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Old 08-21-2006, 11:57 AM
Mike S's Avatar
Mike S Mike S is offline
Senior Curmudgeon
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 16,539
Default pressure

Well, water is 43.4 pounds per 100 feet so a one foot coloumn is .43 psi.

Av gas is about 2/3 the weight of water.

I estimate your one foot of fuel will create about 1/3 psi.

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Old 08-21-2006, 01:21 PM
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rvpilot rvpilot is offline
Join Date: Jan 2005
Posts: 343
Default Theory??

After pondering this situation during my walk at lunch, I have come up with a theory. Throwing it out for discussion.
Here?s what I?ve seen mentioned-

1. Happens on the fuel tank rivets, not in other areas
2. Only seems to occur on the top surfaces
3. Seems to happen mostly on dark colors (which would see the most heat) but I think there have been reports on light colors also (which may have taken longer to develop?)
4. Only seems to be air in the bubble, no notice of fuel that I?ve seen mentioned
5. Doesn't seem to be a major pressure buildup in the tanks themselves, but does seem to be a pressure related problem

Okay, since the bubbles only have air in them, and we are not seeing any fuel come out of the bubbles once they?re opened up, is it possible air, or vapors of some type, for whatever reason, are being trapped in the dimple area of the rivet? This air, over repeated heat and cool cycles (expansion and contraction), is finally breaking the adhesive bond of the paint and forming these bubbles. While all areas are well prepped, because of the dimple, the area around the rivet doesn?t get the prep other areas receive, simply because you can?t get to it, you?re real careful in these areas, whatever. So the adhesive bond in this area could be weak and fairly easy to break loose. Why doesn?t it happen elsewhere? Because rivets in other areas of the plane are not sealed on the back side like the fuel tank rivets. They cannot build up this pressure.
Other questions do occur to me though. If this is the case, why do so few planes seem to have this problem? Could it be the chemistry of the new materials, or different materials, has changed or differs such that the flow is not the same, hence sometimes not flowing in these voids behind the rivet? Are people who put their rivets in wet having this problem? They would be the most likely not to have the voids.
Bill Waters
Based KCVC (Covington, GA)
RV6A - Gone, but not forgotten!
RV8 - Gone too, now winning races in the RV Gold Class!
RV4 - Flying!!!

Last edited by rvpilot : 08-21-2006 at 01:27 PM.
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Old 08-21-2006, 01:56 PM
casper casper is offline
Join Date: Jan 2005
Location: Derby Kansas
Posts: 146
Default Tank rivet blisters

I have been pondering this for three yrs. The only common thread here is tank sealer, When you get it figured out would you please tell me.
Doyle Reed, Casper 2
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Old 08-21-2006, 04:04 PM
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Rick6a Rick6a is offline
Join Date: Jan 2005
Location: Lake St. Louis, MO.
Posts: 2,346

Originally Posted by rvpilot
After pondering this situation during my walk at lunch, I have come up with a theory......... Are people who put their rivets in wet having this problem? They would be the most likely not to have the voids.
Interesting point. I wonder if specifications called out for the construction of the quickbuild tanks specifically include wet installing the rivets. If so, (and it should be) are the assembler/laborers who actually build the tanks always complying with the spec? How likely is it the contractor/vendor would freely volunteer such information? In a previous post I suggested drilling out an easily accessed tank rivet to visually confirm once and for all that traces of sealer exist around the countersink. If you do not find sealer traces in one countersink, chances are you may not find it in others.
Rick Galati
RV6A N307R"Darla!"
RV-8 N308R "LuLu"
EAA Technical Counselor
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Old 08-21-2006, 05:21 PM
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atreff atreff is offline
Join Date: Jan 2005
Posts: 215
Cool Solvents expanding?

My ship is not yet painted nor flying, but last week, I was touching up some interior fuse pieces with Raldolph epoxy primer followed by PPG concept. In an attempt to harden the paint, I put the parts in a 170F oven for a few hours. I got bubbles! Some small, some larger, made the part look like it has poison ivy.

