David,.......we could rule out fuel because there is no fuel at the aft bulkhead outside flange.....
Jim,Rick, How would you rate this example? Positives? Negatives? Thanks! -Jim
David,
.....Are you sure your quickbuild tanks were built with that attention to detail? Given that you stated in a prior post you observed no shop rivet head encapsulation when peering inside your quickbuild fuel tanks, I kinda doubt it....
Dave,If your wings were painted and the blisters did occur, what would your thinking on the subject be?
This is scary. I had one rivet blister on the top of my right slow build RV-7 tank. My paint is the complete House of Kolor system from Epoxy primer up through the white base coat, pearl stripe and clear top coat. Happened a couple of weeks after I started flying. The right tank had other problems with weeping rivets on the bottom. Haven't had any problems after fixing the weepers and repainting the tank. All I did on the one with the blister was sand it down, prime and repaint. Now have about 60 hours on the plane and all is holding with no weepers or blisters.Blisters on my 7A quickbuild. Mostly on the passenger side top of tank but some on bottom. Plane was painted with epoxy primer and house of color top coat/clearcoat. Took about 6 months to show up. Has anybody successfully repainted the tank and no longer had the bubbles?
I have an RV8 QB about one year out of the paint shop. The first blisters appeared within a month of painting only on top of the tanks. Especially this past summer MANY more appeared both top and bottom--tank only. There are now probably 75 or 80 blisters between the 2 tanks.
There is no fuel grossly visible upon rupture.
I would like to start moving toward repairing this....is there any semblance of consensus on what to do? Other than build new tanks.....
Hi Dan,
You observed my blisters first hand at Rhodes Flyin.(
This is an unacceptable situation.
Ok, let's humor Vans for a moment. Bill, walk us through your entire paint prep process. Exactly what prep did you do prior to shooting DPLF?
I was told by mothership that it was the way it was prepped before painting because all the solvents used to clean the wing was not allowed to evaporate properly.
If, as Vans claims, it was just a matter of solvents being trapped then why would the problem be restricted to the fuel tanks. Can this make any sense.
Rick Galati's previous astute observations and comments on this thread about the problems with rivet shop heads not being encapsulated will ultimately be proven to be correct.
QB builders have variously reported in the past that some Vans fuel tanks have encapsulation of the rivet shop heads and some do not. That is a fact.
My best guess is that the Philippines subcontractor is fabricating these tanks to the same instructions that slow build builders receive in their construction manual. I cannot see why a subcontractor and a builder would receive different instructions to build the same fuel tank.
My Van's tank construction instructions specifically say: "Dab a bit of sealant over every rivet head". To me this clearly says ENCAPSULATE THE RIVET SHOP HEAD WITH PROSEAL.
I think we can safely assume from this that in some instances the subcontractor is not following Vans instructions consistently in this regard. I think we can also safely assume that Vans has not been checking the tanks internally (at least not in the past) to see whether their instructions are being followed.
The fact that some QB tanks have encapsulated shop heads and some do not is clear proof that there has been a breakdown in quality control procedures in terms of tank construction. For those with blisters developing under their very expensive paintwork that is a disaster.
Dan,
I used scotchbrite pads (maroon) and dawn dish detergent with a firm scrubbing for tooth adhesion for the paint.
Dave,....why so many blisters are occurring at the aft bulkhead rivets which are outside of the fuel tank. Most of mine are in the line of rivets exposed to air top and bottom, not exposed to fuel.
Beyond all that, I would like to build a new set of tanks but that too poses a problem - match drilling the Z brackets to the spar sheer web. Normally, that is done before the bottom wing skin as closed out. I am still in the discovery phase of determining if it can be done.
Dave,
Oh but those rivets ARE (potentially) exposed to fuel! Without a proper fay and filet seal to otherwise block the path, fuel or fumes can seep between the bulkhead flange and skin and then up and out a rivet hole.
As for match drilling the Z brackets...of course it can be done:
http://www.vansairforce.com/community/showthread.php?t=11999&highlight=transfer+punch
Thanks Bill. The "unevaporated prep solvent in the rivets" theory makes no practical sense for several reasons. However, we need data and yours is valuable.
Anyone believe dish detergent and water can generate a chemical reaction when applied to a prosealed rivet?
Let's get behind Andy's proposal to gather an information database.
