Stability of landing and forward flight of unmanned aerial vehicles near the ground is one of the challenging problems in the quadrotor control system. In real-time operation, when the rotary-wing vehicle flies close to the ground, the thrust increases are called ground effect. According to the flight and environmental conditions and the quality of ground surface, the aerodynamic ground effect is varied continuously. In this paper, a backstepping controller is designed and adjusted by using particle swarm optimization. Controller adjustment is referred to as the process of online estimation of the ground effect in various conditions. The stability analysis is performed and guaranteed by Lyapunov theory. The simulation results indicate that the proposed method is highly practical and capable of tracking the desired trajectory appropriately.

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