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Everything posted by RiggerLee

  1. I'll expand on that with some caviots. Perfectly good model but like most models it breaks down when you try to extend it into the range where the systems behavior becomes nonlinear. That kevlar thread is actually stronger then the nylon tec 500. Sew loops at both ends of a peace of kevlar webbing one with the stronger kevlar and the other with nylon. Pull. The kevlar will break first every time. The nylon junction is stronger not by a little bit but by quite a lot. So on places that are protected and not subject to aerodynamic heating we use nylon where we can. The little bit of give in the nylon let's it share the stress more evenly over the stitch pattern. As you try to get more strength, more stitches, in a joint there is a point of diminishing returns where when you pull on it only part of the stitch pattern bears the load. So the pattern breaks progressively from one end to the other. This relates to the elastisticy on the webbing. It is exaggerated if there is a discrepancy between layers of webbing. Say there are three layers and you are pulling on the top layer. The bottom two layers are stiffer then the top layer. When the top layer stretches it loads the first part of the pattern those stitches break first. Some one once told me that a reinforcing, like a tape on a canopy, should have an elastic coefficient a certain percentage of the substrate to avoid point loads and shear forces between the two. In the same since the stitch pattern must have the ability to stretch and deform to match the material being joined. That is why it's advantageous for the stitching to be as far as possible angled relative to the load. Notice that most of the stitches in a 3 or 4 point are angled. When you pull on it the highest load points are at the corners where the side stiches are straight. This is actually less then ideal. In fact the straighter the stitches the higher the load at the points.. So there is kind of a minimum angle that you would like to maintain in the pattern. Therefore there is a limit as to how long you can make a three or four point or the number of points you want in a pattern. So if you want a larger longer pattern it can be better to dubbel or triple the pattern. Imagine two three points end to end. Now imagine the stitches continuing rather the turning where the points meet. Basically the pattern bounces back and forth from side to side of the webbing like a big zigzag. Think of the dot in the old pong game. Try drawing it you will have an over sew when you get back to your starting point to move to the next half of the pattern. You'll wind up with the same amount of over sew as you would have in an equivalent pattern. But a multipattern can be better then one long four point. The maximum length of the pattern tends to depend on the stiffness of the webbing. The most extreme example of shortening and widening the pattern would be to sew it in a diamond pattern like to sew the four point sideways on the webbing and I've seen this in some heavy load applications on nylon. They actually sewed it back and forth from side to side in a big square block. It defenintly let the nylon stretch but a don't favor this because I think you would tend to snap the webbing at the end of the pattern. But I have seen it done. Most extreme example I've run into. An early project I was given was to test seam designs for a prospective canopy. So I had to figure out a way to load seams to destruction in f111 and zp. Trickier then it sounds. Wanted to load a decently wide area. Clamps didn't work. When the fabric stretched under load the fabric it self would tear under shear at the sides of the clamps. Ultimately I wound up sewing leaves of wide webbing to the fabric to pull on. It was an interesting stitch pattern. Boxes, 3 points, 4 points won't work. Any thing with a straight corner would cause the same shear as a clamp and tear the fabric before the seam. It needed a smoother transition to the unloaded fabric. I wound up with a two point with the points in the middle of the pattern not at the edges let the fabric avoid that sudden shear load. I don't like to think about how many of those test articles I had to sew up. Lee
  2. That's cool I'd never seen that on a pilot rig. I thought I was a radical when I ran a horizontal below the leg junction on a harness. That harness didn't have a container attached to it. It was worn under clothing and that lower band made it feel very comfortable and secure with out a back pad. The container was a separate jansport looking backpack. It also had no hardware on the leg or chest strap. You wiggled too it from the top. Lee
  3. That's cool I'd never seen that on a pilot rig. I thought I was a radical when I ran a horizontal below the leg junction on a harness. That harness didn't have a container attached to it. It was worn under clothing and that lower band made it feel very comfortable and secure with out a back pad. The container was a separate jansport looking backpack. It also had no hardware on the leg or chest strap. You wiggled too it from the top. Lee
