Crossbows vs. Longbows

[Maerlande]

Dhaeron,

Welcome to the conversation. The primary point of bumping this thread is to remind Lingchih that he can never live down starting it.

But I have some rebuttals for you

The big problem with using a strong bow is not so much aiming (which works very well) or learning how to use it, but to build up the muscles needed to use it.

I don't agree with this. I shoot archery maybe 10 times a year. And I shoot a 55 lb recurve bow. It was my first bow and I've had it for 25 years. I can't shoot all day, but I can easily shoot 40 arrows which is a pretty big bunch for any quiver. And I'm a desk jockey. So it's not like I work out regularly or do anything in particular to pump my strength. I am strong and big, but it's all just native ability.

If I was a peasant forking hay onto wagons I would easily be able to shoot a 100 lb bow. Forking hay onto wagons is an over the head move. Also using a scythe builds massive arm and shoulder muscles. I used to be able to place a 60 lb hay bale onto a wagon above my head using a fork. A fork of hay is not light. Do that all day and you'd find drawing a big bow easy.

We all tend to forget that medieval peasants worked all day at hard physical labour. It's unrealistic to compare them to modern couch potatoes.

The mongols shot 150lb composite bows from horseback.

Another fun fact is that medieval and ancient crossbows (the greeks already used them) reached mostly the same projectile velocity as bows, mostly because that's limited more by the materials available for the arrows & bolts, than by the materials available for the bows & crossbows

This is incorrect. The physics of the problem are reasonably simple. It's conservation of energy. The archer puts the integral of force times draw into the bow as energy (or the work done by the archer). If we want a simple calculation, using 100 lbs force for 28 inches (assuming a straight line force curve from zero to 100 lb on a longbow) the energy put into the missile is exactly 159 J or 0.15 BTU. I have converted to SI for the calculations.

Assuming 100% efficiency the missile when fired will have exactly 159 J of energy since energy is conserved. This does not account for energy lost as heat and sound in the string and bow but will be good enough for our calculation. The kinetic energy of the missile is then mass time velocity squared. I found some modern replica arrow heads online that mass about 2 oz each. Add that to the mass of a 1/4" diameter by 36" long cedar arrow (the material I use) we get a total mass of 0.54 oz. The velocity of the arrow is then 333 ft per second.

Let's now try this with a simple goat's foot type crossbow with perhaps a draw of 200 lbs. The draw length of a goat's foot crossbow is about 12 inches. Assuming the same type of force curve we get a input energy of. If the bolt is made of cedar as well with a similar point, it's mass is now 0.27 oz. The bolt velocity is 436 feet per second.

So basically, the velocity of a missile fired from any type of bow is a function of the input energy and mass of the missile. There is no direct comparison possible between crossbows and bows. It's all variable.

This is also why the material of the bow is irrelevant to the discussion. For what it matters, the bow could be made of adamantium or kevlar. The input energy doesn't change since it comes from the human archer. And a human archer has a very strict limit on the energy available. Crossbows can put potentially more energy into the missile because they over come the limits of human power by mechanical leverage. The trade off is loading time.

Of course, someone will argue that the bolt could be made of steel. And it could but then carrying them would be difficult. If we change the bolt shaft to steel the bolts weigh 4 oz each and then 40 bolts would weigh 10 lbs. Pretty heavy but I suppose not impossible. The worst problem is that the velocity drops to 113 feet per second which is so slow that you could simply step out of the way and the ballistics are such that range would deteriorate.

Summary

It is a standard rule of thermodynamic analysis in energy conversion that finding the output from a certain input you do not require to know anything about the internal workings of the energy conversion machine. A simple efficiency rating (to account for losses) is adequate. In the case of bows, they convert human force and distance into kinetic energy. On this basis, the materials, shape, construction, etc are irrelevant. All that matters is the input energy and the efficiency of conversion.

As far as output energy, a crossbow simply does one thing. It increases the energy input by allowing more time for the human to apply the energy. Whether it's simply a goat's foot, windlass or lever action, the job of a crossbow is to mechanically leverage the force of a human. And it takes more time to do so.

