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Posts posted by pchapman

  1. " when you play with the volume with slats "

    Sorry, that whole example with the diagram doesn't apply to this situation. A slat does a lot more for an airfoil than just extend the chord.

    The lift coefficient won't change much with a change in an airfoil's size, within some reasonable range close to the original airfoil's size and speed used.  So just leave that diagram out of it. (Saying this as someone with an aeronautical engineering degree.)


    I don't think canopy volume is the way to characterize how hard a canopy is to fly -- at least in comparison to wing loading modified (in a not precisely mathematical way) by size

    Let's say you have a guy on a 200 canopy who weighs 200 lbs geared up. And a small girl on a 100 who weighs 100 lbs geared up. (Not trying to be realistic here, but to make the numbers easy.)  Wing loading is the same, 1.0. We already know that a tiny canopy will be a lot trickier to fly, even though the wing loading is the same. We know not to say, "They fly the same because the wing loading is the same."

    But it is little use to talk about canopy volume instead. The canopy volume on the 100 would be about 35% of that of the 200 canopy. (Volume changes with the cube of the line length. Halve the canopy area, line length becomes 1/root(2) = .707.  Cube that =.353)

    How does it help us to know the canopy volume is about a third of the original?  "Same wing loading" sure doesn't mean "just as easy to fly", but "about a third the canopy volume" doesn't mean three times harder to fly??

    (Canopy volume on its own is a small factor, and isn't entirely irrelevant, as there is a mass of air in the canopy that has to be accelerated around when maneuvering. It can be some pounds of weight, with much less mass in a smaller canopy.  But I wouldn't make canopy volume the main focus.)

    We know line length changes less fast than the area of the canopy changes. (eg, half canopy size = 71% of the original line length, or 29% less length) And that line length will affect dynamic canopy behaviour -- shorter pendulum swing will affect turning and stability, and a shorter control range to deflect the canopy trailing edge to the same degree. And the combination of those effects will be something else again.

    So in this example we have all sorts of different size factors:

    - wing load is the same, 100% of the original one could say

    - line length is 71% of original (but maybe line length dynamic and control effects somehow multiply the difficulty for the jumper, creating a lower percent value)

    - area is 50% of the original

    - canopy volume is 35% of the original

    None of these numbers alone seem to be "correct" in giving a guide to a jumper how much different a 100 lb jumper is on a 100 canopy, compared to a 200 lb jumper on a 200 jumper. I think it will be somewhere between that 100% the same and the 50% change of the area. The volume change (of about 35% of the original) is way too much to be useful for this.

    In conclusion, while you might be concerned that "wing loading plus an adjustment for smaller canopies being trickier" is a vague way to give a guide to how a canopy will fly for a jumper, canopy volume isn't the way to go.

    So things are pretty much as wolfriverjoe already stated.


  2. There's a short thread on the Search issue in Suggestions & Feedback. The site admin Meso is aware that the Search functionality sucks at finding all sorts of stuff that still exists on Dropzone from the old days.

    I don't see a quick fix happening, but Meso is looking into what can be done.

    You will have better luck just by searching on google and including "dropzone.com" in the search.

  3. Keener lists those 1 1/2" bands which I also call "Medium" as an alternative Micro size:



        Micro                1-1/4 x 3/8 x .062

        Micro                1-1/2 x 3/8 x .062

        Standard            2 x 3/8 x .062    

        Tandem             2 x 5/8 x .062


  4. Why did the rigger suggest new lines? Very fuzzy lines?  Wear at a specific point? (eg, at the soft links)  Or some particular trim measurement? (eg, "Wow, the outer A's are already shrunk nearly 3 inches!")
    In skydiving we don't have any strict Go / No Go rules on these sorts of things, so there's a lot of room for different opinions.

  5. The Search function is terrible now, making much of the "old dropzone.com" inaccessible.

    For example, I have saved the text from various posts over the years, and when I search on some very specific phrase from the post, copied exactly from the original post, the search finds NOTHING. 

    Same when I search very specifically on the exact title of the old thread, whether or not it is the basic search or search for titles or search for exact phrase.  

    How can one possibly maintain a body of knowledge if it is near impossible to find and reference that knowledge?

    (It is easier to do a Google search with 'dropzone.com' in the title.)

