Stabilizing a Bio-Inspired Rotating Empennage Fighter Aircraft in Multiple Trim Scenarios

This paper considers the problem of stabilizing a bio-inspired fighter aircraft at its Air Combat Maneuver Condition in steady-level and coordinated-turning flight. The aircraft equations of motion are linearized, and an infinite-horizon linear quadratic regulator design is conducted. The open-loop system is unstable in the short-period and Dutch roll modes. This is mitigated in the closed-loop system, which is analyzed in the time and frequency domains. Included in the simulation dynamics are first-order actuator models, actuator deflection limits, and actuator rate limits. These are particularly important for this bio-inspired aircraft because control actuation requires rotation of the empennage, which has relatively large inertia. Simulation responses to initial condition dispersions, aerodynamic model error, and atmospheric turbulence are analyzed to characterize time-domain properties: settling time, region of attraction, control saturation, and robustness. Due to poor singular values for the throttle setting and rotating tail inputs, analysis is dedicated to control designs with these inputs fixed at trim values. Within the scope of these analyses, fixing the rotating tail at trim does not significantly degrade system performance.