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Gary Teuscher





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PostPosted: Fri 23 Jan, 2009 8:00 am    Post subject: Long vs. Composite bows         Reply with quote

I've been researching bows for a little while now, including crossbows, composite bows and the "longbow". I was under what I now believe to ba a mistaken assumption, that much of the longbows power came from it's greater drawlength. After looking at some pretty good sources, as well as a site someone else posted there there are composite replicas made, many based on period finds, I believe this to be incorrect.

As the maker of these composite bows told me, bows were not made with drawlengths according to the length of the bow, but according to the draw if the user. This of course makes perfect sense, but it escaped me Big Grin

That being the case, A composite bow of similar draw weight should have numbers similar to that of a longbow of similar draw weight. Actually, there can be an argument made that the composite should have more power - per about every bowmaker, composite construction is higher in efficiency to wood construction, thereby giving the composite a better ability to transfer more stored energy to the arrow.

I guess one question would be were the bows of similar draw weights? I have not heard much about turkish bow draw weights. Most estimates put the Mary Rose bows in the 100-150# draw, actually 2 schools of thought one more in the 100#, one more in the 150#. I have read mongol bows also were estimated to have draw eights in the 100-150# range, so there is not a reason to assume high draw weight bows cannot be used mounted.

As far as range, I have read the Turkish bows had a range of about 300 yards, longbows more in the 240 range. This is tough to draw true conclusions from though, for me more of a rough guide. As far as I know, we don't know any good estimates for turkish arrow weights in grains, and either bows could of course loose a flight arrow further than a standard one.

Reason this is of interest to me - If both should have similar kinetic energy, therefore similar penetrative power, the reports of arrows effects on crusaders would be similar to the effects on French knights/men-at-arms, based of course on similar period armour.

We know that the long range fire of turkish bows did little to mail clad warriors, maybe sticking in the padding, possibly some very superficial wounds. Actually IMO longbows would have had less of an effect injuring armoured opponents than composites, and here is my reasoning. Turkish tactics in addition to any long range bombardment also including loosing arrows within 10-30 feet of their opponents - the mobility of a mounted archer allowed this. On the other hand, a lonbowman with a charging french knight at 10-30 feet would probably break well before having a chance to loose an arrow at that range (unless defended by a static defensive measure).

We do know that on occasion a knight was severely wounded through mail by a turkish arrow - I have no idea at what range, but one would guess this might often be at that 10-30 foot range.

As far as the bodkin arrow being the mail killer - the lack of hardened bodkin finds does not bear this out, I'd be more inclined to believe the theory from the Royal armouries (and Dan Howard's as well Big Grin ) that the bodkin was a flight arrow more than anything else.

I'd be interested in anyone's thoughts on this matter.

Anything with period weights of turkish arrows, turkish bow draw weights or similar would also be appreciated.
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Xan Stepp




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PostPosted: Fri 23 Jan, 2009 9:00 am    Post subject:         Reply with quote

Gary,
I don't want to sound critical here, because I'm really not, and I do think that you bring up some important points. For that reason I would ask you to provide a list of sources that have influenced your thinking (Then again, I don't know how many I'd be able to access from my present location), and hopefully that would keep the discussion a bit more academic. But I do think that you do have a very good point about the added mobility of the mounted archers enabling them to achieve a greater number of close, penetrating shots, which will influence statistics.

But with that said, my next comments might rack up a bit more on the "speculation" side of things. I for one think that we tend to place too much emphasis on the draw weight of bows. It stands out to us because it is something that we can feel, and so I think that we tend to see it as the dominating factor in the performance of the weapon. I have commonly seen draw weights in the 100-150 lbs. range quoted for the longbow, but see much higher values quoted for crossbows. However, the crossbow's performance is not much different from the longbow.

I was thinking about it from a physics perspective, and certain things stick in my mind. (By the way, I've done no math here, so feel free to correct me, I'm just thinking things through, and it doesn't always give the most accurate results.) First of all, I believe that most people tend to think of draw weights as constant, in that the released string exerts the same force on the projectile for the whole length of its motion. But when you think about it, I think that mot people would agree that the force has to go to zero at equilibrium. So at the very least the force exerted is linear, or possibly a higher order function. I tend to think the latter because it seems to me that it gets much harder to draw the bow over the last little bit to the cheek. But that might just be a biological reaction. However, if anyone has a good period bow, and a scale to measure the pull as a function of distance, please post the results here.

So assuming that the function is linear, then the kinetic energy imparted to system is:

E=.5*(Draw weight)*(Draw length)

This partially explains why a longbow and a crossbow have similar performances, but some of that energy goes into the limbs of the bows as well. I tend to think that the energy imparted into the limbs of a crossbow would be greater as well, since they would have a higher velocity, since the projectile is accelerated over a shorter distance.

However, when thinking of the case of the composite bows, total energy for a longbow and a crossbow should be the same if the force varies linearly with the draw length. (If it doesn't all bets are off, and we would need experimental data to have any idea about how the energy is distributed.) However, we still have the same issue as with the crossbow; the composite bow is shorter and therefore more of the stored potential energy would be imparted to the bow rather than to the arrow, which should reduce its performance. However, this does not agree with the range information that you presented, which means that either I have thought about the physics incorrectly (if so, explain how) or that the ranges listed are not accurate comparisons (unequal arrow weights, greater drag, poor measurement, etc.).

So those are my thoughts.

Deyr f, deyja frndur
deyr sjlfur i sama;
en orstr deyr aldregi
hveim er sr gan getur.
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Gary Teuscher





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PostPosted: Fri 23 Jan, 2009 10:00 am    Post subject:         Reply with quote

Xian - I'm very well familiar with the formulas for transferable KE.

It's not exaclty 1/2 Drawlength x draw weight - The bow is a spring, wanting to go back to straight. At the strung position, there is a brace length. At this brace length, the bow is already exerting tension, so the draw is not from "0" tension at rest, as rest would be straight.

