Another question for the tech gurus:
I know arrows have both static and dynamic spine characteristics.
I also know that arrow spline refers to the “stiff” (less resistant to flexing) side of the arrow shaft. In older carbon composite arrow technology, this came from the over-lapping procedure during shaft manufacture. Wooden arrows exhibit this phenomenon due to the grain formations of the growing plant.
I have read one way to determine the spline of a composite shaft is to plug both ends of a shaft and float it in water. The side that faces up is the light side and the down facing side is the heavier (and therefore stiffer) side of the shaft. I have also read of adjusting (rotating) the nock on composite shafts to “tune” all of your arrows to leave the bow consistently thereby producing better groups.
If the “bathtub test” can be applied to modern composite shafts, would not the lack of wall concentricity produce rotational imbalances negatively impacting group sizes?
In the realm of firearms, this problem was dealt with by the application of rifling imparting rotation to the projectile. Archery tries to deal with the issue by use of imparting rotation through offset or helically twisted fletching. Firearms research has found projectiles of differing weights and velocities require different rates of spin imparted to the projectiles to achieve optimum stability. Experimentation has shown that “over stabilization” and “under stabilization” produces poor accuracy.
I would imagine that archery projectiles would benefit from research along these same lines and wonder: Has this research been performed in the archery industry?
