曝光台 注意防骗
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poor optical instrument (you would
get a better picture from a pinhole
camera), and it is your brain that is
responsible for turning the image the
right way up in the first place, and
for resolving the many colours the
eye is capable of distinguishing.
What this boils down to is that
above about 40 feet, it is very
difficult to judge height properly,
especially through your central vision
(the weakest part), and handling
depth perception needs some
practice. It is for this reason that you
should always look at the load
through the same medium
(preferably none at all) so you give
yourself the best chance. For
example, you are not helping
yourself by looking at the load with
one eye directly and the other
through a panel. Having the Sun on
the opposite side of the machine to
you is a useful tactic as well, so you
can use the load's shadow to tell its
height from the ground better.
The Astar is particularly bad for
looking out of as the pilot's door is
further away from the fuselage than
other machines. As a result, it needs
a minimum line of 100 feet (some
say 130) just to see the load through
a hole in the floor between the door
and the seat. However, even then
you only really see it when lifting, or
on delivery, which is why you need a
mirror as well (I once had to do a
job with a 75' line on a TwinStar,
and had to deliberately swing the
load so I could see it, at least once in
a while! In this case, long tag lines
helped the ground crew to catch it).
Some machines won’t allow you to
look out with shoulder straps on, or
when wearing a helmet, so try it all
out on the ground first. Note where
your hook attachment is and see if
you can make control movements
with reference to its position.
Naturally, there is some skill
attached to longlining, but it isn’t too
hard to learn, although you will have
to watch for vortex ring when
delivering the load, as you have
minimum speed with power on and
a high rate of descent if the load is
pulling you in. Anticipation is the
key, but you can only learn this after
some experience, wherein lies the
Catch-22 of needing experience but
not being able to get it. Fire chasing
offers the best free training, as you
are often out on your own, and
nobody is using a stopwatch.
Although it's not the complete
answer (for example, I can drop way
more water in a given time with a
short line), many pilots prefer
longlining, if only because problems
with the load occur further away
from the aircraft, and therefore
produce less hassle with the controls
and tail rotor (and downwash
doesn't artificially increase the load’s
weight or throw up dust). You’re
also that bit further away from
mechanical turbulence, although
almost always out of ground effect
and right in the avoid curve, which
may cause a legal problem. One big
plus is that, if your engine fails, the
ground crew have more of a chance
to get out of the way. Another is that
the delivery point doesn't necessarily
have to take the helicopter as well
(of course, the real reason why pilots
like slinging in the first place is that
there are no passengers!).
190 Operational Flying
However, with a crowning fire (that
is, with only a small area in the
smoke at the head that you can get
your helicopter into), longlining can
be dangerous, because all you will
see is a bucket flying around – you
certainly won't see the line, and the
pilot won't see you, being in the
smoke. As a result, some authorities
have banned its use, at least in
concert with short-lining.
There are three variations on the
longlining theme:
· Operational longlining, which can
be done by just about any
competent pilot and is fairly
undemanding, provided there is
a reasonable margin of power
available, subject to a couple of
caveats which are mentioned
below - it's when you are
operating to the limits of the
load and the machine that the
real expertise comes into play,
but even this is nothing more
than good downwash
management and smoothness
on the controls coupled with
anticipation. There is little
accuracy or speed involved with
operational longlining, and it
can be regarded as just an
extension to normal slinging—
it's commonly used in fire
support, where you dump a
water bucket's contents into a
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