pchapman

For the Protrack mount zip tied to the outside of my Protec, I hand sewed a narrow piece of webbing around the clip and Protrack, vertically around both of them, and through the helmet (used one existing ear hole and cut a slot too). It was a bit fiddly to get it snug enough. It's not an ideal solution but seems to work. To view or remove the protrack I can push the 3/8" wide webbing off to the side. It is stiff but there's just enough slack to force it away. In use, the webbing is still snug on the protrack, tends to keep the clip tight, and provides a little protection to the face of the protrack in case the helmet is dropped or whatever.

Question for riggers: Who builds safety stows vs. buying them from the manufacturers? In my area it seems common just to make them, instead of grounding the rig & ordering one from the manufacturer. Do many riggers really go the absolutely professional route versus building them? Comments welcome on any of the many issues that are possible for safety stows... There are some very poorly made stows out there, some old ones that are very stretched out, and some that are built ugly but functional. I'll admit to a few of the latter in my earlier days, before getting the thread tension figured out on the sewing machines. Lots & lots of tension needed to keep the bottom thread from getting all messed up. Some companies publish safety stow info, some will let you know if you ask, and some won't tell you. It is a TSO'd component, they say. I can understand that they are hesitant about people building these things. But what if you're rigging outside the USA? Or if they don't tell you, then how do you tell if the old one is out of spec? :) Some rules of thumb have been published by experienced riggers, so some riggers are building stows. There are bungees of different stretchiness but similar diameter, which may cause some confusion out there. (E.g., Paragear item W9651 vs W9654 vs W9655 - the latter apparently being the stretchier stuff that appears best to use.) Sometimes somebody has to build the stow because the original company is out of business. Sometimes one has to build a stow to match the particular canopy, one which is either a bit loose or crammed into the freebag. Some riggers don't seem to pull stows out of their channel enough to inspect them. Sometimes it is only the sheath that is holding stows together, with all elastic strands broken. I do try to replace stows like that, more so because of increased stretch and general age than strength. (I've put 150+ lbs of force on stows like that and seen no obvious effect.) Should more be published about building safety stows to encourage riggers to get things right about these secretive little devices, or would that just encourage riggers to screw up things they shouldn't be playing with? I've met a number of jumpers who had no idea what a safety stow was, when I told them I had replaced theirs and showed them the old bungee. All in all, given the variations one sees out there, it's surprising that there haven't been more problems with bag strip on reserve deployments!

There's some learning going on in this thread! Anyway, what the heck, here are a couple graphs to provide examples of the kind of tracks that people are talking about. The "j1368" one is a straight track. RW suit, no booties, skinny jumper. Even in the reduced air density at altitude, true vertical airspeeds are consistently in the 76 to 82 mph range. "j1544" is for another dive where I did a 180 turn which caused a spike in speed. It compares GPS output to Protrack data. (Raw protrack data reworked to provide a 3 second centered average rather than it's normal 6 second lagged average.) Although there is some confusion during the turn, the GPS seems to confirm that the Protrack is not totally out of whack during long, steady state flight. Of course I can't prove I didn't just spend all afternoon creating fake graphs. :)

I'll add that in some conditions it takes even longer to dry, especially deep down in multi layer fabric, webbing, and foam areas. So I like to add a fan in front of the rig to keep the air circulating to speed drying.

Yes it is a good book to read. I'll note for others that if one prefers a paper copy, it is available from Skydiving Book Service (from the Skydiving magazine folks, skydivingmagazine.com). Quite pricy, but one gets a full colour, spiral bound printout on heavy paper.

Previous answers are good -- the official silly FAA rules, the peace of mind issue, and the general idea that a main that has been sitting a while doesn't need a repack. Even for those who have a rig sitting unused over the winter, some will repack in spring, some might not. Typically one would do a repack anyway after hooking the main back up after the reserve gets packed. (& doing a line check to see that the main went back on right.) A zero-p canopy tends to get a little stiff when it has been sitting packed a long time. Probably not an issue, but its the type of thing where if it is a snivelly canopy to begin with, some owners might choose not to make their first jump on it a hop and pop at under 2500'. In rare cases certain canopies may be susceptible to being very stiff when packed a long time. One main canopy that I pulled out of the bag after the winter was brick-like enough that a moderate shake was not sufficient to spread it out. One had to peel cell from cell, they were so stuck together. This was on a mid 90's PISA product, a Hornet, with a zero-p fabric that I don't think is being used now. Even for that canopy, I don't know how much worse it would have made a deployment.

I can't disagree much with that at the moment. I haven't figured out any good way to get a 3rd deployment mechanism on the rigs in question, without an extensive rebuild. Not a lot of space to put yet another cable. A question is whether the FXC can be considered sufficient to replace a separate handle for a reserve side PFF instructor. (Some rigs of course do use 3 deployment methods although it gets 'busy' at the pin. E.g, Vectors where the end of the RSL has a pin, and the end of the ripcord has an eye that loops over the pin, and there's an FXC fitting over the pin as well.)

