Stability of Flapping Flight Dynamics of Large Birds by Gianmarco DUCCI

For the degree of Doctor of Engineering Sciences and Technology

Birds have inspired human innovation and technology for centuries. The first documented human flying attempt dates back the late 800, from Abbas ibn Firnas who created what is considered the first aviation experiment. Later in the years, around the 15th century, Leonardo da Vinci dedicated long time of his research to formally understand bird's flight, leading him to the famous ornithopter invention. Biological fliers are still nowadays a source of scientic inspiration for unsolved research questions, both invoking a deeper understanding of sophisticated flight mechanisms, and sparking new engineering ideas.

This Thesis aims at contributing in the field of flight dynamics of migratory birds, trying to understand the role of biological and kinematic parameters on flapping flight stability. From a physical point of view, the flapping represents a forcing term in the equations of motion of bird flight. Generally speaking, due to this action, these equations do not display fixed points of equilibrium. The problem of studying stability of bird flight is therefore re-formulated via a limit cycle analysis of such equations of motion.

We leverage such a formalism to provide evidence that the morphological and kinematic parameters responsible for the generation of the pitching moment, are the most impacting the longitudinal stability. Our numerical results suggest that passive stability cannot be achieved in absence of the tail surface. However we show a trade-off between passively stable flights, and power expenditure, suggesting explanations for the elds observation that birds flap with furled tail during long flights.

We conclude by validating a multi-body approach for modeling the bird dynamics, that can be of direct help in understanding the role of bio-inspired compliant elements on flight stability. A preliminary investigation modeling the shoulder joint compliance of the wing is proposed.

Jury members :

• Prof. Renaud Ronsse (UCLouvain, Belgium), supervisor
• Prof. Philippe Chatelain (UCLouvain, Belgium), supervisor
• Prof. Sandra Soares-Frazao (UCLouvain, Belgium), chairperson
• Prof. Pierre-Antoine Absil (UCLouvain, Belgium)
• Prof. Emily Shepard (Swansea University)
• Prof. Mark Lowenberg (University of Bristol)
• Prof. Julien Hendrickx (UCLouvain, Belgium)