曝光台 注意防骗
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where an aerofoil that is rapidly
stalled can produce double the
normal lift, just for a moment,
because the breakup of the boundary
layer on top is delayed for a while, if
indeed you don’t actually create a
little vortex along it that improves
lift even further. Do not try to gain
speed, as you will split the lift vector
and increase your rate of descent.
If you're likely to be ending up in
trees, as you might if you have the
choice between them or power lines,
aim between two tops, tail first or
low, or at least moving gently
backwards. The worst thing to do is
go in nose first, because the engine
and gearbox will hit the ground
before you do. The height of the tree
is less important than the height at
which the branches start, and if you
are over them regularly, you might
like to carry a good length of rope to
help yourself get down. Having said
that, it will be easier for the SAR
guys to pick you up from the top.
With short trees, denser areas
provide the most shock absorbency
– don't worry about branches
overlapping, as long as the trunks are
far enough to allow the fuselage to
settle and the main rotors to miss
them (actually, the main rotors can
be used as an umbrella to reduce
descent). Fewer trees in an area
actually become obstacles. Dead
ones provide no absorbency at all.
Pull the collective when you are in
the trees.
If the surface is sloping, try to land
nose up. If you flare a little, you will
increase your chances of getting it
right first time as the attitude of the
skids will match the slope of the
ground better.
Whereas an aeroplane is better suited
to protecting the occupants from
forward impact, the helicopter is
better suited to vertical motion, so
forward movement should be
reduced as much as possible,
especially over hostile ground – the
cabin can be distorted badly just
from the couple between its forward
motion against the drag from the
skids on the ground. As it happens, a
Techie Stuff 123
zero speed touchdown at 1500 feet
per minute on soft terrain would
probably not result in many injuries.
If it looks like you are going to hit
hard vertically, do not lean forward,
but brace your back against the
complete area of the seat to maintain
a natural curvature. Spinal injuries
are most often caused by flexing.
In fact, there are two broad types of
injury to consider. Contact injuries
arise when you hit something, or
something hits you (such as loose
articles in the cockpit). Decelerative
injuries result purely from motion of
the body, or loads applied through
seats and safety belts. They are
internal in nature, such as the spinal
injuries mentioned above, or in the
abdomen. Other injuries, like
burning, may occur after the crash.
Although it helps to crash as slowly
as possible, dissipation of whatever
speed you have is the main
consideration, and this is never
usually uniform. Every obstacle the
fuselage hits is responsible for a peak
deceleration and the potential for
damage to the people inside, so it
makes sense to try and protect this
as much as possible at the expense
of rotors, undercarriage, tail booms,
etc. This is where the proper use of
shoulder straps is important – if you
don't wear one, you will jackknife
over your lapstrap and your head will
hit the instrument panel at a speed
over 12 times that of the cockpit
deceleration. Also, when only
wearing a lapstrap, your tolerance to
forward deceleration reduces to
below 25G, from a normal total of
over 40.
Some things you can do to prevent
injuries can be done before you get a
problem, by selecting clear routes
wherever possible, and flying higher,
which increases your range of
choices (but not so high that it takes
too long to get down in a hurry).
Once you've landed:
· Close throttle & fuel valve
· Turn off Battery
· Evacuate aircraft
Power-On Recoveries
These are an increasing trend in
many companies, intended to reduce
the number of autorotative accidents
when practicing engine-off landings,
and ensuring that some pilots don't
get to practice real ones for years on
end. The examiner is looking for a
correct entry into autorotation and
flare initiation height, but, thereafter,
the process is a coordination
exercise, and you should treat it as a
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The Helicopter Pilot’s Handbook(82)
