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What is the highest speed possible without supersonic flow over the wing?
  • A
    Tuck under speed.
  • B
    M = 1.
  • C
    Critical Mach number.
  • D
    Initial Mach buffet speed.

Critical Mach number (MCRIT) is the free stream Mach number at which local speed of the airflow somewhere around the aircraft reaches local sonic speed (M = 1).

For all aircraft in flight, the speed of the airflow around the aircraft is not exactly the same as the airspeed of the aircraft due to the airflow speeding up and slowing down to travel around the aircraft structure. At the Critical Mach number, local airflow near some areas of the airframe reaches the speed of sound, even though the aircraft itself has an airspeed lower than Mach 1.0.

  • We can also say that MCRIT is the highest flight speed where there is no supersonic flow (M>1) over any portion of the airfoil.

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