# Design of a Hand-Launched Solar-Powered Unmanned Aerial Vehicle (UAV) System for Plateau
## 3 Detailed Design  
### Layout Design  
Solar-powered UAVs adopt various forms of layout, such as flying-wing layout, tandem-wing layout, conventional layout, etc. Among them, the flying-wing layout solar-powered UAV is typically representative of NASA's 'Pathfinder' and 'Helios'.  
Compared with the conventional layout, the wing layout has the advantages of light structure weight and high aerodynamic efficiency, which are crucial for long-endurance aircraft. However, the static stability of the flying-wing layout is usually weak, and it is more sensitive to the changes of flight altitude and speed. Moreover, the flight angle of attack of the flying-wing layout UAV is less robust, and the pitching moment is easy to diverge in the state of high angle of attack, which is usually solved by split-drag-rudder or differential thrust control. Therefore, the flying-wing layout is usually used for large wingspan solar UAVs, and the takeoff and landing should be carried out in good conditions.  
The tandem wing layout consists of two wings, the front and rear, and has a higher lift coefficient with the same wingspan. When the aircraft is disturbed, the fuselage has good aeroelastic characteristics compared with the conventional layout. The stall characteristics of this layout are similar to those of the canard layout. In order to ensure good stall characteristics, the front wing stalls before the rear wing stalls, which has good longitudinal safety in flight. However, in the takeoff and landing stage, the rear wing cannot reach the maximum lift point, so good landing site conditions and long takeoff and landing distance are required.  
The conventional layout facilitates the design of the fuselage and the arrangement of loads and equipment. Moreover, it has the advantages of high robustness and better stability at high angle of attack, and low takeoff and landing speed, which is especially suitable for small solar-powered UAVs with hand-launched takeoff and hard landing.  
A fully functional prototype was built, named Mini-Phantom Solar (MP Solar). Considering the extreme flight environment (4600 m altitude, \(-\)30 \({}^{\circ}\)C temperature), the MP Solar UAV (Figure 6) is of a conventional configuration with an aileron-free rudder and an all-moving elevator. It is worth mentioning that the full-motion elevator is designed to facilitate disassembly and transportation, and during the landing phase, the full-moving elevator is deflected at a large degree so that the UAV enters a deep stall before it touches ground, which allows the aircraft to achieve a lower landing speed.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Unit** & **Description** \\ \hline \(m_{pld}\) & 0.1 & [kg] & Payload mass \\ \(\eta_{turb}\) & 0.85 & - & Irradiance margin factor \\ \(P_{pld}\) & 2 & [W] & Payload power consumption \\ \(\rho\) & 0.78 & [kg/m\({}^{3}\)] & Air density (4500 m) \\ \(T_{day}\) & 14.3 & [h] & Summer day duration (34.3\({}^{\circ}\) N) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mission parameters for Mini-Phantom UAV.  
The main wing, with a 3.2 m wingspan, can be split into three segments of similar size to facilitate transport. The aileron-free design of the rectangular wing ensures the wing's integrity, which increases the proportion of solar cells laid (14 units of solar cells laid as two rows on each wing segment). The outer wing has a dihedral angle of 9 degrees to improve the lateral stability of the aircraft. The layout characteristics are summarized in Table 3.