ATPL General Navigation - Class 5: Direction.
Summary
TLDRIn this educational video, Grant explores the complexities of navigation using a compass, which isn't as straightforward as it seems. He explains the Earth's magnetic field, generated by the molten iron core, and its misalignment with the geographic poles. The video delves into concepts like magnetic variation, deviation, and the impact of wind on navigation. Grant teaches viewers how to convert between magnetic and true north and highlights the importance of compass calibration, especially in aviation, to account for metal and electrical components that can affect compass readings. The summary also touches on the difference between heading and track, and the necessity of wind correction angles to maintain course.
Takeaways
- 🧭 A compass points towards the magnetic north pole, not the true geographic North Pole.
- 🌐 The Earth's magnetic field is generated by its molten iron core, which is offset and changes over time.
- 🔍 The magnetic field's offset causes a difference between magnetic and true north, known as variation.
- 🌀 At the magnetic equator, the compass would not point downwards but would spin flat due to the lack of vertical force.
- 📍 Close to the magnetic poles, the magnetic dip can be so high that the compass becomes unusable.
- 🔄 The horizontal component of the magnetic force is called directive force, which spins the compass, while the vertical component is known as magnetic dip.
- ⚖️ Variation can be either east or west, and it affects the accuracy of a compass reading.
- 🔄 To convert between magnetic and true north, use the equation: Magnetic + Variation = True.
- 🛫 Aircraft generate their own magnetic fields, causing an error in compass readings known as deviation.
- 🔄 Deviation is corrected using the equation: Compass + Deviation = Magnetic, with similar rules for east and west as variation.
- 🚀 For accurate navigation, pilots must account for both variation and deviation, as well as wind effects on heading and track.
Q & A
Why doesn't the Earth's magnetic field align perfectly with its geographic poles?
-The Earth's magnetic field doesn't align perfectly with its geographic poles because it is formed mainly by the molten iron core at the center of the Earth, which is liquid and has a life of its own, causing the magnetic field to be slightly offset and change year to year, day to day.
What happens to a compass if you stand directly on the magnetic north pole?
-If you stand directly on top of the magnetic north pole, the compass would be pulled all the way down and try to stand up vertically because the magnetic force is directly beneath it.
What is the term for the imaginary line at the halfway point of Earth's magnetic field?
-The imaginary line at the halfway point of Earth's magnetic field is called the magnetic equator.
What are the two components of the magnetic force experienced by a compass?
-The two components of the magnetic force experienced by a compass are the horizontal component, known as the directive force, which spins the compass around, and the vertical component, known as magnetic dip.
Why can't a compass be used near the magnetic north pole?
-A compass can't be used near the magnetic north pole because the horizontal component of the magnetic force becomes so weak and the magnetic dip is so high that the compass becomes unusable and can't spin effectively.
What is the difference between magnetic north and true north called?
-The difference between magnetic north and true north is called variation.
What is the significance of the term 'variation' in navigation using a compass?
-Variation signifies the difference between magnetic north and true north. It is crucial for accurate navigation as it accounts for the inaccuracy when using a compass due to the misalignment of the true and magnetic north poles.
How can you convert between magnetic and true north?
-You can convert between magnetic and true north using the equation: Magnetic + Variation = True. Remember that east is positive and west is negative.
What is deviation in the context of aircraft navigation?
-Deviation refers to the error in the compass readings caused by the aircraft's own magnetic fields due to its metal structure and electric components. It is corrected through a process called compass swinging.
How is the error check for variation and deviation performed?
-The error check for variation and deviation can be performed using the phrase 'if the variation is east, the magnetic will be least; if the variation is west, the magnetic will be best' and similarly for deviation.
What is the difference between heading and track in aircraft navigation?
-Heading refers to the direction in which the aircraft's nose is pointed, while track is the actual path the aircraft is following. The difference between the two is due to factors like wind, which can cause the aircraft to drift off course unless corrected.
How can you remember the order of operations for converting between compass, magnetic, and true north?
-You can remember the order of operations using the acronym 'CDMVT', standing for Compass, Deviation, Magnetic, Variation, and True, which can be associated with 'Cadbury's Dairy Milk', a popular chocolate bar in the UK.
