# Design, Manufacturing, and Flight Testing of an Experimental Flying Wing UAV
## 2 Aircraft Conceptual Design  
As mentioned above, the energy density of an electric- or solar-powered aircraft is much lower than that of a traditional aircraft that uses petrol. Therefore, the aerodynamic configuration design of an electric aircraft is difficult compared with that of a traditional aircraft. Most aerodynamics design parameters are interrelated in the aircraft conceptual design process. It is not easy to find the best methodology for each type of aircraft. In practice, most designers often essentially complete a baseline configuration in the first design process. Then, they need to complete several iterations of the baseline configuration. The number of iterations depends on the designers' experience and the design database. Traditionally, iterations are used to obtain an acceptable solution for the overall design. A good designer can usually intuitively decide what should be changed to complete the design or to reduce the number of iterations.  
Considering the battery's energy density and weight of structural materials, the critical challenge in reducing production costs and achieving design goals is to optimize the efficient use of battery energy. With the interaction between lift and drag forces, there is a specific cruise speed that minimizes the power required for a particular cruise altitude. Based on polar drag, the power required for a particular cruise altitude can be expressed in terms of the zero-lift drag coefficient and induced drag factor, assuming that the power required can be reduced through optimal design. Thus, the battery capacity and weight can be reduced, thereby reducing the aircraft weight. The lift required for cruising can be adjusted downward. In other words, the optimal design can effectively reduce the aircraft cost.  
For aircraft design, most design parameters are interrelated. Re-evaluation of aircraft performance and recomputation of all other parameters are required to adjust a particular design parameter. The aircraft's zero-lift drag coefficient and induced drag factor are selected as parameters for the design procedure. The details of the design procedure are discussed below. Figure 1 shows the design procedure for the experimental flying wing UAV. At the start of the design process, empirical values for the aircraft's zero-lift drag coefficient and induced drag factor from the first calculation can be used temporarily. The matching plot is used to find the appropriate wing loading and power loading that can satisfy all given requirements. In the weight estimation approach, the maximum take-off weight is formulated and is estimated systematically. Then, the energy consumption and wing reference area of the aircraft are obtained. Aircraft aerodynamics and stability design starts with the given wing reference area. Then, the shape and configuration of the aircraft are determined. Software such as XFLR5[17] and DATCOM[18] can be used to estimate the zero-lift drag coefficient and induced drag factor of the aircraft. When these parameters are obtained, we can check their variations to ensure that the empirical value of the first calculation is appropriate. If the variations are smaller than desired, the design is considered complete. If the variations are larger than desired, the new zero-lift drag coefficient and induced drag factor of the aircraft are substituted into the next design process.  
The matching plot is used to find the appropriate wing loading and power loading that can satisfy all performance requirements in the conceptual design process. The following subsections show the derivation of the performance requirements between wing loading and power loading [3; 4; 5]. A typical design process starts with the mission requirements for a new aircraft. The first process is conceptual design. In this section, the performance requirements of the electric-powered UAV include the stall speed, maximum speed at cruising altitude, absolute ceiling, and turning radius and speed.