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  #71  
Old 09-14-2007, 06:44 PM
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cthelan cthelan is offline
 
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just started to form the blisters on our quick build 8a too
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  #72  
Old 09-22-2007, 06:18 PM
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wyoflyer wyoflyer is offline
 
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Default blister picture

I've noticed through all of these threads that no one has posted a picture. Here is mine. As a data point....paint is Dupont, base/clear, primer is DB40 epoxy, skin was scuffed with scotch brite and washed down with laquer thinner. Although the pressure in the tank theory may be correct for some tanks, mine is definitely not one of them. All of these rivets are on the non-fuel side and one tank only. Whatever the cause, I just don't think it's a pressure thing.
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  #73  
Old 09-22-2007, 08:28 PM
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wyoflyer wyoflyer is offline
 
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Oops, let me try again.....
http://img233.imageshack.us/img233/6537/dscf0765mi5.jpg
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  #74  
Old 09-23-2007, 05:24 AM
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Rick6a Rick6a is offline
 
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Quote:
Originally Posted by wyoflyer View Post
I've noticed through all of these threads that no one has posted a picture. Whatever the cause, I just don't think it's a pressure thing.
My theory is well known....so naturally I'd be interested to know if the shop heads of the rivets were properly encapsulated. So far, I've seen no real evidence....none so far....that would cause me to abandon my theory about the root cause of this problem. Since in your case the blistering seems to occur along the back baffle, removal of the tank from the wing would very quickly confirm if the rivets were encapsulated or not. If they are encapsulated...and you provide us with detail photos of acceptable encapsulation......I would then resume my place among all others who have no real idea as to what is causing the problem. If however, in your case the shop heads of the rivets are not properly encapsulated, I believe you (unlike many others) can anticipate a relatively easy fix.
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Last edited by Rick6a : 09-23-2007 at 05:46 AM.
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  #75  
Old 09-23-2007, 06:13 AM
rv72004 rv72004 is offline
 
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To put this whole blistering story to bed. IT IS CAUSED BY FUEL !!!
Blisters only occur on the tanks. So only the tank sealant or its application is to blame. Start by using a different brand of sealant .
This is my opinion and I would put money on it. FWIW I also had blisters as well as sealant going soft on the outside of the root rib.QB tanks. I tried replicating this using a different supplier of tank sealant with no success.
If i were to build again I would go slow build on the tanks with a better tank sealant.
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  #76  
Old 09-23-2007, 07:23 AM
David-aviator David-aviator is offline
 
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Quote:
Originally Posted by wyoflyer View Post
First evidence of blisters with my QB tanks was along the bottom aft flange as per the image. That was some 3 years ago. The blisters now are evident top and bottom at nearly every rib. I've seen a couple new ones this summer. They just keep coming. An inspection with flashlight through the fuel cap reveals some shop heads not covered with pro seal.

Is there a way to forward this entire thread to Van's? Seems like they ought to be interested in getting to the bottom of this problem and coming up with a fix. If it is affecting just 10% of the fleet, that is some 500 hundred paint jobs screwed up. Considering that many affected tanks are QB, the cause is related to factory methods to build the tanks.
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  #77  
Old 09-23-2007, 08:36 AM
rv72004 rv72004 is offline
 
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Not meant as any disrespect to Vans, but I have always felt they market their product as "affordable" and things like the blistering does not bother them as it is not a safety issue.
Forwarding this thread to them will be futile. IMHO.
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  #78  
Old 09-23-2007, 10:59 AM
BillL BillL is offline
 
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Default Other factors to consider?

I signed up just to weight in on this blistering issue - I was thinking about some other factors to consider:

Fuel types - potental failure mode 1.- if the proseal (or its likeness) is permeable to short chain HC fractions of the fuel then the higher temp of the sealant could be penetrated by this vapor and since primers are porus, then the minute amount of vapors are stopped at the top coat layer. Either flying or sun heating and expansion results in the separation of the top coat and thus a blister. pressure collects factor 2. #1 + debonding of topcoat to lower adhesion due to vapor type.

Just a thought, but in looking up the mil spec (mil-s-8002XXX) it always looked at aviation fuels using a "jet reference".

Idea #2: Temperature of fuel - what is relevance of fuel system type - recirculation types (injected) are more prone to add temperature to returning fuel and possible increase the vapor pressure of some fractions. ( a low probability, little out on a limb here)
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  #79  
Old 09-23-2007, 11:29 AM
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Mike S Mike S is offline
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Bill, welcome aboard.
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  #80  
Old 09-23-2007, 12:37 PM
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wyoflyer wyoflyer is offline
 
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Just a few more points. I too would be curious what the back side of the baffle around those rivets looks like. I haven't had the tank off yet to look but it will be easy to check, once I do. Also, that tank is the only one that has only had Av gas in it. I keep one tank solely for Av and the other has auto or Av gas. I really think it is a fuel issue also, but am hesitant to just strip the tank and paint it again and have the same problem.
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