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the groundspeed column first,
meaning you are just using the
triangle of velocities at this stage,
using information in the question
itself. Find the climb and descent
groundspeeds (check the question),
deduce the distance travelled, and
subtract the figures from the first
and last legs. Once you know your
groundspeeds and distances, you can
figure out how long each leg will
take, which is the starting point for
fuel calculations.
For big aircraft, the tricky bit is that
fuel flow changes with aircraft
weight, the flight level and
temperature deviation. At the start
of a leg it is artificially high, so you
have to estimate the mid-weight, or
average, flow from the data sheets
for the aircraft, which means
interpolation. Don't worry, it doesn't
need to be exact, so you can round
up or down or make assumptions to
your heart's content. You need to try
and get a rate per minute, to apply to
the probable time to the mid-point.
For example, if the aircraft weighs
126,000 kg at the start of a leg, the
associated fuel flow is 7500 kg/hr,
and the leg time is 35 minutes, you
can immediately round the time up
to 36 minutes for a mid-point time
of 18 minutes. You could probably
assume 7000 kg/hr, which means
just under 120 kg per minute. 18
minutes at that rate means you will
burn off 2160 kg, meaning that your
approximate mid-leg weight is
124,000, which is what you use to
enter the charts (make sure you use
the right line).
TOC/TOD
To calculate these, find the mean
height and temperature ad use them
to get the mean TAS (on the
whizzwheel). Use the mean W/V to
get the mean heading and
groundspeed.
Figure out the times based on the
height change and rates of climb or
descent, then use the mean
groundspeed for distance travelled.
Then work inwards from the start
and end points of the journey for
distance and time.
The Dalton Computer
This is a device with a sliding scale
through it, marked with drift angles
and TAS arcs, with a frosted circular
screen for the business end of the
triangle of velocities:
There is a dot in the centre of the
screen, around which is a compass
rose that can be rotated to bring
your heading or track under the
332 Canadian Professional Pilot Studies
lubber line. All you need to do is
draw in the wind vector to see how
they all relate to each other.
Note: there will be an instruction
book supplied with your computer,
so the instructions given here will
necessarily be brief.
The first thing to do is move the
sliding scale to make your TAS
appear underneath the dot in the
centre of the frosted screen. Then
rotate the screen so the wind
direction lines up under the lubber
line at the top.
Draw in a line vertically downwards
from the centre dot equal to its
speed in knots. Rotate the screen
again until the track is under the
lubber line. The end of the wind line
will point to a drift arc and a TAS
arc, which you just apply to your
track and airspeed to get the missing
bits, namely the true heading to fly
and the resulting groundspeed which
you use for flight planning. Then
apply the magnetic variation and
compass deviation to get the proper
heading to fly.
CR Series
These were invented by Ray Lahr
and marketed by Jeppesen. They are
circular, with no sliding scale, and
are based on trigonometry (they are
easier to work with one hand, but be
aware that, as the angle of drift
increases, there's a small angular
correction to be applied on top).
Below is a picture showing how you
would work out the details for the
PLOG above. The cross to the right
of the 10 near the centre of the
instrument (bottom of picture) is the
wind velocity (180/15). Its position
to the right of the main line going
towards TC (True Course) means
the wind is from the right, and the
crosswind component is 8 kts.
Looking across from the 80 on the
outside scale, you will see that 5° is
the correction to be applied to
obtain the heading (the white arrow
above the letters TAS must be
opposite the aircraft's TAS for this
to be correct).
The headwind component is 12 kts,
which should be subtracted to obtain
a groundspeed of 78 kts.
The very small ones have some
functions left out, which are
unimportant to most aircraft anyway,
to pack everything else in, but don't
get one too small, because your eyes
　
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