Something worth knowing about arrow to bow tuning
What has tuning of a violin to do with the skills of the person playing it? The answer is: Nothing!
Nevertheless, correct tuning is an indispensable prerequisite for any violinist, no matter if beginner or top violinist. No beginner will ever reach a satisfactory level of playing routine on a mistuned violin, whilst a perfectly tuned violin will allow him to steadily develop and improve upon his playing abilities. On the other side, a top violinist will continuously loose his precision and skills if playing on a mistuned instrument for a prolonged time period.
The same applies to the tuning condition of a bow and arrow unit. A perfect tune will enable a beginner to improve upon his shooting form whilst a wrong tune will at long sight inevitably destroy even a top archer’s precise shooting routine.
Be sure to understand that arrow-to-bow tuning is not the same thing as the standard requirements a bow should meet like e.g. the correct alignment between limbs and riser or the bracing height or the number of strands in a bow string and the like, in accordance with bow manufacturer’s specifications.
Clearly spoken, a bow and its arrow are one unit consisting of two components cooperating in harmony, not working against each other. A perfectly tuned arrow is understood to be the one leaving the bow string on a zero-angle of attack, i.e. on the line exactly pointing to the centre of the target. This condition can be achieved either by time-consuming selection out of a wide variety of different spines, point weights and shaft lengths or by applying proven methods for adjusting the parameters of arrow shafts preselected out of the well-known arrow charts.
In fact, fletched arrows leaving the string on a horizontal angle of attack, either to the right (stiff shaft shot right-hande) or to the left (soft shaft shot right-handed) will go fishtailing, the more intensively the larger the initial angular error was.
In the same way, an arrow leaving the string on a vertical angle of attack, either to the top or bottom (caused by wrong nocking point setting) will go porpoising.
Both of these types of angular deviation can be made visible by recording the trajectory of a bare shaft prepared to have the same centre of gravity as that of an identical but fletched arrow. With a horizontal angle of attack, an improper bare shaft will not go fishtailing but move on a trajectory definitely curved either to the left if stiff, or to the right if soft.
Wrong nocking point setting will force a bare shaft into an upward curved trajectory if low and/or a downward curved trajectory if high.
The shorter the distance at which a bare shaft is leaving the about 6 inches wide area between the two tolerance lines to the right or left and/or to the top or bottom, say from about ten metres on, the wider the initial angle of attack was, and vice versa. Perfect tune is understood to generate a straight flight trajectory over the first 25 to 30 metres.
The procedure and setup to be used for testing and tuning in accordance with scientific rules are presented in Gerhard Gabriel‘s booklet titled „Pfeilflug wie auf Schienen“ which means ‚Arrow flight as on rails‘.
N.B.: The meaningfulness of the test results does in no way depend on wether the testing was done by a beginner or a top archer, a grandchild or a grandfather..
Something that may yet be unknown to many archers and even archery coaches is the fact that the draw length has no effect whatsoever upon the tuning degree of a bow-and-arrow unit. In fact, a perfectly tuned bare shaft will always fly straight, no matter if shot at full or half draw or whatever fraction thereof, as long as the physical parameters of the bow-and-arrow unit remain unchanged.
The classifications ‚stiff‘ or ‚soft‘ do not only depend on the spine of a shaft but, to about the same extent, also on its weight and c/g length (length from nock bottom to centre of gravity) acoording to the following relationships:
a) increasing spine figures make a shaft softer
b) increasing weight makes a shaft softer
c) increasing c/g lenght makes a shaft softer.
We remember that using a heavier point makes a shaft softer, by increasing the c/g length,
and vice versa in each case.
For example, an 1818 aluminium shaft, though statically stiffer, turns out to be dynamically softer than an 1814 , because of its heavier weight.
Now, what is behind the big secret about arrow-to-bow tuning? It is nothing but a simple little formula:
tlarrow = tabow
where: tlarrowl = arrow’s natural period
and: tabow= bow’s acceleration time
which means that the time the arrow needs to fiinish the first oscillation cycle must equal the time the bow needs to acceelerate the arrow to take-off velocity.
If both these times end simultaneously, the arrow’s take-off heading will be the same as it was during aiming prior to release, namely straight towards the target centre.
That is why we talk about ‚arrow-to-bow‘ tuning.
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By Gerhard Gabriel
in November 2019