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Timo Nieminen




Location: Brisbane, Australia
Joined: 08 May 2009
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PostPosted: Mon 02 Feb, 2015 2:07 am    Post subject:         Reply with quote

The key point of the composite bow isn't that the sinew and horn have a higher elastic modulus than wood (sinew has a much lower elastic modulus than wood, and horn is about double that of, say, yew), but that they can survive much larger strains.

The sinew backing is pre-strained by the shrinkage as the backing dries, and when the bow is strung, it's even more pre-strained (just compare the unstrung reflexed shape with the strung shape). The horn is pre-strained when the bow is strung, but the same applies to a wooden self-bow. Both the horn and sinew will withstand much higher strains than wood.

The importance of maximum strain versus elastic modulus is clear when you look at what makes good bow woods. Plenty of woods have much higher elastic moduli than yew (e.g., double), but yew copes better with strain.

What might we be missing with steel prods? Are they reflexed? If not, why not? I don't recall seeing an old unstrung steel prod, or contemporary artwork of one. A lot of reflex will give a lot more stored energy for the same draw weight and draw length.

"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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Joseph Gora





Joined: 28 Mar 2014

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PostPosted: Mon 02 Feb, 2015 12:25 pm    Post subject:         Reply with quote

Hi Timo,

Yes, I am aware that the modulus of elasticity is not the only thing that counts in a composite. I was more concerned with the fact that if that doesn’t change from steel to steel, then you probably wouldn’t get the compression/tension resistance differences between hard and soft steel either. That might make differential treatment of steel in a prod an unnecessary complication.

Unfortunately, if you do a google seach, there are many crossbows that are either unstrung or whose string has gone slack. There is no evidence that the bows were recurved as far as I can see.

Another considration is that we are only reconstructing a subset of bows – and not the most powerful. Look at this video of a medieval crossbow procession from Maremma in Tuscany:

https://www.youtube.com/watch?v=MMDMB5QJETA

Sizewise, they are more in line with this painting:

http://upload.wikimedia.org/wikipedia/commons...man%29.JPG

If their tradition is old and reliable, those things were bigger than typical Western reconstructions I have seen. It might also explain something that struck me as odd: the fact that – so I have read - many Italian crossbowmen kept their pavise bearers as separate troop units, whereas Western Europeans depict their crossbowmen apparently carrying all of it themselves. You wouldn’t want to be doubly burdened with a shield and a crossbow as big as those Italian ones.
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Jean Henri Chandler




Location: New Orleans
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PostPosted: Fri 06 Feb, 2015 2:49 pm    Post subject:         Reply with quote

I wonder (and have long wondered) how those weapons they use in the Italian festivals perform. Does anyone know?

J

System D'Armes Historical European fencing in New Orleans

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Jean Henri Chandler




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PostPosted: Thu 30 Jul, 2015 7:40 pm    Post subject:         Reply with quote

Don't know if this one has been posted in the thread before or not, but it's interesting

https://www.youtube.com/watch?v=76mbOMFjlu0

System D'Armes Historical European fencing in New Orleans

Essays on Hroarr

Introducing the Codex Guide to the Medieval Baltic
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Pieter B.





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PostPosted: Fri 31 Jul, 2015 8:39 am    Post subject:         Reply with quote

Jean Henri Chandler wrote:
Don't know if this one has been posted in the thread before or not, but it's interesting

https://www.youtube.com/watch?v=76mbOMFjlu0


That's quite a velocity at 57 m/s. Looks like it gave quite a punch too.
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Joseph Gora





Joined: 28 Mar 2014

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PostPosted: Sat 01 Aug, 2015 6:38 pm    Post subject: Italian x bows         Reply with quote

And despite that 'punch' - if you read the comments - they got more penetration with a bow. I bet the arrowheads have something to do with it. Here is another clip:

https://youtu.be/vk7Oyhu3EsY

Look carefully at the crossbows used wit the windlass - especially clear at 1:20 (although there is another one of similar dimensions at the beginning) and also take note of the apparent size of the bolds in the quivers. It could be just me, but that looks like a weapon with an awful lot longer power stroke than six inches and with much longer bolts to match. As I said before, I suspect we are reproducing just one strand or subset of crossbow. The Italian ones which the Genoese were famous for may very well have been bigger than the norm, and the English/Germanic/French ones may have been lighter for mobility or whatever reason.

Cheers,

Joseph
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Joseph Gora





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PostPosted: Sat 01 Aug, 2015 6:42 pm    Post subject:         Reply with quote

It seems superfluous and too obvious to add that the variety of different bows and bow dimensions in that clip is impressive. WE just aren't reproducing that degree of variation - yet.
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Jean Henri Chandler




Location: New Orleans
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PostPosted: Mon 05 Dec, 2016 7:39 am    Post subject:         Reply with quote

Forgive me if someone already posted this

Here is another test with another 579 kg draw (1280 lbs) composite-prod crossbow, 150 cm prod length, where shooting some very heavy bolts they got 57.7 fps with a 260 gram bolt for 433 joules (see 01:26), and 348 gram bolt for 488 joules (01:33). He's saying that weapon has a 'potential energy of over 1200 joules, though I don't know what that is based on.

https://www.youtube.com/watch?v=nY2untEwCnU

I don't think even this guy has quite figured it all out yet but he is clearly much closer to the reported medieval performance than in some of the older tests I've seen with composite prods where the prods seemed to fail after just a few shots and they had very poor performance.

Looks like he published a book or a paper or something, here:

https://www.amazon.de/Jahrblatt-Interessengemeinschaft-Historische-Armbrust-2016/dp/3741250201

Maybe some of our German speakers on the thread could find out more about this test.

System D'Armes Historical European fencing in New Orleans

Essays on Hroarr

Introducing the Codex Guide to the Medieval Baltic
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