Helicopter

Helicopter, exceptionally maneuverable aircraft able to take off and land vertically, hover, and fly in any horizontal direction without necessarily changing the alignment of the aircraft. Lift is provided by 1 or more rotors mounted above the craft and rotating horizontally about a vertical axis. Change in the speed of rotation or in the pitch (angle of attack) of all the blades at once alters the amount of lift; cyclic change in the pitch of each blade during its rotation alters the direction of thrust. Most helicopters have only a single lift rotor and thus have a tailmounted vertical rotor to prevent the craft from spinning around; change in the speed of this rotor is used to change the craft's heading. Helicopter toys were known to the Chinese and in medieval Europe, but because of problems with stability, it was not until 1939, following the success of the autogiro (1923), that the first fully successful helicopter flight was achieved by Russian-born U.S. engineer Igor Ivanovich Sikorsky. Used in combat in Vietnam, the helicopter has become increasingly important in military use. It has given ground forces entree to areas hitherto inaccessible. Its firepower and maneuverability permit close air support of ground forces. Its extreme mobility allows evasive action and the potential to surprise the enemy. Its capacity to hover makes it a relatively stable weapons platform.

In civilian use, helicopters have proved valuable for city-to-airport and city-to-suburb transportation and for monitoring traffic, spotting forest fires, patrolling pipelines, and performing rescue work.