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Joined: Tue Jun 16, 2020 1:51 pm

TAS question

Tue Jun 16, 2020 1:53 pm

How does TAS vary in a constant Mach climb in the troposphere ( under ISA conditions ) ?

Does TAS increase or decrease ?
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Re: question

Tue Jun 16, 2020 2:49 pm

TAS does decrease. The speed of sound is only a function of temperature. Speed of sound in m/s is c ≈ 331.5 + (0.6 x ϑ) , with ϑ=Temperature in °C.
Therefore speed of sound decreases with decreasing temperature. So with a constant Mach number, but a decreasing speed of sound due to lower temperature at altitude, TAS does decrease. You may check out google for articles about the crossover altitude, e.g.
"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
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Re: TAS question

Wed Jun 17, 2020 12:15 am

The ECTM graph is a neat memory aid which most pilots memorise for the ATP/ATPL exams. You see people literally holding four fingers up in front of their face during the exam in order to visualise things. :)

As long as temperature decreases with altitude, this will always be the relative relationship.In the OP's case, M is constant, so that line will be vertical, meaning the top of the TAS line will be farther left. In other words decreasing with altitude.


"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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