Brodhead Pietenpol Association

Original Posted By: "jimboyer(at)hughes.net"

Original Posted By: "Glenn Thomas"

Original Posted By: "Owen Davies"
Following this materials thread a tad late. But gotta point out a couple very important things to you folks that have decided the materials selections normally used by homebuilders can use improvements: 1) epoxy resins, especially made for homebuilt aircraft have a very long good record, tried and test for over 40 years, 2) one of the absolutely most important characteristics needed by a resin for homebuilts is- resistance to thermoplastic creep. I worked quite a few years in the polyurethane and epoxy industries, supplied Rutan and just about everyone else in the composite homebuilt industry with polyurethanes and epoxies, sooooo can tell you first hand, there ain't no such thing as a good polyurethane resin for structural parts on an aircraft. Polyurethanes by their very chemical nature are going to have more "rubbery or thermoplastic" type chemical bonds when polymerized. One component polyurethanes that are cured by the ambient moisture in the air or in the substrate ie. the H2O in the wood, are just not going to be thermoset enough to not creep when under load.. Just the wing's weight hanging out there 15' is going to make the resin want to creep under this load, especially on a nice hot day. But this is a hobby for folks with free will and afterall you get to be the test pilot. Just remember one thing, as the spars sag with heat or slowly creep out of shape, you were warned.Gordon----- Original Message -----