captain_stan

I know we're getting off-topic here, but why would you not gather 4 A-lines, 4 B-lines, 4 C-lines, and 4 D-lines on both the L & R sides of your Triathlon when flaking a pro pack? What do you mean by 3 + 1? Which of these is the "+1" line and what are you guys doing with it?

not according to my arithmetic.

What's that all about?

Para-Gear catalog #W9655. Confirmed by Sunpath before they prohibited us making our own.

I haven't seen this condition on an Aerodyne canopy that I have owned either. But several years ago I saw this same mfr's fresh reline of one of their mains that resulted in a huge amount of fuzz at all the fingertrapped joints after a minimal number of jumps. I'd never seen anything like it. This spectra line in question had a lighter coating than what I typically see on a sport main. Without being able to inspect this rig, there are certainly several possible causes.I hope that Mr. B will share his findings with us.

I've also seen similar deterioration of spectra line on an Aerodyne canopy that was rigged to a different mfr's H/C. This problem may be more with the main canopy's line material or construction than with the design of the H/C.

BTW, if you want a bullet-proof kill-line material for repairing these PCs, try some 400 lb, flat-braided Dacron available from Para-Gear. It's plenty strong doesn't shrink like Specta, wears better than HMA, isn't too bulky, and only costs about 40c/yd.

I'm hoping these fine points may result in more service life from a PC and maybe even prevent damage to a canopy or a PC in tow. Didn't I mention I design my PCs to have 2-3" of slack kill line in the bag when cocked? This corresponds to a lanyard being aprox 2-3" longer than the apex lines. During cocking, the maximum stroke permitted by the lanyard is stopped short by the length of the apex lines. The length by which the lanyard exceeds the apex lines is equal to the amout of slack kill-line that will appear in the bottom of the bag when cocked. Call this excess a safety factor. If you have no extra lanyard length, there can be no extra kill-line length. If that's the case, then any stretch or shrink of these components can put the PC out of trim. Kill line and bridle are made from different materials that stretch or shrink by different amounts over time and under load. During lab-testing, I notice that my PCs undergo dimensional changes as I apply tension to the assembly. By providing extra length to these components as mentioned, I ensure that the PC will perform well not only during static testing and measuring, but during varying loads and varying conditions, and after undergoing normal service over extended periods. Again there is much more potential for harm if the kill-line and lanyard are made to minimum lengths for service in a dynamic environment. Without actually seeing the PCs in question, and just from your description I'd expect that your solution may be as simple as lengthening the kill-line. That would prevent your expected case of "excessive-retraction" and yet would still permit full inflation. Of course any increase in length must be limited by the need to still retract fully. Excess kill-line length may result in bridle spin-up as some of us here have experineced. The Lanyard would be the last thing I'd alter, but I have done so in some cases.

Some smart guy invented that & solved 2 problems: 1) Eliminated entanglement possibility inside the bag for those of us who cock the PC after we bag the canopy. Even those who cock the PC first no longer need to separate/dress the lanyard & kill-line inside the bag before cocking. 2) Eliminated the possibility of pinching/tearing the main top skin when the kill-line shrinks and draws the attachment point down tight against the grommet every time the PC is cocked. If the kill-line shrinks excessively, it can only reduce performance by not allowing PC to fully inflate. Wake-up call from slower deployments, but no damage to gear.

Nah, I think I'll let you disagree w/ me on that one. I consider the greater priority of having a kill-line that's of adequate length to match the lanyard. If everything else is in trim, a longer lanyard just requires a longer kill-line. Yes, it determines the maximum length of retract stroke, but the stop-point at the "retracted" end of that stroke is also limited by the length of the kill-line. Unless you just make the kill-line longer so it can't utilize the full stroke and retract that far. BTW, this won't affect the "cocked" end of the stroke because the apex lines will act as the stop-point to limit that. ??? If your lanyard is the same length as the apex lines and you have excess kill-line slack in the bag after cocking, this assembly will stop short of full retraction by an amount equal to that slack. Try it and see for yourself. I have retrimmed these by lengthening the lanyard. God forbid! Where the fun in that? I'll say it again and apologize to our many bored readers. Extra lanyard length is not problematic as long as the kill-line is trimmed to correspond to it. In a perfectly trimmed retractable PC, you could add an equal amount of length to both the lanyard and the kill-line without affecting function. Longer lanyard requires longer kill-line. However at some point in extra length, you're gonna end up with a bunch of unnecessary kill-line & lanyard wadded up in the bottom of the bag with the packed canopy, and this can lead to entanglement inside the bag. I allow only a token amout of extra length so these materials can stretch or shrink a little but still stow neatly and continue to function. I don't mean to be argumentive, but that's as well as I can explain it. Sorry for the repetitioin.

