The whole question of bare shaft tuning and the validity of bare shaft tuning and then going on to shoot a fletched arrow is a very interesting one. This may be of some interest to some members.
In 2001, I was supervising two PhD. students who were investigating postural balance recovery mechanisms in patents following C.V.A. and head trauma. The investigation involved applying ramped loads to displace the centre of mass of the patient using orthognally mounted linea actuators moumted on two force platforms. The students involved were both
recurve archers, so conversations soon got around to the mechanics of archery and in particular the dynamic characteristics of a fletched -v- unfletched arrow. Finding ourselves with a little time on our hands we decided to modify the postural balance apparatus into a shooting mechanism to identify the position of impact between fletched and unfletched arrows.
We began by mounting a bow (Yamaha Eolla) to one of the actuator mounting frames. We then connected a modified Cascade release aid to a S beam load cell (L.C.M. Systems) and connected the load cell to one of the accuators (I.D.Mod). The release aid was activated by a small servo micro switch triggered by a pre set threshhold load from the load cell.
So the shooting system was quite simple:- A rigid mounted bow was drawn back at a rate of 0.3 mt/sec via a linea actuator to a pre set load determined by a S beam load cell. The arrow was released by a servo micro switch which controlled a release aid. The entire system was position adjustable in all three spatial planes and mounted on force platforms (Kistler Instruments) to measure and check for vibtation and displacement.
In order to measure the positional difference between fletched and unfletched arrows we custom printed target faces with 40 concentric rings spaced 5mm apart. We added radient lines from the centre at 5 degree intervals. This would give us a co-ordinate reference system for locating and recording the arrows position on the target.
To eliminate any variables we used a single unfletched arrow. The arrow was shot from the bow to the bow's owner considered optimum set up. The whole shooting assembly was moved to centre the point of impact on the centre of the target.
25 unfletched arrows were shot (1 per target face) to record a base line accuracy. All 25 shots were within 5mm of the centre and a 5 degree displacement. We then Fletched the same arrow and shot the arrow again. All fletched arrows impacted around line 28 (14 cms from centre) @around 55 degrees.
We then decided to change some of the bow set up perameters (knocking point, button spring tension, button position etc) We made one change at a time and repeat the test.
The results were very interesting.
We could not duplicate the impact positions of the fletched and unfletched arrow with any bow set up combination we tried. The fletched arrow was constantly impacting the target high and right. All changes we made to the bow set up resulted in both unfletched and fletched arrow changing the position of impact.. In short we could not get the two types of arrow to impact the same position on the target.
This started some interesting discussion as to the validity of bare shaft tuning, the main one being, Why would you tune a bow and arrow set up with a bare shaft and then go and shoot an arrow that has differing mechanical characteristics (drag co-efficient, centre of mass position, weight, etc) from the one used to tune the bow?
Perhaps it would give better results to tune a bow with the arrows you are going to use in competition.
