| Author |
Message |
|
Gary Teuscher
|
 Posted: Thu 15 Mar, 2012 10:11 am Post subject: |
 |
|
| Quote: | | Yes that follows what I was thinking. I think steel especially is just mechanically not as efficient as wood and both are less effective than a longbow. That said I think in part it is smaller draw lengths. Though I assume in part this was compensated by heavier bolts. I have weighted several that were in the 150s and 160s grams region which is near double to double what most testing uses. This would have a serious change in impact energy in short distances especially. |
Are you familiar with the below listed testing, Randall?
http://www.atarn.org/islamic/akarpowicz/turkish_bow_tests.htm
It's not particularily illuminating, but does point out that the heavier grain of the arrow, the more efficient the bow, even the light pound pulls. The Heaviest of bows tests are not very efficient with a lighter arrow - and a crossbow is going to see even more of this bleed off, as the increased energy assuming similar weighted projectiles can only be transmitted one way , to velocity - and it seems the closer you get to that maximum, the more serious the energy bleed. It seems to progress more exponentially than in a straight line.
As far as wood being less efficient than a longbow - both are wood, correct? and if meaning the D shape bow with sapwood on one side, that's pretty well how all wooden D shaped self bows were made, I would assume the same method would be used on a D shaped type crossbow.
From waht I have seen, the most effective self bow is the recurve composite, at least in regards to transference of energy. That probably has more to do with the higher initial draw weight as a percentage compared to maximum draw weight due to the recurve bow desiring to get back to straight, and it is further from it's "straight" than a longbow style selfbow.
What I am trying to say is that the increased efficiency of a composite is not as much due to the materials but due to the physics of how the bow is strung - but I guess the materials of the bow allow it to be strung differently giving it the different physics, so indirectly the material do matter.
I have not heard that wood is more efficient than steel though - I've heard arguments onboth sides of the fence here.
I think it's extremely tough to truly compare efficiencies, as they were used for two different types of bows, and the steel bows are generally or far greater pull, skewing efficiency tests against them.
|
|
  |
 |
Randall Moffett
|
| Posted: Thu 15 Mar, 2012 12:44 pm Post subject: |
|
|
Gary,
Very interesting experiment. I often have wondered if that was not why crossbows show such ineffectiveness because the light bolts used. The problem ultimately is that we need a great deal of testing on them to see what effect arrow weight plays. I often think they likely had bolts of similar types just like warbows.
One thing regarding bows and bows on crossbows is limitations of the bow themselves. They tend to be short. Some of them are squat but you cannot make them thicker after a certain point and still gain power from it. So for wood bows for crossbows there are many limitations that are less difficult on a longbow as you gain power by both length and width.
RPM
|
|
|
|
|
|
Gary Teuscher
|
| Posted: Thu 15 Mar, 2012 12:54 pm Post subject: |
|
|
| Quote: | | So for wood bows for crossbows there are many limitations that are less difficult on a longbow as you gain power by both length and width. |
I see what you are saying, though I'm not sure how much of a factor it is. There was a wooden crossbow, dated to I think the 14th century on exhibit in a museum, in England I believe. The estimated draw weight was well over 400 pounds, of course they were not going to test it itself. I forget the exact specs on draw length, but I think it was over 10".
I forget the dimensions, but they struck me as certainly field portable.
I think wooden ones were still effective, later than many may commonly think. There was mention of wooden crossbows being replaced by metal ones in the records of some lowland cities I believe, and the was in the late 15th century.
Just a guess or more of an extrapolation perhaps, But I would think 500-750 pound wooden bows could have certainly been used, and have been portable field bows. They would probably have had longer drawlengths than the later steel hunting crossbows, so would have carried a pretty good punch, better than that of a longbow.
I might mention I hate the use of the word "longbow", as it implies a rather unique wepaon, when D shaped 6' or so bows have been used throughout history.
