Date: Sun, 04 Jan 1998 22:25:58 -0500 From: Ian Douglas Subject: COZY: Perforated sheet in vac layup Hi all, Just want to know if any of you have a perforated sheet used for vacuum layups. If so I would like to know the size of the holes and the spacing between (we are going to make our own punch to create our own sheets). -- Best regards, Ian D.S. Douglas Director of Technology Workplace Technologies Corporation If you write software, send me your resume! From: Greg and Jill Hilliard Subject: COZY: vacuum bagging Date: Tue, 14 Apr 1998 22:18:23 -0500 Well, I've finished chapter 5, vac bagging everything but the 4 ply und = over the longerons. ( long story, without an "a ha" or a "well that = makes sense" at the end, so i'll just leave you wondering why). My part = weights came in at 10.10 lbs for the starboard side and 10.12 lbs for = the port, which I think are pretty good from what I can tell. To anybody who has never tried vacuum bagging, try it. Aside from just = being very cool, it helps keep part weight down and completely = eliminates the possibility of air bubbles. As I was finishing the = longeron layup ( the conventional way), I spent a whole lot of time = fretting over whether or not I had air bubbles in the layup. With the = bag, you just stick it on and forget about it. My vac pump, a $10 used = refrigerator compressor, is holding up fine now that I've got a small = box fan blowing on it (it got quite warm). My bag material, paint = dropcloths purchased at the local Menard's, work great. If it sounds = like I am happy with this so far, well, duh. If it sounds like I know = everything there is to know about fiberglass and vacuum bagging, I'm = sure that what I don't know eclipses what I do, which brings me to my = next question. To anybody who has gone through this: All the literature I've seen = deals with bagging in a mold, not moldless aircraft construction. There = are fine nuances, like how not to crush a foam core or torque tube holes = that some of you have undoubtably addressed and solved. If you are one = of these people, could you please share this?=20 Yes, of course you can build a lightweight cozy without vacuum bagging. = Yes, it takes a little longer (not much). Yes, it costs a little more = (again, not much). There is a lot of misinformation about this practice = out there that I couldn't say for sure was wrong until I tried it. This = topic is one that could apply to anyone on this list, we should hear = more about this from those who have been there. Greg Hilliard Cozy mk4 #456 gjhilliard@idcnet.com P.S. Marc: please update my build status to ch. 5.5, re-screening all = the windows in the house. From: Jim Hocut Subject: RE: COZY: vacuum bagging Date: Wed, 15 Apr 1998 08:12:27 -0400 Greg and Jill Hilliard [SMTP:gjhilliard@idcnet.com] wrote: > There are fine nuances, like how not to crush a foam core or torque > tube holes that some of you have undoubtably addressed and solved. If > you are one of these people, could you please share this? I vac bagged a fair share of what went into the basic fuselage, as you said it wasn't all that difficult. When I got to the canard I decided against it because I just didn't see any easy way to avoid introducing any twist. I went ahead and vac bagged my elevators, held them flat with weights to avoid any twist. They came out beautiful, with one small problem. Epoxy got squeezed into the hinge pin holes, and the elevators aren't much use without the hinge pin being installed. I haven't yet built my second set of elevators, but I'm leaning toward not vac bagging them this time because I can't think of any method to RELIABLY keep epoxy from where it doesn't belong. (If someone comes up with an idea for this - and is brave enough to test it on their elevators first - please be sure to let us hear about it.) (One thought I had was to do a single ply BID layup locally in the hinge insert area first, but don't think I'm going to pursue it.) Besides, in the great scheme of things, vac bagging isn't going to save any great amount of weight on the elevators. From: lschuler@cellular.uscc.com Date: Wed, 15 Apr 98 10:16:09 -0600 Subject: Re[2]: COZY: vacuum bagging Jim Hocut wrote: >snip >They came out beautiful, with one small problem. Epoxy got squeezed >into the hinge pin holes, and the elevators aren't much use without >the hinge pin being installed. I haven't yet built my second set of >elevators, but I'm leaning toward not vac bagging them this time >because I can't think of any method to RELIABLY keep epoxy from where >it doesn't belong. >snip Ouch! Might try small pieces of box-tape over the holes and covering the inside of the hinge notches (knife-trim flush with the edge of the torque tube); then, shape some pieces of scrap foam for a snug fit in the notches and match the surface of the tube (or slightly inset). The foam and tape get pulled out later when cutting the glass at notches. Just don't put any grease in the holes as called out in the plans unless you can be positive you don't get any on the inside of the notches (keeps the tape from sticking/sealing properly). The box-tape and a good glue line on the outer edge (see plans) will keep any epoxy out of the hinge pin holes. I plugged the holes per above before microing the tubes in the cores. Worked for me. As for extra time in bagging: the above is a good example. There is definitely additional time in thinking through solutions ('cause it isn't in the plans for you) and then implementing the solution plus bagging. I agree with Jim's assesment; not a great deal of time once you get rolling; but still measurable. I didn't do my canard either.... same reason: twist control. Larry Schuler Plans #500 on ch-10 (tip filling/contouring) and ch-12 (mounting) lschuler@cellular.uscc.com From: Greg and Jill Hilliard Subject: COZY: re:vacuum bagging Date: Wed, 22 Apr 1998 21:28:24 -0500 Bob Berg wrote: Greg & Jill, Just read your notes on vacuum bagging your Cozy, and I'd like to pick = your brain on a couple of issues. Are you using bagging film and = release film? Or are you just using the drop cloths for everything?