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could sieze the engine within 50
hours or less.
If the starter light remains on after
you release the starter button on a
piston engine, you should shut it
down, as it indicates that the starter
is still engaged with the engine and is
being driven by it.
The "LL" in 100LL stands for low
lead, but there is still about four
times more than is needed. As well
as the lead (in the form of TEL—
Tetra-Ethyl Lead), a scavenging agent
(Ethylene DiBromide, or EDB) is also
added to ensure that the lead is
vapourised as far as possible, ready
to be expelled from the cylinder with
other gases. Unfortunately, this is
not 100% successful, but the results
are best at high temperatures and
worst at low ones - the unwanted
extras result in fouling of spark
plugs, heavy deposits in the
combustion chamber, erosion of
valve seats and stems, sticking valves
and piston rings and general
accumulation of sludge and
restriction of flow through fine oil
passages, so it makes you wonder
which is worse (in fact, petrol is not
the only fuel you can use – Japanese
Zeros used to outfly American
aeroplanes because they used ethyl
alcohol). TEL, by the way, is actually
a liquid gas, which was developed by
a subsidiary company (Ethyl, Inc)
belonging to General Motors and I
G Farben sometime before WWII.
In June, 1940, just before the Battle
of Britain, it could only be obtained
through the Anglo-American Oil
Company, or Esso - when the fuel
was changed from 87 octane to 100,
German pilots got a real surprise,
because the Spit could suddenly
climb a whole lot quicker.
Oil
An engine that is not used enough
develops corrosion very quickly on
the inside, and rust flakes, which are
very abrasive, will circulate when the
engine is started, which is why you
have to change the oil even when
you don’t fly a lot. Another reason is
an increased water content, which
will have an acidic effect once it
mixes with the byproducts of
combustion. The most wear takes
place in the first seconds of a cold
start, after the oil has been allowed
to settle. Priming will wash whatever
is left off the cylinder walls, so don't
do too much, and maintain the
minimum RPM to let it circulate.
Synthetic oils have come from
turbine oil development, but they
have one drawback, in that the
sludge in tends to centrifuge out
inside the dome of a constant speed
propeller and make cycling a bit
difficult. They also hold
contaminants longer.
Many Flight Manuals recommend
not changing brands of oil (e.g. the
JetRanger), but if you check with the
engine manufacturer’s manual (in
this case Allison), you may find that
it is permitted on a top-up basis, that
is, if you already have one brand in
130 The Helicopter Pilot’s Handbook
there, just start using the new stuff
until eventually the contents change
completely. Do not drain your
present oil, and replace it in one go,
because oils have different cleaning
characteristics—your new brand may
be more efficient and you get bits of
coke and carbon floating around that
could cause a seizure. However, this
is something you should discuss with
your maintenance people.
Carburettor Icing
This is actually one aspect of induction
system icing. The other two are fuel
icing, arising from water suspended in
fuel, and impact ice, which builds up
on the airframe around the various
intakes that serve the engine. Even
on a warm day, if it's humid,
carburettor icing is a danger,
especially with small throttle
openings where there's less area for
the ice to block off in the first place
(as when descending, etc.). Also, the
temperature drop (between the OAT
and that in the venturi) can be
anywhere between 20-30°C, so icing
(in an R22, anyway) can happen even
when the OAT is as high as 21°C
(70°F), or more. Tests have
produced icing at descent power at
temperatures above 30°C, with a
relative humidity below 30%, in clear
air. Because it is more volatile, and
likely to contain more water, you can
expect more fuel and carb icing with
MOGAS than AVGAS.
It usually arises from the action of
the venturi in the throat, just before
the butterfly valve, which regulates
the amount of fuel into the engine.
You will remember the venturi's
purpose is to accelerate airflow by
restricting the size of the
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(87)