Open-Loop Stability and Closed-Loop Gust Alleviation on Flexible Aircraft Including Wake Modeling

This paper numerically investigates the dynamics of a flexible, lightweight, unmanned aircraft, evaluating its stability boundaries and focusing on the response of the aircraft under atmospheric disturbances. This is achieved by integrating a time-domain 3-D unsteady vortex-lattice aerodynamics method with a geometrically-exact composite beam model encompassing elastic and rigid-body degrees of freedom. The resulting framework is a medium-fidelity tool for the analysis of vehicles that exhibit substantial couplings between their aeroelastic and flight dynamics responses. In its general nonlinear form, the unified model captures the instantaneous shape of the lifting surfaces and the free wake, including large geometrically-nonlinear displacements, in-plane motions, and aerodynamic interference effects. The linearization of the equations leads to a monolithic state-space assembly, ideally suited for stability analysis and control synthesis. The numerical studies illustrate these capabilities, designing linear PID controllers in order to alleviate gust-induced loads and trajectory deviations.