## 2 Literature Survey  
[PERSON] et al. [1] investigated the propeller of a UAV. Computational fluid dynamics (CFD) and experimental approaches were used to select the design parameters for a two-bladed UAV propeller. Standard theoretical calculations were used to estimate the boundary conditions of the CFD problem. The principal estimated conditions were the thrust generated by the propeller, velocity conditions of the propeller, and Reynolds' number of the flow. The same procedure was planned as an extension to the current study, although the working propellers were different. [PERSON] et al. [2] theoretically constructed high-payload-based multirotor UAVs for complicated applications. The authors derived the relationship between the payload weight and the overall weight of the UAV using historical data. The theoretical estimations were extended to the selection of the UAV's primary components. Finally, a coaxial-propeller-based Tricopter was constructed and tested in complicated environments. The current study considered successful surveillance for high-payload and complex applications; therefore, theoretical derivatives were implemented based on a literature  
Figure 1: Conceptual design of proposed octocopter, with its components. Figure 2: Concept involved in this study. survey [3]. The current study's targeted application is the clearance of dirty/dusty environmental conditions through non-hazardable liquids, such as seawater and urea. Thus, the liquid weight was fixed at 1000 g, and the subordinate equipment was finalized. The cumulative payload weight of the multirotor UAV was determined in the context of the proposed relationship. Many researchers have modeled and controlled multirotor vehicles. In [4], the mathematical modeling of an octocopter was developed by including the thrust and torques generated by the propellers and adding gyroscopic torque. A full-state feedback-based hybrid controller scheme was designed against a linearized model based on motor dynamics. In [5], a physical model of an octocopter was developed using the theory of rigid-body mechanics and aerodynamics. The unknown parameters in this model were determined through several identification experiments. An attitude-estimation algorithm was designed and implemented on the target hardware. The algorithm is referred to as a nonlinear complementary filter, and it uses a quaternion rotation representation and onboard measurements to compute an estimate of the current aircraft attitude. Two different attitude controllers have been designed and evaluated [5]. The first controller was based on proportional-integral-derivative techniques, which are commonly used in multirotor flight-stabilization systems. The second controller used a novel control structure based on the L1 adaptive-control techniques. A baseline attitude proportional-derivative (PD) controller was augmented with an L1 adaptive controller in the rate-feedback loop. The two controller structures were compared using a simulation environment based on the developed octocopter model. In [6], the theoretical and analytical portions of the octocopter modeling and control were considered, focusing on the development process. A complete nonlinear model of the octocopter was derived, using [PERSON]'s second law of motion in a rotating reference frame. Additional effects, such as aerodynamics, precession torque, and motor dynamics, were analyzed and modeled. In this study, control laws and approaches for controlling the vehicle in six degrees of freedom were proposed for position and attitude control. The position controller uses a nonlinear Lyapunov-based controller, where the control inputs are converted to the desired attitude-reference inputs and sent to the attitude controller. The attitude-control method was based on a full-state feedback controller, and a reduced observer was used to observe motor dynamics. The control laws were evaluated using a Simulink model in which a complete nonlinear system was implemented.