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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

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โˆ™ 2008-09-29 10:46:37
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Q: How does mach number vary with temperature and altitude?
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