# Design of a Hand-Launched Solar-Powered Unmanned Aerial Vehicle (UAV) System for Plateau
## 3 Detailed Design
### Aerodynamic Design  
The lift-drag ratio of an aircraft is used to evaluate the aerodynamic efficiency and is the key parameter affecting the endurance of solar-powered UAV. The flying-wing layout has a high lift-drag ratio due to the absence of fuselage and tail. In order to improve aerodynamic efficiency, the layout of flying-wings is used for reference in aerodynamic design. The airfoil of the main wing is optimized on the basis of the low Reynolds number laminar airfoil to make its tail have the characteristics of reverse camber (Figure 7b), reduce the nose-down pitching moment generated by the main wing, and thus reduce the requirement for the horizontal tail volume (Tables 1 and 3). The airfoil of tails is NACA0009, which is developed by National Advisory Committee for Aeronautics (NACA).  
The aerodynamic efficiency of the UAV can be improved by increasing the reverse camber of airfoil, reducing the area of the horizontal tail and the length of the rear fuselage, and the stability of the UAV at high angle of attack can be guaranteed by the existence of the tail.  
Figure 6: The Mini-Phantom Solar UAV. Dimensions are given in mm.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Unit** & **Description** \\ \hline \(AR\) & 10.6 & - & Aspect ratio \\ \(b\) & 3.2 & m & Wingspan \\ \(S_{unit}\) & 0.934 & m\({}^{2}\) & Wing area \\ \(S_{de}\) & 0.06 & m\({}^{2}\) & Horizontal tail area \\ \(S_{vert}\) & 0.08 & m\({}^{2}\) & Vertical tail area \\ \(S_{rad}\) & 0.017 & m\({}^{2}\) & Rudder area \\ \(V_{H}\) & 0.21 & - & Horizontal tail volume \\ \(V_{V}\) & 0.28 & - & Vertical tail volume \\ \(m\) & 2.9 & kg & Total mass \\ \(m_{bat}\) & 1.2 & kg & Battery mass \\ \(m_{Mpld}\) & 0.6 & kg & Max payload mass \\ \(V\) & 10 & m/s & Flight speed \\ \hline \hline \end{tabular}
\end{table}
Table 3: Design characteristics of Mini-Phantom Solar UAV.  
Aerodynamic calculations were carried out for the shape of the UAV, among which the turbulence model was the Spalart-Allmaras model, and the calculated state was: Flight altitude was 5000 m, speed was 10.5 m/s.  
Figure 8 shows the change of aerodynamic parameters of the aircraft with the angle of attack. When the UAV cruised at an altitude of 5000 m at a speed of 10.5 m/s, the maximum lift-to-drag ratio was 18.4, which was obtained at 2 degrees of angle of attack, which was consistent with the UAV's trim angle of attack. At the trim angle of attack, the lift coefficient of the UAV was about 0.8 and the stall angle of attack was about 9 degrees.  
It can be seen from the pitching moment curve that the pitching moment converged in the whole process and maintained a good linear relationship. The static stability margin was about 13.8% near the cruising point. With the increase of the angle of attack to more than 6 degrees, the pitching moment curve became steeper, which means that the UAV had stronger longitudinal static stability at large angle of attack and also means that the UAV had good takeoff and landing characteristics and stall characteristics.  
Through the analysis of aerodynamic data, it can be seen that the method of improving the UAV's aerodynamic efficiency by increasing the reverse camber of airfoil and reducing the horizontal tail area was effective, which brought good aerodynamic efficiency.  
Figure 8: _Cont._  
Figure 7: (**a**) Aerodynamic computing grid model. (**b**) Optimized airfoil of main wing.  
The mature conventional layout ensured the longitudinal stability of the UAV in the high angle of attack and adjacent stall state, which can meet the requirements of hand-launched takeoff and hard landing in the extreme environment without runway.