The string's material and number of strands change the arrow's speed

The summary today

The mechanism has been known since 1937: to calculate the speed, about a third of the string's mass is added to the arrow's, so a lighter string leaves a larger share of the bow's energy to the shaft; a 1969 model arrives at the same rule and notes that, with a string much lighter than the arrow, the term counts for little. On material the two measurements point the same way. In kyudo, ten university archers shooting fifty arrows per string transfer about 69 per cent of the energy to the arrow with Kevlar, Technora and Vectran against 67.7 with hemp: every synthetic beats hemp in a paired test, but the difference is smaller than the shot-to-shot variation, and among the three synthetics there is practically no gap. On a recurve in a rack, with a mechanical release, laboratory tests reported in a 2007 chapter send the same arrow off at 49.73 metres per second with Dacron and at 52.09 with Fast Flight, with Kevlar and Twaron in between: here there is a difference between synthetics too, and the author links it to Dacron's stretch. On the number of strands, however, the tests disagree. In the same laboratory, taking up to six strands out of a sixteen-strand Fast Flight string leaves the speed between 51.43 and 51.88 metres per second, with no trend, because the lighter string is also less stiff; on a shooting machine, going from twenty strands to twelve sends the arrow off faster in every set-up tested, by 0.3 to 1.1 feet per second out of about 215, that is half a percentage point at most. Nobody has measured this with archers on an Olympic recurve.

Also phrased as: "a string with fewer strands is faster"; "which material for a bowstring"; "number of strands and arrow speed"; "lighter string faster arrow"; "synthetic or hemp bowstring"

Evidence

• 1937
  For Model Published later

  A paper on the dynamics of the bow: to calculate the arrow's speed, about a third of the string's mass is added to the arrow's, a rule the author says comes from his own earlier measurements; in the example, a 350-grain arrow with a 105-grain string gives an effective mass of 385 grains. It is the mechanism by which a lighter string sends the arrow off faster, with no strings compared.

  The Dynamics of A Bow and Arrow · C. N. Hickman

• 1969
  Context Model Published later

  An analytical model of the recurve: with the string's mass included, the efficiency becomes 100/(1 + m/3M), where m is the string's mass and M the arrow's, which amounts to adding a third of the string to the arrow, in agreement with Hickman's rule. Since the string weighs much less than the arrow, the author concludes that it can be left out of the rest of the calculation.

  Ballistics of the Modern-Working Recurve Bow and Arrow · Burton G. Schuster

• 1997
  For Model Published later

  A modelling study of ancient bows, with its calculations checked on replicas: in the simple Hickman model it takes up, the string is treated as inextensible, a third of its mass is added to the arrow's and the other two thirds to the limb tips. It follows that a lighter string leaves more kinetic energy to the arrow, and that with a massless string all the energy stored during the draw would pass to the arrow. This is the mechanism, with no tests on different strings.

  An approach to the study of ancient archery using mathematical modelling · B. W. Kooi, C. A. Bergman

• 2001
  For Kyudo archers Published later

  10 university kyudo archers (8 men, 2 women), the same glass-fibre bow, four strings, 50 shots per string. Transmission efficiency, that is the arrow's kinetic energy over the potential energy of the drawn bow, lies between 69.0 and 69.4 per cent with Kevlar, Technora and Vectran, with standard deviations around 3.5, against 67.7 ± 3.9 with hemp, and each synthetic differs from hemp in a paired t test. The authors use efficiency rather than speed because draw length changes from shot to shot. The difference between strings is smaller than the spread of single shots.

  BOWSTRING EVALUATION BASED ON Kansei ENGINEERING TECHNOLOGY · Satoshi Hosoya, Takashi Kawamura, Yosuke Horiba

• 2001
  Context Kyudo archers Published later

  Among the three modern synthetics efficiency is practically the same, between 69.0 and 69.4 per cent: in kyudo, switching from one synthetic to another does not shift the energy reaching the arrow. For eight of the ten archers the Kevlar string was the one they used every day.

  BOWSTRING EVALUATION BASED ON Kansei ENGINEERING TECHNOLOGY · Satoshi Hosoya, Takashi Kawamura, Yosuke Horiba

• 2007
  For Equipment tests Published later

  Laboratory tests from 1992 reported in a chapter on materials: a Greenhorn recurve in a rack, a mechanical release, an 18.1 g arrow, four strings of almost equal weight. The arrow leaves at 49.73 m/s with Dacron (6.55 g, efficiency 0.70), 51.25 with Kevlar (6.48 g, 0.738), 51.68 with Twaron (6.53 g, 0.75) and 52.09 with Fast Flight (6.45 g, 0.762). The author links Dacron's slowness to its stretch: to lengthen by one per cent a Dacron strand needs about 22 newtons, a Kevlar strand about 70.

