RiggerLee

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RiggerLee last won the day on May 5 2019

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  1. 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
  2. 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
  3. 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
  4. RiggerLee

    Patches

    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
  5. RiggerLee

    Patches

    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
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. Variations of this idea have been in discussion forever. I remember them all the way back to the otter crash at Paris when I was a young jumper. All of them were better then what we are doing now. None of them have gone any where. Do you think any manufacturer wants his harness to officially be part of the restraining system? There are a lot of hurdles in the way of a new idea. Lee
  13. First to be clear. I think what you mean by bi cell is that there are two sections to each cell instead of three. One vertical unloaded rib inbetween the loaded ribs. Like a normal canopy. That would put both diagonal ribs running to the same seam. Well that's kind of over kill to support that seam. This would of course work but it's not very efficient in terms of the bulk of the canopy. Turns out that a 7 cell 3 section is more efficient bulk wise then a 2 section 9 cell. If on the other hand you ment a 5 section cell with 4 diagonal ribs per cell then I can tell you that there is an issue with the vertical rib between the diagonal cells. They build nice long bridges like that all the time but that vertical member has to be able to withstand compression to really work properly. There is kind of an inbetween. There is at least one design out there by... Airborne systems? They make the unloaded rib shorter. So the bow, the support, is all in the bottom skin. The top is smooth, all the top skin seams at the same hiath. The individual skins still inflate and how but no distortion as the unloaded rib shifts upwards. Basically the same thing you get from a crossbarace with out the bulk. PD played with it as well but felt that it didn't give them enough rigidity. But that is some thing that is out there in a "bi" cell. Lee
  14. At normal operating speeds, with full fuel exaustion, the absolute slows it down to about 100, the openings are about average, 3 g. So pretty soft. Early shut down can double the mass of more. So the terminal goes up. You can be dealing with four times the kinetic energy on opening. If it's a flat shot, like a guidance failure, you can be going fast horizontally. If it's high enough it will wait a few seconds to let it slow down before deploying the main. Lee
  15. Strong c1200 cargo canopy. 1200 sqft 15 cells. A,b,c,d,e,f,g lines. grommet spacing can't really be wider then the cell so you wind up with an inner and outer set of grommets to allow three cells to inflate with the slider up. It gives you the area you need to deccelerate the payload before the rest of the canopy opens. You wind up with four grommets front to back in four rows and six on the back edge for break lines. They extend the back edge of the slider and have there own slider stops to increase its area. You actually have eight primary risers that give you inner and outer on each side. They Y near the top front to back to allow the slider to come all the way down, accommodate those four grommets in each row. 16x7 noncascaded 1000 lb lines and 6 primary break lines 2000 lb split to 12 attachment points. So ya, it's a beast, 68 lbs of joy, but I've seen it survive 20,000 lb opening shock. Lee