# Model-Based Design of Aircraft Landing Gear System
## 4 Simulation Results
This is potentially related to how the aerodynamic performance has been implemented: in fact, during landing, an aircraft deploys flaps and ailerons, which highly increase aerodynamic drag; meanwhile, due to the unavailability of detailed aerodynamic maps, the drag was considered to be constant throughout the simulation. **The tire/wheel sizing:**: Regarding the tire and wheel sizing values, the results are quite comparable to the actual ones. The larger difference is noticeable for the ATR 42-600, which could be solved with an improvement of the regression models for lower values of tire rated load. In any case, this latter value was found within 10% of the real value, thus making it possible to assume that the found tire/wheel combination is still suitable for the specific application. In terms of masses, instead, it seems that the model needs an important tuning, considering that the formulas used only allow for a high level estimation, which does not take into account the material properties of the components. **The brake sizing and performance:**: For what concerns the brake sizing, it is quite difficult to retrieve actual data. However, we can verify that the sized component is compatible with the available space provided by the actual wheels of the aircraft. Meanwhile, the temperatures achieved during landing are in line with what can be expected from the capabilities of the chosen materials, as presented in Section 2.2. **The shock sizing and performance:**: Finally, the comparison of the sized shock absorber with actual values suffered from a similar unavailability of data as the brakes, thereby making it difficult to confirm them with certainty. However, it can be noticed that, as expected, there was a clear correlation between the shock parameters and the mass of the aircraft: in fact, the piston area, the spring stiffness, and the damping coefficient tended to increase with higher mass; meanwhile, the shock travel reduced. The increase of the first three quantities was clearly related to the need to absorb the heavier landing impact characterizing an aircraft of a larger mass. The reduction of shock travel is instead related to the higher deformation that affect the tires of a heavier aircraft, thereby prompting the need to have a lower shock travel to avoid contact of the underbody with the ground. With regard to the dynamic model, it is then possible to plot numerous aircraft characteristics, thereby allowing the designer to further understand the aircraft performance and behavior. \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & \begin{tabular}{c} **ATR 42-600** \\ **Actual** \\ **(Error *)** \\ \end{tabular} & \
\begin{tabular}{c} **F-15D** \\ **Actual** \\ **(Error *)** \\ \end{tabular} &
\begin{tabular}{c} **B737-800** \\ **Computed** \\ **(Error *)** \\ \end{tabular} \\ \hline \(t_{bdisc}\) **[m]** & 0.0140 & 0.0164 & 0.0215 \\ \(m_{parkac,act}\) [kg] & 31.44 & 41.65 & 33.29 \\ \(L_{brack}\) [l/m\({}^{2}\)] & \(3.03\times 10^{7}\) & \(4.15\times 10^{7}\) & \(7.34\times 10^{7}\) \\ \(F_{brack,act}\) [N] & 9291 & 11,426 & 18,771 \\ \(T_{brack}\) [\({}^{5}\)C] & 370 & 931 & 1505 \\ \hline \(S_{shock}\) **[m]** & 0.4149 & 0.4051 & 0.3945 \\ \(A_{piston}\) **[m\({}^{2}\)]** & 0.0078 & 0.0191 & 0.0315 \\ \(c_{shock}\) [Ns/m] & 88962 & 218,990 & 359,910 \\ \(k_{shock}\) [N/m] & 738,180 & 1,861,200 & 3,141,000 \\ \hline \hline \end{tabular} Model inputs are reported in black, sizing results in blue, dynamic model outputs in red. * With respect to actual values; ** Estimated values.**  
\end{table} 
Table 2: _Cont._