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QB fuel tank paint bubbles

KWFlyers

I'm New Here
Recently completed QB RV-14 painted by a professional 10 months ago. Spectacular paint job. Both fuel tanks bubbling along the same single rivet line (top only). Anybody have any history with this?
 

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Recently completed QB RV-14 painted by a professional 10 months ago. Spectacular paint job. Both fuel tanks bubbling along the same single rivet line (top only). Anybody have any history with this?

Yes, not on a 14 but on a -10. It has to do with the poor workmanship done in the Philippines. Unfortunately, this is the price you pay for having someone else assemble part of your aircraft.

-Marc
 
Yes, not on a 14 but on a -10. It has to do with the poor workmanship done in the Philippines. Unfortunately, this is the price you pay for having someone else assemble part of your aircraft.

-Marc
Can you elaborate what is the cause/poor workmanship and what would prevent it?
 
Can you elaborate what is the cause/poor workmanship and what would prevent it?

What we have seen is inadequate use of proseal on mine and other QB wings. In one of my wings there was still a paper sticker on the aluminum INSIDE the fuel tank! Vans instructions say to test the fuel tank for leaks but those leaks don't always show with the slight pressurization recommended.

If I were going to buy a QB kit I would try to have it done sans tanks and do them myself. Otherwise your only option is to use the Vans tank repair kits and personally seal each tank bay.

-Marc
 
I have no personal history with this (my tanks have never leaked, knock on wood!) but it's almost certainly from inadequate sealing (proseal) inside the tank in that location. The fix would be removal of the tank and cutting access holes in each bay (see: https://vansairforce.net/community/showthread.php?t=189357) so you can get in there and strip and re-seal the affected rivet lines.

Or a new tank.

EDIT: Specific cause could be just poor application of proseal, or not enough on the mating surfaces or rivet heads, or inadequate scuffing / cleaning of the surfaces, or poorly driven rivets, or some combination - take your pick.
 
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This has been a big topic of discussion here on the forums over the years - it goes back to the very beginning of VAF, so you should be able to do a search and find some great threads. A lot of data collection has been done in the past, and while folks like to throw out specific causes for it, the data has ben somewhat inconclusive when actually analyzed - there are a number of causes that have been cited, and some specific fixes.

The factory is well aware of the issue as well, and has contributed to the discussions in the past - if it had a simple solution, it would have been solved - but apparently, it is still elusive.

Just some background from an “old timer” (who has had one or two suspect bubbles, but nothing extensive).

Paul
 
DISCLAIMER: I'm not a chemist!

Here is an article from Boeing on "Rivet Rash". Seems to be similar to what is happening on these Quickbuild RV tanks. I'm not sure why it only seems to happen on the tanks, but the sealant most likely contributes, otherwise it additionally would be seen elsewhere on the wings/fuselage.

The theory is that the chromate conversion on the rivets has an adverse effect on adhesion of the subsequent alodining preparation of the skins prior to priming and painting. My guess is that any outgassing of the tank sealant is the catalyst to start the bubbling. From what tanks I've worked on resealing them, the rivets aren't leaking any fuel under the bubbling, it is simply lifting the paint coating. This means that the preparation prior to painting is suspect.

My slow build tanks have not had any issues with bubbling. I kept everything super clean. First I soaked my rivets in MEK to remove any contaminants, then let them air dry on a paper towel prior to setting them with sealant under the heads. MEK is super volatile and evaporates completely, so when I hear other theories about MEK being a problem, I don't buy it. I wiped off any excess sealant with MEK after riveting. I didn't paint my airplane, but it was scuffed and alodined prior to priming and painting by the paint shop.

I'd be interested to hear the Van's theories on this issue. The bubbling issue has been very pervasive over the years.
 
What we have seen is inadequate use of proseal on mine and other QB wings. In one of my wings there was still a paper sticker on the aluminum INSIDE the fuel tank! Vans instructions say to test the fuel tank for leaks but those leaks don't always show with the slight pressurization recommended.

If I were going to buy a QB kit I would try to have it done sans tanks and do them myself. Otherwise your only option is to use the Vans tank repair kits and personally seal each tank bay.

-Marc

If anyone needs to see photo proof, just read my blog on the repair of Marc's tank.
 
MEK

It needs to be said, MEK = Death. Methyl Ethyl Ketone is a great solvent. It is also a great way to damage your organs. Where gloves and a mask or use outdoors with good ventilation,etc.:(
 
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This has been a big topic of discussion here on the forums over the years - it goes back to the very beginning of VAF, so you should be able to do a search and find some great threads. A lot of data collection has been done in the past, and while folks like to throw out specific causes for it, the data has ben somewhat inconclusive when actually analyzed - there are a number of causes that have been cited, and some specific fixes.

