From: Marc J. Zeitlin Subject: Main Spar hints? Date: Mon, 11 Sep 95 7:26:31 EDT People; I've got my main spar (Chapter 14) jigged up and ready to glass the inside layup (probably Wednesday night). It looks to me as though the layup of the BID (especially around the bulkheads) might be tricky. If anyone has any hints, tips, or tricks on how to do this (or anything else related to the main spar, I'm listening...... Thanks. -- Marc J. Zeitlin Mail Stop: MS-460 Email: marcz@an.hp.com Date: Tue, 12 Sep 1995 15:59:37 -0700 (PDT) From: Eric Westland Subject: Re: Main Spar hints? 1) Plan LOTS of time. My wife came to my rescue around midnight and it still took a while to finish. 2) Those aluminum inserts are going to want to slide when you weight them down. I held mine in place with some small brads that I pulled out through the front after it cured. There may be a better way, but plan on something as they are not going to stay in place. Good luck, Eric On Mon, 11 Sep 1995, Marc J. Zeitlin wrote: > People; > > I've got my main spar (Chapter 14) jigged up and ready to glass the > inside layup (probably Wednesday night). It looks to me as though the > layup of the BID (especially around the bulkheads) might be tricky. If > anyone has any hints, tips, or tricks on how to do this (or anything > else related to the main spar, I'm listening...... > > Thanks. > > -- > > Marc J. Zeitlin Mail Stop: MS-460 Email: marcz@an.hp.com Date: Thu, 14 Sep 1995 01:58:53 -0400 From: KSPREUER@aol.com Subject: Re: Main Spar hints? The thing to do is to cut out a cardboard support that will lay against the bottom of the inside of the spar. Wet out the ply that will bo around the corners on plastic or aluminum foil. Fold the ply around the cardboard as you do the corners of a gift wrap. Then place the cardboard into the spar so that the outward facing wetted cloth is against the bottom and in the right orientation. Then un fold the ply and press against the sides. You will have to cut darts for the corners. Make the dars so that the end face and sides over lap at least an inch aat the top. This technique really comes in handy when you put the rib in the inboard end of the wing. Hope it works out. Date: Fri, 15 Sep 1995 20:18:55 -0400 From: JIMWHI@aol.com Subject: Main Spar/Wing Match Up I have not mounted my main wings to the main spar yet, but I recall hearing from two other builders that their main spars did not line up perfectly with wings. It appears that the end of the main spar is too thick and requires filling in the wing to get a smooth transition from spar to wing. Those of you that have not completed your main spar may want to hear from other builders about slightly modyfying the main spar dimensions so that this does not occur. I'm not talking about changing the structural aspects of the main spar. Any of you that have matched your main spars to the main wing care to comment? On another note, those of you that have not completed your main wings may be interested in some of the difficulties I experienced. 1. The jigs as shown in the plans were too small and had to be enlarged by a considerable amount, up to a 1/4" in some cases to get the foam cores to fit inside. 2. Be careful in mounting the jigs for the inner-most foam core. This short foam core jig placement determines the dihedral/antihedral of your wing. My first wing ended up with dihedral (about three inches at the wingtip). Talking with Nat he seems to think that it shouldn't hurt, and confided that he thought the plane might benefit from some dihedral. 3. I made flush attachment bolt hole covers that are held in place by a single screw. They look nice, and I think are an improvement over covering the holes with white tape. I can send a sketch of it to anyone who might be interested. "Free to roam the heavens in man's noble quest to investigate the weirdness of the Universe." "Bill Watterson" Jim White Date: Mon, 18 Sep 1995 12:16:35 -0400 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: Main Spar/Wing Match Up Jim White Writes. >........... Any of you that have matched your main spars to the main > wing care to comment? I had the same problem, only my mismatch was only a couple of mm of error. I agree that thinning the amount of urethane foam in the early stages would be a good idea and I would certainly do it that way a second time. > 1. The jigs as shown in the plans were too small and had to be enlarged by a considerable amount, up to a 1/4" in some cases to get the foam cores to fit inside. Again I had the same problem but I put this down to the thickness of wood used for the templates/jigs. I think that if I had used 1/4 inch or less then the problem would not have occurred. Your covers sound cool. Phillip Johnson From: Marc J. Zeitlin Subject: Main Spar Shear Web Layup Date: Tue, 10 Oct 95 18:09:54 EDT People; On Sunday I layed up the Main Spar shear web. It went reasonably well, and took about five hours (in contrast to the 7 hours for the interior layup the Sunday previously). I thought that I might impart a couple of things I THINK I learned while doing this layup. The spar is ~12 feet long, and with four layers of UNI at 45 degrees (alternating), I was continually switching back and forth between positioning, straightening, and patting down the UNI glass, and applying the 2427 epoxy with a squeegee and brush. 