In kyudo the twist the hand gives the grip shifts where the arrow lands

The summary today

That twisting the grip of the Japanese bow changes the arrow's path was first said by a model, in 1997, and then by a test bench, in 2008. The three-link model, calibrated on a launching rig, finds that for the same total twist it is the timing that matters: change only the initial value and the trajectory changes completely, while arrow speed varies by less than one per cent. The test bench takes the archer out of the picture: bows of 13 and 15 kg on a mechanical launcher, a single duralumin arrow, a target at 28 m, and the torque applied to the grip alone, between zero and about 14 newton metres, is enough to move the landing point from one side of the target to the other. The relationship is not linear, and according to the authors too little twist pushes the arrow further off line than too much. The limits are real: it is a single outdoor test, with crosswind disturbing the data and no statistics at all, and nobody has yet measured, on the same shot, the twist an archer applies and where the arrow lands. Nineteen university practitioners, measured in 2007 with an instrumented bow, twist the grip about the bow's long axis by around 0.6 newton metres, but in that study the impact point of the shots is left out of the analysis; and on the launcher the torque, which acts about the same axis, reaches more than twenty times as much, so much of the tested curve lies outside what people do when they shoot.

Also phrased as: "tenouchi"; "tsunomi"; "the left-hand twist in kyudo"; "twisting the Japanese bow"; "the bow hand in kyudo"

Evidence

• 1997
  For Model Published later

  Three-link model of the Japanese bow, checked on a launching rig with strain gauges: three sinusoidal twist profiles set so that the integral over the 26 milliseconds, and so the rotation passed on, was the same. With profiles differing only in their initial value the trajectory changes completely, while arrow speed varies by less than 1 per cent.

  Dynamics of Japanese Bows and Arrows : Analysis of "Tsunomi" with Link Model and Experiment · Koji Kobayashi, Keiji Kyogoku, Tsunamitsu Nakahara

• 2007
  Context Kyudo archers Published later

  Bow instrumented with strain gauges on the grip, 19 university kyudo archers, 8 shots at 28 m each: the twist about the bow's long axis is 0.57 to 0.61 newton metres in most participants, the moment pushing the upper limb forward between 1 and 5 newton metres. The impact point of the shots is recorded but plays no part in the analysis.

  B39 Quantification of TENOUCHI for Playing Kyudo · Sekiya Koike, Takuro Sugiura, Sakura Murata, Toshio Mori

• 2008
  For Equipment tests Published later

  Japanese bows of 13 and 15 kg on a mechanical launcher, one duralumin arrow, a target at 28 m outdoors, grip torque from zero to about 14 newton metres, two data series (2005 and 2006): varying the twist alone moves the landing point from roughly minus 40 to plus 80 on the graph's scale, from one side of the target to the other. The relationship is non-linear and shown only in a graph, with no statistics.

  B4 Effect of Te-no-uchi in Japanese-style archery · Tetsuhiko Yamamoto, Hiroshi Kinjo, Motoki Tanaka

• 2008
  For Equipment tests Published later

  Reading the same graph, the authors conclude that more twist is not always better, but that too little twist sends the arrow further off line than too much. It is their interpretation, on data disturbed by crosswind and with no statistical test.

  B4 Effect of Te-no-uchi in Japanese-style archery · Tetsuhiko Yamamoto, Hiroshi Kinjo, Motoki Tanaka

• 2008
  Context Equipment tests Published later

  From the same tests at 28 m the authors note that the arrow hits more often when the bow is supported just below the nocked arrow. It is a qualitative observation, with no count of hits.

  B4 Effect of Te-no-uchi in Japanese-style archery · Tetsuhiko Yamamoto, Hiroshi Kinjo, Motoki Tanaka

Status history

1. 1997 Transferred The question enters the bibliography with a three-link model of the Japanese bow, checked on a launching rig fitted with strain gauges. The authors set three twist profiles so that each passes the same total rotation to the bow over the 26 milliseconds of the launch, and find that profiles differing only in their initial value give completely different trajectories, while arrow speed changes by less than one per cent. It says that twist matters and that its timing matters, but it is a simulation, with no archers and no target: transferred.
2. 2007 Transferred The first measurement on people shooting arrives. With an instrumented bow, nineteen university kyudo archers shoot eight arrows at 28 m: the twist about the bow's long axis sits between 0.57 and 0.61 newton metres in most of them, and the moment that pushes the upper limb forward between 1 and 5 newton metres. Twist now has a real order of magnitude, but the impact point of the shots plays no part in the comparisons and nobody varies the twist to see where the arrow goes: for the landing point there is still only the model, and the status holds.
3. 2008 Reported A mechanical launcher tests the point directly on the equipment: bows of 13 and 15 kg, one duralumin arrow, a target at 28 m outdoors, and a torque on the grip ranging from zero to about 14 newton metres. Varying that alone moves the landing point from one side of the target to the other, with a total spread of about 120 on the graph's scale; the relationship is not linear, and too little twist sends the arrow further off line than too much. For a claim about equipment this is direct evidence, but it is a single test, with crosswind disturbing the data and no statistics: reported.

Related

Related articles

• The yumi through engineering: materials, asymmetric limbs, draw force and tenouchiHow the Japanese bow works according to the measurements: bamboo and core woods, animal glue, asymmetric limbs, the draw force curve and tenouchi twist.
• The bow hand: where it pushes, how much it closes and how much torque mattersHow the hand sits on the grip, how much expert archers squeeze, and what the measurements say about grip pressure, its consistency and bow torque.

Research lines

• 10 studiesThe Japanese bow through engineering
• 17 studiesGrip pressure and bow torque: from 1971 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