The in situ scaling-up methods for the efficiency and pressure rise for axial and centrifugal fans give satisfying results in the design point for low Mach number flow only. At higher Mach numbers these methods result in a significant difference between prediction and measurement. To end up with a better understanding of the effects caused by the compressibility and incidence between incoming flow and profile a predictive physical model for the incidence loss for compressible flows is introduced. This model is validated by cascade measurements at different incidence angles and Mach numbers up to 0.7.