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Air Drag On Sling Cords & Pocket (Read 27956 times)
mgreenfield
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Re: Air Drag On Sling Cords & Pocket
Reply #75 - Apr 12th, 2004 at 10:02am
 
Chris, .....the white glande in the inset pic looks just like the "magic" rock I pitched.   About the same size & all.    I pitched it again.  Same result.   Wouldn't we all really like to know why that shape is "magic"!!  Makes  "superslingsters" out of common guys.   Grin  mgreenfield
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justin Ball
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Re: Air Drag On Sling Cords & Pocket
Reply #76 - Apr 12th, 2004 at 11:56am
 
I'm really surprised at 3 things, folks

1- that this topic caused 8 pages of replies in just a day or so...

2- that this topic hasn't been beaten to death...I'd been slinging oh, maybe 20 minutes when I made a second sling using 0.75 to 1mm nylon line, as I'd worked out the surface area, just like Mr. Greenfield. Same goes for large hood ornaments- save 1% of your fuel a year by removing yours! A loose woven pouch would also help reduce surface area.

3- the tear drop shape can be found in many things that must move through fluids- sumarines of the 60's, airfoils, concept cars...I'm supposing that a tear drop shape would probably perform better than a symetrical football- though harder to make.

Justin

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mgreenfield
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Re: Air Drag On Sling Cords & Pocket
Reply #77 - Apr 12th, 2004 at 12:51pm
 
Justin, ....we think it's more than simple streamlining.  There's something else going on.  Perhaps an interaction between the pouch and "almond shaped" glande.  Cross section of these glandes isn't circular like a torpedo, and round cross section glandes dont work nearly as well.

These glandes have cross sections flattened to maybe a 3:1 ratio oval, with surprisingly small-radius curves at the sharp edges.   This is the "magic" shape that takes off like a rocket from a sling.    mgreenfield
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WildAtHeart
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Re: Air Drag On Sling Cords & Pocket
Reply #78 - Apr 12th, 2004 at 5:19pm
 
Perhaps the "airfoil" or almond shape of the rock gives it lift! That is, assuming it doesn't tumble through the air.

Also, I think we should try and find a textile engineer who could tell us what types of thin filaments don't tangle and twist. I'm sure there are some that are less likely to get tangled simply because of their molecular structure - I believe someone mentioned steel cable. That might be the best.
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Re: Air Drag On Sling Cords & Pocket
Reply #79 - Apr 12th, 2004 at 11:35pm
 
Hello All,

New here, nice forum, appreciate lack of profanity and lack of flames.

Am experimenting with air resistance, anyone try making a pouch from net material such as fishing net? 

Thanks for any ideas (smile).

Slingmeister ><>
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Re: Air Drag On Sling Cords & Pocket
Reply #80 - Apr 12th, 2004 at 11:46pm
 
Welcome Slingmeister,

We all try to run a clean ship Grin We love sling stories and info so keep on posting!! Check out the Gallery and videos
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Chris
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Re: Air Drag On Sling Cords & Pocket
Reply #81 - Apr 12th, 2004 at 11:53pm
 
Welcome Slingmeister,

Matthias made a sling from netting.  You should talk to him.

...

Chris
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« Last Edit: Apr 14th, 2004 at 1:25am by Chris »  
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Re: Air Drag On Sling Cords & Pocket
Reply #82 - Apr 13th, 2004 at 12:01am
 
Chris,

Neat sling! Who is Matthias? Has he posted here before? The name does not sound familiar.
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« Last Edit: Apr 14th, 2004 at 1:26am by Chris »  
 
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Matthias
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Who's Matthias?
Reply #83 - Apr 13th, 2004 at 1:14am
 
I am  Grin (a he though - and just recently delurked)  (chris - mistake corrected)
Thanks! The pocket is not made from netting (as in already made - hard to find suitable stuff and a pita to attach) but rather netted in place.

The net pocket works pretty nicely for irregular ammo... I made it mostly as a challenge based on the materials at hand (It is made with a single 6ish foot length of trawl twine, unbroken (including the net). The netting cuts down on the "sail area" quite significantly. It will obviously have more drag than some of the spartan twin-aircraft cable designs shown in this thread.

