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CAS TAS MN

Asked by: 2041 views Instrument Rating

When climbing at a constant Mach number below the tropopause trough an inversion, what will happen with CAS and TAS?

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2 Answers

  1. Best Answer


    John Hobbs on Mar 02, 2019

    Using my handy E6B calculator (my own)

    At IAS 110 kts (similar to CAS) at 4000 ft, and 10 C, TAS is 118 kts on a certain day. (29.80 inHg)
    If temp goes up to 14 C, TAS goes up to 119.
    Increasing altitude to 4500 ft, TAS goes to 120 kts
    Increasing temp to 19 C, TAS goes to 121 kts
    Increasing altitude to 5000 ft, TAS goes to 122 kts, 5500 ft to 123 kts

    This seems like pretty big temp inversion?

    TAS is calculated using air density, specifically the SQRT(Barometric pressure@seaLevel) divided by the Barometric pressure@altitude) x’s EAS (close to IAS at lower altitudes).

    So it depends, however TAS trends up.

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  2. John Hobbs on Mar 07, 2019

    Using my handy E6B calculator (my own), just now corrected for slight error.

    At IAS 110 kts (similar to CAS) at 4000 ft, and 10 C, TAS is 117, not 118 kts on a certain day. (29.80 inHg)
    If temp goes up to 14 C, TAS goes up to 118, not 119.
    Increasing altitude to 4500 ft, TAS goes to 119, not 120 kts
    Increasing temp to 19 C, TAS goes to 120, not 121 kts
    Increasing altitude to 5000 ft, TAS goes to 121, not 122 kts, 5500 ft to 123 kts

    https://www.hobbsdronephotography.com/e6b

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