Any word as to how Vented Pilot Chutes (like CR is developing) are working in the field ? I'm considering one,,just sounds kinda Scary having a hole in the top ! Any Imput would be helpful. Thank you;-)
Any word as to how Vented Pilot Chutes (like CR is developing) are working in the field ? I'm considering one,,just sounds kinda Scary having a hole in the top ! Any Imput would be helpful. Thank you;-)
I don't jump any unvented pilot chutes anymore, unless it is an object where an off-heading just doesn't matter that much (Perrine, for example). I've seen enough video of PC oscillation, and had enough jumps on vented PCs (75 or so) to both see and feel the positive difference venting makes.
There aren't many things in BASE that I personally consider essential for safe jumping of routine objects (tailgate slider down, Big Grab toggles, exposed center cell, properly set deep brakes, etc.), but a vented PC is now one of them.
Peace,
D-d0g
ddog@wrinko.com
www.wrinko.com
D-Dog,
I use one vented PC currently, a 46 from CR. I have used it as low as 325' (I know, not really low by y'alls standards) and have no problems. HOWEVER I had a friend go off a B in front of me and towed a 42" vented pc for almost 4 seconds(on video), He said he noticed it a little, but after watching all the video he opens noticebly lower than the others jumpers on the load. So I ask you, ever had any hesitations?? I would HAVE to believe that in theory, a vented PC would take longer to inflate, thus delaying the opening sequence. Just trying to gather some more info on these things, as I would like to replace all my PC's with vented ones one day...
Also, isn't it funny how non-believers are so quick to shout BLACK DEATH!!! freaks
c-ya
Red:P
To what degree would you say is the difference in on-heading performance? 75 jumps would be a good sample size for statistical comparison. For example, how many off-heading openings worse than 45, 60, 90 degrees if any...?
I use a non-vented zero-p 48" PC for the low stuff. Would you use a vented PC on 200-foot freefalls, or would you still use non-vented?
Michael
I switch to non-vented PC's around 250', depending on object type and landing area.
I think a vented PC is more likely to hesitate at zero airspeed (and possible slightly more likely to hesitate overall--so I won't use one on low pulls, etiher).
--Tom Aiello
tbaiello@mac.com
That's what I was thinking... Thanks, Tom!
Michael
Woah now - I'm far from an expert on vented PCs. I think all the real experts are out jumping, and this poor old Dog is stuck at home working. Boo hoo!
Anyway, some answers based on my experience:
1. I have one of the vented 46 CRs, and frankly I think the vent is way too big. I call it the "scary chute" because it does open slower than a usual 46, more like a 43 or so based on my gut. I heard a rumor that they have made the vent smaller on new model CR 46 PCs, but not sure. I still jump it (regularly of a 330 foot to impact B, no problem), just not someplace where I need super-fast opening. See below.
2. Regarding hessies in general, it's all about vent size. A huge vent will result in a slower opening, of course. However, I have 40+ jumps on a custom vented 42 PC (the "Soft Cock special") and there is, I think, a tiny but irrelevant difference in opening speed versus a non-vented 42. I regularly take it very deep slider down and do not hesitate (pun intended) to do so. If the vent is big enough to really cause hessies, then I personally believe it is just overdone. A properly-vented 46 should open. . . ooooh. . . sort of like an unvented 45 at appropriate airspeeds.
3. And, no, I don't jump vented stuff on really low objects (less than 200 feet) - but I rarely freefall this stuff with my big, fat, broken-up ass anyway. I don't think oscillation is much of an issue with these really low objects, but then again jumping big unvented PCs even at low airspeed with a hard sideways throw (instead of the more correct "out and up" throw) could cause at least a partial oscillation cycle and off-heading. And off-headings below 200 feet with hard objects behind you are no fun!
3(b). I don't know this for sure, but my gut is that even a small vent on a 48 or 50 inch PC for low, heading-dependent freefalls could help and not really slow down opening noticeably. I have NOT tested anything like this, so this is just my horse (err, dog) sense. Your mileage may vary; some assembly required.
3(c). For the sake of clarity, I also still jump unvented PCs when PCA/static line jumps are in order.
4. Regarding heading performance overall with vented PCs, my dear readers must keep in mind that the Dog is well-known for his more-than-occasional, flailing, head-down exits. I consider them a sub-specialtiy of BASE acrobatics, really. Anyway, I've had. . . hmmm. . . two openings with a greater than 100 degree off-heading since I started jumping vented PCs about 80 jumps ago. Both of those, I think, were primarily if not fully caused by flailing, head-down, rolling-up-the-windows body position at deployment.