I can keep going, but let's see if anyone has the knowledge to try to refute my facts. So far, 80% of this discussion is simply annecdotes and opinion. It's very shy on fact.

For anyone interested, I can share my calculation pages by irc or here.

[Illuminated One]

Well, firstly of course the material matters. That's why noone built bows from stone or ice.
Of course if you are saying when I have a bow made from material x that shoots an arrow weighting y with the speed z and another bow from material q that does exactly the same thing with the same arrow than yes, the material matters not (ignoring all other things that might be important for a soldier like weight or ruggedness), then yeah, but that's a truism.

And it is not quite as simple as (energy put in)*(effeciency) = 1/2 (mass of projectile)*(speed of projectile)².
You'll have a maximum velocity that you can archieve, as that's the maximum velocity with that the bow snaps back into shape. This is dependent on material and bow shape and weight but bugger me if I can provide a formula. (Still, it's easy enough to verify: you can't throw a table tennis ball faster than a golf ball because your arm is at full speed then already).
You'll still put in the same amount of energy into the bow but that isn't imparted on the arrow but on the bow.

[chrispedersen]

Originally Posted by Maerlande

Dhaeron,

Welcome to the conversation. The primary point of bumping this thread is to remind Lingchih that he can never live down starting it.

But I have some rebuttals for you

I don't agree with this. I shoot archery maybe 10 times a year. And I shoot a 55 lb recurve bow. It was my first bow and I've had it for 25 years. I can't shoot all day, but I can easily shoot 40 arrows which is a pretty big bunch for any quiver. And I'm a desk jockey. So it's not like I work out regularly or do anything in particular to pump my strength. I am strong and big, but it's all just native ability.

If I was a peasant forking hay onto wagons I would easily be able to shoot a 100 lb bow. Forking hay onto wagons is an over the head move. Also using a scythe builds massive arm and shoulder muscles. I used to be able to place a 60 lb hay bale onto a wagon above my head using a fork. A fork of hay is not light. Do that all day and you'd find drawing a big bow easy.

We all tend to forget that medieval peasants worked all day at hard physical labour. It's unrealistic to compare them to modern couch potatoes.

The mongols shot 150lb composite bows from horseback.

This is incorrect. The physics of the problem are reasonably simple. It's conservation of energy. The archer puts the integral of force times draw into the bow as energy (or the work done by the archer). If we want a simple calculation, using 100 lbs force for 28 inches (assuming a straight line force curve from zero to 100 lb on a longbow) the energy put into the missile is exactly 159 J or 0.15 BTU. I have converted to SI for the calculations.

Assuming 100% efficiency the missile when fired will have exactly 159 J of energy since energy is conserved. This does not account for energy lost as heat and sound in the string and bow but will be good enough for our calculation. The kinetic energy of the missile is then mass time velocity squared. I found some modern replica arrow heads online that mass about 2 oz each. Add that to the mass of a 1/4" diameter by 36" long cedar arrow (the material I use) we get a total mass of 0.54 oz. The velocity of the arrow is then 333 ft per second.

Let's now try this with a simple goat's foot type crossbow with perhaps a draw of 200 lbs. The draw length of a goat's foot crossbow is about 12 inches. Assuming the same type of force curve we get a input energy of. If the bolt is made of cedar as well with a similar point, it's mass is now 0.27 oz. The bolt velocity is 436 feet per second.

So basically, the velocity of a missile fired from any type of bow is a function of the input energy and mass of the missile. There is no direct comparison possible between crossbows and bows. It's all variable.

This is also why the material of the bow is irrelevant to the discussion. For what it matters, the bow could be made of adamantium or kevlar. The input energy doesn't change since it comes from the human archer. And a human archer has a very strict limit on the energy available. Crossbows can put potentially more energy into the missile because they over come the limits of human power by mechanical leverage. The trade off is loading time.

Of course, someone will argue that the bolt could be made of steel. And it could but then carrying them would be difficult. If we change the bolt shaft to steel the bolts weigh 4 oz each and then 40 bolts would weigh 10 lbs. Pretty heavy but I suppose not impossible. The worst problem is that the velocity drops to 113 feet per second which is so slow that you could simply step out of the way and the ballistics are such that range would deteriorate.

