Arrow stiffness?

[Yew Bow]

So back to my original question. Why bare shaft tune?. The test was an attemp to identfy the fact that the two types of arrow are the same in terms of their behavoir. They are not. We could not under any recognised tuning modification to the bow get the arrows to the same location on the target.There was always a difference Therefore arrow flight with a bare shaft does not represent arrow flight with a fletched shaft.

[joetapley]

"why bare shaft tune?"

No short answer to that one.
For my own take on the topic see the section on bow/arrow tuning at archery mechanics

Also covers why I think direct assessment of arrow flight is generally better than the bareshaft approach.

[Yew Bow]

We did use the Pekalski model as quoted in the Journal of Sports Science for our initial set perameters

[joetapley]

Lets assume that what is called 'button tuning' is adjusting the bow so that the rotational kinetic energy of the fletched arrow at launch is a minimum, ideally zero (the only sensible explanation IMO).

Because of the difference in behaviour of the fletched and bareshaft arrows if you vary the bow tuning through the optimim position re arrow grouping and measure the fletched arrow rotational KE and distance between the fletched and bareshaft arrow hits at varying bow setups then the minimum displacement between arrows would correspond (approx) to the minimum fletched arrow rotational KE.
Its because the behaviour of the two arrows is different that the process works.

Speed tuning works the same way. You vary the tuning through the optimum position and record the measured difference in speed between the fletched and bareshaft arrows. The setting which gives you the minimum measured speed difference corresponds (approx) to the fletched arrow having the minimum rotational KE at launch.

The grey area is that the fletched and bareshaft arrows behave differently mechanically on the bow so the two arrows at any setup will launch with slightly different angular velocities. However this difference does not invalidate the method. Perfection you don't get and any tuning process is limited by the skill range of the archer.

[Yew Bow]

There are two issues here ..one.. is the optimum set up for a bow with a particular specification of arrow, and two, the validity of bare shaft tuning to establish an optimum setup. From our studies we established there is a difference in the outcome of shooting the two types of arrow so unless your intention is always to always shoot bare shafts the validity of bare shaft tuning is questionable.

[joetapley]

The setup of the bow is irrelevant other than how it affects the initial arrow launch properties.