Mach wave Mach wave In fluid dynamics, a Mach wave is a pressure wave traveling with the speed of sound caused by a slight change of pressure added to a compressible flow. These weak waves can combine in supersonic flow to become a shock wave if sufficient Mach waves are present at any location. Such a shock wave is called a Mach stem or Mach front. Thus, it is possible to have shockless compression or expansion in a supersonic flow by having the production of Mach waves sufficiently spaced ("cf." isentropic compression in supersonic flows). A Mach wave is the weak limit
Critical Mach number not designed to fly at or above the critical Mach number, the shock waves that form in the airflow over the wing and tailplane are sufficient to stall the wing, render the control surfaces ineffective, or lead to loss of control of the aircraft (such as Mach tuck, when shock waves in the airflow over the elevator send the aircraft into an uncontrollable dive). These problematic phenomena appearing at or above the critical Mach number became known as compressibility. Compressibility led to a number of accidents involving high-speed military and experimental aircraft in the 1930s and 1940s. Although unknown at