Wind tunnel experiment with an EPP-wing to investigate aeroelastic effects of nonlinear elastic stiffnesses

Abstract

Background: Nonlinear elastic, especially degressive, stiffnesses can reduce the wing root bending moment for design loadcases, while the cruise flight shape remains unchanged. Objective: The aim of the wind tunnel experiment is to show up the behaviour of a wing with a degressive stiffness. The tested wing is made of expanded polypropylene foam (EPP). Method: A flexural bending test is conducted to gain the bending stiffness of EPP for different densities and a wind tunnel test is performed to obtain the dependency between bending moment and deflection. The findings are compared to the results of an aeroelastic method based on a nonlinear elastic beam. Results: The bending stiffness of EPP material exhibit a nonlinear degressive stiffness. The foam wing has a softening characteristic for ascending loads. The numerical beam method for nonlinear elastic wings shows up a good agreement with the experiment and points out the load reducing effect of nonlinear structures.