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Optimum Shape for Range (Read 6703 times)
jungle
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Optimum Shape for Range
Sep 10th, 2006 at 2:32pm
 
It's the MK 82 500lb bomb, carried by a variety if US aircraft, designed for low drag in flight and on release. It has a fineness ratio of 6:1, that is length to width including four small fins at the tail. Such a shape scaled down and cast in lead is likely to provide near optimum results for low drag and the small fins assure point on flight without spin.
Google MK 82 for photos.
Not exactly traditional, but the concept is well proven.
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siguy
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Re: Optimum Shape for Range
Reply #1 - Sep 10th, 2006 at 3:50pm
 
that's interesting...it would be hard to cast the fins on the glande.  perhaps fins of a harder metal could be soldered to the glans, so that they would not be so easily smushed on impact, and so that it would be easier.  it sure is interesting...
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jungle
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Re: Optimum Shape for Range
Reply #2 - Sep 10th, 2006 at 4:09pm
 
A few trolling style fishing weights are near this shape. Perhaps some dense plastic or brass fins could be epoxied in place after making a cruciform cut with a hacksaw.
The CD and sectional density of a 2-3OZ shape would be superb. I know the record holder used something similar, but if somebody is trying for the record this could be the way to go.
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Re: Optimum Shape for Range
Reply #3 - Sep 10th, 2006 at 6:00pm
 
With the right technique & grip, ellipsoid ammo can be pitched point first with no fins, ....like a football pass.  Trick is palm forward release and a wide grip.
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Re: Optimum Shape for Range
Reply #4 - Sep 10th, 2006 at 7:14pm
 
True, but they have a much higher CD and lower sectional density.
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Re: Optimum Shape for Range
Reply #5 - Sep 11th, 2006 at 1:37am
 
A 6:1 shape scaled down to a length of three inches (7.5 cm), would be half an inch (1.2 cm) wide.  That's a pretty long and skinny projectile for a sling.  I think the practical difficulties would outweight the pure aerodynamic efficiency of the shape.

But it needs to be tried.  I've got a 3-inch piece of 1/2-inch steel rod lying around somewhere, I'll see how it slings... not aerodynamic at all, and no way am I going to file it to shape.  But the unshaped rod will still tell me if it can work in a sling or not.
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siguy
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Re: Optimum Shape for Range
Reply #6 - Sep 11th, 2006 at 3:01pm
 
it is a shame you don't have a lathe for that rod...can't wait to hear the results
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Re: Optimum Shape for Range
Reply #7 - Sep 12th, 2006 at 4:51am
 
isn't that a kind of barreled arrow? i've heard barreled ones are used for flight shooting
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Re: Optimum Shape for Range
Reply #8 - Sep 12th, 2006 at 1:41pm
 
Have to be a bit careful comparing shapes across different scales, speeds and materials. Bombs are much heavier relative to their surface area than sling stones, for example, and work through a different range of speeds.

Cast in lead, a 1:2 ellipse is close enough to "dragless" thrown point first that further improvements need to be pretty significant to add more than a meter or two. They also fit nicely into a "traditional" pocket. Any longer and you have to worry about presenting even a tiny edge-on angle (which a spin-stabilised glans will do through the final part of arc). Using fins adds drag, but should keep the glans pointed forward (for longer shapes, which again have more area). They also need to be released with little or no spin, or if spiralled, exactly the right amount of spin.

Matthias
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Re: Optimum Shape for Range
Reply #9 - Sep 12th, 2006 at 3:49pm
 
Matthias is right.  And perhaps one of the foremost contributing factors in Engvall's triumph over Bray's record was the fact that more of his energy went into enhancing velocity as none need have been traded to achieving spin stabilization.


On a side note, I heard back from Guiness and the internet must have really pinched their market....as they seem to be a 'shadow' of their former selves and appear uninterested in our sport.  That is unless one is willing to use all natural materials, ammo included.


Interestingly, their requirements say absolutely nothing about prevailing wind direction and speed for the attempt.....!


Ratio of mass density to drag profile is of paramount imoportance to achieving maximum distance, which is why I sometimes use 1/4" Tungsten rod for extreme distance exercise.


Also, regarding fin stabilized ammo (and perhaps even spheroid shapes employing the overhand cast)....an excellent way of adding velocity is to control the timing and release angle such that the dart is made to slide forward along an arcuate contributor mass at the moment of release.


Similar in principle to this example:


...



TS
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Re: Optimum Shape for Range
Reply #10 - Sep 12th, 2006 at 8:57pm
 
Tungsten is the right choice for the best density since depleted uranium is rather difficult to aquire. Lead is very nearly as good without the cost of tungsten.
Perhaps you would share some of your distance and shape data.
It is obvious that a traditional shape is way down on the scale of things aerodynamic.

Bombs are much less dense than lead shapes. Aerodynamic shapes scale down quite well, rest assured they don't test full sized aircraft in wind tunnels.
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Re: Optimum Shape for Range
Reply #11 - Sep 12th, 2006 at 9:58pm
 

Lead is great!....However Tungsten, nearly twice as heavy as lead, performs appreciably better for extreme distance exercise.


TS
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Re: Optimum Shape for Range
Reply #12 - Sep 12th, 2006 at 10:28pm
 
Tungsten at 19.3 g/cc is almost twice the density of lead at 11.34 g/cc. You won't be casting it, machining can be difficult and it isn't exactly cheap. For an all out effort it would be the way to go.

What would the ideal shape be?
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Re: Optimum Shape for Range
Reply #13 - Sep 13th, 2006 at 1:48am
 
Generally speaking, spinning ammo will benefit from a shape that makes use of the high RPMs to offset drag.  Non spinning ammo benefits from presenting a lower surface area at the nose and tail as well as not having to spin in the first place.


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Re: Optimum Shape for Range
Reply #14 - Sep 13th, 2006 at 3:16am
 
How about gold?  Isn't it even heavier than tungsten?

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