Tuning is a process of applying sequential adjustments to bow, arrow and archer to attain close groupings at all ranges. The process is iterative - you start with an initial setup based on the bow's geometry, then you enter successive tuning loops with small adjustments, hopefully getting smaller and more aligned groups on each pass. Frequently there is more than one tuning solution, however one of those solutions is often more forgiving than the others. Tuning is a process of continual improvement.
Tuning Loops
Note that the archer is a vital inclusion in the tuning loop. In general, the novice archers will always find their skills the limiting factor in tuning. The result is the archer and the tuning progress together with the archer deriving great satisfaction in the constant improvement that can be attained.
A significant problem in tuning is identifying the adjustments needed to correct a particular symptom. As your skills develop, you will begin to associated adjustments and symptoms.
From novice, this can be a slow process, but aim to enjoy the journey and the enlightenment, rather than resent the time. And FlyingSticks is here to help! Once you get pass the basics, archery is largely a mind game, so be positive and enthusiastic from the start - believe me, it will make a huge difference.
At some point, there will be no further improvement - you reach a plateau. If your grouping goals have not been meet, you have a problem. You need to identify the likely obstacles to progress and deal with them. The FlyingSticks is designed to assist in this regard. It will give you a feel for the impact of small adjustments. But more than likely you will need to seek advice from an accomplished archer to speed up the process.
At launch all arrows have many superimposed motions including:
a simple high speed forward motion along ideal trajectory,
a small side-ways motion, causing a deviation from ideal trajectory,
an orientation offset (angle of attack) that becomes G. below,
a rotary motion about the center of gravity (CoG) that also becomes G,
lateral vibrations from fundamental (amplitude to ±15 mm, 40-150 Hz) to multiple harmonics at reduce amplitude,
beginnings of spin,
beginning of orientation correction - porpoising and fishtailing - acting on the center of pressure (CoP),
longitudinal vibration of the shaft, generally of no significance and ignored.
These are illustrated in the following diagram:
Associated with these movements are a number of aerodynamic forces and gravity as the following diagram summarizes.
The aerodynamic forces are distributed along the arrow (just like gravitational forces) but can be considered as acting at a single point call the center of pressure (CoP). The lift is generated by the angle of attack on all components of the arrow - even a bare shaft can generate significant lift. The lift can occur in any direction at right angles to the direction of travel.
Drag forces are more complicated and are typically about 1½ times the gravitational force at launch and decrease during flight. It is convenient to divide the drag into three components - normal drag at zero angle of attack, lift induced drag and spin-up drag. Each of these changes with time in different ways - see Arrow Aerodynamics.
Of greatest concern is the aerodynamic lift because it diverts the arrow from the intended path. This diversion can occur in any direction relative to the sight-line, so there can be a mix of porpoising and fishtailing in flight.
The diagram shows the path of arrows with different stability margins. Stability margin is a measure of the distance between the aerodynamic center of pressure and the center of gravity expressed as a percentage of the arrows length. At high margins, the arrow will oscillate at a higher frequency. As the margin is reduced, the oscillation frequency will decrease, all the way to zero.
At zero, the arrow will notionally retain its original motions. This is the idea behind the use of fletchless arrows - original launch conditions are left uncorrected.
With negative stability margins the arrow becomes unstable and will attempt to reverse its orientation. During this action the arrow is likely to divert from the sight-line significantly - possibly dangerously.
Interestingly the porpoising and fishtailing actions do not necessarily mean poorer grouping. Theoretically if the magnitude, frequency and phase of the action is repeatable then grouping need not be compromised, however that implies even more variables to control as well as some sighting issues to address. It is far easier to eliminate the action.
When a release aid is used, then a perfect launch becomes a theoretical possibility, but in practice almost never achieved! As a general comment it should be noted that in a perfect setup, where the nock travels a perfectly straight line during launch, then tuning is totally independent of the arrow's characteristics. For center-shot bows fired with release aids, the tuning focus can be on the bow, release and archer's form, largely ignoring the arrow.
Olympic archery rules require finger release. Traditional archers use finger release techniques. These archers simply cannot escape the need to effectively counter the trouble created by their fingers!
