Antitorque

Antitorque refers to any mechanism or arrangement that counteracts torque produced by a rotating power source. In physics, torque is transferred to the structure when a motor or engine drives a rotor or propeller; by Newton’s third law, the reaction torque acts on the vehicle in the opposite direction. Effective antitorque control is essential for maintaining directional stability and controllability.

In rotorcraft, the primary antitorque device is the tail rotor, which produces a sideways thrust to counter the main rotor’s reaction torque and thus keeps the fuselage oriented relative to the flight path. Pilots adjust tail-rotor thrust to command yaw. To reduce noise, improve safety, or increase efficiency, other approaches have been developed: NOTAR uses a directed airflow to generate antitorque; fenestron, a ducted tail rotor, minimizes exposed rotor blades; and multirotor configurations such as coaxial or tandem rotors cancel net torque without a separate tail rotor.

In fixed-wing aircraft, including those with propellers, engine torque tends to yaw the airframe. Designers typically rely on aerodynamic surfaces—the vertical stabilizer and rudder—to provide counter yaw moments; some propulsion layouts minimize net torque by structural arrangement or engine placement.

In engineering practice, antitorque considerations influence drivetrain design and stability management, including proper gear ratios, torque-splitting arrangements, flywheels, dampers, and braking systems to limit transient torque transmission and maintain equilibrium during load changes.