Nonlinear Gust Response Analysis of Free Flexible Aircraft

Gust response analysis plays a very important role in large aircraft design. This paper presents a methodology for calculating the flight dynamic characteristics and gust response of free flexible aircraft. A multidisciplinary coupled numerical tool is developed to simulate detailed aircraft models undergoing arbitrary free flight motion in the time domain, by Computational Fluid Dynamics (CFD), Computational Structure Dynamics (CSD) and Computational Flight Mechanics (CFM) coupling. To achieve this objective, a structured, time-accurate flow- solver is coupled with a computational module solving the flight mechanics equations of motion and a structural mechanics code determining the structural deformations. A novel method to determine the trim state of flexible aircraft is also stated. First, the field velocity approach is validated, after the trim state is attained, gust responses for the one-minus-cosine gust profile are analyzed for the longitudinal motion of a slender-wing aircraft configuration with and without the consideration of structural deformation. RBA), while the second aims mainly to the analysis of elastic aircraft experiencing relatively small deformations. The idea to not consider cross-coupling effects between these two disciplines has been commonly justified by the large frequency separation of the characteristic motion which is typical of conventional structures. Nowadays, the focus on weight minimization for aircraft, leads toward more and more flexible vehicles. The resulting underlying structures may not exhibit the usual wide frequency separation among the rigid body degrees of freedom and the remaining elastic modes. So that the approach mentioned above can lead to mistakes/errors in analyses of flight performance, flying qualities, and control systems design. In these cases, an integrated analysis of flight mechanics and aeroelasticity is necessary from the very early stages of preliminary design (6).