  6. ^ First Flight Of Sikorsky X2 Demonstrator,[dead link] Aviation Week & Space Technology, 27 August 2008. Accessed: 9 March 2012. Archived on 7 March 2012.
  7. ^ Chandler, Jay. "Advanced rotor designs break conventional helicopter speed restrictions (page 1)" Page 2 Page 3. ProPilotMag, September 2012. Accessed: 10 May 2014. Archive 1 Archive 2 Archive 3
  8. ^ X2 marks the spot for radical rotor designs,, 12 June 2007.
  9. ^ Wilson, J.R. "Defense Interview: Mark Miller" Defense Media Network, 9 September 2011. Accessed: 4 October 2014. Archived on 2 November 2012.
  10. ^ "Sikorsky Innovations Introduces X2 Technology™ Light Tactical Helicopter Simulator" Sikorsky PR
  11. ^ a b c "Sikorsky X2". Flug-Revue. Archived from the original on June 12, 2008. Retrieved 2007-06-25. 
  12. ^ Harris, Franklin D. "Rotor Performance at High Advance Ratio: Theory versus Test" page 119 NASA/CR—2008–215370, October 2008. Accessed: 13 April 2014.
  13. ^ Croft, John (20 May 2010). "Sikorsky X2 breaks helicopter speed barrier". Flightglobal (Reed Business Information). Archived from the original on 28 May 2015. Retrieved 28 May 2015. 
  14. ^ Dubois, Thierry (26 July 2011). "AgustaWestland". Aviation International News. Archived from the original on 11 October 2014. Retrieved 28 May 2015. 
  15. ^ US 20150125299  "Counter-rotating Rotor System With Stationary Standpipe" PDF
  16. ^ Trimble, Stephen. Sikorsky unveils mock-up X2 armed scout., 4 May 2009.
  17. ^ S-97 Rollout video Sikorsky
  18. ^ Parsons, Dan (2 October 2014), "Sikorsky rolls-out high-speed Raider rotorcraft", Flightglobal (Reed Business Information), retrieved 3 October 2014 
  19. ^ Warwick, Graham. "Sikorsky Talks To Customers About Potential Raider Applications" Aviation Week & Space Technology, 6 October 2014. Accessed: 3 October 2014. Photos Archived on 3 October 2014
  20. ^ Majumdar, Dave. "Sikorsky and Boeing Team Submit New Army Helicopter Design" -, 17 June 2014. Accessed: 19 June 2014. Archive
  21. ^ Sikorsky and Boeing to pitch ‘X-2’-based design for US Army JMR TD effort -, February 28, 2013
  22. ^ U.S. Army Selects Bell and Sikorsky/Boeing to Build Prototypes for Next Generation Helicopter Program -, 3 October 2014
  23. ^ Trimble, Stephen. "Sikorsky high-speed X2 prototype starts flight-test phase". Flight International, 2 September 2008.
  24. ^ Lynch, Kerry. "Sikorsky X2 Flies With Engaged Propeller"[dead link] Aviation Week, 13 July 2009. Paywall
  25. ^ Croft, John. "Sikorsky completes third-phase X2 tests with 181kt flight". Flight International, 27 May 2010.
  26. ^ "Rotorcraft Absolute: Speed over a straight 15/25 km course". Fédération Aéronautique Internationale (FAI). Note search under E-1 Helicopters and "Speed over a straight 15/25 km course". Accessed: 26 April 2014.
  27. ^ "X2 Technology Demonstrator Achieves 225 Knots, Sets New Top Speed for Helicopter - Target Milestone of 250 Knots Looms in Q3 2010"., 26 July 2010.
  28. ^ Croft, John (September 15, 2010). "Sikorsky X2 hits 250kt goal". Flight International. Retrieved 2010-09-16. 
  29. ^ Sikorsky's X2 Chases World Speed Record
  30. ^ "Sikorsky X2 Technology Demonstrator Achieves 250-Knot Speed Milestone". 15 September 2010. Retrieved 23 September 2010. The speed, reached during a 1.1-hour flight, is an unofficial speed record for a helicopter. 
  31. ^ Paur, Jason. "X3 Helicopter Sets Speed Record At Nearly 300 MPH" Wired (magazine), 11 June 2013. Accessed: 17 June 2014. Archived on 31 March 2014
  32. ^ Finnegan, Joy editor-in-chief (1 October 2010). "Sikorsky Breaks 250 KTAS Record". Rotor & Wing. Retrieved 6 October 2010. 
  33. ^ Robb, Raymond L. Hybrid Helicopters: Compounding the Quest for Speed p49, Vertiflite, Summer 2006. Quote: "Ultimately, the XH-59A achieved an incredible 303 mph"
  34. ^ 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.
  35. ^ a b c d e f Jackson, Dave. "Coaxial - Sikorsky ~ X2 TD" Unicopter, 18 September 2010. Accessed: April 2014. Archived on 13 September 2013.
  36. ^ 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.
  37. ^ Paur, Jason (15 July 2010). "Sikorsky’s Record-Setting Helicopter Retires". WIRED. Retrieved 15 July 2011. 
  38. ^ "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.
  39. ^ Warwick, Graham. "Sikorsky's X2 - Collier Win, Commercial Next?"[dead link] Aviation Week, Mar 16, 2011. Accessed: March 8, 2014. Archive
  40. ^ Larson, George. "Sikorsky's X2 and the Collier Trophy"[dead link] Aviation Week, Mar 23, 2011. Accessed: March 8, 2014. Archive
  41. ^ "Howard Hughes Award", American Helicopter Society
  42. ^ Note: this is the disc area of one rotor set, not the effective area of the whole coaxial rotors set.
  43. ^ Tomkins, Richard. "Sikorsky powers on S-97 avionics" United Press International, 17 June 2014. Accessed: 19 June 2014. Archived on 18 June 2014.
  44. ^
  45. ^ a b Green, Ronald D. Flight Plan 2011 - Analysis of the U.S. Aerospace Industry, Rotorcraft Developments p18, U.S. Department of Commerce / International Trade Administration, March 2011. Accessed: 2 March 2012. Quote: "Several companies--including Sikorsky, Eurocopter, and Carter Aerospace Technologies--are developing compound helicopters to combine vertical/short take-off-and-landing capabilities with one or more propellers for increasing forward speed over conventional helicopter design."

External links

External video
Official Sikorsky X2 videos
16px X2 technology Video on YouTube, mitigating dissymmetry of lift and air compressibility near rotor blade tip
16px X2 record flight Video on YouTube in 2010
16px Sikorsky X2 Collier Trophy on YouTube, pilot and staff commentary