Rudder assist mechanisms and methods are capable of being operably connected to an aircraft's rudder control system. The rudder assist mechanisms most preferably have over-the-center spring biasing functions so as to cause either substantially no spring force (i.e., when the linkage is over the spring-bias center) or substantially all spring force (i.e., when the linkage is left or right of the spring-bias center) to be exerted on the rudder control system. The rudder assist mechanism may include a control spring assembly, and a linkage assembly which operably connects the control spring assembly to the rudder control assembly. The linkage assembly is moveable operably between a null position wherein substantially no spring force of the control spring assembly is transferred to the rudder control system by the linkage assembly, and right and left spring-biased positions wherein right and left spring forces of the control spring assembly are transferred to the rudder control system, respectively. The null position may therefore establish a dead zone of rudder deflection within a selected range of right and left rudder control surface deflection angles. Thus, right and left spring forces may be transferred to the rudder control system when the rudder control surface is deflected at an angle which exceeds the selected range of deflection angles. Some embodiments include an actuator unit which is operably capable of moving the spring assembly and the linkage assembly connected thereto between a thrust symmetrical mode (TSM) condition and a thrust asymmetrical mode (TAM) condition so as to cause different spring forces to be exerted on the rudder control system in such different thrust conditions.