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Pat Kilbane
Location: Los Angeles, CA Joined: 09 Apr 2014
Posts: 5
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 Posted: Wed 23 Apr, 2014 3:07 pm Post subject: Calculating a Sword's "Swing Weight" |
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I've read that experts in baseball mechanics use the term "swing weight" to describe the perceived weight of a bat independent of its actual mass. Two bats with the same mass but with varying weight distribution have different moments of inertia (MOI), and will therefore swing "heavier" or "lighter" than each other.
I thought it would be a helpful shorthand if the same term were used for swords and other hand weapons. Swing weight describes a weapon's handling much more specifically than simple weight or POB.
Here are some weapon swing weights I calculated based on their MOI as compared to a 32 oz major league bat:
Albion Swords Hersir Viking: 19.21 oz.
Angus Trim 1508: 20.01 oz.
Arms & Armor Iberian Mace: 28.43 oz.
Arms & Armor Nordland Axe: 13.56 oz.
24" 16oz Nylon Police Baton: 5.18 oz
Any thoughts?
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Mark Moore
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| Posted: Wed 23 Apr, 2014 3:46 pm Post subject: |
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I find this interesting. I know one fact. There is a near 0% chance of swift recovery swingin' my Hanwei claymore. In other words....Don't stand behind me. I believe it weighs a little over four pounds....could be wrong. Maybe more. Beast of a sword. I'd like to know the actual PSI different swords deliver, as well as their actual speed at impact.  ......McM
''Life is like a box of chocolates...'' --- F. Gump
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Timo Nieminen
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| Posted: Wed 23 Apr, 2014 3:47 pm Post subject: |
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Could just give the MoI, rather than comparing with a "standard bat". Any of oz.inches^2 or lb.feet^2 or kg.m^2 should do.
MoI about what point? Usually, if one gave MoI without any information about what point, it would be assumed to be about the centre of mass. But a more useful default for a sword is about the grip. But mid-hand, or top-of-hand, or what?
Vincent Le Chevalier gives his MoI data as "dynamic length" and "blade weight" in hist article http://www.myArmoury.com/talk/viewtopic.php?t=21670 ; these have the advantage of us being more familiar with lengths and weights than quantitative measures of MoI. The disadvantage is that calculation is required to compare MoI of different swords based on these figures. Your comparison with the "standard bat" has the same advantage of familiarity, without requiring any further calculation for comparison.
"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Pat Kilbane
Location: Los Angeles, CA Joined: 09 Apr 2014
Posts: 5
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| Posted: Wed 23 Apr, 2014 4:10 pm Post subject: |
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| Mark Moore wrote: | | I'd like to know the actual PSI different swords deliver, as well as their actual speed at impact. ......McM |
If you have the length, weight, POB and COP of the weapon, I can give you a pretty close approximation on tip velocity, velocity at COP, effective mass at COP and the resulting pounds force of impact.
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Pat Kilbane
Location: Los Angeles, CA Joined: 09 Apr 2014
Posts: 5
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| Posted: Wed 23 Apr, 2014 4:21 pm Post subject: |
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| Timo Nieminen wrote: | | MoI about what point? Usually, if one gave MoI without any information about what point, it would be assumed to be about the centre of mass. But a more useful default for a sword is about the grip. But mid-hand, or top-of-hand, or what? |
I doubt I have the experience you do, but I'm a fan of using the point beneath the middle of the hand for one-handed weapons and the middle of the top hand for two-handed weapons. That point coincides with the axis of rotation of the vertical flexion of the wrist. Baseball studies have shown that before ball impact the arms are still swinging for a fraction of a second after the wrists are fully extended, meaning that the true axis of rotation is some inches beyond the bottom of the bat handle. Not so easy to test your COP from that point, though.
| Timo Nieminen wrote: | | Vincent Le Chevalier gives his MoI data as "dynamic length" and "blade weight" in hist article http://www.myArmoury.com/talk/viewtopic.php?t=21670 ; these have the advantage of us being more familiar with lengths and weights than quantitative measures of MoI. The disadvantage is that calculation is required to compare MoI of different swords based on these figures. Your comparison with the "standard bat" has the same advantage of familiarity, without requiring any further calculation for comparison. |
That looks like an interesting read... thanks! Yeah, saying that a sword has an MOI of .18 kgm^2 takes some getting used to.
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Pat Kilbane
Location: Los Angeles, CA Joined: 09 Apr 2014
Posts: 5
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| Posted: Wed 23 Apr, 2014 5:33 pm Post subject: |
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| Mark Moore wrote: | | Beast of a sword. I'd like to know the actual PSI different swords deliver, as well as their actual speed at impact. ......McM |
Hey Mark, here's what I came up with based on the numbers at KnifeCenter.com. They listed the COP at a dubious 31" on the 41" blade, so the starting data may be suspect. Here is that link:
http://www.knifecenter.com/item/CISH2060N/cas...more-sword
And here are the resulting numbers:
Effective Mass at COP: .65kg (22.9oz)
Velocity at COP: 24m/s (53.7mph)
Tip Velocity: 29.1m/s (65mph)
Avg. Impact Force: 13,635N (3068 lbs force)
Peak Impact Force: 27,270N (6136 lbs force)
Note that the "pounds force" measurement of impact is not the same as pressure, which is measured in lbs/in^2. To go from force to pressure, you'd have to know how much of the blade was in contact with the target.
6138 lbs of peak force is huge for a sword! It's as much as a baseball bat, which is tough to do considering a bat has a proximal taper.
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