Variable stiffness spar approach for aircraft maneuver enhancement using ASTROS

An innovative variable stiffness spar (VSS) approach is studied for improving aircraft roll performance. In this concept some of the existing wing spars are replaced by the adaptive-structure VSS to control the stiffness as a function of Mach number and altitude. The VSS stiffness scheduling is designed to maximize the roll rate while satisfying flutter, control surface hinge moment, and maximum deflection constraints. The VSS mechanism consists of a segmented spar having articulated joints at the connections with wing ribs and an electrical actuator capable of rotating the spar, The wing stiffness provided by the spar varies sinusoidally as a function of the rotation angle. The objective of the present study is to explore when and how to best apply this concept and assess its payoffs in terms of performance gains. The F/A-18 pre-roll-modification aircraft was selected as the baseline aircraft for its low torsional wing stiffness and available flight data. The multidisciplinary design optimization software ASTROS* was used for performing the analyses in the Mach number range of M = 0.8-1.2 at altitudes up to 35,000 ft (40,668 m). Results show that VSS can amplify the aeroelastic forces and significantly enhance roll performance of aircraft.