# Introduction to Pressure_ Temperature_ and Density by hcj

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```									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

Static temperature:
measure of the tempe
rature
at the surface of the ai
rcraft
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˚

rule of thumb: ambient
temperature drops 1˚ C for
Delta ISA
every 1000 feet increase in
θ = (Tamb + ∆ISA) / (TSeaLevel +
∆ISA)
altitude

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

Static Pressure:
Measure of the pressu
re at
the surface of the airc
raft
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

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