Compass Flashcards
Compass
read the orizzontal component H of the earth magnetic field
Magnetic field for compass
is reliable dor 6 microTesla
Dip
is the vertical component Z of the Magnetic Field
Max Poles
Min Equator
Horizontal compenent
it is what the compass feel
Variation
the angle between MN and TN
Magnetic Meridian
direction of H component to the earth field
Deviation
angle btw Compass needle and Mn EASA +- 10 tollerance
Swing procedure
Determine the deviation
Accelerator Error
the error is because during the accel and decell the CG of the magnet assembly will move away from his normal position, below the pivot.
error present in acceleration to West and East, no value to N/S
Max error to Poles and no on the equator
ANDS NH
Accelerate toward Accelerate
North to the close pole
Decellerate toward Decellerate
South far pole
Turning Error
cause by the dip, during a turn accelerate force act on the curve and the Centrifugal force that act on CG
A turn will have max error on N/S and 0 to W/E
UNOS NH
Under throught the near pole, over throught the far pole
Unsershoot overshoot
turn to the near pole the liquid swirl will increase the error
turn to the far pole the liquid will decrease the error
line with the same variation
Isogonical line
Compass requirment
Horizontal
Sensitive
Aperiodic
Horizontal
the magnet assembly is ‘pendulously suspended’, the CG of this assembly being lower than its supporting pivot. The Z of the earth’s is opposed by Wheight ,only a very slight residual tilt of the magnets 2° in mid-latitudes - in the NH.
Sensitive
The magentic field of the earth is sometimes weak, so they find a way to increase the magnetic moment:
-the pole strength is increased using 2, 4, 6 short magnets in alloy.
Sensitivity is increased by reducing friction:
• using an iridium-tipped pivot in a jewelled cup.
• lubricating the pivot with the liquid which fills the compass bowl.
• reducing the effective W of the magnet assembly acting down through the pivot
Aperiodic
means that it should settle down quickly on a steady indication after being displaced by turbulence or manoeuvres.
Several short magnets - mass near the centre
liquid in the compass bowl is to act as a damping liquid
