I thought I would write an update to this discussion we had in early October regarding polyester fuel tanks. Especially since I referenced the polyester tip tanks in the Cherokee 235 and Cherokee 6 aircraft as proof of success using polyester resin for fuel tanks. This week I have a Cherokee 235 in my shop and am rebuilding the tip tanks. The owner bought the Peterson Autogas STC 5 years ago and has been running Mogas in the these tanks for the last 5 years. The owner also states that he has carefully tested for alcohol every time he has purchased mogas to use in his plane, so these tanks have never been exposed to alcohol.
The tank construction consists of a two laminate outside shell of polyester impregnated woven glass cloth much like the 5.85 oz KR glass, then a layer of polyester impregnated non-directional glass matting used as a core material, then an inner shell of polyester impregnated woven glass cloth. There was a final painted on coat of polyester resin used to seal any pinholes in the tanks. The aft and side bulkheads are a thick built up multi-laminate layer of woven glass cloth. The result of 5 years exposure to mogas: The mogas has permeated through the inside polyester resin impregnated cloth weave and soaked into the glass matting core of the tank causing numerous pockets and voids in the glass mat core between the lamina in fuel tanks. The resin in the mat core material is very soft and gooey and all of the pockets along the bottom of the tank were still full of gas even though it has been over a month since the tanks were drained. The damage at the top of the tank where the fuel was sloshing against it was even worse than the bottom of the tank. The tops of both tanks had voids in the lamina as large as 6 inches in diameter that had to be cut away and patched. The polyester resin has softened and delaminated to the point that the fuel tanks were deforming in flight. The tanks were also dropping much of the interior resin coating into the fuel also causing fuel particulate contamination. The built up bulkheads appear to be mostly unaffected other than peeling of the final painted on coating of polyester resin used to seal the tanks. These tanks have been in service since 1969, never had a service difficulty or any damage, and were never exposed to mogas until 5 years ago. I have had to cut and grind away most of the insides of the tanks and am building them back up with a good quality epoxy resin, literally building a tank within a tank. I have also advised the owner to not expose the tip tanks to mogas in the future even though they will now be lined with an epoxy based resin. OK, so this is some real world data regarding long term exposure of Polyester Resin to Mogas. Jeff Scott Los Alamos, NM ------------------------------------------------------------------------------------------------------------- Date: Oct 1, 2009 7:30 PM I thought it didn't do well with auto gas among some shrinkage issues similar to what you see on old boats. Steve Glover ------Original Message------ From: Jeff Scott Sender: [email protected] To: KR Net ReplyTo: KR Net Subject: Re: KR> RE: vinyester vs polyester Sent: Oct 1, 2009 6:21 PM Don't know. Piper never intended for their planes to have alcohol in them. That may very well be the reason why Steve Glover says not to use it. -Jeff Scott Los Alamos, NM On Thu, 1 Oct 2009 16:18:01 -0700 "Fred Johnson" <[email protected]> writes: > How well will it hold up to alcohol? > > > Fred Johnson > Reno, NV ____________________________________________________________ Liberty University Online Earn a bachelors degree online in Nursing. Get free info now! http://thirdpartyoffers.juno.com/TGL2141/c?cp=uU5PrT8NeQD7MVNL6R8UWgAAJ1A9mk8a0luj1TJO2sh3zRLgAAQAAAAFAAAAAJanMT8AAAMlAAAAAAAAAAAAAAAAABSGmAAAAAA=
