| X2 | |
|---|---|
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| |
| Sikorsky X2 Demonstrator | |
| Role | Experimental compound helicopter |
| Manufacturer | Sikorsky Aircraft / Schweizer Aircraft |
| First flight | 27 August 2008[1] |
| Retired | 14 July 2011 |
| Status | Retired |
| Number built | 1 |
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.
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;[2][3][4] 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.[5][6]
Other features include slowed[7] "de-swirling"[8] rigid rotors two feet apart, active force counter-vibration inspired by the Black Hawk,[9] and using most of the power in forward flight for the pusher propeller rather than the rotor.[2] 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.[10]
Test flights and flight simulations were combined to improve test procedure.[11][12] 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.[13] The rotor hub can have 10-20 times the drag of the blade.[14] Sikorsky intended to test hub fairings to reduce drag by 40%,[15] and test flew fairings on the hubs themselves but not the central hub fairing ("aero sail") in between the hubs.[16] Sikorsky has since patented a "Standpipe" (fixed tube between rotating rotor axes) suitable for a central hub fairing.[17]
On 4 May 2009, Sikorsky unveiled a mockup of a Light Tactical Helicopter derivative of the X2,[18] and unveiled a prototype in October 2014.[19][20][21]
In June 2014, Sikorsky/Boeing submitted the SB-1 Defiant helicopter design for the Future Vertical Lift program based on the X2 principle,[22][23] which was approved by the Army in October.[24]
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.[1] This began a four-phase flight test program, to culminate with reaching a planned 250-knot top speed.[25] The X2 completed flights with its propeller fully engaged in July 2009.[26] Sikorsky completed phase three of the testing with the X2 reaching 181 knots in test flight in late May 2010.[27]
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.[28][29]
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,[30][31] an unofficial speed record for a helicopter.[2][32] The demonstrator then reached a new record speed of 260 knots (300 mph; 480 km/h) in a shallow 2˚ to 3˚ dive,[33] which was just short of the 303 mph achieved by the Sikorsky S-69 technology demonstrator helicopter.[34] 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[35][36] 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.[37]
On 14 July 2011, the X2 completed its final flight and was officially retired after accumulating 22 hours over 23 test flights.[38][39] With the end of development, the X2 will be followed by its first application, the S-97 Raider high-speed scout and attack helicopter.[40] 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.[41][42]
The Sikorsky Aircraft Corporation and the X2 Technology Demonstrator Team was awarded the 2010 Robert J. Collier Trophy by the National Aeronautic Association[43][44] "...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).[45]
Data from Flug-Revue[13] NOTE: No other specifications have been released by Sikorsky.
General characteristics
Performance
