Curved or Straight Blade?

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Re: Curved or Straight Blade?

Postby admin » 11 Oct 2012 10:42

I just wrote a long post and the forum swallowed it. :roll:
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Re: Curved or Straight Blade?

Postby admin » 11 Oct 2012 10:57

To summarise - yes, curved blades don't seem to 'wobble' as much as curved ones. I don't know why, maybe something to do with oscillation waves travelling in straight lines more easily etc?

Curved blades do enter the target at a more slanted angle, ie. less friction entering. But I agree that in many cases this difference may be very marginal.

I think that it is more significant to mention that curved blades free themselves from the target more easily - this is more or less irrelevant to parts that are completely bisected, like a neck or wrist, but if only slicing part of the way into a target, such as a thigh or torso, then having gone some way into that target the blade will have to be drawn out of it - curved blades do this more naturally as they follow the arc of motion.

Really curved swords are poop for thrusting. Yes you can do some funky angled thrusting with them, but many of these thrusts are without blade opposition and therefore uncovered (I would say unsafe). Thrusting with a curved blade also has the tendency to wrench the hilt in your hand because the energy is send out sideways. By and large I would say that straight or nearly straight swords are far better for someone intending to thrust much. It is well documented that Asian cavalry with curved swords presented the curve of the edge rather than the point in a charge. So the impact with result in a long slice rather than a point.
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Re: Curved or Straight Blade?

Postby Reinier » 11 Oct 2012 13:06

admin wrote:Yes you can do some funky angled thrusting with them, but many of these thrusts are without blade opposition and therefore uncovered (I would say unsafe).


From my understanding of rapier fencing I really agree with this (I did not want to derail the topic for this though).

What I gathered is that curved blades can be thrust well with, so long as their point falls on the line of the hilt.
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Re: Curved or Straight Blade?

Postby Andreas Engström » 11 Oct 2012 15:44

A curve of about 2-3 cm IMHO is enough to significantly open new possibilities while retaining decent thrust mechanics (and of course I agree that the point should be in line with the handle).

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Postby Ulrich von L...n » 12 Oct 2012 06:55

Andreas,

How do you measure a blade curvature? Is there a standard way of measuring it?

sword_curvature_a.jpg
sword_curvature_a.jpg (16.15 KiB) Viewed 14168 times

So A or B?

PS.
I have used a drawing by Tomas Eriksson (Stockholm, Sweden) from swordforum.
... well, I´m sitting here with a reference book about Swedish swords. It is full of pictures and measures. I try to identify my own old cutlasses against those references, but since some models look identical and only differ in blade length and curvature, and the book does not specify how the measures are taken, well it is not very easy.
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Re: Curved or Straight Blade?

Postby Andreas Engström » 12 Oct 2012 07:27

Yes, that's the measurement I meant. In Swedish it's called "pilhöjd" (arrow height) for some reason. Put simply, if you rest the back of the blade on a table, what's the greatest width of the space between the table top and the back of the blade?

It's a bit of a simplistic measure since it doesn't take into account where on the blade the curve starts and ends, nor whether the point is aligned with the hilt(and if not, how much it deviates).

Good enough for most common western sabre models, though.

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Re: Curved or Straight Blade?

Postby admin » 12 Oct 2012 10:24

Andreas Engström wrote:Yes, that's the measurement I meant. In Swedish it's called "pilhöjd" (arrow height) for some reason.


It's called that ("brace height" in English) because with a bow it is the furthest distance between the bow and the bowstring when the bow is strung. In this case the blade becomes the bow and the line (or table) the string.
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Re: Curved or Straight Blade?

Postby Andreas Engström » 12 Oct 2012 12:37

admin wrote:It's called that ("brace height" in English) because with a bow it is the furthest distance between the bow and the bowstring when the bow is strung. In this case the blade becomes the bow and the line (or table) the string.

Makes sense. Should have realised it on my own. :-)

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Re: Curved or Straight Blade?

Postby Mink » 12 Oct 2012 17:42

It's the same for japanese blades, the length in question is called sori. Interestingly they also have different terms depending on where the curvature occurs, towards the tip, the hilt or the center, which start to address Andreas' second point.

Good catch on etymology, in French it's called "la flèche" (literally "the arrow") and I never actually realised that this length is indeed just where the arrow would sit :)

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Re: Curved or Straight Blade?

Postby CaptainAbrecan » 12 Oct 2012 20:59

Maybe it's just the draftsman in me (I consider this supreme advantage here :mrgreen: ), but the nature of any edge contacting that round circle in the diagram, the edge is always going to be perpendicular to the center, just not to you. The angle of the curved sword is the same as the dotted line, if you rotate the diagram.

The proportion of the blade moving through the circle is actually larger in the curved sword than in the straight one, which creates more resistance. But the curved sword presents the cross-section in an oblique manner, which creates less resistance. It probably comes close to cancelling out in the end, with variables such as the cross section and such being the same.

http://i.imgur.com/qSJyj.png

I made a diagram to show what I mean. Look at the green lines, which are tangent to the blade (I traced a google search image of a albion regent for this and scaled it to match the other image). The green line is always perpendicular to the center, because the shape is a circle. The angle doesn't matter at all on circular targets (which is all we are concerned about; limbs, torsos, target fodder).

