PBL;
Your theory is fine for a given "geometry", which term includes a given angle of attack. For an airplane at a given weight, AoA (1g) at constant Mach (free stream) increases with altitude, and hence Cp (absolute).
BTW, according to Wikipedia, Prandtl-Glauert "is derived from linearized equations".
regards,
HN39
Last edited by HazelNuts39; 10th October 2010 at 16:40.