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
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
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
I doubt Tex in the photo was familiar with this problem,
but you are now!
For those unfortunates not blessed with the ability to live in Paradise, heed CS's advice; it is timely and very appropriate.
The pilot reported elevated oil pressures as one hint of this problem. It's a rather drawn out narrative that doesn't really add much to what CS wrote but thought some might be interested.
Colonel Sanders wrote:Last year a friend of mine landed his Robinson helicopter forgas on a very cold day (for us) here in Eastern Ontario. Inoticed what looked like brown snot hanging down from thebreather tube. I broke it off, and realized that it was pluggedsolid.I got my jacknife out, and dug out 4 inches of solid ice thathad formed, plugging the end of the breather tube. Fortunatelythe manufacturer had drilled 2 tiny holes further up the tube,and they were venting the crankcase gases.
Those tiny holes werent put there by the manufacturer but probably a forward thinking AME at some point. Ive seen that happen in an R44 before, the vent tube is straight down, so landing in soft snow plugged the warm tube then solidified as ice. In that case there was a rupture in the engine, loss of oil and forced landing. I enquired about a psv in the crankcase vent inside the cowl or somewhere else in the engine but no ones stc'ed such a thing yet.
SAFELY IN A PRETTY AND WELL PRESERVED BODY, BUT RATHER TO SKID IN BROADSIDE, THOROUGHLY USED UP, TOTALLY WORN OUT, AND LOUDLY PROCLAIMING"
WOW... WHAT A RIDE
I really doubt they are even aware of the problem. And given that the solutionmanufacturers have not solved this problem by other means
to the problem is so simple - drill a hole or two, a distance up from the exit - I
don't know why you would need to engineer a more complicated solution.
You may or may not have been alive on 28 January, 1986 when the Space
Shuttle Challenger exploded shortly after launch. You probably don't remember
the blue-ribbon panel that was appointed to find the mysterious cause of the
accident. This blue-ribbon panel consisted of Neil Armstrong, Chuck Yeager,
and many other distinguished people such the genius Richard Feynman, who
worked on developing the atomic bomb during WWII, later won the Nobel
prize in physics, played a mean set of bongo drums, and was also widely
known for seducing his co-workers' wives.
Anyways, this panel of certified geniuses, after many months, eventually
discovered that o-rings shrink in the cold and then stuff leaks, which if you
live in Florida might not be obvious, but if you're a Canadian and you've
lived through a winter or two, you've probably noticed that stuff - including
o-rings - shrinks in the cold. Heck, even George on Seinfeld eventually
figured that out!
Don't take cold wx ops for granted. A good example: what is the "pour point"
of your aircraft engine oil? Why would you care? What indications would you
observe that you have encountering problems with it?
I am absolutely certain that the manufacturers involved (engine and airframe manufactures) are 100% aware of the problem.Colonel Sanders wrote:I really doubt they are even aware of the problem.
I work for an aircraft manufacturer, in Flight Safety, and I can assure you that whenever there is any kind of incident reported involving an aircraft that we manufacture, the incident (and causal factors) are very closely looked at, if for no reason other than to determine if a change in procedures, maintenance practices, or product design is required.
Hence I am wondering - if moisture freezing in the crankcase breather tube and blocking the breather tube is a known issue - and it certainly appears to be a known issue - is it possible that some kind of Service Letter, Service Bulletin, or alternative maintenance procedure has already been promulgated by the engine or airframe manufacturer that provides mitigation for this problem? The 'home-made' solution of drilling a hole or holes further up in the breather tube, to allow gases to escape if the distal end of the tube becomes blocked, sounds like it might work, but I would expect the OEMs to device and publish a solution themselves.
I guess what I am getting at is this: Before going out and implementing an unapproved repair scheme (drilling holes in the crankcase breather tube), it might be appropriate to have an AME who is familiar with both the engine and the airframe do a careful literature search of the SLs, SBs, maintenance practices, and continuing airworthiness instructions to see if the OEM has already published an approved solution for this problem.
