What is the effect of mounting vortex generators on the rudder of twin-engine aircraft?

• A. Increase Vmca.
• B. Decrease Vmca.
• C. No effect on Vmca.
• D. They are not used on rudder.

Answer: (B)

Vortex generators energize the boundary layer on the rudder, helping the airflow stay attached at low speeds and higher angles of attack. In a twin-engine aircraft, loss of an engine reduces directional stability and increases the need for rudder authority to counter yaw. By improving the rudder’s effectiveness, you can maintain sufficient control at a lower airspeed, which lowers the minimum controllable airspeed with one engine inoperative (Vmca). So, mounting vortex generators on the rudder decreases Vmca.

They wouldn’t increase Vmca, and they do have an effect by enhancing rudder performance, not no effect. Vortex generators are indeed used on rudders to improve control surface effectiveness.