The real advantage of undulating blades !

[Roy Robinson Stewart]

There has been much discussion in sword collecting circles about the possible function of the undulating flame like blades found on some swords. The theories suggested usually concentrate on possible advantages in cutting via a 'bread knife' effect due to the serrations, but practical cutting tests have not shown that there is any such advantage.

Now that we are aware of the properties of leading edge tubercules, it is clear that a sword blade with such a shape will have aerodynamic advantages.

More here: http://olosurfer-woodensurfboardsatpipeline.blogspot.com/2010/06/undulating-flame-blades-and-whale.html

[Sal Bertucci]

Very logical and well thought out. Now we just need to convince some poor Engineering Masters Student to test it and see if it works

Very cool!

[Vincent Le Chevalier]

I'm not convinced yet...

The tubercules you show on the rest of your pages are a lot bigger and make for a greater change in properties. On blades the modification seems ordinarily less dramatic.

Also, I'd like to see a hard figure on the relative importance of aerodynamic effects on sword handling. My starting hypothesis is that they are really small compared to the effects of mass and possibly elasticity. I certainly never felt that a sword had too much drag, even with wooden swords...

Regards,

[Roy Robinson Stewart]

Thankyou Sal

Vincent regardless of the specific size of the tubercules they will still improve the aerodynamic properties of sword blades , just as they do for wind turbine wings. The size of the tubercules is not critical.

Long wide blades which are swung swung fast inevitably experience times when they stall during quick redirections, this can be felt and it definitely slows the blade down and reduces control. The ability of a blade to handle an increase in the angle of attack of 30% is a big advantage as the blade will turn much more quickly. It will also help to reduce the speed inefficiency caused by misalignment during a cut.

This won't be felt anywhere near as much with narrow more thrust orientated blades, nor will it be noticed as much in dealing with a single opponent, when compared with the more continuous circular movements required for control of a 360 degree area.

Wide thin cutting blades are just like wings with very low chord ratios in that they only accept a narrow range of angles of attack. Wide cutting blades have very low chord ratios around 6 percent, making high speed maneuverabilty a definite issue.

In broad terms the undulations can increase overall efficiency by up to 20 percent, that's a huge increase and would not only be felt in increased speed and maneuverability but also as less of an energy drain on the wielder of the sword, which could be significant during long battles.

The fact that the sword undulations have rounded sine curve like tips rather than pointed serrations also points to aerodynamic efficiency as the goal rather than the 'bread knife' cutting effect sometimes put forward as their reason for being.

By the way it's also the case that blades with spatulate tips generate much less tip drag than pointed blades. Tip vorteces contribute a large proportion of the overall drag produced by a wing.

So, in addition to giving the sword a longer cutting reach, the spatulate tip reduces drag and thus increases blade speed. This is even more the case because the tip is the part of the blade which is travelling the fastest and thus produces proportionally the most drag.

As has been noted countless times by RMA practictioners and ARMA scholars, sword makers were far more knowledgable than
has been commonly supposed in recent times, and in my opinion the undulating blades are another example of their enlightened creativity and practicality.

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[Vincent Le Chevalier]

Vincent regardless of the specific size of the tubercules they will still improve the aerodynamic properties of sword blades , just as they do for wind turbine wings. The size of the tubercules is not critical.

The absolute size no, their size relative to the width of the sword may. From what I read these things work because of the vortices generated downstream on the wing, but if the object is not so wide it's not obvious that it work nearly as well.

And even if it did work it would have no bearing on whether or not drag, lift or other aerodynamics properties have a significant impact on sword performance (in air). I'm sure there are formulas somewhere to estimate drag power, let's see what that gives at sword cut speeds. My gut feeling from sword handling is that the power needed to overcome drag is a very tiny fraction of the power needed to accelerate the sword around, therefore trying to reduce it would be a bit pointless.

Regards,

[Roy Robinson Stewart]

Thankyou very much for your thoughts Vincent

The benefits will be much less with the kind of movements used in typical longsword sparring with a single opponent, than with those used to control a 360 degree space containing multiple opponents, using a very long wide bladed sword.

The aerodynamic effects of the undulations are unavoidable. . . one can't introduce that sort of change to a blade without significant effects.

A possible 20% increase in aerodynamic efficiency is a major advantage, and I'm 100% sure that such an advantage is what the swordmakers intended.

Stall reduction is also useful. A stalled cutting blade is like a big paddle. . . a very inefficient and high drag producing object. Increasing the angles of attack the sword can accept without stalling by 30% is definitely useful.

