Alternative Oil Breather

I have read all the postings about oily belly's, high consumption/waste and separators. I had my hand on my wallet for a separator but 100's of dollars and the installation stalled me. So I started thinking about the physics and the function of the breather and came up with something that was easy, functional and so far is doing just what it's supposed to. The filter is local auto parts store manifold breather, the brass fitting is from hardware store, I had to buy a new pre-bent flex hose at the same parts store, because the Van's original had already been cut too short (per the plans).
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Good looking installation there Bud!! Please keep us updated about the "oily belly" status.
I regularly go underneath to dutifully inspect and looks things over; but I really dislike having to go under to clean off oil film.
I have some neighbors building RVs and its always good to have problem solving options.

Cheers,

A couple of issues that you might consider

If you have any intentions of going upside down once in a while that little filter will get saturated with oil. This would lead to an oily firewall which would be far more messy then an oily belly.
By mounting the breather in what is effectively the lower plenum pressure area you are pressurizing the crankcase to that level of pressure, which is higher then the pressure surrounding the airplane. This has the potential of creating minor leaks around your engine as well as robbing a bit of horse power from your engine.
Keep checking the filter and report back.

I think you are going to have an oily mess in your cowl area, if you don't it probably means you are adding pressure to your crankcase as mentioned in the previous post. Let us know what you find.

The upside-down problem is a result of the breather located at the lowest point of the case when the airplane is upside down. Perhaps if one were using electronic ignition and had one of the mag holes covered the the whole thing could be built into the mag hole cover, no firewall mounting required...then just plug the existing breather...maybe a standpipe on the inside pointing down and to the side to prevent oil from entering...hmmm.

Radiator hose?

It looks like your hose is a regular coolant hose, if so it may not last long. Oil will swell regular coolant hoses.
Also I'd be concerned about the filter plugging with oil and moisture from the engine, there is not a lot of area in that filter. Do you plan to clean it?
Tim

I would have a problem with that rubber not being compatible with oil. It will soften and break down from the inside.

A better choice would be clear tubing from ACE hardware. All around stronger..... and oil compatible.

If plugging the filter is a concern, a whistle slot in the hose would take care of any potential case pressurization problems.

One of the issues I noticed when I ran a test with a firewall mounted collection can was the smell of oil in the cabin. I was testing to see how much oil I was venting overboard in the breather line, which was suprisingly very little. The fumes seemed to exit the cowl along the hinge line and then were picked back up by the NACA vents. (Phew!) My firewall is completely sealed and I get no other smells from the engine. Your system might do the same thing although only a live test will prove/disprove this.

The radiator hose grades are not suitable for breather line installations. The rubber will become saturated after a while and become oily on the exterior. I used aircraft MIL-6000 grade hose and have had good luck with it.

As Joe Blank pointed out, the cockpit will smell like hot oil. My concern, although unlikely, is what happens if you do get a lot of crankcase pressure from a failure like a piston or piston ring issue. The vented pressure and a lot of oil is going to be released at the top of the firewall and run down to the (very hot) exhaust system along with some exiting the rear of the cowl probably getting on the windshield.. One does not need an oil fire to go along with an engine failure.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

I have found that the location of the NACA vents inline with the cowl split will does have an effect on smells. Several years ago the GAMI folks had a video of a V35 Bonanza where they tufted the inside of the cowl and found that some of the air flows forward along the crankcase. In both my RV-6 and the one I fly now it can be in the dead of winter, 20 degrees OAT and warm air will come thru the NACA vents. So really this is a problem related to the NACA vent location, not necessarily the breather exit.

I overhauled a 300hp angle-valve 540 a couple of years ago that had two cylinders with broken rings and did not find any appreciable amount of liquid oil flowing from the breather tube or on the belly. When I pulled the cylinders pieces of the rings fell on the floor.

What I suspect here is since the breather hose is uphill the oil mist is settling on the walls of the hose and flowing back into the engine.

Also for the record I've found that there are two different types of blow-by. Crankcase blow-by due to windage in the case and valve blow-by where excessive guide wear causes oil to be sucked into the combustion chamber and burned. Either way a drop every few revolutions adds up to appreciable oil consumption numbers.

