Rotorcraft
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| A USAF CV-22 in flight |
A rotorcraft is a heavier-than-air flying machine that uses lift generated by wings that revolve around a mast called rotor blades. Several rotor blades mounted to a single mast is referred to as a rotor. Rotorcraft may also include the use of static lifting surfaces, but the primary distinguishing feature being lift provided by one or more rotors. Rotorcraft include helicopters, autogyros, gyrodynes and tiltrotors. In the United States, the Federal Aviation Administration places helicopters, autogyros (which it calls gyroplanes), and gyrodynes in the category Rotorcraft, and tiltrotors in the category Powered lift.
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[edit] Helicopters
A helicopter is a rotorcraft whose rotors are driven by the engine(s) throughout the flight, to allow the helicopter to take off vertically, hover, fly forwards, backwards and laterally, as well as to land vertically. Helicopters have several different configurations of one or more main rotors.
Helicopters with one driven main rotor require some sort of antitorque device such as a tail rotor, fantail, or NOTAR, except some rare examples of helicopters using tip jet propulsion which generates almost no torque.
[edit] Autogyros
Unlike a helicopter, the rotor of an autogyro (sometimes called gyrocopter or gyroplane) is driven by aerodynamic forces alone, and thrust is provided by an engine-powered propeller similar to that of a fixed-wing aircraft.
[edit] Gyrodynes
A Gyrodyne is a rotorcraft with a rotor system that is normally driven by its engine for takeoff, hovering and landing like a helicopter, but which also has an additional propulsion system that is independent of the rotor system. At higher speeds, the rotor system acts similar to that of an autogyro, no longer driving the aircraft but simply providing lift. A technology proposal by Carter Copter Technologies, as well as a research project funded by DARPA both refer to gyrodyne-type concepts as heliplanes.
[edit] Tiltrotors
As the name implies, a tiltrotor aircraft uses tiltable (rotating) propellers, or proprotors, for lift and propulsion. For vertical flight the proprotors are positioned horizontally to direct their thrust downwards, providing lift for vertical take off and landing, and hover. In this mode of operation the craft is essentially identical to a helicopter. As the craft gains speed, the proprotors are slowly tilted forward, eventually becoming perpendicular to the ground. In this mode the wing provides the lift, and the wing's greater efficiency helps the tiltrotor achieve its high speed.
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