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speed and maintaining the lower
main rotor RPM limit. Best
endurance speed will give the best
lift in autorotation (i.e. minimum
sink). Where winds or density
altitudes are high, expect to increase
speed a little, but decrease it when
winds are calm or density altitudes
are low, or you need a little time to
choose a landing area or be a little
Techie Stuff 121
more precise (see below). If you
deliberately decrease the RPM to
increase range (and possibly lessen
the rate of descent), don't forget to
build it up again for landing.
A typical helicopter has a power
curve looking like this:
If you are aiming for a particular
spot, you will have a better chance of
hitting it if you keep your speed
below the best speed mentioned
above (60), as anything faster will
cause you to float, and force you to
anticipate the glide more (that is, the
aiming point is different from the
landing spot, and the faster you go,
the more they will be different. If
you only have one clearing, you will
have a better chance of getting there
and flaring very close to it if you
keep your speed tight). If you are on
the backside of the curve, remember
to get your full speed up by 100 feet,
or the flare will be just a change in
attitude and fail to do its proper job
of slowing you down (see below).
Having entered autorotation:
·  Select landing spot
·  Transmit MAYDAY
·  Warn passengers
·  Turn off electrics, but NOT
battery (for the intercom)
·  Close throttle if required
For a clear area, when about 70 feet
from the ground (depending on
whether you think you are
descending or travelling across the
ground too quickly), use rearward
cyclic to slow down vertically and
horizontally. The amount is
proportional to your speed and
serves to increase the total lift
reaction (which stops the sink) and
shifts it to the rear (which stops
forward movement). It also increases
the rotor RPM.
Continue the flare progressively to a
nose-high attitude (in a 407, the
instrument panel should hide the
horizon), applying collective as flare
effect decreases (and the sink starts)
to allow the machine to flop forward
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
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
122 The Helicopter Pilot’s Handbook
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,
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(81)