Matthias

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« Last Edit: Apr 14th, 2004 at 1:26am by Chris »  
 
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Re: Air Drag On Sling Cords & Pocket
Reply #84 - Apr 13th, 2004 at 9:26am
 
Matthias ,
I was going to ask how you did that. Half heartedly playing with some netting left over from my guillie suit just caused more head scratching. The "how-to" on that would make a great article IMHO... Somewhere in my piles of junk is a sack full of P-cord gut. Other than patching my jungle hammock,guillie suit and making some simple sling cordage that's all that's been done with it. It would seem to be perfect for split pouch and net pouch slings.(Yeah I know I'm a bit slow sometimes  Undecided. )
  I'll try and get some pics posted this weekend of some of my sling stuff and prehaps some other sillyness that I call hobbies.
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Re: Air Drag On Sling Cords & Pocket
Reply #85 - Apr 13th, 2004 at 6:54pm
 
Mathias,

It looks like you made the net part yourself. If so, how did you do it?  Making it myself would probably be better because I could make a pocket in it to hold the stone.

slingmeister
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Matthias
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Re: Air Drag On Sling Cords & Pocket
Reply #86 - Apr 13th, 2004 at 10:03pm
 
Ok, here goes... (knots are pretty hard to describe unless you are working with a common vocabulary... I'll try pics) I'm guessing at the embedded pic tags, If Chris changes them I'll edit the post - they won't show up at first.


...


The Sling:

This was a first experiment. The twine used was 3.5mm polyethylene/polyester braid (8 strands of each) with a filament polyethylene core. We use a range of fibres in trawl nets, up to and including dyneema/kevlar. The modern PE twines match up pretty well with the super-high-tech stuff, at much lower cost.

The challenge here was to make a sling with ONE piece of twine. The sling was eye-spliced in the middle for the retention loop and "sleeved" until the split.  The core was withdrawn from 3/4 of the length and braided. The two halves (both sans core) then rejoin coax style again until the retention knot.

In the photo below, end 2 is spliced for the loop, and drawn through the hollow core until the pouch split. End 1 (with core) is spliced into the hollow end 2. You can use "real" splicing tools, or you can tape a point onto the end that you are threading. Taping the end to a piece of wire or similar can make it easier too.

...


The top image to the left shows the path that I netted the pouch with. A further refinement would be to carry the number of cords needed through the sling cords, or split a larger core into several. Even numbers are probably better - 6 seems to be about right. A planned refinement is to try another sling using a twelve strand round braid for the cords, split into 2 three strarnd braids for the pocket edges and 6 for the netting. All 12 strands rejoin in the release cord... The lower pic might help explain. I think this will be a pretty elegant braided sling - a little different.

The Netting:

And here is the crux... Netting is easy once you get the hang of it. Watch Greek fishermen mending their nets for a knot speed tying clinic.

Traditional diamond mesh nets used to be made by hand using a netting needle to hold twine and a mesh stick to gauge the size of the meshes. The mesh in the sling is too tight for a needle, so I had to thread the knots by drawing the entire length through each mesh. The mesh stick assures consistency, but isn't neccesary - I used a pencil for some of the meshes and the corner of my pinky for others.

The first row of meshes is cast on the sling cords using Clove Hitches. Lark's Heads could be used to, but 98% of fish nets use clove hitches - there must be a reason that I don't know; I'll ask my friendly neighbourhood Icelander next time I see him!

...


The knots used to make the net are Sheet Bends. When tied in a net they are known by various names, including Netting Knot, Weaver's Knot, Mesh Knot... They can be tied a few different ways, depending mostly on what village or island you grew up on.

The pics describe it better than I can. Using the technique shown is quite a lot faster and more accurate than methodically tying individual sheetbends the way most people are taught. The mesh stick (shown with the hanging meshes looped around) gives you nice even meshes. Care must be taken when drawing the knot tight to avoid "capsizing" the knot - at this scale it is a little bit easier to misform the knots.

Try practicing with larger meshes and twine before tackling a sling pocket - it will go much smoother. The pouch on the green sling tapers at the ends in a mostly freeform way. I think the second design with all six strands carried through to the ends might be a little tidier.

Hope that helps a bit! Questions welcome...

Matthias
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Chris
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Re: Air Drag On Sling Cords & Pocket
Reply #87 - Apr 14th, 2004 at 1:28am
 
Matthias,

Great description and images.  You think you could write than up into a mini article and submit a copy to me for the articles section?

Chris
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Re: Air Drag On Sling Cords & Pocket
Reply #88 - Apr 14th, 2004 at 8:11am
 
Matthias,

Thanks for your effort! Really good work. Your drawings are excellent. Pity I haven't proper skills to do the same Sad Veeerrrryyyy nice sling!

Jurek
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In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.
 
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Re: Air Drag On Sling Cords & Pocket
Reply #89 - Apr 14th, 2004 at 11:56am
 
Thanks guys. Man it is tough trying to get concepts across in text - I'm quite proud of the knot tying sequence! we won't discuss the rest...) You can see why there aren't any 16 strand braiding articles yet  Shocked... I'll wait to see if this generates any dialog that could be incorporated but I'd be happy to rework the info into a proper article.

Matthias
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