Soot on fuselage

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Charles
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Soot on fuselage

Post by Charles »

Despite replacing most of the exhaust fittings on my plane not too long ago, I get sooty streaks on the fuselage after every flight in heavy rain. No big deal, they come off with a wet rag. Is this normal or do I have an excessive exhaust leak somewhere?

Sorry that the plane is so dirty, I've neglected washing it for several months... :oops:

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Steve
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Re: Soot on fuselage

Post by Steve »

Charles: It looks like you have streaks on both sides, which makes a localized exhaust leak in one area less likely. I’ve never seen anything like that on my airplane, although I rarely fly in rain. Are there any “hot spots “ on the interior of the cowling that could point to an origin?
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Charles
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Re: Soot on fuselage

Post by Charles »

The long streaks are only on the left side starting from the side of the cowling (bottom picture) all the way to the back of the cabin (3rd picture). Soot oozes from the bottom rivets on both sides, but more so on the left side. There are no exhaust marks on the inside of the cowling but there is some evidence of exhaust leaking at some of the joints in the pipes. Mechanics says that's normal, but I suspect that's the source of the soot. I'll try to get a picture of that at some point.
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briankelly327
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Re: Soot on fuselage

Post by briankelly327 »

How are your cylinder temps? Curious if you have a baffle leak causing (wet) high pressure air to escape thru the cowl seams.
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Charles
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Re: Soot on fuselage

Post by Charles »

Cylinder temps are below 380 in cruise at 75% power. The baffles were re=done a few years ago so that's certainly something to look into, but I don't think the soot coming out of the bottom of the cowling (3rd picture) would be caused by a problem with the baffles?
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Re: Soot on fuselage

Post by Derek »

Wow that’s not right. Is it a diesel or 100ll engine? Could it be spilled oil or an oil leak from a gasket or poorly fitting sump plug or something? Fwiw my 100ll burning da40 doesn’t do that at all and I fly through a lot of rain.
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Re: Soot on fuselage

Post by Karl »

It looks like chaffing of loose rivets, worn or loose cowling fasteners and chaffing from the cowling itself.

Also called smoking or fretting.

https://youtu.be/tQ11iHO0dVI
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Steve
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Re: Soot on fuselage

Post by Steve »

I initially thought smoking rivets as well, but those rivets are not structural, and only affix the internal heat shields to the cowling. Plus, the same black effluent is visible in areas where there aren’t any rivets.
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Karl
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Re: Soot on fuselage

Post by Karl »

Steve wrote: Wed Oct 06, 2021 2:16 pm I initially thought smoking rivets as well, but those rivets are not structural, and only affix the internal heat shields to the cowling. Plus, the same black effluent is visible in areas where there aren’t any rivets.
If they are structural or not makes no difference. If they are loose they will fret and produce black streaks.

Black streaks in other areas can be cowling fasteners or the cowling itself.
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Steve
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Re: Soot on fuselage

Post by Steve »

Karl wrote: Thu Oct 07, 2021 1:34 am
Steve wrote: Wed Oct 06, 2021 2:16 pm I initially thought smoking rivets as well, but those rivets are not structural, and only affix the internal heat shields to the cowling. Plus, the same black effluent is visible in areas where there aren’t any rivets.
If they are structural or not makes no difference. If they are loose they will fret and produce black streaks.

Black streaks in other areas can be cowling fasteners or the cowling itself.
True, but on non-structural fasteners, not subject to repeated stress loading, loosening and smoking is less common. Plus, all of those pop rivets being loose...
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