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glandes single or multiple projectiles? (Read 15450 times)
Yurek
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Re: glandes single or multiple projectiles?
Reply #15 - Dec 2nd, 2003 at 8:22pm
 
Jesús,

First of all, thanks for showing interest and your words of encouragement. I begin to believe in my chanse, but first, must do the proper tests and get certainty. There is too much unknowns. So I'm not serious and declared myself pretender for the nonce. However my mind is working on various technical detailes more and more. I hope I will be able to materialize my ideas soon (about the sling design, making of the lead projectiles, an optimal mass of the ones, choice the way of measurements and the good spot for projectiles recovery etcetera...).

I'm going to consider your notes about elongated projectiles. I think my own tests can't be better than secular experiences Smiley About the range, I supposed before that it is from 30 to 50%, so it's not very different from your calculations, but I would like 50 Wink

Saludo,

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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David_T
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Re: glandes single or multiple projectiles?
Reply #16 - Dec 3rd, 2003 at 11:06pm
 
Does anyone have any thoughts on the importance of the size of the pouch? Would a smaller pouch add any significant or greater range to the projectile flight? I would guess that it would not make a very big difference.
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Re: glandes single or multiple projectiles?
Reply #17 - Dec 4th, 2003 at 12:35am
 
Not sure, since most of the surviving slings seem to be stone throwers, and not glandes throwers. Due to lower density a larger stone must needs be thrown.
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Whipartist
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Re: glandes single or multiple projectiles?
Reply #18 - Dec 4th, 2003 at 2:54am
 
Remember that air friction increases exponentially in relation to velocity.  I believe a specially made sling with tiny cable release cords (maybe 1/16") and a tiny cradle that could securely hold the gland but not have any excessive size- would improve your range greatly.  You'll never get your gland flying faster than you can make your sling fly.  Your sling won't fly as fast if it's bulky and not aerodynamic.  The more aerodynamic the better.  You need every inch you can get to beat the record.

I've dealt a lot with these issues as a professional whipmaker.  Interestingly enough, the faster a whip's action is, the less energy it transfers to the cracker.  All other things being equal, the slower actioned whip doesn't waste as much energy in friction loss and thus imparts more energy to the cracker.  Similarly, the denser the whip's thong, the more power the whip has.  The smaller and denser the thong for a given weight, the more power. 

If you made such a sling, you could easily encorporate a nice finger loop and release cord in the first foot of the cords next to your hand.

My newest sling has wider cords than the other ones I've made.  I can't quite get as much range out of it as a result. 

Interestingly, the Peruvians seem oblivious to these issues.  Some of their slings had very large cradles.
                                   
   Ben
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Yurek
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Re: glandes single or multiple projectiles?
Reply #19 - Dec 4th, 2003 at 5:20pm
 
Sure, the lighter projectiles, the more influence of air drag of the sling. If the projectiles are heavy, then it isn't so very important because you must put a more energy for the mass acceleration relative to the loss caused by the air drag.

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: glandes single or multiple projectiles?
Reply #20 - Dec 6th, 2003 at 5:21am
 
I agree with you, Ben, in the design of the sling for glandes: the smaller the better, since if the pouch is much greater than the projectile, it takes much unnecessary friction in the turning around and launching, and even accumulates air pressure and not aim in a  regular way the shots. For that reason the peruvian and balearic slings  have a splited pouch, to avoid that pressure and to diminish the friction with the air, besides to obtain an optimal adaptation of the projectile to pouch. In the museum of my Web there is a light experimental sling for glandes done by me, who obtains a good adaptation to the projectile, although I am not an expert in this type of slinging.
By the way, the URL of my site has changed and I have extended it with some new subjects. The new URL is:

                      www.armas-primitivas.com

Saludos
Jesús
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Chris
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Re: glandes single or multiple projectiles?
Reply #21 - Dec 6th, 2003 at 10:38am
 
I don't think a split pouch would decrease the air pressure around the pouch/projectile much (noticeably?).  If you think about how the pouch rotates in the air, it's moving sideways, which doesn't "catch" the wind.  The main drag is from the projectile situated in the pouch.  Sometimes people put holes in the pouch allowing air to escape from around the projectile.   But split (andean) pouches are pretty snug around the projectile.  Their advantage aerodynamically is that they are much smaller in surface area than that of a simple pouch, which reduces drag.  But I don't think the actual split-ness of the design is what reduces the drag.  Or does it?

Chris
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David_T
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Re: glandes single or multiple projectiles?
Reply #22 - Dec 6th, 2003 at 3:12pm
 
This is going back to an earlier question of projectile rotation.
I can almost guarantee that if anyone came with me to the "concrete pit" that I sling at, I could prove to them in less than 20 slings that everything slung from a sling will have rotation.

