I remember Mark Langford saying that public confessions were good for the soul or something like that. That also makes it more difficult to get elected to political office. I am looking for neither of those concerns. I once recommended building fiber glass fuel tanks using Vinyl Ester Resin. All sources that I could find did say that Vinyl Ester was compatible with the Ethanol found in most automobile fuels today. Conversely, Epoxy was not compatible with Ethanol. I built the wing tanks in my Diehl wing skins using Vinyl Ester Resin per the Diehl instructions. When I put in 92-octane auto fuel containing 10 percent Ethanol, I got the same reaction as if the tanks were made with Epoxy. Surfaces slowly started to dissolve, fuel turned yellowish brown and a sticky brown goo starting clogging the sumps. I researched my sources on the internet and all still confirmed my previous conclusion. Looking a little further on solvency chemistry, I found internet sites that address ways to enhance solvent action. Pure Ethanol, gasoline and water are excellent solvents by themselves, but none of these alone will effect cured Vinyl Ester. Adding 6 percent water to Ethanol will produce a solvent that will slowly dissolve Vinyl Ester. So, how much water would that actually be in auto fuel containing 10 percent Ethanol? The math is easy: 10 percent of 6 percent is 0.6 percent. That's less than 1 ounce per gallon. Where does the water come from? From the moisture in the air, the Ethanol will readily adsorb the water in half full tanks, especially if there is a vent like most aircraft tanks (like mine). I now have drained the tanks and left the caps off. After 2 weeks the goo on the inside surfaces has "re-cured" hard just like the original. The quick-drains had become clogged and have been replaced. One concern is the integrity of the tank walls; there is an imprint of the foam layer sandwiched between the inner and outer wing surface, top and bottom, that outlines the wing tanks. This imprint pattern appeared when the drying out process was started. Any ideas what is going on with that? Long term plan now is to use 100LL.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA [email protected]
