Years ago - about 1970 - Harry Schneider laid up a sheet of GRP on a base of Vorgelat. The cured sheet was nailed up on the Eastern wall of the workshop after it had been divided into three sections.
One remained in the original Vorgelat gel-coat and the other two were covered respectively with a coat of white and red acrylic lacquer. The Vorgelat surface began to fail after a short time while that covered by the lacquer showed no deterioration until we removed small areas of lacquer then failure occurred as it had on the original surface. Harry also laid up another small sheet, half of which was on Glasflugel's original epoxy gel- coat and the rest on Schwabelac. After more than 20 yrs. neither surface showed sign of cracking though the epoxy gel did display surface chalking which could be restored to its original gloss with a cut and polish. That surface did have a finite life and eventually needed a coat of paint when the primary structure began to appear as a light shade of grey. Rudi Lindner realised this issue early on after being involved in the design and manufacture of all the Phoenix' and so - when he was involved in the Phoebus production decided to use P/U as a surface finish over gel-coat. My first introduction to problems with P/U came when Dave Fergusson asked me to advise on an issue re. his syndicate Phoebus C which had apparently developed white chicken pox. When we pulled the wings out of the trailer their upper surfaces were covered in pimples of various dimensions. So were all other upper surfaces and it transpired she'd been put in her trailer without being dried off after a rain shower. The only conclusion I could make was the P/U was not water proof and the rain droplets could, in fact, pass through it into a hygroscopic primer. When the structure was interned in its trailer and heated the only way the absorbed water could go was to its outer surface. The water could not reverse its direction slowly enough to escape through the P/U and so created the pimples. Based on this I suggested Dave get the finest hypo syringe - insert it into the pimple and use its suction to withdraw the water. Can't remember the outcome. If you download any of the aircraft re-covering manuals that use woven synthetic fabrics there will be a "WARNING". If this fabric is exposed to UV without prescribed sealing and painting it will become un-useable in a very short time. However, the ORATEX manual claims its material is un-affected. I'm in the process of replying to Ian McPhee's request re synthetic re-covering and will post to all when completed. Stand-by. Noel. -----Original Message----- From: Aus-soaring [mailto:[email protected]] On Behalf Of DMcD Sent: Thursday, March 16, 2017 12:31 PM To: Discussion of issues relating to Soaring in Australia. Subject: Re: [Aus-soaring] Oratex UL600 and the unexpected Regarding the fading of the red Oratex…… Back a few years ago, a major supplier of paraglider Nylon brought out a fluoro range… paraglider pilots love(d) that sort of thing… but they found that some colours were very badly affected by UV compared with others and some of these fluoro colours were degrading within a season. Paragliders are more critical because the fabric is so lightweight but back in the litigious 80s, a pair of US airline pilots parked a Quicksilver (?) in the open for some time and were killed when the fabric tore. The fabric supplier was successfully sued by their widows on the basis that airline pilots are not expected to know about UV degradation. I have also heard from fabric suppliers, that white is to be avoided compared with darker colours because the white requires more bleaching from the base greige cloth and that makes the fibres weaker. Water absorption makes many fabrics weaker too. And you get mould wicking into the fibres over time, especially in humid climates. All this means that the best idea is to put a full range of samples on your hangar roof and forget about them for 15 years while you sit inside and worry. Interesting topic though. D _______________________________________________ Aus-soaring mailing list [email protected] http://lists.base64.com.au/listinfo/aus-soaring _______________________________________________ Aus-soaring mailing list [email protected] http://lists.base64.com.au/listinfo/aus-soaring
