Evaluation of hexagonal chiral structure for morphing airfoil concept

In this paper a concept of hexagonal chiral honeycomb is proposed as a truss-like internal structure for adaptive wing box configurations. In contrast with classical centresymmetric cellular structures like rectangular or hexagonal grids, the proposed honeycomb did not present inversion symmetry, and featured an in-plane negative Poisson's ratio behaviour. The cellular structure considered exhibited this Poisson's ratio behaviour under a large range of strain. A set of numerical (finite element, FE) simulations have been carried out in order to correct the initial theoretical predictions to take into account axial, shear and elastic deformations of all elements composing the unit cell when subjected to uniaxial loading. The homogenized linear elastic mechanical properties were then introduced in an FE wing box model of a racecar wing coupled to a panel code to simulate unidirectional static fluid-structure coupling between the wing box and the flow surrounding the airfoil. The cellular solid proposed as the internal layout of the wing box allowed conforming deformations with the external flow, giving a variation of the camber line and trailing edge displacement, and acting as an aileron.