Aeromechanics Analysis of a Hummingbird-Like Flapping Wing in Hover

Abstract

This paper presents an in-depth investigation into the instantaneous forces, flowfield, and wing deflections of a flapping wing used on a hover-capable robotic hummingbird. The goal was to understand the relationship between instantaneous lift and wing shape. An experimental rig was constructed, which flapped the wing at 20 Hz and measured instantaneous loads normal to the stroke plane. To separate inertial and aerodynamic loads, a novel approach was developed in which the wing spatial and temporal displacement was obtained using digital image correlation. From this, the instantaneous inertial force normal to the stroke plane was calculated based on mass distribution. The flowfield on the wing was resolved using particle image velocimetry, which revealed attached flow at steep angles of attack and several strong vortices. It was found that lift was sensitive to both unsteady aerodynamics and deflection. This study marks the first time that these quantities have been measured for a flapping wing used on a hover-capable vehicle, using a procedure developed for extracting pure aerodynamic force on a flexible structure. This effort has resulted in experimental data useful for validating high-fidelity flapping wing aeroelastic computational models.