# Design of a Hand-Launched Solar-Powered Unmanned Aerial Vehicle (UAV) System for Plateau
## 2 Conceptual Design Method
### Weight Estimation Model
The flight environment of MP solar UAV was the plateau area in winter. In order to study the influence of low temperature on battery capacity, the low-temperature discharge test of energy system was conducted in a low-temperature and low-pressure test chamber, experimental instruments are shown in Figure 3.  
The test subjects included propulsion systems (brushless motor, propeller, and motor controller), autopilot systems, and a lithium-ion battery rated at 230 Wh for low-temperature resistance. The test chamber provided a -25 \({}^{\circ}\)C, 540 hPa low-temperature, and low-pressure simulation environment. During the test, the propulsion system operates with a constant throttle command until the voltage reached the battery's protective voltage, and the sensor recorded the output power, voltage, and current of the battery bus. Figure 4 shows the test results of the low-temperature discharge test, which are the changes of power, voltage, and current with time, respectively. In the test, the system worked normally under low-temperature conditions, the voltage fluctuation range was small, basically linear decline. The amplitude of current fluctuation was about 0.4 A and the smoothed current-time curve also presented a linear decline. By integrating the power-time curve discretely, the total output energy of the battery in the test can be obtained, which was about 159.01 Wh. At a low temperature of -25 \({}^{\circ}\)C, the discharge efficiency of the battery was about 69.1%. In the discharge experiment at room temperature (20 \({}^{\circ}\)C), the output energy was about 220.73 Wh and the discharge efficiency of the battery was about 95.9%. Therefore, solar-powered UAV flying in extreme environments, temperature impact factor \(k_{temp}\) must be considered in the design process. In this test, the temperature influence factor was about 0.72. In order to prevent the low temperature from damaging the battery performance, the weight of the insulation material or the temperature control system of the battery also needs to be considered in the high-altitude, solar-powered UAV design. The battery weight model considering the effect of low temperature is shown in the Formula (17). \[m_{bat}=\frac{T_{night}}{\eta_{dctrg}k_{bat}k_{temp}}P_{ecc\_tot} \tag{17}\]  
Electric propulsion systems usually contain propellers, motors, controllers, gearbox, etc. For small, solar-powered UAVs, a gearbox is not necessary to reduce the system complexity and cost. In order to simplify the model, the propulsion system is considered as a whole, and the weight of the propulsion system is positively correlated with the maximum power. Factor \(k_{prop}\) is used to predict the  
Figure 3: The discharge test of energy system in low-temperature and low-pressure test chamber. weight of the propulsion system, whose value is obtained by statistical data. The weight model of propulsion system is shown in Formula (18). \[m_{prop}=k_{prop}P_{lev}=k_{prop}\frac{C_{D}}{C_{L}^{3/2}}\sqrt{\frac{2 ARg^{3}}{ \rho}}\frac{m^{3/2}}{b} \tag{18}\]  
The total energy consumed during day and night flight can be obtained by the aerodynamic model and the weight model system. The closed loop of the energy balance is reconstructed by the weight model of each component. Figure 5 presents a detailed loop that visually represents the conceptual design process of the solar-powered UAV in this paper. Figure 4: Test result of low-temperature discharge test at \(-25\) degrees Celsius, \(540\) hPa: (**a**) Power, (**b**) voltage, (**c**) current. The parameters contained in Figure 5 can be divided into three categories. The first part is the weight prediction model, which consists of the weight models of each component. The parameters are mostly constant, representing the development level of products in various industries at the present stage. These constants, which are shown in Table 1, are partly fitted from statistics and partly from actual measurements.