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musings on dynamic properties of barreled arrows

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joachimM:
I'm starting to think that for flight arrows (static) spine as we typically measure it, is much less important than we often think (or at least, than I thought).

When shot, the arrow extremities oscillate around the centre of pressure of the arrow. A barreled arrow has less mass at the extremities. which means less terminal and proximal inertia. so for the same static spine, a barreled arrow oscillates less and less heavily than a non-barreled arrow. meaning less drag during flight.
I think the barrel shape is most important for this aspect, than for mass saving purposes, but how much barrel-shape is needed for ideal tuning to the bow?

I think we might find the solution in tillering arrows. A non-barreled arrow on a spine-scale will show most bending at the centre, least at the extremities. My gut feeling tells me we need arrows that bend evenly when spined, in a slightly elliptical tiller shape. This should give higher frequency oscillations that return more quickly to a static shape, even at rather low static spine weights. 

Basically, it would reflect the difference between a bow with and one without hand shock.

Any thoughts?

JNystrom:
Makes sense! Really simple but good idea. The barrel form might actually come close to that elliptical bent shape, but it's interesting to understand more why. I will pay attention to this when I start building arrows for our competition in may!

Badger:
     I agree with you, I like to tiller an arrow to bend most a little behind center.

willie:

--- Quote from: joachimM on March 15, 2018, 03:11:42 am ---I'm starting to think that for flight arrows (static) spine as we typically measure it, is much less important than we often think (or at least, than I thought)

--- End quote ---
Joaquim, have you seen the buckling test used by atlatl dart makers? It seems to work better for darts, than spining. It might be interesting to give that buckling test to proven performing arrows.

--- Quote ---This should give higher frequency oscillations that return more quickly to a static shape
--- End quote ---
I found some quite primitive dart designs that seem to utilize quicker cycles, and have been impressed with how they fly. Higher frequencies seem to attenuate better in many types of systems.

JNystrom:
If oscillation is what we want to improve, shouldn't the optimal shape be symmetrical? In other words, pile and nock end equally tapered and balance point in middle.

My resent best shot was with this kind of arrow profile. It's weird how the turkish flight arrows have balance point back and uneven barrel...

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