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In supersonic flight, any disturbance around a body affects the flow only:
  • A
    in front of the normal shock wave.
  • B
    within the Mach cone.
  • C
    outside the Mach cone.
  • D
    in front of the body.

Refer to figure.

Mach Cone
In three dimensions, the disturbances propagating from a moving point source expand outward as spheres, not circles. Considering figure 1, if the speed of the source (V) is greater than the local speed of sound (a), these spheres are enclosed within a Mach cone, whose semi vertical angle is μ.
The Mach angle (μ) continues to decrease with increasing Mach number. The Mach angle is inversely proportional to the Mach number and is defined by:

sinμ= 1 / M

When travelling at supersonic speeds the Mach cone represents the limit of travel of the pressure disturbances created by an aircraft: anything forward of the Mach cone cannot be influenced by the disturbances. The space inside the Mach cone is called the area or zone of influence.

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