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brainfart

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Everything posted by brainfart

  1. How will you test it? Trying to tear out the anchoring points?
  2. Nice. But I really worry about post-curing with balsa in there. 200 degrees Farenheit (110°C ?) is quite a lot. The Tg of MGS is somewhere up there, and you don't need to raise the post-curing themperature to or even above the glass transition temperature. Heating to 20°C (40F) below ultimate Tg for 5-8 hours or so is sufficient, there's no need to heat it up that much. Are you going to try this out on one of the smaller molds first? I'd hate to see the bigger ones ruined since the balsa started to outgas or something.
  3. If you redo it anyway then why don't you try removing the glass, or practise doing repairs on that part. Don't throw it away.
  4. Is there any other aircraft/canard related stuff out there that copyright-infringing evildoers might consider worth downloading?
  5. *** Bump *** http://www.reaa.ru/cgi-bin/yabb/YaBB.pl?num=1189771013/870
  6. From my experience (lots of glass and visible carbon surfaces) it is best to work the epoxy through the fabric from the bottom with a DRY brush or squeegee if you want bubble and pinhole-free layups. When resin is poured on glass it gets impermeable for air and the bubbles are trapped in the layup. If you let the resins oak through the fabric from below the air can get out and there will be much less bubbles and pinholes.
  7. > Correct me if I'm wrong, but in Europe... Europe is a big place. In some coutries you might not, in others you can.
  8. > down side is that my girlfriend got to see a couple of Cozy IV and Long EZ up > close and want me to buy/build a Cozy IV Get that in writing, put it in a frame in your shop and then marry her!
  9. > it is also hard to know if the fuel has alcohol in it. the pump gas may or may not. > it only says it may contain alcohol. how do you know that the sample you have does? If in doubt, add some alcohol intentionally.
  10. Got any links so we don't have to read through countless pages of info?
  11. > How about some tests. Can't hurt to do them, but what's the benefit of a limited sample made under possibly questionable circumstances tested with non-adequate equipment... There are thousands of laminated aircraft flying. These tests have been done countless times before under controlled conditions by experts. Just do it the way the experts and commercial aircraft builders do it. Even if some of the information might collide with 30 year old videos or outdated books written in the seventies.
  12. Been playing around with the Arduino a few years ago, as a way to start learning about microcontrollers. I've heard about the arduino autopilot but haven't checked out the details yet so I can't really comment. Might be a nice addition that is easily upgradeable, but then again it might not. Just reminding that a bunch of accelerometers do not substitute for real gyros.
  13. INTRODUCTION TO COMPOSITE MATERIALS http://ocw.mit.edu/NR/rdonlyres/Materials-Science-and-Engineering/3-11Mechanics-of-MaterialsFall1999/5991E176-AC60-4399-87F0-86AE35963750/0/composites.pdf I guess that's why countless texts like the above mention stuff like "fiber volume fraction" and "matrix volume fraction" all the time, in a subtle kind of way... All I'll tell you is what the industry and academia uses and expects, and how it gets measured, at least outside the USA.
  14. > Volume fractions are used when mixing the two (or more) EPOXY components. Sometimes, by some people... > Mass fractions are used when determining fiber/mixed epoxy ratios. I guess we disagree on the volume fraction stuff then. Strange world, there are quite some differences between the two sides of the pond. Americans measure fuel consumption in miles per gallon, we use liters per 100km. Most epoxies are weighted here, rarely mixed by volume. And for fiber content comparisons of laminates we use volume fractions. > Again - how would one determine the volume of woven cloth? Density of the raw material is known. Yarn diameter is known. Weight per lenght is known (1 tex = 1g/km), grammage (weight per area) is known. Thickness of the cloth and the laminate is known. More than enough data to come up with a volume ratio, don't you think?
  15. In all (mostly non-English) language publications I have seen so far, volume fractions are being used. Yes, many people indeed confuse mass and volume fractions.
  16. > I would not want silicone calk anywhere close to a layup. That's why I said acrylic. Not all of them are made of silicone.
  17. I've briefly worked in an aircraft composite repair shop and have visited several commercial aircraft manufacturers. You might be surprised to hear that they all regularly used plain cheap TRASH BAG plastic from the grocery store for vacuum bagging. You really don't need all those high-priced supplies. $20 per roll bag sealant tape? Forget it, for most parts a cheap caulk gun (?) and some cheap acrylic caulking compound (? that stuff you use in your bathroom) will work just as well. Same is true for batting, release film etc.
  18. Vacuum bagging isn't expensive. You don't need those super expensive bagging supplies, many everyday items can substitute. Some plastics are permeable to air though. It doesn't need a real leak in the bag, if the whole bag is leaking on its whole surface resin starved parts will be the result. There are electronic devices which can detect leaks (since leaks cause ultrasonic noise). These devices are expensive though. Someone I met on another forum built a bat detector (plans and kits available online) to detect leaks, and it seems to work great (and costs much less).
  19. > that is a pretty bold statement that you know that they all are most > certianly post cured. At least all the manufacturers I know and all the shops I have seen on this side of the big pond use post curing, for a variety of damn good reasons. One of the reasons being that epoxies with reasonably long working times REQUIRE it for a full cure. Another one has something to do with epoxies being approved for aviation use and legalities. If the regulations say: heat it, then the manufacturers better not cut any corners and get caught doing so. > should I start naming the ones that I know are not. Please do. > there are plenty of commercially built aircraft parts that are hand layups and > are not post cured. Scary. Please don't tell me they use West System, too...
  20. > there is a plane that was built with a "better foam" and that airplane was > falling apart and delaminating and was to cut up into pieces before it killed > someone. I assume that was built with polyurethane insulation foam. Which ages and converts to dust after being subjected to vibrations after a few years. Rohacell, in case you don't know that material yet (don't blame you, it has only become available in the US in the last few years), does not show that behavior. It has a great track record being used in trains, transportation, race cars, aviation and space applications (Delta, Ariane, Boeing, Airbus, rotor blades for helicopters and wind energy...). It's not quite the same as flotation billet or roof insulation foam.
  21. > most of the aircraft built are not post cured. Maybe the homebuilt canard variety isn't. Every commercially built composite airplane most certainly is post-cured. > My question has to due with the temperature breakdown or Tg, I think Tg has nothing to do with breakdown. It's a temperature where some of the mechanical properties of the composite start to change. Many polymers (rubbers for example) are constantly well above their Tg and they do not break down.
  22. http://www.aerokurier-markt.de/index.php?page=detailansicht&id_anzeige=32552
  23. The heating unit doesn't have to be located inside the cabin. Its exhaust of course goes overboard, so I don't really see how CO poisoning is an issue. These units are installed in literally hundreds of thousands of cars worldwide, and you don't hear about cars going up in flames because of them. They could be used in planes without liquid cooling too. Interestingly these units are offered by the manufacturers of many European cars but that option is not available for cars exported to the US (one example being VW, from small beetles to the biggest one, the Phaeton), due to US product liability laws. Someone might use these units in a hermetically closed garage and manage to poison themselves...
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