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Gary Teuscher





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PostPosted: Thu 15 Sep, 2011 12:29 pm    Post subject:         Reply with quote

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" Halb rustung " class crossbow with steel prod with bolt mass not more than 80 gram - about 67 m/s


Seems to fall in pretty well with the weight of longbow arrows tested by Stretton.

It seems the crossbow tranfers energy MORE efficiently than the longbow then, if using about a 80g arrow and a 48 m/s for the longbow, and a 80g 67 m/s for the 500kg crossbow. The crossbow bolt has almost twice the kinetic energy of the Longbow arrow with these numbers, when stored energy seems to indicate the crossbow should deliver about 1.5 times or so the stored energy.

Of course, this is based on my guess of about a 6" powerstroke for the crossbow, a longer powerstroke would indicate energy transfer closer to that of the longbow. Of course a shorter powerstroke would indicate the crossbow is far more effective in transferring it's stored energy.

Maybe you have something there about the better efficiency of the crossbow with it's shorter limbs Big Grin

Something slightly off topic but interesting about Stretton's tests - the long bodkin seemed to be the least efficient in transferance of stored energy - they had similar weight to the short bodkin, but a lower exit velocity.

The "lozenge" type (Many Viking arrowheads found seem also to be of this type) was the heaviest arrow, but had about the same exit velocity as the long bodkin.

Not sure what all this means or points to, this has nothing to do with penetration, just found it interesting Big Grin
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Timo Nieminen




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PostPosted: Thu 15 Sep, 2011 2:11 pm    Post subject:         Reply with quote

Jean Henri Chandler wrote:
Lists the force at 3,000n and 4,000n respectively. What does 3,000n mean?


That's the force in newtons. 3000N = approx 300kg. To convert to lbs, divide by 10 (approximately, 9.81 is more exact) to get kg, multiply by 2.2. So, 110lb is 500N.

("N", not "n", for the symbol.)

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Timo Nieminen




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PostPosted: Thu 15 Sep, 2011 2:34 pm    Post subject:         Reply with quote

Gary Teuscher wrote:

Hey Leo, I was curious about something. From the testing on turkish bows, it indicates there was a greater loss in ebergy transference efficiency the lighter the arrow was compared to the bow.

[...]

Would this also be true of crossbows? a 900lb crossbow with a 6.5" draw would theoretically store almost 1.5 times the amount of energy as that 140 lb longbow, which would indicate it would be best served by a 2000+ grain bolt, which seems to me way heavy for a bolt.

[...]

It seems the turkish was arrows from what I have been able to gather were about 650g - and they did not maximize energy transmitted, though the exit velocity was higher and would theoretically giave them more range than a heavier arrow, though a lighter arrow bleeds energy faster.


It's general - heavier arrow gives you more energy, and less speed, and a lighter arrow gives you less energy and more speed. This works for bows, crossbows, and mechanical artillery. Similar also for hand-thrown weapons, but that's more complicated since there are muscles involved.

Of course, you want a compromise between energy and speed. What arrow mass gives you this depends on the mass of the bow (and the distribution of the mass).

Ottoman military flight arrows were about 20grams/300gr, and their heavy war arrows about 40g/600gr. Looks like the general purpose optimum arrow mass would have been 30g/450gr.

I did a graph of how the energy and speed vary some time ago. Here it is. A good arrow/bolt weight is where the curves cross.


"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Gary Teuscher





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PostPosted: Fri 16 Sep, 2011 9:36 am    Post subject:         Reply with quote

Quote:
Ottoman military flight arrows were about 20grams/300gr, and their heavy war arrows about 40g/600gr. Looks like the general purpose optimum arrow mass would have been 30g/450gr.


Any sources for this? these are also the numbers I have run across, but can't find any actual historical specs on the arrows.

I'm not sure about that "general purpose" arrow though. From what I have read it seems like 2 types - flight or war, flight possibly used in war to for long range attacks. But I don't think there was a "general purpose" arrow that I know of.

