Torque and anti-torque[PDF]


Torque is a force that produces rotation or torsion.

To explain the principle of torque: If one takes an electric drill to drill a hole into a piece of wood, the motor has to exert a force to the drill bit so it overcomes friction. This torque has to be counteracted by the hand of the person using the drill, otherwise the drill body would turn.

The anti-torque system of a helicopter (usually a tail rotor or similar system) counteracts the torque applied to the helicopter fuselage by the engine driving the main rotor.


If we imagine a hovering helicopter, the rotor blades encounter drag by the air, that would slow down the rotor blade and by this, the main rotor rpm. The engine exerts a force to the rotor system in order to keep rotor rpm stable. This is the main source of torque in a helicopter. Without an anti torque system (for example: tail rotor, fenestron, NOTAR), this would lead to a rotation of the helicopter fuselage.


The tail rotor works very similarly to an airplane propeller, with one notable difference.

The tail rotor is driven by the main rotor gearbox. In most modern helicopters, main rotor rpm is kept constant by a governor (a system that measures the rpm and controls the power output of the engine).

Thus, the tail rotor is also turning at a constant rpm, its thrust is controlled by changing the tail rotor blade pitch (angle of attack). This pitch is being controlled by the pedals.

See also


  • None


  • VID 174413 - Creation


  • 01:14, 23 February 2021


  • This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.


  • The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.