  4. It's hard to tell from the above picture but I might consider running the horizontal/leg strap through the center of the mlw as opposed to running the mlw through the center of the leg strap. In theory ether would work but in practice I've seen the two outer layers of the leg peal outwards and down breaking the stiches one by one. By putting the leg on the inside with the tension on the upper mlw I think you force the stitching on ether side into shear. I didn't do this on my rigs because I had stagger in them and I wanted to wrap the leg around the mlw in case it failed. This added redundancy but it did not make it stronger. It made it weaker. If you are going with a continuous leg strap like this I would samwich the leg inside the mlw. You might even think about spreading the leg strap in a v from the hardware to the back pad. Gives you a bit more room for sticking in that joint and makes for a thinner transition at the end of the over lap which is generally to the good in the strength of a junction. Don't be afraid to sew half an inch above and bellow the leg strap but glue that section. Glue helps to stiffen the webbing and makes it easier to sew the ends of the four point with less shrinkage and stress at those points. Don't run the tension higher then you need to to get a good centered stich in the thickest hardest part of the joint. I don't know what's happening up inside your back pad but I'd put a U'd three point by your leg hard wear. On a separate matter. Looking at weight of webbing and weaves and dissimilar webbing vs thread in stich patterns. Interesting things I've seen. Been doing a lot of work with heavy kevlar webbing. Stuff in the 20,000+ range. Kevlar does not stretch very much. There are interesting things that happen with elastic coeff icents and stich patterns. There is something to be said for the ability to stretch and sort of distribute the load across the junction. To maximize the strength you have to have the ability for something to give whether it's in the weave, the thread or the material itself to allow all the stitches to share the load. And it won't be even but I mean as close as you can. Some day I want to do a more organized study but there are relationships between stitch density thread strength thread elasticity length of joint and elasticity of the webbing. We've done some destructive testing of our risers line attachments etc. The kevlar has has allowed/ required us to go to some rather long stitch patterns to get the strengths we need. It's interesting to see how the patterns break. The kevlar is so stiff that we can break just a few stitches at a time pulling it in the hydroloc tester. I think nylon would just go kapow like a rubber band. As an example were ever possible we have been going with a heavy Tec 500 nylon cord rather then a stronger kevlar in our patterns because that little bit of stretch allows for the load to be better shared across those long joints. I don't think I could use that long of a joint with nylon webbing. I think the stretch of the webbing would mean that only part of the joint would be loaded and you would fail the first part of the stitch pattern before the rest. But with the heavy kevlar and the nylon thread we just kept going longer and the failure point just kept going up. It's been interesting trying to get the most out of these materials. Lee
  5. In regards to the racer. Part of the reason he had to do this was that he was using a single layer type 13 mlw. If he had just layed one on top of the other and sewed them together it would never hold. By samwiching it like that with the extra piece running an inch higher you change the failure mode. Now when you pull on that top corner the leg strap webbing is supported by the stitch on both sides. When you try to pull the leg out of the mlw each stitch is supporting the leg on both sides where it passes into the mlw. Looking at other designs. The early vector ones had stagger. They plugged the leg strap into the mlw between the two layers. At some point they started wrapping the webbing of the leg strap around the inner layer of type eight. The sticking of the four point ran down bellow the junction far enough that if the joint failed that loop would probably save them. Javelin looped both around the mlw so that it slipped on. I've seen the stitching fail but because they had some harness stitching in the leg strap, just a box, no one fell out. And the tightening on the leg is not that bad. The National pilot rigs don't even sew that joint. They leave it a slot that the mlw can slide through so it's "adjustable". Some people have spread out the leg strap in a V to get more area in the joint that they are sewing. And yes you can angle it down at a bit of an angle to try to get a more natural loading with out so much of a stress concentration at the top. You can also get creative. Example. John Stanford with the prestige container. I worked for him for a while. That's where I learned most of what I know. He ran the diagonals on his back from one shoulder junction diagonally to the opposite hip to the leg strap back across the lower back to the opposite hip to the leg strap back up diagonally across the back to the opposite shoulder. One big long piece. The leg strap junction instead of being at a 90 degree angle was about 60 degrees and the webbing was spread out. The mlw went between the two layers. He sewed it with a boxed three point. All the stitches of the three point were within the box. If you over stepped it that stitch tended to pop. He found that in drop testing. A lot of the original military harnesses were built with variations of that kind of diagonal harness. Another example was the... Eos container. It had an interesting harness design with an angled joint if I remember correctly. I think I only ever saw one of them and it's been a while. Lee
