introduction of the Magnetic compass .pptx

A magnetic compass is a simple navigational instrument that shows direction by using the Earth’s magnetic field. It consists of a lightweight magnetized needle mounted on a pivot, allowing it to rotate freely. The needle aligns itself with the Earth’s magnetic north and south poles, helping users determine cardinal directions

1. Magnetic Compass

2. Introduction A compass is an instrument design to indicate direction on the surface of the earth. The magnetic compass uses the horizontal component of earth’s field as its directional datum. The purpose of a magnetic steering compass in an aircraft is to indicate heading, the direction in which the aircraft is pointing to.

3. Direct Indicating Magnetic Compass Pilot can directly read his heading in relation to the pivoted magnetic assembly. There are two types of direct reading magnetic compasses used in aircraft, Vertical card compass Grid ring compass

4. Vertical Card Compass

5. Vertical Card Compass Is the direct reading compass in general use. It consist of circular compass card attached directly to the magnet assembly This combine unit is suspended in liquid within the compass bowl A vertical lubber line in the glass window of the bowl, enables the heading to be read off the compass card.

6. Grid Ring Compass

7. Grid Ring Compass Is found on older aircraft and it is more accurate than the vertical card compass. It is heavier, bulkier and more expensive. In addition to that it can only be read in st & Lvl flight, as the grid ring has to be unclamped and align with the north reference before a reading can be taken against the lubber line.

8. Compass Requirements The magnet system must be, - Horizontal - Sensitivity - Aperiodic

9. Horizontality To achieve horizontality the magnet assembly is Pendulously pivoted. The centre of gravity of this assembly being lower than its supporting pivot.

10. Sensitivity The magnetic system required to seek the horizontal component H of earths’ field in all areas except near the magnetic poles. Sensitivity depends on the earth’s magnetic field and on the magnetic moment of the magnet. External field (H) at a place can not be changed but magnetic moment can be increased by increasing the length of a magnet and/or pole strength.

11. Sensitivity is further increased by reducing the friction, By using an iridium- tipped pivot in a jewelled cup By lubricating the pivot By reducing the effective weight of the magnet assembly.

12. Aperiodicity The magnetic assembly required to be aperiodic , which means that it should settle down quickly on a steady indication after being displaced by turbulence or maneuvers. To achieve it, a) use of several short magnets b) liquid in the compass bowl

13. The Compass Liquid Various liquids, including alcohol have been used. The main properties required for the liquid are, Low coefficient of expansion Low viscosity Transparency Low freezing point High boiling point Non-corrosiveness

14. Serviceability Check Compass body no obvious damages such as dents or crackes . Lighting system and the effectiveness of the luminous paint. Compass liquid it should be free from a) sediment and discolouration b) no leaks & bubbles

15. Deviation

16. Acceleration & Turning Errors DRC are subjected to large errors during linear acceleration/deceleration or during a turn. The centre of gravity of the magnet assembly to move away from its normal position, will produce an error. Turning and acceleration error only occur where there is significant vertical component (Z) in the earth’s field and except liquid swirl effect on turns, the errors are non-existent near the magnetic Equator.

17. Errors Caused by the Linear Acceleration

18. Acceleration on 270 M (NH)

19. Acceleration on 090 M (NH)

20. Deceleration on 090 M (NH)

21. Acceleration on 270 M (SH)

22. Acceleration on a northerly hdg (NH)

23. Turning Errors Turning errors are maximum when turning through north and south, and ignoring liquid swirl error is zero when turning through east and west. In a turn, the a/c accelerates towards the centre of the turn, and therefore an acceleration force acts through the pivot towards the centre of the turn, while the opposing centrifugal force due to inertia acts outward through the CG. This results in the magnet assembly tending to swing out from the turn, rotating the magnet assembly around the pivot point and producing the turning error

24. Turning from 045 to 315 M (NH)

25. Turning from 315 to 045 M (NH)

26. Turning from 135 to 225 (NH)

27. Turning from 135 to 225 (SH)

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