Most aerodynamic design tools for horizontal‐axial wind turbines are based on the blade‐element momentum theory (BEM). Due to the nature of this theory, the design tools need 2‐D steady sectional lift and drag curves as an input. In practice, flow over a wind turbine rotor blade is neither two‐dimensional nor steady, and is affected by rotation. Pioneering experiments have identified a consequence: at inboard rotor blade sections stall is delayed. This so‐called Himmelskamp effect [1] gives a larger lift than predicted and, as a result, a higher power and loading than expected. Consequently, an aerodynamic model is needed to explain and predict sectional lift and drag under rotating conditions.