Nonlinear design loads for maneuvering elastic aircraft

A computationally efficient scheme for maneuver load analysis, based on nonlinear aerodynamics, is presented. The kernel of the scheme is a computational fluid dynamics (CFD) code for solving the Euler/Navier-Stokes equations for a fixed-shape configuration. A modal structural model is used for elastic-shape updates, and a trim corrections algorithm is used for varying the incidences and control surface deflections until the user-defined maneuver is attained. Computational efficiency is obtained by performing a few elastic-shape changes and maneuver trim updates, all within the fluid dynamics analysis, during the steady-state flowfield convergence. The modal approach, where the structure is represented by a set of its low-frequency vibration modes, greatly simplifies the CFD-structure interface, minimizes the amount of structural data required, and allows simple shape updates of the aerodynamic grid. It is shown that the total computation time required for flowfield convergence for a maneuvering elastic aircraft is typically almost identical to that of the rigid aircraft with given trim variables. The method is demonstrated with a realistic wing-fuselage-elevator transport aircraft model performing symmetric maneuvers at Mach 0.85.