Optimizing energy from those bows would seem to have been best accomplished by using a 1000+ grain arrow - though I see no record of this weight of arrow, other than in the Turkish bow testing we are probably both referencing.
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Timo Nieminen




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PostPosted: Fri 16 Sep, 2011 2:03 pm    Post subject:         Reply with quote

Gary Teuscher wrote:
Quote:
Ottoman military flight arrows were about 20grams/300gr, and their heavy war arrows about 40g/600gr. Looks like the general purpose optimum arrow mass would have been 30g/450gr.


Any sources for this? these are also the numbers I have run across, but can't find any actual historical specs on the arrows.

I'm not sure about that "general purpose" arrow though. From what I have read it seems like 2 types - flight or war, flight possibly used in war to for long range attacks. But I don't think there was a "general purpose" arrow that I know of.

Optimizing energy from those bows would seem to have been best accomplished by using a 1000+ grain arrow - though I see no record of this weight of arrow, other than in the Turkish bow testing we are probably both referencing.


The 20g/40g numbers are from A. Karpowicz, “Ottoman bows — an assessment of draw weight, performance and tactical use,” Antiquity, vol. 81, pp. 675–685, 2007. That's the range of weights for war arrows. Karpowica cites a Turkish publication as the source. Pant, "Indian Archery" gives weights for some Indian arrows, and most are in this same range, and just eyeballing the numbers, it's a fairly even distribution. Might even be close to normal, with a few more in the centre, and some outliers to about 15g one way, 56g the other.

The "general purpose" comment is just that the two extremes in the distribution are probably speed and energy oriented, so flight and short-range high-energy arrows. A GP would be in the middle. I don't know the distribution of Ottoman or other Turkish arrow weights. One usually only sees the descriptions of both flight/war arrows being carried, and sort arrows shot using the arrow guide (sipar), and no numbers.

From arrow lengths/diameters, (Grayson, "Traditional Archery From Six Continents"), target arrows could be heavier than war arrows. Certainly thicker! Probably to make them last longer. (No weights! Would have been good to see weights in this book.)

As for optimising energy, well, always more energy from a heavier arrow. But you never just optimise for energy alone - always a compromise. Not a big problem, because while heavier is always more energy, past some point, that "more" is only a little bit more, even as the arrow mass grows a lot, and your speed becomes uselessly tiny.

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Chris Gilman




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PostPosted: Fri 16 Sep, 2011 4:56 pm    Post subject:         Reply with quote

I have come to this thread a bit late and have not read every post. I’m on the, arrows didn’t penetrate good armour, side of the fence. (I have done a number of tests with my bows)
With that said, is there any historic eye witness accounts of a person in quality armour of the period, being injured by an arrow (or bolt) through their armour? (My apologies if I missed a previous post) I have never read or heard of one. Through eyeslots or open faceplates and in gaps, yes, but not penetrating the armour itself.

Secondly, I have been friend with Jaap Koppedrayer for many years. He is considered by many to be a world class natural composite bow maker. Over the years he has repeatedly told me that bows have “torque” and “horsepower” and that the shooters skill has a great deal to do with the optimizing these. (He currently holds records for long distance shooting, using set bow weights) Jaap says, in addition to its construction, the pull and release has a lot to do with getting the most out of a bow. He also points out, his natural composite (horn, sinew, wood) bows shoot very differently than a similar poundage one piece or modern composite bow. These observations have made me doubt my arrow penetration tests, which have always resulted in a mild steel point not penetrating a medium carbon steel, (1050 normalized in most cases) enough to reach the “occupant” to any injuring degree.)
We have been discussing the making of a natural composite crossbow prod for some time and it looks like this is finally going to happen. He and I are very curious if the natural composite material will have a significant effect on the performance of a cross bow. (of equivalent poundage.)

Chris
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Gary Teuscher





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PostPosted: Sun 18 Sep, 2011 2:30 pm    Post subject:         Reply with quote

Quote:
With that said, is there any historic eye witness accounts of a person in quality armour of the period, being injured by an arrow (or bolt) through their armour? (My apologies if I missed a previous post) I have never read or heard of one. Through eyeslots or open faceplates and in gaps, yes, but not penetrating the armour itself.


