The main focus of this paper is to design various nonlinear sliding mode output feedback control approaches for attitude stabilisation of a quadcopter UAV using only IMU navigation sensor. Three types of controllers are considered based on asymptotical, finite-time and fast finite-time stability as conventional, terminal and fast terminal sliding mode controllers, respectively. Furthermore, two types of perturbations are applied to the plant as internal and external disturbances. Measurement noises in sensors are selected as internal disturbances, and sensor
biases and wind gust are chosen as external ones. Since the uncertainties in orthogonal rate gyroscopes can be categorised into mismatched ones, extended Kalman filter is utilised. In addition, the performance of the closed-loop system is tested in the presence of uncertain Kalman gain in an unknown harsh environment. Finally, simulation results are presented to validate the analysis.