It just rolls off the tongue easier than "D shaped bow of length greater than 5'" 
|
|
|
|
|
Leo Todeschini
Industry Professional
|
|
 |
|
Benjamin H. Abbott
|
| Posted: Fri 16 Mar, 2012 6:47 pm Post subject: |
|
|
| Gary Teuscher wrote: | | I would think 500-750 pound wooden bows could have certainly been used, and have been portable field bows. They would probably have had longer drawlengths than the later steel hunting crossbows, so would have carried a pretty good punch, better than that of a longbow. |
I think that's fairly likely, but I don't know of any tests of wooden or composite crossbows that actually produced better results than a longbow. See the test I linked for two composite crossbows earlier in the thread.
|
|
|
|
|
|
Gary Teuscher
|
| Posted: Mon 19 Mar, 2012 9:16 am Post subject: |
|
|
| Quote: | | See the test I linked for two composite crossbows earlier in the thread. |
I cannot find the link, if you could post it again that would be great.
But the real question IMO is the drawlength of these crossbows and the length/weight of the bolts. Do we have any true bolts from prior to the 15th sentury that anyone is aware of? Prior to the 14th would even be more interesting for me.
"Bow: length along back 45½ in (115.6 cm)
length along belly 43¼ in (109.9cm)
section – maximum 2¼ in (85.1 cm)
Tiller: length 33½ in (85.1 cm)
width 1 3/8 in (3.5 cm) at fore-end tapering to 7/8 in (2.3 cm) at the butt
bolt guide 12¾ in (32.4 cm)
nut to fore-end 13 3/8 in (34 cm)"
Above are some dimensions of a 14th-15th Wooden Crossbow (could possibly be 13th Century) given by the museum curator.
Nut to for end would seem to mean a 13 and 3/8" draw? With a 3-4" brace, that is a 9-10" powerstroke or so.
I think one of the problems with testing of crossbows - a very short draw and powerstroke are always assumed, based on renaissance era hunting crossbows.
One of the problems with testing steel bows, as explained to me by Leo - we tend to have shorter draws on current netal corssbows because of safety issues. A middle ages crossbow may not care if it snaps on one out of very thousand times used, if an extra inch or two of power is gained.
ETA: Anyone have any idea what draw lengths were being used for the longbow testing or calculations that are mentioned above? I have read in other tests where 30-32" are used. I would think basing the draw on the available draw on Mary Rose arrows would make more sense, these seem to be in the 29" range.
There are a percentage that are 4" or so longer, but I think many believe these to be fire arrows used in shipboard combat,.
|
|
|
|
|
Benjamin H. Abbott
|
| Posted: Mon 19 Mar, 2012 2:15 pm Post subject: |
|
|
|
The test was performed by Andreas Bichler. The 616lb crossbow in this experiment performs about as well as a 100lb longbow. Given its rather long power-stroke, these results confuse me. The lighter crossbow performs about like you'd expect - perhaps a little worse - but I'd have estimated the heavier one to deliver almost double the kinetic energy recorded.
|
|
|
|
|
Jean Henri Chandler
|
| Posted: Mon 19 Mar, 2012 2:27 pm Post subject: |
|
|
| Gary Teuscher wrote: | | I think wooden ones were still effective, later than many may commonly think. There was mention of wooden crossbows being replaced by metal ones in the records of some lowland cities I believe, and the was in the late 15th century. |
I can confirm that the Teutonic Order was definitely still using wooden crossbows in the second half of the 15th Century. It is the most common type they mention in their records, as well as large numbers of yew prods for these. It was rated as the cheapest and least of three types. They called them knottelarmbruste. The second tier up were the stirrup crossbows (stegelarmbruste) and the third were the 'statchel' or stingers, which could be of either composite or steel prod and cost at least 1 mark each.
All three types also show up in the town-armoury archives for Krakow, under the same German names.
| Quote: | Just a guess or more of an extrapolation perhaps, But I would think 500-750 pound wooden bows could have certainly been used, and have been portable field bows. They would probably have had longer drawlengths than the later steel hunting crossbows, so would have carried a pretty good punch, better than that of a longbow.
I might mention I hate the use of the word "longbow", as it implies a rather unique wepaon, when D shaped 6' or so bows have been used throughout history.
It just rolls off the tongue easier than "D shaped bow of length greater than 5'" |
Agree with all of that.
J
Books and games on Medieval Europe Codex Integrum
Codex Guide to the Medieval Baltic Now available in print
|
|
|
|
|
Bartek Strojek
|
| Posted: Mon 19 Mar, 2012 2:28 pm Post subject: |
|
|
Well, with all props for interesting tests, I would guess that bows could have been rather poorly made as far as section and material forming goes - rather poor efficiency and they took some mayor set pretty quickly.
