MULTIDISCIPLINARY OPTIMIZATION OF THE WING-STORE POSITION AGAINST THE DYNAMIC CONDITIONS

Abstract

The chord-wise position vis-à-vis the span-wise position of the wing-stores (fuel tanks, engines, etc.), on both commercial and military aircrafts, significantly influences the aeroelastic behavior of the aircraft wings. A particular position may destabilize the wing at a particular operating flight condition, which can prove catastrophic for the safety of the crew. This research work aims to examine aeroelastic response of a wing with an under-wing store for improved flutter performance during the preliminary design phase. The first part of this study numerically investigates the flutter behavior of a generic aircraft wing with respect to chord-wise position of the under-wing store located at a particular spanwise station. A MATLAB code is established that generates the frequency and damping trends by eigenvalue solution of flutter equations of motion with quasi-steady aerodynamic model and subsequently, determines the flutter speed limits for each chord-wise position of the under-wing store at various altitudes. The equations of motion are modified to incorporate the store mass and store induced aerodynamics in terms of lift curve slope which in turn, is determined by using planar Vortex Lattice Method. The results indicate that the flutter speed increases when the store centre of gravity (c.g) is moved forward i.e. towards the leading edge, and decreases when the store c.g is moved towards the trailing edge relative to the wing elastic axis (e.a). Furthermore, the flutter speed increases with the rise in altitude when store c.g is located aft of the wing e.a and decreases when positioned forward of the e.a. The second part of this research develops a multidisciplinary framework that optimizes the wing-store position during the preliminary design phase. The objective is to maximize the damping ratio by varying the store chord-wise position under the geometrical constraints of the wing-store configuration for a particular span-wise station. The optimization code is formulated in MATLAB that computes the sensitivity gradients of objective function by using analytical Global Sensitivity Equation (GSE) approach and numerical finite differencing technique and further employs these gradients to establish the search direction during optimization. Finally, the optimized solutions in terms of higher damping ratio and feasible wing-store position from both analytically based GSE and the finite difference based optimizers are presented and compared with the results obtained from wing-store flutter sensitivity analysis performed earlier.