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General >> Here Be Maths... >> Paracord popular for modern slings but.. https://slinging.org/forum/YaBB.pl?num=1624597667 Message started by KnollSlinger on Jun 25th, 2021 at 1:07am |
Title: Paracord popular for modern slings but.. Post by KnollSlinger on Jun 25th, 2021 at 1:07am
Paracord is not springy; it is designed to ABSORB energy
when a parachute opens. For slinging, you want all the energy to go into the bullet. So, has anyone thought what would be the ideal material for the sling? I would think springy or rigid, but non-damping. Also, very thin yet strong to minimize air resistance. The hand grip on the end could be of a different, thicker material. ab·sorb /əbˈzôrb,əbˈsôrb/ verb 1. take in or soak up (energy or a liquid or other substance) by chemical or physical action. "buildings can be designed to absorb and retain heat" |
Title: Re: Paracord popular for modern slings but.. Post by Mersa on Jun 27th, 2021 at 7:31am
Dyneema is very good modern material for slings
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Title: Re: Paracord popular for modern slings but.. Post by joe_meadmaker on Jun 27th, 2021 at 12:20pm KnollSlinger wrote on Jun 25th, 2021 at 1:07am:
What do you mean by 'springy'? This makes me think of something that will stretch under pressure and return to its original form. Would that not also be energy absorbing? Paracord will absorb energy, but just like any other cordage it does this by stretching. I don't think the normal forces that occur during slinging are enough to stretch paracord much (if at all). |
Title: Re: Paracord popular for modern slings but.. Post by KnollSlinger on Jun 27th, 2021 at 2:48pm joe_meadmaker wrote on Jun 27th, 2021 at 12:20pm:
How does that compare to this? It should take 200 lb split between the two cords. Aramid rope ARABRAID ø0,4mm 500m reel 6-strand braided by Kanirope® - high-quality product manufactured in Germany, braided of high-quality Twaron® yarns. Aramid rope is very tear- and heat-resistant, non-flammable and extremely low stretchable. Aramid ropes do not melt at high temperatures, but starts charring from 932° F (500°C). Diameter: 0,4mm Length: 500m Construction: 6-strand braided Breaking load: 45daN (kg) Working stretch: <1,5% Breaking stretch: 2-4% Material: 100% Aramid Colour: yellow |
Title: Re: Paracord popular for modern slings but.. Post by KnollSlinger on Jun 27th, 2021 at 2:53pm Mersa wrote on Jun 27th, 2021 at 7:31am:
Energy should all be transmitted to the bullet, not adsorbed by the rope. How does it compare to Aramids? |
Title: Re: Paracord popular for modern slings but.. Post by KnollSlinger on Jun 27th, 2021 at 2:56pm joe_meadmaker wrote on Jun 27th, 2021 at 12:20pm:
spring means the energy is stored and returned to the bullet at release. This is good. Damping absorption of energy just wastes the energy by heating the rope as it stretches. this is very bad. |
Title: Re: Paracord popular for modern slings but.. Post by joe_meadmaker on Jun 27th, 2021 at 10:26pm
Slings do not store energy. If you stop putting energy into the sling, it will just stop. There is no potential energy to be released.
If you're looking for a very thin and strong cordage, that aramid rope sounds like it could work. But from the specs you posted it also sounds awfully thin. At 0.4 mm I would be concerned with the cord twisting. I remember a video that Sarosh did. He tested a sling with very long and thin cords. As I recall, there were definitely problems with them getting twisted up while being rotated. |
Title: Re: Paracord popular for modern slings but.. Post by KnollSlinger on Jun 27th, 2021 at 11:34pm
if you stop energy putting in hopefully that is the release point and the bullet will not stop. I have used springy slings that do store potential energy. I have also used golf clubs whose shafts bend and release that energy as well.
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Title: Re: Paracord popular for modern slings but.. Post by joe_meadmaker on Jun 28th, 2021 at 7:36pm
The stop will need to be after release. At release you'll want to be at max energy.
The only way I could see a sling storing potential energy is if you had an almost completely rigid retention cord (although it would be more of a stick or shaft) that would bend as you threw a projectile. Then it could spring back into form as you came to the end of the throwing motion. A similar idea came up in one of the other topics. I believe the discussion was if one bow limb could possibly be used to throw a stone. The force needed to bend the limb would need to be matched to the weight of the stone being thrown. |
Title: Re: Paracord popular for modern slings but.. Post by J on Jun 29th, 2021 at 5:50am
A lot of focus on reducing air resistance we place on making our cords aerodynamic while neglecting the pouch, yet the pouch is one of biggest drags
Especially pouches that are quite a bit longer than the projectile when the stone is seated, and pouches that are thick. You can get rid of the pouch attachment knots because these also provide drag and figured out various knotless attachments I think a fine split pouch provides the least drag, but since that is unfit for very thin slings in my opinion, a knotless netted pouch or a small a small soft leather cradle that isn't any larger than it need be. |
Title: Re: Paracord popular for modern slings but.. Post by KnollSlinger on Jun 29th, 2021 at 5:36pm joe_meadmaker wrote on Jun 28th, 2021 at 7:36pm:
I was thinking that an elastic springy sling cord could apply acceleration to the bullet even after you reach nearly the end of your effective acceleration due to your hand; at that point you could freeze your body yet the elastic would continue applying force and acceleration. |
Title: Re: Paracord popular for modern slings but.. Post by joe_meadmaker on Jun 29th, 2021 at 8:16pm
I don't think. The stretch of the cord (and therefore the force it creates) are going to be inline with your hand and the pouch. But the stones path when it is released will be at a 90° angle to this. So the stretching of the cord is only really going to give you a larger radius of rotation, and an effectively longer sling.
This isn't an image of a sling but it will do. The circle represents the sling's rotation. The radius represents the sling and direction of any stretch that it has. The tangent vector represents the direction the stone will fly when it's released. Any stretch or spring of the sling will not aid this directly because it's not in the same direction. If your sling had an elastic quality and you stopped your motion, the sling would ultimately be trying to pull the stone back toward your hand because the centrifugal force would no longer be pulling it away. |
Title: Re: Paracord popular for modern slings but.. Post by Mersa on Jul 1st, 2021 at 7:43pm
Definitely want a sling with low or no stretch, stretch will reduce power and accuracy.
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Title: Re: Paracord popular for modern slings but.. Post by KnollSlinger on Jul 5th, 2021 at 9:15pm joe_meadmaker wrote on Jun 29th, 2021 at 8:16pm:
You can only ever apply force nearly 90 degrees to the motion. acceleration vector points to your hand always. i taught hs physics, while i was in hs. |
Title: Re: Paracord popular for modern slings but.. Post by lobohunter on May 27th, 2022 at 10:04am
Wow a lot of long term members came out for this one
When I was experimenting with this. I came to a conclusion that the springy cords did add some distance But I could never gain any control So my favorite has become Spectra type cords for the stiffness and accuracy and control It nice to get a good distance and actually be able to hit something lol |
Title: Re: Paracord popular for modern slings but.. Post by Archaic Arms on May 28th, 2022 at 9:12am
I've noticed a similar effect when using a 17" all leather sling. The springiness seemed to add velocity (with light stones especially). I think it could be that the stretched sling gets shorter after the main part of the power-stroke. Similar to when a spinning skater pulls in their arms, they spin faster.
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Title: Re: Paracord popular for modern slings but.. Post by Hirtius on May 29th, 2022 at 2:07pm
I’ve never noticed any springiness in paracord, with stones from small to large. I can’t imagine it impairs effectiveness much.
Has anyone tried a bungee cord sling or something? |
Title: Re: Paracord popular for modern slings but.. Post by Archaic Arms on May 29th, 2022 at 2:43pm
The military-grade paracord I have is very noticeably springy/spongy to me at 28" The longer the sling, the more noticeable it is.
Another idea is that the springiness temporary delays the projectile's acceleration as the cord stretches, essentially lengthening the power-stroke slightly. That's what I get from the feeling anyway. |
Title: Re: Paracord popular for modern slings but.. Post by joe_meadmaker on May 29th, 2022 at 3:39pm
Do you what type (meaning size) that paracord is AA? Last year when I did all my big stone slinging, the two slings I used were single stand 550 paracord. The largest stone was almost 5 lb. Noticeable stretching was minimal. The sling lengths were 33" and 45" (I think).
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Title: Re: Paracord popular for modern slings but.. Post by Hirtius on May 29th, 2022 at 4:19pm
Maybe people who prefer natural fibers notice springiness more or something. Or it could be that the properties of paracord, being relatively dense, might create a difference in feeling that people think is stretching. I don’t know.
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Title: Re: Paracord popular for modern slings but.. Post by joe_meadmaker on May 29th, 2022 at 5:52pm
That could come into play.
There is variation in paracord too. The last time I ordered some 425 (3 different colors), two of them were nice and tight but one was pretty springy. So I don't doubt folks could be running into brands that have some stretch. Maybe we need to start a database of the best places to get good paracord. :) |
Title: Re: Paracord popular for modern slings but.. Post by Archaic Arms on May 29th, 2022 at 6:21pm joe_meadmaker wrote on May 29th, 2022 at 3:39pm:
Military 550. Proper dense stuff. The stretching is most noticeable to me when slinging smaller stones at max velocity, where there most acceleration is involved. I suppose it's relatively subtle, but being used to completely unyielding fibers like linen, esparto, dyneema, etc. I can definitely feel the difference. |
Title: Re: Paracord popular for modern slings but.. Post by Hirtius on May 29th, 2022 at 11:21pm joe_meadmaker wrote on May 29th, 2022 at 5:52pm:
I’ve had that too. I largely use 550, but there are number of variations. I have one brand that have something woven in the paracord that makes it slightly stiffer, which then makes the pouches completely stiff and horrible at holding stones. Others have weird textures or other things. I’ve largely just adapted to a single brand of paracord. |
Title: Re: Paracord popular for modern slings but.. Post by MMF on Jun 3rd, 2022 at 1:50am
Here's my two cents on stretch.
Paracord is designed to stretch but should not be apparent when dealing with the loads we have during slinging (even for 5 lb rocks - Joe, you're a beast). When a cord is unloaded, the braid is in a relaxed state. Once some tension is applied, it will strain until the braid tightens. For Paracord, that tightening should occur during pre-rotations. Any amount of stretch is bad. Stretch of the cords and pouch, implies that work was done onto the sling. Most of the work you impart to the stone occurs at the start of the power stroke (it will take too long to explain why in this post). As a result, a lot of the acceleration occurs at the start of the power stroke too. As the power stroke progresses, the centripetal acceleration will decrease but the angular velocity (and tangential velocity) will not. Therefore the centripetal force Fc = mv²/r will not decrease. So, any stretch that occurs will not shorten until after the stone leaves the pouch. You might say the stretch lengthened the throwing arm. That would increase power if the acceleration of your arm and not the force available to apply is the limiting factor (which I think is often the case). However, there is an efficiency loss due to friction (which would still increase power if there is sufficient force available). And if you had any observable stretch in the cords, the amount of work you put into that elongation would be way more than just using a slightly longer cord with no stretch. I could be wrong, but this is my understanding. |
Title: Re: Paracord popular for modern slings but.. Post by NooneOfConsequence on Jun 22nd, 2022 at 10:04am
I don’t know if you guys keep up with the academic journals or not, but archaeologists recently found an ancient Peruvian cave poem that addresses this very issue of sling stretch. Obviously paracord wasn’t a thing, but when choosing between grasses and wool, they had many of the same questions we do today. If you can look past the war-like tribal tone, the poem is actually quite technical in how it addresses these questions. Here’s a rough English translation:
“My grass sling don’t jiggle, jiggle. It folds. Your wool sling ammo likes to wiggle wiggle for sure. The blood of your injuries will dribble, dribble you know. Riding in my chariot. You’ve really got to see it…” I won’t bother quoting the rest of the poem, because it goes on about how marrying a cousin is the best way to keep royal bloodlines pure, and that just doesn’t add much to this debate. |
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