Abstract
Automatic Flight Control System (AFCS) Terrain Following (TF) mode allows military aircraft to fly at a certain altitude above ground level at a low altitude. TF mode reduces the probability of aircraft detection by enemy airborne radars. TF mode minimizes the effort the pilot spends to control the aircraft and allows the pilot to focus on other tasks or missions. In this study, the F-16 nonlinear model is linearized around a selected equilibrium point. The state variables of the linear model are decomposed into state space matrices on the lateral and longitudinal axes. Three different control methods, namely PID (Proportional-Integral-Derivative), LQR (Linear Quadratic Regulator), and MRAC (Model Reference Adaptive Control), are used. The results show that the designed algorithms can effectively control the aircraft's altitude, speed, pitch angle, angle of attack, and pitch rate on the longitudinal axis and the aircraft flies in accordance with the terrain profile. Finally, it is observed that MRAC outperforms PID and LQR methods due to its adaptive capability.