Aeroelasticity of Polymorphing Wings

Abstract

Morphing aircraft represent a focal point in aerospace research, promising significant flight performance and control advancements. This study navigates the landscape from traditional 'monomorphing' to the emerging trend of 'polymorphing,' where two or more degrees of freedom integrate into a single-wing structure. The research involves the development and validation of robust aeroelastic models tailored for polymorphing wings as well as their comprehensive aeroelastic analysis. Central to this investigation is the Active Span Extension and Passive Pitching (ASAPP) wing, a cutting-edge polymorphing wing with span and twist morphing capabilities. The wing design delineates the wing's half-span into two distinct sections: the inboard wing, orchestrating span extension and retraction dynamics, and the outboard wing strategically featuring its elastic axis positioned ahead of the aerodynamic center, thereby unlocking load alleviation potential. Beginning with low-fidelity aeroelastic models, the effects of critical design parameters are analyzed, and a comprehensive parametric analysis is conducted, considering scenarios with and without span extension. The investigation scrutinizes the impact of variables such as elastic axis position and torsional spring rigidity on aeroelastic phenomena, including flutter and divergence. The outboard wing's passive twist mechanism is quantitatively assessed through a gust load analysis, revealing its effectiveness in load alleviation. The study extends to nonlinear analysis, introducing a cubic torsional spring to unveil the effects of cubic hardening and softening on aeroelasticity. To capture aeroelastic effects at variable morphing rates, a novel variable domain size finite element model is introduced. Incorporating a structural damping term, this model offers a realistic representation of dynamic behavior. The investigation spans morphing rates from baseline to 25% span extension and vice versa, analyzing aeroelastic boundaries at crucial points during the morphing process. A parametric analysis systematically probes critical design parameters, including the elastic axis location, the torsional rigidity of adjoining springs, and various morphing rates. Finally, a high-fidelity model of the Active Span extension and Passive Pitching (ASAPP) wing is developed using Simcenter Femap and analyzed using MSC Nastran. Significant findings emerge from the analysis: the passive pitching mechanism markedly reduces root bending moments by 115% and 84% at 0% and 25% span extensions respectively. Concurrently, root shear forces experience substantial reductions of 49% and 40% across the same stiffness range and span extension scenarios. An active control surface is deployed on the outboard wing section, capable of twist morphing, to determine its controllability and effectiveness. The results highlight a significant dependence of the roll effectiveness on the torsional stiffness of the adjoining spring. Lastly, a failure mode analysis is conducted to determine the dynamics of the ASAPP wing in case of adjoining spring failure. Investigating stability derivatives, such as Cl δ and Cl p , reveals a noteworthy sensitivity to freestream velocity, marked by a distinct change in the Cl δ sign. The research highlights potential failure modes and the importance of selecting appropriate torsional spring stiffness for optimal aeroelastic stability and controllability of the ASAPP wing.

Date of Award	22 May 2024
Original language	American English
Supervisor	Rafic Ajaj (Supervisor)