The need for energy is an ever increasing problem and most resources that are used today will be exhausted or no longer tolerated by the human kind in the future Omer (2008). Anticipating on the energy demand the development of wind turbines has taken a big leap and to improve the design process efficient and accurate aerodynamic modelling is required. During start-up, stopping and standstill of the turbine, the blades experience very high angles of attack. The flow physics behind this topic is not fully understood yet. In this research it is investigated what the relation is between the leading edge thickness of the airfoil and the maximum drag coefficient, this is done by means of experimental and numerical simulation.