Best way to figure the brace into the equation is you factor KE as you have shown - but take out the bracelength/drawlength x draw weight, so you are taking out the distance of the brace, but at a proportionately lower tension. Other than measuring that draw weight of the "stringing" of the bow, there is not a really good other way to figure. However this should be pretty accurate, and with brace lengths being fairly similar with most bows it does not factor in a huge way, at least from a comparison standpoint, though it does lower raw KE.

The other factor is efficiency - this is how effiecent it transfers the energy to the arrow, and varies by construction material. Modern bows have the highest factor, then composite, then wood, lastly steel, and there is surely some variance even within the given material.

Quote:
However, we still have the same issue as with the crossbow; the composite bow is shorter and therefore more of the stored potential energy would be imparted to the bow rather than to the arrow,


Couple of things here - the issue with a crossbow is far different. The very short draw lengths require much migher draw eights, as in the formular for KE. That's pretty simple.

The composite bow is far different - It has about the same draw length, so this is not a factor. The KE that is imparted to eith Composite bow or longbow is relative to the amount of energy spent getting the limbs back to the starting position. A composite bow's limbs bend more, making it spend more enrgy in this regard to get back to straight. On the other hand, the Longbow has longer limbs, requiring more energy in comparison to the composite bow to get back to straight.

Neither of these use a much of the KE to do so, and they both have issues that cancel the other out, so there should be no real difference realitve to this isse.

With a 1000#+ draw crossbow, it is more of an issue as the limbs are much heavier. On the other hand they do not move as far, plus they have tons of KE stored to compensate.


Quote:
For that reason I would ask you to provide a list of sources that have influenced your thinking (Then again, I don't know how many I'd be able to access from my present location), and hopefully that would keep the discussion a bit more academic


For longbows draw length and weight it's pretty simple, from the excavations of the Mary Rose, for the draw weight there are 2 pirmary schools of thought as to what they were.

For the Draw weights of other bows, that is what I was looking for assistance in.

As far as range goes, nothing is really that good of a source IMO and needs to be taken with a grain of salt, even if we had accurate ranges this would mean little without knowing how heavy the arrows were. I could quote some of the sources, but from what I've gathered this is looked on as more common knowledge, plus there is little that could truly say how accurate these are as they are still estimation from these sources.

As far as the results of turkish arrow fire and it's results are lack of - once again I think thats pretty well common knowledge. There are numerous threads on this forum, some quote sources stating this. Once again though, it's reports from contemporary authors, not testing so it's not exaclty a tried and true test.

If you feel some of the specific statements are inaccurate, please let me know which and I could get specific sources for a specific comment, though most of the above is not "testing" but period commentary if you would.
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Ben Potter
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PostPosted: Fri 23 Jan, 2009 11:26 am    Post subject:         Reply with quote

The main difference is in the arrows and how a bow transfers the energy.

A composite turkish bow can transfer the same amount of energy as a long bow BUT only if you use a light arrow.
The long bow however needs a heavy arrow to transfer the same energy, hence the hardwood shafted "cloth yard" arrows. it is like swinging a hammer, if you are going for distance you want a light weight hammer, but if you want to smash something you use a heavy one.
When it comes to penetration the heavy hardwood arrow with a bodkin point will penatrate better than a light weight softwood or reed arrow with a wider cutting head.

I'm not all that good at physics but I've read a fair amount and talked to lots of archers.

I hope that helps.

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Ben P.




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PostPosted: Fri 23 Jan, 2009 12:08 pm    Post subject:         Reply with quote

Why does it say there are zero replies?
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Xan Stepp




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PostPosted: Fri 23 Jan, 2009 12:11 pm    Post subject:         Reply with quote

First of all, you do seem to know much more about this than I do, so take my questions as such rather than implied challenges. I'll be plenty clear when I disagree. As an example, your KE equation i either unclear or wrong:

Quote:


Best way to figure the brace into the equation is you factor KE as you have shown - but take out the bracelength/drawlength x draw weight, so you are taking out the distance of the brace, but at a proportionately lower tension.



If you mean that the stored energy should be:

U=.5*(brace length/draw length)* (draw weight)

That is clearly incorrect, as this would imply that you get less energy the more you draw the bow, and that you get infinite energy if you don't draw it at all. The equation:

U=.5*(draw length-brace length)* (draw weight)

would make more sense, and was essentially what I was thinking. (I didn't write that, so it deserved correction.)

I also agree that in the case of a longbow or a composite bow, the brace and draw lengths should be essentially the same, so that the stored spring potential in two bows of the same draw weight should be the same, so any differences in performance should come down to more than draw weight or length.

(However, on a side note, it does make me wonder if the two bows did have different draw lengths. Not because one was longer or shorter, but rather that they were build for people of different ethnic backgrounds, and that one group or another might have had shorter average draw lengths.)

Quote:


The other factor is efficiency - this is how effiecent it transfers the energy to the arrow, and varies by construction material. Modern bows have the highest factor, then composite, then wood, lastly steel, and there is surely some variance even within the given material.



I think that difference could be the deciding factor in performance. I would like a source for this, if you have it, especially since "modern bows" and "composite" aren't exactly materials, and that wood is a very general category. However, as I think about some of the mechanical properties of these construction techniques, I'm inclined to agree. But I would like to see a numerical quantification about the comparative efficiency of these materials.

Quote:


Couple of things here - the issue with a crossbow is far different. The very short draw lengths require much migher draw eights, as in the formular for KE. That's pretty simple.