First, as for Trackingderby results, I tend to be a little skeptical as one normally has no clue how much tailwind people were working with. As for tunnel studies, I've seen an aerodynamics text reporting data from wind tunnel tests from the 1950s and 60s in the USA. Even back then the L/D curves were showing peaks of about 0.7 to 0.75. Pretty good.

I'm looking for information on how a rig can be set up for AFF style jumps, if it uses a spring loaded pilot chute and an AAD on the main -- and also needs to have a handle for the reserve-side instructor to deploy the main. I heard Perris Valley used to have such a setup until about 2001. The USAF Academy is said to use a similar concept. How are such systems built? If using a ripcord system, an FXC can be set up to pull the pin, but it gets messier to set up a second handle for the reserve side instructor.

Yeah, those cute little trees are pretty scary.

So this thread is getting derailed. We need one for the Twin Otter production line (that although it has gotten the green light, hasn't yet happened), one for the Quantum Leap lawsuit, and one to hurl insults at effing lawyers. From that news article: Good, so I'm sure all money made in the lawsuit will go directly to aviation safety organizations to lobby the FAA for regulatory change, and to Pratt & Whitney Canada, to sponsor research into short engine cycle stresses on PT6's...

Nicely stated Yuri! I hadn't tried to run those numbers. An extreme example of what Yuri's talking about is seen in those videos of tiny non-landed canopies, maybe 21 or 25 square feet ... where the jumper looks like he's face down about 45 degrees off the vertical because of all his body drag, no matter how efficient the wing might be. But Yuri's point is that this sort of thing has a significant and variable effect for "normal" fast canopies too.

A complicating factor is whether one wants to look at 'risk per jump' or 'risk per year'. I'm making up the numbers but it is interesting to think of the issues: The guy with 1000 jumps may believe that a newbie with only 100 jumps has a ten times higher chance of getting killed when he goes on a skydive. But if the newbie is only making it out to the DZ for 25 jumps a year, and the 1000 jump guy is now pounding out 250 jumps per year, they both end up having the same chance of getting killed in the sport per year... [Mathematically the two situations aren't exactly equal, but for small probability events, 1/10th the risk, taken 10 times more, is about equally likely.] Now that's not to say that maintaining equal risks per jumper per year is the right way to go. If one can only jump once per year, one isn't given carte blanche to make it a really dangerous jump.

Too much time on dz.com today already, but I'll bite. Just briefly: My FX88 was flying roughly 46 mph brakes free, and 1750 fpm descent rate (29 fps!). That's at standard temp & pressure conditions, basically sea level. So the actual speed through the air will be higher in summer and higher altitudes. Getting consistent speed data is tougher with the FX, as even a little movement in the harness, or the tiniest harness turn, would increase the speed a couple mph as it tried to dive off to the side. In very deep brakes I was down to 25 mph and 730 fpm. With a Sabre 120 I was getting about 35-36 mph & 1350 fpm. The Stiletto 120 was the same or marginally faster, but descending slightly slower. Under a Manta I was doing 25 mph or just under. Note that these are flight speeds, so the horizontal speeds will be somewhat less. In a previous post in the thread I wrote: Oops, I misspoke. I actually did things the other way around. Since the anemometer is supposed to show true airspeed, therefore if testing up high, the speeds have to be reduced for density altitude effects, so that one can compare all numbers at sea level conditions.

As for the issue of the instrumentation I used, for those wanting the details: THE SHORT ANSWER Electronic vario and anemometer. Decent, but not professional quality. No need to deal with groundspeed vs airspeed issues. THE LONG ANSWER 1) For rate of descent it was an electronic variometer (rate of descent meter) as used by paraglider pilots. 2) For speed, it was a hand held electronic ducted propeller style anemometer, that is supposed to be accurate within a few percent. (Some cheap ones are shown in the manual to be much less accurate.) The anemometer was held out away from myself, risers, etc. to avoid either blockage or venturi effects. It was simply pointed in the direction of the apparent wind, and rotated up or down a bit to see a maximum value. Also, ducted props show insensitivity to errors due to not aligning them perfectly with the airflow. I once calibrated the anemometer in a university wind tunnel to remove what seemed to be small errors at the high end of the speed range. 3) Altitude corrections. The rate of descent changes with altitude, so I had to correct data from different altitudes to a sea level equivalent. I would get a pressure altitude on the ground using the plane's altimeter, and get a rough temperature reading on the ground and at jump altitude, to work out average air mass temps. Formulas are available to do density altitude calculations, or one can plug the numbers into a pilot's old circular slide rule. Initially I did altitude corrections on the speed data but then realized I didn't need them, as the propeller style anemometer reads True Airspeed, rather than Indicated Airspeed as an airplane pitot system would do. This seemed to be confirmed by comparing results for data collected both up high and down low. This made for small corrections in my original glide ratios, bringing them down a bit. Some day I'd like to put all my data together, double check the calculations, and do a clear writeup on it all. The results won't be perfect, but will be better nothing, which is usually what is available! As for a vane and a tilt sensor, sure, that could work, if the difference between the vane and level measurements could easily be recorded. In some ways it could be better because it would be a more direct measurement, rather than relying on calculating descent rate and speed along the flight path, and then doing the trigonometry. For me, I wanted to get speed information as well as glide angle. Paragliding companies use instruments similar to mine, but I have heard that to get really clean speed data with little effort, they use a 'trailing bomb' system with a vane-pointed ducted prop sensor hanging down below the pilot, well away from the interference of the pilot & harness.

