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lead appears as a result of chemical
changes in avgas as it burns). At
richer settings, the lead either doesn't
form or is swept out of the cylinder
(this may be true for lower
performance engines, too).
Don't forget to enrich the mixtures
before increasing power when at
peak EGT or when increasing to
more than 75% power. Move the
engine controls slowly and smoothly,
particularly with a turbocharged
engine. Harsh movements that (on
older engines) will result in a cough
and splutter and having no power
can be embarrassing.
Although many flight manuals state
that as soon an engine is running
without stuttering it's safe to use it to
its fullest extent, try warming up for
a few minutes before applying any
load, at least until you get a positive
indication on the oil temperature
(and pressure) gauges. This ensures a
film of oil over all parts.
Even better, warm it before you start
it, because the insides contract at
different rates – in really cold
weather the engine may have the
grip of death on the pistons and
cause some strain when you turn the
starter. Equally important is not
letting an engine idle when it's cold,
as it must be fast enough to create a
splash of oil inside (about 1,000
RPM is fine).
After flight, many engines have a
rundown period which must be strictly
observed if you want to keep it for
any length of time. As engines get
smaller relative to power output,
they have to work harder. Also, in
turbines, there are no heavy areas to
act as heat sinks, like the fins on a
piston engine, resulting in localised
hotspots which may deform, but are
safe if cooled properly, with the help
of circulating oil inside the engine
(75% of the air taken into a turbine
is for cooling purposes). If you shut
down too quickly, the oil no longer
circulates, which means that it may
carbonise on the still-hot surfaces,
and build up enough to prevent the
relevant parts from turning. This
coking up 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.
Lubrication
Friction can be handy, but not inside
an engine. Without a way of making
the various surfaces rub smoothly
218 Canadian Professional Pilot Studies
against each other, they would get
hot, and suffer from scoring damage.
Oil actually does many things,
including cooling, cushioning, flushing,
lubrication and sealing (exam question).
There are two main methods of
lubrication, wet sump and dry sump.
The first is very simple, with the
engine oil in a sump under the
engine, in which the crankshaft and
other moving parts rotate, splashing
it all around (splash and mist).
Dry sump uses a tank outside the
engine, and oil is force fed around
under pressure where it is needed
(although wet sumps systems have
pumps, too). The scavenge pump
(which pulls oil from the engine) has
a greater capacity than the pressure
pump, to make sure the tank gets
filled properly. The filter will be
between the engine and the scavenge
pump. The oil cooler is between the
scavenge pump and the reservoir.
Pumps are usually mesh gear types:
Oils come in various thicknesses, or
viscosities, which measure resistance to
flow. The lower the viscosity
number, the thinner it is, so you
would use 120 oil in Summer, 100 in
Fall or Spring, 80 in Winter and 65
in the Arctic. To keep the oil thin, in
the cold, one trick is to pour a few
litres of petrol into the oil system
just after closing down at night, so it
is very thin in the morning and you
can start the engine. By the time the
oil has warmed up, the petrol has
evaporated and you can carry on
(but check your flight manual to see
if this Oil Dilution is acceptable for
your machine).
Oil is cooled by pumping it through
an oil cooler, which is just like a
radiator. An oil filter is used to trap
any impurities, and the pressure relief
valve is there to make sure it doesn't
get too high (if the pressure
increases, due to a blockage, maybe,
the valve opens and dumps the oil
back to the tank).
Chip Detectors are small magnets that
attract slivers of metal suspended in
the oil. Sometimes, they are
connected to a warning panel in the
　
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