# Design and Verification of Large-Scaled Flapping Wings for High Altitude Environment
## 4 Conclusions  
In this paper, several flapping wings have been fabricated, including four planforms (basic shape, increasing the external area of the wing, and elliptical shape), whether to attach additional materials, two numbers of wing ribs (six and seven wig ribs), and two different materials of wing film (polyester and linen materials). Wind tunnel experiments were conducted on a total of twelve wings; then, a BP neural network model was built to predict the trim state of the flapping wings. Taking into account their weight and aerodynamic performance, the most outstanding flapping wing was eventually selected, which was the one with six wing ribs, linen film material, and the platform of increasing the internal area of the wing. In addition to the above study, a transient numerical method based on the overset mesh technique was used to investigate the influence of different altitudes and different states. Finally, the flight tests of the vehicle's load capacity and endurance were carried out in the Xi'an area and Lhasa, respectively, to verify the performance of the flapping wing. According to the wind tunnel experimental results, the lift is mainly affected by wind speed and the angle of attack. In contrast, the major factor in changing thrust is the flapping frequency. Regardless of the planform, the lift and thrust of the flapping wings show a significant upward trend after attaching additional materials, which is at the cost of increased pitching moment and power consumption. As for the effect of the planform, the elliptical flapping wing had the greatest lift performance but also the worst thrust performance, which is the reason for not continuing the follow-up study on it. Taking  
Figure 17: Flight tests in different regions: (**a**) Xi’an, Shaanxi Province, and (**b**) Lhasa, Tibet Autonomous Region. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Altitude (m)** & **No Load (g)** & **Max. Load (g)** & **Time (min)** & **Trim State (_AOA/V/f_)** & **Power Consumption (W)** & **\(Re\)** & **\(St\)** \\ \hline
500 & \(1150\) & \(150\) & 60 & \(8^{\circ}/7\) m/s/\(5\) & 110 & 122,541 & 0.2186 \\  & & & & Hz & & \\
4500 & \(1100\) & 200 & 45 & \(10^{\circ}/7\) m/s/\(6\) & 140 & 87,941 & 0.2623 \\  & & & & Hz & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Flight data at different altitudes. all factors into account, increasing the external area of the wing had the most superior aerodynamic performance. The design of the vehicle has demanding weight requirements, so subsequent research is necessary to reduce the weight of the flapping wing as much as possible for less loss of aerodynamic performance. For the planform of increasing the external area of the wing, the influence of the number of wing ribs and the materials of wing film were explored. The results indicated that linen film plays a slight role in lift compared to the polyester one, and the thrust at high speed is also improved. The wings with six wing ribs have noticeably better lift performance than the wings with seven wing ribs, with a slight reduction in thrust. The trim state is predicted by the BP neural network model, and the flight parameters under the trim state of different wings are compared. The wing with an increased internal area of the wing, six wing ribs, and linen film material is the wing that makes it easier to achieve the trim state. Flight tests were conducted at low and high altitudes, respectively, to check out the performance of the flapping wings. The results show that the flapping wings with careful parameter design can meet the requirements of load capacity and flight time and have excellent flight ability. Conceptualization, Z.Z. and D.X. ; methodology, Z.Z. ; software, Z.Z. ; validation, Z.Z., D.X. and B.S. ; formal analysis, Z.Z. ; investigation, Z.Z. ; resources, B.S. ; data curation, Z.Z. ; writing--original draft preparation, Z.Z. ; writing--review and editing, D.X. ; visualization, Z.Z. ; supervision, D.X. ; project administration, B.S. ; funding acquisition, B.S.