Well folks, the repairs to my fuel tank are done and I expect to turn the key for the first test flight on Wednesday May 27, 2015. Actually, I could do it today, but opted for prudence. Hopefully, by adding a few extra days of resin cure-time, I will ensure that the MGS L285 epoxy used for the repairs develops its full resistance to fuel.
Make no mistake, I was pretty darned upset and angry when I found this mess and saw how difficult and time-consuming any “fix” was going to be. Adding to that was the frustration of knowing we were pretty much “on our own” in executing this repair, inasmuch as I am presently the only Sting owner we know of to embark on the journey (although two or three other early-model Stings have now also been found with fuel-tank issues and are being assessed for repair).
But now that the job is done and I’m about to get my airplane back, I’m becoming mellower. The difficulty I perceived at the beginning was mostly due to my unfamiliarity with fiberglass repairs, especially the vacuum-bagging process. However, I was able to turn that lack of knowledge into a very satisfying learning experience! In fact, although rather costly and physically demanding (working inside that little tank) this all was actually rather fun (though not something I would choose to do again)! In addition, I am now more of a pragmatist: Despite every attempt to make them perfect, all airplanes, including factory-built ones, will invariably have “stuff” that fails or goes wrong. Why should I let one bad event sour my perception of my airplane and its manufacturer–-a craft that’s provided me almost 1,500 hours of sheer joy–-and reliability–-up to now? What I intend to do instead is to help them (i.e., the manufacturer and US distributor) develop appropriate service bulletins for dealing with this issue, however widespread (or limited) in scope and severity it proves to be.
A final reason for mellowing out from my initial “attack mode” over this issue is that fault and blame are going to be difficult, if not impossible, to assign in this case. Was it the E10 gas (i.e., the 10% ethanol), which was supposedly okay to use? Or was it manufacturing defect(s)? Actually, both could be involved. But what about the other “wild cards” in the game, such as all the “additives” that gasoline refineries (especially here in California) put into auto-gas, including MEK (methyl ethyl ketone), with its known composite-dissolving ability? Was repeated ingestion of one of these additives the real smoking gun? And what role did those original owners of my airplane play (such as allowing E10 to sit for long periods in the tank, possibly until phase-separation occurred) during those first 2 years, including while it sat for an extended period in the dealer’s hangar? Or did those stiffeners delaminate (or crack, leading to delamination) during some out-of-bounds G-pulling maneuver by me or the earlier owners, whilst carrying a heavy, tank-load of fuel? There are so many possibilities, but scant hard evidence as yet pointing to the primary culprit.
So now I’m going to refrain from blaming. Nevertheless, I will be minimizing my risks going forward. Most of my flying will be done on the Pure-Gas (alcohol-free, unleaded, auto-gas) I haul in with my little 108-gal fuel trailer. When that’s not available, such as on long trips, I’ll of course be turning to Av-gas. And if and when I do have to use more E10, I’ll be sure to test it first, to ensure it doesn’t exceed 10% ethanol; and I will also ensure it doesn’t sit in the tank for long periods (more than a few days) when the airplane is inactive. (I should reiterate here, that if my fuel tanks were metal, not composite, I wouldn’t be worried about all this and would likely just be running the E10.) Another form of mitigation will be to keep G-forces to a minimum when the fuel tank is loaded with significant weight from fuel.
Anyway, now back to what we did to effect the repair on my main fuel tank (the rarely used wing tanks, which lack stiffeners, were just fine). (But first, just to reiterate: There was no fuel leakage anywhere, yet; the problem was (a) beads and flakes of resin which were being observed in fuel-sump samples, and (b) the tank possibly not being structurally sound with a full load of fuel.) The tank has two laminated honeycomb (Nomex) “stiffeners,” one to the right and one to the left side along the bottom and sides of the tank. The glass surface of the right one was completely delaminated and the Nomex inside was fuel-saturated; we dried and sanded it out, then laminated (i.e., vacuum-bagged) in a new honeycomb stiffener. The original left stiffener was not delaminated, but did appear thin and brittle (with possibly some initial fuel “weeping”), so we dried and dressed up that surface, too, then vacuum-bagged on a new surface-covering of glass. Next, the filler neck was sanded and touched-up as needed, using the L285 epoxy thickened with micro-balloons; no new fiberglass cloth was added and the neck was not leaking (although the initial fiberglass work had been very “sloppy,” at best). Finally, the whole tank was given another sanding, followed by a final over-coating with the L285 epoxy. Then the tank lid, which is the floor underneath my legs, was laminated back in place, with L285 epoxy.
The pictures below show the process as the repairs were made and the plane was slowly brought back to life. One word of caution, however: Do not employ the heat lamps you see in the photos unless they are kept well back and/or used with strategically-placed fans. Otherwise, the foam-core decking (and/or tank lid) will overheat, soften and warp.
Stay tuned. I’ll be providing a follow-up report after I fly a few tanks of Pure-Gas through her. Now, let's just hope that everything works when I hit that starter button!
Last edited by drdehave
on Wed May 27, 2015 9:48 am, edited 1 time in total.