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jaredmt

tangle-less parachute

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As skydivers we can say that tangles aren't a big problem.

But they are a problem.

We have cutaways due to tension knots. Tandems with members of the public have tension knot mals. Sometimes more when the lines start to get worn. Wasn't there that swooper (Marianne?) who died with tension knots in her reserve (whether or not a damp reserve contributed)? Or isn't there that video of the woman, who was dating her instructor, who spiralled into a parking lot, smashing her face, with a tension knot on her reserve? (Maybe she could have cleared it.) And you can find references to and youtube videos of BASE jump tension knots, where there is no reserve.

Even if we want to make fun of someone outside the sport coming up with wild ideas, tension knots (a.k.a. "cords tangling" for the whuffos) are a malfunction mode that we don't have a solution for. Most of us hardly understand the details, because they are hard to study and the rate is low.

So I won't laugh at the issue.

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Mesh wont work on a rectangular parachute. The way modern parachutes work is that they conform to a "ram air" design. I'll try and simplify the way things work these days for you.

Imagine an inflatable camp bed with one side cut off it. The jumper is suspended below on lines which spread the weight of the jumper evenly across the whole of the bed. The weight of the jumper pulls the inflatable bed through the air and air is forced into the open side of the bed by the motion of the bed through the air. This inflates the bed causing it to be rigid. The shape of the rigid bed is like that of a wing on an aeroplane. Thus, as it flies through the air, the inflatable bed-wing generates lift just like on a plane.

The wing remains rigid because the air pressure inside the wing is greater than the air around it. The pressure remains greater because there's constantly air being "rammed" into the open front buy the wing's movement through the air and the material the wing is made of a non-porous construction. Ie, once the air has gone in, it can't leak out through the skin of the wing.

If you start making part of the parachute wing from mesh, all that air leaks out and you are left with a simple drag device like the old-style round parachutes we no longer use. The wing would no longer be rigid and would no longer fly forward or generate lift like a plane's wing. It would simply flap behind you causing drag.

You can't replace the lines connecting the jumper to the wing with mesh as that would cause so much parasitic drag that the whole thing would not move forward through the air. A lot of development has happened in the last 10-20 years in skydiving to reduce the thickness of the lines we use to connect the parachutist to the wing. The thinner the lines the faster and more efficiently the wing flys and thus the more lift it can generate. The "rope" we use these days can be very high tech and ranges from cutting edge nylons and aramids to things like kevlar. Replace that with mesh and everything stops working.

To top all this, you're trying to prevent a problem that simply doesn't exist. Occasionally a tangle will occur or a parachute will have problems with it's lines. This is a very low order of probability however. Despite that, skydivers have a back up system and can easily jettison a problematic parachute and use a second one in its place.

What you have linked to has been arround in skydiving for decades. It works fine for what it does and is still used in certain applications in modern skydiving. As a technology for main parachute design however, it is litterally 30-40 years behind the technology employed in modern skydiving.

1) Yes you could build it.
2) If you did you would probably find copyright issues with someone else who already invented it more than half a centry ago.
3) It would suck by comparison to everything else on the market today.



ahh this was the explanation I was looking for! I guess this is what mark was trying to say. I knew this had already been thought of considering there are toys that use mesh but I couldn't find any information on it being used for skydivers.

I did not realize that drag on the cord was so much of an issue that they even tried to make the cords a thinner diameter. It does make sense though considering how long the cords are and how many there are, it would take up a noticeable amount of surface area. I also have a much better idea of how the ram-air square canopies work. It looks like a mesh won't work afterall unless there is an outside-the-box solution. Thanks for the info

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... Riggerrob had some great information, I’d like to know if there is an article on anything he said. ...

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If you want to see pictures of anti-inversion nets, try looking at websites of parachute manufacturers who sell static-line, round parachutes to the military: Airborne Systems, Pioneer, etc.