True, the crossbow is very different. I mainly brought it up as a method to think about the relationships between some of the intangibles. Just to illustrate my point, if we take the high end of the draw weight for a bow (150 lbs.) and a very liberal 3 ft. draw length-brace length, we get a net of 225 ft.*lbs. of stored energy. This would be the same energy stored in a 1000 lb. crossbow with a draw length-brace length distance of 5.4 in. to get the same amount of kinetic energy. I don't have a ton about crossbows, but this seems pretty small. I think that this comparison is particularly useful because, as I understand it, many crossbows were composite construction, which makes the comparison to composite bows particularly apt.

So what I see is that, given similar construction methods, that the smaller a bow, (small composite crossbows, compared with larger composite bows) the less performance it gets from the same draw weight.

I do see a lot of validity in your statement:

Quote:


Neither of these use a much of the KE to do so, and they both have issues that cancel the other out, so there should be no real difference realitve to this isse.

With a 1000#+ draw crossbow, it is more of an issue as the limbs are much heavier. On the other hand they do not move as far, plus they have tons of KE stored to compensate.



(Even though you technically can't store KE). I'll buy the canceling of the longer limb-longer distance (I won't be completely convinced until I see the math, but it makes sense to me.), but then the same argument should hold for the crossbow as well. I also see the the heavier crossbow limbs making a less efficient transfer of energy than a bow, since they would be carrying more mass per unit length. Which raises the question of whether a composite bow is closer in construction to a longbow or a compositely constructed crossbow. It seems like a mass per unit length calculation for a composite bow and a longbow would be in order! However, it does seem to me that the shorter limbs are a likely category for the difference in performance between a bow and a crossbow.

However, there are a few other possibilities which did occur to me to explain this:
1) Our modeling of a bow as a simple spring is wrong, and that the response is non-linear. This could make a huge difference, but I'm not equipped to measure such things right now.
2) That the observed differences in performance are more greatly influenced by the projectile shot than by the characteristics of the bow. Different projectiles will receive the energy differently, some may be more prone to compression or vibration. Some projectiles may have more drag, which would reduce the range of a more powerful weapon to the point that it appears less powerful.
3) Something else entirely.

So your physical arguments don't convince me. But then again neither do mine. If you know a good source for the physics of bows, I'd love to check it out, and I have a degree in physics, so I can probably follow most technical discussions.

Also, you (and many others) have mentioned the Mary Rose. There has to be a good print source(s) on this and on the measurements for the longbows. Do you know what those are?

But in the end, I think that the direction that I'm leaning is that you have posed a currently unanswerable question and that the only way to resolve it conclusively would be to preform the necessary experiments. Maybe I'll get someone to give me a grant to do just that somewhere down the road.

Deyr f, deyja frndur
deyr sjlfur i sama;
en orstr deyr aldregi
hveim er sr gan getur.
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Gary Teuscher





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PostPosted: Fri 23 Jan, 2009 12:12 pm    Post subject:         Reply with quote

Quote:
A composite turkish bow can transfer the same amount of energy as a long bow BUT only if you use a light arrow.
The long bow however needs a heavy arrow to transfer the same energy, hence the hardwood shafted "cloth yard" arrows. it is like swinging a hammer, if you are going for distance you want a light weight hammer, but if you want to smash something you use a heavy one.
When it comes to penetration the heavy hardwood arrow with a bodkin point will penatrate better than a light weight softwood or reed arrow with a wider cutting head.


I've heard some of this before. As to a turkish bow can only transfer the same amount of energy only if using a lighter arrow, I see no reason why this would be the case, unless the bow were of a lighter draw.

With similar draw lengths, the arrows would be of similar weight if constructed of similar material, unless of course one is thicker than the other.

Are there any sources where Turkish bows use lighter weighted woods for arrows?

The other thing is most believe penetration is KE, or mass x velocity squared. If I composite bow imparts the same or better energy, and uses a lighter arrow, it will also have a higher velocity, compensating to a point for less mass. Penetration is a function of both velocity and mass.

That is if indeed lighter arrows were used, I'd like to see if this is even factual.
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Sean Flynt
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PostPosted: Fri 23 Jan, 2009 12:16 pm    Post subject:         Reply with quote

The Great Warbow (Hardy, Strickland) has detailed MR bow technical data in an appendix, plus tons of other great material.
-Sean

"Everywhere I have searched for peace and nowhere found it, except in a corner with a book"- Thomas a Kempis (d. 1471)
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Xan Stepp




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PostPosted: Fri 23 Jan, 2009 12:22 pm    Post subject:         Reply with quote

Quote:


I've heard some of this before. As to a turkish bow can only transfer the same amount of energy only if using a lighter arrow, I see no reason why this would be the case, unless the bow were of a lighter draw.

With similar draw lengths, the arrows would be of similar weight if constructed of similar material, unless of course one is thicker than the other.



I'm as skeptical as you are Gary. I need some good explanations to believe this one.

Quote:


The other thing is most believe penetration is KE, or mass x velocity squared. If I composite bow imparts the same or better energy, and uses a lighter arrow, it will also have a higher velocity, compensating to a point for less mass. Penetration is a function of both velocity and mass.



I agree that KE is important to penetration, and that, because of the quadratic term in the energy higher velocity is preferred. However, material and geometry are much more important for penetration than KE. i.e. A 24 g dart thrown at 80 km/h is going to penetrate a lot more than a 145 g baseball at 160 km/h even though the baseball has a lot more KE.

EDIT: Sean, thanks for the info. Unfortunately, I'm not in a position to get my hands on the book right now, so I'll have to wait.

Deyr f, deyja frndur
deyr sjlfur i sama;
en orstr deyr aldregi
hveim er sr gan getur.
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Sean Flynt
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PostPosted: Fri 23 Jan, 2009 12:29 pm    Post subject:         Reply with quote

You might be able to borrow the book through interlibrary loan, although international loan might not be possible. It's worth a call to a local civic or university library, anyway. Maybe there's a copy somewhere in Iceland....
-Sean

"Everywhere I have searched for peace and nowhere found it, except in a corner with a book"- Thomas a Kempis (d. 1471)
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Xan Stepp




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PostPosted: Fri 23 Jan, 2009 12:50 pm    Post subject:         Reply with quote

Sean,
Thanks. All the libraries in Iceland are connected to the same network, and there are no hits for the Great Warbow anywhere in Iceland. I haven't tried an international ILL, so I don't know if it would be possible. Even if it were, I have no idea how long it would take to get here. Besides, I should be back in the States in the Summer, so I'll have a look then. Thanks for the suggestion though.

