1. Navigation II
The Compass

2. Navigation 11
Magnetite also named lodestone was understandably considered to have mystical qualities.
BC lodestones were used by Chinese for fortune telling.

3. Navigation 11
The first compass was produced in the 1100’s when it was realized that a freely suspended lodestone always orientated itself in the same direction.
South seeking spoon

4. Navigation 11
Zheng-he undertook the first voyages using these primitive compasses between 1405 and 1433.

5. Navigation 11
In the 15th Century, Columbus (amongst others) noticed the compass did not always point towards the earths north pole.
Halley studied this and produced the first isogonals

6. Navigation 11
Steel ships disturbed the compass. In 1838 G B Airy found a way to correct this with small magnets.
Aircraft have deviation cards to indicate the errors after correction.

7. Navigation 11
Bearings
Know your bearings, read clockwise from North

8. Navigation 11 Reciprocal bearings----add or subtract 180° North 045°
45°+180°= 225°
Outbound Heading=045° Return Heading225°

9. Navigation 11 Fill in the blanks Outbound track° Return track° 011°
??°
167°
355°
209°
101°
064°
262°
332°
086°
143°
295°
179°

10. Navigation 11 Outbound track° Return track° 011° 191° 167° 347° 355°
175°
209°
029°
101°
281°
064°
244°
262°
082°
332°
152°
086°
266°
143°
323°
295°
115°
179°
359°

11. Remember the iron filings experiment?
Navigation 11
Remember the iron filings experiment?
The filings show the magnetic field---(Lines of Magnetic Flux)

12. Navigation 11 Well the earth has a magnetic field too
The bad news is the magnetic North pole is not exactly at the geographic North pole (True North).
This means the compass does not align itself with true North.

13. Navigation 11
The compass attempts to align itself with the magnetic field and therefore Magnetic North
The difference between true North(°T) and Magnetic North(°M) is called Variation

14. Navigation 11
How much Variation depends on your location on the earths surface
In the UK variation is less than 5°, in some parts of the world it is as high as 40° UK
Isogonals are lines joining places with equal variation. This chart shows World wide Isogonals for the year 2000.

15. Navigation 11
The Earths magnetic Field is moving, and so are the earths magnetic Poles
Edition 28
Shift of the 3½° Isogonal, in 5 editions of the 1:500000chart.
(30 months)
Edition 33

16. Navigation 11
We need to convert our measurements on the chart (bearings) into something meaningful on our compass.
Magnetic Variation is given as either East or West of True North.
In the exam you will probably be given variation as 5°West.

17. Navigation 11 Variation West magnetic Best True North Desired Heading
Magnetic North
035°(T)+5°=040°(M)
035°(T)
Variation 5°W
Comparing the magnetic and true bearing, the magnetic is larger—hence the rhyme

18. Navigation 11 Variation East magnetic Least True North Desired Heading
Magnetic North
035°(T)-5°=030°(M)
035°(T)
Variation 5°W
Comparing the magnetic and true bearing, the magnetic bearing is smaller

19. Navigation 11
The lines of longitude on the chart always pass through True North.
The compass always tries to align with Magnetic North
So we draw a line on the chart, measure the angle, and then convert it into a compass bearing---then the compass becomes useful.

20. Navigation 11 °T variation °M Fill in the Blanks—
Variation west magnetic best, Variation east magnetic least °T
variation °M
145°
5°W
??°
349°
16°E
3°E
235°
12 ° W
023°
098°
1°W
157°
6°E
299°
4°E
340°
005°
8°W
085°
4°W
9°E
195°
10°E
288°

21. Navigation 11 °T variation °M Fill in the Blanks 145° 5°W 150° 349°
333°
232°
3°E
235°
011°
12 ° W
023°
098°
1°W
099°
157°
162°
293°
6°E
299°
344°
4°E
340°
005°
8°W
013°
085°
4°W
089°
204°
9°E
195°
298°
10°E
288°

22. Navigation 11 Compass deviation
The angular difference between where the compass actually points and magnetic North.
Deviation is typically caused by metal materials within the airframe, or metallic objects placed near the compass.
You do not need to be able to calculate compass north (deviation west compass best)

23. Navigation 11 Cadburys Dairy Milk—Very Tasty Compass North Deviation
Magnetic north
Variation
True North
The difference between Compass north and Magnetic North is Deviation.
The difference between Magnetic north and True North is Variation

24. Acceleration and turning Errors
Navigation 11
Acceleration and turning Errors
A compass is unreliable in any thing but straight and level flight.
To understand this we need to revisit the Earths Magnetic Field

25. Navigation 11 Earths magnetic field
The only place the magnetic field is parallel with the surface is at the magnetic equator.
The dip angle increases as we move towards the poles.

26. Navigation 11
The compass aligns itself with the magnetic field, and is therefore not horizontal in our latitudes.
Magnetic North Pole
Increasing dip angle as we move towards the pole

27. Navigation 11 At the magnetic Equator Lines of Magnetic Flux
Centre of gravity
Pivot

28. Navigation 11 At the mid latitudes Compass no longer horizontal
Centre of gravity
Pivot
Lines of Magnetic Flux

29. Navigation 11
Plan view
North seeking pole
Pivot no longer at the CofG

30. Navigation 11 Unwanted compass swing Steady state heading West
Decelerate West
Accelerate West
Reading 270° plus
Reading 270° minus
Reading 270°
Maximum acceleration error heading East--West

31. Acceleration error heading North South is Zero
Navigation 11
Decelerate North
Steady state heading North
Accelerate North
Reading 360°
Reading 360°
Reading 360°
Acceleration error heading North South is Zero

32. Navigation 11
Turning error----Courtesy of FAA

33. Navigation 11
The compass is affected by the inclination of the earths magnetic field, except at the Magnetic Equator
The compass is only reliable in straight and level unaccelerated flight