hackish 8 #1 October 13, 2007 Just a point of curiosity. In paragear I see they rate the safety tie used to seal a reserve at 4.75lbs. Does this mean that the standard method of sealing a reserve adds 9.5lbs of pull added to it in order to break the thread? Or is that the reason that 22 lbs was chosen to achieve a total of about 30 lbs when the thread is present? -Michael Quote Share this post Link to post Share on other sites
floormonkey 0 #2 October 13, 2007 Poynters Parachute Manual,v.2, p. 353, section 9.3.2. http://books.google.com/books?id=2PopFBjLZV8C&pg=RA1-PA353&lpg=RA1-PA353&dq=navy+pull+force+test+parachute&source=web&ots=lbvTxbtY7S&sig=EGddmHmASBimgdf7xcAwApipWUE You seem to have lots of questions. Buy and read "Poyters Parachute Manual, version 1 and 2." If you still have questions, buy and read the "Parachute Recovery Systems Design Manual" by TJ Knacke. Still have questions? Go to pia.com and read every manual they have available. If you still have questions after that, let me know. I can show you how to find the awnsers. I found most of mine using google and the above mentioned texts. Also, using the search function on this website will find a bunch of answers. Seal thread (safety tie) tensile strength ranges from 4.25 to 4.75 lbs, not to exceed 5 lbs. All those military studies are available on the internet, if you really want to learn. Of course, the best way to learn is to turn off your computer, buy a case of beer, and head to the DZ. Make some jumps, close your mouth, and open your ears. Every question you ask has probably already been answered, and many of the answers have been written in the blood of those who went before us. Show your respect and become a willing, listening skydiver and knowledge will be dumped in your lap without you asking. By the way, even though I have the books, I found the above link in less then 30 seconds by typing "parachute pull force" into google.com. Quote Share this post Link to post Share on other sites
tombuch 0 #3 October 13, 2007 The pull test is done without the safety thread, so yes, it adds pull force, and the wrong type of thread can be deadly. There are different ways of securing the thread that add different amounts of resistance. The BPA lists a very specific method that is worth checking out. It has been posted here and I used it for a while, perhaps somebody could post a link, or you could do a search. Otherwise, check out the Parachute Riggers Manual, published by the FAA/DOT in 2005. You can download the entire manual for free at: http://www.faa.gov/library/manuals/aircraft/. Warning: it's a 45mb file.Tom Buchanan Instructor Emeritus Comm Pilot MSEL,G Author: JUMP! Skydiving Made Fun and Easy Quote Share this post Link to post Share on other sites
floormonkey 0 #4 October 13, 2007 Tom-that is all covered in the above link (we generally use the Navy method and cite that study). Also, Michael already has the FAA's document that was written by an individual manufacturer. He's found errors in it and, as has been pointed out by many, it is a flawed document. It is published by the FAA, after all. Michael also seems to have an desire for technical knowledge, so I sent names of technical treatises. I'm not knocking Sandy or his opinions (I have great respect for the man), but was the FAA's document peer-reviewied? Quote Share this post Link to post Share on other sites
pchapman 279 #5 October 13, 2007 It has also been pointed out that a reserve is not pulled slowly 'from a standing start'. There's some force to remove the handle from its pocket (not measured), then it may move easily for some more inches until the slack in the cable is taken up. Then the momentum of ones arm moving all of a sudden yanks on the pin. The pin even gets the chance to move a bit before the slack is taken out of the seal thread, and that force is added. There may also be some effect from the dynamic friction while the pin is moving, being a bit less than the static friction to get it started. So the forces one apply can easily be quite a bit more than static pull tests indicate. The Great Bearded One (Bill Booth) mentioned some of that kind of stuff in threads 491650, 144383, and 942674. (Use the search function too, Hackish!) Now I bet a fair number of reserves are packed with pull forces a little bit higher than the 22 lb maximum. One tends to get that with some super tight pack jobs. A day's cooling off period tends to bring the force back down again so in practice it doesn't become an issue. And a rigger can get a feel for what is on the tight side but reasonable, vs. ridiculous and on the way to ripping the Cypres loop while packing. Quote Share this post Link to post Share on other sites
hackish 8 #6 October 13, 2007 I read the pull test procedure in the FAA manual and they specifically said no thread. So I did some searches on this site for 22lb pull test and a few other things. Found some discussion on how to perform the pull test but nothing on the contribution of the thread. You mean using supertack isn't a good idea??? :) Honestly guys, I may have a lot of questions but the ones that are asked here are ones I didn't find the answer to already. Thanks to the guy who PM'd me the sections in the poynter manual I'll read that. -Michael Quote Share this post Link to post Share on other sites
floormonkey 0 #7 October 15, 2007 Sorry I wasn't clear. There's a brief note to it on the link I posted (online version of PPM v2), and the Navy study mentions it I believe (but it's been a few years since I read it). Also to be noted: All riggers I know ALWAYS break the seal thread off the spool BY HAND. This ensures the breaking force is always under 5 lbs. It also makes sure you don't pick up a piece of E thread by mistake. Questions are good. Part of being a (good) rigger is knowing where to find the correct answer. The above mentioned texts are great sources. Quote Share this post Link to post Share on other sites
