Prandtl-Glauert correction

The Prandtl-Glauert correction scales an incompressible pressure coefficient to account for subsonic compressibility, C_p = C_p0 / sqrt(1 - M^2), where M is the freestream Mach number. It comes from linearizing the compressible potential equation for thin bodies at small angle of attack and is reliable up to roughly M = 0.7, breaking down as transonic effects appear. It belongs to aerodynamics, not water-side ship hydrodynamics, where flow is treated as incompressible. It enters naval architecture only in air-side problems such as superstructure wind loading at unrealistic speeds or sail aerodynamics analogies, and it is unused for hull hydrodynamics.