>-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
>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. Or some random unknown thing is happening that could have happened on any of your samples. >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. I agree with this. The mylars should peel off very easily. You should be able to lift one end of the mylar at one wing tip and then just lift the mylar off with not much more than the weight of the wing itself holding it down. If it takes much more force than that or you hear terrible noises as if the skin might be ripping off the wing then you have a problem with your waxing methods. The mylar should come off so easily that it would not even make you think that some damage could be done to the wing by pulling the mylar. You should also be careful handling your cores before they are bagged. You may be denting the foam before they even get in the bag. Perhaps you are even doing some damage to the cores as you roll epoxy into the leading edge fabric. Take a look just before placing the core in the mylar. >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. If you mean a longer cure time for the wax then I can tell you that that is not an issue. You can bag as soon as the wax is buffed. Buffing can be done as soon as the wax is dry enough so that it doesn't just get wiped off by the paper towel. Epoxy should cure to the crisp state before unbagging. >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". Thank you for helping to dispel the "crushed foam" myth. >If you see surface defects, try dropping the pressure as the first >response. I don't think you've shown any evidence that excess vacuum causes surface defects. You should at least have a theory as to how that happens. >If that's not successful, toss the foam and get some new stuff. That >also seems to be implicated in these adventures. I guess it's remotely possible that you have a batch of foam with little voids in it that end up just below the surface of your cut core but that sounds like a long shot and not something I've ever seen. Other than that I don't see a theory for how defective foam could look good as a core but show defects after being bagged. >I doubt I've added much to the body of knowledge here I think that there may be a great many people who have learned a few things from the discussion whether the actual cause for your problems is ever discovered or not. >Now if I can just stop fuzzing up the edges of the carbons, these wings >would look really nice! OK. What's the problem here? At what point does the carbon become fuzzed up? If you just spray the carbon with a light mist of 3M77 and then cut it out as shown in the DVD and set it aside where it won't be bothered until layup time then it should have no opportunity to fray. Phil 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.
