RV-8 engine oil in my fuselage

I'm on the injured list right now, ie, can't fly my own airplane. So an RV 8 buddy offered to take my 8 out to keep the engine and oil limbered up. A few weeks ago, the owner of my hangar called and said "Hey Don, why are there "pools" of oil underneath your fuselage on the hangar floor"? WHAT!! So out to the hangar to check---sure enough, literally pools of oil on the the hangar floor and all over the bottom of the aircraft. Well, the oil filter adapter had just been off from my mechanic, so, of course I thought big oil leak. The mechanic checked all over the engine compartment including the filter adapter and said "No oil leak"

Had my buddy done any acro, particularly negative G's the mechanic asked? ( No inverted oil system installed) Yep, nothing negative, but loops, spins and hammerheads. The mechanic said he thinks big slugs of oil were coming out of the breather tube. (Oil had been 5.9 qts before flight, was now 4.2 qts after flight)

Told buddy and he flew it again a few days later. Did only 2 rolls. Heck, I always do a couple of rolls every time I'm out. A few days after that I went to check for oil again. Still some smaller pools on the floor, but this time, only by the tailwwheel. Nothing on the bottom of the fuselage. Cleaned up the floor and area by tailwheel. Then the plane didn't fly for a week. Went out tonight looking for oil, and sure enough, a small puddle by the tailwheel, and some dripping of a radio antenna mast on the bottom center of the fuselage. ( The 2ed oil on the floor was apparently still oozing out from the first flight, and not a result of the 2ed flight)

SO-o-o-o, we got the wall out from in back of the aft baggage compartment, to look down inside the fuselage, and sure enough, still a bunch of oil on the bottom of the fuselage on the "inside" So my question is, how the heck does engine oil get on the inside of my fuselage One would think that if oil came out of the breather, the slipstream would carry it away. Is it possible that 1.7 qts of oil could be driver into teensie little holes in the fuselage ( about where the wing is) and then along the bottom inside all the way back to the tailwheel?? Who's the aeronautical engineer, is it Kevin Horton? Would he know what the air is doing here (on the bottom of the fuselage right behind the engine compartment) Or has my 8 developed some really unique kind of oil leak.

Sorry this is so long, but no other way to explain it. ( Not a builder)

Same thing

I had the same issue, went slightly negative recovering from a botched loop (1st one this plane) and dumped a 1/2 qt of oil. I had oil on the belly and inside the fuselage floor all the way back to the tail.

My theory is that it entered by the aft corners of the exhaust ramp. I pro sealed the side to help prevent cracking put left the corners open in order to allow moisture to escape.

I washed down the inside with mineral spirits. There was oil in between the front floor sections and every flight I get oil at the aft edge rivet line where the double floor becomes a single floor. This decreased with time, but I still get a tiny bit after a longer flight.

So I would say a big slug of oil came out and some made its way to the inside.

Cheers

oil in fuselage

If you lose oil out the bottom I think that is normal. I have a smoke system and I don't have to worry about rust in the tail cone. Smoke oil is back there dripping on the hanger floor every time it's used.

I also don't know how it gets in to the fuse, but I suspect that the hammerheads are how it got out of the engine. Once you get the oil someplace, it takes a LONG time for it all to get out. A teaspoon full of oil can look like a major oil spill when it spreads out over the belly.

From your description Don, I'd say you have a well-known annoyance, but nothing to worry about (if you were worried about it).

IF this were MY airport, I would be looking around at my fellow pilots to see who looked the most guilty. Seriously, the B*s***ds have been known to pour oil under an aircraft just for fun...

As far as controlling the oil, try a AntiSplateAero oil seperator. I switched to one about a year ago and its actually helped.

wera710 said:

IF this were MY airport, I would be looking around at my fellow pilots to see who looked the most guilty. Seriously, the B*s***ds have been known to pour oil under an aircraft just for fun...

As far as controlling the oil, try a AntiSplateAero oil seperator. I switched to one about a year ago and its actually helped.

Click to expand...

+1 on the Anti-Splat Oil Separator.

I'm still of the notion that its not from the breather tube at all, but rather some sort of very strange leak Anybody got any ideas in that direction?

Same here too.

donaziza said:

I'm still of the notion that its not from the breather tube at all, but rather some sort of very strange leak Anybody got any ideas in that direction?

Click to expand...

I had the same puddles under each fuselage drain hole. I worried in the same direction as you after acrobatics for the first few times. But my new plane's FWF was clean as before. It had to be coming through the breather, then sucked up into the fuselage through drain holes. I pulled seats panels and found no oil forward of the pilot seat. Full Christen system solved the problem.

