Chap A: Atmosphere Flashcards
List the elements that make up the atmosphere
N2 (78.1%)
O2 (20.9%)
Ar (0.9%)
name the 4 regions of atmosphere
1) Troposphere
2) Stratosphere
3) Mesosphere
4) Thermosphere
which regions consist of the lower, middle and upper atmosphere?
lower: troposphere & tropopause
middle: stratosphere & mesopause
upper: thermosphere
troposphere description
altitude of 8km (N/S poles) - 14.5km (Equator) ground up
highest density and pressure of all regions
air temp. decreases with lapse rate of 6.5°C per km to around 217K
greatest weather and climate changes occur here
stratosphere description
extends ~50km above Earth’s surface
air is less dense and drier compared to troposphere
temp. in first 10km is constant at 217K
temp. increases after due to absorption of solar UV rays by Ozone layer
how thick is the stratosphere?
35km
where does most of the weight of air contain?
99% of weight contain within troposphere and stratosphere
Mesosphere description
thickness of 35km, extends to 85km above SL
temp. decreases, as low as 180K (coldest in atmosphere)
Thermosphere description
extends for 515 - 600km above Earth’s surface
temp. goes up as altitude increases (due to Sun’s energy)
as high as 1727°C
chemical states in mesosphere and thermosphere
mesosphere: excited state as they absorb energy from Sun
thermosphere: ionized state, reaction occurs much faster than on Earth’s surface
what is after thermosphere?
exosphere: hydrogen and helium are present here at very low densities
properties of atmosphere
1) invisibility
ISA @ sea level:
2) density - 1.225 kg/m3
3) pressure - 1.01325 bar
4) Temperature - 15°C
flow visualisation methods
1) smoke generation
2) cotton tufts
3) vaporisation
4) oil streaks
is dry air denser than wet air?
yes, as atomic weight of water is 18 whereas nitrogen and oxygen is 28 & 32.
which property of air is the most important for flight?
density
when higher temp or altitude, how will pressure change?
higher temp: higher pressure due to particles having higher energy
higher altitude: lesser pressure as lesser air on top (stacking effect)
ways to measure pressure
barometer (mercury/aneroid)
U-Tube Manometer
how does an aneroid barometer work?
consist of a flexible metal bellow (or capsule) that is filled with ISA SL air
any changes outside of bellow will change the thickness of capsule (bellow will expand or contract)
higher external Patm: bellow contract
lower external Patm: bellow expand
what is absolute and gauge pressure?
P abs: P gauge + P atm
P gauge: pressure gauge reading
what is geometric altitude?
the measure of true height above ground (tape measure)
use of radar altimeter is more practical
why is geometric altitude important?
for aircraft within the airport control airspace as accurate altitude and speed is required for management of all aircraft within the same space by ATC
why is pressure altitude used over temp/density altitude?
pressure is the easiest to measure during flight
why do altimeters need to be reset after climbing to a certain altitude?
as aircraft is presumed to have a lot of airspace such that mid-air collision is rare due to inaccurate pressure altitude measurement
what is ISA?
International Standard Atmosphere, the atmospheric table that is commonly accepted table by all which states that at SL:
P = 1.01325 bar
ρ = 1.225 kg/m3
T = 15°C
values are fixed and do not include variations due to weather/seasons etc.
why is ISA relevant for aviation?
provides standard calculations for aircraft, instruments and performances
density, temperature and pressure ratio symbols
density: σ
temperature: θ
pressure: δ
define viscosity
viscosity is the measurement of resistance of one layer of air to movement over its adjacent layers
what is viscosity dependent on and what can it do?
depends on temperature
can cause eddies (turbulence) when a body moves through air and disturbs it
how does speed of sound change relative to altitude?
higher altitude, slower SOS
2 uses of ISA in aviation
1) basis for comparison between flight conditions
2) standardisation for aircraft instrument and performance calculations
