曝光台 注意防骗
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Visibility, by the way, includes the
inside! When it’s very cold, water
vapour (from clothes, breath, etc.)
will freeze on the windscreen, so
warming up the machine before
passengers get in will help a lot.
Navigation
Sun Tables are used for resetting
your DI in the Arctic, with true sun
bearings taken every 20 minutes or
so (assuming you can see it), based
on the fact that we know where the
Sun will be with reference to True
North for a given time, date, latitude
and longitude. Having obtained the
local time, look in the tables for the
Flight Operations 367
Sun’s bearing, point the nose
towards it and set the DI to True
North. The two types of navigation
are True North and Grid North (to
find Grid North, add your longitude
to True North, and vice versa).
In True North navigation, headings
have to be measured from your
point of departure, using the
longitude of your departure point as
a base line. Every time you cross a
longitude, you add a degree going
East, and subtract going West, so if
you cross 10 longitudes enroute on a
heading of 090T, your return
heading will be 280T, not 270.
Many pilots drop dye balloons en
route so they can find their way
back. Others fly low enough to
create a disturbance in the snow
surface with their downwash, with
the obvious dangers.
Landing
Aeroplanes
See also Performance, above.
Helicopters
Landing Sites should be selected
with a view to pulling out of a
resulting snow cloud if necessary.
That is, you may need to escape
somewhere.
As with landing on mountains, there
are various schools of thought about
landing on snow. One is the
zero/zero method (zero speed, zero
height), for which you carry out a
normal approach, using a constant
attitude with minimum changes,
losing translational lift at the last
minute. Aim to keep going forward
and downward until a few inches
above the snow, so the downwash is
always behind you, using the aircraft
shadow, a smoke grenade or the
landing light to provide texture to
the surface. Even a fuel drum makes
a good visual reference. Another
good trick is to use a dark-painted
stake with a flag on it – the flag
makes the stake behave like a dart,
so the point goes into the snow, and
acts as a wind indicator afterwards.
Do not hover, don’t go beyond the
marker, and try to land just as the
snow cloud develops.
When you commit yourself,
however, you will need to check the
firmness of the surface, which is not
usually a problem at a camp or
something, as the ground crew will
have done this for you. The danger
lies when you're going to an
unchecked site for the first time.
Touch down lightly without delay,
treating it as a sloping ground
landing, as the vibration of the
helicopter itself can cause ice to
crack. Any form of load spreading is
a good idea if you can take
advantage of it, like landing on a log
pad, although your landing gear will
largely determine what you can use.
As an example, a fully loaded
JetRanger on floats weighs 133 lbs
per sq foot, whilst one on skids and
bear paws is nearer 400. Whatever
you choose, it needs to be twice as
thick if you intend staying overnight.
Another method, possibly better for
beginners, is to come to a high hover
(with escapes) to allow the
downwash to clear the snow, then
lower the machine slowly and
smoothly, being wary if you’re heavy.
Still another is a really shallow
approach on the edge of
translational lift, to slowly move
forward onto the site with your skids
on the ground.
368 Canadian Professional Pilot Studies
Once landed, bounce the skids a
little to see if there's a crust,
although you should be careful with
the Astar as too much downward
force on the blades could cause the
head to crack, aside from pushing
the belly panel up into the controls
(watch out for the swinging hook,
too, which could cause loss of fuel).
The belly landing light, if you have
one, is a great snow scoop which
could affect the controls as well.
Keep your RPM to flying levels until
you're sure you're on firm ground.
Always keep the helicopter light on
the skids until passengers are clear,
regardless of the surface. Don’t let
anyone out till you’re happy.
The colour of ice can be a good clue
as to its suitability. White or blue is
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