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Air Drag On Sling Cords & Pocket (Read 27224 times)
Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #45 - Feb 4th, 2004 at 7:18pm
 
Thanks Ben,

I'm glad you like them Smiley It's really pity to toss them Wink

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 #46 - Feb 7th, 2004 at 6:55pm
 
Yesterday finally I had got the replay from GWR. I'm a bit confused. I'm wonder what kind of projectiles are hidden behind the word "a stone" in the rules. Whether "a stone" means exactly "a stone"?  In the short description of the previous atempt they use the word "dart". Nikolas Lloyd has written on his website that there was used the lead glandes. Guys, read please and judge. I'm curious of your opinions.

"Rules
1. This record involves throwing a stone weighing at least 56 g 2 oz as far as possible, using a traditional sling, with a maximum length of 130 cm 51 in. The sling is to be made entirely of leather.
2. The throw is to be made on level ground, or slightly up a hill, but not down hill.
3. It is best if the stones to be thrown are painted a bright colour to make them more visible.
4. It is also suggested that an arc be drawn showing the position of the current record.
5. One official person must verify the point from which the throw was made. The thrower can use a run-up and should throw from a line such as one would have for javelin throwing. Crossing the line would invalidate the throw. Two officials should verify the location of the catch - they will have to follow the flight of the stone as it starts to come down. It would be the first point of impact with the ground that should be recorded. The distance should then be checked with a steel measure."

"The current record is:
The greatest distance achieved in hurling an object from a sling is 477.10m
<I>1565ft 4in</I>, using a 127cm <I>50in</I> long sling and a 62g <I>21/4oz</I>
dart, achieved by David Engvall at Baldwin Lake, California, USA on 13 Sep 1992."

This description is similar or the same like Ben posted before. I hoped to get a little more exact informations. I probably must ask them for additional ones.

It looks like our disusion about a sling tunning went in a bit different drection.

Jurek

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« Last Edit: Feb 9th, 2004 at 7:48pm 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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Chris
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Re: Air Drag On Sling Cords & Pocket
Reply #47 - Feb 7th, 2004 at 7:20pm
 
The record says dart, so I don't think you have to worry about the stone ambiguity.  You can't craft a dart out of stone, so it must have been made of some other material, so I think your lead glandes would be applicable. 

Can you beat the 422m?

Chris
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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #48 - Feb 7th, 2004 at 7:30pm
 
Chris,

I hope you are right abot the projetiles. When the lead ones are allowed I will overlap that distance probably.

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 #49 - Feb 7th, 2004 at 7:42pm
 


Yurek, this old message will interest you. It´s from the record holder of 1980:

>Subject: Re: sling record keeping
>Date: Sun, 22 Sep 2002 00:34:15 EDT
>
>Hi Ed,
>
>I'm glad you persevered and found me. I still love the slingshots and the
>act of throwing but seldom do it anymore.
>
>I was 20 years old in August of 1981 when I broke Melvin Gaylors record. I
>had been throwing since I was about 11 years old. As I got older and
>stronger I realized the record was within my abilities and went ahead and
>made the attempt. My sling pouch was made of elk hide leather and the
>strings were of braided dacron thread. I had a leather loop I would put my
>middle finger through and just a knot on the end of the string to release
>for
>the throw. The stone was oblong and would spiral like an American football
>or a bullet when thrown so it was much more aerodynamic than a round stone.
>I am 5' 9" tall and weigh about 180 lbs. That is the same as I was when I
>set the record.
>
>I have wondered about making another attempt at the record. I have made
>some
>much superior slings compared to what I used in 1981. Also some better
>projectiles. I am confident I could surpass 500 yards. Maybe by several
>hundred feet. I haven't done anything to begin preparing for an attempt
>and
>I don't even know what the current record is. I am happy to correspond with
>you and other interested people. Feel free to share my e-mail, phone
>number,
>etc. with others. I am interested in looking through the info you have
>collected.
>
>Larry Bray
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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #50 - Feb 7th, 2004 at 7:50pm
 
Hondero,

Wow! This is the treasure!!! Thanks a lot!!!

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 #51 - Feb 7th, 2004 at 8:52pm
 
Quote:
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?


From the tiny (emphasis on tiny) bit of aerodynamics I know, the optimal aspect ratio for low drag is 1:8, or so I recall. Something like this NACA 0012 foil.

