sniper1rfa

I have no where near full motion in my shoulder, but the position needed for stable belly flying is not a problem for me. FWIW, I don't think you'll have any problems.

You might be out of luck. Don't jump again until you have it checked out. Dislocating a shoulder almost guarantees you will do it again, probably sooner rather than later. He had arthroscopic surgery to correct a bankart lesion; thread here: http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=3996382 Depends on the damage done. I had a bankart lesion which was corrected arthroscopically and was back in business in fairly short order. I've also had open surgery to fix a shattered socket which left me useless for months.

Wow guys, sorry. I almost didn't post, since I am obviously not very experienced. I ended up posting because it's not such a ridiculous statement as it's been made out to be here. One DZ I've jumped at has a student rig with a 200 main and a student cypres 2. Also, we were very well briefed on the dangers of setting off your cypres while under canopy. Furthermore, is it really that outrageous to read the manual for your equipment and then work with those limitations? No different than any other gear choice. Obviously the better choice would be to have it converted, but it wouldn't be crazy to jump it for a weekend and then send it in when you've got the time. @peek: I did read the manual, which is why I know that 1000 ft. is the threshold for possible activation. Especially if you're already under canopy as your descent rate would be below that of freefall as explicitly stated in the manual. EDIT: and please don't compare me with petejones. I've read his posts - I like to think I, at the very least, use a little more logic and a little more punctuation than he does.

To be fair though, as long as you work within the limitations of the AAD it won't be a problem. Activation altitude is only 250ft higher, and just don't pull any hard turns near or below activation altitude. Then again, mode changes are free.

You're welcome. :) . I think plastics are fascinating. The phrase "plastics make it possible" is not as sarcastic as people think. :P Sadly, their usefulness is often misplaced. I hate seeing plastic wasted for no reason. The cutting board example above, for example, drives me nuts. Wood is better in just about every way. Save plastic (and most other petroleum products) for when there aren't other options.

Just got corrected on this one - i didn't realize that cordura is a brand name, not a branded material (like lexan/polycarb or delrin/acetal). I guess the modern cordura fabrics are mostly polyester or nylon. Reading more, cordura's original product was as I described above, but they've since changed it. No wonder I was confused. Reading along thinking "cellulose acetate? really?". That would be like saying "we make our products out of bakelite for durability!"

oh yeah, nylon (polyamide) is definitely plastic. The problem is actually the term "plastic", which pretty much means "can be molded". Typically it refers to organic polymers, though "plasticity" is a material property that can be applied across all materials. In fact, most of the materials used in parachutes are common plastics. Nylon (polyamide) is obvious. Used for just about everything - the one that springs to mind that people have used are those white plastic screws. http://image.made-in-china.com/2f0j00uBvEGegqYibl/Plastic-Nylon-Screw.jpg Dacron is PET (polyethylene terephthalate). Common use? Soda bottles. Common name? polyester. http://www.kjcf.net/images/index/products/petBottleZ.jpg Spectra is UHMW polyethylene. Common use? plastic cutting boards. Its little sisters PE and HDPE are those whitish-clear tupperware containers. http://www.hospitalitywholesale.com.au/products/haccp-gastronorm-polyethylene-20mm-cutting-board1.jpg and http://feeds2.yourstorewizards.com/3363/images/250x1000/wi-pesc-4.jpg Vectran is a type of polyester (not PET, but the group of plastics). I think it's related to kevlar, but i'm not certain on that. EDIT: cordura appears to be a version of rayon, which from my reading seems to be more like some of the old-school plastics like cellulose acetate, which is what the famous old movie film is made from - the ones that are heinously flammable. :)

Indeed. Just figured I would throw it out there. Lots of plastic bashing going on, which is pretty amusing considering a skydiving rig is made almost entirely of plastic.

No idea. Probably not enough to bother with, especially considering plastic buckles for safety-critical applications would be a specialty item, rather than buying bulk webbing hardware. I don't think plastics would have any real advantage. The hardware used in skydiving is already produced on a massive scale for any one of a million rigging applications, so it's not like we're hard up for quality hardware. Plastic hardware would be re-inventing the wheel. ;) EDIT: I'm reminded of a client I worked with once that wanted us to design a 3/4" drive ratchet extension for a tool kit he was producing; he was convinced he would be able to produce his own for cheaper than he would be able to buy them from an some well-established manufacturer. Boy was that a good one.

Just speaking from an engineering standpoint, there is no real reason why you couldn't make plastic hardware that would hold up. Probably would end up with UHMW HDPE or one of the more high performance plastic (amarids and so on), would be my guess. Nobody would trust it, of course, as you can see in this thread. ;) Plus, if you already have a supply of metal hardware (so no tooling or engineering costs) it would be a little pointless. There just isn't much reason to migrate to plastic, especially given the stigma it has.