Outlines
🧭 Understanding Compass and Earth's Magnetic Field
The script begins by explaining the basic concept of a compass, which points towards the North Pole. However, it clarifies that the Earth's magnetic field, generated by the molten iron core, does not align perfectly with the geographic poles, causing an offset. The video introduces the idea of magnetic poles and how a compass interacts with the Earth's magnetic field, including the concepts of magnetic dip and directive force. It also discusses the inaccuracy caused by this misalignment, known as variation, and how it can be corrected using a simple equation: Magnetic + Variation = True. Additionally, the script touches on the issue of compass deviation in aircraft due to their metallic structures and moving parts, which generate their own magnetic fields.
🔍 Calculating Compass Bearings with Variation and Deviation
This paragraph delves into the specifics of calculating compass bearings, taking into account both variation and deviation. It explains the difference between compass north and magnetic north, and how to convert between them using the equation: Compass + Deviation = Magnetic. The script provides a method for determining the deviation of an aircraft compass through a process called compass swinging, which involves aligning the aircraft with known magnetic directions and noting the difference. The importance of correcting for these variables is emphasized, as even small discrepancies can lead to significant errors over long distances. The paragraph concludes with a practical example that combines variation and deviation to find the compass bearing, using the mnemonic 'CDM VT' to remember the order of calculations.
🌬 Impact of Wind on Aircraft Heading and Tracking
The final paragraph discusses the impact of wind on an aircraft's heading and tracking. It explains how wind can push an aircraft off course unless a wind correction angle is applied. The difference between heading (where the aircraft's nose is pointed) and track (where the aircraft is actually traveling) is highlighted, with the wind drift angle being the difference between the two when uncorrected. The script illustrates how to maintain a desired track by steering into the wind, effectively using a wind correction angle to counteract the wind drift angle. The summary reinforces the importance of these concepts for accurate navigation, especially in high-latitude regions where the Earth's magnetic field's dip can severely affect compass readings.
Mindmap
Keywords
💡Compass
💡Magnetic Field
💡Magnetic North Pole
💡Magnetic Equator
💡Magnetic Dip
💡Variation
💡Directive Force
💡Deviation
💡Compass Swinging
💡Heading and Track
💡Wind Correction Angle
Highlights
A compass points towards the magnetic north pole, not the true north pole, due to the Earth's magnetic field.
The Earth's molten iron core creates a magnetic field that is slightly offset from the true north and south poles.
The magnetic field's alignment changes year to year and day to day, affecting compass accuracy.
Compass points vertically at the magnetic north pole and spins flat at the magnetic equator.
There are both vertical and horizontal components to the magnetic force experienced by a compass.
The horizontal component, known as directive force, spins the compass, while the vertical component is called magnetic dip.
At the magnetic north pole, the compass becomes unusable due to weak directive force and high magnetic dip.
The difference between magnetic and true bearings is known as variation, which can be east or west.
A simple equation, magnetic plus variation equals true, can be used to convert between magnetic and true north.
Deviation is the error in compass readings caused by the aircraft's own magnetic fields.
Compass swinging is a process to determine the deviation of an aircraft compass.
Combining variation and deviation, the equation compass plus deviation equals magnetic, then magnetic plus variation equals true, helps in accurate navigation.
Wind can affect an aircraft's course, requiring a wind correction angle to maintain the desired track.
The difference between heading (where the aircraft nose is pointing) and track (where the aircraft is traveling) is due to wind.
Cabbies Dairy Milk (CDMT) is a memorable acronym for compass, deviation, magnetic, and true north.
Error checks using the phrases 'magnetic least' and 'compass best' help verify compass and deviation calculations.
