Earth’s magnetism is due to the hot molten lava in the crest of the Earth.
The end of magnet that points towards North is called Red End
The end of magnet that points towards South is called blue End.
RED END – North
BLUE END – South
Earth’s lines of forces are not equal they are horizontal at equator and are vertical at poles.
Dip – is the angle of inclination of magnet with the horizontal plane. Dip is 0 at equator and is maximum at poles.
It varies as sine of latitude.
Earth’s magnetic field is divided into 2 parts.
H- Horizontal Component.
Z – Vertical Component
Dip is because of ‘Z’.
As Latitude increases horizontal component decreases and vertical component increases.
Co-efficient of A = Sum of Deviation on all headings ÷ Number of headings.
Co-efficient of A is corrected by loosening the Compass mounting and then rotating the compass by the desired amount to be aligned with the Lubber line and tightening it.
Co-efficient of B = EAST – WEST ÷ 2
Co-efficient of B is corrected by a Micro adjuster located at the top or bottom of the compass.
It is corrected by Lateral pair of the Compass.
Co-efficient of C= NORTH – SOUTH ÷2
Co- efficient of C is corrected by Longitudinal pair of the Compass.
Dip is due to “Z” and directive property of compass is because of “H”.
With increasing in Latitudes “H” decreases and “Z” increases therefore directive property of compass decreases and Dip increases.
Degaussing – De Magnetism of Aircraft
Gauss – is a Unit of Magnetism.
Christmas Tree – When an Aircraft is parked on the ground, it’s direction is changed continuously after a certain period of time so that is does not acquire magnetism.
Magnetic Compass
(i) Horizontality – Compass should remain horizontal at all times. It is achieved by having a pendulous suspension system. Centre of Gravity of compass is kept below the pivot point. It is suspended from the Top.
(ii) Sensitivity – Ability to detect the direction of magnetic meridian. With increasing in latitudes H decreases and sensitivity decreases, sensitivity is increased by increasing the pole strength of magnet.
(a) This is done by using many small magnets.
(b) By reducing pivot friction (by having jewelled pivots.)
(c) By reducing weight of the magnets. (by using light weight magnets)
(iii) Apperiodicity – It should not have periodic motion. It should oscillate less. This is achieved by decreasing the length of magnets, but then the pole strength decreases, to prevent this many small magnets are used. Many small magnets increase sensitivity and small magnets increases Apperiodicity.
Damping wires are attached to a magnet and magnet is dipped in the liquid, to dampen Oscillations.
Liquid is primarily used for Apperiodicity. But it indirectly increases sensitivity as well by-
(a) Reducing weight due to buoyancy.
(b) Lubricates pivot and decreases pivot friction.
Properties required of liquid
(i) Colorless Transparent
(ii) High boiling point
(iii) Low freezing point
(iv) Low Viscosity (High viscosity decreases Sensitivity)
(v) Low co-efficient of Expansion
(vi) Non Corrosive.
Volume of liquid is controlled by expansion ballows.
Magnetic to True- Datum True for Variation Calculations.
Magnetic to Compass- Datum is Magnetic for Deviation calculations.
Gyrosyn Compass has flux valve located at the wing tip.
It does not suffer from any compass errors, therefore it has no Acceleration or Deceleration errors and no Turning errors.
Whenever there is a change of Magnetic flux through a coil, EMF is induced – Electro Magnetic Induction of EMF.
Saturated Magnet – Saturated magnet is when a magnet can no longer by any means be made more powerful.
North seeking end of a Magnet is called RED POLE.
South seeking end of a Magnet is called BLUE POLE.
Soft iron can be easily magnetized and will just as reading lose its magnetism when the magnetizing influence is removed.
Hard iron is difficult to magnetize, but once done it tends to remain Magnetized permanently.
So hard iron magnetism is called “Permanent”.
While soft iron magnetism is called “Temporary “or “Induced”.
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