This. Very, very, this. PT is boring as hell, annoying, and super crucial.

You wuss.

My first jump at a nearby DZ this summer was on a 230 navigator, IIRC. I weigh ~190 out the door. The student canopies (about 15 of them) were 200-260. There may have been a 280 for the fat guys. :) The other DZ's I've jumped at now had similar selections. Rental gear has typically been 150-200. Also, we were warned as students very thoroughly about the dangers of low turns, both due to altitude loss and possible AAD activation. Just throwing that out there.

That was what my first surgery was for. Will you be having open or arthroscopic surgery? A bankart lesion can be done either way. If arthroscopic, I wouldn't bother with the nerve block. It will be somewhat pointless. The pain for that particular procedure is nothing special - at least it wasn't in my case. The surgery worked really well right up until I asploded my shoulder completely. Now I'm waiting for the arthritis to develop and the fake shoulder technology to mature more.

Like the others said, your recovery will be long either way. Regarding pain control - it really depends on your pain threshold. I've had two shoulder surgeries, one arthroscopic under general and the other open with a nerve block and general. The pain from the first surgery wasn't bad, and I didn't use any of the pain killers prescribed for post-op pain. The pain from the second surgery was, IIRC, quite a lot worse, and i recall using pain killers for three or four days after the nerve block wore off. I didn't, however, like the nerve block in lieu of the pain killers. You have no control and no sensation after a nerve block, and IMO your risk of bashing it into something and doing further damage is too high. Of course, i don't know what the pain would have been like without the block - probably pretty bad. My open surgery was about as extensive as it gets without simply replacing the shoulder entirely (this option was discussed and dismissed due to my age). It was amusing when the block wore of on my motor control nerves before it did on the sensation nerves. It's like being able to control somebody else's arm using the Force. What will they be doing during the surgery?

I'm glad you've learned as much about the world as it's possible to learn. Obviously one can never develop a theoretical framework to explain the phenomenon we see in our daily lives, and the only advances in technology and methodology we see are done through real world trial and error. That's why they had to deploy the GPS constellation several times before they got it to work, and why auto makers still crash 50+ prototype cars before they get the design right. That's why FEA is considered a crackpot idea touted by useless engineers and why CAD never really caught on. I'll keep poking away, since I'm interested in the problem, but if I come up with anything interesting I'll just keep it to myself. Sorry for wasting your time.

I'm not totally convinced, but save that argument for a later date. I have an interesting (and far more related to the OP) observation. I just made up a dummy thing hanging from my ceiling, with four line groups going to two attachments on a weight. Just spinning this up normally produces a nice, even line twist which comes out very easily on its own. I think that's pretty likely to be the type of line twist I see under a nice docile canopy, which flies straight even with the twist and comes out quickly without any real user input. http://imgur.com/GwYM8.jpg However, spinning it up with a slightly slack line, or forcing the twist to move up the lines with my finger, produces a much weirder and interesting twist. The twist runs up all four lines, then splits (usually unevenly) up the right and left groups. I bet this is what throws an otherwise good canopy into a turn. EDIT: actually, I just looked more carefully and this develops very repeatable if the jumper is not centered directly below the canopy when the twist occurs. Smaller, twitchier canopies would obviously be much more susceptible to this since they are much more sensitive to line length. http://imgur.com/YSWNF.jpg This configuration has almost no natural tendency to untwist. I looked for it in videos posted online and saw it pretty often (most times the video is not clear enough to tell), especially in line twists people chop. The OP's method of twisting the problem down towards the risers (which I tried on the hanging thing) seems to change the weird twist into a nice even one, which then comes out easily. I don't know the mechanism by which this happens, but it's very repeatable. Spreading the risers apart doesn't seem to help unless you get the twist to travel a pretty long way up the lines. It's actually pretty easy to see in the OP's video: http://www.youtube.com/watch?v=5FD2I8OqbS0#watch-vid-title EDIT: also, does this board's markup allow embedded images? If not, can it be done using HTML instead?

I'm not going to change my EP's without trying a new method out first. I'm skeptical, not stupid.

Well, I'm glad at least a couple people have been willing to think about what I'm saying and respond with some reasonable suggestions and comments, rather than just making willfully stupid remarks. :-/ I'll try some things out, see what I can see.