The factory is well aware of the issue as well, and has contributed to the discussions in the past - if it had a simple solution, it would have been solved - but apparently, it is still elusive.

Just some background from an “old timer” (who has had one or two suspect bubbles, but nothing extensive).

Paul
Paul, I agree completely. I have had two sets of QB tanks that they did not leak at all but they did have the bubble under the paint. I have also seen slow build tanks that had bubbles so it is not necessary limited to the QB tanks.
I do like to see some logic in the argument that not adequate sealing causes bubbles but not leaking AND some evidence of inadequate sealing.
 
A lot of data collection has been done in the past, and while folks like to throw out specific causes for it, the data has been somewhat inconclusive when actually analyzed

Paul, "inconclusive" is hearsay, or personal analysis? And what database?

I'm only aware of one, covering 18 builders and a bit more than 30 variables. Very few have seen it. One who did, a lawyer named Robert Brunkenhoefer, threatened to sue Vans, so it's been buried a long time. Thank him.

There are a few clear conclusions. First and foremost, it's not solely "poor workmanship in the Philippines". The blister database included a high percentage of owner built tanks.
 
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Paul, "inconclusive" is hearsay, or personal analysis? And what database?


There are a few clear conclusions. First and foremost, it's not solely "poor workmanship in the Philippines". The blister database included a high percentage of owner built tanks.

That's true, but the OP referenced QB tanks and those were only made in the Philippines. Certainly a home builder could muck up the tanks on a slow build but that wasn't what the OP was asking about.

In the case of my airplane I spoke with the builder and was told "The tanks leaked like a sieve" when they were tested. Examination of the quality of the tank-build showed poor workmanship.

Now I would think that after assembling a few QB tanks the quality would improve but reports here indicate otherwise.

In dealing with my own tanks I spoke with Paul of Weep No More and he told me that they offered to build the tanks for the QB wings but Vans turned them down. I expect that the price point didn't work for Vans but I really don't know.

-Marc
 
Recently completed QB RV-14 painted by a professional 10 months ago. Spectacular paint job. Both fuel tanks bubbling along the same single rivet line (top only). Anybody have any history with this?

You are a true pilot!! You took the plane out for a flight just to get the correct lighting on the subject for a good photograph!! Why not.;)

To the subject: Paul and Dan's advice can't be beat.
 
Add two more to the database

That's true, but the OP referenced QB tanks and those were only made in the Philippines. Certainly a home builder could muck up the tanks on a slow build but that wasn't what the OP was asking about.

In the case of my airplane I spoke with the builder and was told "The tanks leaked like a sieve" when they were tested. Examination of the quality of the tank-build showed poor workmanship.

Now I would think that after assembling a few QB tanks the quality would improve but reports here indicate otherwise.

In dealing with my own tanks I spoke with Paul of Weep No More and he told me that they offered to build the tanks for the QB wings but Vans turned them down. I expect that the price point didn't work for Vans but I really don't know.

-Marc

My RV-7A with QB wings/tanks has a couple of small paint bubbles now about three years in. Another recent build RV-7A over at Synergy Air South had both tanks with multiple leaks. Once opened up, the quality of the riveting and sealing wasn't very impressive.

 
My QB tanks were works of art, and they came from the Philippines around 2004.

Anyone who has managed humans, particularly in a challenging production environment, knows that good training and quality control is paramount.

Cutting costs and increasing production are desired by the owners, but as the old saying goes "good, fast, cheap - pick two."
 
Ditto for my QB wings, received in 2006. No leaks, no bubbling, rivet workmanship excellent throughout the structures; like new 15 years on. Some irregularities in QC may have snuck in over the years, but for my money the Filipino builders are top notch.
 
Another possible cause is prep solvent getting around the rivet heads and not evaporating completely prior to painting. Paint may seal it in and then if the solvent is heated and vaporized it may create a bubble. However, this would apply to everywhere on the structure, not just the tanks.
 
It is interesting to note that in all the cases I know of, only the top of the tank rivets bubbles and I wonder if sun has any affect on it. I can't understand why not the bottom of the tanks.
 
Paul, "inconclusive" is hearsay, or personal analysis? And what database?

I'm only aware of one, covering 18 builders and a bit more than 30 variables. Very few have seen it. One who did, a lawyer named Robert Brunkenhoefer, threatened to sue Vans, so it's been buried a long time. Thank him.

There are a few clear conclusions. First and foremost, it's not solely "poor workmanship in the Philippines". The blister database included a high percentage of owner built tanks.

