We have come at last to arrow spine and the archer’s paradox. Let us examine the paradox first.
The Archer’s Paradox
This is a much misunderstood phrase. The “paradox” is that if an archer wants to hit a target then the one thing he should not do is line up the arrow with the target. This was noted in the days before centreshot bows and mechanical releases, which minimise the archer’s paradox. As usual, I shall ignore such matters and assume a regular horsebow.
It is easiest, while I explain the paradox, if you imagine holding a bow vertically with an arrow nocked (or even get your bow out and try it). If you hold your bow so that the string and the handle line up with the target then before you draw the bow back the arrow sticks out to one side. It cannot point at the target because the handle is in the way. When you draw the bow this effect becomes less marked, simply because the nock is moving further from the handle and the point is moving closer to it. The angle is still there, however. If the string is released and returns to brace height then a perfectly rigid arrow would not be propelled directly towards the target.
The reason we can hit the target is that arrows are not perfectly rigid. They flex when force is applied. They actually flex quite a lot. If you get the chance, I recommend looking on YouTube for high speed footage of the archer’s paradox. Beiter have some excellent clips.
The fine detail is not terribly important, but basically what happens is that as you release, the string does not go in a straight line to brace height. It rolls off the tip of your fingers/thumb, which has the effect of moving the arrow’s nock end laterally away from the bow (this is easy to visualise if you think about the release). The string is also moving forwards and the effect is to bend the arrow and propel it forwards. The string is now moving on slight angle because it is returning to brace but has been moved to the side on release. This, together with the fact that arrows don’t like being bent, causes the arrow to flex back the other way as it is driven forwards. On release it will continue to flex as it flies, although various factors will help it to straighten out more quickly, notably drag at the nock end caused by the fletchings.
This is where the magic of spine becomes really useful: if we select our arrows to bend exactly the right amount on release then it will bend around the bow’s handle and fly directly at the target.
The next couple of articles will be about spine. The first will deal with the factors that affect spine and the one after it will be on how to test and adjust spine.
One important point before I move on to those topics, however, is that the most important thing is that all your arrows should match. They should be of the same mass and the same spine. That way at least you can shoot one and know where the others will go. If your arrows are of different mass and spine then you cannot know where to aim because you cannot know how each arrow will act. It is better to have all your arrows slightly wrong than some right and some wrong. How close they have to be to each other is a matter of personal tolerance. Personally, I ensure that all of my arrows are within 5gn of each other in mass and within 5lbs of each other in spine.
Next time, we shall look at the various factors that impact on the spine of an arrow.