Traditional archers with traditional bows need to deal with another issue - the offset rest position - and invoke the Archer's Paradox. This demands that the arrow be matched to the bow to ensure center line travel, clearance of the bow and minimal rotation. Achieving all three criteria at the same time is what tuning is about.
Tuning is the process of getting the bow dynamically aligned and if necessary the arrow dynamically matched so that an arrow's flight is an optimal minimal mix of the above motions. Ultimately at launch we aim to have an arrow with:
no unintended contact with the bow,
no angular offset,
no rotation, and hopefully,
a center-line travel path.
The result should be small groups from a flight free of undesirable actions such as fish-tailing.
When the arrow finally disengages from the string, it is in free flight and only influenced by gravity and aerodynamic forces.
The diagram shows the ideal point of disengagement for a finger release. This point is the coincidence of three conditions:
These conditions probably don't represent the only conditions for good flight, but they represent the least sensitive to small variations in the archer's kit or form.
An underlying awareness should be that any initial angular offset or rotation will be present for the entire flight, observed as fishtailing or porpoising, as there is very little dampening of this action. This is why much focus is placed on arrow movement at launch.
All arrows vibrate at launch. It only becomes a problem it it causes the arrow to strike the bow, otherwise it is on little concern.
Sometimes perfect solutions are simply not possible. For example, theory suggest it in not possible to achieve a finger release launch with both zero angular offset, zero rotation and a center-line path at the same time, so an optimal compromise is required.
It is not for want of trying that a full theoretical model of the archer, bow and arrow as a system has yet to be achieved. But, when it is, most likely there will be so may input variables that it becomes near impossible for the enthusiast to measure or otherwise determine all the variables and plug them into such a model. For these reasons it is unlikely tuning tools, including FlyingSticks, will ever be able to provide the full solution, only indicators of what may help.
Many tuning methods have been devised over the centuries. Many of these are dependent on bow or release type. The methods detailed here have been shown to be universally effective and are based on a rational application of modern archery theory. The recommended tuning sequences is:
You can (and should) investigate alternative tuning methods, but I doubt
they will be any more effective, and will probably be more complicated.
The basic tuning does not involve spine tuning - however it does assumes
the spine match is close enough. Once you have completed the tuning and
are achieving good groups, it may be time to upgrade the arrows and
re-tune. Second time around is much faster.
For broadhead hunters who practice with field points, it is desirable both arrow types be matched to the same bow and sight setup.
Tuning adjustments will depend on the bow type. Traditional bows will skip some tuning methods. Generally it is less confusing to focus on one adjustment at a time, but that is no more than a personal preference!
To begin the tuning, we require a starting point. For the novice it is generally best to start with the bow setup according to the manufacturer's basic alignment instructions. If a plunger is fitted, wind to maximum tension (or lock) and set offset to keep arrow on center-line. The bow sights will also need to be setup approximately - on center line and good enough to hit the target face. Next, select a low end arrow from the manufacturer's selection chart. I say low end for you can expect to loose or break a few arrows, and besides you may need to change arrows during spine tuning.
The Initial Tuning Loops
For broadhead hunters who practice with field points, it is desirable both arrow types be matched to the same bow and sight setup. This complicates the setup and tuning, but it is worth the effort.
First decided if the same shaft is to be used for both points - by simply swapping screw-in points. This reduces the tuning and matching options, however we will take this approach because it's convenient.
Starting with the broadhead decided on the minimum fletching required to ensure the center of pressure (CoP) is well behind the center of gravity (CoG) using the FlyingSticks safety margin figure show in Arrow>Aerodynamics. Ensure the fletching satisfies this stability requirement.
With the bow setup, begin the archer form loop. Concentrate on reliably achieving a 300 mm group at medium range (~30 m). There is no point with further adjustments to the bow or arrow until you achieve this minimal grouping: "You can only tune as well as you can shoot". This will require you will be focusing on your form and technique for may be 200 - 1,000 releases. Recurve bow users will generally take longer than compound bow users.
