## 3 Experiments  
To test the performance of the aerial seeding system, three experiments were designed and carried out following a step by step procedure. The rapeseed variety used in the experiments was \"Huayouza-62\", a winter Brassica napus variety developed by researchers at Huazhong Agricultural University in 2011 and is now widely planted in central China. The first experiment was an orthogonal experiment [21]. The aim was to investigate how the performance of the seed feeding component was influenced by the main working parameters and to obtain the best combination of parameter values. The three factors considered in the experiment were  
Figure 3: Seed distributor: (**a**) Schematic diagram with 1/7 removed to show the internal structure; (**b**) Real device. the thickness of the seed layer, the rotational speed of the gear disc, and the air pressure of the fan. For each factor, three levels were set as shown in Table 1. According to the orthogonal experimental design method [22], assuming that the influences of the three factors were independent, an L9 (3\({}^{4}\)) experimental plan was chosen (L9 (3\({}^{4}\)) stands for a standard orthogonal experiment of nine tests in total, four influencing factors, and three levels for each factor). For each level, three tests were carried out, and for each test, the seeding system worked for 1 min. The second experiment was a static workbench test of the aerial seeding system. Figure 4 shows the setup of the experiment. The aim was to obtain the performance indexes while fixing the values of unimportant factors and varying the values of the most important one from the first experiment. The definitions of the performance indexes [14] are given as follows:  
The stability variation coefficient of the total seeding rate \(C_{\text{VT}}\) is calculated by the following formula. \[C_{VT}=\frac{\sigma_{T}}{\mu_{xT}}\times 100\% \tag{3}\]  
where \(\sigma_{T}\) and \(\mu_{xT}\) are the standard deviation and average value of the total seeding rate, respectively. The consistency variation coefficient of the sowing quantity between each port \(C_{VE}\) is calculated by the following formula. \[C_{VE}=\frac{\sigma_{E}}{\mu_{xE}}\times 100\% \tag{4}\]  
where \(\sigma_{E}\) and \(\mu_{xE}\) are respectively the standard deviation and the average value of the seeding rate between each port. To further test the performance of the aerial seeding system in practice, a field experiment was carried out on 10 October 2019 on the outskirts of Maqiao Town, Xianning City, Hubei Province. Since the test fields for the UAV to fly on were surrounded with overhead power lines, ditches and ridges, and the sizes of the fields were small, to ensure absolute safety, a conservative test plan was adopted in which the flying speed was restricted to 4 m/s. Through a preliminary trial using mud boxes on the ground, the flying height was determined at 2 m for the designed working width \(B=2.1\) m. The natural wind force was smaller than level 2 during the experiment. Given the quantity of seeds per unit area \(G=6\) kg/hm\({}^{2}\), the working width \(B=2.1\) m, and the flying speed \(V=4\) m/s, the corresponding seeding quantity per second \(G_{\text{Y}}\) was calculated to be 5.04 g/s using \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Factor Level** & **Seed Layer Thickness (mm)** & **Rotational Speed (t/min)** & **Air Pressure (Pa)** \\ \hline
1 & 15 & 25 & 1960 \\
2 & 30 & 35 & 2450 \\
3 & 45 & 45 & 2940 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Factors and levels of the orthogonal experiment. Figure 4: Static workbench test. Equation (1). Then, a preliminary static workbench trial was conducted to determine the rotational speed of the gear disc. To compare the performance, the seeding operation was also performed using another two systems: one was a ground planter Weiye 2 BFG-4 from Hunan Province and one was an aerial seeding system based on an XAG P20 UAV. The second aerial seeding system was also developed by our team and some results have been published in [13].