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Tim Ward wrote: wrote in message oups.com... Tim Ward wrote: Well, on sailplanes, anyway, you sand to make sure the airfoil is the right shape, (shrinkage can occur over the spars after some time out of the molds), and to make sure that any waves in the contour are less than .004 inches. That's another reason to try scraping. Scrapers can be filed to a particular curve for just that sort of work. The curvature changes continuously chordwise, and most sailplane wings have taper, so the curvature will change with the spanwise station as well. So it's difficult for me to see how you could cut a single curve that would match. You can do that by skewing the scraper and adjusting the angle of atttack between the scraper and the wing. How do you vary the curvature when shaping with sandpaper? Now, for a constant chord wing, that might make an interesting production technique: Build your wing, then build up an extra layer of filler, then "extrude" the whole wing panel through a CNC cut scraper, getting exact, smooth coordinates on the way. Yes, that would be easier though I still don't see how it would be done with sandpaper, and think it would be especially difficult with sandblasting! It is also the case that not all homebuilt aircraft wings are fabricated to the same exacting tolerances as state-of-the art sailplanes, right? -- FF |
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On Sun, 30 Jan 2005 21:14:08 GMT, "Cy Galley"
wrote: You can e-mail Steve Beert at As I understand, the sand blasting prepared the surface for bonding by roughing the epoxy without cutting and weakening the glass. Are you sure he wasn't bead blasting or even CO2 blasting. I've done a lot of sand blasting and it normally accentuates any imperfections rather than smoothing. I'd not want to use it on anything other than steel and even then it will peen the surface causing a warping. On fiberglass the resin is tough and the glass is hard. If there are any variations between wet and dry they should show up. Even the pre molded shells are often sanded through the gel coat and into the resin. Then given a thin coat of microsphere mix which is then block sanded with very fine grit. There have been several G-IIIs at Oshkosh that had the entire wing and tail assemblies done this way to get an unbelievably true surface. If I recall correctly the one guy had close to 4,000 hours in prepping and painting the surface. More than some put into building the same airplane. that was an all white airplane with a little trim, not like the lancair 320 that had the Winged goddess on the bottom. I think he had over 4000 just in the paint and prep. But for me, and fiberglass... I'd not let any one with a sandblaster near it no matter how good they are supposed to be. To me, it's just too risky. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com snip many layers |
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