S. . Abd Al Kareem Mohammed, A. . Hussien Mary, A. . Al‐Abadi, and M. . Ghufran Khidhir Abboosh, “Robust Proportional Integral-State Feedback with Disturbance Observer for 2-DOF Helicopter System”, alkej, vol. 20, no. 3, pp. 11–19, Sep. 2024, doi: 10.22153/kej.2024.04.001.