Deyr f, deyja frndur
deyr sjlfur i sama;
en orstr deyr aldregi
hveim er sr gan getur.
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Gary Teuscher





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PostPosted: Fri 23 Jan, 2009 1:22 pm    Post subject:         Reply with quote

Here is something interesting about arrow construction in arabic bows:

Quote:
The Sylloge and the Ambrosiana Paraphrase the darts are called mice their size of between one and three fingers in length is mentioned by Paul of Aegina in the seventh century. The earliest Arabic darts to be specifically described were as big as the little finger from tip to feathers, allowing them to be stacked in the arrow guide and shot four of five at a time. As heavier armour was adopted due to the Crusades the smaller darts were made less effective, the Arabic treatises suggest using larger darts of about two spans long , with a heavy head and a thick shaft of hard, heavy wood


http://web.archive.org/web/20050328042804/htt...arion.html


Quote:
I agree that KE is important to penetration, and that, because of the quadratic term in the energy higher velocity is preferred. However, material and geometry are much more important for penetration than KE. i.e. A 24 g dart thrown at 80 km/h is going to penetrate a lot more than a 145 g baseball at 160 km/h even though the baseball has a lot more KE.


I agree here, Xian, though we are talking about all weapons using arrows, and an arrowhead that would seem to maximize penetration according to this, the needle bodkin, is considered to be a flight arrow by many now. I don't think the heads themselves would make a huge difference here - unless we assume the turks were particularily bad in making arrows that penetrated armour.

Quote:
U=.5*(brace length/draw length)* (draw weight)


OK, let me try to do the best math sequencing I can here, I hope I get it right:

B= Brace length (inches)
D= Draw length (inches)
A= Draw eight (pounds)

U= .5 x ((D*A) - (B/D) * A * B)

Multiply that by bow efficiency.

Quote:
(However, on a side note, it does make me wonder if the two bows did have different draw lengths. Not because one was longer or shorter, but rather that they were build for people of different ethnic backgrounds, and that one group or another might have had shorter average draw lengths.)


Maybe, but not much. I think the average height varied by an inch, at the most 2, which means .5-1 inch difference in draw.


Quote:
Just to illustrate my point, if we take the high end of the draw weight for a bow (150 lbs.) and a very liberal 3 ft. draw length-brace length, we get a net of 225 ft.*lbs. of stored energy. This would be the same energy stored in a 1000 lb. crossbow with a draw length-brace length distance of 5.4 in. to get the same amount of kinetic energy. I don't have a ton about crossbows, but this seems pretty small.


One thing you are doing that many also seem to do - the draw length on a bow is bow to nock point at full draw (the 36" is still way high). More realistic numbers, take 30" x 100 pounds and it's 3000 Foot inches, and a brace of about 7". The crossbow take a draw of 11" or so, a brace of about 4" (I think you are figuring crossbow draw from braced position of bow string to nut - you have to do it the same for all bows, nock to bow itself). With a 1000# draw, you are looking at 11000 foot inches. You have to take out the brace for both of course, which should reduce both by a similar percentage. You also need to factor in the efficiency factor, of which all bowmakers have said is lower for steel than wood, so the steel bow might lose another 10% in comparison here.

The draw and brace numbers are estimates of Leo, the crossbow maker who graces this forum once in a while. He does not to "powerstrokes" (Brace to nock) of greater than 4-5" on steel bows - but more for protection for himself from product issues. He estimates 6-7" for period steel bows, the 7" number more on windlass types. Of course you need to add a 3-4" brace here to do an apples to apples comparison with selfbows.

Quote:
I would like a source for this, if you have it, especially since "modern bows" and "composite" aren't exactly materials, and that wood is a very general category. However, as I think about some of the mechanical properties of these construction techniques, I'm inclined to agree. But I would like to see a numerical quantification about the comparative efficiency of these materials.


If you look at most bow sites for modern bows, and some for replica bows, you will find either a number assigned or if you speak to the actual bow maker they will have their own efficinecy numbers in mind. I'll put one site that does here, but search and you will find it on many sites. They may vary a bit to bit with the exact nembers assigned to each, but it's a commonplace figure for bowmakers.

http://www.huntersfriend.com/bow-review-400-f...nd-bow.htm

Look midway doen the page on this one. I'm not sure if all calculate efficiency before or after brace reduction, it may be done both ways, if they don't do the brace reduction they would use slightly lower efficiency numbers.

Quote:
It seems like a mass per unit length calculation for a composite bow and a longbow would be in order! However, it does seem to me that the shorter limbs are a likely category for the difference in performance between a bow and a crossbow.


There are plusses and minuses for shorter limbs, but that's rather detailed and hard to quantify. Plus it's not a major impact in energy lost. As far as the composite bow being closer to the crossbow - crossbows were in the 24-30" prod length for the most part. A good average length for a composite horsebow seems to be in the 50" range, we can go with 72" for the longbow. The composite is far closer to the longbow.

Quote:
1) Our modeling of a bow as a simple spring is wrong, and that the response is non-linear. This could make a huge difference, but I'm not equipped to measure such things right now.
2) That the observed differences in performance are more greatly influenced by the projectile shot than by the characteristics of the bow. Different projectiles will receive the energy differently, some may be more prone to compression or vibration. Some projectiles may have more drag, which would reduce the range of a more powerful weapon to the point that it appears less powerful.
3) Something else entirely.

