Abstract: The invention is a proportional rudder boost system for manually controlled aircraft which also have a yaw dampening system. The boost system includes four sensors in the pilot's and copilot's pedals including a summation means which adds the manual inputs from both pilots to provide a combined output signal to the power boost computer. Once the combined output signal exceeds a minimum force level, the boost computer signals the yaw servo to increase its torque applied to the rudder from zero in proportion to the increase in manual force applied to the rudder pedals up to a maximum power assist force level.