Some Say Sikorsky's X2 Is Not, At Least In The Traditional Sense

While Sikorsky continues to claim new helicopter speed records for its prototype X2 aircraft, some are saying that it is not a helicopter at all ... because it derives thrust from a pusher propeller.

Sikorsky Image

The X2 has flown at speeds up to 235 knots, with an eventual goal or reaching 250 knots. That's nearly 100 knots faster than the top speed ever recorded for a conventional helicopter. But Elfan Ap Rees, who is the editor of Helicopter International Magazine in Great Britain as well as honorary president of the rotorcraft committee of the Fédération Aéronautique Internationale, says maybe not so much.

Television station WTXX in Hartford, CT reports that Ap Rees says the X2 is a compound aircraft, and not a true helicopter, because it derives some of its thrust from a pusher propeller driven by the same engine as the main rotors. Because of that, he says, the speed record set by a modified version of Westland's Lynx helicopter in 1986 should stand. AgustaWestland, not surprisingly, agrees with that assessment.

But Sikorsky spokeswoman Marianne Heffernan said in an e-mail "We stand by our claims."

Sikorsky Image

The FAI's own definition of a helicopter says that it is a "rotorcraft which, in flight, derives substantially the whole of its lift from a power-driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft."

There is no mention of how the forward thrust is generated, only the lift. And Sikorsky says the X2 pusher prop generates only thrust, not lift. "The X2 demonstrator is considered a pure helicopter because all of its lift is derived from its rotor system rather than being augmented by wings," Steve Weiner, Sikorsky's director of engineering sciences and head engineer for the X2, said in a statement. "No other helicopter meeting these criteria has cruised at 250 knots to date."

FMI: www.fai.org, www.sikorsky.com