Sikorsky X2

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; 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 2 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. 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") inbetween the hubs. Sikorsky has since patented a "Standpipe" (fixed tube between rotating rotor axes) suitable for a central hub fairing.