ABOUT THE ATMOSPHERE OF OUR SURROUNDING .ppt

The atmosphere consists of mixture of a number of gases which form a layer enveloping the earth.

Nitrogen 78%
Oxygen 20%
Other gases 2%

The higher we go the thinner in water vapour and other gases.

1. 6.3 THE ATMOSPHERE

2. 6.3 THE ATMOSPHERE
The atmosphere consists of mixture of a number
of gases which form a layer enveloping the
earth.
•Nitrogen 78%
•Oxygen 20%
•Other gases 2%
•The higher we go the thinner in water vapour
and other gases.

3. Air Density
•It is defines as the mass/unit volume of the
atmosphere.
•It depend on temperature and pressure.
•Increase in temperature the density of air will
decrease.
•Increase in pressure the density of air will
increase.
Example
•At ground level the cubic foot of air will weight
0.077ib.
•At 30000ft the cubic foot of air will weight about
0.029ib.

4. Air Pressure
•The weight of air will produce the pressure.
•At ground level the weight of air is 14.7 ibs.
•It follows that the pressure atmosphere at sea
level is 14.7 psi.
•As increase in high, the air density become less
and causes reduces in air pressure.
Example
•At 10000 feet the pressure drop to 10.10 psi
•At 20000 feet the pressure drop to 6.75 psi.

5. Variation of Air Pressure With Height.
•In cold air the rate of pressure with height
is greater than in warm air.
•As increase in hight in cold air cause
larger reduction in pressure compared to
warm air.

6. Temperature Changes in
The Atmosphere
•As high we go the gradually drop in
temperature.
•The denser layers of atmosphere near
earth’s surface will absorb more heat than
the thinner layer at greater altitude.
•The rate of drop of temperature is 1ºF for
every 300 feet of ascent.

7. Effect of Temperature on Density
•As the temperature of the air decreases
with altitude an increase in density.
•The reality found that this is more than
counteracted by the drop in pressure as
altitude is increased.

8. Pressure Measuring Instruments
Definitions
Pressure is defined as force per unit area.
•Pressure = Force/Area (the unit is lb/sq.inch).
Atmospheric Pressure
- Is the pressure at any point in the earth
atmosphere. It is caused by the weight of air
above the measurement point. The unit is psi,
inch of mercury or milibar.

9. Absolute Pressure –
-Is a pressure measured with reference to
a complete vacuum. A perfect vacuum is
zero pressure.
Gauge Pressure –
-Is pressure read on a gauge.
-Zero pressure on the gauge is
atmospheric pressure,
-Above zero is positive pressure and
-below zero is negative pressure.

10. Pitot Pressure –
•Is a pressure caused by the movement of
the aircraft through the air.or
•Movement of the air relative to the aircraft.
•This pressure sensed by the pitot tube.
Static Pressure –
•Is the pressure of air at rest.
•This air is sensed by the static tube or
vent.

11. Differential Pressure –
•Is the difference in pressure between
applied pressures actual pressure

12. PITOT STATIC SYSTEMS
•It is a system in which total pressure created by
the forward motion of the aircraft and the static
pressure of the atmosphere surrounding it are
sensed and measured in term of speed, altitude
and rate of change of altitude.
The system consists of:
•Pitot-static tube or Pressure Head.
•Air Speed Indicator.
•Rate of Climb Indicator.
•Altimeter.
•Pipelines and drain.

13. Pitot StaticTube and System

14. Figure 1 Basic of Pitot Static System

15. Pitot Tubes
•It is a metal tubing whose open end aims into
the relative wind (airflow).
•It always located on the nose, wing strut
(bracing) , fuselage side, or tailfin (vertical
stabilizer).
•Must be located in free airstream.
•To prevent rain water accumulate, a small drain
hole is added.
•For large aircraft the anti-icing on tube is
provided.

16. Heating Circuit Arrangements

19. Static Pressure Sources
•In still air easy to measure the static pressure.
•A mercury or aneroid barometer can be used to
measure the static air.
•On moving aircraft the measurement quite
difficult.
• Any disturbance on static vent can caused the
wrong reading on static pressure.
•Actually the static pressure tube is located well
forward of the wing, from the nose, leading edge
or along vertical sides of fuselage.

20. Static Sources
Light Aircraft
•For aircraft which fly at the speed less than
200 knots.
•The static vent is located on the wing strut
or on leading edge.
Helicopter
•The used of a flexible or pivoted static tube
above the center of the rotor.

21. Jet aircraft
•The static vent is located on the fuselage
side.
•Static ports are used in pairs.
•One on each side.
•They are connected together in the
aircraft’s center in order to average the
two pressures and to minimize the error.
•The third system is used as standby or
extra instrumentation.

22. PRESSURE (position) ERROR
1.The error rises from the design of pitot head
which will causes any disturbance to the
airflow.
2.The error rises from not suitable location of
pitot head on aircraft where the head is
affected by air disturbance.
3.As a result of pressure error occurred on Air
Speed Indicator and Altimeter but not affected
the Vertical Speed Indicator.

23. Static Vents
•To prevent any problem facing to the static
vents, they might be separated from the
pressure head.
•They can be positioned at any suitable
places on the aircraft.

24. Location of Pressure Heads and
Static Vents.
•It always located ahead of a wing tip or on
vertical stabilizer or ahead as a stabilizer.
•The most desirable location is always
located on the fuselage nose.
•The actual pressure error due to a chosen
location is determined for the appropriate
aircraft type during the initial flight.

25. Pitot Tube
Static Vent
Figure 3 Pitot Tube and Static Vent

26. Alternate Pressure Sources
•As a safeguard against failure a standby
system is employed.
•The static atmospheric pressure and pitot
pressure from alternate sources can be
connected.
•The alternate static sources is selected by
means of a valve similar to that employed
in the pitot pressure system.

27. Figure 4 Alternate Static Pressure System.

28. Internal Pitot-Static Plumbing.
•Plumbing is used to link the pitot and static
to the appropriate instrument and system.
•It must be leak tight.
•The arrangement of plumbing is done in a
way which they are not collect rain.
•Any trapped water in plumbing must be
drained out.

29. Procedure For The Installation and
Removal of Pipelines.
•The procedure for the installation and
removal of pipelines must be followed as
required. Always refer to the aircraft
maintenance manual.

30. Question on Atmosphere
1.List down the mixture of gases and their
percentage in the atmosphere.
2.Define the density of atmosphere.
3.The density of air is depend
on………….and…………………
4.Why the weight of air decrease when increase
in height.
5.At ground level the weight of air is…………..
And the pressure is………….

31. 6.As increase in height what will happen to
the air density and air pressure.
7.The rate of drop in temperature
is……….for every………..of ascent.
8.Define the pressure.
9.Define the gauge pressure.
10.The pitot static system consists of.
11.Where is the pitot head being located.
12.How do the pilot know that the anti icing
is not functioning.
13.Briefly explain the position error.