Hookitt described this very well. He refers to whether mesh or fabric is showing at the skirt, which will be at the bottom as the collapsed PC is hung upside-down: The priority for establishing the length of these three components is: 1) The length of the apex lines must be established first to permit the PC to inflate to a degree that creates the most amount of drag. 2) The bag-canopy lanyard then must be slightly longer than the apex lines to permit enough stroke to cock/deflate the PC. Excess length here doesn't create a dimensional problem. It just means that the kill line will have to be made longer to corrrespond. However at some point, excess lanyard length coiled up in the bag may be undesireable because it may snag the top skin of the main or entangle w/ the kill-line during cocking. I mfr lanyards 2-3" longer than the apex lines, thus leaving a corresponding 2-3" of excess, slack kill-line in the bottom of the bag after cocking. 3) Finally, the kill-line is fit. I make it long enough that the apex lines are drawn tight during cocking, but short enough that it will fully rectact the PC. If all other dimensiona are correct, there will be 2-3" of slack kill-line left inside the bag when cocked. There is very minimal tension on any of these components once the PC is retracted, because it's drag is then greatly reduced. I believe this wear is the result of kill-line abrasion across the bag attachment point during retraction, which coincidentally reaches a critical degree of damage about the same time the kill-line is worn-out and/or excessively shrunk in length. Again, the requirement for kill-line length is very simple if the other components are correctly in trim: 1) If it is too short, the PC may not fully inflate when cocked, and the resulting pinching/binding inside the bag may damage the top skin of the main, not the bridle. 2) If it is too long, it may not fully retract the PC, a condition that is only likely to cause that annoying bridle spin-up. Sorry for any spelling/grammar errors. Will edit as needed.

... and which may also prevent it from fully inflating and/or tear the top skin of the main by sucking fabric into the bag grommet when cocking. I've seen both of these conditions occurr from a too-short kill line. I would encourage the average jumper to get help from a (competent) rigger.

Some of these are mfr'd w/ Vectran or HMA, which may permanently stretch over time.

We just test-jumped 2 PCs that I successfully altered/repaired because of this same problem. I first thought that these might be slightly non-symetrical/non-concentric, but it's really hard to measure that accurately. However, both of these were not quite fully retracting, so I corrected that issue first, and it did indeed solve the problem. With each of these I ended up replacing the kill-line and the lanyard that connects the bag-end of the bridle to the main canopy. This was necessary because the kill lines couldn't be shortened any farther without creating other problems. By first lengthening the bag-canopy lanyard, I increased the retract "stroke" of the entire assambly. Then I was able to make a new kill-line of the appropriate length (actually longer than original) to permit full inflation and full retraction. I suspect that the mfrs of these PCs failed to maintain good tollerance, hence the need for correcting these dimensions. Caution: The lengths of the kill line, the bag-canopy lanyard, and the apex pull-down line(s) all affect the PCs function. If you change the dimensions of any one of these, the dimensions of the others may require adjustment also.

The FAA made me quit using thoses when one blew up in a guy's closet during the winter and burned down his apartment building.

I use those new disintegrating seals to keep my customers honest. But be careful to buy the 180-day type now or your customers will bitch. Of course I use the old-style lead seals for my personal rig. BTW, I have a bunch of the old 120-day disintegrating seals if anyone has a use for them.

http://www.performancedesigns.com/docs/Pulse_Flight_Characteristics.PDF

Let me know if you find one on the market. I'd be interested in studying it. Is that a joke? Silicone coating was invented to protect Nylon from UV. Not only will it outlast non-coated fabric, but it's superior performance properties were realized as soon as it was put to use. The shaded bottom skin is always gonna hold up better to UV weakening & long term permeability increase than the more-exposed top skin. So why waste a better material in an application where it's properties aren't needed nearly as much?

