Helicopter (the Greek ἔλιξ helix ( spiral ) and πτέρυξ ptéryks ( wing ) ) is a type of aircraft diagonal wings heavier than air, propelled by one or more rotors largest horizontal (propellants) which, when rotated by engine, create lift and propulsion necessary for the flight. Because rotor blades rotate around a mast, they are classified as rotary-wing aircraft, which distinguishes them from conventional fixed-wing ( airplane ) aircraft.
In contrast to fixed-wing aircraft, this allows the helicopter to take off and land vertically, hover and go forward, backward and laterally. These attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft would not be able to land or take off. The ability to hover for long periods of time and vertical takeoff and landing allows helicopters to perform tasks that fixed-wing aircraft cannot perform.
Helicopters were developed and built during the first half of the twentieth century, with some production and limited range, but it was not until 1942 that the Sikorsky R-4, a helicopter designed by Igor Sikorsky achieved large-scale production, with 131 aircraft built.
Helicopters have military and civilian uses such as troop transport, infantry support, firefighting support, rescue of injured people in the metropolises, ship-to-ship operations, transport of crews to oil rigs, transport of businessmen, sanitary evacuation, overhead crane, police and civilian surveillance, transport of goods (some helicopters may carry parachute loads ) etc.
In conventional aircraft, the wing profile (or airfoil ) is designed to deflect air down with great efficiency. This deflection causes two effects: a backlash and a pressure difference. The reaction is based on Newton’s third law, and generates a counter-deflection force, in this case upward. The pressure difference, in turn, is based on the Bernoulli principle, where air moves faster at the top and lower at the bottom of the airfoil. This causes respectively low and high pressure. This pressure difference coupled with the reaction to air deflection causes the lift force in the airfoil. However, the higher the lift produced, the greater the drag generated by the airfoil. The helicopter makes use of the same principle, except that instead of moving the entire aircraft, only the wings (blades, in the case of rotating wings) move through the air.