How does mach number vary with temperature and altitude?

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Answer:

Mach no. is dependant on ambient air temp which is associated with a given altitude. As one ascends the temp drops so does the mach no.

Eg. In a standard atmosphere (ISA - international std atmosphere) sea level temp is 15 degrees C or 59 degrees F. Temp decreases at 2 degrees celcius per 1000' therefore for example, in a standard atmosphere the temp at say 30000' would be:

15C at 0'

-45C at 30000'

Plug that into the equation to find the Local Speed of Sound (LSS) which is:

LSS = 38.945 (square root of)/ Outside air temp + Absolute temp being 273A or 273K

LSS = 38.945 x 228

LSS = 588 kts at 30000'

So if one is doing 480knots at 30000' on a standard, day they are doing 480/588 = Mach0.82

First answer by ID3290038230. Last edit by ID3290038230. Question popularity: 2 [recommend question].

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