A Biomimetically Derived Method for Control of Span-Wise Morphing Wings

Abstract

The development of novel morphing wings follows common milestones. This work presents the modelling and control of the recently proposed avian wing span-wise morphing concept. The concept primarily consists of three structural members heavily mimicking the skeletal structure birds employ for flight. This structure is actuated, through the range of motion achievable by avian, with the integration of pneumatic artificial muscles (PAMs). Arranged in antagonistic pairs, the PAMs actuate an effective shoulder joint between the aircraft and wing through 90⁰. As well as two joints along the wing through 110⁰, allowing a span-wise reduction of 75% the fully extended span. This adaptive structure is capable of supporting several different aerofoil geometries for application specific aircraft. Initially proposed with a biomimetic derived wing profile more traditional and predictable NACA aerofoils have been applied. In this paper the avian wing span-wise morphing concept is modelled and with the application of inverse kinematics a control system is derived to allow simplified span-length positioning. Similarly, desired wing area is also presented as an input for the system. The model is based on PAM force models to individually model the pneumatic system driving each joint. The mechanical system of each joint is subsequently 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 are experimentally tested on a fixed semi-span prototype rig of the morphing concept. Feedback is then introduced. Potentiometers are embedded into each joint to provide joint angle feedback. The tuning of the system is then presented for different dynamic responses. Alongside this development experiments have been conducted into the kinematics avian employ in flight and the flight dynamics they enable. These results are presented and directly applied as parameters for the proposed system. Span morphing retraction and extension rates determined from in vivo flight data of avian, including the Common buzzard (Buteo buteo) and Harris Hawk (Parabuteo unicinctus), are achieved using the avian wing span-wise morphing concept and the proposed control system. These dynamics are used to infer the parameters of an aircraft with the concept wing used as control surfaces.