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Jean is right, "Crossbows in the Royal Netherlands Army Museum" appears to be a good source for the kind of data you are looking for. Here is an old thread, where someone is selling a copy and uploaded a few pages, which show a data sheet for a composite bow.

http://www.vikingsword.com/vb/showthread.php?t=16219

I have ordered a copy at the state library in Munich and will happily make scans of a few pertinent passages, when I get a chance to visit the reading room. Might be a little while, though.
Michael, you are a star! Thank you very much!

Well spotted, Jean! I've not properly read very far in it myself yet, just skimmed through it with increasingly big eyes. So much good stuff!

The metallurgical analysis will be extremely useful. So many questions that we'll have a better handle on! Even with in the usually accepted values for Elasticity modulus of modern steels are spread over roughly a 10% range of the mean value, and the critical stress at which the bow steel begins to plastically deform (take a set) or catastrophically fail is highly variable due to heat treat, carbon content and a host of other factors, and is arguably a more critical design variable - I would guess the heat-treat would vary from workshop to workshop either from differences in trade secrets or design philosophy, or just because they sourced their iron differently and they didn't have computer-controlled furnaces back then (consider how much variation we see in measured metallurgical data of medieval sword blades), but even so, being able to say with confidence that we know how at least one steel crossbow was heat-treated in that period is a huge step forward.

I must try to get my hands on the works of Patterson and Alm referenced in that thesis. Alm's book seems to still be available occasionally second hand, albeit at fairly horrendous prices. I'll see if any local universities have it in their libraries.

It should be possible to get at least an indication of some material properties using less-distructive testing techniques. Something like a vickers microhardness tester will make only tiny indentations in the steel, which if done on the neutral axis of the lath should not affect its structural properties in any way, and would barely be visible (they are apparently typically less than 1mm in diamter). I believe this has been done quite a bit with old sword blades. Lets hope that it either has been or will be done more on extant crossbows too.
Michael, you are a star! Thank you very much!

Well spotted, Jean! I've not properly read very far in it myself yet, just skimmed through it with increasingly big eyes. So much good stuff!

The metallurgical analysis will be extremely useful. So many questions that we'll have a better handle on! Even with in the usually accepted values for Elasticity modulus of modern steels are spread over roughly a 10% range of the mean value, and the critical stress at which the bow steel begins to plastically deform (take a set) or catastrophically fail is highly variable due to heat treat, carbon content and a host of other factors, and is arguably a more critical design variable - I would guess the heat-treat would vary from workshop to workshop either from differences in trade secrets or design philosophy, or just because they sourced their iron differently and they didn't have computer-controlled furnaces back then (consider how much variation we see in measured metallurgical data of medieval sword blades), but even so, being able to say with confidence that we know how at least one steel crossbow was heat-treated in that period is a huge step forward.

I must try to get my hands on the works of Patterson and Alm referenced in that thesis. Alm's book seems to still be available occasionally second hand, albeit at fairly horrendous prices. I'll see if any local universities have it in their libraries.

It should be possible to get at least an indication of some material properties using less-distructive testing techniques. Something like a vickers microhardness tester will make only tiny indentations in the steel, which if done on the neutral axis of the lath should not affect its structural properties in any way, and would barely be visible (they are apparently typically less than 1mm in diamter). I believe this has been done quite a bit with old sword blades. Lets hope that it either has been or will be done more on extant crossbows too.
This is an interesting quote from that Stuart Gorman article (pp 48-49):

"The steel crossbow presents the most significant variation from the core mechanics that govern both bows and crossbows. The same processes for generating power apply for all three materials: the steel arms were drawn back and stored potential energy. When the trigger was pulled, the ends of the steel limbs moved forward rapidly and launched the crossbow bolt. The steel crossbow lathe functioned as a spring and followed the same mechanical principles. Due to the more consistent properties of steel, compared to wood and horn, in theory steel lathes should be easier to analyse than other types of crossbow. However, the mathematics involved are still abstruse. Some authors, such as Egon Harmuth and Erhard Franken-Stellamans, have written very impressive pieces on the mathematics behind steel crossbows, but historians are still some way away from being able to implement these ideas in a practical manner.128While the complexity of the mathematics involved is certainly a problem, accessing detailed and accurate descriptions of medieval crossbows has also proved difficult. To take Franken-Stellamans' work as an example; he has shown how the draw distance of a steel lathe can be calculated with what is relatively simple maths (at least compared to other calculationsmentioned in this chapter) but this requires at least our measurements from the lathe, only one of which is standard in most museums.129The exact quality of the steel used for crossbow lathes in the Middle Ages is not clear, and there was likely significant variation between lathes. Crossbow lathes definitely have to be made of steel, and not iron.

