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02-26-2013, 10:32 AM
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Join Date: Feb 2006
Location: Trenton, SC
Posts: 117
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leaking fuel tanks
Quote:
Originally Posted by BobB
Thanks for the reply. Obviously, I didn't build this a/c. I will clean up the bubbles and repaint the areas. Hope the bubbles don't come back.
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They will come back in time, you need to fix the source of the leak before going to all the trouble to repaint. I have experienced leaks in factory built tanks on RV-7 and RV-10 tanks. Even a factory replacement tank for the RV-10 leaked. I think there is extremely poor QC on the building and testing of these tanks. The only one I had that did not leak was the ones on an RV-6 that I built.
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04-21-2013, 01:07 PM
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Join Date: Feb 2006
Location: Virginia
Posts: 324
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Data point for posterity
Just another data point for posterity:
My RV-6 wings now have blisters.
Data:
1. Slow-build (did it myself), in 1999/2000 time period
2. Std pro-seal methods, no slosh
3. Painted w/Sherwin Williams products (JetGlo/Acryglo)
4. Took 6 years to develop. First flight 2006, first blisters 2012.
5. Correlated with heavier use of 91 octane autogas, laced with ethanol, I started in 2012, although the right wing (which is filled w/100LL 90% of the time) also has the blisters
6. The blisters are still intact, no liquid has ever been noted out of rivets
Plan is to monitor - trying to fix/re-paint would probably make it look worse in the long run, and there is no safety of flight problem at this point.
Cheers,
__________________
Jordan Grant
RV-6 N198G
Monthly donation started Mar '20
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04-21-2013, 08:14 PM
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Join Date: Oct 2011
Location: Kansas
Posts: 332
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Jordan, where on the tank did the blisters appear, i.e. along the rib line or along the rear baffle, interior rib or exterior rib, etc.? So after six years blisters appeared at the same time on both tanks???
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Jim
Lenexa, KS
RV-7A
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04-22-2013, 07:56 AM
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Join Date: Apr 2013
Location: McKinney, Texas
Posts: 5
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Paint blister (semi)repair
My quick-build RV-8 started developing blisters on the tank skins a few months after first flight. It seemed to accelerate when it was out in the sun for a week at Oshkosh. I ended up waiting for about a year for the situation to stabilize before deciding what to do about it.
I figured I would have to repaint the tanks, so I decided to try an experiment. The biggest blister was on the bottom of the left tank, about 1.5 in diameter. I used an Xacto knife to make a small slit, about 1/32 in long in the middle of the bubble. I then used a heat gun (low setting) hoping the blister might shrink down flat. And it did.
This worked so well that I did this on all the blisters. After making the slit (parallel with the slipstream), I would apply some heat for a few seconds and then massage the blister down with a cloth. Then repeated this several times. The result was impressive. Unless someone knows specifically where to look, the repair is not noticeable. It is least noticeable on the white paint, a bit more an the red trim. I did this a year ago and none of the blisters have returned. The result is good enough (so far) that I will not go through the hassle of repainting the tanks
This is, of course, just one data point, and success may be a strong function of the brand of paint used.
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04-22-2013, 08:40 AM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Welcome to VAF!
Ken, welcome aboard the good ship VAF
Good info on the blister repair, another data point for the puzzle, thanks for sharing with us.
Sounds like lancing the blister at first notice may be as good as it gets without having to open the tank??
How about a photo or three of the plane??
__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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04-22-2013, 01:24 PM
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Join Date: Apr 2013
Location: McKinney, Texas
Posts: 5
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Mike, tried to post a picture, but unsuccessful.
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04-22-2013, 02:17 PM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Quote:
Originally Posted by Skyote
Mike, tried to post a picture, but unsuccessful.
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Ken, check your Private Messages, upper right corner of the page.
__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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04-22-2013, 05:48 PM
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Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
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Blisters
BMW Motorcycles made a painted plastic tank for their GS line around 1994 - 1995 , similar blisters would appear , I had one that was blister free for 2 years until I painted it ( DuPont Chroma Base / Clear ) . First day in the sun it looked like a teenager with bad acne ! BMW warranty removed most from the market and replaced with a metal one .
Were there some microscope photos of Proseal posted ? I wonder if there is a minimum thickness that should be used to cover the shop head of rivets on the inside of the tank ?
Tom
__________________
Rv8
N 666 TA
First Flight 2-3-2015 🚀
2017 donation paid
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04-23-2013, 06:38 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by g zero
Were there some microscope photos of Proseal posted ? I wonder if there is a minimum thickness that should be used to cover the shop head of rivets on the inside of the tank ?
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Most of us are using Flamemaster CS3204, while "Pro-Seal" is a trademark of PPG Aerospace. Both are AMS-S-8802 (formerly Mil-S-8802F, Type II) sealants.
Cured sealant is actually much like a sponge, although in theory the voids are closed cell, i.e. not connected. The voids have two sources, (1) air entrained during mixing and (2) bubbles of liquid or vapor toluene, the solvent component used for viscosity adjustment. The solvent evaporates out of the sealant while the chemical cure is proceeding, and apparently for some time after. It would seem the sealant is never totally vapor proof, which is why there is a required thickness.
BTW, there is no test standard for sealant performance with avgas or mogas. All testing is done with what you can think of as a standardized jet fuel equivalent.
Thickness over a shop head? 60 mils with a 1/4" fillet.
This is from the original Essex Chemical document " Polysulfide Sealants For Aerospace". They invented the stuff.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 04-03-2019 at 02:21 PM.
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04-25-2013, 08:18 PM
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Join Date: Apr 2007
Location: Coral Springs, FL
Posts: 65
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QB fuel tank blisters to :(
My -8A QB has a herd of fuel tank rivet blisters. Not going to bother with them at this time, but wondering if sloshing is the only way (yet) determined to correct the issue?
__________________
[left]Jeff WildThing Wirs
RV-8A (sold)
Coral Springs, FL
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