The paint had cured for over a week, the epoxy primer under it cured a week before I covered it with the PPG urethane.

When I picked off the bubbles (in disgust at the waste of my time...) I noticed that they were coming from under my recently applied touch up paint. It was paint that was a few years old and was rattle can stuff, not the epoxy primer. It was a rattle can automotive 'filler primer'.

Now, I thought that this filler was fully cured, which it must have been. Perhaps it absorbed some of the epoxy primer's solvents and did not fully out-gas them.

Could the proseal under the rivets be absorbing some of the paint solvents, thus, entrapping it? Then, the top coat goes on and hardens, not allowing any solvent to pass. Over time, the sun heats the metal, the solvents expand and since they cannot find any where to go, they expand and eventually bubble up the paint.

Just a thought.

Art in Asheville
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Old 08-21-2006, 06:48 PM
szicree szicree is offline
Join Date: Jan 2005
Location: SoCal
Posts: 2,061

Has anyone contacted the folks who make proseal and inquired about its ability to absorb solvents? Ooh, wait! I've got a nice idea: Get a nice glob of cured proseal, drop it into a measured quantity of solvent (I'd use urethane reducer) and let it sit for a bit, pull it out and see how much solvent remains in the beaker. Alternatively, put the glob on a gram scale before and after soaking. My money is on the theory that this stuff holds tiny amounts of paint solvent in the rivet dimple and then gives it back up once it gets heated. It's interesting to note that Roberta reports no problems, and that she took the somewhat unusual step of letting the primer cure before painting. Hmm.
Steve Zicree
Fullerton, Ca. w/beautiful 2.5 year old son
RV-4 99% built and sold
Rag and tube project well under way

paid =VAF= dues through June 2013
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Old 08-21-2006, 10:00 PM
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GaryK GaryK is offline
Join Date: Nov 2005
Location: Zeeland, Michigan
Posts: 417
Default Same issue

My RV7A has been flying for 17 months, the first 5 months it was unpainted. The plane was painted last September by a high end quality shop. I've used them before on a Commander 114. We had a very hot spell in Michigan last month and I started to notice the same bubbles everyone is discussing. Only on the tops skins, none on the bottom. My wings were quick build.

My hanger mates? first flight in his unpainted 7A was in January this year. He had it painted by the same shop in April and is also seeing the same issue to a lesser degree.

Both planes are painted in Mattahorn white on the fuel tanks so the darker color issue doesn't apply. The paint shop will gladly strip the tanks and repaint the effected area but they want to have a good look to see what the issue is first. I'm to busy flying so the repainting will have to wait for later this year.

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Old 08-21-2006, 10:31 PM
David-aviator David-aviator is offline
Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514

Interesting commentary.

To summarize so far, it is not a quick built issue. The problem is occuring with slow build tanks also.

Paint color and heat probably are not an issue. My airplane is hangared with white tanks. The blisters first began on the bottom of the one tank, then the bottom of both tanks, then finally on the top of both tanks. This was progressive over a 2 year period. More rivets are now showing lifted paint than rivets still flat. The tanks have not been subjected to unusual heat or prolonged sun light except in flight.

It seems very logical that proseal is reacting with something used in the paint process. We need to illiminate acid etching. Has anyone had the blisters without acid etch?

Ater acid etch is scratched, and I think it will be, we need to focus on types of primers. i will find out what my painter used and post it in a few days.

David Domeier
Troy, Missouri
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Old 08-21-2006, 11:06 PM
Ted Farmin Ted Farmin is offline
Join Date: Mar 2005
Location: Sandpoint, Idaho
Posts: 104
Default vent pressure

I have been told by an engineer that 2.3ft. of water colum is equal to 1lb.

Ted -4 finishing wiring.
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Old 08-21-2006, 11:14 PM
Ted Farmin Ted Farmin is offline
Join Date: Mar 2005
Location: Sandpoint, Idaho
Posts: 104
Default vent pressure

2.3ft. of water column is equal to 1lb.

Ted -4
finishing wiring
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