Definitions

A helicopter is a heavier-than-air aircraft supported in flight chiefly by the reactions of the air on one or more power driven rotors.

A gyroplane is a heavier-than-air aircraft supported in flight by the reactions of the air on one or more rotors which rotate freely.

Description

A rotor provides lift, which can be employed to keep the aircraft airborne and to provide thrust. A rotor can also counteract torque (tail rotors).

Several rotor designs and configurations have been implemented over time.

Single Main Rotor

Single main rotor helicopters are the most common type of helicopter They need an anti-torque device (tail rotor or other anti-torque system) to counteract the twisting momentum produced by the main rotor, which is powered by one or more engine(s). In a single main rotor helicopter part of the power generated by the powerplant(s) is employed to counteract torque. The most common anti-torque device is a tail rotor, which is designed to compensate the torque produced by the main rotor.