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How the Helicopter Flies ?
They have existed for only 70 years, yet they are without question one of the most versatile and vital vehicles in the world. They transport world leaders and the critically wounded; they fight forest fires and rescue people trapped in burning buildings; they can deliver huge payloads to areas that no other vehicle can reach.
The helicopter is type of aircraft in which lift is obtained by means of one or more power-driven horizontal propellers called rotors. When the rotor of a helicopter turns it produces reaction torque which tends to make the craft spin also. On most helicopters a small rotor near the tail compensates for this torque. On twin-rotor craft the rotors spin in opposite directions, so their reactions cancel each other. The helicopter is propelled in a given direction by inclining the axis of the main rotor in that direction. The helicopter's speed is limited by the fact that if the blades rotate too fast they will produce compressibility effects on the blade moving forward and stall effects on the rearward moving blade, at the same time.
Although the helicopter was only recently fully developed, its concept can date back to the late 1400's. Since then, helicopters have been put into use by society in many ways. One can find helicopters in both civil and military areas. The early helicopters were mainly developed for military use, but later became certified for civilian use. Since then helicopters have evolved greatly, specifically with the design. Because a helicopter can perform more actions than a fixed-wing aircraft can, it is more complicated to fly. The helicopter must compensate for a variety of forces, like the spinning force induced by the main rotors. The engineering behind designing a helicopter is complex with a variety of issues to be understood .