4(b). Other than that, I've had the occasional 30-40 with vented PCs which I think are statistically just part of the game. Save for the two openings listed above, and a few random Perrine openings with slam-packed canopies and stuff, my headings have beein within about 35 degrees either direction (slider up and slider down). I do NOT believe that my findings in themselves are statistically significant - there are so many variables that affect opening accuracy, and PC oscillation is only one. It would take hundreds - or thousands - of jumps with all other variables systematically controlled to really say that vented PCs were proven +-95% accuracy to lower off-heading probabilities meaningfully.
5. We did some fun experimentation while on the boat at the Perrine, holding out vented and non-vented PCs into the 10-15mph windstream and seeing how they behave. That would convince anyone, I think - unvented PCs hop about quite a bit, and properly-vented PCs are almost rock stable.
I do find it funny that, in terms of modern BASE gear, we seem to be paying lots extra to have HOLES in our gear. Vents. . . valves. . . bottom skin venting. . . I always thought I was trashing my gear when I ripped it out of the brambles, now I look on those scars as "next-generation canopy venting technology!"
Peace,
D-d0g
ddog@wrinko.com
www.wrinko.com
>2. Regarding hessies in general, it's all about
>vent size. A huge vent will result in a slower
>opening, of course. However, I have 40+ jumps on
>a custom vented 42 PC (the "Soft Cock special")
>and there is, I think, a tiny but irrelevant
>difference in opening speed versus a non-vented
>42.
I think that PC vent location is also likely to be an important consideration. Did Ray build that PC with the vents in the standard (apex) locations?
--Tom Aiello
tbaiello@mac.com
Fired something off to BR some time ago about vent location... I had been reading in Poynter's manuals that a set of vents, say, halfway between the apex and the lower edge of the nylon would contribute better to stability while impacting grab force less than a vent at the apex. Anyway, I was thinking a person could mesh in three slots on a six-gore pilot chute.
Apparently they've checked that out, and I believe production cost was a big problem on that one. Any thoughts?
When I asked BR if they were considering moving the vents to a position further out on their PC's, I was told
"I will not discuss the research of this shop with customers."
I think that a row of vents in a donut configuration halfway between the edge and the apex would be an improvement in stability. I have some concerns that this configuration might reduce drag considerably (as that would put the vents at the point of maximum pressure--the same reason they ought to be more effective stabilizers).
Another major manufacturer who is a bit more willing to discuss gear and technique with us ordinary jumpers pointed out that PC pack job might become extremely critical with a dispersed vent arrangement. With vents in odd places, a missed fold could potentially obscure an entire vent, resulting in a strange oscillation, spin, or worse on deployment.
I also think that production costs have been an issue in PC venting.
--Tom Aiello
tbaiello@mac.com
If I recall correctly (and I don't have the manuals on hand just this minute), Poynter attributed an *increase* in drag to having vents around the half-circumference instead of at the apex.
I would be very surprised if PC folding became an issue with such an arrangement, since assymetries there would have their greatest effect on the PC while it was still partially folded, which is also when the PC is exerting the least drag and therefore has the least influence on heading. By the time the PC becomes an anchor, it'd be a symmetrical one I'm sure. Worth looking into, though, for sure...
And as to production cost, I imagine the number of jumpers willing to pay a little more for a PC which is spectacularly stable is increasing rapidly.
tom did you get your copy of knacke's recovery systems manual yet? check table 5-1, specifically annular parachutes, associated drag coefficients and degrees of oscillation. I"m afraid to comment without the reference at hand, but I think that jason (above) is right to some degree. a non-PDA round has a lower drag coefficient than an annular parachute of the same flat surface area. and, IIRC, the angle of oscillation is reduced by more than half in an annular. this is where the vented pc's came from, and perhaps where they're going. there are also a bunch of other designs that are kinda neat and perhaps worth investigation.
OK, I've got Knacke in hand. Just looking at the numbers, an annular PC ought to have the best drag and least oscillation. I'd love to see the same table with some PDA numbers, though.
Wow, just looking at figure 5-6 starts my mind spinning. Table 5-3 is pretty interesting too. Hmmm. Thanks for putting me on to this text.
I need to do more research. There's a lot to think about here.
--Tom Aiello
tbaiello@mac.com
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