11.6 CRITICAL MACH NUMBER In this section we deal with several aspects of transonic flow from a qualitative point of view Local M =0.435 What is the definition of M=0.3 Critical Mach Number? The critical Mach number Local M4 =0.77 Ma=0.5 is that free stream Mach number at which sonic flow Local Ma =1.0 0.61 is first achieved on the airfoil surface. Sonic line where M I 0.65>M11.6 CRITICAL MACH NUMBER In this section we deal with several aspects of transonic flow from a qualitative point of view. What is the definition of Critical Mach Number? The critical Mach number is that free stream Mach number at which sonic flow is first achieved on the airfoil surface