If you fly a piston engine aircraft, you should be aware that there
is a tube running from the crankcase to the outside of the airplane,
generally (but not always) running out the bottom of the cowling.
This tube is very important. The piston rings don't seal perfectly,
and there is a certain amount of "blow-by" gases from the combustion
that makes it past the rings.
So, the crankcase is basically pressurized, and the older and more
worn the rings, the more pressure there will be in the crankcase.
To vent the pressure in the crankcase, where the oil is kept in a
wet sump engine, most aircraft manufacturers run a simple tube
from the top of the crankcase to the bottom of the engine. And
that simple arrangement works pretty well in the summer - unless
you put too much oil in the crankcase, and it barfs the extra oil
out onto the belly as the crankcase whips up the oil in the sump.
However, water is a byproduct of combustion, and in the winter,
an emulsification of oil and water is present at the end of the
breather tube, and it can freeze and plug the tube shut.
When this occurs, very bad things happen. The crankcase continues
to be pressurized by blow-by, and the next weakest link is the
crankshaft seal at the front of the engine, where the prop is bolted
on.
The seal blows, and the engine oil gets blown out, covering your
windscreen. You will notice when this happens.
To avoid this, you need to drill a hole or two - some people call
it a whistle valve - farther up the breather tube, inside the engine.
Some people like to wrap the holes with one wrap of electrical
tape and hope it blows before the crank seal, but that makes
me nervous. I don't cover the upper vent holes, and if a little
engine oil makes it into the engine compartment, oh well. That's
why God invented Mineral Spirits and textile rags.
Last year a friend of mine landed his Robinson helicopter for
gas on a very cold day (for us) here in Eastern Ontario. I
noticed what looked like brown snot hanging down from the
breather tube. I broke it off, and realized that it was plugged
solid.
I got my jacknife out, and dug out 4 inches of solid ice that
had formed, plugging the end of the breather tube. Fortunately
the manufacturer had drilled 2 tiny holes further up the tube,
and they were venting the crankcase gases.
Recently, we took up the 3 Pitts. It was below freezing, but
not terribly cold. 2 vents had no ice, and the third was almost
totally plugged up! I have no idea why that one tube plugged
up as the airplanes are almost completely identical.
Anyways. You're Canadian. You fly when it's cold. You should
know about this potential problem, and please check to make
sure that you have a small hole (or two) drilled up in your
crankcase tube, if you're going to fly in the winter!
Guess what happened to these guys, flying across the
North Atlantic? I don't think they planned this landing
in Greenland:
I doubt Tex in the photo was familiar with this problem,
but you are now!
