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The study of objects in motion through air and the
forces that produce such motion.
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INTRODUCTION
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
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TROPOSPHERE
Lower level of atmosphereExtends from the surface upward to the tropopause
Contains water vapour that causes
Clouds and vertical air currents
weather
TROPOPAUSE
Boundary between the troposphere and the stratosphere.
Temperature drop with altitude stops and constant
temperature of 56.5
O
C
STRATOSPHERE
Air is extremely thin above troposphere
No water vapour cause no weather.
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DIFFERENT PRESSURE UNIT
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ATMOSPHERIC PRESSURE DECREASES WITH ALTITUDE
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Air is compressible Compressed airmore dense
(less space occupied by air)
Density = measure of air thickness
Density = mass per unit volume
= m/V
The density of gases is governed
by following rules : Density , Pressure
Density , Temperature
Density at sea level is 1.225 kg/m3
DENSITY OF AIR
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AIR TEMPERATURE
o Decrease with increasing altitude
o Constant (-56.5C) above 37 000
ft (11.3 km)
o Decrease at a lapse rate of
1.98C per 1000 ft
o Standard day temperature at sea
level 15C / 59Fo Temperature does not affect
much on aircraft in flight but it
does affect the variations of
humidity
o Humidity affect flight operation.
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HUMIDITY
Amount of water vapour in air (condition of moisture or
dampness)
Temperature influence the maximum amount of water
vapour 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)
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TEMPERATURE, PRESSURE, AND DENSITY VERSUS ALTITUDE
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AIR DENSITY AND AIRCRAFT OPERATION
Changes in air density affect the operation of aircraft regardless of
whether the changed density results from changes in pressure,
temperature, humidity, or any combination of these.
If the air density drops there will be a reduction in :
The lift produced by wings.
The thrust produced by propellers or jet engines
The power or torque produced by piston engines.
Significant when
checking engine
operation on
ground
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THE STANDARD ATMOSPHERE
The set of standard conditions is usually known as the
International Standard Atmosphere (ISA).
In the aircraft industry this is also known as the ICAO
Standard Atmosphere.
Table of ISA at sea level
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PRESSURE ALTITUDE
Pressure altitude is the altitude in the standard atmosphere
corresponding to a particular value of air pressure.
The aircraft altimeter is essentially a sensitive barometer
calibrated to indicate altitude in the standard atmosphere.
The symbol Hp is used to indicate pressure altitude.