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Actually, Sanders, the problem was well-known to the Morton-Thiokol and NASA engineers, as it had happened a few times before in previous launches. In those cases, however, the O ring had, for whatever reason, re-seated itself and continued to function as per design. The larger problem at work was the normalisation of deviance, which 'allowed' them to keep launching, even though one critical piece was not performing to spec.Anyways, this panel of certified geniuses, after many months, eventually
discovered that o-rings shrink in the cold and then stuff leaks, which if you
live in Florida might not be obvious,
A really great read about this is a book called 'Riding Rockets' by Col. Mike Mullane. He devotes a serious chapter in an otherwise hilarious book to the Challenger accident and its aftermath. http://www.amazon.ca/Riding-Rockets-Out ... 0743276825
Ass, Licence, Job. In that order.
Less efficient actually and more importantly it is not required by emissions standards as far as I know. Much like why they don'tazimuthaviation wrote:Why arent the cranckase gases vented into the intake like every other engine?
-use unleaded gas like every other engine
-have a catalytic converter like every other engine
-use a closed loop fuel injection system like every other engine.
Car engines and airplane engines are are in different eras when it comes to technological innovations. The reasons for this are an entire different subject.
This lycoming document describes the problem.
For non aerobatic planes this hole or slot is open year round but inverted systems you have to open them manually in the winter.
into the exhaust. This improves performance by a few horsepower
but this maddeningly simple thing is distinctly non-trivial, as the
red bull racers found out!
With this setup, you can see the puff of blue smoke out the exhaust
when someone's Christen 801 air-oil separator tank overflows.
I've seen the same situation with crews from warm climates not understanding the import of operating their aircraft, and the cold-weather systems installed on them, in cold climates. Sometimes the attitude seems to be, as they used to say at Air Florida, "We'll cross that bridge when we come to it".
Ask them what the pour point temp of their pistoncrews from warm climates
engine oil is, and what two implications of it are, for
cold temp ops.
Lots of small piston aircraft have had serious problems with engineIn truth, in other than large complex aircraft, the pour point is irrelevant. Once the oil is cooled below it's cloud point temperature, it is not safe to operate the engine without thorough pre-heating
oil pour point. I personally know of a C310 that was crashed because
of it - double engine failure.
If you look at the spec sheet for a straight-grade engine oil (eg Aeroshell
W100) you will find that it has a pour point of -20C. Below that temperature,
in the (constant speed) prop hub or oil cooler, it can congeal. It is no longer
a nice liquid. When it congeals in the prop hub you may find it difficult to
change the prop RPM which is annoying.
But when it congeals in the oil cooler, it plugs it up and the oil pressure
soars far above the redline. There was even a recent episode of Ice
Pilots about this, but as usual for TV it was not explained coherently.
This is why you want to run a multi-viscosity oil in the winter, and
it's not just about the preheat. The pour point of Aeroshell 15w50
is -40C which is far below that of the straight grade W100 (sae 50).
Even with Aeroshell 15w50, do you want to operate below -40C?
Executive summary: even with pre-heat, don't run summer straight
grade oil in the winter.
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I presume the tube comes off fairly easily and once you drill it you can clean it off really well maybe even use a cloth with a magnet in it to help collect metal shavings. Then put it back where you took it off from.
At the front r/h side of the crankcase was an elbow fitting ( breather) that had a rubber tube attached. The tube went down to the bottom inside of the cowl.( Some engine have metal tubes but they will ice up easier than rubber)
On extremely cold days it would freeze from condensation and plug the tube end. No matter because I had a hole in the tube half way up.
I also drilled a small 1/8 hole in the vertical half of the elbow as a precaution.
No issue with drill swarf getting into the crankcase as the pressure is all outbound.
This method worked really well and I never had any issues
second UPF-7 in distance. Bonus points for the Grumman
Tiger peeking out on the right.
It was nice to see both UPF-7's flying overhead in tight
formation. Probably a better sight than me walking in my
first parade in Key West (annual dachshound walk, 31 Dec).
Never thought I would be in a parade in Key West unless I
was dressed as a nun with fishnet stockings and garter belts.