Dunno what's author experience as a bowyer, but craftsmanship makes huge difference as far as bow dynamics go.
|
|
|
|
|
Jean Henri Chandler
|
| Posted: Mon 19 Mar, 2012 2:31 pm Post subject: |
|
|
| Benjamin H. Abbott wrote: | | The test was performed by Andreas Bichler. The 616lb crossbow in this experiment performs about as well as a 100lb longbow. Given its rather long power-stroke, these results confuse me. The lighter crossbow performs about like you'd expect - perhaps a little worse - but I'd have estimated the heavier one to deliver almost double the kinetic energy recorded. |
Thanks for posting this, this looks like a very thorough test!
J
Books and games on Medieval Europe Codex Integrum
Codex Guide to the Medieval Baltic Now available in print
|
|
|
|
|
Benjamin H. Abbott
|
| Posted: Mon 19 Mar, 2012 5:23 pm Post subject: |
|
|
| Bartek Strojek wrote: | Well, with all props for interesting tests, I would guess that bows could have been rather poorly made as far as section and material forming goes - rather poor efficiency and they took some mayor set pretty quickly.
Dunno what's author experience as a bowyer, but craftsmanship makes huge difference as far as bow dynamics go. |
Yeah, that strikes me as a likely explanation. Bow performance varies based the quality of materials and skill of the maker. Many English-style longbows don't produce as good numbers as the Mary Rose reproductions tested in The Great Warbow.
|
|
|
|
|
Jean Henri Chandler
|
| Posted: Tue 20 Mar, 2012 8:13 am Post subject: |
|
|
I imagine it's going to be a while before we can reliably make crossbows of this power, particularly the composite prods, any more than you can learn to paint like a Flemish master in a few months.
We are counting on Leo and a few other folks who are becoming experts to continue to push the envelope for us...
J
Books and games on Medieval Europe Codex Integrum
Codex Guide to the Medieval Baltic Now available in print
|
|
|
|
|
|
Gary Teuscher
|
| Posted: Tue 20 Mar, 2012 8:45 am Post subject: |
|
|
| Quote: | | Given its rather long power-stroke, these results confuse me. |
I agree. The powerstroke on these is 8-9". The wooden bow I listed above had a 9-10" Powerstroke, so that's at least close. I've always though a composite crossbow would have a longer powerstroke for it's size than a wood one, similar to a composite vs. selfbow, but that's merely a hunch based on no specific evidence.
As these are composites, perhaps there is more room for modern manufacturing error.
They appear to be well made and well thought our reproduction weapons though.
Any idea which bolts were used in these tests? (the weight). I read through but could not find anything.
ETA: Found the bolt info.
As far as efficiency goes - I thnk both suffer bleed off as I had mentioend earlier. What I find Interesting - Just a quick calculation leaving out brace length for a comparative analysis only.
The lighter Bow with Draw of 8" x 288 pounds = 2304
The Heavier is 9"x 616 pounds = 5544
The heavier bow has 2.41 times the stored energy of the lighter bow.
We translate this into energy released, only using velocity as bolt weight is a constant -
Heavier 61x61 = 3721
Lighter 53x53 = 2809
3721/2809 = 1.32
So while the Heavier bow stores 2.41 times the energy, it only releases 1.32 times the stored energy. This makes it 55% as efficient as the lighter bow.
Now these maximum velocities were probably with the 41 grain bolt - with the 90 grain bolt I'll bet the heavier one got a bit more efficient, but still less than the lighter crossbow by far.
How more effective theoretically should these be than a longbow? To make calculations real simple, lets just multiply the power stroke times the draw weight, 29" draw for a longbow 5" brace, 150 pounds draw weight.
Longbow - 3600
Lighter Xbow - 2304
Heavier Xbow - 5544
It's not quite that simple, it's a curve on the draw with the maximum being at full draw. And the draw truly starts at the brace, i.e if brace is 20% of the distance, the draw starts at 20% of the max. And with a recurve it's even more difficult, they no not start at straight - at straight they are already somewhat flexed, so depending on how much recurve they could start at 25-45% of max draw if brace was 20% of the drawlength.
And all this assumes straight line increases in draw compared to distance, which is roughly accurate but not fully accurate. Stacking is just one of the issue that effect enrgy stored.