Many new automotive engines have windage trays and so do the 300hp 540's. The tray is there to reduce foaming and adds extra area for oil to settle on.

Bob, I was thinking more of a worst case scenario like a major detonation event. You are right, simple broken rings won't add much crankcase pressure. I have witnessed a piston failure like this in an IO360, but it took an ugly set of circumstances to get to the failure. Sure did blow the oil out the vent though.



John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

Like Joe said, MIL-6000 is good, a lesser expensive alternative is industrial spec 100R6 hose. It is oil resistant, but doesnt like a sharp bend radius. IF you have use a molded hose for routeing purposes, try a silicone heater hose---if you can find them. Ultimate would be convoluted teflon.
Tom

Just terminate breather line above exhaust pipe-----my RV-8 has had it for 15 yrs.----works well, lasts a long time---John Fleurent----RV-8(SKY GODDESS) First flight 1998

Gum Creek

Hey John.....thread jump for a second.........saw some guys over the weekend at Gum Creek Airport in Roopville Georgia that knew you. A great morning for me.

David Watson
49FD

Alt Breather-Some Results

Thanks for all the thoughts and hope someone has DATA for a couple questions that have now surfaced:

-The hose is a temporary solution and will be replaced.
-The filter is bone dry.
-I also believe the oil misty air is slowing down in the hose with the filter allowing free flow and the oil condenses and drips back to the breather port.
-There has been no leakage detected.
-The underside is not oily.

Does anyone have measured delta pressure data for my filter location and various point around the engine, i.e. on top where cooling flow enters, near the oil sump, near exhaust pipe exit? The idea that my filter location is high/higher pressure is worth investigating. Based on my experience and what is reported as normal budging oil doors, the volume between the FW and engine is certainly higher than free stream. Wonder if it gets lower, like free stream at the cowl exit without Dan H. mods for exit area reduction?

John Clark said:

Bob, I was thinking more of a worst case scenario like a major detonation event. You are right, simple broken rings won't add much crankcase pressure. I have witnessed a piston failure like this in an IO360, but it took an ugly set of circumstances to get to the failure. Sure did blow the oil out the vent though.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

Click to expand...

.... I had an acquaintance, Dave Rotundo that had tried a vent setup much like this. His engine developed a major piston problem like you picture in your post from excessive hours, poor upkeep or ?. His engine started to miss and blow copious amounts of oil out of the breather, depositing it inside the engine bay, on the engine and hot exhaust system. This in turn created lots of flammable smoke inside the cowling that burst into flames on final. He escaped with very serious burns, but his flying days were over and the plane was a total loss. Be very careful with anything that could possibly cause or promote an in flight fire. Thanks, Allan...

dbuds2 said:

Thanks for all the thoughts and hope someone has DATA for a couple questions that have now surfaced

Click to expand...

Bud, the lower plenum (including the upper firewall area) is above freestream pressure. I can't tell you exactly how much with your cowl but I can tell you how to measure if you really want to know.

Here are pressure values taken with a smaller-than-stock RV-8 cowl exit (but not as small as the one I use now). All pressures in inches of water:



A healthy Lyc might have a breather pressure in the 1" to 5" H2O ballpark, so yes, you are probably running a higher than normal case pressure.

I think comments about the possibility of dumping oil into the cowl following piston failure are valid. I'd want it breathing overboard somehow.

PerfTech said:

. His engine started to miss and blow copious amounts of oil out of the breather, depositing it inside the engine bay, on the engine and hot exhaust system. This in turn created lots of flammable smoke inside the cowling that burst into flames on final. He escaped with very serious burns, but his flying days were over and the plane was a total loss.

Click to expand...

Off topic question, my apologies. Allan, do you happen to know if the fire burned through the floor, or did it heat something on the cabin side of the firewall to the ignition point, or perhaps this was an open cockpit airplane? How did an engine compartment fire get to the pilot?

Gave up-Oil Separator

My home grown system did about the same as the stock breather system, it allowed the oil vapor to breathe but eventually the filter was saturated and then oil mist on the firewall.

Just installed the complete Anti-Splat system with the clamp on check valve. Can't wait to be able to run more than 4 quarts without it blowing out the vent. Got lucky and was able to drill the exhaust without removing the lower cowl.