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Projectile Shape (Read 16025 times)
justbarak
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Re: Projectile Shape
Reply #15 - Jan 14th, 2004 at 3:12am
 
Yeah, I realized after I posted the picture that the release points were a bit late.  Ok, so the "underhand" throw is the vertical rotation clockwise.  Is that correct?  What is considered overhand?   

I find the vertical rotation gives me good accuracy in a vertical plane - i can hit trees and fence posts with it.  But hitting anything on the X axis (horz), regardless of how I swing it, is completely random.  Judging the arc is definitely more difficult.  I find I aim best with one or two rotations and then release.  There is definitely a timing in the throw that provides the greatest power.  When I have access to my brother's video camera I want to video slinging some rocks and then slow it down and try and quantify the movements involved.  Maybe we could generate some discussion on throwing techniques and see what theories we come up with. 

The projectile weight also seems to factor into efficiency as much as the throwing technique and shape.  At least it does for me.  Too light and I nearly whip my shoulder sockets out and air friction stops the stone too soon.   Too heavy and I can barely manage the rotations and the throw.  Something slightly smaller than a golf ball has about the right weight for me. 

Any thoughts on the subject of weight as it relates to distance and accuracy? 

Barak

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Hondero
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Re: Projectile Shape
Reply #16 - Jan 14th, 2004 at 12:59pm
 
Yurek,
the cross section of the glandes is only a little flat, just to have a good grip into the pouch. Flat spinning missils are not aerodynamics besides humming. Here is an almond glans, point forward,  between my fingers

...


Barak,
the 45º turning in your drawing is the best for a point forward launching, and if you throw from the low position better. You can get the technique and see how
the missil fly launching elongated stones type hot-dog (if not available such stones, can be made in dried clay).
What a nice bull-roarers there are in Papua New Guinea. Did you get some old ones?
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Yurek
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Re: Projectile Shape
Reply #17 - Jan 14th, 2004 at 4:41pm
 
Hondero,

In our climate zone the "almonds" appear mainly as the seeds (stones) in the markets, hence my first image of the word "almond" was the flat "seed of almond",  despite I had seen the pictures of the Roman glandes before Smiley They are really simillar shaped to the almond fruits. There was the small incomprehension Smiley

Saludos

Jurek

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« Last Edit: May 7th, 2005 at 6:42pm 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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Whipartist
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Re: Projectile Shape
Reply #18 - Jan 14th, 2004 at 7:00pm
 
Great picture Hondero! 

I'd say that if this whole theory on the spin effect for added lift, is correct, then the shape of the glands isn't just for added grip on the pocket, but primarily for it's qualities in flight.  A perfectly smooth gland won't produce as much lift as an almond shaped one.  I know this is part of the point already stated, but I think it's the primary one.  I've seen experiments done on baseballs and other types of balls in regard to how much lift is generated by a backspin, etc....  The shape and quality of the surface has effect.
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Re: Projectile Shape
Reply #19 - Jan 14th, 2004 at 7:12pm
 
I'd really-really! like to see slooo-mo film of some good glande launches.   Do they go point-first like NFL football, or sideways with back spin to "fly" like golf ball, or something else altogether?   What slinging hero will come up with the film for us first?   mgreenfield
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justbarak
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Re: Projectile Shape
Reply #20 - Jan 14th, 2004 at 7:45pm
 
So what if the surface of the gland was pitted like a golf ball?  And just in a cartoonish curiosity - I wonder what would happen if you put a super short shaft with fletching (tail fins) on it so that the overall shape is similar to the steriotypical World War II bomb.  I have one of those nerf footballs that whistles when you throw it and has the tail fins on it.  If they were really short, close to gland (like one centimeter max), and flexible like on arrows so it wouldn't catch on a sling, I wonder if the initial drag before the gland straightened out would be to great, or if it would help it fly.

It would be amusing anyway. 

Hondero,
I never encountered bull roarer's in PNG.  We lived in the highlands, and perhaps they were native to the coast where there was more Australian aboriginal influence.  I have one though - a tourist item from Sydney.  They are great fun.

Barak
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Yurek
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Re: Projectile Shape
Reply #21 - Jan 14th, 2004 at 9:37pm
 
Ben, mgreenfield,

If that glans is throwed corectly by the "point first" style it rotates rather around the axis which is approx parallel to the fly direction (probably it gets a bit precession often). So that kind of a fly is similar to a fly of the rifle bullet. Then the rotation doesn't produce the lift bat only helps to keep the direction of the projectile due to the giroscopic effect (as Hondero mentioned once). There is no lift when the axis of the rotation is parallel to the apparent wind direction. In this situation the oval shape is a negative factor because it brakes the rotation. The biggest lift is produced when the axis of the rotation is perpendicular to the apparent wind direction, when the projectile flies crosswise. And if the axis is vertical and the rotation is clockwise then the trajectory turns left. But if the rotation axis is horizontal  and the projectile has the back spin, then lift is directed to up and is beneficial, because prolongates the fly. This fenomenon is known as the  Mangus' Effect. This one is stronger when the suface of the projectile isn't very smooth and regular. I don't think that aventage of Mangus' lift (the crosswise fly) bigger than adventage of the "point first" fly for mentioned glandes.

