Design and Optimisation of Morphing Aircraft

Abstract

Morphing has the potential to improve the aircraft performance by adaptively changing the shape during different flight conditions. The capabilities of changing shape and carrying aerodynamic loads simultaneously make the design of the morphing structure challenging. The weight increase of morphing aircraft should also be considered, which requires system level analysis and evaluation, and the optimisation of the morphing structure. The thesis focuses on morphing wingtip devices, which are small in size but have a significant influence on the aerodynamic performance. A compliant structure based on unsymmetrical stiffness is proposed. The compliant structure has unsymmetrical stiffness allocation, which will have differential axial deflections when it is actuated. The differential deflections lead to a rotation of the compliant structure. A simplified model of the compliant structure is built, and analytical expressions are derived, which highlight the effects of the total stiffness and the stiffness asymmetry. A case study also represents the system level influence of retrofitting a morphing winglet to a baseline wing. Corrugated panels are applied to provide the stiffness asymmetry. An equivalent model is built to predict the deformation of the corrugated panels. A coupling between the vertical deflection and the axial load is found, which will affect the deflections of the compliant structure significantly. An equivalent beam is used to represent the corrugated panel. The equivalent model is verified by detailed finite element models and experiments. The optimisation of the compliant structure is performed. The actuation force is the objective, while the aerodynamic force and the shape change are included in the optimisation. The influence of the different aerodynamic forces and target shape changes are investigated, which shows the compromise made by the optimised variables to satisfy the constraint and reduce the actuation force. The compliant structures in the earlier case study are optimised, which shows a significant performance increase at the system level. A demonstration model of the morphing winglet is designed, manufactured and tested. To fit within the thickness of the airfoil, a sequence of optimisations is performed to find the suitable geometry variables. An extreme stiffness asymmetry is required to reduce the actuation force, which validates the proposed morphing structure concept. Static tests and wind tunnel tests are performed to validate the model. Finally, the contributions of the research are summarised, together with some future work on different aspects