BruceEicher said:

I had the same puddles under each fuselage drain hole. I worried in the same direction as you after acrobatics for the first few times. But my new plane's FWF was clean as before. It had to be coming through the breather, then sucked up into the fuselage through drain holes. I pulled seats panels and found no oil forward of the pilot seat. Full Christen system solved the problem.

Click to expand...

Bruce, What's a FWF?

donaziza said:

Bruce, What's a FWF?

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Fire Wall Forward, under the cowl, engine compartment, place where big noise and wind is produced...and some oil.

I let my friend run my 7 hrough the aerobatic portion of testing, all the various basic aero maneuvers (spins/loops/Immelmens/humpty's/clover leafs/split S/Cuban 8/hammerheads) and +6/-1 G's (no inverted systems and carb). The engine actually quit on the hammerheads. I gave the airplane to him with 6.5 quarts of oil and he returned it an hour later with 3 3/4 quarts. I cleaned the airplane/FWF/belly etc the next day and I'm still finding oil by the rudder and tailwheel 30 hours later.
I've found that I won't lose much/any oil out the breather doing loops and rolls, but anything that starts flirting with >1 G burps it out pretty quick.

As others have stated, it only takes a very short time at close to 0 G to get oil in the breather tube. It will then take several hours of flight time for all the oil to work its way out.

When I was flying my -8, I hated a dirty belly more than I enjoyed the aerobatics. My rolls were always barrel rolls and my loops were egg shaped to maintain at least 1/2 G at the top. I still has some oil on the belly at times.

FYI, I had a strait breather tube with no separator.

Karl

RVG8tor said:

I had the same issue, went slightly negative recovering from a botched loop (1st one this plane) and dumped a 1/2 qt of oil. I had oil on the belly and inside the fuselage floor all the way back to the tail.

My theory is that it entered by the aft corners of the exhaust ramp. I pro sealed the side to help prevent cracking put left the corners open in order to allow moisture to escape.

I washed down the inside with mineral spirits. There was oil in between the front floor sections and every flight I get oil at the aft edge rivet line where the double floor becomes a single floor. This decreased with time, but I still get a tiny bit after a longer flight.

So I would say a big slug of oil came out and some made its way to the inside.

Cheers

Click to expand...

I washed down the inside with mineral spirits. There was oil in between the front floor sections and every flight I get oil at the aft edge rivet line where the double floor becomes a single floor. This decreased with time, but I still get a tiny bit after a longer flight.

Hi Mike, Just read you reply about the mineral spirits. How did you do this? Did you put the mineral spirits in a pump sprayer and then spray the floor of the aft fuselage as best you could reach? A sponge attached to the end of a long pole perhaps?

I have clean oil under the floor of my RV-8A, all the way aft from the pilot's seat back to the tail - can't figure out how it got there. I first noticed it from little oil drips on the hanger floor under/near seams, and when I disassembled the plane to install its avionics MLU, I found a film of oil in the belly. I don't fly aerobatics. At first, I thought the previous owner may have spilled oil from a spare quart in the front baggage compartment. But after reading this thread, I am becoming suspicious. I *believe* the builder installed an oil breather / separator high on the firewall - it's a black oil filter shaped can with several hoses attached. No labels on it. One of the attached hoses dumps overboard, routed down the firewall and porting whatever through the exhaust opening in the cowling. Yesterday, I did find a hole in that hose where it rubbed against a structural member - now I'm thinking that is the source....?

After a couple thousand hours in my 8, I can attest that without an inverted system you will get oil in the fuselage if you do hammers, negative, or zero g stuff.

Heck, I have an inverted system and I still get a little. Going from inverted to inverted when practicing slow rolls that stuff still finds its way out of the engine.

As to running down the fuse floor, don't know how it knows, but it does. I think the Thermos folks invented the system. It just know..

I love acro, and cleaning!

Oil in the Fuselage

I had my rear baggage floor off for annual and found a thin stream of oil going back. This thread helps me see that it is not all that unusual. I prosealed the front of the fuselage bottom skin components but don't think I prosealed the junction of the rear tail skin with the mid fuselage. That seems to be where the oil is sneaking in. Anyone with ideas about how I might seal that joint?

Right now, it's full of oil. Can't imagine how I could get it clean enough to effectively seal. Shame aerobatics are so much fun....

Pressure!

The air inside the fuselage and tail cone is at a much lower pressure than the air flowing past outside. The pressure delta effectively creates a vacuum inside the tail cone which sucks in the oil flowing on the belly when it tries to cross the fay seams.