1) My workshop (basement) was about 70 - 75 deg F, and at this temperature, I found that if I applied the epoxy to more than 4 - 6 square feet of UNI at a time, it would thicken and be difficult to squeegee the excess out. So, I would pour the epoxy on a small area, work it in with the squeegee, and then move on. After finishing a layer, I would inspect for air bubbles, and then apply more UNI. 2) Since the shear web is shaped like a "C", I would continually turn the spar 90 degrees one way or the other like so: ___ ___ ___ a | | b | c | | | |___ ___| so that I was always working on the TOP surface to keep it horizontal for easier epoxy pouring and squeegeeing. I would do "a" first, then "b" and "c". 3) Nat instructs to peel ply the whole layup. If I had waited until I had finished epoxying the fourth UNI layer, the epoxy would have been so viscous that the peel ply would have barely stuck to it. For this reason (and mirroring the reasoning behind (1) ), I epoxied a small area of UNI ply #4, peel plied it, and then moved on to another area. This worked out well (in contrast to the fiasco with the canard shear web :-) [See the "Chap_10" archives if you have no clue what I'm talking about] ). 4) After about 6 hours, I knife trimmed the excess at the base of the shear web. This saved a ton of time over trimming the cured layup with a dremel, air grinder with a cutoff wheel, or a hacksaw blade later (not to mention not making any dust). Hope this helps someone. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Marc J. Zeitlin Subject: Main Spar - Spar Caps Date: Tue, 10 Oct 95 18:13:21 EDT People; While on the subject of the Main Spar, can anyone who has finished theirs give me some estimate of the time it took them to do the top and bottom spar cap layups? I remember the canard spar cap, with ~11 layers, took me about 6 hours - I'm dreading the MS top, with 23 layers!!! Is this going to be a 12 hour deal for the top, and 8-9 for the bottom? aTdHvAaNnKcSe -- Marc J. Zeitlin Email: marcz@an.hp.com From: Marc J. Zeitlin Subject: Re: Main Spar - Spar Caps Date: Wed, 11 Oct 95 8:38:58 EDT Dick Finn writes: >It took me about eight to nine hours to do the first spar cap on the wing >spar. Most of the time was spent playing with pulling out the cross threads. > I didn't realize that you could snip the thread in the middle, pull it out >and then easily pull out the cross threads. I learned!! The second one went >significantly faster. > >You may have already discovered this but: > >1. Suspend the roll of rovings over the trough using a pipe through the >center. This makes it easy to unroll into the trough. > >2. Wet out the trough before unrolling the first layer. > >3. Cut a squeegee in half (3" wide) and use it to work the epoxy in. > >4. Use a hair dryer to speed wetting out. > >5. Keep your epoxy warm (80 degrees or even slightly more). This eases >wetting out. I built a light box to store the epoxy. The light is on a >dimmer switch that I set to maintain an even temp. Got all 5 covered - thanks for the time estimate! -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Thu, 12 Oct 1995 12:45:30 -0400 From: CozyBldr@aol.com Subject: Re: Main Spar - Spar Caps Hi, Marc I went back into my log and found that the bottom spar cap took me 6.25 hours and the top cap took 8.75 hours. I used RAE slow epoxy which helped a great deal in terms of giving me time before it started to set up. I am presently compiling the time I spent on each chapter and will publish it soon. I hope this helps you. Paul Date: Sat, 21 Oct 1995 20:16:10 -0400 From: Marcnadine@aol.com Subject: Main Spar/Wing Fix I started working on the Main Spar this week, and I remember hearing about problems with the Main Spar being too think at the end to fit the Main Wing without a lot of filling.. Could someone that has had this problem tell me how to make the fix. Marc N425CZ From: Marc J. Zeitlin Subject: Main Spar/Wing Fix (fwd) Date: Mon, 23 Oct 95 8:49:28 EDT Marc Parmalee writes: >I started working on the Main Spar this week, and I remember hearing about >problems with the Main Spar being too think at the end to fit the Main Wing >without a lot of filling.. Could someone that has had this problem tell me >how to make the fix. Welcome to Chapter 14. If you look in the "Chapter_14" archives, Jim White and Phillip Johnson note that their spars were a bit too THICK, not THIN. Thes meant they had to fill a bit more on the wing when they matched them up. I have found that if you sand the spar cap trough a little deeper than specified (1 or 2 mm) and then sand down the urethane foam to match the top of the spar caps after laying them up, the spar ends come out a bit thinner than the plans call for. We'll see how that matches the wing, later. