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what distance is represented by 25
cm on a 1/1,000,000 chart, multiply
25 x 1,000,000 to get 25 million
centimetres. Divide that by 100 to
get metres (250,000), then divide by
100 to get 250 km.
Relief
Information about high ground is
given in various ways.
Contours are lines on a map joining
points of equal height (or elevation)
above sea level, so they are similar to
isobars, in that the closer they are
together, the steeper the slope they
represent:
Navigation 147
Some maps may give different
colours or shading to various layers
to make things more obvious,
known as Layer Tinting:
Spot Heights show the elevation of
prominent peaks with small dots.
The actual height will be shown next
to it. The highest one will be
distinguished in some way.
Otherwise, expect water to be blue,
woods to be green, and railways and
power lines to be black.
Speed & Distance
A knot is a measure of speed, that is
1 nautical mile per hour (it was
originally measured by allowing a
long rope to stretch out behind a
ship – knots were tied in it at regular
intervals, hence the name). 1 nautical
mile (nm) is taken as 6080 feet,
slightly more than a statute mile,
which is 5280 feet.
A kilometre is 1000 metres, and is a
1/10,000 of the distance between
the Equator and either Pole. 8 km
equals 5 statute miles.
Triangle of Velocities
In flying between point A and point
B, you will only get there by just
pointing the nose in the right
direction if there is no wind, or if it
is exactly on the nose or tail. This is
very rarely the case, so your aircraft
would drift off course, according to
the wind's direction, if you did
nothing to correct it. In other words,
you would end up a certain distance
left or right of the original target (in
the early days of the North Sea,
when navaids weren't around, pilots
would build in a slight error to their
calculations, so that they would
know which side of the rig they were
just in case it all went wrong).
The smart thing to do would be to
make a heading correction towards
the wind's direction to maintain a
straight track. This, unfortunately
does two things. Firstly, the body of
the aircraft is inclined more sideways
to the track and, secondly,
groundspeed is reduced, because
some of the energy from the engine
is used in keeping it there.
You can see from the above that the
speed of the aircraft through the air
is not necessarily the same as its
speed over ground - if you are flying
into wind, you will go slower relative
to the surface, and faster if the wind
is behind you. An aircraft in flight is
affected by the wind both along its
axis and from the side, or from a
head/tail or beam component.
You work out what the wind's effect
on your trip will be by getting the
forecast winds from the flight
planning office, and working out a
combination of three sides of a
triangle, called the triangle of velocities,
because a velocity expresses a
combination of speed and direction,
and we are concerned with those of
your aircraft, the wind and the
difference between them.
148 Canadian Private Pilot Studies
First of all, a few definitions:
· Track. The path the aircraft
intends to follow over the
ground, represented by the line
on a map from one point to
another (Track Made Good is the
actual path – the difference
between them is Track Error).
· Heading. The direction in
which the aircraft is pointed,
according to its compass, with
reference to True North,
because Track (above) and
W/V (below) are.
· Wind Velocity. The speed and
direction of the wind, based on
True North. The faster your
aircraft, the less its effect.
· True Air Speed (TAS). The speed
of the aircraft relative to the
atmosphere, not necessarily the
same as that indicated, and not
necessarily the same as…..
· Ground Speed, or the speed of the
aircraft over the ground.
· Drift. The difference between
track and heading due to wind.
· Air Position. The position the
aircraft would have reached
without allowing for the wind.
· DR Position. The calculated
position of the aircraft.
· ETA. Estimated Time of
Arrival.
· Fix. Definite confirmation of
position by ground observation,
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