This is an optional and advanced setup or tuning method for compound bows to ensure the nock has linear travel during at least the first 200 mm of travel from release. The rational is while the draw is still in the valley where acceleration is relatively low, it is more susceptible to a poor release, facial contact or other perturbation.
The draw valley or let-off on a compound is achieved by the eccentricity of the cams. If the cams are not matched and perfectly timed to one another, then there will be a mismatch in their mechanical advantage resulting in vertical nock movement. The effect of any perturbation then becomes dependent on its timing. By ensuring linear travel, this time dependence is largely removed.
This tuning step is regarded as optional because most modern compounds come with well-timed cams, the equipment required to complete this test needs to be built or acquired and there are potential safety issues. For these reasons this tuning is definitely not for the novice.
Use a well restrained target of medium density foam, ensuring it is homogeneous and unlikely to deflect an entering arrow. A previously used target can often have a hollowed out center area that can cause arrow to deflect by taking a less resistant path.
An arrow striking the target with a slight sideways movement will tend to amplify this orientation as the center of gravity is offset from the deceleration forces and tends to rotate the arrow. The target must not be allowed to rotate in any fashion during penetration otherwise the entry orientation observation will be corrupted.
Shoot a three arrow group and repeat at a slight (~0.5 m) change in range to confirm trend. The reason for varying the range is to make obvious the effect of any lateral arrow oscillation. On finger release bows this lateral oscillation will be most pronounce in the horizontal plane, while for compound it will be most likely in the vertical plane. At some ranges the lateral oscillation can mask an orientation error and at other ranges it will exaggerate the error. You will know when you have reached the end of the coarse tuning by the fact that no discernible trend appears at different ranges.
Estimate the point-to-nock offset distance from the firing position by moving the eye down to the nock release position and simply estimating the offset error direction and distance. Note the approximate amplitude and orientation error (point-to-nock offset distance) in both vertical and horizontal planes. The suggested tuning adjustments are a percentage of the observed error. This allows a speedier homing in on the solution as the point-to-nock offset error diminishes, so does the adjustment.
Once the basic tuning has been completed it is worth giving the sights a preliminarily calibration although this can be combined with a next level tune.
For recurve bows the focus tends to be on horizontal plane, so it is usually best to sort out the vertical plane first. This is done by small changes to the nock point on the string. If the arrow has been observed as being point down, move the nock point in the same direction by about 10% of the vertical point-to-nock offset error distance. Reverse for point up. For example, if the vertical offset is 30 mm high, move the nock point 3 mm up the string.
For horizontal point-to-nock offsets, the plunger need to be moved. (Remember that in the initial setup the plunger tension has been tightened to maximum). If the arrow has been observed as being point left, then move the plunger to the right by about 10% of the arrows horizontal point-to-nock offset error. Visa versa for point right.
The recurve bow's horizontal plane tuning is very dependent on the archer's finger release technique
For compound bows the focus tends to be on vertical plane, so it is usually best to sort out the horizontal plane first.
For horizontal point-to-nock offsets, the rest need to be moved. If the arrow has been observed as being point left, then move the plunger to the right by about 10% of the arrows horizontal point-to-nock offset error. Visa versa for point right.
Adjustments in the vertical plane can be done by small changes to the nock point on the string as with recurves or by moving the rest up or down. The latter is quicker if it has adequate movement. If the arrow has been observed as being point down, move the nock point down or the rest up by about 10% of the vertical point-to-nock offset error distance. Reverse for point up. For example, if the vertical offset is 30 mm high, move the nock point 3 mm up the string or the rest down by 3 mm.
Compound bows with high let-off can be very susceptible the archers anchor and release form, especially regarding face contact and release hand movement. These form problems can show in both horizontal and vertical planes.
For traditional bows, only the vertical plane can be adjusted in this tune. Adjustments in the vertical plane can be done by small changes to the nock point on the string as with recurves or by moving the rest position up or down.
If the arrow has been observed as being point down, move the nock point in the same direction by about 10% of the vertical point-to-nock offset error distance. Reverse for point up.
The horizontal plane cannot be tuned at this stage. Once the vertical plane tune is completed move directly to Spine Tuning.
