Aircraft instrumentation aerospace engineering

Aircraft instruments

1. 09EI205 AIRCRAFT
INSTRUMENTATION

2. UNIT-IV: AIRCRAFT COMPUTER
SYSTEMS
Terrestrial magnetism, aircraft magnetism,
Direct reading magnetic components-
Compass errors gyro magnetic compass.

3. Magnetic Properties
(i)it will attract other pieces of iron and steel
(ii) its power of attraction is concentrated at each
end
(iii) When suspended so as to move horizontally, it
always comes to rest in an approximately
North-South direction.
Like poles repel and unlike poles attract

4. Terrestial Magnetism
•The surface of the earth is surrounded by a
weak magnetic field which culminates in two
internal magnetic poles, situated near the
North and South true or geographic poles
•A plane passing through the magnet and the
centre of the earth would trace on the earth's
surface an imaginary line called the magnetic
meridian

6. Magnetic vs. Geographic

7. Magnetic Compass

8. Magnetic Compass
•Oldest and most reliable instrument
•Construction of Compass
–Two bar magnets
–Jeweled bearing
–Compass card
–Expansion chamber
–Compass fluid
–Compensating magnet
–Compass weight
–Lubber line

9. Types of Direct-
Reading Compass

11. Compass Construction

12. Different errors
•Oscillation
•Variation
•Deviation
•Compass dip
•Northerly turning
•Acceleration

13. Oscillation
•Result of movement
•Weights in compass
•Correction
–Take average heading

14. Variation
•Difference of true end magnetic poles
•Correction
–Use chart correction

15. Deviation
•Errors in indicated heading due to local
magnetic fields
•Different in each airplane
•Correction
–Weights in compass
–Correction in airplane

16. Compass Dip
•The angle of magnetic flow
•Correction
–Weight installed in compass

17. Northerly Turning Errors
•Compass unbalanced to compensate for
vertical field
•Unbalanced condition causes compass to
overshoot north and undershoot south
•Correction
–UN/OS
–Undershoot North
–Overshoot South

18. Acceleration Error
•When heading east or west
–Compass indicates north on acceleration
–Compass indicates south on deceleration
•Correction
–ANDS
–Use compass only on straight and level flight

19. Conclusion
•Reliable
•Errors
–Oscillation
–Variation
–Deviation
–Compass Dip
–Northerly turning errors
–Acceleration errors
•Be aware of correction
–UNOS & ANDS
–ECT

20. Compass
•Bar Magnet aligns itself
with the magnetic field

21. Compass Errors
•Variation: Difference between the true and
magnetic poles. Use correction indicated on
sectional

22. Compass Errors
•Deviation: Compass error due to disturbances
in magnetic field de to metals and electrical
accessories in the airplane. Use deviation card
in airplane to correct.

23. Compass Errors
•Magnetic Dip: Bar magnet contained in
compass is pulled by the earth’s magnetic
field, it tends to point north and somewhat
downward. Greatest near the poles

24. Magnetic Dip
•As stated earlier, a freely suspended magnet
needle will settle in a definite direction at any
point on the earth's surface and will lie
parallel to the magnetic meridian at that
point. However, it will not lie parallel to the
earth's surface at all points for the reason that
the lines of force themselves are not
horizontal as may be seen from Fig

25. Compass Errors
•Acceleration Error: Occurs when accelerating
or decelerating on an easterly or westerly
heading. As you accelerate, inertia causes the
compass weight on the south end of magnetic
to lag and turn the compass toward north. As
you decelerate, inertia causes weight to move
ahead, moves the compass toward a southerly
heading.

26. Compass Errors
•Turning Error: Most pronounced when turning
to or from headings of north or south.
•When you begin a turn from a heading of
north, the compass initially indicates a turn to
the opposite direction. When the turn is
established, the compass begins to turn in the
correct direction, but it lags behind the actual
heading.

27. The Directional
Gyroscope