    So what is up with Search and how can it be fixed?



  6. On 7/13/2019 at 10:09 PM, tiger93rsl said:

    I've been having really bad problems on my ride up.  I am just getting so nervous, despite the cheery atmosphere in the cabin. 

    It can help to know that plenty of other skydivers have been there before! Being nervous is part of it all. Part of the fun!

    As for socializing and stuff, one skydiving organization (the CSPA) emphasizes both Relaxation, and Mental Rehearsal. You want both. Relaxation can involve joking with others, taking big slow breaths with eyes closed, or whatever works for you. But the rehearsal is good too, as the more mentally prepared you are, the more ingrained the elements of the jump are, the easier it will be to remember it all and act it out when you go out the door.

    If you are stuck on body position issues once out the door, yeah tunnel usually helps a lot.

    If you aren't doing tunnel, then sometimes you  can plan a dive with the instructors that keeps things really simple. No turns or anything, just fall and relax and adjust body position. Do you smile in freefall? Sometimes if the instructor can make you smile or shake your hands or something like that, it can help you relax in freefall. Now you don't want relaxed as in 'limp', but you don't want 'rigid as a plank' either.


  7. So the French term is PAC while the English term is PFF in the CSPA system.  PFF and AFF are pretty similar in a general sense.

    (There are also USPA affiliated DZ's in Canada who will offer the US-style AFF. Perhaps none in Quebec but I'm not sure. The CSPA system works easier there because documents are available in both languages.)

    Normally PFF in the Canadian system uses 3 jumps that are 2:1. The approved Tunnel variation of that is to do tunnel first, then one 2:1 jump. 

    So that all is in accordance with what you heard about learning to skydive in Quebec. Plenty of good, professional DZ's in Quebec.


    • Like 1

  8. I still go with the term two-stage flare as a general convenient and accepted skydiving term. It doesn't properly explain every possible variation in how one might describe or do it, but it is a reasonable term to use. 

    However when teaching a canopy course, I tell newbie jumpers that one could call it a variety of things, like a four stage flare or -- to go to extremes -- an infinite stage flare as one is always evaluating the response and adjusting based on canopy motion and location. Two stages may be all one smooth movement or two completely separate actions with a stop in between, depending on what effect the first stage had for you.

    One could for example talk about stages like this, if the canopy does have some speed:

    1. Start the motion to plane out (plus any feedback, evaluation, and adjustment at any of these stages),  2. Be almost planed out but allowing oneself to slowly descend from an initial plane out height to a desired final plane out height (say, 2 ft off the ground in case of error while learning to do this, to 6" off the ground with legs pulled up slightly), 3. Completely plane out at that final height, 4. Finish the flare to step down onto the ground or run it out,  or give an extra fast final flare to pop up to minimize speed and stand up the landing. 

    Or if it is a newer student on a very lightly loaded canopy, one might say the flare is more like:

    1. Start the flare to some predetermined arm position, 2. Evaluate how the flare is going, 3. Decide whether to wait a bit to descend more before finishing the flare, or whether to finish the rest of the flare right away.

    So there are plenty of different ways to describe a "two-stage" flare, depending on the audience and their experience level and canopy, and how you want to teach it.



  9. 3 hours ago, PhreeZone said:

    Funny - I was just starting to think about shutting the site down since most of the manufacturers are hosting the manuals directly anymore

    I go to the major manufacturers for their latest. I go to a site like parachutemanuals for old or weird or unsupported stuff, or even old versions of regular manuals. (Would be nice if the PIA could take over something like that, but they may not want the hassle either. Nor would the collection be independent of industry pressure if someone didn't want an old version out there.) 


  10. So there's the question of whether to go for option 1 or 2 or maybe a 3rd.

    1. Just do static line jumps, remaining a student.

    Requires the appropriate aircraft and instructor and supervision every jump. Costs more and may not be available at all times at the DZ, depending on how many static line jumps they do. The only gear you can use will generally be dropzone student gear that's set up for static line.

    2. Get a full license.

    Allows you do do hop and pops with regular equipment out of more aircraft and more dropzones. But it requires learning a wider range of skills, as expected for the typical beginning skydiver, including freefall maneuvering skills.

