A helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors - each of which comprises two or more rotor blades. Helicopters are classified as rotary-wing aircraft to

HELICOPTERS

A helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors - each of which comprises two or more rotor blades. Helicopters are classified as rotary-wing aircraft to distinguish them from fixed-wing aircraft (or airplanes). The word "helicopter" derives from the Greek words helix (spiral) and pteron (wing).

Compared to fixed-wing aircraft, helicopters are much more maneuverable. They can hover, take off and land vertically, and fly in reverse or to the side. In principle, helicopters can fly anywhere and land any place with enough space (about twice the rotor disc area). Helicopters gain these advantages at the cost, in comparison to fixed-wing aircraft, of greater mechanical complexity, greater cost to buy and operate, and less speed, range, and payload capability.

Helicopters are designed and used for a wide variety of military, civilian and commercial activities. They include search and rescue, emergency medical service, firefighting, commercial aviation, executive transportation, aerial photography, media reporting, patrolling borders and so on. Helicopters are often used as aerial cranes. Their ability to lift and hover with heavy loads makes them ideal for placing large objects in otherwise inaccessible locations.

For more densely populated countries, passenger helicopters are viewed as a possibly more efficient means of transportation compared to fixed-wing commuter aircraft. Some predict that passenger helicopters can not only revolutionize mass transportation in parts of the world but also improve the quality of life in a country by promoting efficient utilization of its territory.

But helicopters have some disadvantages. The most obvious limitation of the helicopter is its slow speed. Other limitations are vibration and great noise produced during operation.

Fixed-wing aircraft are usually inherently stable. Many small, fixed-wing aircraft are stable enough that a pilot can let go of the controls while looking at a map or dealing with a radio, and the plane will generally stay on course.

In contrast, helicopters are very unstable. Simply hovering requires continuous, active corrections from the pilot. Hovering a helicopter is compared to balancing yourself while standing on a large beach ball. Adjusting one flight control on a helicopter almost always has an effect that requires an adjustment of the other controls.

In identifying helicopters during flight it is helpful to know that when viewed from below, the rotor of a French, Russian, or Soviet designed helicopter rotates counter-clockwise, while that of a helicopter built in Italy, the UK or the USA rotates clockwise.

A helicopter should not be mistaken for an autogyro, which is a predecessor of the helicopter that gains lift from an unpowered rotor.

Some common nicknames for helicopters are "copter," "chopper," "whirlybird," "windmill," or "helo" (common U.S. Navy usage).

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