So your physical arguments don't convince me. But then again neither do mine. If you know a good source for the physics of bows, I'd love to check it out, and I have a degree in physics, so I can probably follow most technical discussions.


There is one aspect that I did not mention, it has to do with the bracing. Many composites were of a recurve style, that which does not desire to get back to "straight" as a non recurve does, but goes past that point. hat this would do is increase the tension where the brace starts, but it's going to cause a slight but not great at all reduction in stored energy due to the fact the brace factor will be higher in reducing stored energy. This allows a bow with less tensile strength but springier to achieve a higher overall pull weight than if the same materials were used not in a recurve fashion. But again this would not be a major factor, and as I mentioned the composite bow is considered by about every bow maker to be more efficient than a wooden bow, which would counter this.

The other issue is stave speed - a projectile can of course be launched no faster than the "spring" can move unencumbered. You will see this come into play with modern bows and very light projectiles, their velocity is not that what their stored energy suggests. With middle ages arrows this was not much of a factor though, they were much heavier than current bows. With some flight arrows it could be an issue.

As far as the other reasons you gave, other than some bows "stack" worse than others (though I have been told by most bowmakers composites have less of a problem stacking than wooden bows), there does not seem any reason to assume that composites would be any worse than a longbow in transferring energy.

The other thing is you seem to disagree with the physics I mention, but the point I am making is not a revolutionary one bay any means. I am merely saying there is no reason a longbow should be more effective in penetrating armour than a composite of similar draw weight. From most reasonably well done tests, longbows were not armour busters. Nothing really indicates they were effective pentrating metal armour at range. There is the old longbow myth of it being the best weapon of the middle ages, but most serious historians already agree with this point. It seems as though turkish horse archers had about the same luck against armoured crusaders, i.e. little or no chance of penetrating mail at range, though they seemed to be able to inflict injuries if close enough, what close enough is is the question, but most likley at the most 50m. They were a danger if they hit a non protected area or a horse, killing horses and disrupting charges seemed to be what bost of these weapon were best at.

Quote:
Also, you (and many others) have mentioned the Mary Rose. There has to be a good print source(s) on this and on the measurements for the longbows. Do you know what those are?


I believe this site has some articles on it, otherwise a simple search for the Mary Rose would give you the info. You can also find out a lot about some of the other issues we discussed in some of the books on the readers list, and on the internet, just if doing it on the internet make sure it is a relaible source.
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Xan Stepp




Location: Ithaca, NY
Joined: 19 Dec 2008

Posts: 54

PostPosted: Fri 23 Jan, 2009 5:16 pm    Post subject:         Reply with quote

It looks like things are back to me Gary. By the way I thought that I should also mention that my name is Xan, not Xian. Happy

Quote:
The other thing is you seem to disagree with the physics I mention, but the point I am making is not a revolutionary one bay any means. I am merely saying there is no reason a longbow should be more effective in penetrating armour than a composite of similar draw weight. From most reasonably well done tests, longbows were not armour busters. Nothing really indicates they were effective pentrating metal armour at range. There is the old longbow myth of it being the best weapon of the middle ages, but most serious historians already agree with this point. It seems as though turkish horse archers had about the same luck against armoured crusaders, i.e. little or no chance of penetrating mail at range, though they seemed to be able to inflict injuries if close enough, what close enough is is the question, but most likley at the most 50m. They were a danger if they hit a non protected area or a horse, killing horses and disrupting charges seemed to be what bost of these weapon were best at.



First of all, I want to make it completely clear that I'm not promoting the longbow as "better" than a composite or as the ultimate medieval weapon. My main points are mainly:
1) I'm not completely sure about the physics.
2) That the problem of armor penetration (or performance in general) must be much more complex than simply draw weight and draw length.
3) That I would like to see some actual facts rather than a bunch of opinions. (Which I will admit, much of my previous musings would likely fall in that category.)

Quote:
OK, let me try to do the best math sequencing I can here, I hope I get it right:

B= Brace length (inches)
D= Draw length (inches)
A= Draw eight (pounds)

U= .5 x ((D*A) - (B/D) * A * B)

Multiply that by bow efficiency.



Now that makes a bunch more sense! However, I'd recommend rewriting it as:

U=.5*A*D*(1-(B/D)^2)

It is a bit more transparent that way, and actually makes tons of physical sense. However, the net difference between this equation and U=.5*A*D is fairly small for normal ranges of B.

I also got online and found two articles that were reprinted from physics journals, so they can probably be trusted (at least for the physics):

http://www.stortford-archers.org.uk/medieval.htm
http://margo.student.utwente.nl/sagi/artikel/...plica.html

The second gives some indications about the performance of a longbow and a composite, but doesn't really give enough comparative data about the bows to really say much about our situation. One thing that it does say is that the composite stores more energy per unit mass than the longbow, however if the total mass of the longbow is higher, it still might store more energy, so it doesn't help much without knowing the masses of both bows (another reason that we need other users' input).

The first of these articles is much more helpful. It would appear that for the same draw weight and length (and assume that we shoot the same arrow) that the major factors influencing velocity are efficiency e and the factor k*M. The second article seems to indicate that the efficiency, e is higher for a composite, but what about k*M? I really don't know about M, so it could go either way, but the smaller, the faster the velocity of the arrow. As for k, it is a factor representing the average kinetic energy of the limbs. My inclination would be that more kinetic energy goes into the composite bow since it would have a higher velocity, and since the kinetic energy term goes as v^2, if the masses of the longbow and composite are anywhere near the same, this k*M term should be smaller for the longbow. But to what factor? Speaking of which I couldn't find the efficiencies for different materials on http://www.huntersfriend.com/bow-review-400-f...nd-bow.htm. I'm probably just blind on this, but could you throw me a bone?

