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Navigation II

Navigation II. The Compass. Navigation 11. Magnetite also named lodestone was understandably considered to have mystical qualities. 221-206BC lodestones were used by Chinese for fortune telling. Navigation 11.

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Navigation II

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  1. Navigation II The Compass

  2. Navigation 11 Magnetite also named lodestone was understandably considered to have mystical qualities. 221-206BC 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

  10. Navigation 11

  11. 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 Fill in the Blanks— Variation west magnetic best, Variation east magnetic least

  21. Navigation 11 Fill in the Blanks

  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. 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. 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

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