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11-20-2012, 07:40 PM
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Join Date: Aug 2009
Location: Redding,Ca
Posts: 633
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3 points
Without meaning to convert anyone one way or the other Id like to make 3 points on this discussion:
1.When a separator is used on certified aircraft they drain back to the sump.
2.When I installed a separator on my Cozy I did before and after oil anylisis specifically asking Blackstone labs about any moisture or acid problems with the oil. The result was negative.
3. Many guys will point to the nasty stuff in their catch can. My opinion on this is the drain from the separator passes both oil and gasses into the catch can. There should be no surprise then the combustion gasses cooled and condensed into a little can will smell and look bad.
I suspect if the catch can were sealed and vented back to the crankcase there would be far less or no "stuff" in the can.
FWIW
Tim
Last edited by tim2542 : 11-20-2012 at 08:03 PM.
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11-20-2012, 08:45 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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The Walker setups for Continental used to drain back through the #6 rocker cover.
__________________
Actual repeat offender.
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11-21-2012, 02:03 AM
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Join Date: Dec 2006
Location: Coventry. England
Posts: 614
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Air oil separator
Several years ago I got into my only serious argument with my Inspector on this subject. I fitted a one to my Tailwind and asked him where I should return the oil back to the engine. He came up with the returning nasty stuff to the engine argument and juts wanted me to vent it overboard or into a catch can.
Well was was the point of fitting it I argued, his response was to say there is no point and I should take it off.
In a previous life I was a mechanic, and one of the reasons gaskets used to blow on some car engines was because the crankcase vent tube used to block with a creamy sludge discharged from the engine, pressurising the crankcase Water droplets would also drip out, so I was well aware of the crud that can come out of a crankcase vent...... what appears to be an oil water suspension.
However, my take on this is. Often the vent tubes on these engines were quite long giving ample time for the gasses to cool and condense on the sides of the tube. Over time this builds up and accelerates leading to the sludge that filled to tube.
What we are fitting to our aeroplane engines is an air oil separator, which is designed to do just that. Secondly, if we keep the tubes to the separator short there is less chance of condensing in the tube forming that suspension. This is relatively easy on a Lycosaurus.
Over time though they can block if not cleaned out, ours did on the Tailwind so they mus be cleaned and say every 50 hours.
Do I have one on my 4, Yes! Oil on the belly is only making a mess, an engine without oil is a dead stick landing and a hefty rebuild bill. Providing the oil is changed regularly there should be no problem, but you have to check these things to make sure they dont block up over time.
__________________
http://www.aerobuilder.blogspot.com
Steve Arnold
England
In completion stage of Loehle P5151
Built and now Flying G.BVLR Vans RV4
Rebuilt G.BDBD Tailwind
Rebuilt G BVTN Kitfox
Built G CDCD RV9A with WAM120
Riveted wings on Glastar G.LEZZ Now (G. SKUA)
Last edited by WAM120RV : 11-21-2012 at 02:06 AM.
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11-21-2012, 07:14 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by erich weaver
... just because the breather system is not designed to cool doesnt mean that it doesnt occur. In fact, it almost certainly IS occurring, wouldnt you agree?
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In some installations, yes. Mine, not much. Remember, I'm the guy with a pair of roaming temperature sensors inside the cowl.
I'm also operating the separator/evacuator at 2"~3" Hg less than atmospheric, a slight reduction in boiling point which helps. The pressure is more or less constant all the way to the exit at the reed valve. I say more or less because in practice it oscillates slightly at some multiple of firing frequency; the reed valve is not perfect.
Which is all neither here nor there. Consider comments from Tom and Tim regarding examination of the drainback oil. Nothing like observation, test, and measurement.
Quote:
Originally Posted by Snowflake
And after 30 minutes of flight, you'd be hard pressed to find any water in your engine at all... Until you shut down, let fresh moist air in, and let it cool.
