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Looking at a digital E6B, there is a function for calculating CAS that I am trying to recreate and program myself.

Inputs:

  • Pressure Altitude
  • Temp in Celcius
  • True Airspeed

Outputs:

  • CAS
  • Mach #
  • Density Altitude

I am 100% sure that you can go from CAS to TAS so in my mind that implies that you can go the other direction, I just have not been able to find the calculations so far. I am not a big math person or physics and AI has not helped either.

For the Mach #, I can successfully calculate that, and while I haven't got the Density Altitude yet, I feel more confident about figuring that one out.

So, does anyone know how one would use these 3 inputs (and probably some constants) to get the Calibrated Airspeed?

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  • $\begingroup$ Yes, it did. I saw this before, but I did not have all the pieces of the puzzle so to speak but went over it again and found away to slightly modify that which worked and got me the expected result. $\endgroup$
    – Bellarose143
    Commented May 7, 2023 at 17:57
  • $\begingroup$ Airspeeds are usually calculated indicated >> calibrated >> true >> ground speed. Calibrated to true calc uses temp and pressure altitude. So I don't see any reason why if you have that information, you can't reverse the calculation if A = B + C then B = A - C. $\endgroup$
    – dashman
    Commented May 7, 2023 at 22:53
  • $\begingroup$ This is a duplicate so I can't leave an answer, but the "excel formatted" version of this would be CAS = TAS * ( 1 - 6.8755856*10^-6 * DA )^2.12794 where DA = Density Altitude in feet. This does not take compressibility into account so will only be accurate for light aircraft speeds (low Mach numbers). Also, the constraint for most altimetry and airspeed functions is below the tropopause at 36,000 feet. Also. remember that all temperature calculations are done by first converting to Kelvin, or you will get crazy answers. $\endgroup$
    – Max R
    Commented May 9, 2023 at 15:46

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