making replicas
I have expressed my scepticism in the past about making replicas of old bows for research. Perhaps I should explain what I meant in more detail.
An original bow was, say, 100lb weight and you choose your target weight of 50lb for the replica. You are, of course, hoping your replica will perform as well as the original bow. It means you want to achieve the same efficiency (defined as the ratio of arrow energy to the stored energy) and the same virtual mass (which corresponds to the total energy losses) for your bow. For the meaningful comparison the two must be the same for both bows.
Now, let's say the original 100lb bow has limbs 34mm wide x 14mm thick, and the tips 12mm wide x 18mm thick. It would shoot a 500 grain arrow at 250fps, which is about 5 grains per pound weight. (This measurements are typical for a Turkish bow)
To have the same virtual mass and efficiency, your 50lb replica must shoot a 5 gr/lb arrow (here 250 grains) with the same 250fps. The only possible way to achieve this would be to make the 50lb replica with exactly the same thickness of limbs (14mm) and the tips (18mm), but with the limbs of only half the original bow's width. So your bow would have limbs only 17mm wide with the tips only 6mm wide. Only then the bending characteristics of your replica and stresses in the limbs would be the same as in the original.
I do not believe anyone would actually ever attempt to make a 50lb bow this narrow. The narrow limbs would be prone to twist and the thin tips may not hold the string securely enough.
So, you make your bow as wide as the original, but sufficiently thinner to reduce the weight and the tips maybe a little smaller. Unfortunately the limbs are now much less stressed than in the original bow - in effect your bow is overbuilt with too heavy (for the draw weight) limbs. It will not show the same level of performance as the old bow. Its virtual mass will be greater and the efficiency lower. This may explain why some of us are dissapointed with horn bows they make.
Now imagine a bow of only 33lb weight - such bow would have to be only 11mm wide with 4mm tips!
I hope this explains the problem of horn- (and other) bowmaking. Please, do not claim you made a bow "like the original", which "is so fast" or "so slow". And use the bow for research on penetration, for example. The dimensions of old bows may be more important than you suspect. A light
weight bow can be tweaked to enhance performance, but this will not be a replica any more.
For credible work, I suggest to follow the dimensions of the originals exactly, whether the draw weight is known or not. And use a machine for the tests, if the bow is too heavy for you.
Adam
An original bow was, say, 100lb weight and you choose your target weight of 50lb for the replica. You are, of course, hoping your replica will perform as well as the original bow. It means you want to achieve the same efficiency (defined as the ratio of arrow energy to the stored energy) and the same virtual mass (which corresponds to the total energy losses) for your bow. For the meaningful comparison the two must be the same for both bows.
Now, let's say the original 100lb bow has limbs 34mm wide x 14mm thick, and the tips 12mm wide x 18mm thick. It would shoot a 500 grain arrow at 250fps, which is about 5 grains per pound weight. (This measurements are typical for a Turkish bow)
To have the same virtual mass and efficiency, your 50lb replica must shoot a 5 gr/lb arrow (here 250 grains) with the same 250fps. The only possible way to achieve this would be to make the 50lb replica with exactly the same thickness of limbs (14mm) and the tips (18mm), but with the limbs of only half the original bow's width. So your bow would have limbs only 17mm wide with the tips only 6mm wide. Only then the bending characteristics of your replica and stresses in the limbs would be the same as in the original.
I do not believe anyone would actually ever attempt to make a 50lb bow this narrow. The narrow limbs would be prone to twist and the thin tips may not hold the string securely enough.
So, you make your bow as wide as the original, but sufficiently thinner to reduce the weight and the tips maybe a little smaller. Unfortunately the limbs are now much less stressed than in the original bow - in effect your bow is overbuilt with too heavy (for the draw weight) limbs. It will not show the same level of performance as the old bow. Its virtual mass will be greater and the efficiency lower. This may explain why some of us are dissapointed with horn bows they make.
Now imagine a bow of only 33lb weight - such bow would have to be only 11mm wide with 4mm tips!
I hope this explains the problem of horn- (and other) bowmaking. Please, do not claim you made a bow "like the original", which "is so fast" or "so slow". And use the bow for research on penetration, for example. The dimensions of old bows may be more important than you suspect. A light
weight bow can be tweaked to enhance performance, but this will not be a replica any more.
For credible work, I suggest to follow the dimensions of the originals exactly, whether the draw weight is known or not. And use a machine for the tests, if the bow is too heavy for you.
Adam
Agreed Adam.
Anytime we make a replica of a historical bow, we also need to make a replica of the people who shot with it; because by and large those sorts of people are not around now.
Yet half-replicas can be interesting. The Khotan bow is a case in point. Grozer explained carefully to me where he was copying the original and where he was not, so I understand the limitations. Certainly, the replica Khotam bow is over-built for its draw-weight.
But I think we now have a whole lot more data on how the original looked and how it was shot compared to looking at half of a mummified bow that I can only handle with gloves and a mask on. Grozer himself also learned a lot (enough, indeed, for him to declare that he would never build another one like that.)
Sometimes, half a loaf is better than no bread :) .
S.
Anytime we make a replica of a historical bow, we also need to make a replica of the people who shot with it; because by and large those sorts of people are not around now.
Yet half-replicas can be interesting. The Khotan bow is a case in point. Grozer explained carefully to me where he was copying the original and where he was not, so I understand the limitations. Certainly, the replica Khotam bow is over-built for its draw-weight.
But I think we now have a whole lot more data on how the original looked and how it was shot compared to looking at half of a mummified bow that I can only handle with gloves and a mask on. Grozer himself also learned a lot (enough, indeed, for him to declare that he would never build another one like that.)
Sometimes, half a loaf is better than no bread :) .
S.
Stephen:
I was not actually referring to the Khotan bow replica by Grozer. This bow, although flawed, was a good attempt to reproduce original dimensions. Now someone can make a next one with a better understanding of the physics involved.
Adam
I was not actually referring to the Khotan bow replica by Grozer. This bow, although flawed, was a good attempt to reproduce original dimensions. Now someone can make a next one with a better understanding of the physics involved.
Adam
I know you were not being specific. :)
I think your post is a good reminder to people - epecially those who are keen on reenactment activities or historical research - that replicas of old bows for research into battle techniques has all sorts of limitations.
On the other hand, reenactment is a major driver of interest in Asian trad. archery and the market for traditional bows, so personally, I encourage it.
S.
I think your post is a good reminder to people - epecially those who are keen on reenactment activities or historical research - that replicas of old bows for research into battle techniques has all sorts of limitations.
On the other hand, reenactment is a major driver of interest in Asian trad. archery and the market for traditional bows, so personally, I encourage it.
S.