M20 Air/Oil separator

On Sun, 15 Aug 2004 06:17:09 GMT, (John_F) wrote:

If you put too much oil in an engine it will heat up the engine more
because the crankshaft hits the extra oil and causes the oil to be
flung around and this also leads to oil foaming.
Extra heat is generated by flinging the oil around and the bearings
don't get enough oil since the pump does not pump foam well.

Any aircraft engine crankcase I've been inside of has relatively small
slots below the crank where the case halves meet effectively isolating
the sump from the crank in regard to "windage".

TC

snip

Any aircraft engine crankcase I've been inside of has relatively small
slots below the crank where the case halves meet effectively isolating
the sump from the crank in regard to "windage".

Ah! The man who truly *knows* weighs in!

:-)

So how 'bout it, TC -- is the M20 a good thing, a bad thing, or 'bout the
same thing with regards to my O-540?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Mike Rapoport wrote:

But you are putting more heat in because of having the crank contact the oil
more of the time. The temp will be higher.

Is this true in Lycs and Contis? I don't know about the airplane
engines, but car engines have the upper fill limit established to
prevent this. Having the crank contact the oil will froth it pretty
quickly and the oil pump can't pump aerated oil very well. This is why
the dipstick always has a warning not to overfill. I'd be surprised if
airplane engines permitted a fill to the point of crank contact. This
is generally only done intentionally on splash lubricated engines such
as those found in cheap lawnmowers.


Matt

Mike Rapoport wrote:

The case has no more area and no more airflow across its surface with more
oil in the sump.

No kidding, but it does have more oil contact area and thus the oil can
transfer more heat to the case.


Matt

The oil level is about 1" higher and the case is highly conductive.

Mike
MU-2


"Matt Whiting" wrote in message
...
Mike Rapoport wrote:

The case has no more area and no more airflow across its surface with
more
oil in the sump.

No kidding, but it does have more oil contact area and thus the oil can
transfer more heat to the case.


Matt

The crank in not in contact all the time but the oil is sloshing around as
the airplane moves. When the level gets down to where it isn't contacting
the crank, the oil stops being blown out the breather (at least in
meaningful quantities.)

Mike
MU-2

"Matt Whiting" wrote in message
...
Mike Rapoport wrote:

But you are putting more heat in because of having the crank contact the
oil
more of the time. The temp will be higher.

Is this true in Lycs and Contis? I don't know about the airplane
engines, but car engines have the upper fill limit established to
prevent this. Having the crank contact the oil will froth it pretty
quickly and the oil pump can't pump aerated oil very well. This is why
the dipstick always has a warning not to overfill. I'd be surprised if
airplane engines permitted a fill to the point of crank contact. This
is generally only done intentionally on splash lubricated engines such
as those found in cheap lawnmowers.


Matt

On Mon, 16 Aug 2004 02:35:58 GMT, "Jay Honeck"
wrote:

Any aircraft engine crankcase I've been inside of has relatively small
slots below the crank where the case halves meet effectively isolating
the sump from the crank in regard to "windage".

Ah! The man who truly *knows* weighs in!

:-)

So how 'bout it, TC -- is the M20 a good thing, a bad thing, or 'bout the
same thing with regards to my O-540?

I've read mixed reports about the M20, unfortunately have no personal
experience. Have heard people swear by them, have heard people swear
at them.

Have taken care of several Bo's with the original Walker (?) air/oil
sep. They were for the most part equipped with wet vac pumps as well.
In those cases, there was what I would consider to be an acceptable
accumulation of oil on the belly.

I can't really speak with any authority on the whole "putting crud
back in the crankcase" deal, but I can add that every 325-350 hp
Navajo breathes through a factory-installed air/oil sep. My guess
would be that these engines tend to be heavy-breathers. When they get
up there in hours, the oil stripe on the bottom cowl gets heavier, in
spite of the air/oil sep.

Was never of the mind to bypass one to see how much difference they
make. Cleaned the inside of them rather infrequently, usually at
mid-time (900-1000 hrs) and at TBO.

We ran the Navajo's at 11 qts after an oil change, usually keeping
them between 10 and 11 in service (dump in a qt when it get down
around 10). Actually, never really thought about the air/oil sep being
a factor in determining that level.

Only ever had one come up shy on TBO-catastrophic turbo failure w/oil
contamination. Don't think I coulda blamed that one on crud from the
ari/oil sep...

TC

Mike Rapoport wrote:

The oil level is about 1" higher and the case is highly conductive.

So, 1" times the circumference of the case is a fair bit of area and
with a highly thermally conductive Al case, that will reject additional
heat to be sure.


Matt

"Mike Rapoport" wrote in message nk.net...
More oil does not improve cooling. If you think about it, it makes sense.
Where would the additoinal heat go? Same oil cooler, same cooling fins,
same baffles producing the same airflow. The oil will actually be hotter
since the crank is going to contact the oil in the sump with 50% more oil.
Thats why the top 4 qts of oil is leaving through the breather in the first
place.

The oil will be somewhat cleaner since the same amount of contaminates are
dilluted by more oil. As a practical matter, you would probably be better
off with a finer oil filter than more oil. There is an article on oil
filters in Aviation Consumer this month that is worth reading.

Mike
MU-2
Helio Courier (arriving today!)


I'm convinced Mike is right about this. Fits in the same category as the
argument that
auto coolant works more poorly without the thermostat 'cuz it goes thru
the radiator "too fast" and doesn't cool properly.

Another triumph of math & science.

Bill Hale

So let me try a theory here.

The lack of positive crankcase ventilation for these
engines is really a bad feature.

A friend measured the PH of the condensate water on the oil dipstick
of an IO-520. PH was 2: Like nitric acid. Having that in
your crankcase is bad.

So why shouldn't we provide PCV by dumping the output of
the wet vacuum pump directly into the crankcase? On the
IO engines, I'd run it into the timing plug in the front.

Then I'd have the air-oil separator on the crankcase breather.

That would give several CFM of air douching the crankcase.

Now the problem is: How much moisture would be condensed out
of the breather air? A gallon/hour? An ounce/hour?

I've wondered if the Airwolf/Walker separator could be modified
so that the oil drain had about a 3/4" standpipe in it with a second
drain added for water that was flush with the bottom of the device.
Then the water could be drained during preflight. The oil would
decant back into the crankcase.

I know there are EPA considerations on this.

Just a thought. I think less corrosion would lengthen the
cylinder life. Bill Hale