Well, maybe I can bring closure to this blasted 'worm' thread I started some time ago. Just finished several things and the result is not very conclusive nor very satisfying. Nickel version:
15psi or 25psi foam at 10in Hg vacuum - no surface defects in any samples. Same result with either the 'Mighty-Mini' continuously running pump or the standard pump (with reservoir) regulated at that pressure. 15psi foam at 23in Hg - one or two defects but much reduced from when this adventure started - even an occasional sample with no defects, 25psi foam at 23in Hg - none So there is some association with vacuum level and foam type. However, much more attention has been paid to handling the cores when peeling the mylars and that may also be a factor. The wing surfaces have been observed to be more robust when heavier cloth is used so the very light nature of this lay-up may be a contributing factor. Whether the lay-up is bone dry or somewhat wet hasn't mattered. Whether the lay-up was 0-90 or 45 bias hasn't mattered. The nature of the breather and whether the beds were inside or outside the bag hasn't mattered. The release wax may be implicated but not from the initial thought of trapped volatiles. If the mylars are harder to peel off the core, you're prone to damaging the surfaces and that may be a factor. I finally tracked down some 100% carnauba (West Marine) and that release is not as easy as I got from plain old fashioned Turtle Wax. However, Turtle Wax is rather soft and will leave a film on the cores when they come out. Pure carnauba is usually a harder wax and does not seem to transfer much to the wings. Maybe a longer cure time or?? would address this issue. Again, the very light nature of the lay-up may exacerbate the ease of release with these waxes. I'd definitely stay away from any carnauba that's labeled as a 'polishing' or 'cleaning' wax. Those have a small amount of filler that tend to grab the mylars a bit while curing. Out here in the boonies that's all we've got in the auto parts stores. Finally, I had expected some compression of the 15psi foam at the higher vacuum pressure as compared to the 25psi. Nope. Wrong again. Just mic'ed a couple of cores of each at the thickest part of the root. 25psi foam thickness average (core plus skins) is 0.428". 15psi foam wings (core plus skins) measured at the same location is 0.429". Bottom line, to be on the safe side, I'd use 15psi foam at ~ 10in Hg and 25psi at any pressure you want. But I can't say that's an absolutely hard line to draw. One lesson learned - absent this surface defect problem, it's pretty hard to screw up the vacuum bagging process. If you see surface defects, try dropping the pressure as the first response. If that's not successful, toss the foam and get some new stuff. That also seems to be implicated in these adventures. At this point, however, there is no bulk density penalty with 25psi vs 15psi foam. And the 25 cuts nicer (so far). 25 psi foam is harder to find out here in the territories but it's worth the hunt. If you need a local supply of carnauba, West Systems and/or PVA, West Marine has dealers around the country and is a good source of all of the above. Hobby shops preferred but quite often they don't carry it (especially PVA). ACS and CST handle everything you need and supply cloth in any variety you want (hard to find anything locally) so they may be the best bet anyway. Thanks very much to all on the forum who shared suggestions and experience, especially Phil, Jon, Jim, Pat and many others. I doubt I've added much to the body of knowledge here - if I hadn't glommed onto the 15psi stuff from Home Depot perhaps a lot of electrons could have been put to more constructive use. Now if I can just stop fuzzing up the edges of the carbons, these wings would look really nice! - Dave R RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
