Download - NASA

Operation 33
From the pressure p = ρRT and the standard day, the pressure altitude is:
hp = T0
1/(g/R|L0|)
ρ T
1 −
|L0|
ρ0
The required parameters are given in table 4-5, including the acceleration produced by gravity, g. The
gas constant is R = p0/ρ0T0, and μ0 is actually obtained from S and β. The ISA is defined in SI units.
Although table 4-5 gives values in both SI and English units, all the calculations for the aerodynamic
environment are performed in SI units. As required, the results are converted to English units using the
exact conversion factors for length and force.
The gravitational acceleration g can have the standard value or an input value.
Table 4-4. Temperatures and vertical temperature gradients.
level base altitude hb lapse rate Lb temperature Tb
km ◦ K/km ◦ K
troposphere -2 -6.5 301.15
0 troposphere 0 -6.5 288.15
1 tropopause 11 0 216.65
2 stratosphere 20 +1.0 216.65
3 stratosphere 32 +2.8 228.65
4 stratopause 47 0 270.65
5 mesosphere 51 -2.8 270.65
6 mesosphere 71 -2.0 214.65
7 mesopause 80 0 196.65
Table 4-5. Constants adopted for calculation of the ISA.
parameter SI units English units
units h m ft
units τ ◦C ◦F m per ft 0.3048
kg per lbm 0.45359237
T0 288.15 ◦K 518.67 ◦R Tzero 273.15 ◦K 459.67 ◦R p0 101325.0 N/m2 2116.22 lb/ft2 ρ0 1.225 kg/m 3 0.002377 slug/ft 3
cs0 340.294 m/sec 1116.45 ft/sec
μ0 1.7894E-5 kg/m-sec 3.7372E-7 slug/ft-sec
S 110.4 ◦ K
β 1.458E-6
γ 1.4
g 9.80665 m/sec 2 32.17405 ft/sec 2
r 6356766 m 20855531 ft
T0