I was really hoping you’d comment on this one Dan, because I knew that you were the one that spearheaded the data collection, and because to be honest, I couldn’t really remember the conclusions….or what happened to the whole topic.

Now I know!
 
Outgassing

Not a chemist but have to wonder if proseal ever completely cures. What effect does a slightly off mixture ratio have on cure? Air humidity content?

How about permeability of less-than-ideal mixed proseal?

There's also the possibility of somewhat bad batches of proseal.

I guess there are so many possibilities when it comes to chemical reactions, interaction of proseal, etch, alodine, primer and paint, not to mention AvGas and MoGas.

No wonder we don't have a final conclusion as to cause.

Yes, the QB tanks on my 2003 RV-3B has the bubbles and paint lifted off of the baffle rivets. No leaks as such.

I'm almost exclusively using 87 octane (10% ethanol) gas.

Finn
 
Solutions

Anybody have any history with this?

KWFlyers,
Yes, my acquired 7a has some paint bubble (blisters) on top. Not bad and not growing, but (to me) annoying. Lots of posts here that drone on-and-on about the problem, but only a smattering of random solutions. So, here is a list (not in preference order) of solutions. I am leaving out the authors, but they may want to interact. Others can chime in with solutions.

(1) pop blister with small sewing needle or knife. Use heat gun, slowly, across the blister and smooth out til flat.

(2) pop blister with small sewing needle. Drain tank. Use (low) suction at gas cap area and apply red loctite to blister hole so it sucks back in. Fix, repaint, bubble area.

(3) pull tank and send to “weep no more” in Minnesota. Couple thousand clams to strip and re-seal the tank. Then, re-paint.

(4) pull tank and repair yourself. Folks have stated that the repair needs to be on the inside, but the (2) solution has worked for a couple of folks.

(5) build new tanks.

Hope this helps. Not sure what Solution I’ll use. Been too busy flying and doing fun upgrades.:)
 
It is interesting to note that in all the cases I know of, only the top of the tank rivets bubbles and I wonder if sun has any affect on it. I can't understand why not the bottom of the tanks.

Well you now know of at least one RV (mine) that had the blisters on the bottom, and I know of others, as does Bruce Hill. I believe that the rivets are "leaking" av gas because they weren't properly sealed during the build. I'm not talking about lots of fluid in the leaks, just vapors that usually leave the tell-tale blue stain.

-Marc
 
Quality control


Gave up reading that 400+ post thread at page 26.

Several wild theories like needing to encapsulate rivet shop heads in proseal. May help for rivets inside the tank but does not make sense for rivets outside the tank, like along rear baffle.

In any case the blisters appear to be caused by gasses, whether from incompletely cured proseal or paths through proseal.

The paper referenced in post #7 in this current thread may be another cause, but then blisters should also appear in other places than on tanks.

A recent thread comes to mind of a builder with a leaking tank who insisted he had a good bead along the rear baffle, but pictures of it, after baffle was removed, showed a non-continuous bead (possibly had already started to cure when applied) with a tiny path for gas or gas vapors to pass through.

Scott McDaniel's method require well scuffed and clean mating surfaces around any hole or opening and relies completely on properly applied amount of proseal on those mating surfaces. Proper consistency (mixture, short time before application, ambient temperature) is essential there.

Others rely on extensive amounts of proseal: mating surfaces, under and around rivets inside and outside, hoping that at least one of those will prevent a leak and path for gas vapor.

Unfortunately, none of this is of any help for owners of QB tanks other than the need to impress upon Van's the need for quality control. Or maybe send them back to Van's and ask for a set of tanks that were properly done :)

Finn
 
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Several wild theories like needing to encapsulate rivet shop heads in proseal. May help for rivets inside the tank but does not make sense for rivets outside the tank, like along rear baffle.

It's not a wild theory. It's an aerospace standard, straight from AIR4069 Rev.A, reproduced below.

The rearmost rivet line, outside the tank, is fay and filet seal only. Apples and oranges. Unlike the rib lines, there is no intentional fuel contact at the rivet location.

Unfortunately, none of this is of any help for owners of QB tanks

Again, this was never a QB-only problem...and solving the riddle meant finding factors common to failed QB and owner-built tanks.
.
 

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Yes, you're right. Inside tanks you have to cover shop heads in addition to the mating surfaces the rivet passes through because you can't count on the proseal on the mating surfaces to completely touch the rivet like an o-ring would.

