###### Abstract  
The Vertical Take-Off and Landing (VTOL) system is a multi-variable system subjected to harsh weather conditions, which creates challenges in proving the stability of the system before takeoff, which is essential for a flight dynamics system. The presented research work is based on the experimental results of the VTOL system to investigate and prove the stability using Lyapunov theory. This is achieved by tracking the pitch along the x-axis using cascaded control and integral super twisting sliding mode control (ISTSMC) algorithms. The motor current of the propeller assembly is regulated based on proportional integral (PI) and proportional integral derivative (PID) controllers. The cascaded control shows the maximum tracking error due to high-frequency fluctuations in the controller input signal, which lead to expensive mechanical losses for the actuators. The comparison of the results shows that ISTSMC outperforms the cascaded control strategy by reducing the tracking error to less than 1% percent and reducing the high-frequency fluctuations in the controller input signal. The hardware results show a minor delay in the transient response during vertical takeoff due to the inertia of the system and the tracking error due to air friction, etc., of the external environment, compared to the simulation results obtained in MATLAB. p _applied_ sciences  
**Citation:** [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] Experimental Stability Analysis of Vertical Takeoff and Landing System Based on Robust Control Strategy  
**2023,** _13_, 11209. https://doi. to operate in any domain [6]. The VTOL aircraft system can be sectioned into two parts: the flight mode and VTOL mode. The flight mode can be operated using a six-servo motor configuration. The first two servo motors are operated for roll control, the second two are operated by a ruddervator, and the last two are connected with brushless motors to drive the propellers on the left and right sides of the ailerons [7]. The autopilot mode regulates the aircraft pitch that the flight crew can use to reduce the workload during cruising and assist the aircraft to land in adverse weather conditions. At the plane's rear section, the horizontal stabilizer attached to the tail is applied to regulate the pitch. The degree of the pitch of an aircraft is maintained by changing the angle and balancing the vertical lift of the rear elevator [8; 9]. One example of a VTOL UAV is based on a ducted air fan craft that uses two main propellers to generate vertical thrust to ensure the vertical takeoff ability. It works with vector thrust to control the system's dynamics by directing the thrust using the set of control surfaces [10]. The VTOL aircraft is an underactuated system having six degrees of freedom (6-DoF), including three for translation and three for rotation. [PERSON] developed a general framework of position, altitude, and velocity control based on a backstepping control strategy [11]. They proposed a multistage idea developed through a series of simpler controllers including velocity control, thrust direction control, and position control. Many researchers have extended the idea with the two-stage design strategy, developed through an outer translational control loop assigning the thrust vector by treating the air vehicle as a point mass [12; 13; 14]. Similarly, the inner altitude control loop applies a torque input to fix the thrust vector to the desired axis, controlling the vehicle headings simultaneously. Furthermore, the later stage is designed based on a backstepping control strategy. Multiple researchers have formulated various control strategies and investigated the various aspects of the VTOL system, including stability analysis and position tracking compensation for various disturbances due to the real environment in harsh weather conditions [15; 16; 17; 18; 19]. Stingu designed and developed a VTOL UAV system based on proportional derivative controllers to regulate hover stability [16].