Free Flight and Wind Tunnel Measurements of the Drag Exerted on an Archery Arrow

We describe two support-interference-free measurements of aerodynamic forces exerted on an archery arrow. The first measurement is performed in a wind tunnel with JAXA's 60 cm Magnetic Suspension and Balance System, whereas the second measurement is carried out by a free flight experiment. In the latter measurement, the trajectory and rotation of the arrow is recorded by two high-speed video cameras and the arrow's down range velocity decay rate is analyzed to determine the drag coefficient. The arrow-shooting system developed by Miyazaki et al. (2013) is utilized, in order to investigate Re number dependence of the drag coefficient for . We attach two points (piles) of different type (streamlined and bullet) to the arrow-head and two kinds of vanes (SPIN- WING-VANE and GAS PRO) to the arrow-tail. The boundary layer remains laminar for any combination of point and vane, if Re is less than . It becomes turbulent for Re larger than and the drag coefficient increases to about 2.6, when the bullet point and SPIN-WING-VANE are attached. In the same Re range, two values of drag coefficient are found for the combination of streamlined point and SPIN-WING-VANE. The lower value (about 1.6) corresponds to a laminar boundary layer and the larger value (about 2.6) to a turbulent boundary layer. In contrast, for GAS PRO vanes, the boundary layer remains laminar at any Re considered, irrespective of the point- shape. These findings confirm that both the point- and vane-shapes have a crucial influence on the laminar to turbulent transition of the boundary layer. We also asked an elite female archer (recurve bow) to shoot the same A/C/E arrow (with bullet point and SPIN-WING-VANE), of which velocity is 58 m/s (). The arrow launched by the archer oscillates along its length (Archer's Paradox), and the drag coefficient is found to be about2.65 (turbulent value), indicating that the oscillation of the arrow induces the boundary layer transition.