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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 |
The Walker setups for Continental used to drain back through the #6 rocker cover.
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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. |
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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:
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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) |
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. |
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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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:
I am sure there are significant periods of negative pressure within the exhaust header: http://www.vansairforce.com/communit...t=92980&page=3 |
I get a 20-25F drop in water boiling point at cruise altitude.
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Why not just run the breather tube through the fuse all the way out to the back of the plane? :D
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