=20 A: I am using drop cloth for the bag only. For release, I am using 60" = wide peel ply, along with bleeder cloth, both available from AS&S & = Wicks. The peel ply sucks up all the extra epoxy. A word of warning, = though. The peel ply comes with a rough "torn" edge that will not later = peel freely. Cut this edge off. Q: It seems to me that at the demo I saw at an Alexander's workshop, the = instructor used cheap dropcloth type plastic for everything, even = condescending to use pins to poke holes through the "release film" into = the foam. I'm wondering whether to spend (waste?) money on the = high-temperature films Aircraft Spruce sells. Are they necessary? A: No, not unless you have your own autoclave or plan to bag your layup = at high tempertures. Q: Are you using a vacuum switch to cycle your pump off and on, or a = bleeder valve? Not sure I want to leave my washing machine motor = driving an air conditioning compressor (my vacuum pump) running all = night when I start using this system. A: No, I let it run all night. Vacuum in a bag has a way of going down = FAST when you turn the pump off. Even with a well constructed bag, there = will be leaks and a pump (well mine anyway) has as much as it can handle = in any case. My pump, an old refrigerator compressor ($10), did get hot = after an hour or so. As designed in the fridge, freon carries heat to = places far away. A box fan set on low blowing over the pump fixed the = problem. I use a bleeder valve ( left over from an aquarium pump ) for = regulation.=20 =20 Q: Nat didn't encourage me to vacuum bag when I spoke with him a couple = of weeks ago.=20 A: He didn't encourage me either, but he has proven a good builder can = make a lightweight Cozy without vac bagging. It is also obvious that it = is very possible to build an overweight airplane. In my opinion, every = little ounce left off the Cozy is welcome, as long as it doesn't = sacrifice strength. Weight has to be compensated by extra lift, lift = creates drag, drag slows the airplane down. Very simple concept, but = often forgotten. Q: Nat said the wings would be extremely difficult to bag. =20 A: I'm not sure they would be difficult, it just requires some creative = thought. I spoke with Jeff Russell at Oshkosh last summer about this. He = expressed that by putting the wing into a bag after the layup would = introduce twist that would create more headaches than the few pounds = saved. I agree, but why not build the bottom of the bag around the foam = cores, jigs and everything, layup the glass, and then bag the whole = thing without twist? There may be hidden evils here, but I don't see = them. If there are any Berkut builders are out there who have bagged = their wings, It would be nice to hear what you all are doing. There are those who think the answer to speed is a big motor, = retractable gear, or other things that add weight. Look at what Klaus = Savier is doing with his VariEze. He wins just about every race he = enters because his frontal plate drag area is next to nothing, even with = fixed gear, and his bird is as light as possible. Even if you don't care = about speed, the weight you save in a layup is that extra heavy doo-dad = that you can now carry with you. Greg Hilliard Cozy Mk4 #456 gjhilliard@idcnet.com Date: Thu, 23 Apr 1998 00:25:11 -0400 From: Rob Cherney Subject: Re: COZY: re:vacuum bagging At 09:28 PM 4/22/98 -0500, Greg and Jill Hilliard wrote: >A: I'm not sure they would be difficult, it just requires some creative thought. I spoke with Jeff Russell at Oshkosh last summer about this. He expressed that by putting the wing into a bag after the layup would introduce twist that would create more headaches than the few pounds saved. I agree, but why not build the bottom of the bag around the foam cores, jigs and everything, layup the glass, and then bag the whole thing without twist? There may be hidden evils here, but I don't see them. If there are any Berkut builders are out there who have bagged their wings, It would be nice to hear what you all are doing. Well, I'm a Berkut builder and I vacuum bagged my wings. It *was* a pain, but I think worth it. I'm glad that this part of my project is done, though. I vacuum bagged my shear webs, spar caps, and the skins. To be able to do this properly, you need to follow all of the steps the Berkut folks have documented on their videos. It's just too much to explain in a short e-mail. It all relates to the accuracy of the cores, the way they construct the wing support jigs (a bit different than the Long-EZ plans), the use of an 1" x 2" x 12' extrusion along the trailing edge, and the accuracy of your jig table. There is no magic. The jigs keep the cores straight, but the jigs are placed on the *outside* of the vacuum bag. The trailing edge is kept straight by the extrusion which is *inside* the bag. There are pitfalls. Don't forget to place caul plates over the wing surface that is near the torque tube cutouts (I forgot once), and don't forget to plug the inboard section hollow areas. Also, plug the ends of the extrusions with duct tape to avoid a puncture of the bag. Call if you want more info. Rob- +------------------------------------------------------------------+ |Robert Cherney Home Phone: (410)465-5598 | |Ellicott City, Maryland e-mail: cherney@home.com | +------------------------------------------------------------------+ From: "Nat Puffer" Subject: Re: COZY: re:vacuum bagging Date: Thu, 23 Apr 1998 16:07:12 -0000 Rob and all, If you are just careful in doing your layups and use peel ply and squeegee well, you should end up with a light airplane. Vacuum bagging is not recommended for first time builders. I doubt whether any weight savings would justify the increased cost and effort. If vacuum bagging is not done correctly, it could turn out worse than not doing it. I have one of the lightest Variezes and Mark IVs and never did any vacuum bagging. Regards, Nat