Ok, ok, I'll try to throw some data in here, although it isn't exactly answering your question in a clear fashion: FX 88 = 2.1 glide ratio brakes free, 2.3 at quarter brakes, 2.8 in deep brakes (Goes way up in deep brakes, unlike old F-111 canopies where the glide ratio would go down.) (All tests at 165-170 lbs suspended) Sabre 135 = 2.1 free Stiletto 120 = 2.4 free (Stilettos were always good at gliding.) a 265 ft sq F-111 7 cell canopy = 2.2 free, 1.7 brakes set an experimental high-glide 11 cell 170 elliptical = 3.2 brakes free, over 4 in quarter brakes (Just to show what can be done largely with different trim.) I haven't confirmed it but figure something like a Manta, although bulky, is a high aspect ratio canopy with a decent glide, so it could be in the 2.75 range. In another earlier thread I wrote about 2.25 to 3.0 glide ratios for skydiving canopies in general, but now I'd revise that down to "2.0 to 2.75". (I've gained a better understanding of the characteristics of my variometer and anemometer instrumentation and thus fixed how I adjusted for density altitude.) Other reminders from an earlier post of mine: ======== Remember that skydiving canopies are often built nose low for speed, rather than trimmed nose up for efficient glide (more like paragliders). So a skydiving canopy's airfoil usually has potential for a higher glide than it actually achieves. Also, for small canopies, the pilot size may not change, so the "payload" gives proportionately more drag. A smaller version of the same canopy, with the same pilot, will therefore glide more steeply. ========== As an example of the above, Paraflite used to publish some detailed flight test results on their canopies. One high aspect ratio zero-p topskin canopy showed a brakes free glide ratio varying between 2.2 for the 154 size, and 2.8 for the 240 size. With all of this, remember that the numbers could easily be off by + or - 0.2. It's hard to get really good data without a lot of test jumps in still air, and well calibrated instruments. So use this as a general guide only.

My friend's Talka does contain a PZ-81, and he has a manual. Unless someone else gets one sooner, I should be able to get it and scan it in, in a few weeks when he'll be at the DZ. As for translating from Russian, that you'll have to figure out separately. Maybe we can get the manual added to parachutemanuals.com too.

Talka. (The "n" is just the Cyrillic "L".) The canopy very occasionally shows up in other threads about rogallo style wings. As for packing, sorry no idea but I'll email a Russian at my DZ who jumps a Talka rig. While it is nice to have TSO standards, it's also nice that here in Canuckistan we can also jump non-TSO rigs.

Anyone got a source of foam for adding to leg straps where the old foam is worn out? Sigma tandems, and I think recent Vector III's have really nice thick padding that retains its springiness a long time. Unlike, say, the padding in old Vector II's that gets compressed to nothing. The Sigma stuff is 1/4" or so of closed cell white foam. I once found something similar, but about 1/8" thick, which worked well for retrofitting. I thought it was something used as a flooring underlay, but can't find anything like it now. Flooring stores either have very thin foams that compress easily, or foams that are too thick -- Like 3/8" to 1/2" for carpet underlay. I've seen people using foam from camping mattress pads, but again that's getting pretty thick. So I'm wondering what type of store or industry might have 1/8" to 1/4" foams, that one can buy in retail quantities.

Oh yeah, that's one thing I was afraid of. I gave the caveat that buying the 'compressible foam' helmet isn't necessary the best strategy, and it is helmets with better certifications that have EPS style foams. Compressible foam helmets are often lower profile than the EPS style ones, which is convenient for skydiving, despite the increased risks. One can also buy sets of low rebound 'memory foam' pads for ProTecs, which are known as the Pararescue liner. (Not built by ProTec.) That should help, if the foam densities were properly chosen. But at $85+ they are pricy for adding to a cheap helmet. So thanks for expanding on the foam info.

