Strategies exhibited by bumblebees when challenged with aerodynamic and obstacle disturbances
Creators: name: Jakobi, Timothy
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401201
subject: Aerodynamics (excl. hypersonic aerodynamics)

description: The articulation evident in the wings of flying insects seems to enable remarkable steadiness when flying in unsteady atmospheric conditions and through clutter. Recently, there has been a substantial growth in micro air vehicles (MAVs), made possible by breakthroughs in battery technology and advances in manufacturing. However, the steadiness of such vehicles is far inferior to insects and there appears to be no commercially viable flapping-wing MAVs. The gaps in our understanding encompass several aspects of flight mechanics and environment, including flapping-wing aerodynamics and control, which, if filled, would enable steady flight through unsteady environments. In this thesis, bumblebees were experimentally investigated to draw a general understanding of the responses that occur when flying through typical disturbances that are ubiquitous in the normal outdoor environment: gusts and obstacles. In the first set of experiments, bumblebees were trained to fly through imposed, documented, repeatable gusts oriented in different directions and their flight responses were characterised. Gusts caused bees to exhibit unique wing stroke changes while responding to each gust case (sideward, upward and downward), with downward gusts causing the greatest flight deviations. The wing changes resulted in linked body orientation manoeuvres that typified the general trajectory changes through the gusts. Further experiments and analyses using a mechanised rotating flapper also indicated that downward gusts cause more adverse aerodynamic effects than the upward gusts. In addition, analytical models based on the actual wing strokes of bees recovering from gust perturbations gave insights into the kinematic strategies observed in bees when counteracting gust effects. In subsequent experiments, bees were made to encounter a sudden-appearing obstacle that forced them to engage in “all-out” braking. Bees showed consistent body re-orientations when dealing with the spontaneous braking demand. The magnitudes of active manoeuvres were found to be linked with the initial inertial properties of bees (mass, velocity, heading). The roll, pitch and yaw manoeuvres were significantly larger for bees with a greater braking challenge ahead of them (heavier and faster on approach). The handling via roll-based manipulation of the body—as opposed to exclusive use of pitch, as initially hypothesised—suggests that bees employ body rotations about the axes of lower moment of inertia, optimising for speed to rapidly engage in required force production. In addition, bees generally chose to undergo manoeuvres in the direction of initial heading offset. Both proclivities suggest awareness of the initial state and force modulation via body orientation changes. The behaviours of bees in both disturbance types revealed that body motion is an indicator for the underlying strategies of disturbance mitigation, as well as perception of flight state and modulation of response dynamics according to the control demand. The coordinated actions of bees were reasoned to provide control advantages for the perturbations studied, serving as inspiration for improved small-scale biological and engineered flapping systems.