Supersonic Wing Box Weight Optimization Using Curvilinear Spars and Ribs (SpaRibs) Davide Locatelli * , Sameer B. Mulani † , and Rakesh K. Kapania ‡ Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061-0203 The need of lighter structures in aerospace industry is pushing engineers to find new design concepts which allow a weight saving without degrading the performances in term of maximum wing load factor, divergence and flutter velocities and other constraints. EBF3SSWingOpt is a tool being developed at Virginia Polytechnic Institute and State University to carry out supersonic wing weight optimization subjected to stress and buck- ling constraints. The true new innovation in the optimum design of wing boxes, introduced by EBF3SSWingOpt, is the use of curvilinear spars and ribs, termed SpaRibs since in the optimized supersonic wing structure, as presented in this paper, there is no longer clear distinction between the spars and ribs of the wing box and their structural function, as is the case for classic wing design. In this paper, the general optimization framework developed is presented, including two different methodologies, a one-step optimization methodology where topology and sizing optimization are carried out together and a two- step optimization methodology where topology and sizing optimization are carried out separately using different constraint and objective functions. A description on how the general optimization framework is applied to optimize wing-like structures is explained and the optimization problem formulation is stated. Two practical design problems, solved using EBF3SSWingOpt, are presented: a rectangular supersonic wing box and a generic fighter wing. Nomenclature λ 0 Fundamental Buckling Eigenvalue ρ Kreisselmeier-Steinhauser Constant σ i i th Finite Element Von-Mises Stress σ u Ultimate Tension Stress σ y Yield Stress of the Material σ VM Von-Mises Stress x Design Variable Vector A i i th Finite Element Area BF 0 Buckling Factor CFD Computational Fluid Dynamics DV Design Variable EBF 3 Electron Beam Free Form Fabrication f (x) Optimization Objective function FE Finite Element g i (x) i th Optimization Constraint Function GA Genetic Algorithm KSC σ Kreisselmeier-Steinhauser Stress Coefficient n iter Number of Iterations * Research Assistant, Department of Engineering Science and Mechanics. † Post Doctoral Fellow, Department of Aerospace and Ocean Engineering, AIAA Member. ‡ Mitchell Professor, Department of Aerospace and Ocean Engineering, AIAA Associate Fellow. 1 of 24 American Institute of Aeronautics and Astronautics 51st AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference<BR> 18th 12 - 15 April 2010, Orlando, Florida AIAA 2010-2673 Copyright © 2010 by Davide Locatelli. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.