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Helicopter – a rotary-wing aircraft, in which the lifting and driving forces at all stages of flight are created by one or several rotors with a drive from one or more engines.
Like an airplane wing, the rotor blades of a helicopter are at an angle to the plane of rotation of the propeller, which is called the angle of the blades. However, unlike a fixed aircraft wing, the angle of the aircraft’s blades can vary widely (up to 30 °).
Almost always the helicopter rotor is equipped with a skewing machine that, for flight control, provides displacement of the center of pressure of the propeller in case of a hinged connection of the blades or inclines the plane of rotation of the propeller in the case of a semi-rigid connection. The swashplate is usually rigidly connected to the axial hinge to change the angle of attack of the blades. In schemes with three or more rotors, the skew may be absent.
The blades of a helicopter, as a rule, in all flight modes rotate at a constant frequency, the increase or decrease in the power of the rotor depends on the pitch of the propeller.
The rotation of the screw is usually transmitted from one or two engines through the transmission and drive shaft to the rotor. In this case, a reactive moment arises, which tends to twist the helicopter in the direction opposite to the rotation of the rotor. To counteract the reactive moment, as well as for the directional control, either a steering device or a pair of synchronized screws rotating in different directions is used.