General Aviation Modifications Inc. is inviting an operator of a wet-wing Mooney to visit its Ada, Oklahoma for a borescope inspection to assess the condition of the sealant in the tanks. "I would like to have the chance to borescope an older Mooney fuel tank that has not been converted over to a bladder," Braly said in post on mooneyspace.com. The invitation was extended after two California owners reported issues with fuel leakage after putting GAMI's G100UL in the tanks. The fuel is available at three California airports.
Similar damage has been witnessed, photographed, and reported to the aviation industry over the last several years with fuels containing aromatic amines. This leaking of sealants, staining, and stripping of paint in this fuel is most likely caused by meta-toluidine, an aromatic amine - and a very aggressive solvent - contained in G100UL according to the safety data sheet and the FAA independent specification. For clarification, Xylene mentioned above is not an aromatic amine - it is a C8 aromatic hydrocarbon also generally described as a solvent.
“Sealant doesn’t last forever” doesn’t win you any friends when you’re trying to introduce a new product. That’s why “You win some, you lose some” never csught on as a slogan.
Mutter mutter at Chrysler who for some reason used an inferior material on fuel lines of 3.3/3.8L V6s in early 90s, instead of well known viton.
Leaks occurred after many years, perhaps exacerbated by owners adding fuel injection cleaner to the fuel tank.
This is the reason we need two grades of fuel at the airports.
For those who don’t what to change their engine to run on UL94 there can be available a very expensive fuel with unknown problems.
For the rest of us we can continue to use the old fuel we always used but without the lead thereby leaving behind all the dangers, risks, and engine damage lead contaminated fuel can cause.
To be fair, wet-wing Mooneys are prone to leaking fuel at the forward spar and landing gear interface because the aft wall of the fuel tank is the spar itself. Flexing and landing gear loads will stress the sealant used to prevent such leakage. Anything that adds to the likelihood of leaking is a risk assumed by the operator.
What is unfair is to accept this added risk by State mandate when suitable and properly vetted alternatives are not made available.
This sounds like an age old problem that should’ve been fixed long ago with the addition of a bladder tank to permanently fix this problem and not try to blame it on a newer fuel or the promoters of that newer fuel by saying it is unfair.
This sounds just like the AOPA Baron leaking at Airventure.
“It was fine last week” Of course it was. Everything works fine right up until it breaks.
If it had started to leak two weeks earlier, this would not be a story.
Some context would be helpful. How many airplanes have had G100UL, for how many years, at this point? And how many have leaked? Two.
Mooney fuel tanks don’t use bladders. The tanks are sealed, from the factory. When they leak you strip the old sealant and reseal them. It’s a normal maintenance item that needs to be done periodically, just like engine overhauls, shock disk replacement, brakes and tires.
It took me a while to figure out that I was looking at a gear door attachment as if I were standing on my head, and that someone had not painted the tarmac sky-blue. The visual cortex is oriented to gravity, which is why flying an ILS inverted is a bigger challenge than usual. I could not find the forum with the original image, but if the mistake was there, I think it would have been within your editorial powers to correct it.
The following is reposted (with permission) from Del Lehmann.
Del Lehmann owns / runs a repair shop in Mena Arkansas.
- - Mountain Airframe LLC.- -
-
His experience with Mooney fuel tanks and repairs is worth understanding in the context of this discussion.
"I can tell you this from my experience re-skinning damaged Mooney wings. Mooney riveted the wings together dry (no faying surface sealant), and then top-coated the rivets and seams on the inside. It’s no wonder they are problematic.
Beech, Cessna, Piper integral fuel tanks have all had faying surface sealant in addition to top-coat (at least the models I’ve worked on). But even done right, we are seeing a lot more integral tank leaks in the last few years that can’t be re-sealed without totally de-riveting the integral tank skins/structure and removing all old deteriorated/compromised sealant.
The lifespan of the sealants used for integral tanks appears to be 40-50 years, which coincides with the introduction (mid/late '70s) of integral cells on 100 series Cessna, intro of wet tips on the 58P and TC. Piper and Mooney have been at the integral cells a lot longer than that, but they also have had many specialty shops and “fixes” available for a lot longer."