A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors (propellers). Helicopters are classified as rotary-wing aircraft to differentiate them from conventional fixed-wing aircraft. The word helicopter is resulting from the Greek words helix (spiral) and pteron (wing). The engine-driven helicopter was invented by the Slovak inventor Jan Bahyl. The first stable, fully-controllable helicopter located in production was invented by Igor Sikorsky.
Compared to conventional fixed-wing aircraft, helicopters are much more complex, more expensive to buy and operate, comparatively slow, have shorter range and restricted payload. The compensating advantage is maneuverability: helicopters can hover in place, reverse, and above all take off and land vertically. Subject only to refuelling facilities and load/altitude limitations, a helicopter can travel to any location, and land wherever with a clearing a rotor disk and a half in diameter
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