Wing Skin Crack?

[Chuck Balogna]

I have two spots under the wing-walk where a little bit of fuel tends to seep when topped off.

one is very obviously a bad seal around a panel. The one closer to the fuselage is more concerning.

it doesn’t appear to be in-line with any rivet or seam lines.

My A&P (who is not a Mooney guy), has warranted concerns about spreading and it’s proximity to the spar.

wondering if anybody here has experience with leaking in this area.

photos attached.

[N201MKTurbo]

It is a common problem. It is leaking at a screw. That cover plate has two stiffeners because it is walked on. There are screws at the ends of the stiffeners. Your leak is at one of those screws. 
 

Most have had good results from removing the screw and coating the screw with sealant and replacing the screw.

[LANCECASPER]

40 minutes ago, Pillows said:

I have two spots under the wing-walk where a little bit of fuel tends to seep when topped off.

one is very obviously a bad seal around a panel. The one closer to the fuselage is more concerning.

it doesn’t appear to be in-line with any rivet or seam lines.

My A&P (who is not a Mooney guy), has warranted concerns about spreading and it’s proximity to the spar.

wondering if anybody here has experience with leaking in this area.

photos attached.

 

[PT20J]

Here’s the location of the cover under the wingwalk.

[Chuck Balogna]

Wow, you guys were fast on that. Thanks for the info and re-direct. Makes me feel better knowing it's unlikely to spread or cause issue. 

[Ragsf15e]

5 minutes ago, Pillows said:

Wow, you guys were fast on that. Thanks for the info and re-direct. Makes me feel better knowing it's unlikely to spread or cause issue. 

And even better, that one’s an easy fix!

[OR75]

you know what the painful parts will be ?

getting the wing walk compound off (without damaging the white paint) and emptying the tank

all downhill from there (I just went through that)

and while you are at it, change the fuel drain to a new one and check that the lower panel is sealed (the large one by the fuel drain) 

 

[OR75]

[Ragsf15e]

56 minutes ago, OR75 said:

you know what the painful parts will be ?

getting the wing walk compound off (without damaging the white paint) and emptying the tank

all downhill from there (I just went through that)

and while you are at it, change the fuel drain to a new one and check that the lower panel is sealed (the large one by the fuel drain) 

 

What?  No!  Emptying the tank is the fun part!  Go fly it and get some training in!  But you’re right about the wing walk removal and reapply being painful.

If you can isolate to just one or a couple screws, people have good success pulling the screw, putting fuel sealant on it and retightening.  If it’s more than a screw or three or out a seam, that’s a little more work…

Edited October 3, 2023 by Ragsf15e

[MikeOH]

Why is it necessary to empty the tank if you are going to rework the seal/screws on a TOP cover plate?

What am I missing?

[Hank]

The same thing that I am . . . . . . .

[EricJ]

2 hours ago, OR75 said:

you know what the painful parts will be ?

getting the wing walk compound off (without damaging the white paint) and emptying the tank

You don't need to empty the tank, or even drain it much, and the wingwalk is easy to remove on the screw with a small steel pick.

It helps if the tank isn't full and below the level of the screw, but sometimes that isn't even necessary.

The only wing walk material that needs to be removed is that attached to the screw head, so a little pick that just digs out the cross for the philips screw bit and then pops the wing walk material off the screw head only, allows the screw to be removed for sealant (e.g., Permatex 3) to be applied to the screw.  

After the repair it's only necessary to reapply wing walk to the top of the screw.   The stain will remain, but can be covered with a light coat of the wing walk material if desired.

https://web.archive.org/web/20190103195252/http:/donmaxwell.com/fuel-tank-repairs-how-we-fix-them/

[N201MKTurbo]

A little black paint with a brush does wonders. If you mask the whole thing and hit it with a roller it will look brand new. Spray paint works good too, but you should throw a drop cloth over the whole plane.

[OR75]

12 hours ago, MikeOH said:

Why is it necessary to empty the tank if you are going to rework the seal/screws on a TOP cover plate?

What am I missing?

Because it looks like the panel is also leaking on the left side in the first picture and that’s not just a screw . 

[MikeOH]

37 minutes ago, OR75 said:

Because it looks like the panel is also leaking on the left side in the first picture and that’s not just a screw . 

So? Even if that’s not a screw but the panel itself(looks like #10 in PT20J’s posted diagram) I still see no reason to drain the tank.

If you’re thinking the skin is cracked and needs rivets drilled to R&R a skin….then, yeah, I guess you would drain the tank.

You said you’d just been through this. A leaky top panel/screw or something else that necessitated draining your tank?

[OR75]

39 minutes ago, MikeOH said:

So? Even if that’s not a screw but the panel itself(looks like #10 in PT20J’s posted diagram) I still see no reason to drain the tank.

