The Atmosphere Flashcards
Explain the air density, and describe the effect of temperature, pressure and humidity on atmospheric density.
Density - the number of molecules and how. Closely packed they are in a given volume of any substance.
Effect of temperature and pressure -
High temp - low density and poor performance
Low temp - high density and better performance
High pressure - high density and better performance
Low pressure - low density and poor performance
High humidity - low density poor performance
Low humidity - high density better performance
What is pressure and its characteristics
Total force acting on a given area
- if air is more dense = more molecules in a given parcel of air = more pressure
Less dense = less molecules in a given parcel of air = less pressure
What is temperature in regards to density and its characteristics
The measure of how much energy the molecules of a substance have.
As air is heated it expands and air molecules move apart. Cooled it contracts and air molecules move closer together.
State the ISA sea-level pressure and temperature conditions, and the approximate lapse rates in the lower atmosphere.
Sea level pressure - 1013.2
Temp - 15
Temp lapse rate - 1.98º per 1000ft until -56.4º
Pressure lapse rate - 1hPa per 30ft to 5000ft
Density - 1.225kg/m^3
Describe the approximate altitude bands in which atmospheric pressure and density are reduced to 75, 50 and 25% of their normal sea level values.
75% by 8-10,000ft
50% by 18-22,000ft
25% by 34-41,000ft
Describe the normal changes in pressure, temperature and density with increased altitude in the atmosphere.
Pressure temperature and density decreases with altitude until the tropopause where pressure and density continue to decrease and temperature remains constant (30,000ft at poles, 60,000ft at equator)
Explain the meaning of density altitude (DA) and, in broad terms, the effect of pressure, temperature and humidity on DA and thus aerodynamic and engine performance
The altitude in the ISA that has the same air density as the actual altitude.
Low density = decreased performance and high = increased performance.
Explain the term viscosity, when related to air.
The tendency for molecules of a fluid to stick together and to cling to any surface they come into contact with.
