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in a self-levelling process, watching
for drift. The “check”, mentioned
above, is a more positive application
of collective, used with some
machines to level better. Otherwise,
there should just be small pause in a
continuous movement, and you
should find the rear skids touching
the ground gently well before you
run out. Get used to the visual clues
required for the correct approach
256 Operational Flying
and flare attitude – there's no time to
look at the ASI, and the one on the
407 is dampened anyway, so is fairly
useless under these circumstances.
Get up on a nice day and practice
autos to a cloud, getting used to the
horizon's position through the
screen during descent, flare and
turns on your machine.
In every flare there is a point called
the apex, which is where the trading
off of airspeed for lift is essentially
all over and you just have to get
yourself on the ground. Put another
way, it is the point where there is no
further benefit from the flare
manoeuvre, so you may as well pull
the pitch (a little later in a 206). As
the flare ends, and the kinetic energy
of the rotors is used when the
collective is raised, the airflow
through the rotors is reversed,
assisting the level, ready to cushion
the landing with collective. This is
where correct use of airspeed during
the descent will have had the most
beneficial effects—as the kinetic
energy stored in the blades is what
slows you down, it follows that any
you have used already to slow an
unnecessarily fast descent is not
available for the final stages of
touching down.
But what if you are going into a
clearing? Or don't get that much
practice? The above method is fine,
but you need to be doing it a lot to
get it right every time. One way that
will cover both the above situations
is to start the flare very much earlier,
so that you are virtually stopped
quite high up. Then carry on as if
you had an engine failure in a high
hover, that is, dump the pole to get
going vertically downwards and haul
it all in at the end. In a vertical
autorotation, there is a phenomenon
known as dynamic stall that will help,
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
Techie Stuff 257
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
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,
　
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