# A Survey: Future Smart Cities Based on Advance Control of Unmanned Aerial Vehicles (UAVs)
## 4 Control Theory Progress for UAVs
This adaptability and agility are particularly important in modern warfare scenarios, such as the conflict in Ukraine, where UAVs have played an increasingly prominent role. In Ukraine, both sides have deployed a range of UAVs for surveillance, reconnaissance, and attack missions, and these vehicles have demonstrated their effectiveness in gathering intelligence, targeting enemy positions, and disrupting enemy operations [39]. Nonlinear UAVs offer several advantages in this context, including their ability to operate in GPS-denied or jammed environments, their resistance to detection and interception, and their ability to perform complex maneuvers and fly at high speeds with greater stability and accuracy. Overall, the importance of nonlinearities in UAVs reflects the growing importance of these vehicles in modern warfare and the need for advanced control and navigation systems that can help them operate effectively in complex and unpredictable environments [40]. A helicopter is an aircraft that is lifted and moved by one or more rotors, which are typically arranged in an even number. The key advantage of a helicopter lies in its capability to control lift and direction by modulating the rotor speed using motors. This makes helicopters particularly useful in congested or remote areas where fixed-wing aircraft are unable to take off or land. In order for the closed-loop system to achieve the desired response, it must manipulate the controlling variables through control action. The experimental setup for a prototype helicopter involves various components and instruments that are used to test and evaluate the performance, stability, control, and other characteristics of the UAV [38; 41]. To model this coupling effect, the dynamics of the UAV must be represented using a set of equations that capture the interactions between the different degrees of freedom. These equations typically include terms that describe the forces and moments acting on the UAV as a result of its motion through the air, as well as terms that capture the effects of the rotor dynamics and control inputs [41]. The UAV setup described above is a system with limited degrees of freedom that is highly nonlinear in nature. It consists of two primary components: a mechanical component (consisting of the main rotor and tail rotor) and an electrical component (comprised of DC motors for both rotors). The mechanical component, which is susceptible to various perturbations, is the primary focus. The main rotor, which controls pitch angle, allows for motion along the vertical axis (in the vertical plane), while the tail rotor, which controls yaw angle, enables motion along the horizontal axis (in the horizontal plane). To regulate the UAV in the presence of coupling effects, a linear controller is implemented, complete with all of its requisite attributes, as expressed in the system's equations [23; 41]. Variable structure systems (VSSs) have long piqued the interest of the control engineering community because of their significant nonlinear behavior, dynamical changes over time, coupling influences, and susceptibility to parametric disturbances when treated as controllers. Due to matched and mismatched disturbances, controlling unmanned aerial vehicles (UAVs) can be particularly difficult, and Table 3 represents the challenges and tasks of our research. These technologies are interesting because regular security services and security missions increasingly utilize them in a variety of contexts [42]. TRMS is a class of UAVs that have drawn interest because of their capacity to hover, take off, and land in unexpected places, as well as tilt their angle of flight. Control researchers must overcome the strong coupling, nonlinear dynamics, ambiguities, and gyroscopic torque of UAVs. Applications for these systems are growing in a variety of sectors [35; 42]. Rotorrotation, the linkage between rotors, fluctuating propeller rotation speed, susceptibility to parametric perturbations, and the time-varying character of the system are the key difficulties in UAVs [43].