My inclination would be that the math favors the longbow, but not by much. I could also make a historical argument. It seems that the main advantage of a composite bow is that it is small enough to be used from horseback, while still providing performance similar to a longbow. And since composite bows were known to longbow using cultures, it would make sense to use the bow that had superior performance since you were not employing mounted archers and the size had no bearing. However, economics and culture may also greatly influence the usage of the longbow.

So, while my inclination (lacking any reliable values for e, M, and k) is that the math favors the longbow, but not by much.

Quote:
There is one aspect that I did not mention, it has to do with the bracing. Many composites were of a recurve style, that which does not desire to get back to "straight" as a non recurve does, but goes past that point. hat this would do is increase the tension where the brace starts, but it's going to cause a slight but not great at all reduction in stored energy due to the fact the brace factor will be higher in reducing stored energy. This allows a bow with less tensile strength but springier to achieve a higher overall pull weight than if the same materials were used not in a recurve fashion. But again this would not be a major factor, and as I mentioned the composite bow is considered by about every bow maker to be more efficient than a wooden bow, which would counter this.

The other issue is stave speed - a projectile can of course be launched no faster than the "spring" can move unencumbered. You will see this come into play with modern bows and very light projectiles, their velocity is not that what their stored energy suggests. With middle ages arrows this was not much of a factor though, they were much heavier than current bows. With some flight arrows it could be an issue.



I'm inclined to agree with you on both of these points, i.e. that neither makes a big difference. Additionally, an added benefit of the recurve is that brace length is smaller, but the math indicates that this isn't much of a benefit either.

So, I think that where I'm ending up is about where you started, that the arrow velocities would be about the same for both bows. I just feel much better about making statement now that I have gone through the math a bit and looked at more than just draw length and draw weight. You have a slight inclination toward the composite and I to the longbow, but in the end it is much more likely that the penetrating power is much more dependent on the arrow and the situation than on the bow.

I do want to reiterate that I think that your idea about the added mobility of horse archers resulting in more penetrating shots seems very good, and probably is the main reason for an apparent disparity in historical reports for bows which now appear to be pretty similar.

However, what I do want to dispute is this:

Quote:
I agree here, Xian, though we are talking about all weapons using arrows, and an arrowhead that would seem to maximize penetration according to this, the needle bodkin, is considered to be a flight arrow by many now. I don't think the heads themselves would make a huge difference here - unless we assume the turks were particularily bad in making arrows that penetrated armour.



First of all, any bow hunter will tell you that you get vastly different penetrations from broadhead and field points, even though they are supposed to be the same mass, and approximately the same flight characteristics. So I was looking for some math on armor penetration and found the Thompson "F-factor" equation. The equation would be too sloppy to try to input here so have a look here:

http://www.combinedfleet.com/formula.htm

The equation indicates that penetration is related to velocity, thickness of the armor, hardness of the armor, mass of the projectile, and diameter of the projectile. Most of these factors have nothing to do with the projectile itself. The greater the mass or velocity, the greater the penetration, and the lower the diameter (or better stated the average cross sectional area) the greater the penetration. Since so many things having to do with the construction of the bow determine the mass of the arrow, we might as well consider it to be a constant, and something we can't vary. Now the ability of a projectile to penetrate varies linearly with velocity and inversely with diameter. However, it is much easier to decrease the cross section by a factor of 2 than double the velocity. So, everything else being equal, the geometry and material of the head is much more likely to make a difference than any other factor. A pointed, hardened steel head will give you much better penetration than a round lead ball of the same mass.

Quote:
and an arrowhead that would seem to maximize penetration according to this, the needle bodkin, is considered to be a flight arrow by many now.



I would agree that the needle bodkin would seem to be the ideal armor piercer, but it may not actually be the case. First of all, I have been lead to believe that the heads were not made from hardened steel, and would have likely deformed. This would increase the cross sectional area and make them less likely to penetrate. And from what I have seen on these boards, this seems to be the major argument for bodkins being flight arrows rather than armor piercers. However, even if they were hardened it does not necessarily mean that they would be the best armor piercers. At short range, yes, but at longer range, the decreased mass of head would probably mean that the bodkin hit with less velocity after a high arch. So all things point to it being a flight arrow, good for distance, but it won't hit nearly as hard.

Deyr f, deyja frndur
deyr sjlfur i sama;
en orstr deyr aldregi
hveim er sr gan getur.
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Gary Teuscher





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PostPosted: Fri 23 Jan, 2009 5:52 pm    Post subject:         Reply with quote

Quote:
My inclination would be that the math favors the longbow, but not by much. I could also make a historical argument. It seems that the main advantage of a composite bow is that it is small enough to be used from horseback, while still providing performance similar to a longbow. And since composite bows were known to longbow using cultures, it would make sense to use the bow that had superior performance since you were not employing mounted archers and the size had no bearing. However, economics and culture may also greatly influence the usage of the longbow.


A few things on this issue. The Composite was not just an archers bow - foot used it as well, it was the common foot bow among Romans and Byzantines among others.

As far as why it never "caught on" in europe - For me, it's mostly cost. A composite bow is more labor intensive, uses varied and perhaps costlier items as well. Plus the time needed to make one was at least a year to allow proper drying and other issues, could even be longer.

The other issue is that it handles moist climates worse, some of the problems are with the glue. Certain glue was more resistant to this, but it was still not as resistant as a straight wood bow.

And for foot archers it's not really a big deal - the bows a bit longer but probably cheaper, and handles moisture better. The ventians used both aboard their Galleys - in addition to crossbows.

But you don't really gain anything with a foot archer with either bow - you can only draw so much of a weight so far, so even a foot composite bow would be similar to a longbow in performance.

Quote:
That I would like to see some actual facts rather than a bunch of opinions. (Which I will admit, much of my previous musings would likely fall in that category.)


