Numerical and experimental analysis of the static compliance of chiral truss-core airfoils

Abstract

This paper presents an innovative wing profile featuring an internal truss-like structure of chiral topology. The chiral design is selected because of its unique deformation characteristics, which produce a theoretical, in-plane Poisson's ratio of -1. Such a Poisson's ratio yields a very high shear modulus, which in principle does not require the wing profile to be defined by a closed section or stressed-skin configuration. In addition, the peculiar deformation mechanism of the chiral configuration allows large decambering deflections to occur, with all the members of assembly behaving within the linear range of the material. Hence the proposed design combines large chordwise compliance and large in-plane shear stiffness. Such conflicting mechanical properties can be achieved through the proper selection of a limited number of geometric parameters defining the core configuration. The objective of the paper is to investigate the compliance characteristics of the airfoil. Two-dimensional profiles, designed according to results from previous investigations, are manufactured and tested to assess compliance and evaluate decambering deflection limits. The experimental analysis is guided by numerical models that account for deviations from the ideal configuration due to manufacturing limitations. Numerical and experimental results demonstrate the influence of core geometry on the compliance and confirm the ability of chiral-core airfoils to sustain large deflections while not exceeding yield strain limits.