What mechanism is most commonly used to compensate for the torque produced by the main rotor of a helicopter?

• A. A vertical fin
• B. A rudder on the tail
• C. A swashplate
• D. The tail (anti-torque) rotor

Answer: (D)

When the engine drives the main rotor, the rotor’s rotation creates an equal and opposite reaction on the helicopter fuselage. To keep the aircraft from yawing uncontrollably, most single-rotor helicopters rely on a tail rotor that provides anti-torque thrust. By varying the tail rotor’s pitch with the anti-torque pedals, the pilot can generate the exact sideways thrust needed to counteract the main rotor’s torque, keeping the fuselage aligned.

A vertical fin and rudder on the tail help with directional stability during forward flight, but they don’t actively counter torque. The swashplate controls the main rotor’s cyclic and collective pitch, which changes lift and the helicopter’s attitude, not the anti-torque balance. So the tail rotor is the device specifically designed to compensate the main rotor’s torque.