AIRSPEED INDICATOR USED IN AIRCRAFT .ppt

about airspeed indicator used in aircraft

1. AIRSPEED INDICATOR

2. General
•An instrument that measures the speed of
an aircraft relative to the surrounding air.

3. PRINCIPLE OF THE
INDICATED A.S.I.
•It is a differential pressure gauge which
measures the different between pitot and
static pressure and indicates it in knots.

4. Construction
PITOT PRESSURE
( INTO CAPSULE )
STATIC PRESSURE
( INTO CASING )
GEAR SECTOR
POINTER
SHAFTDIAPHRAGM
Figure 12 Simple of Airspeed Indicator
PINION

5. Construction
Consists of:
•A diaphragm assembly.
•A linkage system.
•A rocking shaft.
•A pinion.
•A gear sector.
•All units are contained in a case.

6. Operation
•When the diaphragm expends
•The rocking shaft pick up the motion.
•Transmits it to the sector.
•The latter turns the pinion and tapered
staff.
•Then turns the pointer around the dial.
•The hairspring keeps the linkage taut and
takes up any back lash.

7. Error
•Any factor which disturb the pressures applied
to instrument, causes a different between the
indicated air speed and true airspeed.
1.Instrument error
2.Position error
3.Density error
4.Compressibility error
5.Lag error
6.leaks

8. •Instrument error–the error cause by the
defects in the instrument itself.
•Position error–arises from aircraft movement
which alter the static pressure. It depends on.
a. The position of pitot head.
b. The speed of aircraft.
c. The angle of attack of the aircraft.
•Density error–the changes in density of
atmosphere as height compare to the density of
indicator is being calibrated.
•Compressibility error–due to compress of air
in the pitot tube.
•Lag error-

9. Leaks
•If pitot head fractured, the pressure enter
the capsule almost the same as static
pressure the ASI will not show the speed
of aircraft.
•If the static lead broken and the pressure
greater than static the ASI will read low.
•If the pressure lower than static the ASI
will indicate high.

10. Different form Airspeed Reading
Four of different form:
1.Air Speed Indicator Reading (ASIR) –is the
uncorrected reading on a specified Air Speed
Indicator.
2.Indicated Air Speed (IAS) –the reading of the
Air Speed Indicator which corrected of
Instrument Error.
3.Equivalent Air Speed (EAS) –the IAS
corrected for pressure error and
compressibility error.
4.True Air Speed (TAS) –the IAS corrected for
density error.

12. Question on ASI
1.What is the purpose of ASI?.
2.State the principle of operation of ASI.
3.In the ASI the static pressure go
to………and the pitot pressure go
to……….
4.What is the purpose of hairspring in the
ASI?
5.List down the errors which cause the
unreliable indication on ASI?

13. 6. What is the instrument error.
7. Briefly explain the position error on ASI?
8. What will happen to the ASI indication if
the pitot pressure greater than static
pressure?
9. What is the Equivalent Air Speed?
10.How do we get True Airspeed?