## 6 Design and Analysis of Main Landing Gear Strut
### Design and Analysis of Retractable (Curved) Main Landing Gear Strut
The value of the Tsai-Wu failure factor reduced significantly for a combination of bolts, nuts, bolt load and washers; however, the assembly could not meet the Tsai-Wu failure criterion for given dimensions of landing gear strut under the one point landing load condition. The results of the same analysis are shown in Table 9. It is pertinent to note from the results mentioned in Table 8, that a strut \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Model No.**} & \multirow{2}{*}{\begin{tabular}{c} **No. of** \\ **Laminea/Files** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Thickness** \\ **(mm)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Width (mm)** \\ **Failure Criteria** \\ \end{tabular} } & \multirow{2}{*}{**Mass (kg)**} & \multirow{2}{*}{**Deflection (cm)**} \\ \hline \multicolumn{8}{c}{**Carbon T-300/Epoxy (\(V_{f}=0.60\))**} \\ \hline
1 & 220 & 52.8 & 52.8 & 1.52 & 5.32 & 13 \\
2 & 220 & 52.8 & 66 & 1.12 & 6.65 & 8.3 \\
3 & 220 & 52.8 & 75 & 0.98 & 7.56 & 6.4 \\
4 & 220 & 52.8 & 80 & 0.92 & 8.1 & 5.6 \\
5 & 220 & 52.8 & 88 & 0.83 & 8.86 & 4.7 \\
6 & 240 & 57.6 & 95 & 0.7 & 10.48 & 2.7 \\ \hline \multicolumn{8}{c}{**S-Glass/Epoxy (\(V_{f}=0.60\))**} \\ \hline
1 & 220 & 59.4 & 59.4 & 1.52 & 7.67 & 19.8 \\
2 & 220 & 59.4 & 75 & 1.19 & 9.69 & 11.2 \\
3 & 220 & 59.4 & 80 & 1.11 & 10.34 & 9.8 \\
4 & 220 & 59.4 & 85 & 1.03 & 10.38 & 8.4 \\
5 & 220 & 59.4 & 90 & 0.96 & 11.63 & 7.3 \\
6 & 220 & 59.4 & 95 & 0.91 & 12.27 & 6.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Results of computational analysis of composite main landing gear strut without mounting brackets. Figure 9: Variation of Tsai-Wu failure criterion factor and mass of the strut for T300 carbon fiber/epoxy and S-glass fiber/epoxy materials. having the same dimensions qualified when analyzed without a mount under the one point landing load condition. The reason for the failure of the assembly with a mounting bracket was the stress concentration around the bolt holes of the composite strut. To overcome the failure of the landing gear assembly with respect to the Tsai-Wu failure criterion, the option of hybrid joints was also analyzed. The hybrid joints (bolted + bonded) have 100% and 5% more load carrying capacity compared to the bolted and bonded joint, respectively [32]. In this analysis phase, the mounting was joined to the strut by bolts and the contact surfaces were assumed to be perfectly bonded. Additionally, based on the trend observed from Table 8, the thickness-to-width ratio of the designed strut was further reduced within the allowable limits of dimensions for the retraction test to obtain the safest Tsai-Wu failure criterion factor. After certain iterations, the design models of T300 carbon fiber/epoxy, having dimensions of (52.8 mm \(\times\) 100 mm), and S-glass fiber/epoxy, having dimensions of (59.4 mm \(\times\) 120 mm), were considered for analysis of the complete landing gear assembly with a mounting bracket under the one point landing load condition. Satisfactory results of this analysis showing the Tsai-Wu failure criterion, mass and deflection of the strut are shown in Table 10. The same analysis was also performed for the two point landing load condition and the results of the this are shown in Table 11. The computational results for the landing gear strut for both the landing conditions are also shown in Figures 10a-d and 11a-d. The stress analysis of the mounting bracket under the one point landing load condition is also shown in Figure 12. These results indicate that the designed structures were safe for operation against the required maximum loads encountered at the time of one point and two point landing scenarios. As the strength-to-weight ratio is considered to be the most important parameter in this research, the T300 carbon fiber/epoxy is recommended as the most suitable material for the manufacture of composite main landing gear struts for the given lightweight aircraft.