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New Pictures--Range Boost (Read 20475 times)
Matthias
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Re: New Pictures--Range Boost
Reply #30 - Jul 16th, 2004 at 10:35am
 
Here is a nice "dimpling calculator" it only works for spheres, and only gives forces. The drag coefficients calculated by this one give very slightly less of an edge to the dimpled shape than what I used above (and the previoudly linked article claims) - not enough to make a very big difference.

http://www.mame.syr.edu/simfluid/redder/dragforce/DragForce.html

You can answer the length/diameter question (like most questions actually) without using any math/engineering. Historical glandes are shaped that way for a reason, as are bird bodies and (american) footballs. All with different constraints, of course. If you take pure aerodynamic drag with a ton of assumptions, the trade off between form drag (what we're talking about) and skin friction, usually occurs somewhere around 30%

...
Figures borrowed form Dalhousie Univeristy, and I'll be willing to bet theat they "borrowed" them from White, the standard first year fluids text...


Turbulent flow (induced or otherwise) will flatten the curve, so that anywhere from 2:1 to about 4:1 should be just fine. By the time you take into acount the effects of a possible "off-axis" (even by a small amount) throw, 2:1ish is looking pretty attractive...

...

One thing to keep in mind with these graphs is that we are only looking at cd for a shape with no scaling. An ellipse of same mass as a sphere will have a smaller projected area, so total drag for matching projectiles will be as much as 50% lower again (1/4 sphere drag! why was it that we like these things so much Cheesy) The other nice thing is that as cd goes down, the advantage you get from lead is reduced as well, which gives some of us other guys a fighting chance!

Matthias
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Hondero
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Re: New Pictures--Range Boost
Reply #31 - Jul 16th, 2004 at 11:33am
 
Matthias, very interesting your ballistics information. We have discussed before the subjet and didnīt find a proper way to calculate the ballistics of the sling. I think you are the right person to make such a calculator, that moreover is essential to have online in a site like this. Questions like the max. range with a stone or lead projectile, the optimal weight of a projectil, or the start speed for the distance world record (let us say 500 meters), will find a proper answer Cheesy

Which parameters uses your spreadsheet?
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Yurek
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Re: New Pictures--Range Boost
Reply #32 - Jul 16th, 2004 at 12:34pm
 
I see that the question has been revived again!

Here is the other nice toy, the Golf ball Trajectory Simulator:

http://www.ecs.syr.edu/centers/simfluid/green/traject.html

Matthias could compare his result with that one. Pitty it doesn't allow to change the density and ratio as parameters Sad

Mgreenfield,

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Yurek, how abt your 120-gram lead glandes with dimples?


I rolled the glande model of heat-hardened modelling paste for children, and next imprinted the dimples with the rounded ending of one of my ball pens Smiley That one seemed to have the suitable shape and size.

Here is the reposted picture, alas that one is from the flat scaner and its quality is poor.

...

Jurek
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« Last Edit: May 7th, 2005 at 6:07pm 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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Yurek
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Re: New Pictures--Range Boost
Reply #33 - Jul 16th, 2004 at 5:40pm
 
Ooops! I didn't read Mgreenfield's inquiry correctly before. I thought he asked how I made the dimpled glandes.

Well, I tried the dimpled ones only one time among the smooth ones, which you can see on the above picture. There was too little tries in order to get the clear conclusion. For me they flied similar to the smooth ones. Some of them reached pretty good ranges, indeed, but the best range I got with a glande without dimples. There are a lot factors, I'm not able to get the 100% constancy in each range throw. The launch angle, orientation of glandes durring a fly, my timing and energy put into throws are a bit different evry time, I do it nearly the limit of my possibilities after all. Durring that try I got about the 100-120 m diference between the best and the worst range. I couldn't see any regularity regarding to the dimpled glandes, which would prove the adventage of them.

Now I use the smooth ones because making them is easier, it is only reason. Probably the dimples can help a bit, but the adventage is difficult to percceiving. Curently for me the proper technique is a more important factor.

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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Matthias
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Re: New Pictures--Range Boost
Reply #34 - Jul 16th, 2004 at 6:52pm
 
Yup, I guess we are going to have to keep dredging up old threads until we come up with a definive answer. I'll put some more effort in this weekend. You can tell that this week has been mind-numbing because my post freq has gone waay up... I've been doing sling calcs at work to spite my boss, who won't give me any time off... that guy is a loser (the joys of being self-employed)

I'd suggest that Yurek's dimples are much too large for the size of the glandes, to the point where they would start to harm performance. If you can achieve consistent point-forward flight, the ideal could be a single raised sharp edged ridge (or dashed ring) about 25-30% back from the forward edge.

