Transcript 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 ►

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
► 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
Navigation 11
► Zheng-he
undertook
the first voyages using
these primitive
compasses between
1405 and 1433.
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
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.
Navigation 11
► Bearings
Know your bearings, read clockwise from North
Navigation 11
► Reciprocal
bearings----add or subtract 180°
North
045°
45°+180°= 225°
Outbound Heading=045°
Return Heading225°
Fill in the blanks
Navigation 11
Outbound track°
Return track°
Outbound track°
Return track°
011°
??°
167°
??°
355°
??°
209°
??°
101°
??°
064°
??°
262°
??°
332°
??°
086°
??°
143°
??°
295°
??°
179°
??°
Navigation 11
Outbound track°
Return track°
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°
Navigation 11
Remember the iron filings experiment?
The filings show the magnetic field---(Lines of Magnetic Flux)
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.
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
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.
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
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.
Navigation 11
► Variation
West magnetic Best
True
North
Desired
Heading
Magnetic
North
035°(T)+5°=040°(M)
Variation 5°W
035°(T)
Comparing the magnetic and true bearing, the magnetic is larger—hence the rhyme
Navigation 11
► Variation
East magnetic Least
True
North
Desired
Heading
Magnetic
North
035°(T)-5°=030°(M)
Variation 5°W
035°(T)
Comparing the magnetic and true bearing, the magnetic bearing is smaller
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.
Fill in the Blanks—
Navigation 11
Variation west magnetic best,
Variation east magnetic least
°T
variation
°M
°T
variation
°M
145°
5°W
??°
349°
16°E
??°
??°
3°E
235°
??°
12 ° W
023°
098°
1°W
??°
157°
5°W
??°
??°
6°E
299°
??°
4°E
340°
005°
8°W
??°
085°
4°W
??°
??°
9°E
195°
??°
10°E
288°
Fill in the Blanks
Navigation 11
°T
variation
°M
°T
variation
°M
145°
5°W
150°
349°
16°E
333°
232°
3°E
235°
011°
12 ° W
023°
098°
1°W
099°
157°
5°W
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°
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)
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
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
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.
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
Navigation 11
► At
the magnetic Equator
Lines of Magnetic
Flux
Centre of gravity
Pivot
Navigation 11
► At
the mid latitudes
Compass no longer
horizontal
Centre of gravity
Pivot
Lines of Magnetic
Flux
Navigation 11
► Plan
view
North seeking pole
Pivot no longer at the
CofG
Navigation 11
Unwanted compass swing
Decelerate West
Reading 270°
minus
Accelerate West
Reading 270° plus
Steady state heading West
Reading 270°
Maximum acceleration error heading East--West
Navigation 11
Decelerate North
Reading 360°
Accelerate North
Reading 360°
Steady state heading North
Reading 360°
Acceleration error heading North South is Zero
Navigation 11
Turning error----Courtesy of FAA
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