  6. Perfectly good canopies. Open well. Land well. But they do come in two different versions. If you get the chance to jump if you might note on the card whether it is a "r" or "l" varrent. Lee
  7. I'm with you 100% but I can sew straight and I don't have much of an esthetic since. Taking the time to change thread is a pain. Manufacturers are obsessed with the appearance of there rigs. And matching the thread hides a host of sins in there less then perfect sewing. They have chosen over and over again that looking cool is far more important to them then functionality. Lee
  8. At one of the pia meetings before the symposium where all of the mil contractors and government purcurment people get together to bitch at each other this was one of the topics of conversation. I'd did indeed come from a joint not being sewn. Not a heat issue. All the contractors were trying to come up with mechanical jigs and clamps to hold every thing straight during sewing. There was a lot of suppressed grousing under all the "please please can I keep my government contract?" Underneath all the ass kissing was the universal sentiment that hot glue was better faster easier and more accurate. There was a faint hope that the speed would pick back up if they could ever get the clamps to work and not slip but that arranging the peaces and getting them clamped straight even and on the mark was... Challenging. For small production glue is so much easier and has a proven track record. As a rigger I could get behind the idea of contrasting thread but I don't see it flying estheticly. Also it makes less then perfect sewing blatantly obvious and I don't see manufacturers volunteering to produce unsightly rigs. Lee
  9. Sounds like you have another fun project. I can't see a lot of the rig but it doesn't look bad... If you've got access to a double set up as a binder and a 7 class you should be in decent shape. Honestly just copy what every one else has been doing forever. That's all we did when we started. In many ways it's far easier then a canopy. If your asking for general thoughts you know what kind of can of worms that is. I'll toss out a few. Do you need three rings? Landing near water etc? If you skip them it makes it easier and lighter. Lighter is good. Depending on where you plan to jump it it could be several hours of hiking up hill for 3 to 180 sec of freefall. You might ask your self some questions like how much padding do you need in those leg straps? Do those flaps really need to be dubble layer? Why would you need hip rings? Etc. Pin rigs have become the norm but there are some real advantages to Velcro. I don't know what your plans are but pin rigs are more figgity and less forgiving in design and packing. Actual issues people have had... There have been some flap/pin/bridle issues in the past. There was a big long thread on basejumper about some pin hesitations seen at perion. Turned into a long discussion on flap design, pin clearance, pin orientation, bridle piercing, etc. If it still exist it would be worth finding. There was an incident of a failure of the upper harness junction. It was a peeling issue. Bottom line is that back side loading is better. That's the best way I can phrase it. Example. Look at a skydiving rig. Main three ring back side, no peeling, good. Reserve risers, front side loading, bad. But reserves have always been built that way. They don't put my.p after jump on them. Base openings can be brisk. Body orientations can be more whippy. And skydiving rigs have the main three ring there to kind of act as a loop. Bottom line, we blew up that harness. Another big thread. Some people started using a slink design but I still favor an L bar. Looks like you have a continuous harness with no stagger. That's fine but I would encourage you to include redundant stitching. The hip junction takes a lot of tork. I've seen it tear.assume all stitching in the hip joint will fail. I've seen it happen. The only reason the guy did not fall out was that there was some redundant harness stitching in the leg strap by the buckle. How big of a pc pocket do you want? Just about have to make a choice. Large or small. Long delay or short delay Need more pics but looks good for a first try. Lee
  10. Nice. Wish I had one of those. Speaking from absolutely no experience, the head doesn't look all that different. Could you use a shaft out of another machine? Like a 110 series? A 110 w 140 or 110 w 116? Lee
  11. I've seen it fail a number of times during deployment. I would guess in the 10% to 15% range is about right. It is and I believe that it was designed to be a less aggressive system. It was only like the third system designed and the second to be marketed. I believe the thought process was more along the lines of it might help you but it probably would not kill you. Or so we thought till it did... But it's on the conservative side by design. Lee
  12. A few years ago I was tossing around the idea of improved curved pin design with some people on basejumper.com I had a batch lazer cut but before I had the stamping dies made I found a guy in Europe doing the same thing. He already had the dies so I dropped the project. If you can find that old thread he might be another source for you and a better pin as well. Lee
  13. I was actually referring to his reopening in the nineties but that is another good example of alternative income streams. Which just goes to make my point. How to make money with a drop zone... Lee
