When you shoot an arrow it is not possible to see the details
of how the arrow flies as it's going too fast and because of the
distance and perspective. The walk back approach is a method of
looking at the the flight of the arrow through the air.
When you shoot an arrow, where it hits the target is where the
arrow is in the air at that particular distance. If you shot an
arrow through a set of paper sheets, as illustrated, then
the holes in sucessive sheets would give you a record of the
arrow flight. Another, practical way, to do much the same thing
is to have a fixed target and for the archer to shoot sucessive
arrows at increasing distances. What defines the approach as a
walk back is that the aimed at point is the same for all
distances. The arrow pattern on the target is a record of the
arrows' flight through the air. Note that there is in reality no
actual point on the target which the archer is trying to hit. The
'target' if any is the centre of the group for the arrows
at the longest distance. Because the arrow pattern is derived not
from a single arrow's flight but from a number of different shots
(and each shot by the archer is invariably going to be slightly
different) you cannot look at a single arrow set pattern but have
to look at the pattern of arrow groups at each distance.
Assuming you aim at the same point on the target at each distance you end
up with something like the following;- the arrow groups will tend
to get larger and hit lower on the target with increasing distance and the left to right movements of the groups represents, for a non tuned bow, the effect of the arrows'
fishtailing/porpoising.
Having got a visual picture of how the arrows fly can anything
useful be got from it?
The first description of using a walk back approach for bow
tuning I am aware of was in a pamphlet, 'Bow Tuning', by Roy
Matthews published in 1984. The 'theory' described is
that the shape of the arrow pattern on the target indicates to
the archer whether an adjustment to the pressure button position
or spring tension is required and in what direction to improve
the tuning of the setup. Following Matthews' description of the
idea is a comment that boils down to that at least for him the
idea doesn't work. Whatever its origin, the idea that you can
determine whether a change in button position or spring
tension to tune the setup can be determined from a walk back
arrow pattern is nonsense. As mentioned in the introductory
section on arrow flight you can't tell from how the arrow flies
whether or not the bow even has a pressure button fitted let
alone discriminate between the effects of button position or
spring tension. Despite the fact that it doesn't work this tuning
method has proved remarkably durable in terms of being put
forward as a viable method in archery magazines, catalogues etc.
My guess is that the origin of the walk back pattern-what you
do with the pressure button myth originated as a piece of false
logic. If you have a perfectly tuned bow then the arrow pattern
is a straight line down the target. As you mistune the bow more
and more then the arrow pattern you get becomes more and more
curved. A 'tweak' of the button position will mistune a bow more
than a 'tweak' of the spring tension. So if you start with a
perfectly tuned bow you get a more curved pattern if you change
the button position then if you change the spring tension. The
false logic is reversing this observation - if I change the
button position (from tuned) it gives me a curved pattern,
therefore if I have a curved pattern changing the button position
will give me a tuned bow. This cock up is usually presented as
"a cow has four legs, therefore everything with four legs is
a cow". Anyone you see trying to milk a table is likely to
be an archer who advocates this walk back tuning approach.
In order to get anything out of a walk back arrow pattern we
need to start with a viable pattern in the first place and this
requires establishing the pattern baseline and having the correct
setup for the bow sight and the mark aimed at.
The baseline is where the vertical plane corresponding to the
string running down the centre of the (vertical) bow limbs cuts
the target. Unless the arrow pattern is looked at with reference
to this line then the pattern can be misinterpreted.
In this and following diagrams the 'x' represents the centre
of the arrow groups at different distances. The baseline for this
pattern could be anywhere e.g. the blue and green lines.
The pattern needs to be looked at with respect to the right
baseline. The top of the baseline represents where the arrow
would hit at no distance.Looking at the pattern with respect to
the first (highest) arrow hit is meaningless.
The sideways position of the bowsight should be such that the
pin lies in the plane of the baseline i.e. with the string
centred on the bow limbs the string should 'cut' through the pin.
This results in the baseline being a line dropped vertically from
the mark being aimed at on the target. Any sideways movement of
the pin away from this position will have the effect of a
rotational distortion of the arrow pattern on the target. e.g.
suppose you have a perfectly tuned bow and the pin in the correct
position. The arrow pattern will be a straight line down the
target. If you screw the the pin in towards the bow (RH archer)
and repeat the walk back then the arrows will hit increasingly
more to the left as the distance increases. The following diagram
illustrates the effect. - lots of different arrow arrow patterns
and all with a perfectly tuned bow!
You get, at least in theory, a similar distortion of the arrow
pattern with a vertical movement of the pin. In order to get a
true arrow pattern then the pin position and the height of the
mark on the target should be such that the arrow leaves the bow
horizontally at all distances (so don't try a walk back on a hill).
If say the bow is canted up and you shoot each arrow the same way
then as you walk backwards the arrows fly higher and the arrow
pattern is bent upwards. Alternatively if the bow is say canted
up and you keep aiming at the same mark then the bow angle has to
be continuously reduced as you walk backwards. In practice, over
the short distances involved in a walk back, the bow being canted
up (or down) will make little difference.
As an aside, unless you are doing a walk back with bareshaft
arrows which naturally fly in a curve (see the section on
bareshaft arrows), it is physically impossible to get a concave
arrow pattern i.e. one that bends in towards the baseline. You
sometimes see write ups on walk back tuning illustrating this
pattern (the reason being of course that no consideration is
given to the baseline, only to the first arrow hit).
