The more the vanes are angled, the sooner the arrow spins up and the more turns it makes in the first metres of flight

The summary today

It is physics that can be calculated well, and so far it has mostly been calculated. The 2011 spin model gives the distance the arrow travels per turn, once it has reached its stable spin rate, as the shaft diameter times pi divided by the sine of the vane angle: more angle, less distance per turn and more turns. On a Protour 470 with vanes angled at just under half a degree that means one turn every 2.12 metres, and the spin measured by shooting from a machine between one and fifteen metres follows the calculated one; but only one angle was tried, chosen precisely to match the stable spin. In 2017 the same method compares angles on an X7 2315: with Diamond 235 vanes the arrow makes 8.4 turns in the first twenty-five metres and completes the first at 6.9 metres at 0.9 degrees, while at 2.1 degrees the turns become 19.6 and the first comes at 4.4 metres; with the 280 vanes the picture is the same. According to the model the arrow starts to rotate as soon as it leaves the string whatever the angle: what the angle changes is how quickly it spins up. Nobody has yet measured spin at more than one angle.

Also phrased as: "fletch angle and spin"; "vane offset"; "how many turns the arrow makes"; "arrow spin in flight"; "helical vanes and spin"

Evidence

• 2011
  For Model Published later

  Model of an arrow's axial spin: at the stable rate the distance per turn equals π times the shaft diameter divided by the sine of the vane angle. For an Easton Protour 470 with three X vanes angled at just under 0.5 degrees, shot from a single-cam compound on a machine, one turn every 2.12 m, 237 rad/s and 0.46 m/s of speed lost to spin energy; the spin measured between 1 and 15 m follows the calculated one, but at a single angle, chosen to match the stable spin.

  The aerodynamic drag and axial rotation of an arrow · J L Park

• 2017
  For Model Published later

  Spin model applied to X7 2315 arrows with Diamond vanes: with the 235s, 8.4 turns in the first 25 m and the first turn completed at 6.9 m at 0.9 degrees, 19.6 turns and the first at 4.4 m at 2.1 degrees; with the 280s, 10.3 turns and 5.5 m at 0.7 degrees, 24 turns and 3.5 m at 1.7 degrees. Calculated values, not measured.

  Effect of arrow shaft straightness on arrow grouping · James L Park, Patrick J Aitchison, Adam J Bielby, Vincent Bleakley, Trent P Carberry, Richard M Ellis, Richard D Kerner, Andrew D MacDonald, Danie Oosthuizen, Scott B Pankhurst, Konstantinos Psarakis

Status history

1. 2011 Transferred The first model of arrow spin ties the distance travelled per turn, at the stable rate, to the vane angle: it is the shaft diameter times pi divided by the sine of the angle, so more angle means less distance per turn and more turns. On a Protour 470 with X vanes angled at just under half a degree the calculation gives one turn every 2.12 metres, and the spin measured by shooting from a machine between one and fifteen metres follows the calculated curve. Only one angle was tried, though, chosen to match the stable spin: for the comparison between angles there is only the formula, and the status is transferred.
2. 2017 Transferred The same method compares angles on an X7 2315: with Diamond 235 vanes the arrow makes 8.4 turns in the first twenty-five metres and completes the first at 6.9 metres at 0.9 degrees, and 19.6 turns with the first at 4.4 metres at 2.1 degrees; with Diamond 280 vanes, 10.3 turns and 5.5 metres at 0.7 degrees, 24 turns and 3.5 metres at 1.7. These figures are calculated, not measured, so the status stays transferred, even though in the same work the arrows with more angle group better.

Related

Related articles

• Vanes, feathers or Spin Wings: what actually changesLarge or small vanes, feathers or plastic, vane angle and orientation on the shaft: what the studies measure, and where research has not yet reached the target.

Research lines

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

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