What rotor system eliminates the need for a tail rotor by using two contra-rotating rotors on the same axis?

What rotor system eliminates the need for a tail rotor by using two contra-rotating rotors on the same axis?

• A. Tandem Rotor
• B. Coaxial Rotor
• C. Intermeshing Rotor
• D. Single-rotor with Tail Rotor

Answer: (B)

This arrangement tests how anti-torque is achieved without a tail rotor by using two rotors that counter-rotate on the same axis. When two rotors on concentric shafts turn in opposite directions with equal torque, their reaction torques cancel each other out, so the fuselage doesn’t experience a net twisting moment. Because there’s no tail rotor, yaw is controlled by adjusting how much torque each rotor produces—typically through differential collective pitch between the two rotors—so the helicopter can turn without a dedicated tail rotor. This design keeps the rotor system compact and can improve lift efficiency, but it adds transmission complexity since the power train must drive both rotors in opposite directions in sync. The other configurations either place rotors on separate masts or planes (and use different methods to manage torque) or still rely on a tail rotor for anti-torque.

This arrangement tests how anti-torque is achieved without a tail rotor by using two rotors that counter-rotate on the same axis. When two rotors on concentric shafts turn in opposite directions with equal torque, their reaction torques cancel each other out, so the fuselage doesn’t experience a net twisting moment. Because there’s no tail rotor, yaw is controlled by adjusting how much torque each rotor produces—typically through differential collective pitch between the two rotors—so the helicopter can turn without a dedicated tail rotor.

This design keeps the rotor system compact and can improve lift efficiency, but it adds transmission complexity since the power train must drive both rotors in opposite directions in sync. The other configurations either place rotors on separate masts or planes (and use different methods to manage torque) or still rely on a tail rotor for anti-torque.