Aeroelastic Loads and Sensitivity Analysis for Structural Loads Optimization

Abstract

An aeroelastic integrated loads subsystem (AILS) is being developed and verified for the calculation of aeroelastic loads for analysis and design. AILS will fit within the aeroelastic design optimization program. The purpose of AILS is to integrate the maneuver and gust loads calculation process with structural analysis and optimization. AILS' active control capabilities and analytical sensitivity analysis will allow a simultaneous optimization of loads, structures, and active load alleviation system with flutter and other aeroelastic constraints. This first version of AILS includes a linear analysis for steady maneuver and unsteady aeroserv oelastic gust loads and their sensitivities to structural design variables and control parameters. AILS static aeroelastic analysis offers 1) full aircraft aeroelastic trim using aircraft angles of attack and sideslip, control-surface deflections, and/or motion rates and accelerations; 2) balanced distributed aeroelastic loads; 3) stress-based critical loads selection; 4) wing jig shape calculations for a specified nominal cruise wing shape and loading; 5) static aeroelastic stability and control derivatives and control effectiveness; and 6) static aeroelastic load sensitivities to structural design variables with constrained or variable nominal cruise shape to be used in optimization. The aeroservoelastic gust load capabilities in AILS include 1) random frequency response analysis for displacement, velocity, acceleration, element force, and stress; 2) flight control and active load alleviation system; 3) calculation of rms and zero-crossing frequency; and 4) analytical derivative of random gust response to control gains. These analyses are compared with MSC/NASTRAN and a proprietary dynamic analysis program (C4EZ). The results of comparisons for the static aeroelastic and gust response analyses of AILS are shown for two commercial transport aircraft: one is a wide-body subsonic transport and the other is a high-speed civil transport configuration at subsonic conditions. The static loads and stability derivatives for two models are compared with MSC/NASTRAN for both aircraft, and gust loads are compared with a production gust-load analysis for the subsonic transport case. In all cases excellent agreement is obtained. Validation of AILS' load sensitivity calculations was done through comparison with the finite difference approach. Excellent agreement was obtained between analytical and numerical derivatives.