This paper aims to simulate motions of wind turbine with free yaw and the rudder under wind direction change. Rudder's contribution to yaw alignment under operating condition is presented in this paper using simulation of traditional fixed rudder wind turbine model. Related to this, swing rudder system is also modeled in this paper. Swing rudder is a rudder pivoted on the nacelle. The yawing motion is simulated using aeroelastic simulation code FAST developed by National Renewable Energy Laboratory. Models of wind turbine are based on Zephyr Airdolphin GTO. In order to evaluate the efficiency of swing rudder, Simulation condition is set to be one wind direction change with steady wind speed. As a result, it is revealed that aerodynamic force on the rudder is far lower contribution compared with rotor aerodynamic force. Moreover rudder's inertia acts as obstacle on yawing. In the same condition, swing rudder contributes more than fixed rudder and reduces maximum yaw error when wind direction change is fast.