A rotorcraft is a heavier-than-air flying machine that uses lift generated by rotor blades revolving around one or more masts.
A rotorcraft, or rotary-winged aircraft, is a heavier-than-air aircraft that uses (as the name implies) one or more spinning rotor (also known as rotary-wings) to produce lift. In some types of rotorcraft, the rotor(s) also provide thrust for forward (or backward or sideways) motion, while other types require a separate source of thrust (typically an engine-driven propeller).
There are four main types of pure rotorcraft:
- The most-common-and-best-known-by-far is the helicopter, which uses one or more engines to drive its main rotor(s) directly, and obtains forward/backward/sideways thrust by tilting the rotor(s) (and helicopter) in the desired direction. As such, helicopters can hover (unless severely overloaded), and are fully vtol-capable.
- The oldest type of powered rotorcraft, the autogyro (also known as an autogiro, gyroplane, or gyrocopter), uses an unpowered main rotor, which is tilted back slightly relative to the rest of the aircraft; the engine, instead of driving the main rotor directly, is used to provide forward thrust, and the resulting airflow through the main rotor causes it to spin (auto-rotation), and, thereby, produce lift. As a result, an autogyro requires at least some forward airspeed in order to maintain altitude, and (unlike a helicopter) cannot perform a vertical takeoff, although a vertical landing is still doable.
- A rotor-kite (or gyrokite or gyroglider) is essentially an autogyro sans engine. It is the rotorcraft equivalent of a glider, and, like a glider, must be towed and/or catapulted into the air, dropped from an already-airborne aircraft, or rolled down a hill in order to become airborne; once airborne, a rotor kite will slowly but continuously lose altitude unless/until it finds a good updraft. The rotor kite is the oldest type of rotorcraft, with the earliest known flight in 1891, decades before even the first autogyro (due - again, like a glider - to not having to worry about finding a suitable engine).
- A gyrodyne is a kind of hybrid between a helicopter and an autogyro; it has a powered main rotor, like a helicopter (giving it VTOL capability, like a helicopter), but it uses separate propellers for forward thrust, like an autogyro. When hovering, or ascending or descending vertically, the main rotor is driven entirely by the engine(s); however, as the gyrodyne accelerates forward, an increasing proportion of the force spinning the main rotor comes from the air passing through it, until, at cruise speeds, the craft is functioning essentially as an autogyro, with little or no engine power being provided to the main rotor.
Some additional types of aircraft (sometimes known collectively as powered-lift aircraft) function as rotorcraft during some flight regimes, but as airplanes at other times:
- A tiltrotor functions as a helicopter when taking off or landing, with lift provided by a set of (almost always two) powered rotors mounted on a set of otherwise-normal wings; however, as it transitions to forward flight, the rotors tilt forwards and more and more lift is produced by the wings rather than the rotors, until the rotors are pointed directly forwards and functioning solely as propellers (albeit very large propellers), and the aircraft is flying as an airplane.
- A tiltwing is quite similar to a tiltrotor, but, as indicated by the name, tilts the entire wing rather than just the rotors; it is more efficient than a tiltrotor, as the wing is aligned with the local airflow at all times (reducing drag) rather than just during forward flight, but is much more mechanically complex (due to the need to tilt the entire wing rather than just the rotors), and, as such, less common.
- A tailsitter is similar, in principle, to a tiltrotor or tiltwing; however, where a tiltrotor or tiltwing tilts the rotors or wings, respectively, a tailsitter instead tilts the entire aircraft, so that, during takeoff and landing, the aircraft is (as the name indicates) sitting on what is, in horizontal flight, the tail. Tailsitters have never been particularly successful, as entering or exiting the aircraft generally requires a ladder or crane, transitioning successfully between vertical and horizontal flight is problematic, and landing the aircraft without damaging/destroying it or its pilot is somewhat difficult when said pilot can't see the ground they're landing on.
- A stopped-rotor aircraft is similar to a gyrodyne; however, where a gyrodyne's main rotor continues to rotate during forward flight, that of a stopped-rotor aircraft stops turning (as you probably guessed from the name), and is locked in place to act as a conventional wing. This is theoretically more efficient, but, in practice, it has proven extremely difficult to successfully transition from vertical, spinning-rotor flight to horizontal, stopped-rotor flight, with most designs so far having an unfortunate tendency to crash during the process.
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