about operating piston aircraft engines in the cold weather.
The four-stroke, air-cooled internal combustion engine in your
aircraft has what is called a "crankcase breather vent tube"
which exits the engine, almost always down low on the belly
where you probably can't see it very easily.
Because the piston rings don't seal perfectly, the crankcase
is pressurized, and that air needs to escape. Hence the
breather tube. But not just air escapes - you've got an
emulsification of oil and water going out the breather tube,
too - which is how the belly of the aircraft gets greasy.
During the summer, the water in that greasy mixture is
harmless - it evaporates. However, during the winter,
the water in the greasy mixture can freeze and plug
the breather tube.
When the crankcase breather tube gets plugged like
this, the pressure increases inside the crankcase and
the next weakest link is the front seal around the
crankshaft, behind the prop. When that seal lets go,
the engine oil is pump out of the engine onto your
windshield (in a single) or over the nacelle of a twin,
like these guys who were flying across the North
Atlantic and made an unplanned stop at Greenland:
To avoid this, you need to drill a small hole or two
in the crankcase breather tube a few inches above
the end of the tube, to act as a pressure relief in
case water plugs the end of the tube up. Some
people like to put one wrap of electrical tape
around the holes, but I have mixed feelings about
that.
Next subject: oil
I personally like to run straight-grade oil (such as
Aeroshell 100Wplus) in the summer in private
aircraft. The reason why is that it is cheaper than
multigrade, and if you don't fly it every day, the
oil doesn't run off the internal engine bits as fast
as multi-viscosity oil does, in the warm weather.
You can run multi-grade oil in the summer if you
have some extra cash that you don't need, and
you fly it every day (eg FTU aircraft).
Decades ago, we only had straight-grade oils
for aircraft, so in the winter, people just went
for a thinner oil, which was better for the start,
but not the best when the engine got hot.
However, these days we have approved multi-viscosity
oil for aircraft engines, and I strongly recommend
their use for the winter. They will really reduce the
metal-on-metal wear at startup because they flow
so much better at cold temps. And, you don't need
to wait for the engine oil temp to get up before you
take off - again, because it flows better at cold temps.
So, in the summer I like to run Aeroshell 100Wplus
and in the winter, Aeroshell 15w50. Good stuff (tm).
There is something called "pour point" of oil, which
you need to know about. The pour point of W100
(sae 50W) straight-grade is only -20C. This can
cause oil to congeal in your cooler and cause your
oil pressure to skyrocket. This happened on an
episode of Ice Pilots and they thought it was something
magical. Uh huh.
However, the pour point of 15w50 is -42C. This
means that the oil is far less likely to congeal in your
prop hub or cooler. Much safer for winter ops!
Next subject: Preheat
Most people think you preheat an engine in the winter
to make it start. That's actually not true. A side effect
of heating the engine is that you make the fuel evaporate
better, which makes it easier to start.
However the reason you pre-heat an engine is to reduce
the internal damage caused by a cold start. You've got
metal-on-metal wear occurring, and you've got differential
expansion and contraction rates of dissimilar metals which
can reduce internal clearances. Neither of these are good
for making TBO.
To make the point, you could probably start a Lycoming
at -20C by spraying highly volatile ether into the intake.
It would probably burn and the engine would run. But
you could expect to see a lot of metal in the oil.
It is worth mentioning that mogas evaporates a lot
faster than 100LL in cold temps, and as a result, it's
a lot easier to start a cold aircraft engine with mogas
in the tank. Mogas has it's own problems, though.
How to preheat? Well, you can buy all sorts of
expensive (and not so expensive) aircraft engine
heater systems which have pads which glue to the
crankcase, bands you strap around the cylinder,
heating elements you plug into the CHT holes.
They're slick - just run an extension cord out to
the engine and plug it in. If you're doing a lot of
winter flying, they're a good idea.
However, you can also buy 1000W 120VAC
little heaters from Canadian Tire that you can
put in your engine cowling. Depending on the
temps, after an hour they get the engine to a
good temperature.
You can buy expensive engine tents/covers from
places like Kennon (very nice) or if you're a cheap
bastard, cut the zipper off an old sleeping blanket
and drape it over the nose. Doesn't work very
well outside in the wind, though. Works ok in a
cold hangar.
When to preheat? As always, what the engine
manufacturer says is golden. It has been my
experience that TCM engines frost the plugs if
you try to start them below 0C. You can start
a Lyc colder than that, but it might not always
be a good idea (see above).
Call me a candy-@ss, but if it's below 0C, I
preheat. Cold starts can do a lot of damage
to your engine, and if you take care of your
engine, it will take care of you.
Note that a heater in the cockpit is a really
good idea, too. I destroyed a really nice
attitude indicator on a crisp February morning,
learning that gyros don't like extreme cold.
Note that with multiple heaters, you may trip
a circuit breaker (or blow a fuse). Two 1000W
heaters is really straining a single 15A 120VAC
circuit. I like to wire hangars with "split receptacles"
like a kitchen or bathroom, for this reason.
BTW, if you're going someplace in the winter,
toss a engine blanket or blanket in the back of
the aircraft, and as soon as you park someplace
(if you intend to fly again that day) immediately
get the engine covered up to retain the heat for
the next start. You wouldn't believe how fast
an engine, pointed into a cold wind, can cool down.
Do it before you pee, or buy gas or food.
Hopefully there are some useful hints and tips
for people here. If I can stop one engine from
being destroyed this winter, that will make it
worthwhile! If you feel the need to personally
attack me (as usual), go right on ahead as well,
because I honestly don't care what a wanker
like you thinks.
easy to carry preheater, 10# propane bottle, adapter to standard propane soldering torch, 4" of 3" stovepipe/ w a 90 elbow, and another 4' of flexible tubing ie: dryer duct, tuck it into your cooling outlet. Use with caution open 3" flame. Also works on your truck aim at the oil pan