Having got the correct set up for a walk back arrow pattern it
can now be used for basic bow tuning. The method is pretty much
the same as bareshaft tuning of the pressure button. The
difference is that instead of using a bareshaft arrow to 'point'
towards the position of the baseline, you know where the
baseline is. If the walk back
arrow pattern moves away from the baseline and then curves back
towards it, the shooting distance which gives the maximum
horizontal displacement of the group from the baseline is the
most sensitive distance with respect to tuning. The actual tuning
approach is much the same. With a sensible button position if the
group pattern starts off going to the right of the baseline then
(RH archer) increase the spring tension and vice versa.
A variant of walk back tuning is to shoot arrows at different
distances and look at the sizes of the arrow groups at each
distance. Arrow groups result from the variation in how the
archer shoots. One way the archer's shot varies is in how much
rotation the arrow has leaving the bow which gives rise to
fishtailing. The effect of fishtailing is that the group size
varies in area with distance in an oscillatory fashion. For an
archer of given ability the variation with distance depends on
the rotational properties of the arrow e.g. its weight, FOC,
fletching area etc.
The chart illustrates the variation in the area of the
arrow group with distance for a blue arrow and a red arrow. In
this example the only difference between the two arrows is the
FOC value. For the blue arrow the group size is a minimum for the
blue target distance. If the target is nearer or further away
then the arrow group size will be larger. The same effect happens
with the red arrow with respect to the red target. The point is
that because the characteristics of the two arrows are different
the optimum target distance with respect to arrow group size is
different. This raises the possibility of 'arrow tuning' i.e.
selecting/designing an arrow with good characteristics for the
specific distance and fine tuning the arrow by e.g. changing the
pile weight or fletching size to minimise the groups at that
distance. The arrow flight profiles above represent the worst
shot arrows. The better shot arrows will have less rotation and
the optimimum distance re group size will be further than for the
worst case. The better arrows will however always be inside the
worst arrow envelope.
When you shoot an arrow, where it hits the target is where the
arrow is in the air at that particular distance. If you shot an
arrow through a set of paper sheets, as illustrated, then
the holes in sucessive sheets would give you a record of the
arrow flight. Another, practical way, to do much the same thing
is to have a fixed target and for the archer to shoot sucessive
arrows at increasing distances. What defines the approach as a
walk back is that the aimed at point is the same for all
distances. The arrow pattern on the target is a record of the
arrows' flight through the air. Note that there is in reality no
actual point on the target which the archer is trying to hit. The
'target' if any is the centre of the group for the arrows
at the longest distance. Because the arrow pattern is derived not
from a single arrow's flight but from a number of different shots
(and each shot by the archer is invariably going to be slightly
different) you cannot look at a single arrow set pattern but have
to look at the pattern of arrow groups at each distance.
Assuming you aim at the same point on the target at each distance you end
up with something like the following;- the arrow groups will tend
to get larger and hit lower on the target with increasing distance and the left to right movements of the groups represents, for a non tuned bow, the effect of the arrows'
fishtailing/porpoising.
The baseline is where the vertical plane corresponding to the
string running down the centre of the (vertical) bow limbs cuts
the target. Unless the arrow pattern is looked at with reference
to this line then the pattern can be misinterpreted.
The sideways position of the bowsight should be such that the
pin lies in the plane of the baseline i.e. with the string
centred on the bow limbs the string should 'cut' through the pin.
This results in the baseline being a line dropped vertically from
the mark being aimed at on the target. Any sideways movement of
the pin away from this position will have the effect of a
rotational distortion of the arrow pattern on the target. e.g.
suppose you have a perfectly tuned bow and the pin in the correct
position. The arrow pattern will be a straight line down the
target. If you screw the the pin in towards the bow (RH archer)
and repeat the walk back then the arrows will hit increasingly
more to the left as the distance increases. The following diagram
illustrates the effect. - lots of different arrow arrow patterns
and all with a perfectly tuned bow!
Having got the correct set up for a walk back arrow pattern it
can now be used for basic bow tuning. The method is pretty much
the same as bareshaft tuning of the pressure button. The
difference is that instead of using a bareshaft arrow to 'point'
towards the position of the baseline, you know where the
baseline is. If the walk back
arrow pattern moves away from the baseline and then curves back
towards it, the shooting distance which gives the maximum
horizontal displacement of the group from the baseline is the
most sensitive distance with respect to tuning. The actual tuning
approach is much the same. With a sensible button position if the
group pattern starts off going to the right of the baseline then
(RH archer) increase the spring tension and vice versa.
The chart illustrates the variation in the area of the
arrow group with distance for a blue arrow and a red arrow. In
this example the only difference between the two arrows is the
FOC value. For the blue arrow the group size is a minimum for the
blue target distance. If the target is nearer or further away
then the arrow group size will be larger. The same effect happens
with the red arrow with respect to the red target. The point is
that because the characteristics of the two arrows are different
the optimum target distance with respect to arrow group size is
different. This raises the possibility of 'arrow tuning' i.e.
selecting/designing an arrow with good characteristics for the
specific distance and fine tuning the arrow by e.g. changing the
pile weight or fletching size to minimise the groups at that
distance. The arrow flight profiles above represent the worst
shot arrows. The better shot arrows will have less rotation and
the optimimum distance re group size will be further than for the
worst case. The better arrows will however always be inside the
worst arrow envelope.