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radio aids or astro nav.
The velocity of an aircraft in flight
will therefore consist of its heading
and airspeed, the former usually
expressed with reference to True
North:
In the diagram above, the heading is
270°(T) - the single arrow is the
symbol for the heading vector,
pointing the right way, of course.
When plotting, a scale is used, so if
the heading vector were 3 inches
long, at 50 kts to an inch it would
equal an airspeed of 150 kts, or the
air position after one hour of flight. If
we added the wind speed and
direction, the resultant between
them would represent track and
groundspeed, also to scale:
In this case, the wind vector is half
an inch long, meaning 25 kts,
coming from the North. Joining the
ends would therefore show your
ground position after one hour, and
your track and groundspeed, after
measurement (you will have deduced
already that two arrows are used for
the track and three for the wind –
the track arrows always go in the
opposite direction to the other two).
The drift angle is the difference
between track and heading, from the
heading to the track, in this case
about 10°, so the track is 260°.
Navigation 149
The above diagram shows what
would happen if you simply pointed
the aircraft nose towards the West –
you would drift to Port for the
amount indicated. If you wanted to
arrive over the intended destination,
you would have to point the nose to
the right (i.e. Starboard) enough to
counteract the drift.
All you need to do is draw the same
wind vector on the opposite side of
the line, and measure the length and
angle of the new line to find out
what heading to steer (280°). Don't
forget the variation and deviation
(See Instruments).
Dead Reckoning
This involves the calculation of your
best known position without navaids
or visual fixes. In essence, it involves
drawing the equivalent triangles of
velocity you would create on your
Dalton computer (see below) on a
map, although it is important to
grasp that the triangle's purpose is
more to do with finding directions
and speeds rather than finding a
position. As mentioned above, the
lines you draw will be to scale, so
one 3" long at 50 miles to the inch
would represent 150 kts. When
climbing and descending, take the
mean TAS for the leg, and mean
wind velocity.
If you happen to fly over an object
that can easily be identified from a
map, you have a fix, which can be
used to find what the real wind is,
and your actual groundspeed. Simply
connect a line from your air position
to the fix, and measure the resulting
line between them (the wind vector).
The line between your start point
and the fix would be the Track Made
Good, which could be used to solve
the above problem on the computer.
Remember that these velocities go
together: Heading & Airspeed, Track
& Groundspeed, Wind Direction &
Speed. However, you will be involved
in finding mixed pairs, such as
heading and groundspeed, rather
than the combinations mentioned
above, because you start with a mix
in the first place (you usually know
the airspeed and track already).
Given any four of them, you can
figure out the others purely by
measurement, but you can do this
mechanically with the flight
computer, or whizzwheel, described
in the Flight Planning chapter.
The 1 in 60 Rule
This is a common method used in
solving tracking problems, based on
tangents, which, if you remember
from Pythagoras, can be found by
dividing the length of the opposite
side of the angle to be found by the
adjacent side. Or, in terms of
aviation, dividing the distance off
track by that of the desired track. We
needn't go into the proof here, but
you can end up with a formula:
Error= Distance Off x 60
Distance
Gone
So if, after flying for 40 nm, you are
8 nm off track, your track error angle
would be:
150 Canadian Private Pilot Studies
Error= 8 x 60
40
or 12°. This would be doubled the
opposite way to get you back on
track, then applied as a single figure
to keep you there (applying the
correction once would make you
parallel the original track).
To track directly to the original
destination, you would need an extra
bit, called a closing angle, which you
can find by altering the formula:
CA = Distance Off x 60
　
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