Flight Dynamic Simulation Modeling of Large Flexible Tiltrotor Aircraft

A high-order rotorcraft mathematical model is developed and validated against the XV-15 and a Large Civil Tilt-Rotor (LCTR) concept. Rigid body and inflow states, as well as flexible wing and blade states are used in the analysis. The separate modeling of each rotorcraft component allows for structural flexibility to be included in the presented formulation, which is important when modeling large aircraft where structural modes effect the frequency range of interest for flight control, generally 1 to 20 rad/sec. Details of the formulation of the mathematical model are given, including derivation of structural, aerodynamic, and inertial loads. The linking of the components of the aircraft is developed using an approach similar to multibody analyses by exploiting a tree topology, but without equations of constraints. Assessments of the effects of wing flexibility are given. Flexibility effects are evaluated by looking at the nature of the couplings between rigid body modes and wing structural modes and vice versa. A model following control architecture is then implemented on full order LCTR models with and without structural flexibility. The rigid wing model is shown to give Level 1 handling qualities, whereas the wing flexible model exhibits poor handling qualities. Notch filters are introduced to eliminate wing structural dynamics from the output equations. The aircraft response with notch filters is shown to be much improved with respect to stability margins and handling qualities requirements for the LCTR.