Quick question from my last aero test We are given an incompressible Cp of -0.18, the freestream V and the altitude. The question is to determine the local velocity at the Cp point. The flow is compressible. Can I simply do -0.18 = 1 - (VL/V0)^2 and solve VL? Or do I need the Prandtl-Glaubert approximation of Cp = Cp_incompressible/Sqrt(1-M0^2) ? I did it without using prandtl, but I don't know if that is ok or not. I can't seem to get a clear answer from the prof and solutions haven't been posted. Thanks all!!!