If you’re thinking the skin is cracked and needs rivets drilled to R&R a skin….then, yeah, I guess you would drain the tank.

You said you’d just been through this. A leaky top panel/screw or something else that necessitated draining your tank?

no , the skin is not cracked and no need for riveting.

at this stage, the OP does NOT have to do anything (no leak), but if he wants to fix the eyesore, might as well fix both area where the sealant is failing (the screw on the right and the curved part of the panel on the left)

removing the panel will make some sealant pieces / crumbs fall in the tank/fuel (and personally I would not like that even if there is a filter at the fuel pick up. but thats just me)

Of course, the OP can also simply take care of the biggest eyesore (the screw) with simply removing a little bit of the wing walk  

[N201MKTurbo]

I got a clean used oil drum (it actually had some plastic precursor that is used to make glue). It was very clean with no residue. I got a drum pump from Harbor freight. If you put a hose on the pump and crank it backwards, it will suck all the fuel out of the tank in short order. It will get all but about 4 gallons out. Then just remove the fuel sump drain to drain the remaining into a bucket. I got a giant galvanized funnel from the Tractor Supply to pour the bucket gas into the barrel. It takes about 10 minutes to drain the tank start to finish. The drum, pump and funnel cost about $50.

[N201MKTurbo]

4 minutes ago, OR75 said:

no , the skin is not cracked and no need for riveting.

at this stage, the OP does NOT have to do anything (no leak), but if he wants to fix the eyesore, might as well fix both area where the sealant is failing (the screw on the right and the curved part of the panel on the left)

removing the panel will make some sealant pieces / crumbs fall in the tank/fuel (and personally I would not like that even if there is a filter at the fuel pick up. but thats just me)

Of course, the OP can also simply take care of the biggest eyesore (the screw) with simply removing a little bit of the wing walk  

Not to pick nits, but the OP's cover plate sealant probably isn't failing, it was probably assembled with insufficient sealant and there are voids in the sealant. The screws at the end of the stiffeners should have a dab of sealant applied around the screw holes. It is sometimes overlooked.

[OR75]

1 hour ago, N201MKTurbo said:

Not to pick nits, but the OP's cover plate sealant probably isn't failing, it was probably assembled with insufficient sealant and there are voids in the sealant. 

yes, usually happens if either the panel or skin is even slightly warped leaving a channel for the fuel.

It does not make the fix trivial. Adding sealant on top will look ugly for sure (and not necessarily fix the issue)

only other option is to remove the panel     

[EricJ]

Just now, OR75 said:

yes, usually happens if either the panel or skin is even slightly warped leaving a channel for the fuel.

It does not make the fix trivial. Adding sealant on top will look ugly for sure (and not necessarily fix the issue)

only other option is to remove the panel     

It looks like what is happening here is just a leaking screw with the seeped fuel following a seam.   If the leak was beyond the screw the stain would likely be propagating out more from the seam.   One can never say for certain, but the easiest thing to do would be to seal the screw and see if the stain stops propagating.

[PT20J]

4 minutes ago, EricJ said:

It looks like what is happening here is just a leaking screw with the seeped fuel following a seam.   If the leak was beyond the screw the stain would likely be propagating out more from the seam.   One can never say for certain, but the easiest thing to do would be to seal the screw and see if the stain stops propagating.

Good advice. Always try the easiest fix first. 

[N201MKTurbo]

1 hour ago, OR75 said:

yes, usually happens if either the panel or skin is even slightly warped leaving a channel for the fuel.

It does not make the fix trivial. Adding sealant on top will look ugly for sure (and not necessarily fix the issue)

only other option is to remove the panel     

I always straighten the wing skins before I replace the panels. Some small wood blocks, vice grip clamps and a little hammering with the wood blocks, usually gets it done without screwing up the paint. They get warped by not thinning the sealant enough.

[OR75]

4 hours ago, EricJ said:

It looks like what is happening here is just a leaking screw with the seeped fuel following a seam.   If the leak was beyond the screw the stain would likely be propagating out more from the seam.   One can never say for certain, but the easiest thing to do would be to seal the screw and see if the stain stops propagating.

certainly a cheap fix to try but my bet is that if it was a seep, we would see streaks rather than that pattern   

[EricJ]

4 hours ago, OR75 said:

certainly a cheap fix to try but my bet is that if it was a seep, we would see streaks rather than that pattern   

That's a pretty typical stain for a leaky screw.   It's staining the wing walk material from underneath, and apparently it absorbs it so it just propagates out like that.   It's pretty common.

[OR75]

4 minutes ago, EricJ said:

That's a pretty typical stain for a leaky screw.   It's staining the wing walk material from underneath, and apparently it absorbs it so it just propagates out like that.   It's pretty common.

The one on the right in the picture (close to the door ) is. The curved one on the left is not .