Myself as well, which is why I put the post out there. Anyone with specific knowledge of arrows and bows of the composite type would be of help. I think the longbow info is pretty easily available.
Quote:

. First of all, I have been lead to believe that the heads were not made from hardened steel, and would have likely deformed. This would increase the cross sectional area and make them less likely to penetrate.


The other issue is that it takes energy for a bodkin head to "deform", which means if it deforms, less energy transfers to the impact.

I guess my point was the armour piercing type arrows used by both the composite and longbow likley had very similar characteristics. I would think both were broadheads, I do not know. Both cultures knew how to harden the heads (there are references to european knights being told how to armour themselves to counteract hardened mongol arrows).

So the only issues where there could be a marked difference is the diameter and mass of projectile. For the mass, assuming similar KE form the bow, what is lost in mass will be increased in velocity. This being the case, I also do not see 500 grain arrows in use by composite bows, I think they would be somewhat similar in weight, perhaps the longbows a bit heavier, but not by much, and the composite would have greater velocity.

I would think arrowheads were not entirely uniform - some variances here and there, but they would seem to have been similar unless someone knows otherwise, with specific information. And it really a function of the arrow head, not the shaft for penetration, at least the initial inch or two, so this is what we need to compare. A softer shaft could lose a bit of energy bending on impact, bit I don't think there would be a huge difference in shaft diameter, i.e. neither looses crossbow bolts.

Quote:
Speaking of which I couldn't find the efficiencies for different materials on http://www.huntersfriend.com/bow-review-400-f...nd-bow.htm. I'm probably just blind on this, but could you throw me a bone?


That lists the efficiency of modern bows towards the middle. I'll dig around and look for a more comprehensive list.

Just be careful looking at efficiency numbers. Some don't take out the bracing factor but lower effiiciencies a bit, for me I think limb speed should be a bit seprate from efficiency because limb speed onnly effects the top end velocity of a very light projectile (think 500 grains or less on the 100# longbow). Another crossbow maker used efficiency numbers of about 1/2 of what I have seen elswhere - then I realized he did not have the stored enrgy, which made his numbers come out about right. There does not seem to be a tried and true scientific equation for efficiency.
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S. Mighton





Joined: 16 Aug 2007

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PostPosted: Fri 23 Jan, 2009 6:14 pm    Post subject:         Reply with quote

For bows of equal draw weight, a steppe-style composite recurve will equal or outperform an English longbow for all arrow weights. However, although I've never tried horse archery, I imagine that it's much more difficult to shoot the super heavy bows (150lbs+) from horseback. Maybe the armies that used composites used lighter bows for their horse archers and heavier bows for their foot archers? Has anyone every seen evidence of this, out of curiosity?
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S. Mighton





Joined: 16 Aug 2007

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PostPosted: Fri 23 Jan, 2009 6:22 pm    Post subject:         Reply with quote

For bows of equal draw weight, a steppe-style composite recurve will equal or outperform an English longbow for all arrow weights. However, although I've never tried horse archery, I imagine that it's much more difficult to shoot the super heavy bows (150lbs+) from horseback. Maybe the armies that used composites used lighter bows for their horse archers and heavier bows for their foot archers? Has anyone every seen evidence of this, out of curiosity?
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Jason Daub




Location: Peace River, Alberta
Joined: 14 Jan 2005
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PostPosted: Fri 23 Jan, 2009 7:36 pm    Post subject:         Reply with quote

The composite bow will loose an arrow of the same weight faster than a straight staved bow of equivalent draw. The composite bow has the following advantages, a "fatter" force-distance curve that allows more work to be done for a given draw weight and less mass in the bow limbs. Due to its reflexed limbs and tips the composite bow is harder to pull in the early and mid-stages of the draw and stores more energy. In the traditional bowmaking materials there is APPROXIMATELY no difference in recovery speed, this, coupled with the smaller arch, allows the composite a high cast. It also allows the loosing of light weight turkish style flighting arrows to enormous distances without damage to the bow. To loose an arrow of this design from a straight staved bow would be quite close to dry-loosing it. Therefore an arrow of moderate weight from a composite would allow great distance and still strike with a respectable blow.

I believe that the ELBs reputation benefits from a bowyers rule of thumb,"heavy arrows shoot quieter than light arrows". Because the longbow is, well, long and it is tillered "safe" it is quite massive near the ends of the limbs. The size and weight of the limbs result in a slower cast, it also results in massive hand shock with light arrows. The answer to this is heavier arrows, which results in 3/8" ash shafts weighing 1/4lbs for a 100lbs+ ELB. I would think that a 4 ounce projectile at 150fps+ would be enough to cause some consternation among the recipients.

I have not yet seen evidence that would convince me of the ability of either the composite or the ELB to penetrate quality harness. I believe that they are effective against lightly armoured troops and horses. I am also of the opinion that the bow was effective in irritating men who were effectively proof against arrow fire to make less than optimal battlefield decisions.

'I saw young Harry, -with his bevor on,
His cuisses on his thighs, gallantly arm'd,-
Rise from the ground like feather'd Mercury,
And vaulted with such ease into his seat,
As if an angel dropp'd down from the clouds,
To turn and wind a fiery Pegasus,
And witch the world with noble horsemanship.'
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Xan Stepp




Location: Ithaca, NY
Joined: 19 Dec 2008

Posts: 54

PostPosted: Sat 24 Jan, 2009 2:05 pm    Post subject:         Reply with quote

Gary, I forgot to comment on this last time:

Quote:
Maybe, but not much. I think the average height varied by an inch, at the most 2, which means .5-1 inch difference in draw.


Looking at the math, I totally agree with you.

Quote:
A few things on this issue. The Composite was not just an archers bow - foot used it as well, it was the common foot bow among Romans and Byzantines among others.

As far as why it never "caught on" in europe - For me, it's mostly cost. A composite bow is more labor intensive, uses varied and perhaps costlier items as well. Plus the time needed to make one was at least a year to allow proper drying and other issues, could even be longer.

