Crossbows vs. Longbows

[Maerlande]

not only does it affect the weight of the bow but also its elastic ability. the more elastic the material the less force the archer needs to use in order to pull the bow, or give you more pulling effect for the same energy.

Incorrect: The energy input to the bow by the archer is exactly the work done in pulling the bow. It is the integral of force times distance. A variance in the pull force does affect this energy, therefore compound bows place more energy into an arrow by using mechanical pulleys to use high pull at the start of draw and much less pull at the end thus taking advantage of the fact that an archer is stronger at the beginning of the draw and then can hold a light pull longer for more accurate aim. However, the effect of a compound bow is irrelevant to the material. It is the result of the pulley system which is not medieval and irrelevant to this converstation. There are also medieval bows that to some extent make use of this feature. Recurve bows have a more linear force curve while longbows tend to be easy to start to draw while much harder to hold.

Strength to mass ratio of wood one the highest of all known materials used by man. Here is a chart showing the excellent specific strengths of materials. http://www-materials.eng.cam.ac.uk/m.../NS6Chart.htmlNote that top woods such as oak and pine rate better than most metals. And the metals in the higher specific strengths are strictly modern. Keep in mind that in the medieval period only bronze, brass, and mild steels were known. Whereas they had access to wonderful woods and tremendously effective materials such as sinew.

oh and if you use metals or something that isn't elastic at all than a strong enough pull might just break the bow due to its lack of elastic ability...

You are misusing the term elastic. Elastic means a material that returns to it's original length after the application of force. Metals are very elastic as long as you don't exceed the yield strength. But then so is wood. All materials have an elastic limit. You can break a rubber band to take an example of an extremely elastic material. Plastic materials deform under force. The best example is probably plascticine. It has near zero elasticity. Metals are also plastic after the yield strength is exceeded. This is why you can form metals with extreme force and/or heat. The elastic limit is reduced by the application of heat.

Styrofoam is very light. So a 150lb draw styrofoam bow would only actually be about 15lb. Clearly you did not understand anything at all we were talking about on IRC. I thought you engineering types studied physics in school. Not just beaver dams. Titanium on the other hand is really heavy, so a 150lb draw titantium bow would be about 400lbs actually.

Haha: Took me a bit. I thought you were serious on first read.

Crossbows use a mechanical advantage to pull back the string. Even the ancient crossbows seem to have higher kinetic energy, because of larger projectiles but has a slower projectile speed. So, theoretically, they could penetrate armor better.

Correct: You trade speed for force. I agree that crossbows can be built with much higher penetration since you are not limited by human arm strength. The ultimate example is a ballista. Crank wound and probably only shoot every minute or so, but they can shoot a gigantic bolt of probably 10 lbs at somewhere in that 300 fps speed. Now that is penetration.

But we started with the basic discussion that simple goat's foot type crossbows that are fairly quick to load (say 2-3 per minute) have more penetration than a longbow.

The lesson seems to be that you need several times as many similarly skilled crossbows to be as effective as longbows would be. Because crossbow archers were frequently unskilled, you would need many more, and even then you might have, at least, range problems.

I think this is the crux of the matter. It's very difficult to learn to shot a longbow. While crossbows are quite easy to learn to shot. There is another very important advantage to a crossbow. You can carry it loaded. Which brings into play the huge advantage of volley fire. It takes a great deal more coordination to get volley fire with bows. It's quite difficult to hold a longbow drawn for any time and aim gets worse as you hold it. You can hold a crossbow ready to fire for a long time.

Well, interesting discussion. I know I'm annoying the heck out of LingChih by keeping it going but I'm having fun.