Archer's paradox

The term archer's paradox refers to the flexing of an arrow shaft that occurs when it is shot from a non-centershot bow. Coined by Robert P. Elmer in the 1930s, the archer's paradox centers around the idea that, in order to be accurate, an arrow must have the correct stiffness, or "spine", to flex and return back to the correct path as it leaves the bow. The word paradox refers to the fact that in order to strike the center of the target, the arrow must be pointed slightly to its side.

Less powerful bows require arrows with more spine (literally, the ability of an arrow to curve - like a spine). Less powerful bows have less effect in deforming the arrow as it is accelerated from the bow and the arrow must be "easier" to flex around the riser of the bow before settling to its path. Conversely, powerful bows need stiffer arrows, with less spine as the bow will have a much greater effect on the arrow as it is accelerated around the riser.

As the diagram shows, an arrow with too little spine for the bow will not flex and as the string comes closer to the bow stave, the arrow will be forced off to one side. Too much spine, or flexure, will result in the arrow deforming too much and being propelled off to the other side of the target.

In archery, compensation of the archer's paradox led to the invention of the Plunger button, also known as a pressure button or Berger button (after its inventor, Vic Berger).

References

* Cosgrove, Gabriela (1994). "Wooden Arrows" in The Traditional Bowyer's Bible - Volume Three, Guilford: The Lyons Press. ISBN 158574087X
* [http://www.texasarchery.org/Documents/ArchersParadox/Archersparadox.htm Texas State Archery Association article]