An arrow shot by an archer has more consistent drag from shot to shot than one launched by a machine

The summary today

The finding comes from a single Japanese experiment from 2014, by the same laboratory that measured arrow drag in a wind tunnel and in free flight. Easton A/C/E arrows were launched in four ways, by two expert recurve archers, by a robot with a finger-like mechanism, by a robot with a mechanical release and by a compressed-air launcher that does not make them flex, for 72 launches in total filmed with two high-speed cameras. At the speed at which archers shoot, mean drag shows no appreciable change with the launch method, but the spread from shot to shot does: the standard deviation of the drag coefficient is 0.073 with the archers, 0.103 with the mechanical fingers, 0.119 with the release and 0.267 with compressed air, almost four times the archers' figure. The authors conclude that flexing of the right amplitude is needed to make the layer of air round the shaft turbulent, and with it the drag repeatable: avoiding excessive flexing is not enough, because too little flexing also harms consistency. The arrow's vibration frequency is the same with every method, around 85 to 87 hertz, but with the mechanical release it is the least repeatable. In 2017 the same laboratory returns to the subject with an expert female archer: the arrow flexes by 6.9 millimetres at the point, the layer of air becomes fully turbulent and the drag coefficient varies by about 3 per cent, with the same standard deviation of 0.073; but the comparison with the launcher is not at the same speed and the laboratory is the same, so it does not count as an independent replication. The limitation is that of a single experiment, with few launches per condition and no statistics on the differences, and no study in the registry checks whether more consistent drag shows up as a tighter group on the target.

Also phrased as: "arrow drag consistency"; "shooting machine versus archer"; "arrow flex and consistent flight"; "hand-shot versus machine-shot arrows"

Evidence

• 1998
  Context Model Published later

  A mathematical model of the interaction between bow and arrow, tuned to high-speed footage of a national-level archer: for the model to match the footage, the string has to leave the fingers along a contact line of 3.5 millimetres lengthwise and 2.29 crosswise, values found by trial and error, against the 18 millimetres of initial nock offset assumed in the earlier model. It is the mechanism by which the fingers start the flexing, and it depends on the archer's technique; the model says nothing about drag in flight.

  Bow-arrow interaction in archery · B. W. Kooi

• 2014
  For Equipment tests Published later

  Easton A/C/E arrows launched in four ways (two expert archers, mechanical fingers, mechanical release, compressed air), 72 launches in total filmed with two high-speed cameras, drag coefficient derived from the slowing in flight: the standard deviation of the coefficient is 7.27 × 10⁻² with the archers, 1.03 × 10⁻¹ with the mechanical fingers, 1.19 × 10⁻¹ with the mechanical release and 2.67 × 10⁻¹ with compressed air, which does not make the arrow flex. The authors conclude that avoiding excessive flexing is not all that matters: too little flexing also harms consistency, and the amplitude an archer gives is the one that works best.

  J0520102 Aerodynamic properties of an archery arrow : Influence of flexural oscillation · Ryu Ando, Kyouhei Okawa, Takeshi Miyazaki, Hiroki Sugiura

• 2014
  Context Equipment tests Published later

  The frequency at which the arrow vibrates is the same for the three methods that make it flex: a mean of 84.8 hertz with the mechanical fingers, 87.0 with the release and 86.8 with the archers, but with standard deviations of 2.26, 4.71 and 2.77 hertz over five repetitions per condition: the mechanical release is the least repeatable.

  J0520102 Aerodynamic properties of an archery arrow : Influence of flexural oscillation · Ryu Ando, Kyouhei Okawa, Takeshi Miyazaki, Hiroki Sugiura

• 2017
  Context Equipment tests Published later

  A paper by the same laboratory on drag in free flight: an expert female archer shoots the same A/C/E arrow with two types of vane, 36 shots each, at 58 metres per second. The flexing, 6.9 millimetres at the point and 87 hertz, makes the whole boundary layer turbulent, and the drag coefficient has means of 2.68 and 2.63 with standard deviations of 0.073 and 0.077, about 3 per cent. With the compressed-air launcher, at a lower speed and with four nozzles used on purpose to vary the initial rotation, the coefficient scatters between 1.2 and 3.2. The authors conclude that flexing of the right amplitude makes expert archers' shots more consistent, but the two comparisons are not at the same speed and the launcher's spread is partly deliberate.

  Indeterminacy of drag exerted on an arrow in free flight: arrow attitude and laminar-turbulent transition · T Miyazaki, T Matsumoto, R Ando, J Ortiz, H Sugiura

Status history

1. 1998 Not studied A mathematical model shows how the fingers start the flexing: the string slides off along a few millimetres and takes the nock a couple of millimetres out of the plane of the bow, by an amount that depends on technique. Whether this makes the arrow's drag in flight more or less consistent has not yet been measured.
2. 2014 Reported The only direct comparison arrives: the same arrows launched by two expert archers, by a robot with mechanical fingers, by a mechanical release and by compressed air. Drag varies least from shot to shot with the archers, with a standard deviation of the coefficient of 0.073, and almost four times as much without flexing, 0.267, while the mechanical fingers and the release fall in between. A single experiment with no statistics on the differences: reported.
3. 2017 Reported The same laboratory returns to the shots of an expert female archer: with the arrow flexing by 6.9 millimetres at the point, the layer of air round the shaft becomes fully turbulent and the drag coefficient varies by about 3 per cent from shot to shot, while with the compressed-air launcher it scatters between 1.2 and 3.2. The comparison, though, is not at the same speed, the launcher's spread is partly deliberate, and the archer's standard deviation, 0.073, is the same as the one found in 2014 with two archers. From the same laboratory and with an unmatched comparison, it is not an independent confirmation: the status stays reported.

Related

Related articles

• The archer's paradox: the physics of the flexing arrowAt full draw the arrow points to one side and still reaches the centre: how it flexes and clears the riser in the first twenty milliseconds, and how spine matches it to the bow.
• How much the air slows an arrow down, and what really changes the dragHow much speed an arrow loses in flight, how much the shaft, vanes and point add to air drag, and how much of it actually reaches the target.
• The release in archery: anatomy of a few millisecondsHow the archery release works according to the measurements: how long it lasts, how the fingers open, what the arrow does and what you can train.

Research lines

• 32 studiesArrow aerodynamics: drag, boundary layer, vanes
• 29 studiesThe archer's paradox in research: from 1987 to today

Other claims in this domain

• CorroboratedAlong its flight the arrow loses an appreciable part of its launch speed12 studiesStatus since 2011
• CorroboratedAs it leaves the bow, the arrow flexes and snakes around the riser instead of leaving straight19 studies · 47 archers measuredStatus since 2012
• ReportedA camera-based scoring system misreads some arrows: the ones barely sticking out and the ones that shift the target face7 studies · 2 archers measuredStatus since 2017
• ReportedA chest band with fibre optic sensors measures breathing and mean heart rate with small errors, and an archer can wear it while shooting2 studiesStatus since 2019
• ReportedA compound bow stores between 70 and 100 joules and sheds about two thirds of the force at full draw4 studiesStatus since 2015

See all claims on equipment and tuning