Saturday, December 13, 2008
Covering: doors
I finally have reached a major milestone and have begun the covering process. I decided to start with the doors since they are not control surfaces and look fairly simple. I'm using the Superflite product process which encompasses covering, adhesive, primer paint and topcoat paint. The adhesive is called U500 and needs to be thinned with methyl ethyl ketone (MEK). MEK is highly volatile compound which allows the glued areas to dry quickly. I have learned that the Rans fuselage is epoxy primed and remainder of painted parts are powder-coated. It turns out the MEK compound will quickly dissolve the powder coating so several coatings of straight U500 needs to applied first as a foundation. When the fabric is applied, thinned U500 (3 parts MEK to 1 part U500) is applied to the top of the fabric and the underlying basecoat is then dissolved and wicked up through the fabric. Outside of the wings and fuse, all of the parts to be covered are powder-coated and will follow this application regimen. Dacron fabric is the covering and an iron is used to taut the fabric at three temperature settings: 250, 300 and 350 degrees. Each temp setting results in a greater degree of fabric shrinkage so that at the final temp the dacron approaches a snare drum type quality. The iron also smooths out the surface of glued edges where any wrinkles might be present. Following is a pic of one side of the door covered and ironed to 250 degrees. I'm amazed at how uniform and tight the dacron got at 250 degrees. Need to apply each temp to alternate sides of surface stepwise to distribute shinkrage tension or piece could severely warp. It is important to have each fabric layer glued nearly completely around each structural member in order hold fast to the fabric shrinkage.
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