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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
260 Operational Flying
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
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
minimum, making necessary
movements at a rate of travel not
faster than one full displacement,
stop to stop, per second. The failure
won't be sudden, so switch off early
to keep fluid in the system.
If you ever have to leave the
controls of a helicopter with the
engine running, do not switch the
hydraulics off, but use the control
locks only, in case the controls
motor by themselves.
Overpitching
In a helicopter, overpitching is
where the rotor RPM are too low to
maintain flight, giving the impression
of "labouring". It's the nearest
equivalent to stalling and is
commonly caused by being
overweight for the particular
conditions. Reduce power to
maintain RPM.
Engine Handling
One of the biggest things to unlearn
when transitioning from piston to
turbine is to keep your finger on the
starter button once things start
happening (with a piston, you tend
to take your finger off straight away
when the engine starts). You take
your finger off when the engine
becomes self-sustaining. Before then, it
relies heavily on the battery or start
trolley to keep it turning. It follows
that, if the battery is weak to start
with, the engine won't spin as fast,
Techie Stuff 261
the airflow is reduced, the whole
process becomes hotter and you
could melt the back end with a hot
start. You should always check the
voltage available from the battery
before starting a turbine engine. A
hung start exists when the engine fails
to accelerate to normal idle RPM. It
just sits there, weakening the battery
and leading to a hot start.
Pulling full power just because it's
there is not always a good idea.
Limitations may be there for other
reasons—for example, the
transmission might not be able to
take that much, which is why you
can’t go faster than 80 kts in a
Jetranger when pulling more than
85% torque (actually, in this case, the
transmission ends up in a strange
attitude). Excessive use of power will
therefore ruin your gearbox well
before the engine (and will show up
as metal particles in the oil). Many
turbine failures are the result of
pulling too many cycles from
minimum to maximum Ng, so if you
don't need 100% torque, it's best not
　
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