DRAWING INSIGHT FROM NATURE: A BAT WING FOR MORPHING AIRCRAFT

Being the only flying mammal, bats have evolved unique flight devices affording them high maneuverability and efficiency despite their low flight speeds. By selecting bats of three different ecological niches - a highly efficient fishing bat, a nimble insectivorous forager, and a large soaring bat of the 'flying fox' family - passive wing shapes can be demonstrated as capable of attaining very different aerodynamic performance characteristics. The aerodynamics of man-made equivalents to these wing shapes, using thin airfoils rather than skeleton and membrane construction, are studied both computationally through a lifting-line approach and experimentally with quasistatic wind tunnel data of 'morphed' and 'unmorphed' wing shapes. Results confirm that shape inspired by the larger soaring bat has higher lift-to-drag ratios, while that of the foraging bat maintains lift at higher angles of attack than the other wings. The advantages are more pronounced by morphing, increasing both lift coefficient and lift-to-drag ratios by up to 50% for certain wings. This is validated both numerically and in the Cornell University 4'x4' wind tunnel. Analysis of these shapes provides the first phase of wing design for use on a morphing aircraft vehicle. In order to take greater advantage of vehicle morphing, wing shapes with camber and twist distributions unique from those found in nature will evolve to suit a man-made structure. In this way, a wing shape intended for cruise may extend its practicality into highly maneuverable operations through the use of wing morphing. Starting from the bat planform shapes, a series of optimizations determines the best camber and twist distributions for effective morphing. Given a fixed degree of shape change at any point along an airfoil based on mechanism constraints, improved morphing performance can be found compared to initial assumptions of the natural shape change. Heuristic optimization employing simulated annealing determines the required morphing shapes for increased performance, broadening the abilities of each wing shape by increasing parameters such as lift, rolling moment, and endurance.