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winds – any found in updraughts will
be from mechanical effects, such as
trees. Smoke grenades are often used
if there’s nothing else.
Aside from picking a speed slow
enough to detect changes and yet
give enough for a margin of safety
(and cope with any turbulence),
when testing for wind, you should
also fly about 50-100 feet below the
top of the peak you want to land on,
to keep yourself away from the
demarcation line and reduce the
chances of getting the rotors in an
updraught on the leeward side. Also,
keep tight in to the side, to stay
inside the boundary layer.
The demarcation line is the point at
which smooth air is separated from
turbulent air around a peak, rather
similar to that over an aerofoil.
Above or to the side of the line, air
is relatively smooth and upflowing –
below, it is downflowing. It steepens
as wind velocity increases (and the
severity of the slope), as does the
area of downflow, and moves
toward the top of the hill. One tip:
you don't have to keep the whole
helicopter one side or the other—
many pilots work the line by keeping
only the blades on one side of it. The
fuselage by itself is not affected
much by turbulence. However, this
is a lot of work, and an easier
method is to make sure you can see
down the windward slope, and
approach at 45° to get a safer angle.
Having decided on wind direction in
general, you now need to look more
closely at your proposed landing site.
In strong wind conditions, you won't
need the contour crawl at all,
because it's obvious where the main
body of wind is coming from, but it
may have very little influence over
your final approach anyway.
The basic manoeuvre is a figure-ofeight
type inspection, making all
turns away from rising ground
(returning towards the site) to give
you a good view all the time. You
could go round in a circle, but the
landing point would be out of sight
most of the time.
As with any other potentially dodgy
landing site, you need to check for
Size, Shape, Surroundings, Slope,
Surface and Sun (you don’t want it in
your eyes). The most important,
however, in this case, is Slope, as
there's no point trying at all if you
72 The Helicopter Pilot’s Handbook
can't land. You will get little idea of
ground conditions if you overfly the
site, so what you must do is have a
look at eye-level, which results in the
aptly named Eye-Level Pass (if the
site isn't surrounded by trees).
The most economical way is to start
with a downwind pass, turn round
and land, which is entirely possible if
you know the wind direction before
you start. Sometimes, though, this is
not obvious at all, so just make an
educated guess and fly at about 40
kts in the direction you think is
downwind very close to the site, level
with your eyes. This point is crucial. As
you do so, note the reading on the
altimeter (those people used to QFE
may want to set it to zero), and
climb up an extra hundred feet as
you increase speed to about 60
knots, using the collective.
At 100 feet, turn round for another
approach and repeat the process,
taking note of the new groundspeed
and deciding which way the wind is
coming now you are closer. If there
is no real difference in speed, check
for vibration through the pedals, aft
cyclic, etc, or anything that might
indicate the wind is from behind.
The next step is an initial approach
and overshoot, but if you have to
make a circuit, you may as well do
another eye-level pass and get as
much information as you can.
Turn in at around 50-60 knots (at
the 100 feet), taking particular note
of escape routes, up and down
draughts and turbulent areas.
Maintain a constant angle, aiming
directly for the point you wish to
land on, controlling your speed with
collective and avoiding any last-minute
corrections. The idea is to keep the
fuselage as level as possible, so don't
move the cyclic at all, if you can help
it. One reason for using the
collective in this way is to minimise
large control movements in the final
stages, as this is a shallow approach.
Approaches
There are several schools of thought
about these, but no real standard –
as with many other activities
involving helicopters, there is more
than one “right” answer to this one.
A fairly flat, disc-loaded (shallow)
one will (in theory, anyway)
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(48)