  14. I missed part of the conversation but I'll try to clarify my remarks. First some of the examples given have been comparing different canopies one being steeper then the other. Often what they mean by that is that one has a longer dive then the other which is not exactly the same thing. In doing this they are also comparing two different air foils, plane forms, break line configurations etc. So for example the location of the maximum thickness may be at a different location cord wise on an air foil. Or it may be thicker. The pitching moment may be different affecting the pitch stiffness. The point is that you tend to be stuck comparing Apple's and oranges which tends to be anecdotal. I'm looking at this from my experience tinkering with crw canopies. Crw canopies are one of the very few examples where you can get the same canopy in different trim configurations. Steep of flat. Short or long. You name it. And that's just the starting point. No crw dog deserving of his hook knife has ever been able to resist tinkering with and retrimming their canopy. I mostly did bigger way stuff but this was kind of the thought process at the time at least among the people I knew. Keep in mind that the ideas of how best to set up your canopy are constantly evolving and vary from one team to another. So of the three disciplines rotation sequential and eight way. Their thought was that in rotation you wanted to be able to drop as fast as possible relative to the formation. Ether by stalling back over the top and dropping through the wakes behind the stack or by turning off to the side and cutting back in behind it in a quick sashay. The thought was you wanted the canopies as flat as you could get away with. You wanted the stack to be floaty. But more important you wanted the rotating canopy to be maxed out on Cl. When he popped the toggles or rears to drag him back over the top of the stack you wanted to already be on the edge of stall so there was no more lift to pop you high up off the top of the stack. Pretty much the same thing if you were going to turn off to the side. You didn't want extra lift. So basically you trimmed it real flat adding an extra link and then trimming the lines. Some of the canopies were so flat that you flared them with the front risers. The the thought process was reversed with sequential. They had the thought that in flying peaches or changing slots that you wanted to be able to float relative to the formation. They trimmed steep to be able to get on the rears and float relative to the other canopies with out dropping behind. Or at least that was the idea behind the old expresses. So you got to play with the same canopies at both ends of the spectrum. This is where my observations come from. That when you trim the canopy flat the fronts become soft and are easy to pull down. When you trim it steep. The load on the front risers increases. One secret of pulling down the fronts on a heavy canopy is to tap the breaks to rock it back before grabbing the fronts as it rocks back forward. It will soften it up enough to let you get locked in. Part of that is the angle of attack and part the dynamic easing of the load. The increase in load towards the front of the canopy is why I tell people that it's in some ways safer to trim a canopy more nose down when tinkering. More lift at the front of the canopy improves the stability and you have plenty of room to increase the Cl so you can have flare authority to kill your sink rate on landing. Contrast that with a very flat trim on the same canopy which tends towards soft front risers. When you try to flare there is nothing left. It just stalls. That is why you wind up doing front riser approaches may be with a bit of turn and killing your sink rate by letting up on the front risers and just finish out the landing with your toggles hoping you can slide or run it out. Going flatter is defenintly trickier and should be approached with more caution. That got longer then I intended. This information is some what out of date. I hear the newer crw canopies are much nicer and not even scarry to land. I would really like to put some jumps on them some day. But right now I'm stuck here in isolation playing nurse maid. Lee
  15. It relates to load in the since that it will be a percentage of the load of the canopy. Load in this context is not wing loading but total suspended weight but is also controlled by g loading. If you are in a 2 g pull out the loading and control forces are doubled. Trim is a factor. The steeper the trim of the canopy the more the canopy will be front loaded. Nose down, front riser pressure higher. Flatter trimmed, front riser pressure lower. In terms of toggle pressure nose down means lighter toggles and flatter canopies heavier pressure. Some people will argue that the added airspeed of a steeper canopy increases the toggle pressure but I think they are confusing it with the g loading. To examine it rationally you have to look at the percentage of load on the toggles. Lee
  16. We used to spray tandem lines with silicone and other things. Trying to reduce the wear and reduce friction knots. My experience was that it picked up dust and grit off the floor and actually accelerated the wear of the lines. A dry Teflon spray might do better but having been burned before.... Lee
  17. RiggerLee


