Accurate prediction of control surface aerodynamics has been a challenge since the dawn of aviation. Whereas this has been an important problem for many years, recent increases in the use of control surfaces for active control (load alleviation and e utter suppression ) have increased the importance of accurate steady and unsteady control surface aerodynamics. Because of the strong ine uence of viscosity on the pressures on a trailing-edge control surface, the aerodynamic theories based on the linear potential equation have had only marginal success in predicting control surface aerodynamics, and in practice, large corrections (based on wind-tunnel data ) are often required for acceptable accuracy. Recent advances in computing technology and unsteady aerodynamic codes based on the Navier ‐Stokes equation areallowing moreaccurate analysesto be performed. Unsteady aerodynamic calculations due to control surface oscillations are made using a linear potential code (N5K) and a Navier‐Stokes code (CFL3D.AE-BA version 4.1 ). The Navier‐Stokes calculations are performed in the time domain using an exponential pulse technique and are transformed to the frequency domain using Fourier transform. For low reduced-frequency cases, theNavier ‐Stokes calculations arecompared to the doublet-lattice method and to experiment, and the advantages of the nonlinear analysis are clearly demonstrated. Correlation between Navier ‐Stokes and doublet-lattice results is then studied for higher reduced frequencies.