    3. Get a restricted license.

    Here I'll have to defer to those in the USPA instructing system. Blind people and others have gotten licenses with certain restrictions, I think. Is it possible to get one that would work for hop and pop's only??    Just sticking to static line jumps might be pretty awkward unless your current dropzone really wants to work with you and does a lot of static line.  You would be able to use normal freefall gear and supervise yourself (taking much less time to arrange each jump), but not have to learn freefall skills you don't plan to use.

    As Seth says though, once you do a bunch of jumps and get to a particular stage, you like many others might want to go a little further, beyond just static line or even hop and pop jumps. Scaring yourself a little with new things (including those first practice ripcord pulls) is part of skydiving...

  11. I'm also OK with the use of "streamer" for a square that snivels forever but never has the slider come down.

    Maybe some of you remember the big laminated malfunction photos / giant flashcards that some DZ's had for their FJCs? I don't know who buys them now, but they've been around, who knows, maybe 30 years. Their list of mal photos does include the streamer:

    1. Broken Lines
    2. Line Twists
    3. Bag Lock
    4. Slider-up with Spin
    5. Slider-up Snivel
    6. Pilot Chute-in-tow
    7. Closed Endcells
    8. Line-Over
    9. Slider-up with Twists
    10. Square Reserve Out with Main Out
    11. Round Reserve Out with Main Out
    12. Streamer
    13. Horseshoe
    14. Pilot Chute Under the Nose

    (Source: SkyHi Video Productions website.They are still around!)

    Hmm, but now I'm wondering, how is #5, the "Slider-up snivel" any different?


  12. I recall the PISA Naro being one of the ugliest rigs around at the time. But it seemed to be functional. Can't recall how freefly friendly the flaps and covers were. PISA was absorbed into Aerodyne in 2003, and discontinued their harnesses at that time. (At least according to a press release I have of the era.)  The Naro wasn't seen much in North America. No service life limit - why would there be? Oh... you're in Australia where you sometimes get those funny rules.

    So the value of the rig is likely minimal, although technically probably just fine to jump.

  13. On 6/7/2019 at 4:34 AM, Islander-O said:

     This makes me think that quoted at the beginning of this post sentences commented Icarus in configuration 6+2 that forces TM to fly long straight approach making canopy the most vulnerable to wind gusts, turbulence, and thermals.



    I use the landing pattern of 270-degree turn with a toggle pulled down to the top of my shoulder.

    Haha! That's considered evil in places using UPT rules or the US Tandem Commandments -- no turns over 90 below 500', stabilized on final by 100'. They all want long boring unaccelerated final approaches. They don't care if you say, "I never banked more than 20 degrees" or "I never brought my toggle below my shoulder".
    But yeah I know what you're getting at. A gentle curving approach consistent with traffic does improve canopy rigidity and resistance to turbulence for pretty much any canopy.
    Still, the idea is supposed to be that one should be able to land one's tandem canopy without resorting to such measures. So saying 'the Icarus is great if you swoop it a little' isn't going to win you fans in some circles.

  14. Still jump my Maverick from time to time. My go-to canopy for demos and general stupid stuff one doesn't want to do on modern small ZP.

  15. I could have been more precise and correct about how the main can end up "around" the reserve:

    1) I said how I thought the PC & freebag went between risers or lines (within a riser group). Additionally, they could have gone above the slider. Same issue though: It would need some line caught on the rig or jumper to create a gap to go through.

    2) Or an entanglement can happen with nothing of the reserve going "through" the main, if the reserve extended but "barberpoled", wrapping itself around the malfunctioned main, especially if the jumper and main were spinning generally along the axis from jumper through main. That's a more traditional main-reserve entanglement. But it would take more than 1/10th second of cutaway delay for that. A full second might be enough though, who knows. 

  16. Yikes.

    There's long been the worry that someone might occasionally get the Cutaway & Reserve just a little out of order, if they are trying to "pull simultaneously", or even do a "quick one-two", which is a better strategy.  Maybe the cutaway handle takes a little more force (whether due to forces on the cables or just good velcro), so the reserve pull ends up early.

    I'm wondering if maybe you had a line or line group caught on you or around the bottom corner of the rig or something, after deploying unstable or head down. Only that seems to explain the situation. So I'm guessing you were entangled in your main after all.

    (I'm not expecting you to know 100% what's happening behind you during a nasty malfunction whipping you around!) 

