Reducing Induced Drag and Maneuver Loads by Active Aeroelastic Alteration

Abstract

Induced-drag reduction and maneuver load relief are two recent benefits of active aeroelastic wing technology. Judiciously deflecting wing-edge flaps can alter an unfavorable force distribution aeroelastically. Active distribution matching control to reduce induced drag and active load alleviation control by reducing wing bending moments are such active aeroelastic wing applications. Kolonay and Eastep (“Optimal Scheduling of Control Surfaces on Flexible Wings to Reduce Induced Drag,” Journal of Aircraft, Vol. 43, No. 6, Nov.–Dec. 2006, pp. 1655–1661) posed a least-squares problem to match the calculated distribution to an elliptic distribution. Zink et al. (“Maneuver Trim Optimization Techniques for Active Aeroelastic Wings,” Journal of Aircraft, Vol. 38, No. 6, 2001, pp. 1139–1146) posed aircraft trimming as bending-moment minimization to provide external-load relief at the wing root. Analytic gradients, exact aeroelastic analyses, and closed-form trim solutions are unique features of the Automated Structural Optimization System. Both teams employed the Automated Structural Optimization System to solve their multidisciplinary optimization problems but still encountered inconveniences in obtaining required sensitivity data and in performing required trim optimization. This paper treats two forms of active aeroelastic alteration, with each being a generalization of these active distribution matching control and active load alleviation control formulations, and it develops analytic solution techniques that render the sensitivity evaluations and optimization calculations natural and convenient. Two strategies combine to resolve the inconveniences and enable in-process noniterative trim optimization and analytic sensitivity evaluation. The active aeroelastic alteration solution techniques are demonstrated by results of initial test and verification on a classical forward-swept wing example.