There's also nothing in the proportions of the blades and undulations compared with other applications which suggests that the effect won't work, nor any theoretical basis for such a theory, as far as I know.

One thing is certain, and that is that the undulations are not just decoration. That leaves only two possible purposes which I can think of: increased efficiency during impact or increased efficiency prior to impact, (or both) . Looking 'cool' isn't an option.




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[Corey Roberts]

Interesting theory, I like your thinking but am not yet wholly convinced. One of the reasons it isn't totally working for me, is I do not believe true two-handers were ever used in wide 360 degree sweeping circles like some sort of wushu competition. Certainly large wide swings are sometimes made, but the fighter is not going to be continuously "flying" the weapon around his body. Swords are subject to constant accelaration and sudden deceleration that to me precludes much lift generation. Additionally, my understanding of Bernouli's principle (which may be flawed, I dont' have much of a physics background if any) is that wings generate lift due to air flow being faster over one side than another, being that one side of a sword blade is not substantially mure curvi-linear than another, lift generation on sword blades seems unlikely as they are not particularly "wing shaped". Additionally, your theory does not really set forth why it is some thrust-centric blades such as rapier's sometimes featured this blade form. The wavy or flame bladed style is sometimes even found on daggers, and even plug-bayonets of the 17th century which under no circumstances are used in a swinging or wooshing manner that would generate any significant lift or "flight-like" properties. I think the jury is still out on this one.

[Vincent Le Chevalier]

One thing is certain, and that is that the undulations are not just decoration. That leaves only two possible purposes which I can think of: increased efficiency during impact or increased efficiency prior to impact, (or both) . Looking 'cool' isn't an option.

Why is that? What's wrong with looking cool ?

I've plugged some numbers in the wikipedia formula for drag power:

P = 1/2 rho C A v^3

taking
rho = 1 kg/m^3 (air)
v = 20 m/s (probably near the top speed during a cut)
A = 0.5 m x 2.5cm (assuming the blade is flat-on, and considering only the fastest 50cm)
C = 2 (pretty much the worst case of a big paddle)

I find P = 100W.
Well, wikipedia (again) tells me that 100W is he order of magnitude of the basal metabolic rate for a human (the power you consume when you're not doing anything). Now consider how much power you consume through sword handling, possibly ten times more, probably a hundred times more. Now relate that to the 100W found in the worst case of literally cutting at full speed with the flat. Frankly, given these orders of magnitude, I don't think getting less drag is a priority...

Regards,

[Roy Robinson Stewart]

Hi Vincent.

You suggest that the maximum amount of energy consumed by a person during sword handling could be up to 10,000 watts or 13.4 horsepower.

I don't have figures for the energy consumed by an adult during exercise but the sustained power output which an adult male can produce in a variety of full body exercise is less than one horsepower or 745 watts, and is typically less than half a horsepower or about 375 watts.

Now, assuming that your figure for the drag produced by a stalled sword blade of the dimensions given is approximately correct, we have stalled blade drag consisting of between 12% and 25 % of the energy applied to the sword by the user. That is certainly significant, and supports the wind generator blade tests which show a 20% improvement in efficiency. . . it's in the same zone of magnitude.

Stalling a wing ( or a blade ) not only produces a huge increase in drag, it also negatively affects control. The effects on control are probably unquantifiable but in other applications ( wings, fins etc ) can be catastrophic. Personally I notice the effect of blade stalling quite easily.

So, contrary to what you conclude, I think that your drag figure supports the idea that blade undulations were designed with aerodynamic efficiency in mind.

Note: "500 W - biomed: power output (useful work plus heat) of a person working hard physically"

http://en.wikipedia.org/wiki/Orders_of_magnitude_%28power%29

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[Roy Robinson Stewart]

Interesting theory, I like your thinking but am not yet wholly convinced. One of the reasons it isn't totally working for me, is I do not believe true two-handers were ever used in wide 360 degree sweeping circles like some sort of wushu competition. Certainly large wide swings are sometimes made, but the fighter is not going to be continuously "flying" the weapon around his body.

I've read a historical document recently which says that two handed swords were used in order to deal with multiple opponents, and that they both needed and commmanded a lot of space. Using a large predominantly cutting blade while probably surrounded by opponents inevitably requires a lot of sweeping movements and turning the blade at speed.

Swords are subject to constant accelaration and sudden deceleration that to me precludes much lift generation.

blades operate at speeds at which lift and drag are significant.

Acceleration and deceleration do not preclude lift, it is speed, angle of attack and blade shape which determine lift.

Very large two handed cutting swords are a different kettle of fish from cut and thrust longswords in terms of handling.

