1
$\begingroup$

I try to calculate the correction of cold temperature for altimeter , i use for this the equation 24 of the Engineering Sciences Data Unit (ESDU) publication but it give me very high number . if i take for example the given conditions altitude of aircraft 1000 ft 0 ft for aerodrome altitude t0 288 K temperature deviation from the ISA = 259.9812 L0 = 0.001981 the result is 599777.4389 ft is too big , the expected result is 60 ft So where is mistakes ? enter image description here

EDIT : So i corrected the ISA dev according to what Ralph said but the result still incorrect i joint the step of calculation : enter image description here the expected result is 60 ft enter image description here

$\endgroup$
4
  • 2
    $\begingroup$ 259 degree temp dev from ISA is unreasonable by an order of magnitude. You may be mixing C and K units there. Please fix that & edit your question accordingly. $\endgroup$
    – Ralph J
    Jan 24, 2021 at 3:09
  • $\begingroup$ Infact 288degK at 0 ft altitude is = 15degC = ISA, so intended dev from ISA seems to be zero for purpose of the example question. $\endgroup$
    – skipper44
    Jan 24, 2021 at 4:34
  • $\begingroup$ I agree, you are mixing temperature scales (K and C) and hence your incorrect result. $\endgroup$ Jan 25, 2021 at 1:55
  • $\begingroup$ T aerodrome = 273K, T isa = 288K. so dT = 15K. Applying the correct formula (see Namsters' answer below) gives 15/0.001981 * ln (1+ 1.981/288) = 51.90ft (since dH aerodrome = 0). The table from PANS OPS Doc 8168 uses an approximation which works for temps above -15C (4 times the alt above the aerodrome in thousands of feet, times dT which equals 60). $\endgroup$
    – Sacha
    Jul 21, 2022 at 15:22

1 Answer 1

1
$\begingroup$

Finaly i have found the answer the error is on all book that published the equation there is the true equation enter image description here

$\endgroup$
3
  • $\begingroup$ What is the source of the original screenshot (i.e. what published the wrong equation)? $\endgroup$
    – Ralph J
    Jan 25, 2021 at 15:22
  • $\begingroup$ Yes the original equation is given in PANS OPS Doc 8168 Chapter 4 section 3.4 $\endgroup$
    – Namster
    Jan 25, 2021 at 15:48
  • $\begingroup$ Can you specify what each variable is? I'm attempting to recreate this myself in excel. It would help greatly. $\endgroup$
    – Johnnyduke
    Feb 27, 2023 at 22:04

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .