Causes of mals, off headings, etc

[baseninja]

If jumpers knew what caused 180's, line twists, hesitations, and all the other unnecessary stuff, we would have already fixed them.

With that, a couple of us were talking about what the weakest link is within a single-canopy parachute system, and most of us agreed that the pilot chute is pretty much it. The canopy wants to open, and most off-headings I've watched open perfectly, just on the way to inflation, weren't pointing away from the object anymore...

Of course, this brought up brainstorming to solve this problem once and for all, and we had two main ideas...

1) Why isn't there a ring, slink or metal, to join the bridle and PC? Isn't the bridle going straight to the PC going to insert an inherent 90deg angle? Why aren't PC attachment loops sewn together to prevent misrouting, and also to prevent sliding and therefore asymetrical connection?

2) Other than apex venting, which seems like an incredibly great idea especially for high speed, smaller PCs, they have not really improved upon a disc of ZP, disc of mesh, and a line to the Apex. Has anyone, or why hasn't anyone, researched a better PC? What would be the disadvantages of a 3-D, tandem drogue style of PC? One that each panel was cut individually? Of course, tandem drogues are not big PCs, but the desired function (snatch and non-oscillation) appears to have some potential similarities and benefits.

It seems that if pilot chutes are responsible for a majority of the off headings, and bad stuff, why isn't more energy devoted to make them better? I would be willing to spend $150 for a 42" badass PC, when I am already paying $80 for a simple design that might be inherenly flawed...

Ideas, comments?

[Tom Aiello]

1) Why isn't there a ring, slink or metal, to join the bridle and PC? Isn't the bridle going straight to the PC going to insert an inherent 90deg angle? Why aren't PC attachment loops sewn together to prevent misrouting, and also to prevent sliding and therefore asymetrical connection?

The bridle isn't stiff enough to transmit the twist down to the canopy bundle. You can put a handful of twists into the bridle, and it still won't have a significant effect (try this if you want, I know I have). I don't think adding a link or swivel is going to matter much.

2) Other than apex venting, which seems like an incredibly great idea especially for high speed, smaller PCs, they have not really improved upon a disc of ZP, disc of mesh, and a line to the Apex. Has anyone, or why hasn't anyone, researched a better PC? What would be the disadvantages of a 3-D, tandem drogue style of PC? One that each panel was cut individually? Of course, tandem drogues are not big PCs, but the desired function (snatch and non-oscillation) appears to have some potential similarities and benefits.

It's pretty much been a manufacturing cost issue. I agree that I'd pay a couple hundred bucks for a PC that would noticeably improve heading. But we have to convince the manufacturers that there is a market there.

Personally, I can think of several things I'd like to try, mostly adapted from tandem drogues. 3-D PC's would be first, followed by changes in the ZP/mesh ratios.

[baseninja]

Ok Tom,

Now that we are two that are willing to spend a little extra for some higher production cost PCs, lets get it done.

I'll have my check in the mail tonight, if any manufacturers are reading this..?

Anyone else?

[ZegeunerLeben]

>>PC design and functionality has recently become an item of great interest to me. A PC hesitation will flat-out kill you and there's nothing you can do but ride it in. I'd love to see new PC designs that eliminate hestitations. A buddy and are I going to buy a parachute design manual and just have a rigger sew up some experimental PC designs for us, and test em. I think if we could present a manufacuturer with a semi-viable design they might run with it. I'd give it away if it meant keeping people off the list.

[Tom Aiello]

I've got pretty much the full spread of design manuals. If you want, I can email you some sketches you can use as a starting place to create your designs. I'm also willing to volunteer to do daytime test drops (and test jumps, once I'm satisfied with the drops).

[scdrnr]

I too would gladly pay a couple hundred bucks for a PC that substantially improved heading performance, especially in the 38 and 42 sizes. In the meantime I was thinking of attaching a dedicated loop of webbing to my PC's, similar to BR's static line bridle extension, but shorter and with a stiched loop instead of a larks head knot on the PC. The other end would have a loop to larks head the bridle onto. I was thinking this would be easier than stuffing my bridle through the existing attachment (which is very tight) and worrying about symetry or misrigging. Any thoughts?

[baseninja]

Whoa, doggie... Couple hundred bucks? They might be listening... You have to approach it like this-

"I have a crisp $20 bill for a high-tech, badboy PC? Any takers?"

I was thinking the same thing, kind of putting a slink, or bartacked/fidded heavy dacron loop on there or something to allow the attachment to spin free and prevent asymettry. Seems that maybe, possibly, the hard bite going direct from the bridle to the PC load tapes might cause it to be attached unevenly, if it was free to spin, it could naturally take its most symettrical position. And it would be easier. But I have heard it from reliable sources that the bridle itself is pretty much incapable of transferring twists.. But the potential for the larkshead attachment the way most people have it now might be something to look into?

I think?

[pBASEtobe]

...I was thinking of attaching a dedicated loop of webbing to my PC's, similar to BR's static line bridle extension, but shorter and with a stiched loop instead of a larks head knot on the PC. The other end would have a loop to larks head the bridle onto. I was thinking this would be easier than stuffing my bridle through the existing attachment (which is very tight) and worrying about symetry or misrigging. Any thoughts?

I think this is a good idea and wouldn't be hard/much different/extra cost to manufacture. Others have had special PC's made to eliminate this problem of asymmetric attachment but from the pictures I've seen of them (I've only seen 2 or 3 pictures) they seemed like quite some extra sewing was needed.
Having a PC with a dedicated short bridle already sewn on I think would eliminate asymmetric attachments.

edited for spelling

Man, I swear the "edited for spelling" sentence might as well be in my signature!

[Tom Aiello]

In the meantime I was thinking of attaching a dedicated loop of webbing to my PC's, similar to BR's static line bridle extension, but shorter and with a stiched loop instead of a larks head knot on the PC. The other end would have a loop to larks head the bridle onto. I was thinking this would be easier than stuffing my bridle through the existing attachment (which is very tight) and worrying about symetry or misrigging. Any thoughts?

Why would you want to complicate the system with an extra piece of webbing?

Just go buy a bridle with a bigger hole. They're only like 10 bucks (5 with a PC, in some places).

[pBASEtobe]

I thought the asymmetric attachments had something to do with the apex pulled down line (what are they called) within the PC? There are actually 2 loops to attach a PC. One is the loop that all the mesh creates and then one is for the apex pull down line. I thought when you attached a PC to those two loops if one of them wasn't straight (i.e. when loaded direction of force wouldn't be at the correct angle) when the larkshead of the bridle was pulled tight then that is what would cause PC oscillation?
If this is right then how would a larger loop on the end of the bridle help?


Crap...I reread the post and realized you were talking about this part of the post:

"I was thinking this would be easier than stuffing my bridle through the existing attachment (which is very tight) and worrying about symetry or misrigging."

You're right a bigger loop would be easier. But that wouldn't prevent asymmetric attachments.

[Tom Aiello]

If you have a PC made with the old style "loop" attachment (fixed size sewn loop outside the mesh), you can pretty much eliminate the assymetric attachment problem. I've got a full spread of PC's made this way, custom for me, by Marty at Asylum. It is harder to manufacture them symmetrically, but I think worth the effort (hence extra cost) to get them.

Either that or learn to attach the PC symmetrically. But I'm all in favor of making the gear as foolproof as possible. I can find plenty of other ways to be a fool. ; )

[tfelber]

First, I'd like to understand the cause and effect of PC to off heading opening, but from what I've read here it seems like the "floating" attachment would create a more symmetrical pull about the attachment point because the attachment would seek a point of equillibrium. However, if a PC was sewn assemmetrical and pulled distinctively to one side or the other the PC attachment point would be moot ;-) and the bridle attachment on the top of the canopy would then become the point of induced stress.

If you drive your car, bike, or whatever with the PC attached to a bridle, hangin out and it fly's in relatively the same position in space then the attachment should be symmetrical enough to not induce an off heading opening, right? It seems like an unbalanced opening, causing a surge left or right, would be more of an issue.

[Tom Aiello]

...from what I've read here it seems like the "floating" attachment would create a more symmetrical pull about the attachment point because the attachment would seek a point of equillibrium.

Are you talking about the attachment between the PC and the bridle, or between the bridle and the canopy?

A self equalizing attachment to the canopy is an interesting idea. I'll definitely ponder that.

A self equalizing attachment to the PC would take a whole redesign of the PC, because you'd have to make all the load lines self equalizing. Interesting idea...

[Tom Aiello]

First, I'd like to understand the cause and effect of PC to off heading opening...

Well, we'd all like to understand that. The best we can do is generalize and speculate. But here's my best guess:

When the PC pulls off to one side consistently, it extracts the canopy in that direction. When the canopy hits line stretch to one side, it loads one riser before the other, and that effect causes it to turn during inflation (much as if you were pulling on that riser). This is the kind of thing that seems likely to happen with a strong crosswind (by "strong" I generally mean a crosswind the absolute magnitude of which exceeds the relative updraft due to the jumpers fall rate at deployment).

When the PC orbits around the jumper, it pulls the canopy different directions at different times in the opening sequence. This is going to create a bunch of chaos, which means we've really got no idea what's happening on any particular deployment like this, aside from it's getting pulled every which way. I've seen orbiting PC's result in everything from line twists to on-headings. I would say that my observation has been that orbiting PC's generally result in worse openings than non-orbiting PC's. This is usually the kind of thing you see when a PC is attached or constructed assymetrically, although (especially at low airspeed) you can see it resulting from a vigorous toss to one side even with a properly constructed and connected PC. Both vented PC's and F-111 PC's appear to dampen this orbiting (whatever the cause).

If you drive your car, bike, or whatever with the PC attached to a bridle, hangin out and it fly's in relatively the same position in space then the attachment should be symmetrical enough to not induce an off heading opening, right?

Not necessarily. Wind effects aside (and if you have wind, they're never going to be something you can ignore), the actual toss of the PC can induce an orbiting, even if the same PC eventually stabilizes (say, when drag tested). The important thing is what happens in the second or two after you pitch--not where the PC ends up if it has a large amount of time to correct itself.

It seems like an unbalanced opening, causing a surge left or right, would be more of an issue.

I'm not following. Can you explain what you mean by "unbalanced opening"?

[pBASEtobe]

A self equalizing attachment to the canopy is an interesting idea. I'll definitely ponder that.

Self equalizing doesn't necessarily mean you'll get a straight pull. It just means that there will be the same force on each load bearing part. That load may still be off to one side. Tom, I'm picturing an equalized climbing anchor. Is this what you were thinking about when self equalizing was mentioned?