Spanwise wing morphing using multistable cellular metastructures

Abstract

Morphing wings have the potential to provide additional functionality or increased performance to aircraft that serve in multiple roles and exhibit distinct aerodynamic characteristics. In-flight aspect ratio adaptation from spanwise morphing is one avenue for achieving this potential. This shape adaptability would allow the aircraft to extend the wings for an efficient loitering mode and retract them to better enable a high-speed dash. Spanwise morphing has historically been accomplished through the use of telescoping mechanisms, which lead to greater mechanical complexity and increased weight. This paper proposes a novel, lightweight, compliant structure composed of cellular metamaterials exhibiting multiple stable shapes. These metastructures enable spanwise morphing by allowing large, elastic deformations while maintaining their ability to bear loads. The physical and mechanical properties of a selection of multistable honeycombs with different unit cells are characterized using analytical and numerical methods. Their in-plane and flexural mechanical properties and their structural efficiency are compared to each other and to a conventional hexagonal honeycomb. Two multistable honeycombs are selected and utilized to develop a beam-like metastructure capable of shape adaptation in a single direction. The flexural mechanical properties of this metabeam are investigated using numerical and physical methods. We demonstrate the viability of the metabeam as a shape adaptable metastructure by developing a hybrid span-morphing wing concept that combines conventional, rigid structures with the compliant metabeam. The wing is analyzed using an uncoupled static aeroelastic tool to assess its performance under aerodynamic loading, showing the ability to increase lift from spanwise morphing without increasing wing flexural deflection.