A Discrete-time State-space Model with Wake Interference for Stability Analysis of Flexible Aircraft

This paper investigates the coupled aeroelastic and flight dynamics stability of flexible lightweight aircraft. The aerodynamics are modelled by the discrete-time unsteady vortex lattice method, which can capture the large deformations of the lifting surfaces, and includes 3-D effects and in-plane motions. A geometrically-exact composite beam formulation is used to model the nonlinear flexible-body dynamics, including rigid-body motions, and the equations are accommodated to discrete-time formulation. The governing equations are linearised around an equilibrium configuration, which can be highly deformed, performing a small perturbation analysis and assuming a frozen aerodynamic geometry. The resulting framework is a monolithic discrete-time state-space formulation, which provides a powerful tool for the stability boundary prediction of a flexible vehicle through a direct generalized eigenvalue analysis. It offers increased fidelity as compared to traditional tools, and at very low computational cost. As a suitable test case to illustrate the capabilities of this approach, the flutter of a T-tail is examined. In addition, previous open-loop results are extended in order to asses wake interference effects on flexible aircraft dynamics.