The Royal Netherlands Museum allowed Jens Sensfelder to undertake some metallurgical analysis of a lathe in their possession. This process is very rarely done because it is necessarily destructive to the lathe. Only an unattached lathe of little historical value can realistically be permitted to be destroyed. The lathe was a small steel lathe for a target crossbow and could only be dated to sometime during the sixteenth to eighteenth centuries. Sensfelder found that the lathe was made of several pieces of varying qualities of steel mixed together to create a single pattern welded lathe.130

There seemed to be a belief among some medieval warriors that the steel crossbow would become brittle and break if it was used during times of great cold. The Teutonic Order, who mostly campaigned in Eastern Europe during winter, had a noted preference for composite lathes over steel.131Arthur Credl and,however, noted that in the early modern period several tribes in Nordic Lapland used steel crossbow lathes which to him suggested that this belief was at the very least falsely held, if it was held at all.132Jens Sensfelder found that reducing the temperature of the lathe he was testing to minus fifteen degrees Celsius increased its draw weight by approximately 12%. This increase could easily have been too much for the lathe to take, and could have caused damaging breaks.133It is possible that this could have been mitigated by making the lathe slightly weaker in the first place, since the increase in power would not cause harmful stress to the lathe. Josef Alm suggested that composite crossbows would experience a similar rise in rigidity in cold weather, so it might be a more general flaw in non-wooden crossbows rather than exclusively a problem with steel crossbows.134More experimentation is necessary for historians to better understand these technologies."


Does any of that sound familiar? ;) So it sounds like rather complex pattern welded lathes made of different grades of steel were a thing, just like with the swords in the same period. Something to keep in mind.

All in all, from that description, it does not sound like a simple analysis will sort this out, it's not just a matter of a few basic calculations, the prod shapes are quite complex (analysis involving 'abstruse' mathematics), and it also doesn't sound like we actually know that much about these crossbows, in fact they are really just starting to take a closer and more systematic look at them.

None of this is a surprise to me, gentlemen.
Andrew Gill wrote:

I must try to get my hands on the works of Patterson and Alm referenced in that thesis. Alm's book seems to still be available occasionally second hand, albeit at fairly horrendous prices. I'll see if any local universities have it in their libraries.
.


I think you will be able to find a PDF scan of this somewhere. Hard copy looks like it will be a challenge.

With regard to art, the article mentions this piece by Hans Memling in Bruges, one of the numerous depictions of the martyrdom of St. Sebastian. The depiction is not the far distant cartoon-like image of the various schützenfest with tiny figures, but a close up. I'm no expert on the longbow but I would suggest based on this painting, if you were going to use paintings as evidence at all, it does seem to be an indication that Memling (a German living in Bruges - Flanders - in the 15th Century) was familiar with the longbow. The specific association with St. Sebastians famous martyrdom (which is the basis of his association with bows) may even link it to the Bruges St. Sebastian guild, though that is just a guess I don't know the provenance of the painting.

[ Linked Image ]
"Steel crossbows could easily equal, and often exceed, the power of composite crossbows, and yet these weapons had a tiny fraction of the thickness of their composite counterparts.442"

He lists his source as Josef Alm, European Crossbows, pp. 34-7.
Hi Jean

Jean Henri Chandler wrote:
"Steel crossbows could easily equal, and often exceed, the power of composite crossbows, and yet these weapons had a tiny fraction of the thickness of their composite counterparts.442"

He lists his source as Josef Alm, European Crossbows, pp. 34-7.


