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boom and vertical stabiliser, for
example. It's the sort of situation
where it pays to be creative
sometimes. After all, the aim is to
walk away, not necessarily to
preserve the machine. Two other
things you can try if you finally make
the hover—stirring the cyclic so as
to dump lift, and pumping the
collective to produce a similar effect.
Both will serve to confuse the
machine enough so it forgets which
way to turn! With a jammed power
pedal (left, in a 206), what also works
is to crab in the way the machine
wants to, come to a high hover
sideways and let the machine settle
by itself. You will find very little
input is required by you.
If you want to run-on for landing,
get the wind and/or nose off to the
retreating blade side, so the fuselage
is crabbing, and control your
(shallow) descent with a
combination of throttle and
collective, applying more of the
latter as the throttle is closed just
before touchdown so you run on
straight. Note that some helicopters
(such as twins, or the AStar) won’t
let you use the throttle as precisely as
that. Not only that, you may well be
so busy that worrying about minor
details like the wind’s exact quarter
will be the last thing on your mind.
For a running landing, on most
machines, about 30% torque at 30
kts will put you in a good position
for landing at 30 ft, and a little
power at the last minute will put
your nose nicely straight. For the
non-power pedal, keeping straight
involves either more speed or less
power, and you have to accept more
of a run-on.
In an AStar (or TwinStar), the
recommendation in the book is to
come in with some left sideslip (i.e.
crabbing right). Slow down until the
nose starts to move to the left, and
you have your landing speed.
Loss of Tail Rotor Effectiveness
This is sometimes known as tail rotor
breakaway, or a stall, which is not
strictly correct, as thrust is still being
produced – it’s just not enough for
the task in hand. It shows up as a
sudden, uncommanded right yaw
(with North American rotation), and
has amongst its causes high density
altitudes, high power settings, low
airspeeds (below about 30 kts) and
altitudes, and vortex ring, not
forgetting turns in the opposite
direction of blade rotation. Your
helicopter will be more susceptible
to it if the tail rotor is masked by a
tail surface, like a vertical fin, and it
can be especially triggered by tail and
side winds (this is actually a
significant reason for maintaining
main rotor RPM – as the tail rotor
runs at a fixed speed in relation to it,
lower NR will reduce tail rotor
effectiveness in proportion).
Recovery in this case comes from a
combination of full power pedal,
forward cyclic and reduction in
collective, or autorotation.
Prevention lies in keeping into wind
and always using the power pedal
(left in a 206 or one with similar
blade rotation). If you use the other
one, not only will the fuel governor
ensure that the aircraft will settle
after a short time (using the power
126 The Helicopter Pilot’s Handbook
pedal by itself makes it climb), but a
large bootful of the power pedal in a
fast turn the other way will create a
large torque spike.
Jammed Controls
Aside from jammed tail rotor pedals,
discussed above, your cyclic or
collective may jam as well. Both
cases will result in a run-on landing.
To get out of a jammed collective,
just bring the speed right back. This
will cause you to descend, and you
can use your speed to aim at the
ground. Hopefully, your cyclic will
jam in the centre. Anyway, leaning in
the desired direction (passengers as
well) will cause enough of a shift in
C of G to turn the ship in the
desired direction.
Hydraulic Boost Failure
Indicated by feedback forces in the
controls, which will be negligible
when they are held in a fixed
position. Hopefully, your failure will
be just from fluid leakage, but it
could be a hydraulic pump drive
failure—in a JetRanger, this will be
confirmed by looking at the NR
gauge, as the pump is driven from
the transmission. Note that the
Hydraulic CB sometimes relates to
the switch as the idea is to have it
fail-on – electricity keeps the switch
off, so if it fails, it stays on and so do
the hydraulics. Reduce forward
speed and control inputs to a
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(84)