The idea is to find a way around the physics that limit the speed of a conventional helo. With any helicopter, the top rotor provides lift as the blades slice the air. When the helicopter is flying forward, air moves around the the blade spinning in the direction of travel faster than it does around the retreating blade on the opposite side, causing something aerodynamicists call dissymmetry of lift. The faster you go, the more severe the effect and the less stable the helicopter. Aerodynamicists know how to compensate for most of that, but the challenge mounts as the blades approach the speed of sound. An advancing blade hitting the sound barrier creates aerodynamic instabilities engineers cannot compensate for.
So Airbus engineers added two short wings extending from each side of the fuselage. The wings meet at a point and support a rear-facing prop driven by the engines turning the main rotor. In forward flight, the wings provide additional lift, and those small props provide additional propulsion. All of this allows the helo to achieve higher speeds without pushing the main rotor into an aerodynamic red zone.
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