The only advantage the curved blade has, is that the blade profile is oblique because the green line is not vertical like the dashed yellow line. But the curved blade also puts more material through the target (because shortest distance between two points is always a straight line, no?). So it cancels out, IMHO.

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Re: Curved or Straight Blade?

Postby Mink » 12 Oct 2012 21:46

You forget the speed in your analysis, I think. The speed of the edge is tangential to the blue arrow, horizontal in your diagrams in both cases. The advantage of the curved sword lies in the fact that the speed of the edge at the point of contact is at an angle, unless a specific technique is employed with the straight sword of course. In effect it's as if the edge was pulled along the target, instead of just being pressed into it, which is more efficient on some targets.

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Re: Curved or Straight Blade?

Postby admin » 12 Oct 2012 21:57

CaptainAbrecan wrote:the edge is always going to be perpendicular to the center, just not to you.


Only one point of the edge. A portion of the edge will contact the target, not just one point. The curved edge therefore acts as a different cross-section to the straight edge - the straight edge will act in the same way at any point on that portion in contact with the target, the curved edge in contrast curves away from that perpendicular point.
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Re: Curved or Straight Blade?

Postby CaptainAbrecan » 13 Oct 2012 07:41

Shit this is a lot more complicated than I thought.
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Re: Curved or Straight Blade?

Postby Herbert » 13 Oct 2012 08:52

You seem to assume a hacking motion where the blade enters in a straight line.
As every one of you knows, a good cut is done with a cutting motion, a pulling or pushing of the blade.
This alters the whole thing, especially regarding the angles.

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Postby Ulrich von L...n » 13 Oct 2012 09:57

Andreas Engström wrote:...Put simply, if you rest the back of the blade on a table, what's the greatest width of the space between the table top and the back of the blade ...

So definitely variant A.
And additionally a fascinating piece of historical etymology: sori, brace height, la flèche, pilhöjd.
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Re: Curved or Straight Blade?

Postby admin » 13 Oct 2012 16:42

Herbert wrote:You seem to assume a hacking motion where the blade enters in a straight line.
As every one of you knows, a good cut is done with a cutting motion, a pulling or pushing of the blade.
This alters the whole thing, especially regarding the angles.


This is irrelevant to the point above Herbert :). The cross-sectional area passing through the target is still different if the same blade is made curved.
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Re: Curved or Straight Blade?

Postby John H » 13 Oct 2012 18:59

Herbert wrote:You seem to assume a hacking motion where the blade enters in a straight line.
As every one of you knows, a good cut is done with a cutting motion, a pulling or pushing of the blade.
This alters the whole thing, especially regarding the angles.

Herbert


Actually that’s kind of the point of a curved blade. To create a nice clean cut with a strait blade I need to push, pull in the process, I trust I don’t need to go into that you seem to grasp it fully. This takes technique and is something you must be trained at. With a curved blade the process of drawing the blade across the target like you do in the push pull process can be accomplished by a ‘hacking’ cut.

When giving the blade to an untrained person who has no understanding of a push/pull technique the curved blade with act in their instinctual hacking cut.

Back to usage, the curved blade is almost always an artifact of a light cavalry weapon, then adopted for foot. When striking an opponent while moving on a horse the ability to accomplish a push/pull slicing cut is going to be considerably diminished. If you just held a curved blade sideways and galloped past, you will get a better cut than you would if it was a strait blade. Here’s the old SFI article on Cavalry swords, the beginning has their explanation of how the cuts are different with strait and curved blades.

http://www.swordforum.com/forums/conten ... artin-Read

As I also use a Rapier quite regularly, I’ll state that if I am going to be thrusting I’ll pick a strait blade any day, while if cutting I’ll take a curved blade.
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Re: Curved or Straight Blade?

Postby Herbert » 13 Oct 2012 20:05

Hmm... I start to get convinced.
Or to put it in other words:
Now that the statements got cleared and the parameters set, I tend to agree.

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Re: Curved or Straight Blade?

Postby Chidokan » 11 Nov 2012 01:05

A curved blade used close in gives a nasty wound if thrust horizontally.... far worse than a flat blade, as you open the wound up to the width of the blade, the more goes in to the top of the curve the bigger the hole you make. This is how I use a japanese blade, not just 'poke it' to keep the entry wound small as it were...then twist and cut it out, which makes an even bigger mess...

There used to be an interesting youtube video of a guy trying to make a banana, (I will have to try and find it again), but basically he found it hard to control the shape during forging as flattening only one edge would cause the blade to twist all over the place. Quite funny to watch him trying to control the thing! :D
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Re: Curved or Straight Blade?

Postby admin » 12 Nov 2012 08:54

Whilst you certainly could make a massive hole like this, it means your weapon is spending a long time inside the opponent, during which time you can't use it for anything else, such as defending yourself from an afterblow or another opponent. Many soldiers are recorded as being killed for this reason - see D A Kinsley's books.
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