Coupled Flight Dynamics and Aeroelasticity of Maneuvering Aircraft: Nonlinear Modeling and Linearized Stability Analysis

Modern aircraft designs are trending toward increasingly lightweight, high-aspect-ratio, and highly flexible configurations for improved aerodynamic efficiency and performance. As structural flexibility increases, the traditional separation between flight dynamics and aeroelasticity becomes less valid: elastic deformations influence rigid-body motion, and maneuver-induced accelerations and loads impact the structural response. This study investigates the coupled flight dynamics and aeroelastic behavior of flexible aircraft, focusing on the effects of maneuvering on flutter instability.
A unified analytical and computational framework is derived for modeling both nonlinear and linearized coupled equations of motion, capturing the interaction between rigid-body dynamics and structural elasticity. A general formulation of the nonlinear equations of motion is first derived for a general coordinate system. The equations are then linearized about steady maneuvering flight conditions and cast in state-space form. A modal representation is then introduced, yielding a compact formulation suitable for aeroelastic stability analysis. This process reveals eight inertial coupling terms, including both stiffness and damping contributions, expressed explicitly as functions of flight parameters such as airspeed and load factor.
The formulation is applied to multiple configurations, including the Active Aeroelastic Aircraft Testbed (A3TB) flying-wing UAV and an F-16 fighter jet aircraft model. For the A3TB configuration, maneuvering conditions significantly alter flutter characteristics and reduce flutter onset speed. For the F-16, a comprehensive survey of a wide range of external store configurations highlights the sensitivity of flutter behavior to operational conditions. The results show that neglecting rigid-elastic coupling leads to non-conservative flutter predictions. Overall, this work provides both insight and practical tools for analyzing maneuvering aeroelastic systems, improving the prediction of flutter boundaries, and advancing the understanding of coupled flight-mechanics–aeroelastic interactions.