Yes, that part I did come across. Note that he says power, not efficiency, which is a big difference, as I've mentioned before. He also notes that 16th century steel crossbows were, on average, somewhat heavier than composite crossbows, which is not conclusive but is intriguing as you'll recall that I expected something like this to be the case. I don't consider it to be remotely conclusive either way, though; we dont' even know what fraction of overall mass is the lath.
Edit: when I posted, I claimed that the static deflection of the steel and horn bow tips under equal force would be equal - this was the result of a stupid calculation mistake - there is actually a factor 10 difference, very roughly. Also note that this is static, not dynamic

That steel crossbow prods are more slender than their horn and composite brethren in no way surprises me. Firstly, I've seen enough photos of historical examples of both types to have noted the difference - it is pretty striking, visually. But more importantly, Steel has a modulus of elasticity of something like 50 times that of horn (it varies between types of animal and moisture content for the horn, type of steel alloy and so on, but importantly its nearly 2 orders of magnitude stiffer. For a similar reason, aluminum diving cylinders are far thicker than steel ones, or so I've been told by a friend who is a technical diver, and it makes sense engineering-wise. By the way, the density of steel is roughly a factor 7 increase over horn, by the way - roughly an order of magnitude. So the steel bow could be one seventh of the thickness (belly to back) and still the have same as a horn bow of equal span and limb width.

Now, estimating static draw weight of a steel bow lath is a relatively simple calculation that I can do with a pencil and paper to a fair degree of accuracy (I've confirmed this on known examples), but calculating the energy imparted to bolt (without measuring like Tod did) and thereby efficiency, which depends on this, is pretty complicated, which is why I'm resorting to FEM. The crossbow limb moves in a complex way on string release, which depends on the mass distribution of itself, the mass of the string and the mass of the bolt, among other things. The efficiency not something that the soldiers of the time would necessarily have been able to calculate (how many people can do it today, even with a computer?). And would they likely have cared about it? What they would have cared about is raw power - and it is clear that steel bows have that in abundance if properly made. How many modern soldiers know or care about the efficiency number for the propellant in their assault rifle ammunition? Muzzle velocity, yes, muzzle energy and bullet momentum, probably, but efficiency I would guess efficiency isn't even considered by most users of firearms. (You have evidently done some military service, and can correct me if I'm wrong.) Usually people are more worried that something can do the job it is intended for than than how efficiently it does it (especially as you don't pay for petrol for crossbows :lol:)

The complexity of the efficiency calculations, together with the fact that I can't find anyone actually putting numbers to this, is why I want to do do this study. I suspect fairly simple order-of-magnitude calculations were done, and we can do much better than that - such calculations are useful, but they definitely don't tell the whole story.

Andrew
I finished the Stuart Gorman article.

I'd say it's a good overview of most if not all the mainstream published literature on both the longbow and the crossbow. It's helpful that he specifically lists dozens of specific examples of the latter with some basic data such as weight and dimensions of prod / lathe and tiller / stock. He also covers both Central European and 'Western' crossbows, as well as Spanish weapons, which is interesting and useful, but he neglects Italian sources altogether, which is a major omission. Apparently the Italians weren't cooperating, maybe he should have paid them a visit and bought somebody a nice dinner.

However for your purposes, weight and width are about all you get, and those dimensions aren't specific enough about the prod to tell you that much.

The previously mentioned "Crossbows in the Royal Netherlands Army Museum" seems to be a potentially useful source, with more detailed measurements of the prod, plus the destructive analysis of at least one prod showing the complex, 'pattern welded' type construction. This is quite significant. The use of different alloys in different parts of the prod can be one way to help explain why performance isn't precisely as anticipated with the back of the envelope calculations.

By the way I agree with you about the composite prods Andrew, I have seen some which are as thick as my forearm. It was interesting to get a thorough breakdown in the article of the distinct subtypes of the composite prods too.

Egon Harmuth's Die Armbrust, though based on Gallwey's book, also sounds like he gives a lot more detailed analysis of specific crossbows and would be worth a look.

His ultimate purpose was to compare longbow and crossbow as weapons. Here I think he fell down. He bases his comparison almost entirely on the famous 100 Years War battles between England and France, without looking at cases where the longbow was used against the crossbow on the continent. This is a completely separate issue (and another major can of worms) but trying to figure out those two weapons on the basis of France and England isn't going to tell you that much. France had a notoriously tough time organizing infantry, had to rely on mercenaries, and tended to use (and abuse) their mercenaries very badly, before finally settling on the Swiss.