Additionally, my understanding of Bernouli's principle (which may be flawed, I dont' have much of a physics background if any) is that wings generate lift due to air flow being faster over one side than another, being that one side of a sword blade is not substantially mure curvi-linear than another, lift generation on sword blades seems unlikely as they are not particularly "wing shaped".

Unfortunately that's a myth which has been propagated in high schools all over the world. In fact Bernoulli's principle applies in theory and in practice to symmetrical wings, keels, fins, and even flat plates all of which produce lift. More camber on top of the wing than the bottom is not required for lift production, it merely improves efficiency.

Sword blades ( especially double edged ones) have cross sections which are reasonably efficient lift producers, however the sharp leading edges are highly susceptible to stalling even at relatively low angles of attack, and for this reason it is probable, in my opinion, that the efficiency improvements for sword blades to be gained with undulating leading edges are likely to be much higher than for wings which are designed solely for aerodynamic efficiency.

Blades are required to cut in two mediums: air and the target. Wings cut only in one medium.

Additionally, your theory does not really set forth why it is some thrust-centric blades such as rapier's sometimes featured this blade form.

Although the gains to be made are smaller with such blades, they still exist whenever the blade is used with a cutting motion or moved laterally.

The wavy or flame bladed style is sometimes even found on daggers, and even plug-bayonets of the 17th century which under no circumstances are used in a swinging or wooshing manner that would generate any significant lift or "flight-like" properties.

The goal is not to produce lift but to reduce drag.

I can't explain the use of wavy blades on daggers and bayonets.

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[Steven Ott]

The way I think about it, the people who used them in combat thought them better. That means more to me than people cutting carpet or pool noodles. I believe the people that used them knew more than us. Everyone acknowledges that the curve on a katana or kukri aid in slicing. I dont think it was just for looks, nor do I consider serration. This is good research. I believe our ancestors knew swords. People who criticise the flame blade in modern times dont use them for war. There is no simulation. Our ancestors weren't stupid in sword fighting for war

[Roy Robinson Stewart]

Thanks Steven

I just wanted to add that the speed of the blade at 20 m/s assumed by Vincent is possibly quite slow. From what I've read speeds of 30m/s are achieved, and although I'm not sure of the relaitive speeds of large two handers, it seems likely that given enough room to accelerate, and/or with assistance from the leverage given by the long handle, speeds of 30 m/s or more are possible.

In any case if we assume that speeds of 30m/s are possible, then the calculation changes a lot.

Because drag increases with the square as speed increases, a 50% increase in speed increases drag by 125 percent.

Thus the proportion of stalled sword drag to sword energy becomes, at 30m/s more like 25 percent to 40 percent of the total energy available.

Given that wide cutting sword blades with chord ratios well under 10 percent and with very thin leading edges are going to stall at very low angles of attack, it's clear that even moderate edge misalignment will cause large amounts of drag.

I also contend that large angles of attack would be experienced by the blade of any big cutting two hander swung through the arcs required to deal with multiple opponents.

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[Andrew F Ulrich]

Well, when you say test cutting hasn't shown any advantages, were they simply flat-out hewing, or did they also try drawing cuts/slices? The fighting manuals repeatedly state that there are three ways to use a blade: cutting, slicing, and thrusting (and sometimes using the flat, but that's another subject). Drawing cuts and slices are an essential part of combat, and I'm not yet convinced the idea of serration is ruled out, unless it's been shown that the design does not really work in a saw-like motion.

Also, if the aerodynamics of the blade actually did provide significantly less drag in air, then I'm just guessing that maybe there would be less drag when travelling through flesh, which would mean that flat-out cutting should show that the undulating blades can cut deeper than the regulars.

Also, with larger blades, I would imagine half-swording is just as important as it becomes more like a pole-arm, and the long-range cuts are certainly going to have more reach, but so are thrusts.

Thanks for your research though, and sorry this thread can't be more enthusiastic about your idea. It is an interesting idea, but I hope you can still be open-minded to other possibilities.

It would certainly be interesting to handle one of these blades and see how they feel firsthand.

[Sal Bertucci]

This is exactly why we need a Masters student to do a thesis on this! Ok college boys, get crack'en!!

[Roy Robinson Stewart]

Wind tunnel tests should be easy to do ideally with the original weapons.

Certainly if the gains made with wind generator blades are an indication, the undulations would give a big advantage.

Anyway I'll leave you good gentlemen with the idea for a while, as I'm snowed under with work.

One thing's certain: a custom two hander with an undulating blade is on my must have list, or perhaps a pair, one with a a straight blade .