Yeah, most accounts of arrow injuries with plate armoured troops are something along the lines of "they lifted their visor and were struck in the face by an arrow".

Now this is a javelin, not an arrow, but -

Quote:
This statement is undoubtedly derived from the Chronicles of Froissart in which the Duke of Lancaster is quoted as saying:

To which the duke's squire replied:
You say truly, for I saw more bodies transfixed at these assaults than I ever saw before in all my life. We lost one whom we much regretted, Senhor Joao Lourenço da Cunha, who was struck by a dart that pierced through his plates and his coat of mail and a gambeson stuffed with silk, and his whole body, so that he fell to the ground.


A javelin seems to genberate a lot of joulles - and this was from a mounted javeliner, which could have been using the mounts momentum as well. Numbers of 360 joulles can be achieved be an olympic javelineer with a run up - I'd guess a mounted javelinman could possibly get close to that.

This does a very good job of combing various period sources regarding mail vs arrows. Uses the term "chainmail", and talks about 2000 lb warhorses, but otherwise the author seems to do a good job.

http://www.capnmac.com/archery/maille/Chapter3.htm

And now I cannot find the exact source, but it was a period reference, a grandmaster of a fighting order in mail taking a turkish arrow in the armpit so deeply that in penetrated almost to the feathers.
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Jean Henri Chandler




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PostPosted: Wed 16 Nov, 2011 7:42 am    Post subject:         Reply with quote

Only slightly relevant but I thought interesting

http://www.ctmuzzleloaders.com/ctml_experimen...etbow.html

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William P




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PostPosted: Thu 17 Nov, 2011 4:31 am    Post subject:         Reply with quote

so allow me to doublecheck.

i have been told that pound for pound, a crossbow has a much lower cast than a regular bow mostly due to the short distance the arrow is propelled and the short length of the bow prod
and this explains why you need a 500-800lb crossbow to achieve roughly the same results as a 140-180 lb longbow??

or are there other factors that determine how the bow transfers power to the projectile.
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Bartek Strojek




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PostPosted: Thu 17 Nov, 2011 4:51 am    Post subject:         Reply with quote

Crossbow prod gathers less energy in the first place.

A lot of force is being used, by over relatively short road = so less energy is in result stored in bent bow.
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Randall Moffett




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PostPosted: Thu 17 Nov, 2011 6:21 am    Post subject:         Reply with quote

William I thing your general concept is right but your numbers are off. according to some RA tests a 100lb bow is about the same as a 300-400lb crossbow as far as meters per second. I'd suspect from Jean Liebel's work this is actually a bit off in favor of the crossbow but they are certainly not equal by poundage. That said by the late medieval period personal crossbows are getting super heavy draw weights, perhaps starting at 350-450lbs draw (see Liebel).

I'd be careful as the one factor still left largely unexplored in a large scale is bolt weight. Added mass will change the initial and impact energy.

I keep hoping we will see some good testing that will cover some of these things but recently it seems firearms are getting much of the love.

RPM
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Jean Thibodeau




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PostPosted: Thu 17 Nov, 2011 8:01 pm    Post subject:         Reply with quote

Randall Moffett wrote:

I'd be careful as the one factor still left largely unexplored in a large scale is bolt weight. Added mass will change the initial and impact energy.


RPM


I've written about this a few times in much much earlier posts in more detail but to give a simplistic comparison of bow versus crossbows, and using very heavy bolts, the assumption I make is that one quickly reaches a point of diminishing returns where a heavier draw doesn't produce a bow or a prod that can accelerate an arrow or bolt much more than a much lighter bow or prod.

So any extra draw weight won't do much to increase the feet/sec. velocity much over 300 feet/sec: The bow or prod limbs will just not move any faster than a certain upper limit and their speeds define the speed the bow or prod string will attain as the same maximum speed for arrow or bolt.

