Meeting Abstract
Many animals have evolved the ability to engage in flapping flight as a method of sustained hovering in aerial environments. Within this category, there exists a large range of wing geometries, flapping kinematics, and corresponding flight strategies. A key feature present in the flapping flight of some insects is wing rotation along the longitudinal axis (pitching), which controls the lift and drag forces generated on the upstroke and downstroke. Evidence suggests that prominent characteristics of this wing pitching behavior- pitch reversal during stroke transitions and maintenance of a high angle of attack during the mid-stroke – are influenced by inertial and aerodynamic forces with largely passive contributions from the wing hinge joint, which can be accurately modeled as a torsional spring. In this work, we study the relationship between aerodynamic, inertial and elastic forces in the regulation of wing pitch and the generation of forces in hovering flight with passive-pitching flapping wings. We demonstrate an experimental system consisting of an underactuated robotic model of a two degree of freedom wing with a prescribed wing stroke and an elastic wing hinge joint. We measure wing kinematics and aerodynamic forces over a range of wing geometries, hinge stiffnesses, and flapping frequencies. Our results reveal a consistent dependency of the lift coefficient on the Cauchy number (the ratio of aerodynamic pressure to elastic stiffness) over a range of parameters. The lift coefficient initially increases with Cauchy number, attains a maximum, then gradually declines, a finding which is consistent with previous results (Ishihara et al, 2009) for a system in a very different flow regime.
