Atmospheric Density Calculation

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Atmospheric Density Calculation

Post  Admin on Tue Dec 01, 2009 6:34 am

The average density of dry air in temperate climates is about 1.225 kg/m³ at mean sea-level; the density decreases with increasing altitude.

There are several gas laws that relate the temperature, pressure, density and volume of air. The equation most pertinent to aeronautical needs is the equation of state:

r = P/RT where:
r (the Greek letter rho) = air density kg/m³
P = static air pressure in hectopascals
R = the gas constant = 2.87
T = air temperature in kelvins [K] = °C + 273

We can calculate the ISA standard sea-level air density, knowing that standard sea-level pressure = 1013 hPa and temperature = 15 °C or 288 K

i.e. Air density = 1013 / (2.87 × 288) = 1.225 kg/m³

If the air temperature happened to be 30 °C or 303 K at the same pressure, then density = 1013 / (2.87 × 303) = 1.165 kg/m³, or a 5% reduction.


By restating the equation of state as: P = RrT , it can be seen that if density remains constant, pressure increases if temperature increases.
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