Helicopter needs that tail!

Why is it that a helicopter has a tail with a propeller on ONE side? Humans like symmetry, and helicopter's odd tail does not make sense.

Humans are emotional beings and tend to forget the laws of nature, more specifically the laws of physics. A quick refresher on Newton's Third Law of Motion:

"For every action there is an equal and opposite reaction" 

A helicopter flies up with a huge propeller mounted on top it that is powered by a huge motor. When this huge motor rotates (clockwise) it creates an equal and opposite rotating force (counterclockwise) that is called torque. Keeping this thought, lets now consider the small propeller that is oddly installed on one side of Helicopter's tail. Naturally, this propeller creates force in the opposite direction due to the wind draft it creates. 

Without the tail propeller the helicopter would spin due to the counter torque of the motor! the tail controls this spin, keeps the helicopter pointed in the same direction. The tail propeller is also used to turn the helicopter by adjusting the speed of propeller. 

Taken from http://www.start-flying.com