 studi flow chang associ airfoil drag rise supercrit speed studi flow chang associ airfoil drag rise supercrit speed studi experiment pressur distribut characterist moder thick airfoil section correl appear exist drag-diverg mach number free-stream mach number sonic veloc occur airfoil crest chordwis station airfoil surfac tangent free-stream direct mach number sonic veloc occur airfoil crest estim satisfactorili prandtl-glauert rule method provid drag-diverg mach number airfoil angl attack estim low-speed pressur distribut airfoil profil method predict reason degre accuraci drag-diverg mach number consider number airfoil section divers shape wide rang thick-chord ratio pressur distribut forc characterist moder thick airfoil section mach number drag-diverg mach number analyz characterist flow airfoil supercrit mach number discuss 