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Outside air can't readily enter my breather, as the only port to the atmosphere (via the #4 exhaust header) has a reed valve. Since internal pressure must equalize with external after cooling, it would enter via the intake tract. Is there a difference? I dunno.
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For the most part, what comes out your breather will be one of two things: First, overspray of the liquids, and "breathing" in and out of the gases, just from the mechanical splashing around that goes on inside.
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I doubt there is any respiration in and out. It's just out. The driver is combustion gas leaking past the rings. The breather is just another exhaust port, low volume as compared to the others but an exhaust port none the less. What comes out the breather is the same as what comes out the exhaust pipe, with the addition of suspended oil droplets.
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Dan Horton
RV-8 SS
Barrett IO-390
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11-21-2012, 08:28 AM
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Join Date: Jan 2007
Location: Battleground
Posts: 4,348
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2300+ hours on my 0320 in the Bucker with the Christen system. If it is returning contaminants in the oil, my engine must like em.....
Sadly, my 6 has a dirty belly. I think I might win the dirty belly contest right now. I clean it once a year whether it needs it or not 
(ok, maybe twice a year)
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Smart People do Stupid things all the time. I know, I've seen me do'em.
RV6 - Builder/Flying
Bucker Jungmann
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.
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11-22-2012, 12:36 AM
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Join Date: Aug 2009
Location: Redding,Ca
Posts: 633
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And the verdict is?
Dan
Could you please share any performance or other improvements you have seen with your crank case evac system?
I'm running Allan Nimo's separator and have been thinking of adding the exhaust and check valve.
I understand the reduced boiling point benefit, but Allan also claims ~8 HP on a 0-360 using crankcase evacuation. I would expect this can change dramatically depending on the exact placement and angle of the probe.
A local RV guy has found a Jegs threaded fitting that will allow easy changes to the exhaust probe to allow experimentation with angles without welding each time.
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11-22-2012, 06:17 AM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,687
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The biggest problem with oil seperators in my opinion is many folks install them to "cover up" engine problems (excessive oil consumption).
A good running engine that uses less than a qt of oil every 10 hrs will not benefit from and doesn't need a seperator.
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Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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11-22-2012, 09:33 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by tim2542
Dan
Could you please share any performance or other improvements you have seen with your crank case evac system?
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Not enough run time to make any specific claims about this Lycoming installation other than a bone dry belly.
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I understand the reduced boiling point benefit, but Allan also claims ~8 HP on a 0-360 using crankcase evacuation.
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The boiling point reduction isn't a lot, 4~5 F, but I'll take it.
Case evacuation should increase HP. How much? I'd prefer to see a dyno printout for a Lycoming. What little raw dyno data I've seen for V-8 race motors would have me expecting less than the above 4%. I'd be delighted to be wrong. There is potential because a 4-cyl flat motor has a significant case pumping issue. It forces air volume equal to its displacement through the limited passage area in the center bearing web with each revolution....back and forth, back and forth. Any reduction in air density is a plus.
Quote:
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I would expect this can change dramatically depending on the exact placement and angle of the probe. A local RV guy has found a Jegs threaded fitting that will allow easy changes to the exhaust probe to allow experimentation with angles without welding each time.
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A quick experiment leads me to think the angle of the probe end does not have much effect on the level of vacuum generated. Again, I shall remain cheerfully open minded on that point...show me the numbers.
I am sure there are significant periods of negative pressure within the exhaust header:
http://www.vansairforce.com/communit...t=92980&page=3
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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11-22-2012, 10:25 AM
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Join Date: Apr 2009
Location: USA
Posts: 1,499
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I get a 20-25F drop in water boiling point at cruise altitude.
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Good judgment comes from experience, and a lot of that comes from bad judgment.
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11-22-2012, 01:56 PM
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Join Date: Jul 2012
Location: Western US
Posts: 98
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Why not just run the breather tube through the fuse all the way out to the back of the plane? 
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