...
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« Last Edit: Feb 7th, 2004 at 10:17pm by Dan_Bollinger »  
 
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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #52 - Feb 8th, 2004 at 8:14pm
 
Dan,

You right the suitable (for the projectile velocity) NACA shaped projectile would be the best if it would be throwed correctly. But what is a chanse to do it with the clasic sling. That projectile the most probably will catch the release cord and get the chaotic flight, even if the pouch position is proper. Does it is posible to throw correctly such elongated projectile constantly. There is a chanse reach it with projectiles which have a ratio 1:2 or maybe 1:3 but in this case useing the NACA shape seems doesn't give a significant profit, because the ratio isn't fited to the velocity of slinging. Just only my reflection, maybe I'm wrong.

Hondero,

Here's the interesting fragment from:

http://www.concentric.net/~Ssbray/braygar.htm

I posted that quote in October but I repeat it here again.

" After Larry graduated from high school (in 1979), he married Mary Ellett from Loa, Wayne County, in 1980. They lived in Loa for a while, and in 1981 Larry made it into the Guinness Book of World Records for throwing a stone with a sling 1,434 ft. 2 inches, at Loa, Utah on Aug. 21, 1981. This type of sling is one of the most ancient weapons; it was used by shepherds for defense against wild animals and to help keep their sheep; it was also used for hunting and warfare, and of course is mentioned several times in the Bible such as when David killed Goliath. Garland had taught Larry to use a sling at a very young age, and he had become quite adept in both distance and accuracy, and knew that he could break the record. The old record was around 1000 feet, and it was set in 1970 in England. Larry broke the record in 1980 at the Wayne County fairgrounds in Loa, but the Guinness people wouldn't accept it that year because they said that he didn't have sufficient proof or documentation. So he broke the record again in 1981, and this time he had nearly all of the officials in the county there to watch and certify everything. They marked each stone just before it was thrown, and when the stone was picked up after it was thrown, they checked the mark to make sure it was the same stone, and then the surveyors measured the distance very accurately, and it all had to be photographed, certified, and notarized. It was quite a big event."

I'm full of admiration for this man. I'm very interested on his
next posts, if they exists, of course. Hondero, do you have maybe a contact with this man?

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 #53 - Feb 9th, 2004 at 12:17am
 
Dear Yurek,

How about just moulding one of your optimumly-weighted glandes to best approximate the shape of the front section of that 8-to-1 ideal sectional foil design (which, if it had fins and an attaching hook uderneath its belly, would look interestingly like that picture of the World's Record 500+ meter "sling dart" I saw in the Guinness Book in that elusive book stall which I'm still trying to find.  I'll bet that that was one of their secrets!), and THEN attaching a COLLAPSIBLE tailing section shaped exactly like that desigh with collapsible rubber fins to the BACK END of the glande, thereby achieving the proper shape in flight AFTER release, while maintaining a conventional GLANDE SHAPE in the pouch PRIOR TO  release?

Originally, I envisioned a sort of tiny hard, light plastic Easter egg-like shell container, made up of collapsilbe segments much like one of those collapsible camping cups, which would lengthen with the air resistance and "setback" inertia (like old Soviet-style Tank "setback-armed rounds designed top be fired from non-rifled barrels to achieve higher velocities and mass production simplicity, whereas ours were "spin armed, using centrifugal force to armt he rounds after they were a safe distance out of the barrels, etc.) to extend it once it cleared the pouch/socket.  Otherwise, a small piece of celophane tape stuck to the tip of the tail on the end of an inch-or-so thread could be sewn, of tied to the center, or edge of the pouch, and taped to the tip of the tail to "open" it with negilgible resistance/energy loss as it tore free of the puny tape as lt left the sling socket.  It would extend to something looking sort of like an insect larvae.

But then, I though of using a properly-shaped rubber baloon-like tailing segment, which could also be folded/collapsed over the gland in the socket, and a small lead or copper BB paced inside its tail tip, or the thread-and-tape or similar method could be used to open it up to the 8-to-1 wing foil sectional "dart"shape without hurting the weight or launching characteristics of the glande.

That way, you could throw the thing normally, and it would extend to the proper shape in flight, and hopefully would fly a lot farter from your conventional sling, while not deviating much in design or expense, from a conventional sling stone/glande!

I hopoe you can make this "long-range" bullet work for you, as I know that you are a good practical mechanical engineer as is obvious from your pictures of your sling and glande experiments.

Your friend always,

Jean Bradberry
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Re: Air Drag On Sling Cords & Pocket
Reply #54 - Feb 9th, 2004 at 12:29am
 
Oops, I forgot to mention that tiny fins couls also be moulded, glued, epoxy-ed (even made from some sort of epoxy, perhaps) or taped to the tail segment, which could be made of plastic, rubber, heavy paper, etc.  A hole could be punched inot the center of a tiny square of duxct tape and tied to the thread, which in turn would be tied to the pouch, and the tape then tuchk to the rear of the tail segment, just enough to allow it to extend on release, and then the tail segment and glande to which it was firmly attached could easily pull free with minimal force expended to achieve the extension and separation.
Jean B.
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Re: Air Drag On Sling Cords & Pocket
Reply #55 - Feb 9th, 2004 at 12:44am
 
You could make the fins slightly twisted (like an arrow) so that it cork-screws through the air like a bullet.  Straight ones are ok, but a slight spin on the projectile adds gyroscopic stability and helps diffuse air around the projectile, reducing drag. 

