In helicopters with a single main rotor, what is the tendency to turn opposite the main rotor rotation called?

In helicopters with a single main rotor, what is the tendency to turn opposite the main rotor rotation called?

• A. Torque
• B. Precession
• C. Gyroscopic Effect
• D. Yaw Moment

Answer: (A)

This question is about the reactive effect on the aircraft when the rotor is driven by the engine. When the engine turns the rotor in one direction, Newton’s third law says an equal and opposite torque is applied to the fuselage. That opposite torque causes the helicopter to yaw, or rotate about its vertical axis, in the direction opposite the rotor’s rotation. This relation is what anti-torque systems (like a tail rotor) are designed to counteract, keeping the helicopter from spinning uncontrolled. Other terms describe different rotor behaviors: precession is the 90-degree response of a spinning rotor to a deflecting force; the gyroscopic effect refers to resistance to changes in the rotor’s axis due to its angular momentum; and a yaw moment is a general turning tendency about the vertical axis, which torque directly produces in this context. So the best term for the opposite-rotation tendency is torque.

This question is about the reactive effect on the aircraft when the rotor is driven by the engine. When the engine turns the rotor in one direction, Newton’s third law says an equal and opposite torque is applied to the fuselage. That opposite torque causes the helicopter to yaw, or rotate about its vertical axis, in the direction opposite the rotor’s rotation. This relation is what anti-torque systems (like a tail rotor) are designed to counteract, keeping the helicopter from spinning uncontrolled.

Other terms describe different rotor behaviors: precession is the 90-degree response of a spinning rotor to a deflecting force; the gyroscopic effect refers to resistance to changes in the rotor’s axis due to its angular momentum; and a yaw moment is a general turning tendency about the vertical axis, which torque directly produces in this context. So the best term for the opposite-rotation tendency is torque.