CHAPTER 11. 2D AND3D WAVEFRONTS 11.6
Mach Cone ESCFI
The shape of the MachCone depends on the speed of the aircraft. When the Mach
Number is 1 there is nocone but as the aircraftgoes faster and faster the angle of the
cone gets smaller and smaller.
If we go back to the supersonic picture we canwork out what the angle of the cone
must be.
supersonic shock waveWe build a triangle between how far the plane has moved and how far awavefront at
right angles to the direction the plane is flying has moved:
An aircraft emits a sound wavefront. The wavefront moves at the speedof sound 340
m· s−^1 and the aircraft moves at Mach 1.5, which is 1. 5 × 340 = 510 m· s−^1. The
aircraft travels faster than the wavefront. If we let the wavefront travel for a time t then
the following diagram will apply:
We know how fast the wavefront and the aircraftare moving so we knowthe distances
that they have travelled: