What is the highest speed possible without experiencing supersonic flow over the wing?

The critical Mach number is the maximum speed at which airflow over certain parts of the wing remains subsonic. As an aircraft approaches this speed, shock waves begin to form on some areas of the wing, usually at the points where airflow first reaches Mach 1. Exceeding the critical Mach number results in sectionally supersonic flow, which can lead to a variety of aerodynamic issues, including the onset of shock-induced separation.

Understanding the critical Mach number is essential for pilots as it helps them to operate the aircraft safely within its performance envelope without inducing detrimental aerodynamic effects. In contrast, Mach 1 refers to the speed of sound, stall speed is the speed at which the aircraft will stall, and Vne (never exceed speed) is the maximum speed that should not be exceeded in any circumstances. These other speeds serve different purposes and do not specifically address the context of maintaining subsonic airflow over the wing.