## 1 Introduction  
Many engineering applications have been fully implemented and used in the day-to-day activities of people. In view of the vast range of implementations, there is a perceived need for automatic systems to make life-related engineering applications more convenient, such as those regarding medical transportation, house cleaning, interior painting, and industry monitoring. In this context, unmanned aerial vehicles (UAVs) have been implemented in various applications. UAVs are a type of aircraft that can fly and execute their intended missions without the help of an onboard pilot. The control of a UAV is very complicated and is usually executed based on one of two methodologies. The first involves a fully autonomous flight-control system. The maneuvering of the UAV, its payload control, and its mission execution are handled entirely using preloaded programs. The second is a partially autonomous flight-control system. A ground-based pilot manages the primary controls using a remote controller, and a preloaded program manages secondary controls, such as altitude and attitude holding. UAVs can be classified into several categories. Some of the primary classifications, such as those based on range, endurance, weight, or maneuverability, are fundamentally supported by the selection of the UAV. In UAV construction, the intended engineering application is a key factor; moreover, such decision needs to be finalized to select an appropriate UAV for further processing. Three fundamental types of UAVs are most commonly implemented in engineering applications to efficiently execute missions: fixed-wing UAVs, rotary-wing UAVs, and multirotor UAVs, which were implemented in this study. The results showed that the octocopter is the preferred platform in multirotor UAV configurations, owing to its stability. Apart from the stability, the rotodynamic effect of the rotor plays a major role in the applications under examination, so a UAV with a high number of rotors was chosen for this investigation. The target application of this work is to provide a clear visibility zone in environmentally critical transport terminals such as airports, railway stations, and bus stands. These terminals can be affected by foggy weather conditions, smoke generated from natural disasters, and other visibility-affecting issues. Poor visibility can affect the routine operations of these terminals. Collisions, such as unavoidable accidents between airplanes during takeoff and landing, or accidents between vehicles and humans, can create major problems. Additionally, minor problems can occur due to poor visibility, such as delays in departure and arrival of the targeted vehicles, and loss or delay in the communication systems. Thus, these major and minor problems need to be solved to ensure the smooth and successful operation of these terminals. In this regard, a dynamic mode-based unmanned aircraft system (an octocopter) is here proposed to troubleshoot the aforementioned critical environments. To reduce the poor visibility generated from unwanted environmental conditions such as fog and smoke, a highly dense seawater-relayed sprayer mechanism is proposed in this work. To execute this operation, a separate module is attached to the octocopter. The fundamental details of this module are included in the theoretical construction of the octocopter. The unique module comprises a storage tank, nozzle sprayer, and supportive joints, as shown in Figure 1. The first novelty involved in this work is the shape of the storage tank, which is a convergent-divergent duct-based construction. Aerodynamically, the convergent duct provides an increase in velocity, the divergent duct provides a decrease in velocity, and a combination of convergent and divergent ducts provides a high dynamic pressure for the fluid (seawater); thus, the proposed design can provide increased velocity of the seawater at the exit point of the tank.