The Sikorsky S-97 Raider light tactical prototype helicopter exceeded 200 knots during last month’s flight test. The suite of X2 Technologies enables the aircraft to operate at high speeds while maintaining the low-speed handling qualities and maneuverability of conventional single main rotor helicopters. Raider will be presented for the U.S. Army’s Future Attack Reconnaissance Aircraft (FARA) competition, as the Army looks to revolutionize its aircraft fleet via its Future Vertical Lift initiative. The Sikorsky S-97 Raider is a high-speed scout and attack compound helicopter based on the Advancing Blade Concept (ABC), under development by Sikorsky Aircraft (now part Lockheed Martin). Lockheed Martin planned to offer it for the United States Army’s Armed Aerial Scout program, along with other possible uses.
The S-97 design includes variable speed rigid coaxial main rotors and a variable-pitch pusher propeller, making the S-97 a compound helicopter. The main rotors have hingeless hubs and stiff blades, to improve low-speed handling and efficiency of hover. At high speeds, the close spacing of the hubs reduces drag. The stiff blades allow each rotor to have low lift on the retreating side of its rotor disk, whereas each rotor on a conventional coaxial rotor with “floppy” blades needs nearly equal lift distribution. The propeller relieves the rotor of propulsion, further reducing drag. Maneuverability is improved compared with earlier helicopters because of the ability to tilt the coaxial rotors together or tilt each one differently, and because of the variable pitch propulsor and active elevons. At low speed the S-97 maneuvers by differential torque of the upper and lower rotor, at high speed it uses rudders.
The S-97 will be capable of carrying up to six passengers, in addition to a flight crew of two in a side-by-side cockpit. However, the production S-97 is projected to be capable of flying with either one or two pilots, or autonomously. Space for a targeting sensor has been reserved, however it will not be installed in the prototype aircraft. Based on the technology from the Sikorsky X2 demonstrator, the prototype S-97s will be powered by a General Electric YT706 turboshaft (the same engine used on the MH-60M Black Hawk), however a more powerful engine, developed under the Improved Turbine Engine Program, is expected to become available. Compared to the OH-58D Kiowa, the S-97 has significantly increased performance goals, such as cruising speeds upwards of 200 knots while carrying weapons, turning at three times the force of gravity at 220kt, and a high hover efficiency. Sikorsky also aims for an operating cost of $1,400 per flight hour.