I have also stressed the importance of a good fay/filet seal boundary. I have explained this before but your drawing provides....many of the rivets that are forming blisters are on the upper rear row
of rivets that hold the rear tank baffle on....I pointed out early in this thread that for those rivets,
it would not matter whether they were encapsulated or not...
I have also stressed the importance of a good fay/filet seal boundary. I have explained this before
but your drawing provides me with a convenient way to illlustrate. If any voids exist in the fay/filet seal
boundary because of poor application technique, fuel or fuel fumes will surely find a way out of the fuel
tank along that migration route. Passing a pressure test is one thing...long term exposure to fuel and the
naturally slight pressure that can occur within a fuel tank can reveal more subtle defects at much later
date. In any event, Van's does direct the builder to apply a good bead of sealer prior to inserting the rear baffle.
If not done correctly, the tank may not leak fluid in any obvious way, but over time the subtle effects of that
fuel or fumes in contact with paint may eventually cause a reaction. That is why I stress 3 key areas to pay
particular attention to when sealing a fuel tank. These are not difficult goals to achieve but they are necessary.
#1 Encapsulation. #2 Fay/filet seal. #3 Sealer under the manufactured head of the rivet.
I refer anyone to review my observations of a pair of QB tanks shown in post #100. You tell me. Are they "good enough?"
i find this very interesting, i built a slow build rv-10 using epoxy self etchin primer and topcoated with acrylic enamel with a urethane hardener. the paint job on the entire aircrft was done with the same methods and materials and only the fuel tanks blistered with pinhead size blisters all over the tank not just around the rivets. the only difference between the tanks and the skins is that the tanks were messy with prosel which i then cleaned off with laquer thinner, acetone, mek and naptha basically whatever i had laying around. i'm sure residue of that sealant made its way all around the tank in the wiping off process. the tank was scotch brighted before painting. i want to say that i believe it must be the proseal residue. initially i thought i must have made a boo in prepping for both tanks only but the odds are against that. i'm gonna switch brands of proseal and solvent wipe more thouroughly next time (yes i said next time, i must be crazy)
We do have many slow build guys like me with the blisters.
I don't have any specific idea of what has caused this problem with a small percentage of RV tanks and I am not sure anyone ever will. The reason I believe this is I feel quite certain that the blisters have been caused by different problems on different airplanes.
Here are a few of the reasons I believe this.
- the problem has occurred on standard build and Q.B. fuel tanks
- the problem has occurred on Rv's painted with many different paint systems.
- The problem has occurred on RV's prepped with many different paint prep processes.
One thing I can tell you that I am certain is not the cause of paint blisters...
It is not whether all of the rivet heads were coated in proseal before the tank was closed.
BTW, as far as I know, the only reason that step is in teh construction manual is to give amateur builders every possible chance that they can get, of avoiding a leak.
In my 22 years of building RV's I have built about 15 sets of fuel tanks. I have never coated the rivet shop heads in any of the tanks I have built. I actually remove any sealant from within the dimples before inserting the rivets to make sure that they lay down flush with the the surface of the skin. When I rivet a tank, I am relying on the sealant squeezed around the rivet shank in the small space that is between the rib and the skin to make the seal.
I use about 1/2 of a quart can of sealant to build a standard set of two place RV fuel tanks.
I have never had a fuel leak or paint blister at any rivet on any tanks I have built to date.
I do have a couple of theory's of what has caused at least some of the rivet blisters on some tanks.
One is surface sanding - because of the sealant under rivet heads on the tank, often times there are rivets sticking up above the skin surface. This sometimes doesn't show how bad it is until a coat of primer is sprayed on. I believe some builders have block sanded over the rivet lines to improve the final finish. This removes primer from the high spots on the rivets. If paint is then sprayed, there are small areas on rivets where there is very poor paint adhesion. This coupled with the entrapped paint solvents around the perimeter of the rivet, sets up the opportunity for the solvents to expand and lift the paint into a blister. A strong piece of evidence for this is that there are many instances on different RV's where the only blisters on the tanks were along the line of rivets for the rear baffle flange. As was mentioned in a previous post, a properly installed baffle (one that is not leaking) does not have any fuel on the shop head side of the rivet. One thing that is different about these rivets though, is that they are machine countersunk holes instead of dimple countersunk. A machine countersunk hole is much more sensitive to rivet fit than a dimple countersunk one. Because of this, even the slightest amount of sealant under the rivet makes it look like it sticks up a lot. That makes these rivets much more likely to get some treatment with a sanding block just before shooting the paint.
