getting to grips with aircraft performance 如何掌握飞机性能 1(7)

(hPa)

200 250 300 500 850 1013 38661 34000 30066 18287 4813 0 11784 10363 9164 5574 1467 0 390 340 300 180 50 0
Table A1: Example of Tabulated Pressure Altitude Values

Assuming a volume of air in static equilibrium, the aerostatic equation gives:
dP = -ρgdh
With  ρ = air density at an altitude h g= gravity acceleration (9.80665 m/s2) dh = height of the volume unit dP = pressure variation on dh
The perfect gas equation gives:
P
= RT
ρ
With  R = universal gas constant (287.053 J/kg/K)
Consequently:
.
At Mean Sea Level (MSL):

P0 = 1013.25 hPa

.
Above MSL and below the tropopause (36,089 feet):

0
αα
gR
P = P0 (1. h)
T0
With P0 = 1013.25 hPa (standard pressure at sea level)
T0 = 288 .15 K (standard temperature at sea level)
α = 0.0065 oC/m
g0 = 9.80665 m/s2
R = 287.053 J/kg/K
h = Altitude (m)

Note: For low altitudes, a reduction of 1 hPa in the pressure approximately corresponds to a pressure altitude increase of 28 feet.
. Above the tropopause (36,089 feet):
.g (h.h)
01
1
P = P1e RT
With P1 = 226.32 hPa (standard pressure at 11,000 m) T1 = 216.65 K (standard temperature at 11,000 m)

h1 = 11,000 m
g0 = 9.80665 m/s2
R = 287.053 J/kg/K
h = Altitude (m)

1.1.3. Density Modeling
To calculate the standard density ρ
at a given altitude, the air is assumed to be a perfect gas. Therefore, at a given altitude, the standard density ρ (kg/m3) can be obtained as follows:
P
ρ
=
RT
with  R = universal gas constant (287.053 J/kg/K) P in Pascal T in Kelvin
. At Mean Sea Level (MSL):
ρ
0 = 1.225 kg/m3
1.2. International Standard Atmosphere (ISA) Table
The International Standard Atmosphere parameters (temperature, pressure, density) can be provided as a function of the altitude under a tabulated form, as shown in Table A2:

ALTITUDE (Feet)  TEMP. (°C)  PRESSURE  PRESSURE RATIO δ = P/Po  DENSITY σ = ρ/ρo  Speed of sound (kt)  ALTITUDE (meters) 
hPa  PSI  In.Hg 
40 000 39 000 38 000 37 000 36 000  - 56.5 - 56.5 - 56.5 - 56.5 - 56.3  188 197 206 217 227  2.72 2.58 2.99 3.14 3.30  5.54 5.81 6.10 6.40 6.71  0.1851 0.1942 0.2038 0.2138 0.2243  0.2462 0.2583 0.2710 0.2844 0.2981  573 573 573 573 573  12 192 11 887 11 582 11 278 10 973 
35 000 34 000 33 000 32 000 31 000  - 54.3 - 52.4 - 50.4 - 48.4 - 46.4  238 250 262 274 287  3.46 3.63 3.80 3.98 4.17  7.04 7.38 7.74 8.11 8.49  0.2353 0.2467 0.2586 0.2709 0.2837  0.3099 0.3220 0.3345 0.3473 0.3605  576 579 581 584 586  10 668 10 363 10 058 9 754 9 449 
　
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