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Post by ranstone on Jul 4, 2023 5:33:37 GMT
It's a really, really, really old and over done topic, exhausted to ad-nauseam.
Are there potential physics-based cutting advantages/disadvantages to curved blades?
Now, before anyone jumps to correct me, I'm aware this is SBG, not Reddit. We're all educated enthusiasts here, and facts such as ergonomics dictating a curve of a blade, as well as bio-mechanics (Especially with cavalry sabers), manufacturing, or even culture.
Those topics have been covered hundreds of times, and I wouldn't waste your time with such overly-discussed points.
What has given me a brain itch that I can't quite scratch actually came from aero engineering.
Here's what I'm thinking, and I'd love to hear you input.
The Center of Mass of a curved sword is in front of it's center of drag, assuming the edge is on the convex side. This defies everything I know about energy-efficient geometry and fluid dynamics. In planes, like an arrow, you want your center of drag behind your center of mass for stabilization, however, conversely, my mind plays with the idea that drag and mass is irrelevant at the speed of a cut, and a convex curved blade having it's center of mass behind it's point of impact, turns the point of impact into a 2nd class lever; requiring more force to move the center of mass, as it's farther away form where the potential inaccurate edge alignment is applying torque.
If this is boring as hecc, or I'm over-complicating a really over-discussed topic, my apologies. I have been thinking about this a lot lately, and my physics brain isn't comfortable with the current explanations I see colloquially thrown around the sword community, to support, or to deny advantages or disadvantages of curved swords.
Regardless, it is 1:30AM here, and this is what my physics loving, sword enthusiast brain does to me when I can't sleep. If you have anything to add, or think I missed something, or simply think I have no idea what I'm talking about, please share. I'd love to learn, and scratch this brain-itch.
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Post by treeslicer on Jul 4, 2023 5:56:24 GMT
It's a really, really, really old and over done topic, exhausted to ad-nauseam. Are there potential physics-based cutting advantages/disadvantages to curved blades? Now, before anyone jumps to correct me, I'm aware this is SBG, not Reddit. We're all educated enthusiasts here, and facts such as ergonomics dictating a curve of a blade, as well as bio-mechanics (Especially with cavalry sabers), manufacturing, or even culture. Those topics have been covered hundreds of times, and I wouldn't waste your time with such overly-discussed points. What has given me a brain itch that I can't quite scratch actually came from aero engineering. Here's what I'm thinking, and I'd love to hear you input. The Center of Mass of a curved sword is in front of it's center of drag, assuming the edge is on the convex side. This defies everything I know about energy-efficient geometry and fluid dynamics. In planes, like an arrow, you want your center of drag behind your center of mass for stabilization, however, conversely, my mind plays with the idea that drag and mass is irrelevant at the speed of a cut, and a convex curved blade having it's center of mass behind it's point of impact, turns the point of impact into a 2nd class lever; requiring more force to move the center of mass, as it's farther away form where the potential inaccurate edge alignment is applying torque. If this is boring as hecc, or I'm over-complicating a really over-discussed topic, my apologies. I have been thinking about this a lot lately, and my physics brain isn't comfortable with the current explanations I see colloquially thrown around the sword community, to support, or to deny advantages or disadvantages of curved swords. Regardless, it is 1:30AM here, and this is what my physics loving, sword enthusiast brain does to me when I can't sleep. If you have anything to add, or think I missed something, or simply think I have no idea what I'm talking about, please share. I'd love to learn, and scratch this brain-itch. Generally, with a curved blade, you cut by slicing, not chopping. The curve assists a circular slicing cut.
Also, lift is irrelevant, and so is drag, when using a sword. Think of it as being a symmetrical airfoil with "relaxed static stability", operated at an AOA of zero degrees, with its attitudinal stability maintained by the flight control computer between your ears.
BTW, as my avatar should clue you, you're probably in the wrong subforum to discuss curved blades, anyway.
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Post by ranstone on Jul 4, 2023 23:46:15 GMT
"lift is irrelevant, and so is drag" I definitely didn't mean lift, if I said that, I was absolutely wrong. Drag is a absolutely relevant however. That was the whole foundation of my post. Angle of attack is never 0 degrees, and any offset you have will be exacerbated when it goes through a denser target, like tatami mat.
The farther back the center of mass is from the point it impacts (Center of drag) the more force is required for the tatami matt's mass to exacerbate the sword's angle. What I'm unsure of is if this would increase or decrease the stability while passing through mass.
Since you understand relaxed stability vs static stability, TLDR: Is there physical, mathematical evidence that having the center of mass behind the center of drag (which inherently is relaxed stability.) is enough to have noticeable, perceivable effects when cutting.
Also, if I am in the wrong sub-forem, please explain why. As you can see from my post count, I'm not a long term user, and after re-reading my post, I don't understand how this does not apply to medieval swords.
Thanks for replying!