I would also say from observation that any elongated object will naturally tend toward a "point first" orientation. The spin caused by the snap at release will force it to have less wabble-- and the forward motion will naturally make the foward end stay forward.
I will have to obeserve a specific point next time I sling. That point is: If the projectile has one pointed end and one flat end, will the pointed end always be foward?
I believe from observation that the foward end will remain forward throughout the flight-- no matter if it is the flat or pointed end. The detemining factor of that is whether the point is up or down in the pouch. I am fairly sure that for my overhand release, if the piont is up as I am holding it in my left hand, it (the point) will be forward at release and stay that way. If the flat end is up in the pouch, it will be forward in flight, however; I think because of the increased drag, it tends to drive the projectile toward the ground.
As I said, I will specifically experiment next time out.

Any comments?
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Re: glandes single or multiple projectiles?
Reply #23 - Dec 6th, 2003 at 3:53pm
 
Yurek,

You have got me interested in making those dense, smooth lead glandes. Grin

You need to have every inch or centimeter you can get!
Once you find the perfect size, shape, and weight, you should polish and then spray silicone on the glandes to reduce the friction as much as possible. Just a suggestion for your "fine tunning"
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Re: glandes single or multiple projectiles?
Reply #24 - Dec 6th, 2003 at 7:57pm
 
OK Chris, I believe that we are  both saying the same. I said, or tried to say, that large pouches produce more air friction in the  turning around and launching, and that even accumulates air pressure (in the launching, not in the turning around) that makes difficult  the aim due to an irregular behavior of the pouch in the firing. If we pay attention, the pouch in the launching  catch air pressure, and is that moment the important one, since it is when the true acceleration is developed. Splits or holes in the pouch point to avoid this effect, although I agree with you that some Andean slings, mainly the present ones, use this design mainly to obtain a better adaptation of the projectile. Nevertheless other Andean archeological slings have a pouch  completely divided in two parts, just like the Balearic ones, that look for the effectiveness in the firing and accuracy by avoiding the effect of the air in them. There are others in mesh form that also persecute the same effect.
In general it is a good idea to avoid large pouches, even to send big projectiles. I remember that the Romans used a simple narrow leather strip to send stones of one pound, balancing the projectile in that special sling which they called "librilis", in concordance with the projectiles of a pound that used.

Saludos
Jesús
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Yurek
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Re: glandes single or multiple projectiles?
Reply #25 - Dec 6th, 2003 at 8:45pm
 
David thanks for the advice. So far I have been sure that a smooth projectiles should go further. Recently I found some informations about aerodynamics of golf ball flight and I'm in doubt.

Contrary to intuition a dimpled ball travel much further than a smooth ball. Dimples (unevenneess) make a boundary layer of  air flow turbulent, which separates not so quickly like a laminar layer. As result, the wake is more narrow and the air drag smaller too. Simply say, the smooth ball fly as if  into a "condom made from air" Wink

The better explanation you can find on the site:

http://wings.avkids.com/Book/Sports/instructor/golf-01.html

So guys, what do you think about the dimples on glandes? Wink The smooth or rough surface is better?

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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Chris
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Re: glandes single or multiple projectiles?
Reply #26 - Dec 6th, 2003 at 9:06pm
 
I know that the dimples on golf-balls are for extending range and stability, but I never thought about adding dimples to sling projectiles.  It's actually a really neat idea and the research is already been done.  Maybe Jeff or someone with casting experience can make some really neat glandes and see how they fly?

Chris
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Yurek
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Re: glandes single or multiple projectiles?
Reply #27 - Dec 6th, 2003 at 9:29pm
 
Jesús,

Quote:
large pouches produce more air friction in the  turning around and launching, and that even accumulates air pressure  (in the launching, not in the turning around) that makes difficult  the aim


I think you mean, the folded surfaces of the big pouch produce the lift (similar to wings of  biplane), which can change the trajectorey of the pouch (raise or lower, according to the attack angle). Am I right?  

I agree, it would make sense.

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: glandes single or multiple projectiles?
Reply #28 - Dec 6th, 2003 at 9:41pm
 
Chris,

I cast a few glandes today. They are just rather rough than very smooth:)  I hope I will test them tomorrow, but the weather is terrible Sad

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: glandes single or multiple projectiles?
Reply #29 - Dec 6th, 2003 at 10:04pm
 
My best guess here would be that one should find a plastic ball with dimples and use David T's concrete casting process.  This seems like the best idea to me.

I do, though, have to wonder how much difference it will really make for those of us who are not slinging for a distance record.

This seems to me like firing match style bullets with high ballistic co-efficients from an intrinsically low-velocity gun.  Somewhere there is a velocity threshold that the projectile has to exceed to take advantage of the better dynamics.  Like shooting a 165 grain match bullet made for a 308 or 30-06 fired in a 30-30 instead.  The difference of 500 feet per second or more renders the bullet much less effective.  I will check this in my ballistic software, but think I am right here. ( I just checked some things.  I do belive I am accurate here.)

When I was learning to hand load for my rifles, I discovered something important early on.  Velocity is has a greater effect on trajectory and energy than ballistic co-efficient; and in a big way.  It takes a whole lot of B.C. to equal an increase of just 100 feet per second.  Now, this was at velocities from 2,400 to 4,000 fps, but I suspect it would hold true at sling velocities as well.

This all means that I don't think dimples are going to help us so much at the low velocities we have to deal with.  The improvement over simple spheres would not equal the improvement of the sphere over the jagged rock by any means.

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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