Re: Well, This Will Made My Heart Sink ... Trying to repost with Pics

David J. Gall


That patch of glass you showed that’s “not wetted out enough with dry spots” looks like the original inside layer of the factory fuselage shells. The factory shells were (apparently) not made using BID but using a lighter cloth, and this appears to be a typical bit of that. The shells were manufactured a bit “dry” and it doesn’t surprise me to see such “dry spots.” I have some original factory shells in storage and they look very much the same, absent the damage caused by improper construction and long exposure to fuel. In other words, this appears to be a “normal” fuselage inner skin except for the apparent skipping of some very important steps on the part of the original builder. The inside of the tank was supposed to be sealed during construction by applying liberal coating(s) of Safe-T-Poxy (or EZ-Poxy) and it appears to me that this step was skipped by whoever built this airframe. Or perhaps they used a different epoxy that was inferior in fuel resistance to Safe-T-Poxy (EZ-Poxy) and that layer dissolved and leached away over time.

Since the fuselage shell foam is a urethane that should have been at least fuel “resistant” I would presume that the damage to the foam was caused by long exposure to MoGas (as opposed to avgas that contains less VOCs). So my next concern would be the header tank integrity and the integrity of both the main wing center section and especially the canard center section. Both of these center sections have foam cores that are susceptible to VOCs even in the vapor state without direct contact with liquid solvents. Long-term sitting outdoors with MoGas in the tank could mean that temperature cycling would “pump” VOC vapors throughout the fuselage and could, over time, work it’s way into and degrade the foam cores in the wing and canard center sections without any evidence. I support my hypothesis by observing that there is little or no blue dye present such as would be found if the leaks into the lower fuselage shell had developed with avgas in the tanks. Of course, the canard could have been the recipient of liquid fuel leaking from the header tank, too.

I would urge a rebuild of the header tank since it’s bottom likely has a similar problem as the main tank, and I would urge a very thorough tap test or, better, a sonogram or visual inspection of the wing and canard center section cores. I would also urge a complete replacement of all fuel system components to preclude the possibility that some softened epoxy collected internally in e.g. a fuel selector valve or other fitting (this is a known hazard of some epoxies when exposed to the VOCs in MoGas).

Of course, all of the foregoing is just my opinion and speculation offered for your consideration.

David J. Gall

On Jul 23, 2022, at 10:32 PM, Robert Schmid <robert@...> wrote:

And here is the inside tank later looked like ...



Glass not wetted out enough with dry spots

Robert "TheFrisco" Schmid
(408) 805-5450

Love building planes almost as much as flying. Latest completed build is "Loki", a Chinook Plus 2 bush plane.

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