    If one is just in line twists, each set of risers tends to have front and rear close together, very little space for the reserve to go through. Plus, it wasn't just the reserve pilot chute getting through some part of the main lines, in which case the freebag would have solved the issue and you and the reserve would be free. For the main lines to be around the reserve lines, the whole freebag had to go between risers or lines -- such as when some lines are entangled on you somewhere. That can result in a spinny mess with a line over or just something looking like one.

    You got a little over amped on the main pull (when you had time to wait a couple more seconds easily), and had the same with the reserve pull.

    But great  job on keeping on fighting and actually using the hook knife. And managing to not cut any reserve lines in the process!  It is very very rare for anyone to ever use a hook knife. Not unknown though, so it's still best to have one.

    • Like 1

  17. Now I could be entirely wrong, and I only watched the collapse, not the rest of the vid. Looks familiar, this little incident that was a good advertisement for a Skyhook.

    That came up a while back on DZ.   I know it as the Dubai swoop comp collapse, Dec 2011.  Think it was blamed on turbulence, causing the frontal stall or frontal collapse (negative angle of attack).  Possibly in some way combined with it being on an early non-production version of a Petra, a prototype if you will. But I don't know the details. Search for "JPX Petra - stability issues?" thread.


  18. At the OP:  Rigger Lee got at this a bit, but you'll be pushing the certification limits of standard gear.

    Some rigs are certified to the old traditional 254 lbs (jumper plus gear), others as high as 300 lbs, but I'm not sure if there's anything beyond that. (Unless one uses adapted tandem or military gear.)  So it might be hard to be totally legal.  Not that people haven't slightly overloaded gear before. People over 230 lbs (without gear) skydived even when nothing was certified past 254 lbs, so with the available gear they were always overloading it a little. 

    Reserve canopies have a similar issue to the rig itself. E.g, the biggest PD reserves, whether regular or Optimum variety, max out at 290-300 lbs for certification.

    So, similar to what Lee is saying, you at least want to maximize things in your favor by considering gear features that are more forgiving of high weights and speeds.

  19. at OP:

    I figure you're just talking about being stopped from jumping in "some weather" due to winds. Not that you're hoping to jump through 10,000' of rain and cloud. (I personally think Skybitch's comments seem a bit harsh if they are a riposte to your comment, but are educational when talking about weather issues in general.)

    Your being stopped from jumping in higher winds is probably more a function of what is allowed at your license level (assuming you are under USPA rules or similar), than the size of the canopy. One can fly big canopies in strong winds... it just gets a lot more challenging. I have jumped student size canopies where I've backed up right to touch down. Takes a little more planning and of course one can't do a regular pattern.

    In some locations and cases, tons of wind will lead to tons of turbulence, in which case fewer and fewer jumpers, even experienced ones, will want to be in the air at all. In that case it isn't just about wind speed.

    So yes you may feel more comfortable when maneuvering around with a smaller canopy when winds are higher, and may indeed be safer.  If an instructor grounds you due to winds though, it's likely because they are grounding all Students, and not just because you're on a 280. Still I hope you get to downsize a few sizes quickly from that level - especially when you've already flown smaller. (At a different DZ?)

  20. I've seen it done and am OK with it. The mechanics of the RSL pull shouldn't introduce any forces too much different than normal.

    Have to watch the RSL routing though. Depending on where the RSL is situated (on the reserve risers or under or inboard of them), someone might route the RSL UNDER the reserve risers instead of over top, to get to the outboard side instead of inboard. (Might still work despite dragging the RSL under the risers before the reserve is released. Even weirder and scarier if a MARD were involved.)

    Plus it just looks weird and is confusing to anyone who is helping with a gear check.

    So I tend to recommend it as temporary only, until one gets some new risers shipped in...


  21. 54 minutes ago, timski said:



    watch me experience said event. watch me fix the malfunction. 

    For others: Skip to 2:25. And turn your volume down.
    Nice job getting out of spinning line twists. And then dealing with the popped toggle. The video is kind of good in that it shows less than instant & perfect reactions too (not a "See I'm great" video), as it takes a while to reach up far enough to get to the toggle. (Sunk in harness a bit from G's? Wingsuit restricting arms?) Actually he happens to get to the stowed toggle just before the popped toggle. Whatever works!