### Pressure, Temparture, Density

```Temperature, Pressure, and Density
Danielle Hettmann and Chris Saleh
SYST460 – Fall 2011
Ambient temperature:
measure of the temperature of the
air in the region surrounding the
aircraft
Ambient temperature varies with altitude:
Below 36,089 feet: ambient temperature (˚R) = -3.566˚ * (altitude/1000)
Above 36,089 feet: ambient temperature (˚R) = 389.988˚
θ = (Tamb
rule of thumb: ambient
temperature drops 1˚ C for every
1000 feet increase in altitude
Delta ISA
+ ∆ISA) / (TSeaLevel + ∆ISA)
Temperature Ratio
Below 36,089 feet, Tamb/TSeaLevel = θ = 1 – (6.8753 X 10^-6) * pressure
altitude
Above 36, 089 feet, Tamb/TSeaLevel = θ = 0.7519
Ambient Pressure:
Measure of the pressure of the air
in the region surrounding the
aircraft
Pressure Ratio :
=Pamb / PSeaLevel
Below 36,089 feet, the Ambient Pressure (lb/ft2)
= (1 - ˚ * 6.88 X 10-6 * Pressure Altitude)5.26
Above 36,089 feet, the Ambient Pressure (lb/ft2)
= 0.223360 e ( (36.089 – Pressure Altitude)/20.8057)
Ambient Density:
Measure of the density of the air in
the region surrounding the aircraft
Density Ratio:
= (Slugs/ft3)
= amb / SeaLevel
Boyles Law:
Density (), pressure (),
temperature (θ)
=  / θ
```