There might be a brief explanation in Poynter's Manual, Volume 2.
I vaguely remember an explanation of anti-inversion nets in Theo Knacke's book on Aerodynamic Decelerators ... probably the best textbook for engineers.
Both Poynter's and Knacke's books are available from Para-Gear.

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... just wondering, how do you know all this? did you serve in the military? ..."

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Yes!
How did you guess?
I served 13 years in the Canadian Armed Forces - including 96 jumps. Along the way I also did enough jumps with the West German Army to earn Bronze Paratrooper Wings.
Unfortunately, people as curious as me do not last very long in the military, because we ask too many embarrassing questions.

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There might be a brief explanation in Poynter's Manual, Volume 2.
I vaguely remember an explanation of anti-inversion nets in Theo Knacke's book on Aerodynamic Decelerators


Yes to both. There's a few paragraphs on the net and they pretty much say the same thing. Poynter goes into a bit more detail about inversions so it may be a better choice for this question.

I definitely second the recommendation for all three books, they're wonderful :)

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You can't replace the lines connecting the jumper to the wing with mesh as that would cause so much parasitic drag that the whole thing would not move forward through the air.



How do you know that? There are different kinds of "mesh". At the extreme a fishing net is a kind of mesh that might prevent twisted lines and tension knots (or create more knots, at least if there are objects stuck in the net...). Sure it will be a lot of drag, but maybe the net can be made large enough to prevent linetwists and tension knots while still giving enough performance and not adding too much bulk. I doubt it, but I won't say it is impossible.

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2) If you did you would probably find copyright issues with someone else who already invented it more than half a centry ago.



I don't think "copyright" means what you think it means. Maybe you are thinking about patents, but they don't offer protection for half a century in most countries.

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Not a chance could you have a mesh that contributes less drag on the system than the equivalent suspension line setup. As much work as we've put in developing thinner, stronger lines, suspension line drag is still a significant component to the total system drag (we're talking around 15-18%).

If you make a closed mesh, the drag is going to be ridiculous, it's going to be a pain to inspect, repair, and pack. If you make an open mesh, it's going to have less drag than the closed mesh but still going to be a pain to inspect, repair, and pack (try dealing with a screwed up anti-inversion net on a round if you don't believe me). Either option creates more trouble than it solves.

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And i'm an engineer.



Doesn't this sound like another annoying troll we have on here already? Lets see, new profile, an "engineer", sounds like #2 to me.



Just a noob but DAMN YOU BEAT ME TOO IT!!



Don't look at me! The last smart I idea I had was a sonar based altimiter on students feet so we could have another tool to teach our eyes how high we were.
Turns out simply talking to friends and videos work just as well and you get to make new friends.

So don't look at me on this one!
Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

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There must be some reason ropes & rings fell out of fashion years before I started skydiving... Maybe the OP can make a reefing system using magnets or velcro. You know, velcro all the attachment units together to reef the canopy...

I believe there was an accuracy canopy using nylon re-enforced attachment points like the OP describes. Sort of a micro-version of what I think he's got in mind... Albeit I don't think they used them for the same purpose. Can't remember what they called those things? eiffs maybe???

I'm sure Rob knows.

-Michael

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Not a chance could you have a mesh that contributes less drag on the system than the equivalent suspension line setup. As much work as we've put in developing thinner, stronger lines, suspension line drag is still a significant component to the total system drag (we're talking around 15-18%).



Who said that the mesh should provide less drag than current lines? I didn't anyway.

The statement I responded to was that it would cause so much drag that it was impossible for the canopy to fly at all and I don't really see that.

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If you make an open mesh, it's going to have less drag than the closed mesh but still going to be a pain to inspect, repair, and pack (try dealing with a screwed up anti-inversion net on a round if you don't believe me). Either option creates more trouble than it solves.



I think so too.

As for the risk of tension knots on reserves that was mentioned, I think a bigger reserve is a better solution. It will of course not eliminate the problem, but at least give you a bigger chance of survival.

