###### Abstract
In addition, a nonlinear control algorithm was proposed to mitigate the aircraft control problem using dynamic control and feedback linearization methods, and they applied the backstepping control strategy and sliding mode control scheme. Efe initiated a sliding mode controller to control quadrotor robots at low altitudes. They achieved the desired elevations using a hierarchical control system and dynamic model for the aircraft [20]. Similarly, a PD control method with linear feedback and dynamic inverter control was applied to evaluate numerous VTOL UAV flight controls [21; 22; 23]. To enhance the stability of the flight dynamics system model, a predicative current control method was investigated, which included the number of candidate vectors, reflecting the vector selection more accurately. The amplitude of the vector can also be adjusted while suppressing ripples [24; 25; 26]. A sliding mode controller is a robust control strategy that alters the dynamics of a nonlinear system while applying a discontinuous control input. The vital significance of the sliding mode controller is its finite time convergence, insensitivity to interference, and sensitivity to steady-state error [27]. To address disturbances with finite time convergence properties, the integral terminal sliding mode control strategy has played a significant role in various UAVs. The integral terminal sliding mode control along with backstepping control was developed for altitude and position control [28]. This study performs a comprehensive stability analysis of the QNET VTOL system with an experimental investigation in LabVIEW and MATLAB using various control strategies, including cascaded control (PI, PID) and the ISTSMC nonlinear control algorithm. The first core objective of the presented research work is to identify the significance of the nonlinear robust control technique for flight dynamics systems, which is obligatory to verify the stability of the VTOL system before takeoff. The presented work strengthens the stability analysis of the VTOL system using Lyapunov theory, showing the finite time convergence of the ISTSMC strategy and insensitiveness to disturbances. Moreover,ISTSMC is more immune to parametric variations, referred to as model uncertainties and disturbances that affect the VTOL system in terms of air pressure and friction, etc. The next objective of the presented research is to compare the performance of ISTSMC with the cascaded control strategy. Linear control techniques such as PID are also compared as a reference, but they lack analysis in terms of verifying the stability of the VTOL system. The open loop analysis of the VTOL system after deriving the transfer function considering the air pressure and temperature of the ambient environment is simulated in MATLAB and LabVIEW using an experimental hardware setup. The actuator model in QNET VTOL consists of a DC motor used to drive the propellers and is primarily operated through a PI controller to investigate the altitude of the system in terms of pitch (deg) along the horizontal axis. The PI controller shows reduced performance in terms of tracking the error of pitch (deg) with oscillating behavior, and it deviates from the equilibrium position. The proportional, integral, and derivative gain of the PID controller for the current system is calculated using the polynomial method for the third-order system. The simulation analysis based on PID for the VTOL system achieved in MATLAB shows better performance than the experimental results achieved using LabVIEW in terms of the tracking of pitch (deg), overshoot, rise time, and steady-state error. The last objective of this paper is to perform the experimental analysis of the VTOL system. ISTSMC is applied to overcome the magnitude of the tracking error being observed using a cascaded control strategy in a steady-state condition. The results presented show that ISTSMC outperforms the cascaded control algorithm. The rest of the paper is organized as follows.