Dynamic stall is a complex unsteady flow phenomenon that produces detrimental effects in many aerodynamic systems. The most common example is the dynamic stall of the retreating blade of a helicopter rotor in forward flight. The dynamic stall pre- diction and the associated pre and post aerodynamic loads is critical for analyzing the stall flutter, vibration response, aeroacoustics, and control system loads for helicopters. The objective of this work is to use a RANS solver to investigate the phenomena of dynamic stall for airfoils and three-dimensional wings at helicopter rotor operating conditions. One and two equations turbulence models are investigated for the RANS closure for two-dimensional cases. Based on these results, SST - kω is used for three- dimensional problems with NACA0015 profile and all results compare well with the experimental measurements.