So after this long preamble: Given a maximum speed of 300 ft/sec the only reason for a heavier crossbow prod is to be able to use a heavier projectile at the same maximum attainable velocity.

If your crossbow bolt is travelling at the same speed as an arrow the effect on target will be identical if they both weigh the same, but if your bold is 2X, 3X or more you double or triple the momentum and energy on target.

Experimentation is what we need to find what is the weight of bolt that is optimum for using efficiently the power stored in the prod of a drawn super heavy crossbow.

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Gary Teuscher





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PostPosted: Fri 18 Nov, 2011 8:17 am    Post subject:         Reply with quote

Quote:
So any extra draw weight won't do much to increase the feet/sec. velocity much over 300 feet/sec: The bow or prod limbs will just not move any faster than a certain upper limit and their speeds define the speed the bow or prod string will attain as the same maximum speed for arrow or bolt.


Eaxactly, coincides with everyting I have read. And you cannot compare the velocity capable of modern bow construction using modern materials.

That's why the heavier the bolt/arrow, the higher the efficiency of the bow. Of course, I assume there is a trade off at some point by going too heavy on the arrow, but every test I have seen even with 1500 grain arrows/bolts, the higher the weight the more efficient the bow.
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Jean Henri Chandler




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PostPosted: Tue 06 Dec, 2011 11:46 am    Post subject:         Reply with quote

Bartek Strojek wrote:
Don't have the thing handy, especially don't feel like checking, especially, that, unfortunately " ich verstehe nicht" is about the pinnacle of my German. Big Grin

Fortunately found some guy citing:

" Halb rustung " class crossbow with steel prod with bolt mass not more than 80 gram - about 67 m/s

Halb rustung would be half a tonne, generally, so ~500kg.


Can you give me a citation / source for that? I'd like to use it in my book.

J

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Bartek Strojek




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PostPosted: Tue 06 Dec, 2011 12:05 pm    Post subject:         Reply with quote

Jean Henri Chandler wrote:

Can you give me a citation / source for that? I'd like to use it in my book.

J


It's "Die Armbrust" by Egon Harmuth

http://www.amazon.com/review/R2MSUO3GUKPMZC

I've seen some preview on the Net once (even legal I think, with a lot of pages missing etc. Razz ) but can't find it anymore.

Anyway, I've seen someone citing those numbers from this book, so all in all they're somewhat second hand data....
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Leo Todeschini
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PostPosted: Tue 06 Dec, 2011 3:01 pm    Post subject:         Reply with quote

Hi,

I know I have done nothing to add to this topic in ages, but I have my fingers in a few pies and do find it hard to gather data. However I have another big bow to make early next year and I now own a chronograph so perhaps I will soon be able to add something.

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Gary Teuscher





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PostPosted: Wed 07 Dec, 2011 11:38 am    Post subject:         Reply with quote

Quote:
" Halb rustung " class crossbow with steel prod with bolt mass not more than 80 gram - about 67 m/s

Halb rustung would be half a tonne, generally, so ~500kg.


That gives roughly twice the kinetic energy I have seen from testing with period longbows in the roughly 140 pound range or so.

I have seen roughly the same weight arrows as opposed to bolts in the 45-49 meters per second range.
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Randall Moffett




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PostPosted: Wed 07 Dec, 2011 1:51 pm    Post subject:         Reply with quote

Leo,

Wish I could be there to be part of it. After looking after a few original crossbows I grew very impressed by the items. They really are something that needs much more work and study.

Heard you and Glennan were in the shop the other day and became very envious of all the super cool stuff you are working on.

