# Modeling and Application of Dynamic Soaring by Unmanned Aerial Vehicle
## 4 Discussion  
The UAV dynamic soaring test flight results mainly focus on the dynamic soaring trajectory, energy gaining, and the energy harvesting mechanism model. This section will analyze the result deeply. The core index of the UAV is the flight distance and endurance, which are concluded as the trajectory. Hence, we first analyzed the result related to the UAV trajectory. The data of the trajectory are summarized in Table 3.  
The UAV traveled 2185.10 m in 70 s through dynamic soaring without any energy consumption. This result illustrates the dynamic soaring that the UAV can use to enhance its flight range and endurance. The UAV flight direction can be divided into two parts: windward flight distance and crosswind flight distance. The results show that the UAV flight direction better angle to the crosswind. Besides verifying the feasibility of the dynamic soaring application, the new trajectory decision method was tested. From the results, the detailed trajectory information is unnecessary for the achievement of dynamic soaring. Figure 16: The control surfaces change during the dynamic soaring. Figure 17: The energy change calculated by the energy harvesting mechanism. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Initial Position (m)** & **Final Position (m)** & **Initial Airspeed (m/s)** & **Final Airspeed (m/s)** \\ \hline
[0,0,1] & \([-1247.63,1793.90,3.01]\) & 30.69 & 38.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Trajectory data. The specific variables can also guide the dynamic soaring. Table 4 takes a close look at the energy part. The energy change shows the main energy harvesting term is kinetic energy, which is in accordance with the literature. The kinetic energy has increased 55.19% compared to the initial state. Meanwhile, the potential energy has risen 200.74%. The detailed energy variation curves are shown in Figure 18.  
Take the soaring cycle 3 for the detailed research. The typical dynamic soaring can be divided into four phases: windward climb, high altitude turn, leeward descent, and lower altitude turn. Considering the dynamic soaring phases and drawing the energy change in the soaring cycle 3;, the total energy state at the beginning of soaring cycle 3 was 3136 J consisting of the kinetic energy (2998.30 J) and potential energy (138.41 J). After one dynamic soaring cycle, the total energy state raises to 3363.05 J, 7.22% compared with the initial state. The most energy increased is from the kinetic energy, which has a relative growth of 226.16 J (7.54%). The energy change in the potential energy is 0.19 J (0.14%). These data confirm that the kinetic energy is the main energy harvesting part for dynamic soaring. Although the energy variation shows both gaining and consumption, the total energy state increases eventually, which is also one of the reasons that this flight mode is called dynamic soaring. From Figure 19, the variation shows that the energy harvesting phases are windward climb and leeward descent. The leeward descent takes a longer time and more energy harvesting compared with the windward climb. The energy-consuming phases are the high altitude turn and the lower altitude turn. The high altitude turn phase loses more energy but is less time consuming compared with the lower altitude turn phase. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Energy Type** & **Energy Level at Initial** & **Energy Level at Final** \\ \hline Kinetic Energy (J) & 2213.52 & 3435.19 \\ \hline Potential Energy (J) & 46.06 & 138.55 \\ \hline Total Energy (J) & 2259.58 & 3573.74 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Energy data. Figure 18: The three energy changes during the dynamic soaring. Finally, we verified the energy harvesting mechanism with this flight test. The energy variation cures calculated by the mechanical energy and energy harvesting model are drawn in Figure 20.  
It can be noticed that the trend of the curves is similar; the only difference is the gap between the two curves.