Eriselle
Member
Hi there, I am working on an unfortunate project and I'm trying to figure out how far I need to go with it. The airplane is an RV-12 Legacy, SLSA factory built by Synergy Air back in 2016.
I recently was experiencing some avionics issues and needed to access the avionics bay to make the required repairs. When I attempted to remove the avionics bay cover (F-1240 Skin), I found that it had been bonded to the F-1201H Upper Fwd Fuse Doubler and F-1202H-L & R Canopy Ribs with RTV black. The KAI instructions 29A-06 step 8 call for a release agent such as Boelube to be used to prevent the F-1240 Skin from bonding- because the RTV is only supposed to create a gasket, not permanently attach the skin. It took about 18 hours of labor to carefully separate the F-1240 Skin from the F-1201H doubler and F-1202H-L & R ribs. After that, it took another 10 hours to clean up all the RTV from both mating surfaces.
Unfortunately, this all had a secondary consequence. The RTV black was bonded to the fuel tank sealant used on the perimeter of the F-1201A Firewall Upper assembly (see KAI 29A-03 step 7). From the looks of it, the fuel tank sealant and the RTV black mutually cured to each other, there was no clean break between them. As a result, it was not possible to remove the RTV without also removing fuel tank sealant. The removal of the RTV was done with a combination of manual effort with plastic razor blades and the usage of Digesil NC depolymerizer, which is designed to chemically break down RTV silicones. As pro-seal fuel tank sealant is also a kind of RTV polymer AFAIK (polysulfite, different chemically to RTV black AFAIK), the depolymerizer was also somewhat active on it, although it didn't do much to it. I'm not sure if there would be any long lasting effects to this exposure had I chosen to keep that fuel tank sealant, but I decided I do not want to find out the hard way that it is weakened, and chose to remove it as well. The fuel tank sealant is now damaged by partial removal and needs to be redone. Some googling suggested that Polygone will do a better job on the pro-seal than the Digesil NC, so I'm going to try that to finish up the cleanup.
It is not possible to fully remove the old sealant without drilling out rivets to separate the parts that the sealant is applied to. This is because it is wedged into and spread between mating surfaces. I can manually remove most of it, but it's far from perfect without disassembling riveted assemblies.
This leaves me with a couple of questions.
First, will pro-seal fuel tank sealant bond to already-cured older pro-seal fuel tank sealant? If the answer to this is yes, then it is at least possible that I can avoid removing rivets by just running new fillets over the old ones that I've mostly gouged and scraped out with a plastic razor blade. I may decide this is unacceptable anyway though due to the exposure of most of the seal to depolymerizer, which may have unknown impact on the sealant. It also may not really be possible to clean the fragmented pro-seal enough to be a reasonable bonding surface, even if the material itself clean would support a bond.
Do you think I can get this back to a watertight seal all the way around without doing a major disassembly of the upper firewall assembly? I'm very concerned that it will lose strength by being reworked, and the scope of how many parts I'd have to disassemble, redo the sealant on, and reassemble, is pretty daunting. Rivet holes stretch, dimples crack, drill bits slip, there's just so much that could go wrong here the more I muck with it. But I'm not sure I really have a good alternative at this point.
Small vent: I'm really upset that this wasn't done correctly by the factory. They saved some time I guess, but it really created an unnecessary mess for me to deal with here.
I recently was experiencing some avionics issues and needed to access the avionics bay to make the required repairs. When I attempted to remove the avionics bay cover (F-1240 Skin), I found that it had been bonded to the F-1201H Upper Fwd Fuse Doubler and F-1202H-L & R Canopy Ribs with RTV black. The KAI instructions 29A-06 step 8 call for a release agent such as Boelube to be used to prevent the F-1240 Skin from bonding- because the RTV is only supposed to create a gasket, not permanently attach the skin. It took about 18 hours of labor to carefully separate the F-1240 Skin from the F-1201H doubler and F-1202H-L & R ribs. After that, it took another 10 hours to clean up all the RTV from both mating surfaces.
Unfortunately, this all had a secondary consequence. The RTV black was bonded to the fuel tank sealant used on the perimeter of the F-1201A Firewall Upper assembly (see KAI 29A-03 step 7). From the looks of it, the fuel tank sealant and the RTV black mutually cured to each other, there was no clean break between them. As a result, it was not possible to remove the RTV without also removing fuel tank sealant. The removal of the RTV was done with a combination of manual effort with plastic razor blades and the usage of Digesil NC depolymerizer, which is designed to chemically break down RTV silicones. As pro-seal fuel tank sealant is also a kind of RTV polymer AFAIK (polysulfite, different chemically to RTV black AFAIK), the depolymerizer was also somewhat active on it, although it didn't do much to it. I'm not sure if there would be any long lasting effects to this exposure had I chosen to keep that fuel tank sealant, but I decided I do not want to find out the hard way that it is weakened, and chose to remove it as well. The fuel tank sealant is now damaged by partial removal and needs to be redone. Some googling suggested that Polygone will do a better job on the pro-seal than the Digesil NC, so I'm going to try that to finish up the cleanup.
It is not possible to fully remove the old sealant without drilling out rivets to separate the parts that the sealant is applied to. This is because it is wedged into and spread between mating surfaces. I can manually remove most of it, but it's far from perfect without disassembling riveted assemblies.
This leaves me with a couple of questions.
First, will pro-seal fuel tank sealant bond to already-cured older pro-seal fuel tank sealant? If the answer to this is yes, then it is at least possible that I can avoid removing rivets by just running new fillets over the old ones that I've mostly gouged and scraped out with a plastic razor blade. I may decide this is unacceptable anyway though due to the exposure of most of the seal to depolymerizer, which may have unknown impact on the sealant. It also may not really be possible to clean the fragmented pro-seal enough to be a reasonable bonding surface, even if the material itself clean would support a bond.
Do you think I can get this back to a watertight seal all the way around without doing a major disassembly of the upper firewall assembly? I'm very concerned that it will lose strength by being reworked, and the scope of how many parts I'd have to disassemble, redo the sealant on, and reassemble, is pretty daunting. Rivet holes stretch, dimples crack, drill bits slip, there's just so much that could go wrong here the more I muck with it. But I'm not sure I really have a good alternative at this point.
Small vent: I'm really upset that this wasn't done correctly by the factory. They saved some time I guess, but it really created an unnecessary mess for me to deal with here.
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