Atmospheric Properties Flashcards
Why learn about the atmosphere?
•The properties of the air mass in which the aircraft is flying largely affect the aerodynamic forces created by an aircraft in flight
•Therefore we must have a very good understanding of the atmosphere we’re flying in
Atmosphere composition
Atmosphere is comprised of:
●78% nitrogen
●21% oxygen
●1% other stuff
Composition doesn’t change with altitude
Static pressure
Weight per unit area of air
●Force exerted on the surface of an object by an air mass
At sea level on a standard day a one-foot square column of air will weigh 2116 lbs.
●2116 lbs./144 = 14.7 psi
●How else is static pressure measured?
Aerodynamics use pressure ratios to cancel units
●Use the Greek letter delta
Static pressure ratio
P = static pressure
P0 = static pressure at sea level on
standard day
The pressure ratio for 18,000 feet is 0.4992
Temperature
•Average energy of microscopic motions of a single particle
•Average Kinetic energy of Atoms
•Most common forms to measure temperature are Fahrenheit (ºF) and Celsius (ºC)
•Not good measure because they have no “absolute zero”
Temperature ratio
•Denoted by Greek letter theta
•T = absolute temperature
•T0 = absolute temperature at sea level on standard day
•Note = temperature will decrease with altitude until the tropopause (approx. 36,089 ft) remains constant until 85,000 ft
•Temp at tropopause is approx. -69.7ºF
Density
Defined as Mass per unit of volume
●Greek letter rho used to symbolize density
●Single most important property
How density is affected
Air Density is affected by multiple factors
●Temperature
●Humidity
●Pressure
Universal Gas Law States:
●Density is directly proportional to pressure
●Density is inversely proportional to temperature
R = gas constant
T = absolute temp
P = absolute pressure
Viscosity
Fluids resistance to flow.