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... As for the risk of tension knots on reserves that was mentioned, I think a bigger reserve is a better solution. It will of course not eliminate the problem, but at least give you a bigger chance of survival.

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Hee!
Hee!
Too true!
When landing a partially-malfunctioned canopy (e.g. tension knots) there is no substitute for square footage!
The only reason many of us survived the early days of skydiving was because 220 square foot canopies were fashionable.

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"[reply... Imagine a hybrid canopy only instead of F111 you have mesh. :S That's several orders of magnitude over even a shagged out old F111 canopy and not even in the same ball park as the pin-hole leaks from a seam of a ZP canopy.

At best the thing's going to fly something like a paradactyl, ...

I'm trying to help the guy out with some low level explanation rather than baffle him with science. :P

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Good point!

I have jumped Paradactyl, Delta II and have a PZ-81 rogallo canopy lurking in my closet.
Second generation rogallo canopeis flew almost as well as second generation squares (e.g. Cruisair), with vastly smaller pack volumes.
The primary disadvantage of rogallos is their instability in turbulence.

Sure, you could build a square canopy with mesh ribs and bottom skin. It would probably open, turn and flare just fine. The only disadvantage would be the greater incidence of collapse in turbulence.

IOW, I tore up a bunch of first-generation tandem mains (all F-111 fabric) and concluded that the bottom skin is the least important part of the canopy.

IOW The primary function of two skins (top and bottom) on a square canopy is hold internal pressure, which stiffens the canopy in turbulence.

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There must be some reason ropes & rings fell out of fashion years before I started skydiving... sure Rob knows.

-Michael

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Simple explanation: ropes and rings required far too much time an precision to pack. That 64 feet of rope was heavy and bulky and if you packed it any less than perfectly, it burnt holes in the top skin.

Worst case scenario, ropes and rings suffered far more tension knots and mal'd far more often.

I jumped ropes-and-rings Strato-Clouds with the 1981 Skyhawks Team. My fingers bled after every pack job! I always had to pump end cells open after (soft) opening shock and the end cells had an annoying habit of closing as I turned onto final approach.
By 1981, the only civilian skydivers - still jumping ropes-and-rings were hard-core style and accuracy competitors who liked to deploy their accuracy canopies on the bottom of every style jump.

Hint: most modern style-and-accuracy competitors own one rig for style (high-speed openings) and a second rig for accuracy (low-speed openings on hop-and-pops).

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...

I believe there was an accuracy canopy using nylon re-enforced attachment points like the OP describes. Sort of a micro-version of what I think he's got in mind... Albeit I don't think they used them for the same purpose. Can't remember what they called those things? eiffs maybe???

I'm sure Rob knows.

-Michael

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Yes!
The "keels" on John Eiff's accuracy canopies and Performance Designs' "Zero" accuracy canopy.

John Eiff introduced keels circa 1984 on his Challenger/Classic series of accuracy competition canopies. Eiff's canopies have two keels per loaded rib.
These keels are made of F-111 fabric with re-inforcing tapes.
The first keel is deep (as deep as the rib) at the "A" line, half as deep at the "B"line and tapers to zero at the "C" line.
A second keel starts deep at the "C" line, is half as deep at the "D" line and tapers to zero before the trailing edge.

Yes, keels do serve as line attachment points, but their primary function is to steer the turbulent air straight aft along the bottom skin. You see, accuracy competitors like to fly final approach in "deep brakes" close to stall speed. Airflow gets really turbulent and un-predictable close to stall speed, ergo the need for keels to straighten the flow.

Most accuracy competition canopies also have vented stabilizers than allow air to escape the bottom skin SIDEWAYS, again to smooth the air flow into more predictable patterns.

If you made keels out of mesh, they would reduce the incidence of line tangles and the mesh (parallel to the line of flight) would contribute insignificant amounts of drag.

Oh! And you can use pretty big mesh as anti-inversion nets, with square 4 to 6 inches per side. Anti-inversion nets look like 200 pound, maybe 400 pound nylon suspension line.

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