Re: Crossbows vs. Longbows
I hope I'm not bothering anyone by repeating something from earlier in the thread. But I did a quick read and didn't see any of this.
I am an archer as a hobby. And a mechanical engineer. Here are a few bits of the physics of a bow.
1) The killing power of an arrow and also it's armour piercing ability is a function of the kinetic energy. Which is mass times velocity squared.
2) The kinetic energy imparted into an arrow or bolt is not a linear function of the draw strength. It is actually closer to the area of the draw from bow tip to tip versus the area of a strung bow not drawn. Therefore, the taller the bow the more energy for the same draw weight. So, simply put, a 100 lb composite bow 4 feet tall puts less energy into the arrow than a 100 lb long bow.
3) Cross bows have VERY short draws and generally very small bows. 36 inch is quite big. Longer and they are unweildy to shoot through crenelations. These two combined mean that crossbows must have much greater draw strength to put the same kinetic energy into the bolt.
4) Crossbow bolts have less mass than arrows. Both are usually the same diameter and made of much the same material. But arrows are 2-3 times longer.
5) In bow hunting, a 50 lb regular recurve bow is acceptable by law in my province. To hunt with a crossbow you must use 150 lb minimum. This is due to the clearly superior penetration of bows for comparable draw. Lighter crossbows are banned because the have insufficient penetration.
6) One clear advantage to using a crossbow to hunt is it may be carried drawn. Drawing a bow can be noisy enough to spook the prey.
I am also a recreationist. Our club uses draw weight to define acceptable sizes of bows and crossbows for combat archery. Bows may not be more than 30 lb. Crossbows may be 60. Having been hit many times by these using blunts, I can clearly say that a 30 lb japanese long bow hits MUCH harder than any recurve or crossbow within those rules.
As an archer there are some very interesting effects of bow shape. Recurve bows draw hard initially and remain fairly hard to hold drawn. Long bows are quite easy to start to draw but the weight increase rapidly at full draw. They are extremely hard to hold drawn.
I typically shoot a 55 lb recurve bow for traditional target archery. I'm a very large man and quite strong but I can only hold full draw for about 10 seconds. However, I can shoot 6 arrows in 30 seconds quite easily. It's not as accurate as a bit slower, but I can hit the target and score fairly well. My accuracy does not improve much by shooting slowly. With my large bow, my arm shakes and I lose accuracy if I hold it.
So, the real physical effects of bows and crossbows suggest some answers to these questions. English and Japanese longbows in the hands of a strong and skilled archer have very high penetration. The only comparable crossbows are the crank type. The simple goatsfoot crossbows that load moderately quickly have no where near the penetration. And that's simple physics. Even the 150 lb horseback composites typically have less penetration than a long bow.
PS: The thugs informed me I misread the date. I'm a year too late.
Last edited by Maerlande; February 16th, 2010 at 06:30 PM..
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