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Mon, 6 Nov 1995 23:44:54 -0500 From: JIMWHI@aol.com Subject: Re Wing/Main Spar Match Up Marc, In a message dated 95-10-23 21:16:59 EST, you write: << Could you pass along the amount to shave off the Main Spar to fix this problem. I would be most greatfull. >> Larry Sligar mentioned that the end of his main spar was thicker than the wing and required extra fill material on the wing to make up for it. I checked my wing and spar and found them to be similar to his. I found that the end of the main spar was 1/8" and 3/16" thicker than the wing connection at that point. The inner attach point seems to match the wing thickness at that point. If I were doing it over I would reduce the thickness of the end of the main spar by 1/8". Note that I am talking abount the total thickness of the main spar, not the spar caps! On second thought, its not as easy as I thought it would be. The urethane foam piece "CS2" is pretty thin on the aft face of the end of the spar, so there doesn't leave much room to shave off any material. Secondly, the dimensions for the attachment points are very close and critical at this point. Therefore, there is not much you can do about the aft face, except add some fill material to the wing. The forward face of the main spar end may also be slightly larger than the wing.Slightly reducing the height of the bump marked by layup "6" in section C-C on page 14-9 should aleviate any fill where it lines up with the wing. Hope this helps. From: "Niels Oestergaard Kjaer" Date: Sun, 26 Nov 1995 21:47:26 +0000 Subject: Re: Main Spar hints? Reply-To: wow@cybernet.dk Marc >related to the main spar, I'm listening...... Just to let you know that the Danish FAA weren't too happy with no calculations has been made on the Cozy Mark 4. They spend some time doing this and one of their results were that when I reach the spar chapter I'm supposed to deliver some samples and they will tell how many layers I should use based on their calculations. They believe that if the number of layers is used as per plans, only unnessesary weight is added to the plane. BR Niels DK Mon, 27 Nov 1995 11:27:14 +1000 Date: Mon, 27 Nov 1995 11:18:07 +0200 From: parkyn@citr.uq.oz.au (Nick Parkyn) Subject: Re: Design Allowables (Main Spar hints) / Forum Tape on finishing composites. Composite Design Allowables: Niels wrote: >Just to let you know that the Danish FAA weren't too happy with no >calculations has been made on the Cozy Mark 4. They spend some time >doing this and one of their results were that when I reach the spar >chapter I'm supposed to deliver some samples and they will tell how >many layers I should use based on their calculations. >They believe that if the number of layers is used as per plans, only >unnessesary weight is added to the plane. It all relates to what design allowables (properties) you use. These properties have to be conservative as we are dealing with wet layup by amateurs and the properties which can be re-produced will vary widely. Test samples are fine, but you have to test a large number of samples to get accurate figures. After testing initial test samples, samples should be taken from the actual layup to confirm that these samples reproduce or exceed the properties indicated by the initial test samples. These test samples will relate to the properties that Niels can reproduce and may be better or worse than what another builder may be able to reproduce. FAA required minimum safety factor for composites is 2.0, which may be higher than required in other countries! Design allowables used on the Cozy MK IV would be conservative - this is a good thing! If this was a pre-preg skinned kitplane the allowables could be less conservative, with some weight savings - but these laminates could not be built in your garage! Oshkosh Forum Tape - "Contouring & Finishing Composite Laminar Flow Enhancement / Drag Reduction". I have had a lot of experience with finishing composite structures and would highly recommend this tape. The use of plastic microspheres and the technique for filling pinholes are very useful. My experience indicates that most polyurethane topcoats will not "fill" scratches from paper coarseness with grit size < 120. So finish off sanding with 120 or finer paper before topcoat. Nick #0019