And this is just stored energy, has nothing to do with the effiency of releasing that stored enrgy which takes into account a myriad of things.
|
|
|
|
|
Leo Todeschini
Industry Professional
|
| Posted: Tue 20 Mar, 2012 5:27 pm Post subject: |
|
|
Gary Teuscher wrote | Quote: | | One of the problems with testing steel bows, as explained to me by Leo - we tend to have shorter draws on current netal corssbows because of safety issues. A middle ages crossbow may not care if it snaps on one out of very thousand times used, if an extra inch or two of power is gained. |
Well actually I did not in fact say that, and perhaps I got my original post confused, but whatever, I am sorry for any confusion caused.
The reliability of modern steels and heat treatment means that we can reliably and safely draw modern bows back more than they could in history. Modern reproductions tend to run with a wider bow and a longer draw that historical examples as it offers better efficiencies than historical patterns and practices allow.
Roughly speaking steel bows had the following sizes. (there will be exceptions to this)
Hunting bows were between 550-620mm and had a powerstroke of 4.25 to 4.75" /115-135mm
Windlass bows were between 690-740mm wide and had a powerstroke of 6 to 6.75" / 150-170mm
Modern reproductions tend to run between 6-8" and so have a stroke 1-2" longer and they tend to be around 3.5"/100mm wider the medieval counterparts they are based on; so in fact it is the inverse of Garys' quote.
The only bow I have come across that was radically outside of this approximate width/stroke layout was a hunting bow of Maximillians that used a bow under 600mm wide and drew to just over 150mm/6" maybe 6.25" (I forget now) so was very distinctly at least 1.25"/30mm longer in the stroke than you would expect. It was a heavy bow too and so was right on the absolute limit of what is possible before either deformation or fracture.
Tod
www.todsworkshop.com
www.todcutler.com
www.instagram.com/todsworkshop
https://www.facebook.com/TodsWorkshop
www.youtube.com/user/todsstuff1
|
|
|
|
|
|
Gary Teuscher
|
| Posted: Wed 21 Mar, 2012 9:36 am Post subject: |
|
|
| Quote: | | Well actually I did not in fact say that, and perhaps I got my original post confused, but whatever, I am sorry for any confusion caused |
My apologies Leo if I misquoted you.
I had corresponded with you and a few other crossbow makers a few years ago about some crossbow issues. One of the emails I received stated that their steel crossbows were made an inch or two shorter than middle ages draws.
The reasoning for this they gave is they had to observe tolerances in the metal, and they would only allow a certain amount of stress to be placed upon the metal because they were concerned about the bows snapping, and injury, and then a products lawsuit.
Whomever it was stated that there would be less concerns with middel ages crossbow makers in a less litigous society.
I'll try to pull up the exact email, then I can more accurately say who said that. I apologize, I thought it was you but did it from memory without pulling the exact quote.
|
|
|
|
|
Leo Todeschini
Industry Professional
|
| Posted: Thu 22 Mar, 2012 2:58 am Post subject: |
|
|
As a commercial operation I am pursuing bow performance with an eye on understanding my products better and maximising their performance so I am trying to find the section that works best and then will go on to look at bolt weights so the information is a little erractic but once I have settled on bow sections I will pursue bolt weights. Once I have a set of bow measurements I am entirely happy with, then I will spend some time with variable bolt weights to look at energy delivery.
I hope this is useful as a start point.
400lb, 130mm draw, 72gram bolt, 38.8ms = 54j
42gram bolt, 44.5ms = 41j
530lb, 135 draw, 50g bolt, 50ms = 62j
250lb, 130 draw, 50g bolt, 50ms = 39j
Tod
www.todsworkshop.com
www.todcutler.com
www.instagram.com/todsworkshop
https://www.facebook.com/TodsWorkshop
www.youtube.com/user/todsstuff1
|
|
|
|
|
Jean Henri Chandler
|
| Posted: Fri 27 Jul, 2012 1:25 pm Post subject: |
|
|
Any new developments Leo?
J
Books and games on Medieval Europe Codex Integrum
Codex Guide to the Medieval Baltic Now available in print
|
|
|
|
|
Leo Todeschini
Industry Professional
|
| Posted: Sat 28 Jul, 2012 4:36 pm Post subject: |
|
|
Hi Jean,
Sorry I have been holding off for a while as I have been trying to get my data a bit more organised, but I keep running out of time. However I have made some progress and can let you know where I have got to.