The modified French tune is a quick (5-15 minutes) and easy method for center tuning before progressing to finer tunes. On a target mark a small aiming point in the center of the vertical 400 mm line. Firing from ~3 m at the aiming point, adjust the sight's windage until arrows are grouping about the vertical line. Firing from ~10 m at the same aiming point, adjust the rest or plunger in the opposite direction to the misaligned longer ranged group. Repeat until short and longer range vertical alignment is achieved, and the sight's windage adjustment is near perfect. Remember to always adjust the windage at each short range test.
Note that as only the horizontal offset is of importance, it is wise to aim at slightly different points on the vertical line to avoid FlyingSticks Hoods. For greater precision consider extending the longer rang progressively out to 60 m.
For compound bows, the Modified French Tune may adequate and eliminate the need for Walk-Back and Sight Center Tune and subsequent tunes, especially for non-competitive compound bow archers.
As the name suggests, walk back tuning involves shooting at increasing ranges. Traditionally the sight would be locked and the sighting done on the same point for each range. Here we recommend using the sights to avoid the need for a tall target with a vertical reference line to cope with the drop at longer ranges.
This approach assumes the sight's ranging axis is in close alignment to the bow's vertical center-line. Indeed, it has the advantage that a small error will be corrected.
The goal is to have the groups at the different ranges having no horizontal offset. Vertical displacement does not matter at this stage - it's just seen as a sighting error. For recurve bows the adjustment is done by adjusting the plunger and for compound bows adjusting the rest's lateral position.
The tuning should be done without any cross winds. A light head or tail wind is acceptable but best avoided.
Starting with say a 10 m range, set up the sight range and windage so the grouping is horizontally centered of the sighting point. Mark the 10 m point on the sight scale and lock the windage adjustment. Wall back to say 40 m and set up the sight range and mark. Now, note the 40 m group offset from the 10 m group center. If the offset is small walk back to say 60 m and repeat.
Make the adjustments for the bow types (below), then repeat the procedure, bearing in mind the windage settling will need to re-adjusted at the short range and locked again.
The focus should be on getting the shortest and longest range groups aligned. It sometimes occurs that when this has been achieved, the intermediate range group remains out of alignment, indicating something more complicated is involved. See the Advanced Adjustments below.
Initial position for the plunger needs to be changed from that determined by the basic tune as we aim to establish the plunger's stiffness and position. Adjust the pressure setting to about middle of the range and move the plunger about 2 mm out from the basic setting.
For compound bows, the main adjustment is the horizontal rest position. If the longer range groups are to the left, then the rest needs to be moved a little (say 0.5 mm) to the left or visa versa. Unfortunately, most compound rests do not have the very fine control the recurve's plunger.
If using a drop rest there is a potential for the rest to drop too soon and fail to constrain the arrow during the early launch, making it more susceptible lateral nock movement. Contact with the rest can be expected and required for the first half of the arrow's travel during launch, just as with a recurve's plunger.
Walk-back tune is not relevant to most traditional bows. Advance to Spine Tuning.
Spine tuning is a dark art often accompanied by misinformation. The aim is to ensure the arrow clears the bow during launch, that the arrow leaves the bow with minimal rotation, and ideally that the arrow moves along the bow's center-line. This is the same as most other tuning goals! Present research indicates a perfect solution may not be possible for most bows, but spine tuning is likely to provide a good compromise.
Spine tuning is most needed with finger release setups due to the
significant and unavoidable horizontal movement of the nock caused by the
finger action.
If left untuned it is likely the arrow will:
hit the riser due to the lateral bending of the arrow and /or
launch with an angular offset and / or
launch with rotary motion about the center of gravity.
Release aids used with any center shot bow greatly reduces horizontal nock movement, so reduce the magnitude of horizontal arrow bending. The nock may still move along a non-ideal path due to tiller or cam balance issues, however the magnitude of this on the modern bow is usually small. In these cases, spine tuning can often be ignored and the focus be moved to addressing fine balance issues.
The following diagram is should give a feeling for the spine versus grouping by bow type:
The chart shows likely spine versus grouping for various bow types. While a total confection it seems to match observation!