Transcripts
everyone knows that a compass points us
towards the north pole it's a bit of
knowledge you pick up when you're
growing up and it's very easy to
understand but it's not quite as simple
as it might seem
[Music]
hi i'm grant and welcome to the fifth
class in the gnab series today we're
going to be looking at direction and how
it isn't quite as simple as just north
east south and west
the earth has a magnetic field formed
mainly by the molten iron core in the
center of the earth
this core has a life of its own and it's
liquid so annoyingly it doesn't create a
magnetic field that lines up perfectly
with the true north and south poles it
is slightly offset
and actually changes year to year day to
day
an easy way to think of it is if there
was a
giant stereotypical magnet straight
through the earth at an angle like this
and the magnetic field comes out of the
south field and around and back in to
the north
magnetic pole as so it is important to
note that the compass will always point
towards the magnetic north pole so if we
were standing directly on top of the
magnetic north pole our compass would be
pulled all the way down and it would try
to stand up vertically
conversely when we are at the magnetic
equator this kind of imaginary line at
the halfway point of this magnet
then there would be no force pulling us
down
and the
compass would spin perfectly flat and
point towards the magnetic north pole
essentially what i'm trying to say is
there's a vertical
and horizontal component to the magnetic
force experienced
by the compass
the horizontal component is the
component that
spins the compass round and it is known
as the directive force so you can
imagine if you're looking at a compass
from a side on angle it would be the one
that kind of spins it this way
this is what we're seeing down here this
is the sideways angle and it's just
gonna um
spin the compass
and then
there's also the vertical component
known as magnetic dip and as you get
further and further towards the
magnetic north pole you get more and
more dip and the compass becomes less
and less able to spin
and at a certain point when we are very
close to the magnetic north pole you can
find that the horizontal component of
this magnetic force is so weak and the
magnetic dip is so high
that the compass actually becomes
unusable
so because the true north pole and
magnetic north pole are not aligned it
means that there is a certain amount of
inaccuracy when using a compass the
compass aligns itself with magnetic
north using the directive force for that
position that we are standing in and the
true north is always at that point very
at the top of the earth
so if we measure a magnetic bearing
there would be a difference between it
and the true bearing the difference
between the two is known as variation
and depending on where you are in the
earth variation is either east or west
in this example is east which we
consider to be positive variation
because the magnetic north is to the
east of true north
so while our true bearing is about 90
degrees
our magnetic bearing would only be from
the magnetic north and it would be this
angle in here
which is about 80 degrees
and you put a little m to signified
magnetic or a t to signify true we can
use a simple equation to convert between
magnetic and true north
so the easiest way
is doing magnetic
plus variation
equals true
and
remembering that uh east
is positive
and west
is negative
and then you can do a simple error check
using a little um
phrase
you basically say if the variation is
east
the magnetic will be least
if the variation is west
the magnetic will be best
as in the higher number or the lower
number when we're using our compass to
navigate using magnetic directions which
is common for most regions of the earth
apart from very close to those magnetic
poles where the dip
is too high to be able to use compasses
then there is often an error in the
compass
this error comes around because
planes are metal basically and they've
got lots of electric and moving parts so
they generate their own magnetic fields
when they're powered up so we have to
account for this error
or the aircraft would point us in
slightly the wrong direction
this difference is known as deviation
and it works very similarly to variation
so basically we have a compass north
which we give this little c arrow to
and that is pointing to a different
um north than our magnetic north and
just like variation we can use a simple
equation to
convert between one and the other so
what we say is compass
plus deviation
equals magnetic with the same rules
where east is positive and west is
negative
so for this example here we can see that
the west
variation here
means it's negative so we could do our
compass which we don't know plus the
deviation would be minus 10
equals the magnetic which is 90 then we
would take it over and it would be a
heading of 100 which as you can see from
our diagram makes sense
and again you can use that simple tool
to error check if the deviation is
leased
the compass will be leased and if the
deviation is west the compass will be
best as in the higher number
to figure out the deviation of an
aircraft compass a process known as
compass swinging is carry out where an
aircraft is lined up with known magnetic
directions and the reading on the
compass is compared the difference is
then noted down and you create a table
which looks
like this but probably a bit neater and
more tidy so you would say four zero
zero zero for a heading of north you
need to steer zero zero one
for a heading of
east zero nine zero you would need to
steer zero eight nine
this is typical the differences are only
ever
a few degrees off but a few degrees off
over long distances makes a huge
difference
so we can combine the concepts of
variation and deviation together and the
best way to do this is through this
little example that i've shown
so if the true bearing of an aircraft is
305 degrees true
deviation is 3 degrees west and
variation is 7 degrees east what is the
compass bearing
for once and probably the only time
in g nav i'm going to tell you to don't
bother drawing a picture
these equations are actually easier
if here or sorry these examples are
actually easier if you just use the
equation
so we can combine the two
equations that we've just seen together
so we know that compass
plus deviation equals the magnetic
and then the magnetic plus variation
equals true
an easy way to remember this is that c
d
m
v
t
and the way that i was taught to
remember this is
there's a type of chocolate bar here in
the uk called a cadbury's dairy milk
or chocolate dairy milk i suppose you
could call it
so cadbury's dairy milk very tasty
cdm vt
that way you can remember the order and
then you just plug in the numbers that
we've got here remembering the east is
positive and west is negative
so we're looking for the compass so
we're gonna leave that as a c
deviation is three degrees west so
that's going to be plus
minus three suppose i could have just
written minus three
equals the magnetic which we don't know
and plus the variation which is seven
degrees east east is positive
equals true which is 305.