Additionally, getting the back spin in the sideways fly, is very little probably due to the pouch position during the release in the typical ways of the slinging. So I think the oval cross section and and the edges aren't good for ranges and accuracy.

I suppose there is different kind of a lift which can be profitable. If the glans goes and rotates point-first and its nose is a little bit "snub" relative to the trajectory (apparent wind) then it should get a lift like a wing. But when the its nose is a bit lowered then lift pushes that one down and is unbeneficial.

Probably mantioned effects wasn't very significant on battlefields, for lead glandes due to their a big density.

Barak,

I think the tail fins should be rather big for quick stabilisation the short and massive glans, so they would probably cause the bigger wake (turbulences) and as result the bigger drag. Additionally the glans would lose quite a lot velocity yet before the its stabilisation.


Jurek, who hopes he is clear
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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: Projectile Shape
Reply #22 - Jan 14th, 2004 at 10:53pm
 
Barak,

Check out my post in the "other" section on bull roarers.

Easy to make and the fun never stops.

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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justbarak
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Re: Projectile Shape
Reply #23 - Jan 14th, 2004 at 11:32pm
 
yeah, the tail fins were a flight of wild imagination. 

Jeff, I actually saw your bull roarers earlier today and was quite inspired.  I promptly went to my little woodshop to see if i could find some suitable wood, but all I had was light weight narrow planks.  I think I'll make a run to woodcraft and see if they have some nice cocobolo planks.  I love wood grain.

Well, unfortunately I ran out of intelligent contributions to this thread several posts ago... lol, so I will go back to my shop and continue making more sawdust.

Barak
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Hondero
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projectile Shape
Reply #24 - Jan 15th, 2004 at 4:20am
 
Yurek, Ben, mgreefield... etc,
Interesting the debate on glandes flying. I thing the Magnus effect in glandes, whatever was the position of them in the flight, is not meaningful due to high density of the missil, as we say about dimples in glandes. So neither loss of accuracy nor elevation by bakspin would be considerable in glandes. In my opinion the aerodynamic advantage is due to the stability of the position (more o less parallel to the advance), as the cross section (important in air drag) is less than the one of a spherical missil of the same weight and of the same glans in an erratic flying. Is the same principle of fire guns bullets.
The effect would be more importat if the pouch was striated as barrel rifles   Cheesy    But here the striated is the missil. In fact there are anothers glandes that have four edges.
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Chris
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Re: Projectile Shape
Reply #25 - Jan 15th, 2004 at 2:10pm
 
The idea of fetching might be a bit overkill and fragile, but what about a little length of sling attached to one of the points; maybe 5 inches worth.  It can be a thin piece of cotton or something.  It only would cause lots of drag when it's not oriented in the "dragging" position where it just stays in the projectiles wake.  It would be simple to add, and durable (attached with a little drop of super glue or something). 

I really have serious doubts about people consistently casting projectiles with perfect orientation and spin.  It just doesn't seem like an easy thing to do repeatedly, especially in a battle scenario, where time is limited and conditions may be less that ideal. 

Chris
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Re: Projectile Shape
Reply #26 - Jan 15th, 2004 at 2:48pm
 
The orientation of a glans in flight is an interesting question that might be answered by having a target such as a block of plastercine. The impact marks might make it clear which way the projectile was orientated when it struck. Just a thought....
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Re: Projectile Shape
Reply #27 - Jan 15th, 2004 at 5:09pm
 
Chris,

I think that consistent "point-first" throwing is possible but not easy. If you once find the way of geting it, you can copy this way next times. There are conditions however, the cords must be distant in the palm, and a minimum amout of rotations of the sling is necessary and the projectiles should be consistent too.


Cornelius,

Wouldn't be easier to beat into something big and hard (for example the conrete wall)? The lead glandes are soft so they should get the marks.


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: Projectile Shape
Reply #28 - Jan 15th, 2004 at 7:02pm
 
Jurek, ....see post "Correctly Slinging Footballs" down the list a little.     I think there is a "standard" technique that will propel glandes consistently point first, and stable in that orientation.    Lots of what we know indicates this.  We just have to somehow reclaim this knowledge from the dust of ancient history.    mgreenfield
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Yurek
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Re: Projectile Shape
Reply #29 - Jan 16th, 2004 at 7:01am
 
mgreenfield,

You have pointed all condition very well. I think it make sense.  One day I observed step by step my stone slinging on the "high speed shutter" video. The pouch positions were rather similar in the most releases, although I didn't try to control it at that time.

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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