Experimental force measurement study of Pantala flavescens in tailwind flight

Wind compensation is vital in insects migrating under the influence of tailwinds and crosswinds. An insect requires tailwind compensation to cover large distances and crosswind drift compensation to stay on course. The aerodynamic force measurements can provide insight into the mechanism involved in the migration in tailwind and crosswind configurations. We conducted a tethered flight experiment in a wind tunnel at a wind speed of 2.7 m/s on the dragonfly species Pantala flavescens, a long-distance migrant migrating between India and Africa. We positioned a dragonfly in a tailwind and three crosswind-tailwind configurations at 5°, 10°, and 15°. On average, the dragonfly generates thrust three times its weight at all orientations. Our results show that the dragonfly employs a new flapping mode for high lift generation and generates a mean lift equal to its weight. It produces side force approximately 0.5 times its weight, opposing crosswind to compensate for wind drift. Wind drift compensation becomes increasingly difficult with an increase in crosswind angles. In tailwind and crosswind flights, the strategy is to generate large amounts of thrust to propel itself and lift to sustain a level flight while compensating for wind drift by generating an opposing side force.