A helicopter flies off, its propellers rotating. Why doesn't the body

[alphabeta1720]

A helicopter flies off, its propellers rotating. Why doesn't the body of the helicopter rotate in the opposite direction?

 

[rcgldr]

A tail rotor is used to generate a sideways force that results in an opposing torque. The side force causes the helicopter to drift to the side a bit unless the helicopter leaned a small amount.

 

[Studiot]

Yes you are correct in observing that the torque driving the main rotor has to be balanced or the body of the copter will rotate the other way.

If you ever visit the Helicopter Museum at Weston Super Mare in England (recommended) you will see examples of all the schemes developed to achieve this.

The principle method is a secondary rotor, revolving about an axis perpendicular to the main rotor, driving the tail the other way.
Other important methods, used particularly in very large helicopters, are to have a second lift rotor, rotating in such a direction as to produce a balancing torque on the body. The second lift rotor is contra-rotating and either mounted vertically above the first or the two rotors are mounted at opposing ends of the body.

 

[Danger]

There is also the NOTAR system, which is pretty cool. A brief quote from Wiki:

NOTAR is the name of a helicopter anti-torque system which replaces the use of a tail rotor on a helicopter. Developed by McDonnell Douglas Helicopter Systems, the name is an acronym derived from the phrase NO TAil Rotor. The system uses a fan inside the tailboom to build a high volume of low-pressure air, which exits through two slots and creates a boundary layer flow of air along the tailboom utilizing the Coandă effect. The boundary layer changes the direction of airflow around the tailboom, creating thrust opposite the motion imparted to the fuselage by the torque effect of the main rotor. Directional yaw control is gained through a vented, rotating drum at the end of the tailboom, called the direct jet thruster. Advocates of NOTAR believe the system offers quieter and safer operation.[1]