Chris
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Re: Air Drag On Sling Cords & Pocket
Reply #56 - Feb 9th, 2004 at 1:09am
 
Dear Chris,

Twisting the fins slightly like an arrow is a TOTALLY COOL IDEA!!   8) WOW!  Perhaps that idea of painting half of a glande to see how fast and in which direction it tends to want to spin when Yurek throws it (that was mentioned the other day) could be used to determine at what angle they should ideally be curved?  Or might just doing it similar to how they do it for an arrow also be a good place to start?
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Re: Air Drag On Sling Cords & Pocket
Reply #57 - Feb 9th, 2004 at 8:52am
 
Quote:
That projectile the most probably will catch the release cord and get the chaotic flight, even if the pouch position is proper. Useing the NACA shape seems doesn't give a significant profit, because the ratio isn't fited to the velocity of slinging. Jurek


Jurek, An aerodynamicist could tell us the best aspect ratio, no need for us to guess. A slingstone leaves the pouch at 30m/s (67mph) in order to fly 145m (Richardson). To go ten times that distance the velocity is going to be faster. Such speeds will profit by a well-shaped stone.

I think a special sling pocket would have to be made for this projectile. Pehaps lined with thin rubber to help spin the projectile?

Quote:
... the shape of the front section of that 8-to-1 ideal sectional foil design, which, if it had fins and an attaching hook uderneath its belly, would look interestingly like that picture of the World's Record 500+ meter "sling dart" I saw in the Guinness Book. Magnumslinger


Attaching hook?  Now THAT's interesting. About three years ago I worked on this same problem of long distance throws. I came up with that NACA shape for the glandes, and I came up with a pocketless sling, too. The pocket is a huge velocity thief. Lots of air resistance at the high speed end of the sling. My design used an internal release mechanism, not external like the 'hook', but the idea was the same, eliminate the pocket which Jurek points out is going to be a problem with the glandes/bolt/dart,
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Re: Air Drag On Sling Cords & Pocket
Reply #58 - Feb 9th, 2004 at 9:32am
 
FYI, at an aero museum near here there are models of the x2 bombs dropped on Japan to end the war.   These bombs are VERY! short and fat, with fins on the rear end.   They're much shorter/fatter than Jurek's cast lead glandes.

But are we sure fins are needed?   I recall one of the record-setters saying his football shaped stone did fly with a spin that kept it point first.   

Also, it seems like a pocket maybe could be designed to fit a particular projectile, that would not add much drag on spinup.   Jurek's wire sling used with slightly grooved glandes seemed promising.        mgreenfield
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Yurek
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Re: Air Drag On Sling Cords & Pocket
Reply #59 - Feb 9th, 2004 at 3:02pm
 
Quote:
Jurek, An aerodynamicist could tell us the best aspect ratio, no need for us to guess. A slingstone leaves the pouch at 30m/s (67mph) in order to fly 145m (Richardson). To go ten times that distance the velocity is going to be faster. Such speeds will profit by a well-shaped stone.

I think a special sling pocket would have to be made for this projectile. Pehaps lined with thin rubber to help spin the projectile? ...


Dan, You have quoted my words in this way:

Quote:
That projectile the most probably will catch the release cord and get the chaotic flight, even if the pouch position is proper. Useing the NACA shape seems doesn't give a significant profit, because the ratio isn't fited to the velocity of slinging. Jurek


I believe you did it only due to compactness, but that quote gives a false view of my thinking and opinion about the profit of useing the shape which you showed. Your quote changes a sense of my post. I don't question that this shape (1:8 ratio) is the best for "sling velocities". I only fear that proper release of such elongated projectile must be a problem with a clasic sling which is required by GWR.

I think the quote should be rather like following, and I hope that one is clear.

Quote:
...But what is a chanse to do it with the clasic sling. That projectile the most probably will catch the release cord and get the chaotic flight, even if the pouch position is proper. Does it is posible to throw correctly such elongated projectile constantly. There is a chanse reach it with projectiles which have a ratio 1:2 or maybe 1:3 but in this case useing the NACA shape seems doesn't give a significant profit, because the ratio isn't fited to the velocity of slinging...


Excuse my finicality 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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