I agree Del, when the arrow needs to flex spine is critical, on a center shot bow there really is no need to flex. One thing that has always puzzled me is how critical the spine is on an atlatl dart. If they are too stiff, they just dive bomb.
An atlatl dart that is too stiff needs to be thrown very hard to get going straight. The tail end of the dart needs to deflect easily because the nock is rotating in a substantial arc due to the length of the throwing stick, and if the dart is too stiff, it will rotate the entire dart around the fore and aft center of gravity. BTW, stiff darts tend to launch nose high, while it is a soft spined dart (or a dart that is thrown too hard), that dives towards the ground.
It's interesting that Harry Drake never worried about spine.
could this mean that Harry never worried about measuring spine or tried to make adjustments to his arrows based on spine measurements? He must have had other more important criteria when making arrows ie. weight, length or diameter. I am guessing he still must have appreciated as much stiffness as the materiel would give, once the other criteria was met?
If you can barrel and arrow to 5mm at each end, is it better if it is 5mm all the way along.
interesting question about whether a tapered/barreled arrow or a straight shaft makes much difference aerodynamically. the maths of aerodynamics seem to be concerned with maximum diameter, at least with rockets and missles anyways as they seem to do well as cylinders
fuller diameters at the ends of arrows should make maintaining points and nocks easier tho, if not creating excess weight, but smaller max diameters in the mid section seem to be desirable for distance.