Traditional bows with their lateral launcher offset and initial shaft contact with the bow, are far more critical to tune. For this reason feather fletches are preferred over less forgiving plastic fletches when avoiding or minimizing bow contact.
Ultimately the objective is tight groups on center-line.
A bow applies great force to the nock of an arrow. Ideally this would be perfectly aligned to the arrow's axis, but in reality this rarely happens. Indeed, when the rest is off center as with most traditional bows, proper alignment is impossible. When misalignment occurs, the misaligned component of the force will tend the bend the arrow in that direction. The much larger aligned component of the force places the arrow under great compressional load and it amplifies the bending with Euler buckling effect.
During launch the bending can be very complex. One reason for the complexity is the change of constrains during the progress of a launch. Initially the nock is constrained by the tort string, the vertical movement by the rest and the horizontal movement by the plunger. When the arrow breaks contact with the string near the brace height, its vibration mode changes from an end constrained mode to a free mode. Another complex constrain is provided by the plunger and rest that both apply a force that moves along the shaft during launch.
Spine tuning involves matching the bending characteristics of an arrow to the bow's dynamic draw curve. Spine tuning is particularly important for traditional bow's where a well matched setup will ensure the arrow not only clears the bow but also travels the center-line despite the fact the arrow is initially pointing well off-center. The fact that this is even possible is the Archer's Paradox.
Simplified lateral arrow movement during and after launch from a recurve bow. Red line is the nock path and the blue line point path. The vertical axis is exaggerated by factor of ten.
With all modern center-line bows, the arrow no longer needs to move around the riser, it simply needs to avoid any unintended contact and follow the center line.
An arrow has just three practical adjustment parameters: static spine, length and point mass. This gives ample scope, provided arrow mass can be kept within an acceptable range for the archer's goals.
The most important initial tuning issue is clearance. Other requirement are secondary.
It is assumed the archer has chosen the arrow static spine to the manufacturer's recommendation. This hopefully ensures the dynamic match to the bow is within a sensible range. The implication of a miss-match is that the rear of the arrow can strike the bow. An aim of the tuning process is to get a feel for the clearance margin and to ensure it is large enough to ensure ALL looses clear.
For the recurve bow the arrow is likely to strike the plunger or other vertical part of the riser. For compound bows the risk is more likely strike on the rest. Such strikes are always undesirable as they lead to variable arrow flight.
Check the arrows for wear along the back third of the shaft, especially on the plunger and rest sides. Check the fletching for signs of contact. On the bow in the rest and plunger areas for signs of wear or plastic deposits from fletches. Sometimes arrows can strike the sight when set for long ranges on low draw weight bows.
If a strike is suspected, apply some sort of marker to the bow shelf area or to the arrow's fletching. Talc, flower, spray on foot-powder and lipstick are all candidate materials.
Even if nothing is found, the author likes to add 3-5 mm high strips or beads of Blu-Tack* to likely strike areas to confirm a margin and to get an idea of the effect of tuning adjustments. The great advantage of this method is its 3D - giving a better picture of exactly what is happening. The only problematic area is with drop rests - placing Blu-Tack on the fast moving parts on the rest is likely to impact its timing, so is to be avoided. Leave the Blu-Tack in place while spine tuning, but remove for final tune confirmation shots.
Should strikes be confirmed, in order, try:
rotating the nock so the fletching is more likely to clear,
loosen over tight nocking points by reducing serving thickness,
complete basic tune,
confirm arrows are of same static spine, weight and length,
adjusting the arrow's dynamic spine,
trim fletches a few millimeters.
Should none of the above work, you need help!
By comparing the grouping pattern of bare and identical but fletched arrows, useful tuning is possible. This test assumes that a bare shaft will retain its orientation and any angular momentum applied at launch. If the arrow has an angular offset, then it will plane (due to aerodynamic lift) and move slightly in the direction of the offset without correcting the offset. Fletching an arrow disguises offset this by adding a corrective lift, inducing a damped oscillatory motion (fishtailing and/or porpoising). The result is a fletched arrow is more forgiving to sub-optimal initial conditions.
