8.1 PHYSICS OF THE ATMOSPHERE www.part66.blogspot.com
EASA PART-66 MODULE 8.1 : PHYSICS OF ATMOSPHERE
Nov 11, 2014
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AERODYNAMICS
THE ATMOSPHERE
The study of objects in motion through
air and the forces that produce such
motion.
ATMOSPHERIC CONTENT• Composition of air :-
78% - Nitrogen
21% - Oxygen
1% - Other Gases (argon, carbon
dioxide, hydrogen, helium, neon,
etc.)
OXYGEN
Human breathing
Fuel combustion keep aircraft flying
THE ATMOSPHERE
PRESSURE ‘Air has weight’ Pressure weight (force)
pressing down on a given area Weight decreases with
increasing height Sea level atmospheric
pressure under standard condition ( 15° C / 59° F ) 14.69 psi or 29.92 in Hg. or 1013.25 millibars or 101.325 kPa
PRESSURE
Column of air extending from sea level upward
Atmospheric pressure decreases with altitude
PRESSURE
TEMPERATURE
TEMPERATURE
Sun radiate heat through atmosphere
Earth absorb heat (increase air temperatureon surface)
Warm air rises, expands, cools
o Decrease with increasing altitude o Constant (-55˚C) above 55 000 ft (12
km)o Decrease at a lapse rate of 1.98˚C
per 1000 fto Standard day temperature at sea
level 15˚C / 59˚Fo Temperature does not affect much
on aircraft in flight but it does affect the variations of humidity
o Humidity affect flight operation
TEMPERATURE
Change of temperature with height
• Aircraft requires longer runway for takeoff on damp day than on dry day
HUMIDITY
COLDWINTERDAY
HOTSUMMERDAY
Effect of temperature on take-off run and Rate of Climb
DENSITY ‘Air is compressible’ Compressed air more
dense (less space occupied by air)
Density = measure of air thickness
Density varies directly with pressure
Low altitude more denseHigh altitude less dense
Density at sea level is 1.225 kg/m3
DENSITY
Density affect the aerodynamic performance of aircraft
DENSITY
HIGH AltitudeLESS Density
LOW AltitudeGREATER Density
Greater speedand distance
Same HorsepowerLess speedand less distance
ALTITUDE
HUMIDITY
Amount of water vapor in air (condition of moisture or
dampness)
Temperature influence the maximum amount of water vapor
that the air can hold
Higher air temperature absorb more water vapour
Density of air varies with humidity
Density on damp day (hot day) is less than density on dry day
(cold day)
HUMIDITY
THE ATMOSPHERE
The whole mass of air extending upward
for hundreds of miles from the earth
(320 km in depth)
THE ATMOSPHERE
LAYERS OF ATMOSPHERE
THE ATMOSPHERE
INTERNATIONAL STANDARD ATMOSPHERE (ISA)
o Atmospheric conditions vary around the world due to changes in the properties of the atmosphere
o Established to provide a common reference for temperature, pressure and density at varying altitudes
TEMPERATURE• 15˚C• 59˚F
PRESSURE• 14.69 psi• 29.92 in Hg• 1013.25 milibar• 101.325 kPa• 1 atm
DENSITY• 1.225 kg/m3
ISA
Q CODE
• To similarise the altitude reference of all aircraft• Due to variable atmospheric condition around the
world• 3 type of code :– QFE : aircraft height above airfield– QNH : Aircraft height above sea level (local condition)– QNE : Aircraft height above sea level (ISA condition)
AIRSPEED
• Speed of sound is 331m/s at sea level with temperature 0oc
• Mach number as reference to speed of sound at that altitude
• Speed of sound reduce with reduce in temperature• Indicated Airspeed(IAS) is direct reading from gauge
measured by dynamic air pressure of aircraft• True airspeed(TAS) is true flying speed base on
actual atmospheric condition.• IAS is less thab TAS in altitude.
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