Summary

It is a standard rule of thermodynamic analysis in energy conversion that finding the output from a certain input you do not require to know anything about the internal workings of the energy conversion machine. A simple efficiency rating (to account for losses) is adequate. In the case of bows, they convert human force and distance into kinetic energy. On this basis, the materials, shape, construction, etc are irrelevant. All that matters is the input energy and the efficiency of conversion.

As far as output energy, a crossbow simply does one thing. It increases the energy input by allowing more time for the human to apply the energy. Whether it's simply a goat's foot, windlass or lever action, the job of a crossbow is to mechanically leverage the force of a human. And it takes more time to do so.

I can keep going, but let's see if anyone has the knowledge to try to refute my facts. So far, 80% of this discussion is simply annecdotes and opinion. It's very shy on fact.

For anyone interested, I can share my calculation pages by irc or here.

I'll take a pound of actual results over a two pages of reasoned theory, any day.
(Not to comment on the discourse.. it was pretty good so far as that went).


But the facts are that in medieval ages, in england for example, yeoman were required to spend a day a week in archery training. EVERY yeoman, unless they arranged exceptions. And this was to increase accuracy, and stamina.

Up until the 14th century, and probably well into the 14th century velocities and penetration were almost identical. This wasn't theoretical - the british did penetration tests, both vs oak planks and plate mail.

British quartermaster records go back that far - sadly, I don't recall the name.

Finally, english steel was notoriously poor quality, due to the poor quality ores. HIgh quality steel was done on the north coast of spain (bilbao area), toledo, and damascus.

[Humakty]

Guys, you're getting me wrong, I'm not a crossbow (or longbow) proponent, I was just referring to the Holy Rules of Armor Penetration. My country fielded both in good quantity, and seem to have been satisified by this compromise.

[13lackGu4rd]

I think siege units just don't fit into dominions, seeing how huge a part magic has in here. magic *is* in fact the "artillery", as in "artillery support", "artillery spells", etc.

[Maerlande]

LingChih! I can't believe either! You fool you

[Sombre]

LOL at the CLOTbow fanbois.

[Fantomen]

I made a small traditionally crafted flatbow for my son last summer. I was amazed at the power you get out of it, shoots really far. I thought the smaller size would make it fairly harmless, but I had to limit the useage because it got too dangerous. If those are what markata uses I think they're underpowered.

Now I'm working on a fullsized one for myself, really looking forward to trying it out.

[Wrana]

Originally Posted by Fantomen

I made a small traditionally crafted flatbow for my son last summer. I was amazed at the power you get out of it, shoots really far. I thought the smaller size would make it fairly harmless, but I had to limit the useage because it got too dangerous. If those are what markata uses I think they're underpowered.

Now I'm working on a fullsized one for myself, really looking forward to trying it out.

Well, be careful. My friend once shoot clean through a refrigerator unit with a bow made for re-enactment...
As for ballistae/artillery units - they are quite possible and I'm including them in my WarHammer project. An art is, of course, a beast. But yes, in a base game it's considered there are no light field pieces and heavy ones aren't really transportable - which was the case for most parts of history.

[Fantomen]

I can verify that material and construction matters a lot. A flatbow, along with many other types, depends on the dynamic between the elastic surface wood(front of bow) of the tree and the hard corewood(backside of bow). The bigger the difference between core and surface the more efficient the bow will be relative to its draw weight. That is why different kinds of tree are more or less suitable.

The bow is consequently built by first splitting the tree in four quarters and then you pick the one without branches or other defects. You work out the bow from the "back" leaving the elastic surface intact and carve away enough of the hard wood to get your preferred draw weight.

Laminated bows follow the same principle, but are built with materials of varying hardness/elasticity instead which are then glued or wired together.

You can elevate the effectiveness of your wooden bow by applying a string of elastic material along the front and some hard material on the back. The vikings of Iceland used sinews and bone for example.