Bare shaft tuning is less effective with high FoC values. A high FoC indicates the center of gravity is well forward of the center of pressure, with the result the shafts lift will create a corrective lift moment just like fletching.
A bare shaft will not spin, so any shaft bends or vibrations are likely to increase group size.
Bare shaft flight deviations (from red line) for several different initial angular offset and angular rotation conditions. The plane of movement can be in any direction. Note the G condition's curved path when launched with positive offset but negative rotation.
One can see in the above figure the importance of conducting tests at different ranges. For example, if only the longer range results were being considered case G may be tuned out but at the medium range the result would be worst than expected.
When tuned the bare and fletched shafts groups should be very close horizontally but the bare shaft group may be a little higher due to reduced drag. When out of tune the groups will be apart, possibly with the bare shafts dropping lower due to induced drag.
For recurve bows, if the bare shaft group is to the left of the fletched shaft group (for right hand bows) then the dynamic spine is too stiff.
Simply aiming for the smallest groups at all ranges is a powerful and FITA recommended approach. It takes a scientific mind to succeed and is totally sensible!
If the longer range (lower) group is to the left of the short range group, then
If the longer range (lower) group is to the left of the short range group, then
The above fine tuning methods can be scaled to shorter ranges with an assumed reduce group size. But how far can this be taken?
The limiting factors would appear to be the relative error introduced by fishtailing and lateral vibration at short ranges. The fishtailing decays with range (±10 mm decaying) and the lateral vibration is roughly constant (±8 mm) with range. Clearly longer rangers will always be better. To keep the discussion simple, let's assume the fishtailing linearly decays to zero by 50 m. The situation is expressed in the following table:
| Range (m) |
Uncertainty (mm) |
Group (mm) |
Total (mm) |
Angle (mR) |
|---|---|---|---|---|
| 3 | 17 | 9 | 19 | 6.3 |
| 10 | 16 | 22 | 22 | 2.2 |
| 30 | 12 | 85 | 33 | 1.1 |
| 50 | 8 | 162 | 49 | 1.0 |
| 70 | 8 | 262 | 74 | 1.1 |
| 90 | 8 | 385 | 104 | 1.2 |
| 110 | 8 | 522 | 140 | 1.3 |
where the uncertainty column is the theoretical error discussed above, the group column a typical set of groups, the total column is the approximate total uncertainty based on 6 arrow per group. The angle column is the magnitude of the uncertainty in the launch angle (milli-radians) where small is better. The fine tune worst case accuracy is the sum of the angle for the two ranges. Thus
Tiller tuning is a process of dynamically balancing the bow limbs. This can be useful for improving the vertical grouping after other methods have been tried.
A bow can be vertically out of balance for many reasons:
differences in limb spring,
differences in limb attachment,
differences in limb masses, especially with compound bows,
cams out of balance,
off center nock point,
finger release action,
grip location,
bow center of gravity and its movement path,
stabilizer influences,
and I am sure there would be other causes.
The cams on compound bows can be out of balance resulting in the nock point moving vertically during launch. Depending on the cam design, there are many variables that can be difficult to understand and adjust. To a great extent one needs to have blind faith in the manufacturer's design, construction and setup instructions.
I mention the subject of synchronicity purely as an indulgence. In the bow, arrow, archer and field system there are many oscillations, vibrations, periodicities that may well interact for good or bad. We have already mentioned some in passing such as the archer's paradox.
A characteristic of oscillatory systems is their "Q" - a (quality) measure of their energy retention while oscillating. A high Q system will continue to oscillate many cycles after stimulation - like a piano string or an arrow's lateral vibration. Such a system can be induced to resonate with low level stimuli of a similar frequency. Possible coupled systems include:
arrow spin (particularly fletch rate) - arrow vibration,
arrow vortex shedding frequency - arrow vibration,
arrow vibration - bow clearance,
fishtail or porpoise oscillation - range wavelengths,
lamina-turbulent flow oscillation - arrow vibration,
lamina-turbulent flow oscillation - arrow fishtailing,
bow limb vibration - arrow vibration,
stabilizer - bow - arrow vibration during launch.
Each of these may or may not occur, but an awareness of the possibility is worth maintaining.