Compliant Load-Bearing Skins and Structures for Morphing Aircraft Applications

Open Access
Author:
Olympio, Kingnidé Raymond
Graduate Program:
Aerospace Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 26, 2009
Committee Members:
  • Dr Farhan Gandhi, Dissertation Advisor
  • Farhan Gandhi, Committee Chair
  • George A Lesieutre, Committee Member
  • Eric M Mockensturm, Committee Member
  • Timothy Francis Miller, Committee Member
  • Fabrizio Scarpa, Committee Member
Keywords:
  • multiobjective optimization
  • topology optimization
  • morphing skin
  • honeycomb
  • hybrid multiobjective genetic algorithm
Abstract:
Aircraft morphing has the potential to significantly improve the performance of an aircraft over its flight envelope and expand its flight capability to allow it to perform dramatically different missions. The multiple projects carried on in the past three decades have considerably helped improve the designing of actuation systems and the utilization of smart materials for morphing aircraft structures. However, morphing aircraft and especially aircraft undergoing large shape change still face some significant technical issues. Among them, the skin covering the morphing structure must meet challenging requirements that no current conventional material fully satisfy. The design of such skin, which should be able to undergo large deformations and to carry air-loads, has received some attention in the last several years but no satisfactory solution has been found yet. In the current study, the design of compliant cellular structures and flexible skins for morphing aircraft structures is investigated for two different morphing deformations. The first morphing deformation considered corresponds to one-dimensional morphing which is representative of a wing or blade changing its chord or span. The second morphing deformation considered is shear-compression morphing which can be found in some morphing wing undergoing change in area, sweep and chord such as NextGen Aeronautics' morphing wing. Topologies of compliant cellular structures which can be used for these two types of structures are first calculated using a multi-objective approach. These topologies are calculated based on linear kinematics but the effect of geometric nonlinearities is also investigated. Then, ways to provide a smooth surface were investigated by considering a general honeycomb substructure with infill, bonded face-sheet or scales. This allowed justifying an overall skin concept made of a cellular substructure with a bonded face-sheet. Lastly, the design of an improved skin for NextGen Aeronautics' morphing unmanned aerial vehicle is presented. This design project, carried in two phases, investigates in detail a methodology to design a skin with specific objectives and constraints. Constraints related to the buckling of the substructure walls and wrinkling of the face-sheet were accounted for. Driving factors to improve the skin properties were identified. Among them, pre-strains were used to reduce wrinkling and local deflection of the face-sheet, and the substructure shape and geometry was investigated to reduce strain energy and local strains. The detailed study and these driving factors' effect allowed designing a skin better than the original skin design in terms of number of parts, mass and energy input.