Arrow aerodynamics in the tunnel: Long 2014 study

The study placed four commercial arrows in a water tunnel and a model arrow in a wind tunnel, to see how the flow behaves around the point and vanes, and how much lift and pitching moment appear when the arrow is not aligned with the flow. In water, the flow round the point stayed attached up to 6 degrees of tilt either way and separated from 9 degrees upwards; one of the four models, labelled E1912, had the smoothest point. Helical plastic vanes gave a tidier flow than flat straight ones, which separated even with the arrow aligned.

In the wind tunnel, lift grew with angle and the pitching moment stayed negative between 0 and 16 degrees, so the arrow tended to swing back into line with the flow. With the arrow aligned, changing the wind speed did not alter the coefficients. Changing the point did not alter them beyond the repeatability of the measurement, whereas having vanes, and the angle they were set at, changed them clearly. The largest values measured on the model were 1.65 newtons of lift and 0.49 newton metres of moment.

The tests were run at a Chinese low-speed aerodynamics institute. In the water tunnel, with a 0.4 by 0.4 metre test section and water moving at 0.1 m/s, the four arrows were held by the tail and tilted by hand; dye released from small tubes in front of the point, and then in front of the vanes, showed the flow, which was filmed and photographed. The Reynolds number based on shaft diameter was between 700 and 980.

In the wind tunnel, at 30 m/s, a 2:1 scale model with point, shaft, vanes and nock was suspended in the middle of the test section with its centre of mass on the centre of the balance; the Reynolds number on the shaft diameter was 24,800. Because the loads were small, an existing three-component balance was used rather than one built for the job. Data were sampled at 100 Hz for 5 seconds and reported as mean and standard deviation.

The paper runs to five pages with no figures or data tables: the results are summarised in words, with very few numbers. The method says the wind tunnel angle ran from 0 to 6 degrees in steps of 2 at 30 m/s, while the results mention angles up to 16 degrees and several speeds. The four arrows are identified by codes that cannot be matched with certainty to known products, and the paper says neither which vanes each carried nor how the model was built. In water the Reynolds number is tens of times lower than that of an arrow in flight, and in both tunnels the arrow was held fixed, without the spin and flex of flight; the abstract mentions an effect of roll on lift that does not appear in the text. No arrows were shot. The venue is flagged in the registry for questionable editorial standards.

For archers the study adds little: it confirms that an arrow in flight tends to realign itself and that this stability comes from the vanes far more than from the point. That fits what sounder work shows, but the published data are not enough to compare vanes or points or to choose between products. The authors' preference for helical vanes comes from how the dye looked in very slow water, not from measurements of flight, drag or accuracy.