Unified Control of Flight Dynamics and Actuators Using Local Accelerations

Control surface actuators usually come with their own servo control algorithm, which ensures that the deflection commanded by the flight control laws is quickly achieved. Therefore, flight control and servo control together form a cascaded control structure. Traditionally, the flight control laws (outer loop) and servo control laws (inner loop) are designed independently. However, recent applications demand an increasingly dynamic design of flight control, with actuator dynamics becoming a limiting factor. In this paper, a unified control design for actuators and flight dynamics is investigated. The local acceleration at the lifting surface (empennages and wing), close to the actuator, is fed back within an inner actuator control loop, allowing for faster compensation. The theoretical properties of the suggested control structure are discussed analytically first. Later, the concept is applied to a linear model for longitudinal aircraft motion. A classical state controller serves as a reference for comparison of the proposed strategy against the standard one with the actuator internal control law. Both controllers are designed using eigenstructure assignment, and the pole locations are numerically optimized. The closed-loop behavior is assessed in the time and frequency domains. The results promise significant improvements in terms of disturbance rejection and robustness.