# Technology Identification, Evaluation, Selection, and Optimization of a HALE Solar Aircraft
## 5 Conclusions  
In this paper, a conceptual design and analysis of sensitivity of design parameters of HALE solar aircraft were conducted. Currently, research on HALE solar aircraft has been actively conducted, but most papers have determined the possibility of long-term flight or have studied initial sizing design. In this study, various detailed factors and subsystems that affect solar energy are considered, and the TIES method is introduced to analyze the sensitivity of the design variables. In addition, using the JMP program, the design variables are plotted to easily understand how they affect the performance of the aircraft. In this study, a base configuration was established by referring to the configuration of Zephyr S, which is the most advanced solar aircraft so far in terms of long endurance performance. OpenVSP was employed to create configuration specifications such as wing area, wetted area, and aspect ratio. The aerodynamic characteristics of the base configuration were also found using OpenVSP. The solar aircraft design framework developed by our research team was used to implement modeling and simulation. Since solar aircraft utilizing solar energy as their power source are largely affected by environmental factors the cruise altitude was set at 18 km in this study; place of flight was Anheung (latitude: 34.65\({}^{\circ}\), longitude: 126.19\({}^{\circ}\)), Republic of Korea; flight date was the summer solstice (06/22). Under the conditions, required power and energy balance analysis was conducted using the solar aircraft design framework. Through the design of the experiment, independent design variables were found that could affect design objective parameters; modeling of inter-factor relationships was performed. Using a screening test, seven variables were selected with the largest effects on the design objective parameters. Then, a regression equation was set up that expressed the relationship between the seven selected independent design variables and the design objective parameters. Through the data distribution ratio, the achieved regression equation was assessed and found to have sufficient reliability. After this, for more design variable combinations, 10,000 random numbers were generated to implement the Monte Carlo simulation. Based on the results of the response surface method, sensitivity was analyzed under the conditions of the design objective parameters, with the horizontal axis representing the independent design variables and the vertical axis the performance. Aspect ratio (X1) was found to have a huge effect on factors of power to weight, and lift to drag ratio. Wing area (X2) was found greatly to affect the maximum take-off weight. This means that, if the aspect ratio is increased to increase the lift to drag ratio, these could be an adverse effect of reduced power to weight. Therefore, it is important to find a desired design point while mainly changing the independent design variables that are sensitive to the design requirements. Figure 25: Long endurance performance analysis according to the energy margin for the optimized aircraft. Based on the Monte Carlo simulation results, design feasibility of the design objective parameters was analyzed using the cumulative distribution function. The design probability needed to meet the wing loading was 20%; power to weight was 100%; maximum take-off weight was 92.4%; and lift to drag ratio was 75%. The wing loading has the lowest design probability; but still, it was possible to meet the design objective parameters within the range of the independent design variables set up previously. Optimization was performed using desirability function, and optimized design independent values were derived corresponding to the desirability values of the selected independent design variables. Using HALE solar aircraft framework, the endurance performance was evaluated. In the case of Zephyr S, which is the reference configuration, it is possible to fly for about 56 days, from 5/24 to 7/18.