Multi-objective Eigenstructure Assignment-PID Based Controller Design for Longitudinal Motion of Aircraft

Autopilots maintain the flight balance of aircraft using aerodynamics forces autonomously. Autopilot system design is divided into two section, inner and outer loop. Inner loop act as a stabilizer while outer loop provide motion control such as altitude, speed and path angle. The aim of this study is to utilize eigenstructure assignment (EA) and Proportional -Integral-Derivative (PID) in multi-loop configuration for altitude and pitch angle control. Aircraft non-linear model is obtained using Euler formulism and trimmed at certain flight conditions to achieve the linear state space model of aircraft which is used in this study. Aircraft longitudinal motion is highly coupled and unstable, EA is implemented in inner loop for stability augmentation and decoupling of system. Two different outer loop controllers are designed for altitude and pitch control of aircraft using PID controller. Designing controllers in such a configuration not only reduced the coupling between different state variables but also accurately control and tracked the altitude and pitch angle. Effectiveness of multi-loop control configuration will be illustrated with the help Matlab/Simulink model and results.