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Clocked Speeds (Read 7115 times)
Johnny
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Clocked Speeds
Aug 17th, 2005 at 10:33am
 
Has anyone clocked the speed of a projectile cast from a sling? I've seen the charts on distance and such, but would like to know the speed of a projectile. I'm sure lead bullets would be the fastest and large rocks the slowest. Pro baseball players can throw a ball around 90 miles an hour.....
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Matthias
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Re: Clocked Speeds
Reply #1 - Aug 17th, 2005 at 12:20pm
 
I'm good for just about 50m/s in current trim, which works out to 112 mph. This is measured in various not particularily accurate ways that all support the value. From looking at ranges that people post, I'd say that most of the "medium" slingers here are in the low forties-50 range. Once you get into the mid 50s (m/s again), there is a transition in the type of flow over the glans in flight, and the drag on the projectile goes way down - getting over that "hump" is something to work on!

The density of the projectile should make no difference to the initial speed of the throw. The reason lead goes further is that is slows down less quickly once it is in flight.

Google will do conversions if you type in "50 m/s in mph" for example.

I really need to get back to my simulator project, and the ballistic pendulum, and Techstuf's new "sonic" speed measurement technique... We were making good progress there for a while, but have gotten distracted (and lost Hondero...)

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Re: Clocked Speeds
Reply #2 - Aug 17th, 2005 at 12:23pm
 
165 feet per second, approximately.  That's like a little better than average bow, but the sling would have more range.  And that's with an average slinger, less than average projectiles, varying sling length.... We should really do some tests.
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Re: Clocked Speeds
Reply #3 - Aug 17th, 2005 at 1:23pm
 
Johnny, Matthias,......will try and get Chrono figures and time of flight data for interesting 'pocket velocity' and averaged velocity over distance, for some 'hopefully' revealing velocity/drag ratios for various ammo types.

Got a big old water tower at the edge of town....I'll try and post my 111th take or so.....when I actually succeed in hitting it from 300ft.....(buddum bum, joke, people)

It'll probably only take 50 or so.... Wink


Should be no problem getting an average velocity stat accurate within 12% or so, via this method.  Others who may wish to try this method should obtain better accuracy using a 'referee' to time the flight via sound alone (blindfold him first).....perhaps affixing one of those small 'snappers'/'poppers' (which are thrown down on the ground and emit a report upon impact) above the ammo on the release side of the pocket, will prove more accurate.....as the time of the report upon release as the ammo comes into contact with it at release will be quite near the moment of actual launch.

We'll see.

Also flirting dangerously with the prospect of marketing two radical sling designs.....'R'.....one of which elevates the velocity/accuracy obtainable with a solely human powered sling by an order of magnitude.  The other has multiple advantages, including the inherent optimization and physical alteration of ammo at the moment of release....stealing only a tiny portion of momentum to acquire great advantage.


TS

8)


I am certainly interested in the disparity between averaged velocity via time of flight reckoning and Chrono measurement of 'pocket velocity' (muzzle velocity)

Cute Java applet:

http://www.grc.nasa.gov/WWW/K-12/airplane/sound.html

Take a look at the tiny variable in speed between your altitude/location and sea level.
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Johnny
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Re: Clocked Speeds
Reply #4 - Aug 17th, 2005 at 1:55pm
 
What's "50 m/s" ?

What happened to Hondero?

Johnny

PS- I looked it up- 50 meters......
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Yurek
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Re: Clocked Speeds
Reply #5 - Aug 17th, 2005 at 2:48pm
 
Johnny,

The m/s is velocty unit in the metric meausrement system SI.
m - meter
s - second

m/s = metres per second.
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Yurek
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Re: Clocked Speeds
Reply #6 - Aug 17th, 2005 at 3:22pm
 
An other way of estimate of stone velocity is video analysis. It could provide a quite good accuracy.

For example, lets take the one of my last movies I posted at the forum lately.

http://www.kajakowe.com.pl/sling/hit1.avi

If your video player is able to play a movie step-by-step, the thing is simple.

1. Stop the movie about the release moment;
2. Count steps until the moment when the stone is hitting the target;
3. Divide the distance to the target by the number of steps, and next multiple the result by the frame rate of the camera, and ready.

In case of my movie it looks like follows bellow.

distance = 20 metres
number of steps (frames) = 6 (ok, lets say)
frame ratio of my camera = 15 frames/second

then, averange velocity at the 20 metres range amounts:

v20 = 20/6*15 = 50 m/s = 167 ftps

Consider, that the muzzle velocity must be somewhat bigger, because the stone slows down, especially quickly in the first phase of the fly.

Of course, the bigger frame rate of the camera, the more accurate calculations. The shorter range, the result is closer to the muzzle velocity.

Just an example.

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: Clocked Speeds
Reply #7 - Aug 17th, 2005 at 3:32pm
 
Great suggestion, Yurek.....another easy and interesting exercise to compare to Chronograph.


8) 8)


TS
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sv
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Re: Clocked Speeds
Reply #8 - Aug 17th, 2005 at 4:32pm
 
nice shot jurek!
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me
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Re: Clocked Speeds
Reply #9 - Aug 17th, 2005 at 5:22pm
 
This may be alittle off topic, but has anyone ever done a good comparison of power between a bow and a sling?
My bow might send a 550 grain arrow around 180 feet per second. I don't know the exact fps, but let us say 180 fps for the moment. While a good slinger might send a 3-4 ounce stone within 10-20 fps of the arrow's speed. If 1 ounce equals 437 grains, then a 4 ounce stone is the equivalent of shooting a 1,748 grain arrow at near bow speeds. The sling is incredibly powerful, it's one major drawback being that it relies on crushing force to do it's damage as opposed to the hemmoraging caused by an arrow.
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Re: Clocked Speeds
Reply #10 - Aug 17th, 2005 at 5:44pm
 
I did a product demonstration video in the late eighties which included a comparison between a compound bow which, if memory serves, cast a 648grn arrow at 224fps.  A 1" chrome steel ball bearing was cast from a sling at a distance of 10yrds. into a standing sheet of 3/4"CDX plywood.  The bow was shot from the same position.  All the ball bearings went through the plywood and about half also went through the 1/4"CDX plywood backstop 3ft. behind the target material.   The arrow went nearly halfway through the target material on each shot without making contact with the backstop.  The Ball bearings weighed almost twice as much as the arrows....and had they been 6oz. darts.....they would have really made for quite a show.  

At that time, a man was marketing his invention that shot 6 inch darts which used razors for fletching from a bow via a mounted track and it's penetration compared to a full length arrow was devastating.


TS





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me
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Re: Clocked Speeds
Reply #11 - Aug 17th, 2005 at 6:06pm
 
razors for fletching? ouch.
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Thomas
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Re: Clocked Speeds
Reply #12 - Aug 18th, 2005 at 1:50am
 
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Re: Clocked Speeds
Reply #13 - Aug 18th, 2005 at 10:26am
 
Wow.  Interesting......I had heard of Drake's performance, yet was never aware of his unique setup, nor of his friend who introduced him to the sport!

The fletching is quite similar to that on the darts I have seen.


Thanks for the info!


TS

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Tint
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Re: Clocked Speeds
Reply #14 - Aug 22nd, 2005 at 5:14am
 
Thanks Thomas!

I'd like to shoot one of those!

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