Magnetics and the Standby Compass

Question 1

Example of ferris material

Answer 1

Steel

Cast iron

Question 2

Colour of the north seeking magnet

Answer 2

The blue end

Question 3

To increase a magnets strength

Answer 3

Bigger, heavier and longer

Question 4

Magnetic variation

Answer 4

Variation is the angular difference between 2 meridians

Question 5

Field components

Answer 5

H field - drives the compass towards its respective pole

Z field - caused by dip and increases in as you go towards the pole

Question 6

Aclinic/ isoclinic lines

Answer 6

Lines of 0 dip

Question 7

Magnetic poles move at a rate of

Answer 7

10 miles a year

Question 8

The poles flip every

Answer 8

450,000 years

Question 9

Short term predictable and unpredictable changes in magnetic equator

Answer 9

Predictable - changes in the suns orbit
- daily changes in the height of the ionosphere

Unpredictable - solar winds, interacting with the magnetic field, more significant at high latitudes

The poles moving as the earth rotates

Question 10

Magnetic direction

Answer 10

Taken from magnetic north

Half a diamond/arrowhead

Question 11

Isogonal

Answer 11

Lines of equal variation

Variation is shown on charts as isogonal

Question 12

The compass swing

Answer 12

Re calibrates the compass to minimise deviation

The a/c has to be free from any magnetic interference, engines not running

A/c is turned around for every degree and values are compared with a reference instrument and put on a deviation card

Question 13

E type standby compass

Answer 13

Read visually
No electrical inputs and outputs
Reliable and not easy to read

Freely suspended magnet which will seek its nearest pole either side of the magnet

Question 14

Lubber line

Answer 14

White vertical line on the glass if the compass

Reference to the a/c longitudinal axis

Question 15

Improving sensitivity

Answer 15

Improved by using 2,4 or 6 high quality permanent magnets

Short magnets also help keeping the CG low

More magnets promote sensitivity

Question 16

Aperiodicity

Answer 16

Describes the need for the magnet to settle down quickly after turbulence or a manoeuvre

Achieved by filling the compass bowl with oil which promotes damping

Question 17

Errors

Answer 17

Due to the compass being on a pivot the CG is displaced N or S of the pivot due to the dip causing a “couple”

Manoeuvres cause inertia which acts on the magnets CG

Accelerations due east/west cause the max error
Error is about 20-30 degrees