Control-Oriented Modeling for Flexible Aircraft

Flexible aircraft designs with high-aspect-ratio wings and lightweight structures are increasingly adopted to achieve improved fuel efficiency. To design a controller for a flexible aircraft, a low-order model of its dynamics that captures the aeroelastic behavior is needed. One approach to establishing such a low-order model is to extend the six-degree-of-freedom rigid aircraft model with additional elastic states. However, most of the existing models along these lines are based on simplified aerodynamics models (e.g., experimentally corrected aerodynamic coefficients), which limits the applicability of such low-order models in early design stages. In this work, a semi-analytical model of flexible aircraft is established through the combination of the dynamics of elastic body and the numerical linearization of high-order structure and aerodynamics models. The proposed model is derived in the body-fixed axes formulation, represents full flight dynamics (both longitudinal and lateral), and preserves the physical meanings for the states and all the derived terms. Static residualization is also adopted to enhance the model’s accuracy with a limited number of elastic states. Using the proposed approach, low-order semi-analytical models are exemplified for different complexity aircraft representations and verified against the corresponding nonlinear high-order models.