On the topic of finding ways for swoopers and non-swoopers to coexist: What about the idea of trying to separate a landing area into left and right parts, with 270 degree swoop turns "to the outside of the pattern"? That is, the non-swoopers do a standard left pattern for their landing. The swoopers extend their base leg until they're over the far side of the landing area, then can do a 270 right to land. (See attachment.) Why doesn't this get suggested more often? It seems to be a simple but useful modification of what in practice happens at some places already -- the swoopers follow the pattern through the base leg, then crank their 270 the opposite way. While that at least produces standardized procedures, the danger being pointed out lately exists where swoopers dive onto final approach and have to mix with the slower non-swoopers. Non-swoopers can't well watch above and behind them to avoid collisions, and swoopers can get too focused on their approach to see potential conflicts. For the separated landing method, left or right patterns can of course be chosen depending on DZ buildings, prevailing winds, and who should have to walk in further to the packing area! Sure it doesn't achieve the ideal of a private landing field for each person. But it does allow two fundamentally different approaches to exist, with an attempt at keeping fast and slow apart during the critical part of the swooper's approach. It still demands some discipline, but stops short of banning swooping. At busy DZ's, some limitations on swooping may be necessary for it to coexist with other types of jumping. The same applies for other forms of skydiving, like CRW, wingsuits, freefly vs. RW -- or the limitations that one has to accept for the benefits of a big airplane in the first place. I myself only owned an accuracy canopy for 11 years, but now I want to enjoy my swoops too... One counter argument I won't accept, which I sometimes see in these discussions, is that swoopers wouldn't be following a "proper pattern", as if there is only one god-given definition of a pattern. Our skydiving patterns can be whatever we choose and agree them to be, to suit our sport. They don't have to be the same as a pattern as learned by a student airplane pilot.

And a camera too. How's he going to put a camera on that? Pro-Tec still makes the "Classic Full Cut Water", the usual style used for skydiving, with protection over the ears. The style of foam used on the inside has changed a few times over the last 15 years though. Lately they've added some sort of simple rubber strap at the back of the head. Not sure if it really helps to hold the helmet better in position or just gets in the way. The pic in the original post was of the Classic Skate -- i.e. their skateboarding helmet. It also traditionally uses the 'compressible' foam (that rebounds fully) like the Full Cut Water, rather than an EPS style 'hard foam' / 'one time use' foam found in snowboard or bike helmets. That's what I found when I recently bought one for multi sport use including CRW, that appears to have been built late in '06. Yet Pro-Tec's site seems to indicate that this year's production of the Classic Skate uses the EPS foam?! Their other Skate helmets I believe used EPS but are now moving to what they call SXP, which is similar in feel but is supposed to have some multi impact protection. For skydiving I prefer the compressible foam more for comfort and general feeling that it will cushion better than the very stiff EPS. That is not necessarily the best strategy. The compressible stuff is understood to be better only for minor accidents, but worse for major ones where it can bottom out. That's where the EPS and similar foams win out, and are found more in helmets that have higher certification levels. Oh, and the phone number on the new helmet is 562 565-8267, for Pro-Tec in Santa Fe Springs, California.

Interesting. And the bubbles etc, make it much more difficult to determine what is an actual crack -- everything looks fractured.

To go to silly extremes, if we really wanted to throw the PC a lot further we'd need better pilot chute deployment staging. Put the PC in its own little cylindrical bag or diaper with a lock at the mouth, to keep it's drag low, while it is being propelled outward by the momentum of a deliberately heavy hackey. Sort of like what's done for a mortar-deployed ultralight recovery parachute, or some staging chutes on ejection seat systems. Or if you don't like the heavy hackey idea, we need an even smaller pilot chute to extract our pilot chute, ad infinitum... (Ignoring scale and viscosity effects...)

As a single data point, showing how easily cutter damage can occur: I came across a cracked Vigil cutter insert in February 2007, on a rig which had the Vigil in it for just one pack job. It was a Vector II, on which one doesn't expect problems as much as on a Mirage, due to the cutter location. The rig was also not an extremely small one (as it held a Raven 1 reserve). However, I did note that it was quite a tight pack job when it came to closing the rig. It had been packed by a well known, quite experienced rigger in my region. The cracking and chipping of the cutter insert was minor and on the outside of the barrel only, so AAD/Vigil OK'd packing the rig up again, a decision echoed by the information in their bulletin #3 that coincidentally appeared a day or two later. I wasn't impressed. We may just have to wait one more pack job until the barrel is sufficiently cracked to endanger the closing loop, and get Vigil to send a replacement cutter. It still mystifies my how anyone could have designed the cutter that way and not have a rigger realize within seconds that the insert was going to get crushed given current skydiver expectations and rigging techniques.