11.6 CHAPTER 11. 2D AND3D WAVEFRONTS
Supersonic Flight ESCFH
DEFINITION: Supersonic
Supersonic refers to speeds faster than the speedof sound.If a plane flies at exactlythe speed of sound thenthe waves that it emits inthe direction
it is flying won’t be ableto get away from the plane. It also means that the next sound
wave emitted will be exactly on top of the previous one, look at this picture to see what
the wavefronts would look like:
shock wave at Mach 1Sometimes we use the speed of sound as a reference to describe the speedof the object
(aircraft in our discussion).
DEFINITION: Mach Number
The Mach Number is the ratio of the speed of an object to the speed
of sound in the surrounding medium.Mach number is tells you how many times fasterthan sound the aircraft is moving.
- Mach Number < 1 : aircraft moving slower than the speed of sound
- Mach Number = 1 : aircraft moving at the speed of sound
- Mach Number > 1 : aircraft moving faster than the speed of sound
To work out the Mach Number divide the speedof the aircraft by the speed of sound.
Mach Number =vaircraft
vsoundRemember: the units must be the same before you divide.
If the aircraft is movingfaster than the speed ofsound then the wavefronts look like
this: