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Air Drag On Sling Cords & Pocket (Read 23924 times)
Matolay
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Re: Air Drag On Sling Cords & Pocket
Reply #30 - Jan 12th, 2004 at 6:28pm
 
Made a lil' research inspired by the bottomline quote and found this at some Hebrew site about ancient royal curtains Smiley

'Although the Bible does not specify HOW the KELIOTH
were made we known that KELA means a SLINGSHOT and we know that slingshots were made of NET-LIKE MATERIAL (the holes prevented drag from the air and allowed the slingshot throwers to gain more momentum). It is thus suggested that the COURTYARD curtains were made in NET-LIKE form (With many holes).'

hope its useful.
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Whipartist
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Re: Air Drag On Sling Cords & Pocket
Reply #31 - Jan 12th, 2004 at 8:04pm
 
Matolay,

Yes that is helpful!  Thanks.  I've seen some Peruvian slings made with a cradle with a net center.  Very intriguing. 

                                   Ben
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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #32 - Jan 12th, 2004 at 9:37pm
 
The net is great idea. It would premit to resign the grooves on the projectiles and additionally these could roll (swim) inside the cradle safely durring the sling rotations (I separate the cords by the fingers thus they don't go out from a one point). Maybe the small fishing net would be good?

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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JeffH
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Re: Air Drag On Sling Cords & Pocket
Reply #33 - Jan 14th, 2004 at 12:48am
 
Jurek,

Great looking sling up there my friend.

Keep up the good work.

jeff <><
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So David triumphed over the Philistine with a sling and a stone. (1 Samuel 17:50)
 
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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #34 - Jan 14th, 2004 at 6:32pm
 
I'm going to try the "dyneema" 1.1 mm cord. It is multiple stronger than the stainless steel wire. You can read about its poperties for example here (bottom of the page):

http://www.gnmchandlery.com.au/rope.htm

I have just booked some in the sailing shop via internet. Seems it would be that one we need.

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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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #35 - Feb 3rd, 2004 at 5:45pm
 
More one week ago I tested the lead projectiles. Some was ball-shaped and some prolongated. The weight of the balls was almost 120 g (4.2 oz).  Although I intended to get 100 g but I didn't measured off volume of the modelling paste too precisely. Elongated ones was 100 g (3.5 oz), exactly as I wanted. I used the last ones in the previous test too.

The sling is made of the 1,1 mm (0.043") "Dyneema" thin line, according to the Ben's idea. That line is able to raise 90 kg!

The projectiles had no grooves for keeping in the cradle, so I used the short and narrow sleeve made of chamois-leather. You can see that in the left-bottom corner of the picture.

I throwed the glandes on the frozen and snow-covered lake. Alas, I wasn't able to find any of them due to the traces on the snow and coming dusk. So I have no conclusion what the shape and aerodynamic sling do for a range. I have written about it in some post before, but here are the pictures. My wife had painted the projectiles with the nail enamel Smiley

I see that finding (marking) the fall-points is the big problem. I'm thinking about it. Maybe you guys...  and girls Smiley have a good ideas?

Here are the pictures:

...

...

Greetings,

Jurek
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« Last Edit: May 7th, 2005 at 6:40pm by Yurek »  

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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mgreenfield
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Re: Air Drag On Sling Cords & Pocket
Reply #36 - Feb 3rd, 2004 at 6:52pm
 
.....I'd love to have a bag full of those 100gm lead glandes!    Wow!  Almost too pretty to toss.

For measuring distance to point of impact, how about throwing them onto a quiet open lake, with 2 observers stationed (say) 100m away from you, one on each side.  Each observer to be equiped with a sailor's angle-finding device called a 'Pelorus' mounted on a solid camera tripod.

Lay out the distances on the shore, measure the angles to the splashdowns, then calculate the distances.

Lots of setup and work, but might be the only way given the small glande size and Jurek's strong arm.

mgreenfield
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Dan_Bollinger
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Re: Air Drag On Sling Cords & Pocket
Reply #37 - Feb 3rd, 2004 at 7:15pm
 
Very interesting discussion and one I'd thought about before. But then, what slinger hasn't thought about setting the world's distance record!?

This conjurs up all sorts of old memories. Hondero reminded me offline that I once had offerred to host an International Slinging Competition including distance. I have a piece of property long and skinny. I think it is almost 500 yards long, maybe not long enough!

Some idle thoughts to keep the gears working:

If you are going to place a world's record, it would be wise to observe the Guiness' methodology, even if you weren't going to send it to them. They've worked out the kinks a long time ago.

Stretch in skinny cords is disconcerting (I know) and I'm sure it steal velocity, but it may increase spin. During the release, the cord shortens, pulling the pocket with it, spinning the glandes.

As velocity doubles, drag quadruples. So, at some point, the drag on a long sling will actually REDUCE velocity!

Consider using low drag cords. Not only reducing width like you have all talked about, but making the shape aerodynamic, or adding longitudinal grooves on the surface of the cord.

Also, consider using aerodynamic glandes having a cross-section like a airfoil (plane strut). Somewhere I have a NACA foil shape CAD file that you can resize to any width and length if anyone cares for it.

Finally, use something heavier than lead like depleted uranium to cast your glandes.   Roll Eyes

Ain't this fun!
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JeffH
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Re: Air Drag On Sling Cords & Pocket
Reply #38 - Feb 3rd, 2004 at 8:30pm
 
For those not interested in making their own molds, commercial molds are available in the two shapes Jurek made.

Called cannon ball sinkers and egg sinkers, they are common shapes for fishing and are available in a variety of sizes including 2, 3, 4 and 5 ounce.  They can be made without holes.

Serch the web for the molds, many places have them.

You can also buy the sinkers ready made.  They cost around $0.60 or a little more in the 3 and 4 ounce sizes.  Add shipping to this also.

jeff <><
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So David triumphed over the Philistine with a sling and a stone. (1 Samuel 17:50)
 
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Dan_Bollinger
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Re: Air Drag On Sling Cords & Pocket
Reply #39 - Feb 3rd, 2004 at 8:43pm
 
If anyone cares for the math (it is way beyond me) here is the formula for calculating the drag and power needed to rotate a pair of wires in a circle. How perfect is that!

http://www.mh-aerotools.de/airfoils/control_line_aero_3.htm

What it boils down to is:

Halve the cord diameter, halve the drag and power required.

Doubling the velocity increases drag 4 times (like I mentioned earlier).

Here is what surprised me. Doubling the velocity increases the power required to obtain that speed by 8 times!  We've all experienced this trying to 'helicopter whirl' a sling faster and faster, but hit an upper limit.

With a little more math one should be able to figure out what the ideal cord length would be for the fastest release velocity given the power available in the human arm.

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Re: Air Drag On Sling Cords & Pocket
Reply #40 - Feb 4th, 2004 at 12:09am
 
Dear Dan,

How about a depleted uranium dart (like the one used for the guinness world record, which I'm still trying to find the picture of with no luck, so far!) or very elongated glande?  I just posted a rough description of one of my distance sling designs for one of my ultra-light "magnum" slings under the "single or multiple projectiles" discussion category this morning usning my real name, as a guest, being too lazy, I suppose, to log in until properly, later.  Actually, I was just excited about the slinging slogan discussion, and in a hurry to post, then one thing lead to another, and I also read something that reminded me to post this description for Yurek.  Then, I cam ehere, and saw that this discussion was already going on here, so I then took time to log in.

Anyway, if anyone here is interested, I've posted my own solution to the air drag question, and will hopefully soon have some pictures to post!

Keep slingin',

Jean B., alias, "magnumslinger"!
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Chris
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Re: Air Drag On Sling Cords & Pocket
Reply #41 - Feb 4th, 2004 at 1:16am
 
Yurek!  Those look amazing!  I'll add them to the gallery at some point.  What is the approximate cost of each one? 

Once the snow clears, will you head out to some field for an official range test? 

Chris
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Re: Air Drag On Sling Cords & Pocket
Reply #42 - Feb 4th, 2004 at 4:33am
 
@ Jurek,

I can only agree with the others, they look really very nice!

I have a metall-detector, maybe I should come and search them for you..    Wink

Ulrica

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May the stones go your way&&&&//Ulrica
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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #43 - Feb 4th, 2004 at 6:14pm
 
mgreenfield,

Thanks for an idea of measurment. It is very inventive and would be a good way but I'm afraid that GWR require that the projectiles should be marked and recovered. All must be probably documented pretty exactly, filmed and photographed.

Lately I thougt about the local sport airdrome, the problem would be in good marking the points of impact on the concrete slab. The projectiles probaly will bowl far from the impact points , maybe not (?)

Quote:
.....I'd love to have a bag full of those 100gm lead glandes!    Wow!  Almost too pretty to toss.


Me too, maybe the (mentioned by Jeff) snikers molds are the good way for it? Each time I casted limited number of the glandes in the plaster mold and they was finishing off too quickly Sad

Dan,

Thank you for the quidelines. Each of them is worth consideration. I like that site about a lines drag. The formulas give some image of numerical influence of different factors, interesting.

Jean,

I have read your posts with care. They are interesting and substancial. I like idea of the net pouch and way of fixing it. It is pretty simple to do and really seems working well. I'm under the impression of your privity about different uses and techniques related with a sling. I'm sure I couldn't describe my slinging ways as well as you in my native language Smiley

I never thoguh seriously about a sling as a defensive tool, because I'm not sure what my accuracy would be in the critical situation. Hope I never will be in that situation in the future. However it happened once when I was yang man. Then I really used the sling for the self-defence. But that story seems to be out-topic.

Chris,

They don't cost much money, bacause I have bought some lead cheaply on the scrap yard. The plaster (of paris?) and the modeling paste are pretty cheap too. But making the good mold required a trial-method. Casting and removal of some surpluses eat up a bit time too.

Before I thought to do it at the ice-plate in the winter, but now I see that it require special weather conditions. It is almost impossible for me to hit them with all organisational job . Thus I hope it will happen in the early spring, probably at the airdrome-plate, when we won't be dependent on the weather so much. I would like to do it as quickly as possible.

Ulrica,

Thanks, the metal-dedector is great idea! I have no experience with it and I'm curious how sensitive that device is. I would be honoured seeing you as the second Smiley

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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Whipartist
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Re: Air Drag On Sling Cords & Pocket
Reply #44 - Feb 4th, 2004 at 6:59pm
 
Jurek,

Those glandes are simply beautiful.  I was very impressed.  They are just perfect!
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