Biomimetic Actuation Systems for Morphing Lifting Surfaces

Morphing lifting surfaces are increasingly being integrated into aerospace systems, with uncrewed aerial vehicles (UAV), micro aerial vehicles (MAV), and the general uncrewed aerial systems (UAS) at the forefront of this development. Recent innovations in actuator technology, particularly biomimetic actuators, now exhibit actuation characteristics comparable to traditional electromechanical and hydraulic systems. This dissertation reviews bio-inspired muscle-like actuation systems with a focus on pneumatic artificial muscles (PAMs) and evaluates their suitability for morphing aerospace structures. Actuators are compared to avian muscles using measurable characteristics, and conclusions are drawn regarding their implementation in aerospace applications. Following this avian-based comparison methodology, experimentation has been conducted into the kinematics avian employ in vivo and the flight dynamics they enable. Span morphing retraction and extension rates determined from in vivo flight data of the Common Buzzard (Buteo buteo) and Harris Hawk (Parabuteo unicinctus) Presented is the preliminary design and development of a novel span-wise morphing concept that heavily implements biomimetic design. Specifically, the skeletal structure of avian is mimicked, incorporating humerus, ulna/radius, and carpometacarpus analogues to enable a versatile range of motion, facilitating multiple manoeuvrers and flight types. PAM actuators are employed as a mechanism for actuation, achieving a semi-span length change and variable sweep angles. Initial computational fluid dynamics (CFD) results are discussed in comparison with similar concepts in the field, and a rapid prototype is produced to confirm the viability of the concept. The span-wise morphing wing is subsequently modelled and controlled using inverse kinematics, enabling simplified span-length positioning. The control system incorporates PAM force models to individually model the pneumatic system driving each joint. The mechanical system of each joint is used to produce a direct kinematic model for wing tip position, and the inverse determined for control. The validity of both the model and system is experimentally tested on a fixed semi-span prototype rig of the morphing concept. Feedback is introduced through embedded potentiometers in each joint to provide joint angle feedback, with system tuning presented for different dynamic responses. The dynamic response of the morphing concept is evaluated via external photogrammetry and metrology techniques, analysing wing-tip displacement and actuation repeatability under static and simulated aerodynamic loading conditions. A dynamic case is also evaluated for the concept in relation to the proposed aircraft application, with the resulting dynamic response compared to the similarly observed response in avian species. This static and dynamic case is then tested under aerodynamic loading via a programme of wind tunnel testing. This evaluation establishes a framework for integrating biomimetic morphing wings into UAV applications, contributing to the advancement of morphing aerospace structures and providing a foundation for future adaptive wing technologies in UAV and MAV systems.