  Design and materials in archery · B.W. Kooi

• 2007
  Against Equipment tests Published later

  In the same tests, two, four and six strands were taken out of a 16-strand Fast Flight string: the arrow's speed is 51.88 m/s with 16 strands (6.45 g), 51.43 with 14 (5.82 g), 51.62 with 12 (5.28 g) and 51.76 with 10 (4.64 g), with no trend. According to the author the lighter string is also less stiff, and the two effects cancel out.

  Design and materials in archery · B.W. Kooi

• 2009
  For Equipment tests Published later

  A robotic shooting machine, A/C/E 470 arrow of 29 inches, 44.8 lb, speed measured one metre from the rest: with 12 strands instead of 20 the arrow leaves faster in all five set-ups, bare shaft 215.93 against 215.65 feet per second, and with vanes by 0.5 to 1.1 feet per second more (P175 213.6 against 212.5). The standard deviation of speed falls with 12 strands in four cases out of five (bare shaft 0.116 against 0.197), the exception being the 1-3/4 inch spin-wing (0.221 against 0.202). A single indoor laboratory test, in a conference paper, and the comparison concerns strands, not material.

  Performance analysis based on an emulated archery machine · Kuo-Bin Lin, Kun-Shu Huang, Chi-Kuang Hwang, Chia-Wen Wu

Status history

1. 1937 Transferred The first indication is a rule of calculation: in a paper on the dynamics of the bow, to obtain the arrow's speed about a third of the string's mass is added to the arrow's, a rule the author says comes from his own earlier measurements. It follows that a lighter string sends the arrow off faster, and material and number of strands change precisely the string's weight. No strings have yet been compared: transferred.
2. 1969 Transferred An analytical model of the recurve arrives at the same rule: with the string's mass included the efficiency becomes 100/(1 + m/3M), which amounts to adding a third of the string to the arrow. The author adds, though, that with a string much lighter than the arrow the term can be left out. The mechanism holds but is still a calculation, and its practical weight looks small: transferred.
3. 2001 Reported The first measurement arrives, in kyudo: ten university archers shoot fifty arrows with each of four strings, and with Kevlar, Technora and Vectran the bow transfers around 69 per cent of the energy to the arrow against 67.7 with hemp, with a significant difference in a paired test between each synthetic and hemp. The difference between strings is smaller than the variation between single shots, there is no gap among the three synthetics, and it is a single study in kyudo: reported.
4. 2007 Contested A chapter on bow materials reports laboratory tests on a recurve in a rack, shot with a mechanical release and always with the same 18.1 gram arrow. On material the result goes the claim's way: 49.73 metres per second with Dacron, 51.25 with Kevlar, 51.68 with Twaron and 52.09 with Fast Flight, with strings of almost equal weight, and Dacron is the slowest because it stretches more. On the number of strands it does not: taking two, four or six strands out of a sixteen-strand Fast Flight string leaves the speed between 51.43 and 51.88 metres per second, with no trend, because the lighter string is also less stiff. Half of the claim gains a second study in favour, the other half its first one against: contested.
5. 2009 Contested On the shooting machine, going from twenty strands to twelve sends the arrow off faster in all five set-ups tested, bare shaft and four types of vane, by 0.3 to 1.1 feet per second out of about 215, and in four cases out of five the speed varies a little less from shot to shot. On the number of strands the two laboratory tests now point in different directions, one with a gain of a few tenths and the other with no appreciable difference, while on material the two tests agree: the status stays contested.

Related

Related articles

• What a bow is made of: what the materials of limbs, riser, string and arrows changeWood, horn, carbon, glass fibre: what bench tests on limbs, risers, strings and arrows have measured, and how much of it reaches the archer's hand.
• How fast an arrow flies: the metres per second, what decides them and how much they matter on the targetHow many metres a second recurve and compound arrows fly, what decides launch speed, and how much speed matters on the target and for the score.
• How much energy actually reaches the arrow, and where the rest goesHow much of the drawing work reaches the arrow: models say about three quarters, while the few measurements show where the rest goes and what the arrow changes.

Research lines

• 22 studiesHow much energy passes from bow to arrow: models and measurements since 1937
• 32 studiesArrow aerodynamics: drag, boundary layer, vanes

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