RESEARCH ARTICLE Design concepts of an aircraft wing: composite and morphing airfoil with auxetic structures P R BUDARAPU a,* , Sudhir Sastry Y B c , R NATARAJAN c a Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560 012, India b Department of Aeronautical Engineering, College of Engineering, Defence University, Ethiopia c Department of Aeronautical Engineering, Institute of Aeronautical Engineering, Hyderabad, India * Corresponding author. E-mail: pattabhib@gmail.com © Higher Education Press and Springer-Verlag Berlin Heidelberg 2016 ABSTRACT This paper is categorized into two parts. (1) A frame work to design the aircraft wing structure and (2) analysis of a morphing airfoil with auxetic structure. The developed design frame work in the first part is used to arrive at the sizes of the various components of an aircraft wing structure. The strength based design is adopted, where the design loads are extracted from the aerodynamic loads. The aerodynamic loads acting on a wing structure are converted to equivalent distributed loads, which are further converted point loads to arrive at the shear forces, bending and twisting moments along the wing span. Based on the estimated shear forces, bending and twisting moments, the strength based design is employed to estimate the sizes of various sections of a composite wing structure. A three dimensional numerical model of the composite wing structure has been developed and analyzed for the extreme load conditions. Glass fiber reinforced plastic material is used in the numerical analysis. The estimated natural frequencies are observed to be in the acceptable limits. Furthermore, the discussed design principles in the first part are extended to the design of a morphing airfoil with auxetic structure. The advantages of the morphing airfoil with auxetic structure are (i) larger displacement with limited straining of the components and (ii) unique deformation characteristics, which produce a theoretical in-plane Poisson’s ratio of – 1. Aluminum Alloy AL6061-T651 is considered in the design of all the structural elements. The compliance characteristics of the airfoil are investigated through a numerical model. The numerical results are observed to be in close agreement with the experimental results in the literature. KEYWORDS wing design, aerodynamic loads, morphing airfoil, auxetic structures, negative Poisson’s ratio 1 Introduction The ever increasing demand for light and efficient structures has led the engineers and scientists to use the composite materials in achieving superior performance with unique thermo-mechanical properties and specific strengths, which are not possible with the traditional materials Frolov [1]. The strength to weight ratio of composite materials is superior compared to the conven- tional aluminum alloys. In particular, the use of laminated polymeric composites has many potential applications in a variety of engineering fields: for example, in the aircraft structures Budarapu et al. [2–4] armoured vehicles Benloulo and Sánchez-Gálvez [5] and space vehicles Rawal [6], to name a few. Therefore, composite materials are the most suitable materials in the aerospace industry, where the strength to weight ratio is the prime factor. On the other hand, amorphing aircraft is an aircraft containing multi-point adaptability, probably incorporating macro, micro, structural and/or fluidic approaches for the control. The word ’morphing’ refers to seamless shape changes that are continuous and not to classical discrete aircraft wing adaptation systems, such as flaps or leading and trailing-edge high-lift devices. Therefore, morphing aircraft changes its shape and size during the flight. The concept of morphing is directly inspired by the nature. Gliding birds continually change the shape and size of their wings Tucker [7], probably to exploit the profound effect of wing morphology on aerodynamic performance Weiss [8]. Swifts (Apus apus) are some of the most Article history: Received Jan 12, 2016; Accepted Apr 29, 2016 Front. Struct. Civ. Eng. DOI 10.1007/s11709-016-0352-z