Jet Standard Atmosphere
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Joined: Jun 2002
Posts: 3
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From: northern hemisphere
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?
Joined: Aug 1998
Aviation Qualifications: ATPL
Posts: 6,623
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From: Ex-pat Aussie in the UK
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
Have a look at these previous threads:
machmeter
Mach conversion
Mach vs. IAS