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Post by treeslicer on Jul 5, 2023 3:10:58 GMT
"lift is irrelevant, and so is drag" I definitely didn't mean lift, if I said that, I was absolutely wrong. Drag is a absolutely relevant however. That was the whole foundation of my post. Angle of attack is never 0 degrees, and any offset you have will be exacerbated when it goes through a denser target, like tatami mat. The farther back the center of mass is from the point it impacts (Center of drag) the more force is required for the tatami matt's mass to exacerbate the sword's angle. What I'm unsure of is if this would increase or decrease the stability while passing through mass. Since you understand relaxed stability vs static stability, TLDR: Is there physical, mathematical that having the center of mass behind the center of drag (which inherently is relaxed stability.) is enough to have noticeable, perceivable effects when cutting. Also, if I am in the wrong sub-forem, please explain why. As you can see from my post count, I'm not a long term user, and after re-reading my post, I don't understand how this does not apply to medieval swords. Thanks for replying! Drag before target impact is negligible, and what you have after impact isn't drag, it's friction. If there is turbulence, you'll get a little tachikaze, but the energy losses are minimal. I mentioned lift because it's coupled to drag in the math for subsonic flows. BTW, if you are worried about aerodynamic drag, you might try engraving an experimental saber with riblets.
If AOA is not equal to zero when you swing a curved blade at a target, you are doing it wrong. This goes absolutely for katana, BTW.
The trajectory of the blade through the target is nonlinear, and does not lend itself to trivial calculation or analysis, particularly because it is continuously modified by the person swinging the sword. You do it right instinctively after practicing thousands of cuts.
I previously explained succinctly what the curvature is good for.
The "medieval swords" (all of them Migration, Viking, or Oakeshott this-or-that reproductions, with the odd messer thrown in) discussed on this site have straight blades. Japanese, Chinese, Other Asian, and military swords, which may be curved, have their own sub-forums.
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Post by durinnmcfurren on Jul 7, 2023 19:00:37 GMT
Once the edge bites into the target, any tendency of the blade to turn is going to be counteracted by the fact that the blade is slicing through the target and it would take substantial torque to turn it. So I don't think the fact that the CoD is front of the CoM is going to matter at all. As long as the cut starts, the blade will tend to follow that direction of cutting. Try pushing a blade partly into a cutting target, then try twisting it. It's not easy. Plus your hands will tend to keep it angled.
There were some medieval curved falchions and messers I believe, though that is not my particular area of focus. A curved blade seems to make slicing cuts easier, from what I understand.
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Post by ranstone on Jul 8, 2023 2:16:37 GMT
durinnmcfurren Definitely agree on the twisting inside a material thing. That makes a lot of sense. treeslicerI do appreciate your input, but some of the things you have said lead me to the conclusion you may have jumped to some preconceived conclusions about me,(Mentioning Katana, saying i'm in the wrong forum, ect. You know what I'm getting at.) or might not understand what I was asking. I only am really interested in European swords, and the vast popularity of curved European swords is what inspired this topic. The question was if the change in the center of mass further back or forward give noticeable differences. I work with some pretty fun stuff, and lengthening the bullet in modern ballistics absolutely causes the bullet to tumble only once it's entered a target, once the center of drag becomes significant upon entering a target. (I had a round do a 90 degree turn when passing through some experimental armor once.) I was just wondering if anyone had actually crunched the numbers before to see if this worked with low velocity blades. Anyway, this thread has inspired me to crunch the numbers myself, once I find time. Once I do, I'll link the data here, or explain where to find the info (No outside links, I know mods.). I'll keep y'all posted!
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Post by treeslicer on Jul 8, 2023 4:13:30 GMT
treeslicer I do appreciate your input, but some of the things you have said lead me to the conclusion you may have jumped to some preconceived conclusions about me,(Mentioning Katana, saying i'm in the wrong forum, ect. You know what I'm getting at.) or might not understand what I was asking. I only am really interested in European swords, and the vast popularity of curved European swords is what inspired this topic. The question was if the change in the center of mass further back or forward give noticeable differences. It's not like a ballistic trajectory or an aerodynamic-flight problem because the sword remains continuously under control of your arm, and the sensations felt by your hand and arm are providing a feedback loop to enable continuous corrections, within a frame dominated by visual inputs. I referenced the RSS case to give you a cue that the physics is being overridden by the control system. It being a low energy (low speed) situation with an effectively small area and low aspect ratio, the physical inputs, other than your grip, your swing, and your pulling during impact to create the slice, are negligible.
The ballistic case that you reference has much higher magnitude deflection forces present due to the high (supersonic) velocity and rapid rotational rate of the bullet. There is a lot of vee-squared and omega going on there, which aren't affecting the sword (and it isn't rotating to begin with, so you can't have a gyroscopic deflection like the one you saw; that was bullet wobble).
BTW, the curved geometry is already optimized to deliver a slicing cut tangential to the edge curve (which is much more efficient than chopping with the COP). The slicing cut is a controlled evolution executed by overriding the static balance of the weapon by brute force, of which there's a huge surplus. The amount of force you can supply to the sword without straining yourself, is considerably greater than the inputs from balance or aerodynamics caused by the curve, and so the blade path is unaffected by them, and you deliberately hold the AOA at zero. The slice proceeds without interference at 90 degrees to the path vector. There's your answer, the change in center of mass doesn't matter.