People, even serious historians (somewhat amazingly) seem to overlook the many other examples in French military history where impetuous charges and a general contempt for infantry cost them severe catastrophic defeats every bit as disastrous as Crecy, Poitiers and Agincort. During the Crusades, against the Ottomans, in Spain, in Italy, for Centuries, this pattern repeated themselves. Impetuous lance charges carried the day in many battles but they also routinely led to catastrophic defeats, and it seemed to be a deeply embedded cultural trait with French feudal armies.

Using mercenaries also distorts the impact of particular troops. When English longbowmen were recruited for the armies of Charles the Bold, they fared just as poorly against German and Swiss militia as the Genoese had against English longbowmen, and for somewhat similar reasons. I think Gorman would have benefited from a basic survey of late medieval warfare beyond England and France. He doesn't even seem to be familiar with the basics from Delbrück and Verbruggen.

Anyway, it's still a useful article and I'm glad you found it, definitely keeping it in my archive. He did a lot of good work by systematically gathering the sources on each weapon type. It's clear from reading it how much there still is to learn, but this is the kind of strong basis you need for young academics to take the next steps.

J
Jean Henri Chandler wrote:
His ultimate purpose was to compare longbow and crossbow as weapons. Here I think he fell down. He bases his comparison almost entirely on the famous 100 Years War battles between England and France, without looking at cases where the longbow was used against the crossbow on the continent. This is a completely separate issue (and another major can of worms) but trying to figure out those two weapons on the basis of France and England isn't going to tell you that much. France had a notoriously tough time organizing infantry, had to rely on mercenaries, and tended to use (and abuse) their mercenaries very badly, before finally settling on the Swiss.

People, even serious historians (somewhat amazingly) seem to overlook the many other examples in French military history where impetuous charges and a general contempt for infantry cost them severe catastrophic defeats every bit as disastrous as Crecy, Poitiers and Agincort. During the Crusades, against the Ottomans, in Spain, in Italy, for Centuries, this pattern repeated themselves. Impetuous lance charges carried the day in many battles but they also routinely led to catastrophic defeats, and it seemed to be a deeply embedded cultural trait with French feudal armies.

Using mercenaries also distorts the impact of particular troops. When English longbowmen were recruited for the armies of Charles the Bold, they fared just as poorly against German and Swiss militia as the Genoese had against English longbowmen, and for somewhat similar reasons. I think Gorman would have benefited from a basic survey of late medieval warfare beyond England and France. He doesn't even seem to be familiar with the basics from Delbrück and Verbruggen.

Anyway, it's still a useful article and I'm glad you found it, definitely keeping it in my archive. He did a lot of good work by systematically gathering the sources on each weapon type. It's clear from reading it how much there still is to learn, but this is the kind of strong basis you need for young academics to take the next steps.

J


I know Stuart, and I think he'd agree with you on these points. Part of the problem is that he originally did intend to focus the performance of the longbow but then fell in love with crossbows and switched his focus to them. Rather than throw away a good deal of time and effort he kept the section on bows and used it to provide some context, but it really wasn't his focus in the end.
As an overview of research and sources on late medieval crossbows, I'd say it's quite an important paper. This is the kind of thing you need to take next steps. He should make an extra effort to get some information from Italy, there is a goldmine there. They still do the crossbow contests in a couple of dozen towns.

EDIT: One other thing I think Gorman did that was also very useful was to point out the need for a more detailed typology or basic nomenclature for crossbows. This is something I have also advocated for a long time (from the wilderness beyond the academy ;) ). Even within the relatively narrow range of late medieval crossbows within Latinized Europe, there are clearly at least 3 or 4 distinct types of crossbow which really aren't anywhere near being the same weapon, and when you extend this to Classical era weapons, and those from Asia, Africa and the Middle East, you are talking about at least a dozen distinct types.

If we distinguish between a hand-culverin, an arquebus, a musket, and a rifle, or between an English longbow or warbow, a Central Asian recurve bow, a Japanese Yumi, and a modern compound bow, we should make at least as much distinction between a basic yew prod crossbow; a gothic latchet crossbow; a slurbow, a late gothic 'halbe rüstung' steel or composite prod, cranequin spanned arbalest; and an oversized "wall crossbow" that is spanned with a winch.

In terms of training required for use, effectiveness, operational parameters, and fabrication, they are at least as distinct, if not more so. I think this has been one of the biggest problems in trying to make sense of crossbows in the last 100+ years, so Gorman is smart to point that out.
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