If people want to play around with experimental glans design, I might suggest building large scale, light projectiles. A tennis ball sized series of wood projectiles would give pretty solid feedback (differences in drag are emphasised) and be easier to test and retrieve. Any advantages that turn up would be applicable with smaller/denser ammo...

Matthias
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Sean
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Re: New Pictures--Range Boost
Reply #35 - Jul 16th, 2004 at 11:52pm
 
oh my god you people are smart... or maybe im just really tired im not sure... but anyways i think that golf balls arent solid but are the shell then normally some string and a rubber ball... or was that a baseball... i cant remember right now need sleep be back with you later
Sean
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Re: New Pictures--Range Boost
Reply #36 - Jul 17th, 2004 at 7:53am
 
Matthias, .....this discussion of aerodynamics has gotta end up in the articles section, I say.    It's dynamite good info.     mgreenfield
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Re: New Pictures--Range Boost
Reply #37 - Jul 17th, 2004 at 5:25pm
 
Guys, I think the only way to solve this golf ball mystery is just for one of us to hack one up and find out.  I think I have one around hear somewhere so I'll be on the lookout for it.
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Matthias
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Re: New Pictures--Range Boost
Reply #38 - Jul 17th, 2004 at 7:03pm
 
I've cut up dozens of golf balls... They used to be (10-15 years ago) consistently rubber band wound around around (usually) a grape sized black rubber ball, which was often liquid filled. Lately, every ball I've cut up is a solid resin core with a hard/tough white cover. Some "range balls" are one piece.

A quick survey of an online golf ball shop (golfball.ch) reveals the following selection:

2 wound balls
36 2-piece (white cover around a solid core)
20 3-piece balls (two piece with an extra thin layer under the cover) **cough**-gimmick!-**cough**
6 4-piece balls **cough**-expensive gimmick!-**cough**

Matthias
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Re: New Pictures--Range Boost
Reply #39 - Jul 24th, 2004 at 5:59am
 
i've opened a few golf balls too  we used the rubber filament to tie it on the top of a pencil or ballpen and  tie a  lead pellet (one of those biconical "diabolo") on the end of the rubber .
then hold the pencil with one hand and  the pellet  with the thumb and index fingers of the other hand...
stretch.... aim...  and let go... Short range (1 to 1.5 yards) but deadly for flies, grasshoppers, roaches and some other "wild life" and nice for bothering other kids at class  as well
(Should i post this in the "other primative weapons" section? Grin )
Golf balls were  a rare item in Spain those days, (a minority snob/rich people sport)and i used to get mines at the Torrejon  USAF  base golf course.
Yes... i did a lot of bussiness selling metres of rubber to other kids Grin
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Zorrro
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Re: New Pictures--Range Boost
Reply #40 - Jul 24th, 2004 at 6:02am
 
Jurek
that golf projectile at the left side looks pretty cool   Smiley
Great job!
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Re: New Pictures--Range Boost
Reply #41 - Jul 24th, 2004 at 7:44am
 
This is one of those threads, like the staff sling question, which we will keep going over, when someone new comes along with a neat new idea.  I thought we came up with the idea that dimples would be detrimental for glandes, unlike for golfballs.  I think it was something like, golf clubs do not create their own backspin on the ball, because you are basically just whacking it, whereas a sling creates the backspin anyway, so dimples are not required to grip the air.  Or something.  Maybe I'm wrong.
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Yurek
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Re: New Pictures--Range Boost
Reply #42 - Jul 26th, 2004 at 11:59am
 
Thanks Zorrro!

English, I'm not a golf player but I think that just clubs create  the backspin. The dimples only streighten the Mangus' effect and reduce the air drag of golf balls.

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: New Pictures--Range Boost
Reply #43 - Jul 26th, 2004 at 12:45pm
 
Yes, the club strike creates backspin unless you are a lousy golfer like me Grin Then it creates topspin, or side spin... Shocked  Four!!! That is golf talk for: LOOK OUT or DUCK!
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Chris
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Re: New Pictures--Range Boost
Reply #44 - Jul 31st, 2004 at 6:59am
 
As several people have explained, the dimples do increase range in a few ways, including reducing drag.  This is also why tennis balls are furry. 

Although the density of a lead projectile is far greater than a golf ball, I think dimples would still be beneficial.  One of the things to remember is that sling projectiles have long flight times, perhaps similar to golf balls at their slower speeds, or even greater.  If you could reduce drag by a fraction for a 6 second flight, that could extend your range by a noticeable amount. 

Yurek, how long are your projectiles in flight?

Chris
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