I will do that, though kicking into a twist is not identical to kicking out of a twist, since the twist reduces your number of connections to the canopy from two (your 3-rings) to one (the twist). I'm also debating whether or not to build a hanging harness to try stuff out on. I think this is a pretty fascinating problem. It was actually mentioned in the very first post, so I didn't exactly pull it out of nowhere. First, thanks for considering it seriously rather than just throwing me under the bus. :) Second, very true. My reasoning for considering the jumper as a free body (at least as far as kicking into a rotation) is that the single connection to the canopy (the twist) has very little torsional rigidity, and as such would be difficult to apply a torque to without reaching up and twisting the line groups, which is the method advocated in the OP. Now, It hadn't occurred to me until just now that you can still develop some momentum by swinging under the canopy, which you might then be able to change the direction of and use. I may try hanging myself (yikes!) and fiddling with this. Perhaps two risers to a bearing/swivel, then the bearing to some line groups to the ceiling. That would eliminate any friction at the "twist" location and let me play with it. :P

Not hands above - check out the video trevor posted: http://www.youtube.com/watch?v=5FD2I8OqbS0#watch-vid-title You have to admit, thats a much better video than the usual "see the guy kick a bit and then chop"

Not without an external force. It is not possible to change the angular momentum of a free body by applying only internal stresses. Read the paper[link] I posted up there on the topic. Technically kicking would remove energy from the system, by converting some stored energy into heat which would then be radiated away. You could use that heat to power a radio or something, but without any mass to eject (or something to kick against) it would just be squandered as you cool down. You might even be able to move a tiny bit by the directed emission of electromagnetic radiation from said radio, but you can rest assured the effect would be minuscule. My last post was supposed to say "For the apparent translation he achieved". I assume he's swimming through the air he's breathing, since again it's impossible to translate without ejecting mass or suffering an external force. There is the caveat to those that it is possible in curved space time[link], which technically the spacemonkey in the video is in, however the effectiveness is determined by the *amount* of curvature. You can tell it's not curved very much because you don't feel like gravity is constantly attempting to pull your arms off. A quote from the paper I just linked: " The curvature of space-time is very slight, so the ability to swim in space-time is unlikely to lead to new propulsion devices. For a meter sized object performing meter sized deformations at the surface of the earth the displacement is of the order 10^-23 meters. "

That's a very cool clip. Thanks! I wonder how much torque you can apply to something that way. I mean, you have to expend some energy to do it, so presumably you could apply some torque, even if it's not much. For the apparent he achieved, I can only assume he was swimming.

billvon: Yes - this was something I didn't realize until reading the paper I posted above (which is a super interesting study on torqueless, 0 angular momentum gymnastic moves). Redacted my statement in my last post. However, I still don't think kicking out of linetwist is really the right type of motion to accomplish anything significant. Like I said way earlier in the thread, I've never felt like I accomplished anything by it. I am going to have to spend some time on a trampoline experimenting with these fancy maneuvers, though. Ronaldo: I totally agree. The video trevor posted was very impressive, and makes me want to try that technique. I would *love* to find something which I feel actually works to speed the naturally progression of the line twist.

By reducing the average distance of his mass from the axis of rotation, the speed of his rotation increases. This is a cool little demonstration: http://www.youtube.com/watch?v=yAWLLo5cyfE Another excellent visual is the ice skater: http://www.youtube.com/watch?v=AQLtcEAG9v0 EDIT: it's due to the conservation of angular momentum, basically the same as "an object at rest tends to stay at rest, and an object in motion tends to stay in motion, unless acted upon by an outside force." Like I said, the direction can be changed, but not the magnitude. So a diver can translate a twist into a flip and vice verse (to a large extent), and even slow rotation down enough (by spreading out) to appear stopped - usually just before entry into the water. Starting a dive with a good amount of angular momentum gives the diver a lot of freedom to perform a great deal of spinning. That said, it *is* actually possible to do a torqueless, zero angular momentum twist or flip (i was wrong about the cat being dropped perfectly above), but it requires a significantly more complicated motion than kicking, since you are forced to maintain 0 angular momentum throughout the move. Moreover, once you've done it, you stop. You can't start a spin that continues on its own from a state of rest with nothing to push off. Maybe there is a maneuver which could untwist a line twist slightly, however i think your time could be better spent getting into a position which allows the canopy to do the work. Here's a good read: http://docs.google.com/viewer?a=v&q=cache:2kcSiyZlrG0J:www.physics.princeton.edu/~mcdonald/examples/mechanics/frohlich_ajp_47_583_79.pdf+conservation+of+angular+momentum+diving&hl=en&gl=us&pid=bl&srcid=ADGEESizuxBm6G5gZlEWXaXgvzRbmC3IuHichDOoPB6soC71Jmby_4McbIjfojI8IvWjTVWM6ao_egPNg-SCXVkG8APoVYY7cyWTi8umvMAd4ZrJkCJ4JTJsJJ9bWEQCaQmrLZAm-m0R&sig=AHIEtbRkYXpryv9CzaL7l7gUYDiE97xjbg EDIT: since I can't put an addendum on my first post above: The post states that it's not possible to rotate or translate on flat space-time. This is apparently not *entirely* correct. You can apparently reposition yourself, however you still cannot introduce a sustained spin, nor can you translate. You can still swim through curved space, though, if you're interested in getting up close and personal with a black hole.