Have you ever noticed that the part of a katana that delivers the damage is the foible? It delivers it very efficiently despite this, because it's done by slicing, not impact. You can achieve the same effect with a sufficiently sharp saber or other curved sword.
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Post by durinnmcfurren on Jul 8, 2023 21:15:54 GMT
The question was if the change in the center of mass further back or forward give noticeable differences. I work with some pretty fun stuff, and lengthening the bullet in modern ballistics absolutely causes the bullet to tumble only once it's entered a target, once the center of drag becomes significant upon entering a target. (I had a round do a 90 degree turn when passing through some experimental armor once.) I was just wondering if anyone had actually crunched the numbers before to see if this worked with low velocity blades. Anyway, this thread has inspired me to crunch the numbers myself, once I find time. Once I do, I'll link the data here, or explain where to find the info (No outside links, I know mods.). I'll keep y'all posted!
A bullet is very different than a sword, in part because it doesn't have a sharp cutting edge guiding it. Also because as Tree said, you're guiding the sword still. But even without this, I think a blade entering a solid material will tend to follow the slice it makes. I'm thinking of throwing blades, for example. There, the com is definitely behind the cod, but they don't twist. Bullets don't create neat slices (in fact the terminal ballistics of a bullet are a weird and fascinating thing) and they aren't super sharp, they use their very high velocity to just hammer their way in.
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mrstabby
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Post by mrstabby on Jul 9, 2023 6:59:45 GMT
A blade, depending on stiffness, might also do weird stuff. It will have some wobble when impacting, this can steer a blade unpredictably. A blade that is wider with only a single edge can right itself without input to a higher degree, like a rudder in water, it is most likely also stiffer than a similar sized double edged blade. Also what makes a blade a good cutting implement also makes for less drag and no lift. There should not be lift with a well made symmetrical blade, it should want to slice straight.
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Post by ranstone on Jul 10, 2023 1:44:18 GMT
mrstabby Definitely! I don't think I said lift for this exact reason.
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larason2
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Post by larason2 on Jul 24, 2023 0:11:00 GMT
I talked about this in another forum post. A sword cuts in two ways. For slicing, the relevant force is parallel to the length of the blade, since it is the operator pulling the sword and the micro serrations of the blade that are therefore cutting the material being cut. For standard cuts, the relevant force is perpendicular to the length of the blade, and depends on how keen the edge is vs the resistance of the material that is directly contacting the end of the blade.
Since force is mass x acceleration, and mass can be thought of as constant for two swords, one curved and the other straight, of the same mass, then the acceleration depends on the torque being applied to the sword by the user, the point of the blade which contacts the target, and the resistance of air to the passage of the sword through it.
Now, the force of air resistance depends on the density of the air x the drag coefficient x the area, all over 2, x velocity squared. I would assume the coefficient of drag for a curved sword is lower than the coefficient of drag of a straight sword, just like a plane with swept back wings experiences less drag than a plane with straight wings. So all else being equal, the potential force being transmitted can be higher for a curved sword, however the direction of the force due to drag is perpendicular to the blade length, so it would only increase the potential force of a standard cut.
That being said, most cuts with a curved sword like a katana involve both slicing and cutting motions. So in theory, a curved sword can potentially cut better, all else being equal. This is assuming though, that the user swings both the straight sword and the curved sword the same way (slices with both), since a technique that is not slicing at all can potentially have more force than one that slices and cuts at the same time devoted just to cutting. I would think the effect of drag would be pretty small though, since the difference in the coefficient is likely to be pretty small. So all things told, even though there can potentially be a difference, I would think it's small, and maybe not noticeable.
Stabilization doesn't have much to do with a cut, because as has been said before, the accelerating force is controlled by minute adjustments over the course of the swing of the sword by our muscles in constant communication with our cerebellum and our motor cortex. You would expect someone who has a cerebellar injury to have a shaky sword swing. How shaky it is depends also on the geometry of the sword, with some swords being more shaky than others. For this, the centre of mass relative to the centre of drag matters, but for most sword users with a functioning cerebellum, it probably doesn't matter much.
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Post by toddstratton1 on Jul 24, 2023 4:18:22 GMT
I find katanas are a lot easier to cut with than Long swords. But that might be due to my lack of experience in cutting with double edged swords compared to my more involved training with Kenjutsu. I feel there is more going on there than just it being curved though. The curve doesn't fix bad edge alignment like some theorize how a curved sword is a better cutter since gravity can make it fall on its edge. That doesn't apply when you're gripping it in your hand. Katana are more generally forward blade heavy and the geometry of being single edged also seems to help in making cuts easier. I have a Principe though and that thing can cut better than a lot of Katana. Same with my Matuez Sulowski sword which I actually suspect may be even more superior to the Principe. But too expensive to cut with lol. sulowskiswords.com/types-xvxva-xvixvia/for-sale-type-xvia-big-version/
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