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l'll say it a bit differently. I have not worked withthe Flamemaster product, only the PRC product. Has anyone seen this problem with the PRC product?
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This can begin to tell us the failure rate (or MTBF) in calendar days, etc. |
So is the theory that the leak occurred because the sealant turned to goo.... or the sealant turned to goo because the leak wasn't addressed?
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I've been down this road with quick built tanks that did not leak but showed dozens of blisters at rivets and am not convinced anyone has hit on what is going on with the sealant going goo or blisters that do not show fuel stains or building technique applying the stuff.
What I do know, and it is not conclusive or prove anything for sure, is if you apply enough of the stuff inside the tank at ribs and covers and rivets, the tanks do not leak and the blisters do not appear - at least so far in my history with this stuff. The RV-7A now owned by Jerry Cochran is not showing blisters to my knowledge (about 6 years,new tanks I built) and neither is the RV-8 (about 2 years). So the message is - use lots of sealant, don't be bashful about it, cover every possible place a fuel can leak out with much of it. With any luck at all, it won't leak. And don't get all hung up with the cosmetics of how it looks. The worst cosmetic effect is seeing blue on the outside of the tank. |
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Returning to sealant reversion.... This from a study conducted for the Navy: ![]() The complete paper is available for download here: http://oai.dtic.mil/oai/oai?verb=get...fier=ADA087267 There are some interesting clues regarding oxidation of fuels (which apparently leads to sealant reversion) in this paper: https://web.anl.gov/PCS/acsfuel/prep...08-90_1277.pdf 100LL also has significant quantities of antioxidant added to meet the requirements of long-term storage. This list of approved antioxidants is from the UK 100LL standard; North America and AUS assumed to be similar: ![]() I would suggest a theory ("theory" = an unproven supposition needing work to determine if it is true or false) that when 100LL gets outside the tank (like one of these fuel leaks) the antioxidant evaporates or is combined/dissolved (i.e. all used up), leaving the leaked fuel subject to a high level of peroxide formation. Acid formation may be involved/required per the paper quoted above. The acid contribution seemed to be an unknown at the time of publication (1980). I am not a chemist, which is why I would like to see a detailed technical explanation from the sealant manufacturer. Failing that, perhaps we can crowd source a qualified individual from our ranks; we have a huge collection of intellect and education lurking on VAF. |
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Soft ProSeal
This thread sparked my interest since I recently observed this on an aircraft that was in service for nearly 10 years. Thing is, the softening was occurring on every sealed joint on both tanks. Even those that showed no staining from leaks. If the softening is the result of the presence of oxygen and gas, well guess what, they are both constantly present. If this is the case proseal is a poor choice.
After looking at the multiple threads on this, I tend to agree with the observation that it appears to be manufacturer specific, especially in occurrences after years in service. I wonder if an informal tally of occurrences would point this out. The difficulty is many aircraft are no longer owned by the builder so identifying the product manufacturer will be difficult. Further complicated by whether or not the builder documented the source of the sealant. I have inquired with some jet service center techs that regularly use proseal type products on fuel tanks and none have seen this. The common response was "the older it is the harder it gets". The opposite of what is occurring in these threads. Of course these shops are going to be very conscientious regarding MIL-Spec and source to meet certified standards. Experimentals are not held to that. Maybe we all need to take stock in the old adage: you get what you pay for! There are simply some corners that should not be cut. |
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