The other issue is that it handles moist climates worse, some of the problems are with the glue. Certain glue was more resistant to this, but it was still not as resistant as a straight wood bow.



These are the sort of economic and cultural considerations I was thinking about, but until we get any period sources which discuss this issue (not likely!) it will be a lot of speculation.

S. Mighton:

Quote:


For bows of equal draw weight, a steppe-style composite recurve will equal or outperform an English longbow for all arrow weights.



I keep hearing this, and I'm not inclined to disbelieve it, but I can't really believe it without more evidence. Several people have said it, so it seems accurate enough, but popular culture and fact can be different. Would you mind supplying some sort of evidence? The ideal would be some sort of journal article, but even anecdotal evidence would be useful in a situation where the same person was firing the same arrow from a composite bow and a longbow with the same draw weight. But this idea seems to be related to some of what Jason was saying:

Quote:
The composite bow will loose an arrow of the same weight faster than a straight staved bow of equivalent draw. The composite bow has the following advantages, a "fatter" force-distance curve that allows more work to be done for a given draw weight and less mass in the bow limbs. Due to its reflexed limbs and tips the composite bow is harder to pull in the early and mid-stages of the draw and stores more energy. In the traditional bowmaking materials there is APPROXIMATELY no difference in recovery speed, this, coupled with the smaller arch, allows the composite a high cast. It also allows the loosing of light weight turkish style flighting arrows to enormous distances without damage to the bow. To loose an arrow of this design from a straight staved bow would be quite close to dry-loosing it. Therefore an arrow of moderate weight from a composite would allow great distance and still strike with a respectable blow.



You mention a fatter force curve. Are you implying that the response for a composite bow is not linear? Not that I'd have a big problem if it weren't, but the brief bit of research I've done, seems to indicate that all bows except compounds have a linear force curve. Could you provide a source, particularly one that gives a table or function for the force curve? If the force curve is, in fact, nonlinear then everything else you said seems to make sense, but I do wonder if a lighter arrow will still have the same hitting power. The main contributor to aerodynamic drag for an arrow is quadratic. This may mean that the range is improved but since the drag force is greater it ends up hitting at about the same velocity, but with a lower mass. However, I'd need to do the math to see, and right I don't have the computing power to see anyway.

However, the main reason that I'm posting now is to share some mathematical results about armor penetration. I found a better website (http://www.eugeneleeslover.com/ARMOR-CHAPTER-XII-B.html) about penetration. So using the equations given, I ran the data through for several criteria, based on values given here or on the first article I cited last time. But before I post the results there are a few comments that I want to make:

1) I have no agenda here, I'm just posting what the math shows. I'm not trying to prove that one bow or another can or cannot penetrate whatever.
2) These equations technically only apply to cylindrical projectiles with ogival heads. It's the best I could find, and I'd imagine that a needle bodkin would have better penetration.
3) The math makes the assumption that the projectile doesn't deform at all. This is not really the case as needle bodkins weren't made of hardened steel. However, there is not much that can be done to resolve this in the math. I am aware that it is a problem, and don't really know of a way to incorporate it into the math, so don't comment on it unless you have a mathematical solution.
4) The math also assumes that the armor doesn't deform, which may or may not occur. It's the same as above, I have to deal with the math as it is. But the harder the material, the less likely to deform.
5) I can only give values for wrought iron and nickel steel. I don't know too much about the hardness of nickel steel, but I imagine that it would be as hard or harder than heat treated steel.
6) I'm using data for the longbow, not because I'm preferring it, but rather because the data is easier to get.
7) People will bring up the fact that angle makes a difference. I agree, that's the next project.
8) I had to to the plot on excell, it's not great but will work.

The data does point out some interesting features:
1) The hardness of the material only has a slight effect on penetration, so wrought iron and nickel steel are pretty much the same.
2) Geometry makes a huge difference. I would assume that a good bodkin would be in the 3/16 to 1/4 inch range.
3) This thickness gives poor penetration at long range. Most of the time the arrow will not penetrate, but in places where the armor is thinner the arrow can penetrate. This could account for some of the historical accounts of arrows penetrating armor at long range. I wouldn't shoot one arrow at a person in full harness and expect it to penetrate, but arrows can penetrate thinner portions of armor. So while the probability is low of armor penetration at long range, but with a lot of archers shooting lots of arrows, there will be some penetration.
4) The data indicates that at short ranges that, not only can the arrows penetrate full harness, but that they will.

Hope this was useful.



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deyr sjlfur i sama;
en orstr deyr aldregi
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Benjamin H. Abbott




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PostPosted: Sat 24 Jan, 2009 3:01 pm    Post subject:         Reply with quote

This test suggests that Turkish composite could be more efficient than English longbows. A 136lb Turkish bow shot a 1548-grain arrow at 180.4 fps. In contrast, the 150lb bow tested in The Great Warbow only managed 173.9 fps with a 1480-grain arrow. Note that performance varies a lot amongst individual bows of any given style. Many composites will perform worse than the ones Karpowicz tested, and many wood bows will perform worse than the ones Strickland and Hardy tested. Some might perform better.
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Xan Stepp




Location: Ithaca, NY
Joined: 19 Dec 2008

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PostPosted: Sat 24 Jan, 2009 3:15 pm    Post subject:         Reply with quote

Ben,
That looks like pretty good data. Do you by any chance know the draw length for the Great Warbow bow? That will make a difference. I'd like to see the test I proposed earlier (same person, arrow, and draw weight), but this comparison may be about as close as we're going to get. It does seem to confirm what we reasoned, that the performance would be pretty close, but it looks like it would favor the composite a bit (contrary to my intuition). Thanks for the data!

Deyr f, deyja frndur
deyr sjlfur i sama;
en orstr deyr aldregi
hveim er sr gan getur.
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