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  #21  
Old 08-21-2006, 11:15 PM
casper casper is offline
 
Join Date: Jan 2005
Location: Derby Kansas
Posts: 146
Default Blister on tank rivets

I think Art in asheville is on the right track. As I said I have been pondering this for 3 yrs, can't stop flying to fix. I believe the tank sealer around the rivets is absorbing some thiner and does not gas out right away. As for as acid etch, I think you can scratch that. I did not acid etch, unless you consider self etching Mar Hyde as acid etching. On the my slow build 6 I used vynel wash, epoxy primer and matahorn white, NO problem. On my slow build 7 I used self etching Mar Hyde and matahorn white, Blisters on tank rivets. Mar hyde works but it is a short cut method and I would not do it again. That is my 2 cents worth. Hope it helps.
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  #22  
Old 08-21-2006, 11:17 PM
Ted Farmin Ted Farmin is offline
 
Join Date: Mar 2005
Location: Sandpoint, Idaho
Posts: 104
Default paint blisters

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

Ted -4 finishing wiring
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  #23  
Old 08-22-2006, 05:15 AM
Kevin Horton's Avatar
Kevin Horton Kevin Horton is offline
 
Join Date: Jan 2005
Location: Green Bay, WI, USA
Posts: 2,369
Default

Quote:
Originally Posted by Kahuna
I do think this is pressure related.
If it was pressure related, I would expect the problem to be worse on the bottom of the tank. The pressure is the highest at the bottom when you pull g. The fact that it is only seen on the top of the tank suggests that it is heat related.
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  #24  
Old 08-22-2006, 08:12 AM
Rick6a's Avatar
Rick6a Rick6a is offline
 
Join Date: Jan 2005
Location: Lake St. Louis, MO.
Posts: 2,346
Default

Quote:
.......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......
Quote:
.....I believe the tank sealer around the rivets is absorbing some thiner and does not gas out right away.
While prudence certainly dictates nothing should be ruled out as a possible cause, I do find it difficult to reconcile the above thoughts with the fact that thousands of military and commercial jets.....many of which (for purposes including pressurization) have proseal under the heads of thousands of exterior fasteners including screws, hi-loks, jo-bolts, taper-loks, and rivets. And fasteners represent only a partial list of prosealed items because many parts are fay-sealed onto the exterior airframe and squeezed out sealer is simply painted over. If paint blistering was experienced on the skins of these aircraft, one would think engineers long ago isolated the cause and amended surface preparation to compensate.
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Last edited by Rick6a : 08-22-2006 at 09:03 AM. Reason: spelling
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  #25  
Old 08-22-2006, 08:22 AM
atreff's Avatar
atreff atreff is offline
 
Join Date: Jan 2005
Posts: 215
Default Good call, Rick

Good call on the proseal deal Rick. I totally forgot that if there was something inherently wrong with the combo of proseal and paints the airlines would be hurting.

I'm out of theories for now. Perhaps another variable could be what was used as a clean up solvent during the tank build, different solvents breaking down the uncured sealant differently?

Art
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  #26  
Old 12-07-2006, 07:56 AM
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Dave Cole Dave Cole is offline
 
Join Date: Jan 2005
Location: Roanoke, VA
Posts: 306
Default Is it gasoline vapor pressure?

Since the blisters develop only over a few rivets, let's assume that there is sometning different about these rivets.

Could the difference be a pinhole in the proseal which is small enough not to leak gasoline due to its viscosity, but large enough to allow gasoline vapor to leak into the area around a rivet head, and eventually blister the paint?
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  #27  
Old 01-04-2007, 05:21 PM
dav1111 dav1111 is offline
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Join Date: Jan 2005
Location: Lubbock, Texas
Posts: 659
Default Fuel Tank Rivet Blister

I noticed a single rivet on the top of the right tank was seeping AvGas (Blue) after I filled the tank the first time (QB Tanks). It was obviously lack of a good proseal around the rivet. I thought I had the seepage stopped using penetrating (green) locktite before it went to the paint shop but after about 10 hours of flying after painting I started to see a little AvGas seepage
around the same rivet even after painting.
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  #28  
Old 06-26-2007, 04:23 PM
twlloyd twlloyd is offline
 
Join Date: Jun 2006
Location: Bayview, ID
Posts: 1
Default Blisters on aft tank flange rivet heads

RV8 N842TL

AC painted summer '05. AC assembled and 1st flight 11/05. Blisters appeared late summer 06. Blisters only on rivets of aft tank flange both top and bottom; both tanks. 75% of the aft flange rivets. Similar quantity top and bottom. AC is QB. Prep was soap & water w/ scotch brite on sander for clean up, Alumaprep 33 acid etch then water rinse followed by Aladyne (sp) then water rinse. Northstar epoxy primer and sealer, then Northstar poly white, then poly colors, then clearcoat. Time between primer and color less than a week. Then less then 2 days for clear coat.

No blisters for a year. Noblisters anywhere else on AC, just on the line of rivets that fasten aft flange to tank skin. When cut open there is no trace of gasoline - no odor, no blue die or any other discoloration.

Question - who has repaired the blisters and how successful was the repair?

Tom Lloyd
Sandpoint, ID
posted 6/26/07
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  #29  
Old 06-26-2007, 09:11 PM
casper casper is offline
 
Join Date: Jan 2005
Location: Derby Kansas
Posts: 146
Default

Quote:
Originally Posted by twlloyd
RV8 N842TL

AC painted summer '05. AC assembled and 1st flight 11/05. Blisters appeared late summer 06. Blisters only on rivets of aft tank flange both top and bottom; both tanks. 75% of the aft flange rivets. Similar quantity top and bottom. AC is QB. Prep was soap & water w/ scotch brite on sander for clean up, Alumaprep 33 acid etch then water rinse followed by Aladyne (sp) then water rinse. Northstar epoxy primer and sealer, then Northstar poly white, then poly colors, then clearcoat. Time between primer and color less than a week. Then less then 2 days for clear coat.

No blisters for a year. Noblisters anywhere else on AC, just on the line of rivets that fasten aft flange to tank skin. When cut open there is no trace of gasoline - no odor, no blue die or any other discoloration.

Question - who has repaired the blisters and how successful was the repair?

Tom Lloyd
Sandpoint, ID
posted 6/26/07
This is a twilight zone issue. As far as I know, No one has figured out why.
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  #30  
Old 06-26-2007, 11:31 PM
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N908RV N908RV is offline
 
Join Date: Mar 2007
Location: Warrenton, VA
Posts: 273
Default Me too...

Really glad I spotted this thread - wasn't aware so many were also having this problem.

For the record - for me only 2 blisters so far. Flown my RV-8 230 hours in the last 14 months since completion and no blisters until last month when the hot weather started. 2 blisters on the top of right wing tank only. In the silver section of paint (my leading edges are black - can't get any hotter than that in the sun - so forget about paint color).

QB wings, scotch brited wings, then cleaned with mineral spirits, then used etching epoxy primer (PPG), then dry and more scuffing with scotch brite and PPG single stage paint.

Popped a blister to check it out - no blue dye, no fuel, no nothing. Weird stuff.

I have forward facing fuel tank vents - stock location. My tanks were pressure tested and came out great with no leaks prior to final install.

Weird voodoo stuff going on.

-Rob
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RV-8, QB completed, flown 750hrs and sold
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