Why helicopters have a tail rotor?

Why Does A Helicopter Have A Second Rotor On Its Tail?

 We all know or seen helicopters. Such a marvel of human engineering. It is also called as a chopper, helo or whirlybird.It is a type of rotorcraft in which lift and thrust are supplied by rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally. These attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft would usually not be able to take off or land. The capability to efficiently hover for extended periods of time allows a helicopter to accomplish tasks that fixed-wing aircraft and other forms of vertical takeoff and landing aircraft cannot perform.

Well the obvious question arises now. Why does it require a tail rotor?

Its simple, to counteract the torque effect caused by main rotor.
Lets make it clear. When the helicopter is working, the big main blade rotates and causes the lift necessary to rise up. But as it moves up, there isn't any contact with a stationary object as ground any more. Still the main blade is rotating with great velocity. Since there are no external forces acting on the system, the angular momentum of the system remains constant. Hence the angular momentum of the main blade has to be balanced/canceled, if not the helicopter will find its own way to do that-The helicopter will rotate in a direction opposite to the direction of rotation of main blade.

The speed of rotation will depend upon the moment of inertia of the copter. This causes the pilot to pop! Humans found a way to avoid this - attach a tail rotor such that it will provide the angular momentum necessary for balancing the chopper. It is clearly explained in the picture above.

Hope you have understood why it is needed...


Reference
1. Angular Momentum- Momentum equivalent in rotation. Product of angular velocity and Moment of inertia.
2. Torque-The rotating action of a force .