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 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;XH-59A / X2 comparison IEEE 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.Sikorsky to Build and Test X2 Technology Demonstrator Helicopter . Sikorsky

Other features include slowedFirst Flight Of Sikorsky X2 Demonstrator, Aviation Week & Space Technology, 27 August 2008. Accessed: 9 March 2012. Archived on 7 March 2012. "de-swirling"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 rigid rotors two feet apart, active force counter-vibration inspired by the Black Hawk,X2 marks the spot for radical rotor designs, Flightglobal.com, 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."Sikorsky Innovations Introduces X2 Technology™ Light Tactical Helicopter Simulator" Sikorsky PR 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.Harris, Franklin D. "Rotor Performance at High Advance Ratio: Theory versus Test " page 119 NASA/CR—2008–215370, October 2008. Accessed: 13 April 2014. 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. PDF

On 4 May 2009, Sikorsky unveiled a mockup of a Light Tactical Helicopter derivative of the X2,Trimble, Stephen. Sikorsky unveils mock-up X2 armed scout. Flightglobal.com, 4 May 2009. and unveiled a prototype in October 2014.S-97 Rollout video SikorskyWarwick, 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

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. ArchiveSikorsky and Boeing to pitch ‘X-2’-based design for US Army JMR TD effort - Flightglobal.com, February 28, 2013 which was approved by the Army in October.U.S. Army Selects Bell and Sikorsky/Boeing to Build Prototypes for Next Generation Helicopter Program - News.USNI.org, 3 October 2014

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. 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.Trimble, Stephen. "Sikorsky high-speed X2 prototype starts flight-test phase". Flight International, 2 September 2008. The X2 completed flights with its propeller fully engaged in July 2009.Lynch, Kerry. "Sikorsky X2 Flies With Engaged Propeller" Aviation Week, 13 July 2009. Paywall Sikorsky completed phase three of the testing with the X2 reaching 181 knots in test flight in late May 2010.Croft, John. "Sikorsky completes third-phase X2 tests with 181kt flight". Flight International, 27 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 world speed record of set by a modified Westland Lynx in 1986."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."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.

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

Awards The Sikorsky Aircraft Corporation and the X2 Technology Demonstrator Team was awarded the 2010 Robert J. Collier Trophy by the National Aeronautic AssociationWarwick, Graham. "Sikorsky's X2 - Collier Win, Commercial Next?" Aviation Week, Mar 16, 2011. Accessed: March 8, 2014. Archive Larson, George. "Sikorsky's X2 and the Collier Trophy " Aviation Week, Mar 23, 2011. Accessed: March 8, 2014. "...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)."Howard Hughes Award", American Helicopter Society

Specifications

Sikorsky X2

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