Black Streak under Wing

lr172 · #1 04-30-2017, 03:34 PM

Today I noticed some black streaks running back from the spar area under the right wing on my 6A. It looks like classic aluminum fretting residue, but not sure what could be rubbing in there. It is coming from the seam where the fuel tank attaches and goes backwards. It is w

Tonight I will pull the fairing strip at the wing root and see if I can spot anything with a flashlight and magnet.

Any ideas what this could be from or common issues like this? I would assume a simple fuel leak would leave blue streaking and not black. Though I suppose fuel could be the way the black is working out. This is a new issue at 300 hours.

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Thanks for any thoughts or ideas on this.

Larry

terrykohler · #2 04-30-2017, 04:20 PM

A very slow fuel leak. Speaking from experience, waiting for some steady, warm weather to get at mine.
Terry, CFI
RV9A N323TP

Pmerems · #3 04-30-2017, 04:46 PM

Just another guess. Hope not, but I have seen Proseal soften and get rather gummy in some cases.

lr172 · #4 05-01-2017, 07:43 AM

Thanks for the input here. My first thought was fuel as well, but struggled to understand how it turned black. I suppose the leak could be pretty slight and it is picking up junk as it flows around before exiting.

I'll post an update once I can confirm what is happening.

Larry

Snowflake · #5 05-01-2017, 07:53 AM

That's what my fuel leak looked like until it got bad enough that the volume of fuel outweighed the volume of dirt particles carried by it... :/

Vlad · #6 05-01-2017, 08:00 AM

Could be just a mix of oil,fretting and brake dust. Add some dirt/rain and you get something like these swirls.

lr172 · #7 05-01-2017, 08:08 AM

Quote:

Originally Posted by Snowflake

That's what my fuel leak looked like until it got bad enough that the volume of fuel outweighed the volume of dirt particles carried by it... :/

That's what I was thinking this morning. Good to know your experience to help me confirm it.

Larry

lr172 · #8 05-01-2017, 08:15 AM

Quote:

Originally Posted by Vlad

Could be just a mix of oil,fretting and brake dust. Add some dirt/rain and you get something like these swirls.

Thanks Vlad. that's a good thought. I haven't flown in the rain recently and can't think of how I would have gotten water in there within the last few flights.

Larry

ChiefPilot · #9 05-01-2017, 11:07 AM

Quote:

Originally Posted by lr172

Thanks Vlad. that's a good thought. I haven't flown in the rain recently and can't think of how I would have gotten water in there within the last few flights.

Larry

Many receipts from cash registers will turn color when exposed to gasoline or avgas. Tape such a receipt under the wing in the area of the suspect leak - if it turned color, that's a reasonable confirmation of a fuel leak and if it did not then the cause is likely something else.

pa38112 · #10 05-01-2017, 01:09 PM

Quote:

Originally Posted by lr172

Thanks Vlad. that's a good thought. I haven't flown in the rain recently and can't think of how I would have gotten water in there within the last few flights.

Larry

That trail is being formed by liquid. If you have not flown in the rain, nor washed the plane recently then you must have a fuel leak.