Sikorsky is building a coaxial-rotor high-speed helicopter technology demonstrator that will cruise at 250kt (460km/h), compared with 150-170kt for conventional helicopters. The tandem-seat, single-engine X2 Technology demonstrator is being built by the company's Schweizer Aircraft subsidiary and will fly by the end of next year.
The helicopter harks back to the XH-59 Advancing Blade Concept (ABC) prototypes flown by Sikorsky from 1973 to 1977, which reached 240kt under auxiliary turbojet power, but uses advances in technology to overcome the coaxial-rotor design's problems with weight, drag and vibration. The demonstrator is "100% funded by Sikorsky", says Jeff Pino, senior vice-president of marketing and commercial programmes.
Progress since the XH-59 includes advances in rotor blade technology, rotor-hub drag reduction, fly-by-wire flight controls, active vibration suppression and high power-to-weight integrated transmissions that distribute engine power between the rotor and a propeller mounted in the tail to provide higher forward speed.
In an ABC helicopter, counter-rotating rigid rotors allow the retreating blade on each side to be unloaded as velocity increases, avoiding the tip stall that limits the forward speed of conventional craft. This avoids the hover penalty on a compound helicopter caused by rotor downwash on the wing.
The "light helicopter class" X2 Technology demonstrator will be powered by a single LHTEC T800-801 turboshaft, which will drive the coaxial four-blade rotors and the tail-mounted propulsor. The counter-rotating design removes the need for a tailrotor, and Sikor-sky has overcome the problem of the propulsor continuing to draw power when in helicopter mode, says Pino. A modified Schweizer 333 helicopter will fly before the end of the year to test the fly-by-wire flight control system.
Although a production machine using the X2 technology suite is "a long way off", says Pino, Sikorsky sees the design being applied to manned and unmanned aircraft and scalable from light civil helicopters right up to the USA's planned Joint Heavy Lift rotorcraft. Market surveys included offshore operators, who expressed interest in higher speed, he says.
GRAHAM WARWICK/WASHINGTON DC
Source: Flight International
