Evaluation of aerodynamic parameters from infrared laser tracking of free-gliding white storks

Abstract

Free-flight paths of White Storks (Ciconiaciconia L. 1758) were tracked using a modified laser rangefinder system (Vector IV) based on a 1550-nm diode laser. Field measurements were taken of two flocks comprising approximately 100 adult storks in all. Tracking data allowed mathematical reconstruction of their spatial trajectories using a ground-mounted GPS-based system. Atmospheric influences were accounted for by performing regular observations of ground wind speed and temperature and evaluating recorded trajectories with respect to local disturbances. A model was created by splitting the speed polar into three subspeed polars based on typical wing configurations: “soaring” (V = 7.5–10 m/s), “gliding” (V = 10–14 m/s), and “fast flight” (V = 14–19 m/s). Subspeed polars for a reference stork were derived from 60 measured data couples of sinking speed and forward speed. Multiple regression analysis was used to determine both the induced and noninduced proportionality coefficients. Morphometric data, such as wing span, wing area, and aspect ratio, were collected from 58 photogrammetric examinations. PC-connected outdoor scales provided the body masses of 36 storks from the investigated flocks. Wing loading and aspect ratio vs. forward speed were evaluated to estimate the induced drag factor k. For lift coefficients (CL) of 1.2–1.6, characterizing the range for a fully open primary cascade, k lies between 0.70 and 0.96 at a confidence level of 95 %. Our findings show agreement with the theoretically predicted k values for cascaded wing tips.