Nonlinear Design Loads for Maneuvering Elastic Aircraft

Abstract

A computationally ef cient scheme for maneuver load analysis, based on nonlinear aerodynamics, is presented. The kernel of the scheme is a computational uid dynamics (CFD) code for solving the Euler/Navier-Stokes equations for a xed-shape con guration. A modal structural model is used for elastic-shape updates, and a trim corrections algorithm is used for varying the incidences and control surface de ections until the user-de ned maneuver is attained. Computational ef ciency is obtained by performing a few elastic-shape changes and maneuver trim updates, all within the uid dynamics analysis, during the steady-state ow eld convergence. The modal approach, where the structure is represented by a set of its low-frequency vibration modes, greatly simpli es 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 ow eld 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.

NeoCASS: An Integrated Tool for Structural Sizing, Aeroelastic Analysis and MDO at Conceptual Design Level

“…panel methods, as proposed in. 31 Of course in this case, the terms ∂FR ∂PM e can be used, i.e. the aerodynamic derivatives including aerolelastic effects are used as done in.…”

Procedures and Models for Aeroservoelastic Analysis and Design

“…The modal approach was used to modify computational fluid dynamic (CFD) schemes for calculating non-linear aerodynamic loads on maneuvering elastic aircraft [25]. The resulting computational static aeroelasticity scheme interrupts the CFD convergence process every user-defined number of iteration to introduce elastic deformations to the flow-field grid geometry.…”

“…The four iteration loops (CFD, elastic, trim, and optimization) converged simultaneously in about the same number of CFD iterations as required for the rigid aircraft with fixed aerodynamic shape. Being based on the reduced-size linear formulation described above, and with the help of an efficient structure-aerodynamic spline procedure [25], the added computation time in the aeroelastic optimization run was insignificant in comparison with that required for the CFD solution. …”

“…The control model can be defined at this stage by eqs. (23) and (25) such that the control design variables appear as gain terms in ½G c . In this way, the differentiation of the system matrices of eqs.…”

“…The reasons were that (a) there were no adequate algorithms for deforming the model shape and moving the control surfaces as dictated by the required maneuvers, and (b) the computational cost associated with repeated analyses has been too high. Recent works in the area of computational aeroelasticity facilitated non-linear quasi-steady solutions for maneuver loads [25,26] and reduced-order computational unsteady aerodynamics models for dynamic aeroelastic analyses [27,28]. These works opened the way for the development of non-linear aeroservoelastic methods that will be soon applicable in hi-fidelity aircraft design sessions.…”