# Parametric Analysis on Landing Gear Strut Friction of Light Aircraft for Touchdown Performance
## 4 Conclusions  
In this paper, a numerical dynamic model of the half-axle main landing gear of a light aircraft is established, considering the influence of the flexibility of the shock strut on the friction load. The calculations of the two landing conditions are carried out. The drop test is executed in equal conditions to verify the simulated accuracy of the numerical model for the touchdown performance. Based on the validated model, the energy absorption of friction load in the landing process is analyzed. The results show that the proportion of energy absorption of the friction load accounts for more than 35% of the total landing impact energy, indicating that friction load has a considerable effect on touchdown performance. The energy absorption efficiency of shock-strut and strut friction increase as the increase of the landing impact energy. The four landing responses and eight design variables of the landing gear are analyzed based on the response surface method. The response surface models all meet the fitness evaluation criteria. Based on the [PERSON]'s method, the parameter sensitivity analysis of the four landing responses is carried out. The results show that the lower bearing width (\(d_{B}\)) is the parameter with the greatest influence on max strut friction load, max overloading of sprung mass, and shock absorber stroke. The wheel moment of inertia (\(I_{w}\)) is the parameter that has the greatest influence on shock-strut efficiency. The influence trend of each design variable on max friction load and max overloading are approximately the same, indicating the correlation between these two landing responses. The multi-objective optimization is carried out based on the response surface models. The max overloading of sprung mass in the two landing conditions are selected as the optimization goals. The results show that the optimized max overloading is reduced by 4.84% in LC-1 while the original energy absorption efficiency is already at a high level, indicating that the touchdown performance of the aircraft can be improved by optimizing the design parameters that affect the friction load. These studies provide guidance to the design of aircraft landing gear, including modelling, experiment, performance analysis, and design optimization. The role of friction in landing performance is notable for designers, which can be utilized to improve the landing performance. The response surface method coupled with the numerical model \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Info.** & \(\mathbf{r_{k}}\) **(m)** & \(\mathbf{L_{d}}\) **(m)** & \(\mathbf{A_{A}}\) **(m)** & \(\mathbf{d_{B}}\) **(m)** & \(\mathbf{L_{b}}\) **(m)** & \(\mathbf{I_{1}}\) **(m\({}^{\mathbf{4}}\))** & \(\mathbf{I_{2}}\) **(m\({}^{\mathbf{4}}\))** & \(\mathbf{I_{w}}\) **(kg m\({}^{\mathbf{2}}\))** \\ \hline Coded value & 0.999 & \(-0.881\) & \(-0.200\) & 0.925 & 0.143 & 0.036 & 0.106 & 0.983 \\ Actual value & 0.120 & 0.138 & 0.019 & 0.047 & 0.111 & \(2.31\times 10^{-7}\) & \(5.19\times 10^{-8}\) & \(7.10\times 10^{-3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 10: The optimized values of the landing gear parameters. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**LC-1**} & \multicolumn{3}{c}{**LC-2**} \\ \cline{2-7}
**Info.** & **Before** & **After** & **Variation (\%)** & **Before** & **After** & **Variation (\%)** \\ \hline Max friction load (kN) & 1.13 & 0.99 & \(-12.39\) & 1.83 & 1.81 & \(-1.09\) \\ Shock-strut efficiency & 88.66\% & 92.23\% & 4.03 & 89.45\% & 90.35\% & 1.01 \\ Max overloading (G) & 2.48 & 2.36 & \(-4.84\) & 3.31 & 3.27 & \(-1.21\) \\ Shock strut stroke (mm) & 38.21 & 38.19 & 0.44 & 71.67 & 71.02 & 0.44 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Comparison of the design optimization results. and design optimization provides a feasible scheme for the optimal design of the project with similar properties. Conceptualization, X.W. ; methodology, S.G.; software, S.G.; validation, S.G. and X.F. ; formal analysis, S.G.; investigation, X.F.