How do Helicopters attain Yaw Control?

In aviation, the yaw axis is the direction the nose of the aircraft points in the left/right axis on a flat, horizontal plane. For conventional fixed-wing aircraft, yaw control is accomplished by a vertical stabilizer or rudder built into the tail of the aircraft, which steers the aircraft left or right much like a rudder steers a boat in the water. But helicopters don’t have rudders, so how do they achieve yaw control?

The answer depends on the helicopter’s design. For most conventional designs that feature a tail rotor, yaw control is obtained by adjusting the pitch of the tail rotor, which changes the thrust generated by the tail rotor, which in turn rotates the helicopter on its yaw axis. Say the helicopter has its tail rotor mounted on the left side of the tail. At a negative or low positive pitch, the low amount of thrust generated by the tail rotor will cause the aircraft to rotate right, while a high positive pitch will cause it to rotate to the left.

Not all helicopters have tail rotors, of course. The NOTAR (No Tail Rotor) system achieves similar results by varying thrust in its tail exhaust system, while a tandem rotor arrangement like in the CH-47 Chinook achieves yaw control via differential lateral cyclic. This means that to achieve right yaw, the front rotor tilts up on the left side and down on the right side of the helicopter, while the back rotor does the exact opposite. To achieve left yaw, the front rotor tilts up on the right side, and down on the left side, while the back rotor does the opposite once more.

A quadcopter, such as many popular consumer drones, obtains yaw control by adjusting the speed of its rotors. In a quadcopter, two rotors rotate in one direction, while the other two move in the opposite. By slowing one set of rotors and speeding up the other, the quadcopter can be steered in one direction or the other.

A coaxial helicopter such as the Kamov Ka-50 obtains yaw control by varying the torques of its main rotors (usually by varying the pitch of the blades) simultaneously in opposite directions of one another. Coaxial helicopters also often mount movable rudders like fixed-wing aircraft to reduce the main rotor adjustment needed.

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