## 3 Results and Discussion
### Experimental Validation of the Proposed Model
Figure 8: Nacelle wind turbine on the 6-axle SPMT. Figure 7: Configuration of the experiments to validate the proposed regression model: Crane, trailer and load. A full factorial design consists of several factors and levels where the experiments involve all possible combinations of these levels for all factors. In most cases, the levels are quantitative. However, they can be qualitative, as in the cases of gender or logical values. A 2k design is a kind of full factorial design that has only two levels, which are called \"low\" and \"high\" or \"\(-1\)\" and \"\(+1\).\" All possible combinations without repetition of the two levels and the k factors generate 2k experiments. A 3k design is a full factorial design that has three levels, which are coded as \"\(+1\)\", \"\(0\)\", and \"\(-1\)\", that generate 3k experiments without repetition. In this study, 3k DoE with two factors with central points (\(32=9\) experiments) were selected for validation of the theoretical model. In addition to nine experiments, four additional repetitions or repeated experiments were proposed to measure the variability of the results of the experiments and equipment in satisfying Equation (28):  
\[\sigma=\sqrt{\frac{1}{n}\cdot\sum_{i=1}^{n}(x_{i}-\mu)^{2}} \tag{28}\]  
where \(x_{i}\) is a result of the experiment, \(\mu\) is the mean of this variable, and \(n\) is the number of cases (just repeated). The configuration for all experiments involved a downhill slope of 0.35\({}^{\circ}\) and a camber of 0.1\({}^{\circ}\). However, as the values are very low, it was assumed that the ground was perfectly even. In addition, the configuration of the experiments assumes a wind speed of zero, as the latter was very low. The trailer was configured in 3-point suspension, as Figure 6 shows. The platform was set at a height of 1550 mm from the floor. A crane was employed to move the nacelle wind turbine, whereas the location and configuration of the trailer were unchanged. The output was the oil pressure of each group of hydraulic cylinders. The experimental inputs and pressures that were recorded by the manometers are summarized in Table 2.  
Additionally, the variabilities of each pressure group were calculated according to Equation (28) and are summarized in Table 3. The average variability of the pressures in the table of the first four experiments is 4.45 bar. This represents a value of 4.45/69.55 (6.39%) compared to the average pressure. This means that the values registered experimentally in the pressure gauges show a low variability. This can be considered to be very good, in view of the fact that the values were obtained experimentally. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & & & **Pressures [bar]** & \\ \cline{3-6}  & X & Y & & **A** & **B** & **C** & **D** \\ \hline
1 & 0 & 0 & 59 & 61 & 77 & 75 \\
2 & 0 & 0 & 55 & 62 & 80 & 79 \\
3 & 0 & 0 & 60 & 61 & 75 & 72 \\
4 & 0 & 0 & 64 & 56 & 90 & 92 \\
5 & 0 & 0 & 58 & 63 & 78 & 74 \\
6 & 0 & 335 & 24 & 97 & 80 & 80 \\
7 & 0 & 435 & 13 & 108 & 81 & 85 \\
8 & 675 & 0 & 66 & 75 & 58 & 58 \\
9 & 675 & 335 & 38 & 103 & 58 & 59 \\
10 & 675 & 435 & 27 & 117 & 58 & 58 \\
11 & 1350 & 0 & 79 & 85 & 39 & 40 \\
12 & 1350 & 335 & 47 & 120 & 39 & 38 \\
13 & 1350 & 435 & 38 & 127 & 38 & 38 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experiment inputs (X and Y) and pressures obtained from manometers. After the 13 experimental values were obtained according to the preset configuration of experimental inputs (X, Y) in Table 3, weight (42,500 kg), dimensions of (5133 \(\times\) 2650 \(\times\) 2975 mm), and CoG (97.5 \(\times\) 0 \(\times\) -180 mm) of the nacelle wind turbine, the theoretical values of the pressures of the proposed model were obtained (See Table 4). In addition, the accuracy of the proposed theoretical model is measured by the Mean Absolute Percentage Error (MAPE).