    I had one of those once. Never could get it to sew. Not one stitch. Thread would not pull up around the bodkin case. Never could figure out why. Took it to a shop. They had no luck ether. Remains a mystery to this day. Had such great hopes for it. Not saying that they are bad machines but the one I baught had some mysterious grimlen inside of it. Lee Lee
  18. RiggerLee


    By the way. If you are going to see patches on a sleeve of a jumpsuit. Find a post bed. It's awesome. You'll never want to work on a jumpsuit with with a flat bet again. Sew a patch on an elbow. No problem. Lee
  19. To clarify in the example given we are looking at between 1000 to 2000 lb of snatch force depending on fuel burn off acting on a 65 lb bag. That's why the 80 lb. The locking shows are also made of 1 inch tape. I was thinking more of the bundling of the lines. Tieing them with a light cord at about 12 inch intervals before showing. Since we have eight main risers with a short split to 16 we bundle in 4 groups every 24 inches then then the full bundle in between for a tie every 12 inches. On smaller canopies I've seen them do it in right and left then the full bundle. I was wondering if the larger tandem reserves with non cascaded lines would justify the effort. But I think as things trend small it will be unnessisary. Watching high speed it does make a difference. You can see the bundle deploy. The ties hold through line stretch. The main bundle spreads and you can see the slider splitting the 4 sub bundles as it comes down. Way more orderly then the chaos of a normal deployment. But I have to tell you it sucks. My ass gets sore setting on the floor tieing all those lines. Lee
  20. I haven't looked at the numbers but I've seen friction knots on both. And yes that totally anecdotal. Working with larger canopies we do see some interesting things. I think the first question is the quality of the staging of the line deployment. As canopies get bigger and the bulk and mass of the lines gets larger how they are retained becomes more important to a clean deployment. For example we wound up using 80 lb. Break tie for the line shows. This canopy has 15 cells and 7 non cascaded line groups of 1000 lb line. Which basically adds up to a metric shift ton of line. We also tie the line bundle. Actually we do it twice. Once in four bundles then in one big one. Total pain in the ads but if you look at the really high speed footage of the line deployment it makes a big difference. Some times I wonder if tandem canopies are large enough to justify that effort? I think it's border line but as tandems are trending smaller I think the problem will get better not worse. Lee
  21. I had not seen that video. I'm surprised he lived through it. I would have expected the decent rate to be higher. I guess he was lucky the canopy was not more asymmetric. The one I remember was back in the day and he died. I wonder what the gs were with double line length? Lee
  22. This idea has come up once or twice. I remember one conversation about the value of dacron lines in mitigating hard openings. We use screamers the folded in half and zigzagged kind in some of our designs. It kind of comes down to the amount of kinetic energy absorbed. Force times distance. The bottom line is that the magnitudes are just to high. You just can't make a meaningful difference in the overall opening. But it can effect some things. Openings are not one smooth curve. The canopy is lifted to line stretch and you can feel a sharp jerk when all that momentum runs out of line. Depending on the snatch force size of pilot chute high speed that can be a painful high but brief spike. It can be the highest peak force in an opening. But it's generally followed by a much larger bell curve of some type. In a square it's mostly determined by the slider and at what speed it loses its dominance over the opening. The area of this second curve is just too large to be affected by a small amount of elongation. So the peak of that first spike is within the realm of something you could effect but the main opening just involves too much kinetic energy. Dacron lines play a different role in creating higher friction to slow the timing and decent of the slider. That is meaningful. More so then their elongation. That and improved staging from the rubber bands having a better grip on them is where their reputation really come from. I've changed my mind over the years. I do think that there is value in risers breaking to control super high peak forces. It's not a common occurrence but I've seen fatalities that I attribute to opening shock. It's not a fun idea but there is something to be said for a fuse in the circuit. Maybe type 6 risers weren't such a crazy idea after all. Lee
  23. Sex swings are more often solid saddles then split saddles. Both exist but split saddles are much harder to climb into and almost guaranty a face plant if you fall forward out of them. So I don't think it would be limited by that otherwise it would push the date up to the 70s. There have been female jumpers forever. At least back to the barn stormers in the 20s. Lee
  24. I know that we have some pretty good historians of the sport here. When did we start using hanging harnesses for training? The question came up today of how long have skydivers been using hanging harnesses for sex. As improvised sex swings. I was guessing around ww1 but I was trying to remember the details of early harness design. Does any one know how far back the practice goes? Lee