Helicopters

Even Leonardo da Vinci has developed the project of the helicopter with the rotor, which was driven manually. But the first helicopters, which were of practical interest, appeared only in the 30-ies of the XX century
To stay in the air, conventional aircraft should move forward. The movement of the wing through the air creates a force opposite the downward force of gravity. But helicopters can stay in air without moving forward, because the lifting force created by the rotation of their wings. Just as in aircrafts with fixed wing, the lifting force is created by air flow that goes around the wing surface.
Narrow wings of the helicopter called blades. Thanks to the motor rotates the set of blades, or rotor. But the gyroplane the propeller moves the aircraft forward, and the flow of air that occurs when this causes the rotor to spin like a windmill. Also, like a helicopter, this rotation creates the necessary lifting force.
In the case of a hovering helicopter lift force equal to its weight. The helicopter gained height, the increase in lifting force is achieved by increasing the angle of the front edges of the blades relative to the horizontal which is called angle of attack. To simultaneously increase the angle of attack of the blades, the pilot uses a lever, which is called the modular switch of a step. During the lowering of the lifting force is reduced by reducing the angle of attack.