So what’s with the Longbow, which I hear invalidated the classic knight’s suit of armor? Is it really just using a longer bow? What’s so different about that, and why would it take so long to figure that out? You’re still limited to whatever pull the shooter can put on the string in regards to KE to punch through the armor. Were the previous bows limiting the shooter? Were they pretty much only using crossbows?
There is a lot more to applied KE than the draw weight. A longer bow simply allows more energy to be stored in the limbs for a given draw weight. This is a function of both the limb material, it’s deflection, and the total displacement of the bow’s string.
As a classic example with modern bows, I shoot a 1999 vintage PSE F-1 bow, at about 60lbs draw weight. My hunting buddy uses a 2 year old Hoyt Cybertek (or similar anyway) also at about 60lbs draw weight. Using the same arrows, he gets about 20ft/s more speed out of his shots than I do. This corresponds to an increase in KE. His limbs, and the cam system on the bow simply store more energy, which is then transfered to the arrow. If you’re looking at bows, one of the big factors that people use in shopping is the IBO speed (International Bowhunting Organization speed rating), which is standardized, but usually doesn’t show the true speed of a ‘hunting arrow’. It’s a good comparison, but shouldn’t be taken as the speed YOU should expect to get out of a new bow. This site explains more about the standardized ratings.
The other thing about longbows is that it wasn’t so much the longbow itself that was the revolutionary advancement, it was the longbowman. Longbowmen have to be deployed in large numbers to be effective, which means they’re commoners, not nobility. And they have to be well-trained to build up the needed strength, which means that you have to make an expensive investment in your commoners. And, a longbow is just as effective against your own nobles’ armor as it is against the enemy’s, so you have to trust those commoners you’re investing so much in. Anyone could have made longbows, but only the English (at the time) had the social structures in place to use them.