and then we would find out our magnetic
so our magnetic
in this case equals we take 7 away from
305 and get 2
9 8
plus 7 equals 305 that makes sense
and then we have to
take away 3 from our compass to get to
this so our compass
would be
3
0 1. and then you can just error check
that so 301 minus 3 equals 298 yep
298 plus 7 equals 305 that's correct so
our compass bearing is 301 degrees
and then you give it a little c for
compass instead of magnetic or true
and then you could error check it again
with that magnetic least and
compass least sort of check so if the
variation is
west which it
isn't sorry if the variation is east
that magnetic is least compared to the
true yeah
if the variation sorry if the deviation
is west
the compass is best so compass is best
compared to the magnetic
and you get a final answer which we've
already discussed
so another level of complication can be
added through wind
so let's say we have the aircraft this
aircraft here point is fully true north
and we're traveling straight up a
meridian
if we have wind from the right
then we will be pushed off course
as we travel along unless we correct for
it
in this example we would have to point
the aircraft to the right and as we fly
along the wind would push us and we'd
keep
flying along the correct track
this is the difference between heading
and track where the aircraft is pointed
that is our heading and where the
aircraft is traveling that is our track
and the difference between them
if we didn't correct for it would be
called a wind drift angle and when we do
correct for it would be called a wind
correction angle
so in this example our heading and our
track are the same but that would push
us off course
so i'm going to draw what it would look
like corrected
so as you can see our heading would have
to be into the wind
by a wind correction angle
and the wind drift angle would only
exist if we didn't correct for this and
the wind drift angle will be completely
opposite to the wind correction angle
you only really have one or the other
so for this example while our track
might be true north our heading is maybe
0 1 0 degrees true
because
our wind drift
is 10 degrees to the
west
so that would mean that our wind
correction angle is 10 degrees to the
east
and that would mean that we maintain a
track
of
zero zero zero degrees true or true
north
so in summary then the earth has a
magnetic field which is offset and
constantly changing because of the
molten core
easiest way to think of it is this if
you've got this bar magnet through the
top and the earth's magnetic field
projects out and around from south to
north as so
this magnetic field is also offset from
true north and through south
a compass lines up with these local
lines of the magnetic field so it means
that we get
something known as magnetic dip when we
get close to the poles
and at high latitudes the dip can be so
severe
that it means that the direction
directive force
isn't strong enough to actually pull the
compass around and give us any useful
information
this is sort of a side on view
so at high latitudes you'd be looking
outside on and it'd be dipping down so
much the directive force won't be too
strong
and then at low latitudes aka like the
equator
then you have
a lot of directive force and very little
dip so they're actually more effective
because of this offset of the
magnetic poles it means we get something
known as variation because the true
norse and magnetic north are in
different points and depending on where
you are on the earth
that means that you get a difference
between the two and it could be
as extreme as 180 degrees if you were
standing in between the two
magnetic north could technically be
behind you whilst true north is right in
front of you
and then you also have an error in the
compasses that we use caused by the
aircraft themselves
and the easiest way to think of
all of these things combined together is
with cabbie's dairy milk very tasty
chocolate dairy milk very tasty some
other acronym to remember
and its compass plus the deviation
equals the magnetic
and then you plus the variation and that
equals the true
remembering that east is positive and
west is negative and then you can do
those error checks where
if the variation is east the magnetic
would be least if the variation is west
the magnetic would be best
or if the deviation is east the compass
would be least if the deviation is west
the compass would be best then we can
add a further complication to it by
talking about heading and track
heading think of it as where the
aircraft nose is pointing track is where
we're actually traveling and the reason
we there's a difference between the two
is because of the wind
if we didn't correct for it we would
drift off course by a drift angle
and if we
invert that drift angle and steer into
the wind that's known as our wind
correction angle and that allows us to
stay on the desired track
5.0 / 5 (0 votes)