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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 .