mark 107 #8 October 15, 2007 QuoteAll riggers I know ALWAYS break the seal thread off the spool BY HAND. This ensures the breaking force is always under 5 lbs. It also makes sure you don't pick up a piece of E thread by mistake. I am a rigger who always uses a scissors to cut seal thread. I don't think hand-breaking is a reliable method of testing whether a thread meets strength requirements. A 5.25-pound break wouldn't feel a lot different than a 4.75-pound break, even though only the latter would be acceptable. No rigger I know tries to re-use scraps of threads once they are cut off the spool or bobbin. I don't go rooting around on the floor near the sewing machines looking for a piece of thread long enough to seal a pack, especially since I don't sew anything with seal thread. Most riggers I know do not own a spool of red E-thread, and those that do do not keep their sewing machine thread in the same place they keep their seals, press, and seal thread. E-thread comes in 8- and 16-ounce sizes wrapped around a plastic spool, much larger than the 1- or 2-ounce seal thread size wrapped around a cardboard spool, so it is not hard to tell the difference just by the appearance of the spool. I have heard of E-thread being used instead of seal thread, but I can only imagine a rigger who was confused about that difference would be confused about a lot of other things, too. BTW, nothing in the regulations requires an owner to keep his rig sealed, though long-standing custom (in the US) would lead you to believe a seal is mandatory throughout the life of a pack job. Mark Quote Share this post Link to post Share on other sites
hackish 8 #9 October 15, 2007 The responses have been great. I've now got a few chapters in poynter to read. I always wondered how they arrived at choosing the 22lb limit anyway... So today we were rigging up an old school PC and after a short discussion on the size pilot chute that would be needed this came up... Got a few stares from the old timers and they were like "you're really taking this rigging thing seriously eh?" -Michael Quote Share this post Link to post Share on other sites
drjump 0 #10 October 15, 2007 That is the only way to take rigging-SERIOUSLY. Quote Share this post Link to post Share on other sites
kallend 2,148 #11 October 16, 2007 Quote I always wondered how they arrived at choosing the 22lb limit anyway... Good question. Whenever I see a number like 2.2, 22 or 220 pounds it suggests to me that it started as 1kg, 10kg, or 100kg and was converted. Whenever I see a nice round number for anything ("200 jumps required before you can xxxx", for example) it always suggests to me that no actual research was done and they just chose a convenient number.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
pilotdave 0 #12 October 16, 2007 So you're ok with picking a random round number as long as it's in kilograms? Dave Quote Share this post Link to post Share on other sites
councilman24 37 #13 October 16, 2007 Quote I'm not knocking Sandy or his opinions (I have great respect for the man), but was the FAA's document peer-reviewied? No, it wasn't. Sandy wrote it under subcontract. As I'm sure you've noticed the author isn't identified. While I also respect Sandy's opinions one of my fears is that the methods and procedures in the manual may be considered by some inspectors as the ONLY acceptable method.I'm old for my age. Terry Urban D-8631 FAA DPRE Quote Share this post Link to post Share on other sites
hackish 8 #14 October 16, 2007 There were some studies done considering the amount of force men and women were able to apply. This data was used to determine a more optimal position for the silver and I believe it was used in consideration of the amount of pull force necessary. The reference was to poynters was made earlier in the thread. -Michael Quote Share this post Link to post Share on other sites
n23x 0 #15 October 17, 2007 He didn't say he was ok with it, he just said that's where the number started. .jim "Don't touch my fucking Easter eggs, I'll be back monday." ~JTFC Quote Share this post Link to post Share on other sites
floormonkey 0 #16 October 17, 2007 Mark-I'm sure you can't tell the difference between 4.75 and 5.25, but $10 says you can tell the difference between Safety-tie and E thread. I agree there should be no way to confuse the two, but, as we all know, if it can be fucked up, a skydiver can do it. Terry-Sandy's name only appears once in the entire manual (on a packing data card) and that sucks. The man should have got some glory for his hard work. I agree. Now that there is an FAA document saying "this is how to do it," it puts us at risk when doing something different then that manual specifies. My biggest issue is the ethics section, an arbitrarty opinion that could come back to haunt us later. jeff Quote Share this post Link to post Share on other sites
cpoxon 0 #17 October 19, 2007 QuoteThe BPA lists a very specific method that is worth checking out. It has been posted here and I used it for a while, perhaps somebody could post a link, or you could do a search. Form 215 - BPA Acceptable Reserve Sealing MethodSkydiving Fatalities - Cease not to learn 'til thou cease to live Quote Share this post Link to post Share on other sites
riggerpaul 1 #18 October 19, 2007 QuoteForm 215 - BPA Acceptable Reserve Sealing Method This link didn't work for me. I went to the BPA website and didn't see any way to search for the document. Please check the link or maybe just post the doc. Thanks! EDIT - Doh! I see now that I missed that the BPA main page has a link to the Forms page. My bad! Quote Share this post Link to post Share on other sites
hookitt 1 #19 October 19, 2007 Here ya go ==> http://www.bpa.org.uk/forms.htmMy grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto Quote Share this post Link to post Share on other sites
riggerrob 643 #20 October 19, 2007 Trivial point: do you know why it is called "safety tie" thread? Hint: think back to before reserve pilot chutes contained springs. They needed a bit of seal thread to prevent ripcords from falling out accidentally. Pack-opening-bands helped a bit ... Quote Share this post Link to post Share on other sites
hackish 8 #21 October 19, 2007 Interesting point. I'll have to see what poynter vol 1 has on it :P -Michael Quote Share this post Link to post Share on other sites
riggerrob 643 #22 October 19, 2007 Poynter does not mention that function (of red thread) because he compiled his books long after MA-1 pilot chutes became the norm. Quote Share this post Link to post Share on other sites
hackish 8 #23 October 22, 2007 Yes, I found only a vague mention of using it to seal a main shut and the sealing method for a 2 pin system was also covered. -Michael Quote Share this post Link to post Share on other sites
floormonkey 0 #24 October 22, 2007 Correction: I looked at a new package of thread. It's 4.70 to 4.75 lbs, NOT what I stated earlier. Sorry for the misinformation. Quote Share this post Link to post Share on other sites