The last bow I made a steel of 850lb at 175mm/6.5". I fitted it with a draw length of 150mm/6" and so was drawing to 780lb.
I shot an adjustable bolt ranging from 80grams to 125grams (1 oz =28.4 grams) and tested the speeds using an F1 Chrony.
The 80 grams bolt shot at 49m/s = 161fps
using 1/2MV squared = 96J
What comes next I found very, very surprising.
When I raised the weight of the bolts, the velocity reduced as you would expect, but only very slightly, until I reached 125g and then it started to drop off very rapidly. At 125g the velocity had reduced to 48.5 m/s which is a reduction in velocity of 0.5m/s or 1.6fps.
Using a 125g bolts at 48.5m/s the energy has increased to 147J
This is not the outcome I would have expected and would doubt the accuracy of it, however I know another person with a windlass bow of mine that is performing in a similar way.
Logic says that our predecessors would have worked this out and so I have to conclude that they would have used heavier bolts that I would have previously expected.
Using an Ash shaft of about 15" long/400mm, that is tapered both ways, using 5" wooden flights and has a widest diameter of about 5/8" or 15mm the weight of the shaft is about 35 grams. This means that the bolt heads should weigh about 80-90 grams to optimise the impact energy.
I don't have any more 8-900lb bows on the books at the moment but next time round I will set the draw to 6.5"/175mm and with this extra drawlength I would expect to increase the velocities a little.
I have 1 or maybe 2 orders for 1200lb bows and I will let you know how these work out in due course. I would expect to run these using a 6.5"/175mm draw from brace and have a lsightly thicker bow to increase the poundage. The bolts will of course be heavier.
I hope this data helps a little, though I think it asks more questions than it answers.
Tod
www.todsworkshop.com
www.todcutler.com
www.instagram.com/todsworkshop
https://www.facebook.com/TodsWorkshop
www.youtube.com/user/todsstuff1
|
|
|
|
|
Jean Thibodeau
|
| Posted: Sat 28 Jul, 2012 9:17 pm Post subject: |
|
|
| Leo Todeschini wrote: |
When I raised the weight of the bolts, the velocity reduced as you would expect, but only very slightly, until I reached 125g and then it started to drop off very rapidly. At 125g the velocity had reduced to 48.5 m/s which is a reduction in velocity of 0.5m/s or 1.6fps.
Using a 125g bolts at 48.5m/s the energy has increased to 147J
This is not the outcome I would have expected and would doubt the accuracy of it, however I know another person with a windlass bow of mine that is performing in a similar way.
|
Well this is the " other " Jean: But if I remember correctly in one of my early posts on this Topic thread I sort of theorized that increasing the weight of the bolt would have only a very small effect reducing bolt velocity because the seriously underweighted bolts couldn't efficiently use the energy stored by a heavy crossbow.
Good to see this confirmed by testing the theory: Losing a few feet per second is way overcompensated by a 50% increase in bolt mass and increases the momentum of the projectile by a comparable amount.
Finding the optimum weight of bolt for a crossbow seems very much worth the trouble to get the best performance out of it.
What is surprising is that past the point of diminishing returns the loss of velocity falls off much more drastically than expected.
Just intuitively it didn't make sense to me that having a bolt hardly heavier than an arrow at very similar velocities would justify making crossbows with draws over 500 to 1500 lb if both the bolts and the arrows would have similar energies and momentum, which seems to be the case with a too light bolt.  [/u]
You can easily give up your freedom. You have to fight hard to get it back!
|
|
|
|
|
Jean Henri Chandler
|
| Posted: Sat 28 Jul, 2012 9:43 pm Post subject: |
|
|
This is fascinating and also corresponds to my own expectations.
I'm really eager to learn more, I hope you get a chance to do some test-shooting with heavier bolts. 147 joules sounds pretty powerful, how does this compare with a war-arrow from an English longbow?
Very interested to see what you come up with for the 1200 lb bows.
Thanks for posting Leo,
Jean
Books and games on Medieval Europe Codex Integrum
Codex Guide to the Medieval Baltic Now available in print
|
|
|
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
All contents © Copyright 2003-2024 myArmoury.com — All rights reserved
Discussion forums powered by phpBB © The phpBB Group
Switch to the Basic Low-bandwidth Version of the forum
|
This is a 
Attachment: 187.63 KB