# Design and Manufacture of Composite Landing Gear for a Light Unmanned Aerial Vehicle
## 7 Conclusions  
UAV landing gear should have low weight and high strength. This study designed 8 PLY, 10 PLY, and 12 PLY landing gears with different fiber orientations of CFRP for curved landing gear of a UAV with 5-kg weight and 10-kg maximum payload. Moreover, numerical simulations were conducted, a landing gear was manufactured, and experimental strain measurements were performed. The following conclusions can be drawn from this study.  
1. Landing gear with a non-curved design has almost two times the stress concentration of landing gear with a curved design. A design without corners is the first choice for the landing gear of a UAV because it must withstand take-off and landing with continuous duty and short-time loading.  
2. Considering the requirement of a safety factor of 3, implying that the design can withstand an accident with a heavy landing exceeding 3 g, the 8 PLY and 10 PLY CFRP designs are good in weight reduction except if the factor of safety is lower than 3. A design with more than 12 layers meets this requirement.  
3. The simulation and experimental results show good agreement. The 12-layer zero-degree design \([0]_{12}\) has high strength when subjected to a pure vertical load. The next best design is \([0/90]_{65}\). The \([0/90/45/-45/90/0]_{\text{S}}\) design shows good longitudinal strain when subjected to side forces. For products with a longitudinal design, such as the landing gear, fuselage, and wing of an aircraft, high strength is mainly afforded by fibers along the longitudinal direction.  
Conceptualization, methodology, numerical analysis, and writing--original draft preparation, Y.-C.L.; manufacture, experiment, and measurement setup, P.-C.C. and Y.-P.S.; writing--review and editing, M.-R.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Ministry of Science and Technology, Taiwan, for financial support under grant No. MOST 106-2221-E-013-001.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & \(\varepsilon_{\text{xx}}\) & \(\overline{\varepsilon}\) \\  & **(RMSE)** \\ \hline
**First measurement** & \(14.08\times 10^{-4}\) & \\ \hline
**Second measurement** & \(16.08\times 10^{-4}\) & \(13.86\times 10^{-4}\) \\
**Third measurement** & \(11.41\times 10^{-4}\) & \\ \hline \hline \end{tabular}
\end{table}
Table 6: Measurement error of strains for the \([0/90]_{65}\) design.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \begin{tabular}{c} **CFRP** \\ **Landing Gear** \\ \end{tabular} & \begin{tabular}{c} **[0]\({}_{12}\) (3D** \\ **Model)** \\ \end{tabular} & \begin{tabular}{c} **[0]\({}_{12}\) (ACP)** \\ \end{tabular} & \
\begin{tabular}{c} **[0/90]\({}_{25}\)** \\ \end{tabular} &
\begin{tabular}{c} **[0/90/45/\(-\)45/90/0]\({}_{\text{S}}\)** \\ \end{tabular} \\ \hline
**Simulation \(\varepsilon_{\text{xx}}\)** & \(8.7514\times 10^{-4}\) & \(9.371\times 10^{-4}\) & \(14.163\times 10^{-4}\) & \(17.910\times 10^{-4}\) \\ \hline
**Experiment \(\varepsilon_{\text{xx}}\)** & \multicolumn{2}{c}{\(9.0\times 10^{-4}\)} & \(13.86\times 10^{-4}\) & \(18.53\times 10^{-4}\) \\ \hline
**Error** & \(2.76\%\) & \(4.12\%\) & \(2.21\%\) & \(3.35\%\) \\ \hline \hline \end{tabular}
\end{table}
Table 7: Simulations and experiment results of strains.