Any painter will tell you that paint formulations have changed a huge amount in the last 10 - 15 years because of all the EPA regulations and removal of harmful compounds (like lead). Years ago, we could get away with doing this type of sanding treatment...the paint would still adhere great. Now a days the paints are much more sensitive to proper surface prep and proper use of primers for good adhesion.
Let me reemphasize that I don't mean to imply I think this is the cause of all of the paint blisters. I know that it is not, but I do believe it is the cause of some of them.
My primary point is that I do not think there is a single smoking gun cause and that I do not think anyone should be trying to lump all of the problem under one cause.
If you could look inside my tanks you would clearly know the cause. Very poor workmanship. I looked directly at the rivets under the blisters with a borescope. No encapsulation with proseal. You had the luxury of knowing what had been done in the tanks you built. A QB builder does not.
Bill I am sorry about your problem but I guess you missed one of my points...
Here's my point. Had I built these tanks, I would accept my mistakes and pay whatever needed to remedy the problem. I had no control over this matter. If you bought a NEW car with a leaky tank and was told by the manufacturer it was your fault, you my friend would be in the same boat as I.
I have no reason to doubt your leak proof success record after building more than a dozen fuel tanks. Success does speak for itself and I happen to completely agree with you in that I too do not think there is a single smoking gun cause and no one should be trying to lump all of the problems under one cause.......I have built more than a dozen sets of tanks and I have never covered a single rivet shop head with sealant. None of these tanks have ever had a leak or paint blister at a rivet.
I am very confident that your problem is not purely caused by the fact that you can see exposed rivet heads inside your tank.
One thing I can tell you that I am certain is not the cause of paint blisters...
It is not whether all of the rivet heads were coated in proseal before the tank was closed.
BTW, as far as I know, the only reason that step is in teh construction manual is to give amateur builders every possible chance that they can get, of avoiding a leak.
In any event, to get back to and reemphasize my point about a proper filet seal, I cannot accept this QB example lacking a filet seal as anywhere near meeting my personal standards of acceptability. By way of analogy, no filet seal and no shop head encapsulation effectively eliminated two legs from that 3-legged stool.
This may or may not be an additional issue, but from what I can tell no surface preparation is apparent immediately adjacent to the stiffener as if the stiffener was installed on the alclad skin without any prior "roughing up" of the mating surface necessary to provide the proseal with enhanced gripping power. As you know, surface prep is an extremely important step and may or may not have been omitted in this specific case. I do however, freely concede my suspicion *may* be unwarranted so I'll give the benefit of doubt on this one.
HOWEVER, and this point is clearly undeniable...this QB fuel tank stiffener example is obviously devoid of any filet seal surrounding it. If any voids (migration path) happen to exist and hidden within the fay sealed surface between the stiffener and skin...no amount of rivet shop head encapsulation in the world will be of much help in preventing leaks.
The tone conveys the "message" that even though the builders manual points clearly directs, a dab of sealer (on the rivet shop head) is (in your estimation) really not all that necessary. C'mon. What else in your estimation is contained within the construction manual we may be free to downplay as not all that necessary?
Scott, I have been following this thread, and others on this topic, with considerable interest for some time. To date literally dozens of builders have reported blisters. In all of the blister cases reported for both QB and SB tanks (except for one) the common denominator has consistently been a lack of shop head encapsulation. One person reported blisters and claimed he had shop head encapsulation...but when he was asked to provide further details he evaporated and did not reply. So the statistics to date strongly point to the fact that shop head encapsulation (or lack thereof) is a crucial factor.
I am at a bit of a loss over this statement. Surely if encapsulation "gives amateur builders every possible chance that they can get of avoiding a leak" then the same must apply to professional builders.
I would like to know why some tanks come out of the Philippines with encapsulation while others do not. What is Vans specific requirement of its subcontractor in that regard? Do Vans require encapsulation of the QB tanks or do they not? And if they do require encapsulation then why are some tanks getting through with no encapsulation? In the final analysis one would suspect that inconsistencies in the protocol of QB tank construction are an indication of ambiguous construction specifications and less than satisfactory quality control.