I was trying to outline the two extreme methods:
1) Minimal amount of proseal that yet will block any path that could lead to a leak (gas and vapor).
2) Belt-and-suspenders approach, slopping on proseal like you own stock in it.
An example would be the inside ribs. You could just have a ring around each rivet and cover shop heads. Or you apply proseal on all rib flanges and mating skin surface with fillets on both sides of the rib flange. Yet the fillets will do no good if there is a path from tip to nearest tip rivet. My point being that you can slop on proseal and still have leak paths if not done right. Probably why some people sloshed their tanks in the old days with subsequent slosh peel with blocked fuel pick-ups.

To the one asking about sloshing tanks as a solution to the problem, don't do it! With the tanks already assembled you can't get to the skins and properly clean, scruff and prep them for the slosh and the slosh will peel. Bad, bad, bad!

As for QB tanks vs home built, obviously if the builder messed up it's his problem to solve. But if you've bought QB tanks, a case could be made for it being the supplier's (Van's) problem. Fortunately for Vans the vast majority of builders are a helpful lot that will try to fix QB tanks themselves.

Finn
 
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It's not a wild theory. It's an aerospace standard, straight from AIR4069 Rev.A, reproduced below.

The rearmost rivet line, outside the tank, is fay and filet seal only. Apples and oranges. Unlike the rib lines, there is no intentional fuel contact at the rivet location.



Again, this was never a QB-only problem...and solving the riddle meant finding factors common to failed QB and owner-built tanks.
.

Makes sense - except that I carefully encapsulated all my stringer and baffle rivets, and I still have bubbles - top and bottom.
 

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Cautiously Optimistic

Maybe Greg Hughes will post a response. I would be interested to know how Vans deals with QB tanks that leak. Surely they would work with the customer and not just direct them to buy a patch kit on their website since they payed for this service.

I have spoken to several people that experienced some fuel tank problems.

I ordered my QB 14A wings on 10/09/2020. Crate date of June 2020. I now have an estimated delivery date of Feb 2022-Jul 2022 for my QB wings.

I was concerned about these problems when I ordered the wings. Kim, in shipping explained that every 3rd QB they receive, they inspect it stateside at the factory. She said I could have mine flagged and put that on my order.

When I spoke with someone recently in shipping they were not sure about flagging individual kits and was told that they have been inspecting the kits pretty thoroughly as of late.

I plan on doing the tank test that Vans recommends. Realizing that sometimes this forum ends up being more of a triage as people come to express concerns and find remedies. Possibly the problem isn't as widespread as one thinks. Unfortunately this problem isn't alway easy to fix especially if it sullies and great paint job which requires time and money to fix in addition to pulling the tanks etc.
 
Makes sense - except that I carefully encapsulated all my stringer and baffle rivets, and I still have bubbles - top and bottom.

The standard relates to liquid leak paths, not blisters.

The evidence says blister formation requires gasoline vapor as one of several factors. Fully cured polysulfide sealant is vapor permeable. Although additional thickness helps mitigate vapor permeation, it does not eliminate it.
 
That makes me wonder if the problem then is more related to surface adhesion of the paint to the surface, and possible contamination around the rivet head. If the proseal is vapor-permeable then every rivet is exposed - but obviously the paint over every rivet does not blister.

I used MEK to clean up my rivet lines after setting the rivets - I understand now that was most likely a mistake, I should have let it cured and then mechanically removed it. I'm wondering if that left some type of surface film on the skin in the area of the rivets that was not properly removed during paint prep, resulting in poor adhesion in some areas.
 
The standard relates to liquid leak paths, not blisters.

The evidence says blister formation requires gasoline vapor as one of several factors. Fully cured polysulfide sealant is vapor permeable. Although additional thickness helps mitigate vapor permeation, it does not eliminate it.

If that were true, then every painted tank built with proseal would have blisters. I believe that blisters caused by fuel vapors are a result of poor sealing. I have seen fuel leaks that left the tell-tale blue stain but never appeared "wet". The leaks were so small that the fuel vaporized, but the dye won't.

We (Bruce Hill mostly) repaired my tanks to the point that I no longer have blisters, blue stains or any other evidence of fuel leaks. It was all done from inside the tanks through an access hole covered with the Vans tank repair discs.

Vans initially wanted me to apply a glob of proseal over the leaking rivets on the exterior of the tank! That just doesn't pass the smell test to my way of thinking.

-Marc
 
If that were true, then every painted tank built with proseal would have blisters.

Nope.

In any sort of diagnosis, folks tend to focus on a single item. In reality, the end result is more often the product of a series of factors, or multiple concurrent factors. In aviation, the best known example is the error chain leading to an accident. Break the chain, no accident.

Here vapor permeation is just one factor. Without the other factors, no blisters.
 
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