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AL-EAS

C-130H FS 477 Ext. Skin

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AL-EAS

Hello,

I'm new to this lovely website and forum, I found that quite a lot of you here are quite knowledgeable ( spent some time reading threads ) about Hercs and wondered if you could help me on a confusing situation.

I'm part of a structural engineering support and our MRO is new to C-130s. We have a model 382C in horrible condition and I can't proceed too much in details because of our contract, I will most likely have to remove ( or edit, at best ) the thread in case I wrote anything too "accurate". Sadly, our situation is very complicated and because of this very peculiar situation, we have limited access to documentation and communications are hard to deal with, on top of that our MRO has no one experienced on Hercs, some come from the military but that's pretty much it. Our allowed documentation about the following problem is only SMP 583 and TO 1C-130A-23.

But let's get to the point, this is a simple problem but limitations in the SMP and TO make it confusing. At FS-477, the external skin ( FS 437-477, item 1 of SMP 583 chap. 53-40-01 ) have somewhat deep partially-circular damages around fasteners ( the fasteners rows linked to the attach angle, attaching this skin to the FS 477 MLG WW web ). It seems to come from either the fasteners heads digging into the material because of the curvature or from a drilling operation where the chuck ( or the part below if the drill has a bigger attachment, unsure of the right name ) hit the material.

Anyway, according to SMP, this kind of damage ( once cleaned-up ) would be allowed to go as far as 1/3T ( T being skin gage, here 0.050" ) on a 2.25" diameter, we're out-of-tolerance as this problem is recurrent on the whole length of the fasteners rows, we're far beyond the 2.25" D limit. However we have no specific repair either and generic repair seems a bit overkill for such a thing. Replacing it also seems to be way overkill and should avoided as much as possible. Generic repair also seems to have no max dimensions limit ( ??? ). I'm aware that TO 1C-130-A-3 have some repair answers however we're not allowed to use it ( for now; we're pushing to get access to it unless they want to replace half of the a/c ).

I am unsure whether I explained the problem properly or not, so please ask me for any clarification but keep in mind I can't get deep into a/c details. Please pardon my english, I'm not that used to technical "metal working" and fasteners terms in english as I've not been in the work for long, still learning. However my leader also has no experience on Hercs and has left an hour ago ( he's aware of this thread ) so he's not here to correct the technical words I'm using, doing my best making it clear, but it becomes a bit clunky and has a lot of text.

We have an external engineering support to ( supposedly ) help us whenever we have such problems, but we have been told not to bother them with such things ( so they're pretty much only useful to us to get P/N on prod drawings and for major repairs ). A sheet metal expert came was called over to help us clarify some things but he's barely able to spout numbers in english, despite being a very nice fellow he's pretty much useless to us ( as he can't explain us anything ) and will only be here for a dozen days. Basically none of us had a formation to work on Hercs and we're learning the hard way with no tolerance of failure and hardcore political problems around it, making this job a pain to perform.

Salutations to all those that managed to put up with me and read all of this, thank you.

 

ps: I haven't seen any forum regulations so I'm unsure if anything I've written here is sensible/out-of-chart/etc.

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Metalbasher

Anyway to get a photo of the area in question?  It can be sanitized, i.e. fairly close so as not to divulge geographic location, owning nation etc, just the damage.  Sounds like an external doubler or strap would likely do to resolve the problem.  Fairly straight forward, thickness of the doubler/strap would depend on the original skin thickness as well as size of fasteners currently installed or what will be installed (if you have to upsize them).   

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AL-EAS
11 hours ago, Metalbasher said:

Anyway to get a photo of the area in question?  It can be sanitized, i.e. fairly close so as not to divulge geographic location, owning nation etc, just the damage.  Sounds like an external doubler or strap would likely do to resolve the problem.  Fairly straight forward, thickness of the doubler/strap would depend on the original skin thickness as well as size of fasteners currently installed or what will be installed (if you have to upsize them).   

That's what we were thinking of as well, however that'd make for a long doubler / strap. If length isn't a problem ( after all, SMP doesn't restrict doubler length ), it could work out I guess.

Pretty much sure I'm not autorized to share pictures but as you said, there's no way to identify anything with this. See following picture. Some are deeper than on the picture but the area wasn't clean when I took the pictures ( metal workers were putting on sealant ).

 

DSCN9609.JPG

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Metalbasher

Those look like drill chuck marks from when the holes were initially drilled in the structure.  Structure technicians not paying attention and/or not using drill stops when drilling holes...just punching holes.  Sad to say, not uncommon to see but typically of little concern unless in primary structure, i.e. longerons, end fittings etc where stress is high.  In my 30 years experience as structural technician, I would not be too concerned about it, possibly blend out the deeper ones but that would be the extent of it, no straps etc.  However, I don't work for your company and I'm not your engineer.  

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AL-EAS

In our personnal point of view, we'd agree with you and say they don't matter, there are some deep ones but not enough to worry about.

However on a technical point of view, SMP doesn't allow for any damage around fasteners and these are indeed damages. I understand during production these were accepted as this a/c is military issued ( I guess the TO -3 wouldn't mind these ) but in our case, we're only allowed to use commercial ( civil ) documentation and some TO ( TO -3 not being included in these ). Of course we'd love to leave it as is, it's barely anything worth mentionning, however no one will sign the paper saying "no damage found". We'll discuss with the customer, they told us to leave it "as is", which goes against our contract, so we're going to have them make it a "customer request" so they'll sign the paper themselves as we can't take the responsibility.

Thank you for your advice.

Edit: well, in the end no work order was issued for these chuck marks, problem solved.

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Metalbasher

Completely understand what you're saying...different requirements for different users.  Like you said, best thing is to write it up and let owner hash it out, to fix or not to fix.  In the end, sounds like it worked out for the best.  :)

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tinyclark

I am an avionics guy, but did work structure issues when my APG guy was a away. 

"SMP doesn't allow for any damage around fasteners and these are indeed damages." One would have to define "around fasteners" to figure this out. I've never seen skin replaced for this. Those damaged areas almost look blended now. I think damage would be considered oblong holes or cracking around the holes, not a minor indentation that is almost as far away as the hole circumference. 

Good luck!!  

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AL-EAS
On 04/11/2017 at 3:27 AM, tinyclark said:

I am an avionics guy, but did work structure issues when my APG guy was a away. 

"SMP doesn't allow for any damage around fasteners and these are indeed damages." One would have to define "around fasteners" to figure this out. I've never seen skin replaced for this. Those damaged areas almost look blended now. I think damage would be considered oblong holes or cracking around the holes, not a minor indentation that is almost as far away as the hole circumference. 

Good luck!!  

"around fasteners" is in SMP " 1.5" from fasteners [read, from the center-axis] ".

Anything that deforms/modify the structural cohesion of an item, aside of repair or intentional action, are damages ( even if it's minor enough to be ignored, it's only ignored because it's inside allowable damages ).

As you said, you've never seen a skin replaced for that, thankfully, that'd be a very pointless thing to do. But SMP instructs to do so ( again, only SMP, not TOs ). I'm certain it'd even be an allowed damage, it's just that "allowable damages" from SMP are... well, according to it pretty much everything is out-of-tolerances if damaged.

Since no work order was issued by the client, we just sealed everything as intended without paying attention to these (as it should be, but SMP is a really strange animal).

Thanks for all your answers, it helps us building some insight from your own experience.

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