PPRuNe Forums - Jet Standard Atmosphere

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fixedwingsforever

24th July 2002 07:35

Jet Standard Atmosphere

When you use JSA for calculations the temperature is assumed to be 15 C with at lapse rate of 2 C pr 1000ft (as in ISA) - the difference is that there is no upper limit. So my question is - why do we use JSA and not ISA for calculations regarding the Machmeter?

Checkboard

24th July 2002 08:13

What calculations are you referring to? The Machmeter doesn't use temperature to determine your mach number, as the mach number is independant of temperature (i.e. Temperature effects TAS and the local Speed of Sound in the same ratio, and as Mach Number is a ratio, temperature is cancelled out).

Have a look at these previous threads:
machmeter
Mach conversion
Mach vs. IAS

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