Fuel/Fiberglass Compatibility
October 1979
This year at Oshkosh, Nat Puffer had a partial power loss on take off and safely aborted. The cause was found to be a large amount of orange gummy residue in the carburetor. Our concern was that there might be fuel/epoxy incompatibility, possibly due to the high-aromatic automotive fuel he was using. In August we prepared and sent to all known VariEze flyers a detailed inspection procedure and survey questionnaire, to determine any trends.
Applied Plastics (APCO) also conducted an aggressive accelerated aging evaluation to determine if the aromatics used in high octane low lead fuel will deteriorate the epoxy. Results: APCO, RAES & RAEF showed a very slight amount of material extracted from the epoxy but well within acceptable limits. Under normal conditions such as the way VariEze’s are used it would take years of exposure to extract even a trace.
The new Safe-T-Poxy even under rigorous test conditions was essentially unaffected. Jim Tome ran some tests at a major Midwest lab and found that the aromatics in automotive and some aviation fuel 100LL will craze and leach out the hardener in a hardener-rich Lambert lay-up. This is probably what happened to Nat. Jim also found that the fuel additive ‘canned heat" and MEK can dissolve the new Safe-T-Poxy. The problems are with the aromatics the oil companies are using more and more of.
This is explained more in our fuel compatibility AD letter. Out of the 64 returned survey questionnaires, 52 had no problem at all, 10 reported a trace of gummy substance on the float/mixture needle valve. Several mentioned this could cause the valve to stick, this is becoming a common problem with many other aluminum-tank airplanes using 100LL. One reported a gummy substance in the bowl like Nats. We will be analyzing this sample.
Our conclusion is that the RAEF and the SafeT-Poxy, when properly mixed, should not deteriorate when exposed to aviation fuel. However, as a precaution we are recommending routine carb bowl inspection. If you are a VariEze flyer and did not receive our survey on the fuel contamination inspection/questionnaire, then we don’t know you are flying. Write to us giving your N number, name, address, and date of first flight. We will send you the survey and add you to a confidential list. This list will be used only to mail you any urgent flight safety information.