RPM
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Sime Ivic




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PostPosted: Sun 11 Dec, 2011 1:56 pm    Post subject:         Reply with quote

When comparing bows it is not enough to look just at arrow weights and energy storage curves. Material of which it is made has a huge influence, when you shoot a 70 gram arrow out of a warbow that warbow also has to move itself, which is at most somewhere under two pounds, most commonly between 25-30 ounces, while steel prod is considerably heavier, provided it stores the same amount of energy which is an entirely different topic in itself.
This poundage to limb mass ratio is critical for performance, Adam Karpowicz's book on turkish bows has a great info on this. According to him, bows made of wood have this ratio more favourable than composites up to about 100 pounds of weight, after that composites become bettter while selfbows suffer, that's the reason for the mentioned longbow's sweet spot. After you reach a certain weight you need disproportionaly more limb mass, whoever has made a classic backyard practice selfbow knows that difference between 20 and 40 pounder is few hairbreadths of wood while heavier ones are much more forgiving during tillering. You also need a longer bow because limbs are now thicker and cannot stand the same amount of deformation but then lever effect comes into play and you need more thickness again and so forth and so forth. That's why dense growing yew was favoured, it can pack more weight in the same space. Note difference between weight (poundage) and physical mass.
It is much repeated statement that composites are lighter than wood bows, actually 6 foot composite would weight more than a 6 foot wooden bow, since composites are made of tissues that sink in water for example. The thing is they can be made shorter and put under greater strain to offset this mass disadvantage. Now imagine by how much iron is denser than horn, it would need proportionately higher draw weight to become truly effective in this context. So, sweet spot for steel bows should be determined and that would answer whether they were made for energy effectiveness or knocking out, as Leo said.
To be honest I'm not sure that this same kind of wood-composite swapping is possible with composite-steel, because composites, though denser, are more elastic than wood, while steel has to be even less strained than wood.
Crossbows are by definition made to be held at draw with no effort, but there is a problem to this. Materials like wood, horn and sinew creep when under stress, and longer they are under it the weaker they become. If steel can stand it for much longer it would be a good explanation for it's use, it would be great for mounted soldiers closing in on their targets and picking spots, or for sniping over built defences or any kind of stalking as in hunting. Of course crossbows were used for that before invention of steel but it's introduction could have raised their use to another level, comparable to that of first wheellocks. Or they did it not to increase range but to launch heavier bolts to already common distances. But that opens a new problem when considering sporting hunting bows with steel prods. You dont need armor piercing projectiles when hunting deer. Relative ease of construction and maintenance probably held a big role in it's development.
So there it is, I'm sorry if this is all confusing but it's complicated subject and it's late here, I'm not that good on historical sources but I've made a handful of wooden bows and read a lot on their construction theory so wanted to say something about this part of the story which to me seemed ignored except for this

Quote:
Crossbow arms are heavier, but the longbow arms travel a longer distance.


again I will quote Adam Karpowicz who I believe knocked this whole topic on the head in his book. Bow is a spring, and springs oscillate in a frequency which is always the same and depends on spring length and thickness. Just like a tuning fork. If you clamp a bow by its grip in a vice and pull-release a limb it will go back and forth. It will go back and forth same amount in a a given time and that's it's frequency. The further you pull it away from the rest position actually the faster the recovery so it can meet that frequency. When designing a bow you want to pull it as far as possible without breaking or suffering permanent deformation. With that said if-ever-achieved 300 fps mark set above will not be a consequence of poundage, as Jean Thibodeau said, but of frequency to which a certain prod is "tuned" and how far it is stressed

Sime Ivic
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Jean Henri Chandler




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PostPosted: Wed 14 Dec, 2011 9:29 am    Post subject:         Reply with quote

One small point to make here; the most powerful crossbows were made with both composite and steel prods. One important factor mentioned in some period records, steel prods could sometimes snap apparently under very cold conditions. So while the Burgundians were already using steel prods for their crossbows, the Swiss were still using composite prods, reportedly of equivalent strength but more expensive and time consuming to make, and more sensitive to moisture. This was also reported in the Baltic by the Teutonic Order who did a lot of their campaigning in Winter, though I believe they eventually switched to steel prods by the mid 15th Century (mainly because most of their forces at that time were mercenaries from Bohemia).

So the bottom line is that there were both steel and composite prod crossbows of the strongest "statchel" variety, that had to be spanned with cranequin or winches.

J

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