Although the internal pressure acts equally outward in all directions, the external pressure varies greatly. The top skin is exposed to the low-pressure above the wing, and the bottom skin is exposed to the high-pressure below the wing. That's what makes it fly. The result is a pressure differential that varies, in different areas of the wing. John's right. The highest potential for air leakage is through the top skin because that's where the greatest difference in pressure exists; it's less everywhere else. PD and others have proven that there is much performance to be gained even in making only the top skin from ZP. edited to add: I'll let the engineers decide if air is leaking in or leaking out through the bottom skin. I can say with certainty that there is less pressure differential there than any other area. And our canopies are more rigid by design than your balloon, hence their ability to withstand these differences in air pressure without collapsing (usually).

The first thing I'd have to rule out would be any difference in pilot input. Both canopies would have to be flown in an identical manner with the exact same control input. As difficult as it might be to minimize or eliminate this human factor, it’s the only way to be absolutely objective. Consider a sport cross-country canopy flight from 10,000 feet or higher. An assortment of canopies may all make it back. Some of these pilots might have preferred a longer spot and ended up bleeding off extra altitude by making more turns. Some may have to use more toggle or riser input to extend their glide. But they may all make it back. Because they all have the same glide ratio? No, because they are all canopy pilots and knew how to achieve the desired flight. The second factor I would have to control would be to establish the objective for flying the greatest possible distance across the ground, instead of just trying to reach an intended target. When two canopies, identical or not, are able to reach the same landing target from the same opening point, this does not mean that they have both covered their greatest achievable distance across the ground or have achieved their maximum glide ratio during the entire flight. What if one of these canopies was capable of flying farther but its pilot chose to land on the LZ instead of over-flying it? The only way to eliminate this variable is to have a big enough LZ that each canopy can fly its greatest possible distance across the ground and land at a point that is the farthest possible from the opening point. For test purposes, that means downwind landing w/o flying a standard (or any other) pattern. Less significant requirements include: (1) Identical wing loading. The suspended weight becomes lighter after the main is chopped and the reserve is deployed. Each jumper must also weigh the same and carry the same weight in equipment. (2) Identical drag--body size, body position, clothing, equipment, etc. must be identical. (3) Identical wind conditions. This was satisfied by flying both canopies simultaneously through the same airspace. No problem there.

OK, I'll spell it out for you. Both these incidents are a far cry from a controlled test in which glide ratio is measured in an accurate manner.

to continue flying with the group and make the DZ despite being under a non zp canopy.*** In a similar experience, I reached a different conclusion. I chopped my Stiletto, then flew my Raven reserve to the LZ and landed it right in front of the hangar. But I don't think it proved that both these canopies have the same glide ratio.

Since PD is marketing the Silhouette as a canopy that is "easy to pack," I'm concluding that glide ratio was not the #1 priority in their design. It is popular with the people who own it, and obviously performs well enough to stay in the marketplace. But if the flattest-possible glide ratio was the goal in canopy design, I don't see how any part of such a canopy could be made out of a fabric that "leaked air." (OK--maybe the slider) The most important question is: are you satisfied with your canopy's performance? It's a fact that other canopies on the market will glide farther and I expect that most or all of these will be all Zero-P construction. Of course many other factors will also effect glide ratio. I suggest test-jumping some different canopies for comparison.

Evidence to the contrary is the much-easier packing of a brand-new, all F-111 canopy as compared to a zero-P canopy. There is a measureable amount of air leakage through new F-111 fabric, whereas new zero-P will only leak air through the needle holes in the seams. Anyone who has flown a new, or nearly new, F-111 canopy will tell you it doesn't fly like zero-P. Maybe the accuracy community will weigh in on this one; they fly F-111 canopies for a reason. BTW, the proper term for air leakage through fabric is "permeability."

Niether is larger; both have a 17" MLW. The C-17 has it's lateral junction adjacent to the legstrap junction, so you won't see any length of MLW between these points. The C-17-1 has it's lateral junction set 1" higher above the legstrap junction, so you will see 1" of MLW extending vertically between these points. The corresponding difference in fit is very minor if everything else is equal. Sunpath could probably explain to you how they determine this; I expect it has to do with the jumper's girth and the actual container (J#) size. However: Any two Javelin H/C's with the same yoke/MLW size may differ in "lateral" size to accomodate jumpers of different girth. Lateral size isn't listed on the H/C's label, but may be available from Sunpath if you provide the SN to them.