# Study of Solid Particle Erosion on Helicopter Rotor Blades Surfaces
## 4 Conclusions  
The erosion behaviors caused by solid particles impinging on helicopter rotor blades covered in Ti-4 Al-1.5 Mn, Mg-Li9-A3-Zn3, and Al7075-T6 coating materials, at different particle impact velocities and angles of attack, were numerically analyzed. In addition, two bionic coatings were applied to the blade leading edge. Ti-4 Al-1.5 Mn with the V-type bionic coating provided the best erosion resistance in the simulation experiments. The conclusions from our study are given below.  
(a) In the simulations with different impact speeds, the average accretion rate of Mg-Li9-A3-Zn3 was 96.32% that of Al7075-T6, and the average accretion rate of Al7075-T6 was 94.99% that of Ti-4 Al-1.5 Mn. Ti-4 Al-1.5 Mn demonstrated the best erosion resistance, followed by Al7075-T6 and Mg-Li9-A3-Zn3. The erosion rate increased significantly with the particle impact velocity.  
(b) In the simulations of different angles of attack, the variance in average erosion rate of Ti-4 Al-1.5 Mn, Mg-Li9-A3-Zn3, and Al7075-T6 was 0.0117%, 0.0116%, and 0.0167%, respectively. Due to the variance, the erosion rates of the three materials remained nearly unchanged with changes in the angle of attack. Based on this, we speculate that changes in the angle of attack may only affect the erosion area of the blade.  
(c) In the simulation experiments of the bionic coating, the average erosion rate of the V-type bionic coating was about 26.1%, 26.6%, and 27.4% that of the VC-type coating at impact speeds of 70, 150, and 220 m/s, respectively. The erosion resistance of the V-type coating is significantly higher than that of the VC-type coating. The angle of attack had only a slight effect on the erosion rate of the two types of bionic coatings.  
Previous researchers have only focused on the erosion of materials and have not done much research on how to prevent erosion. So, the research on the anti-erosion of helicopter blades using bionic coatings has been developed in this article. In future, the problems of 'What does solid blade erosion look like when a complete blade rotates?' and 'How does a bionic coating affect flying vibration?' should be discussed and studied.  
Conceptualization, Z.H. and J.Z.; methodology, X.B. and Y.Y.; software, X.B.; validation, Z.H. and S.Z.; investigation, S.Z.; resources, J.Z.; data curation, X.B.; writing--original draft preparation, X.B.;  
Figure 15: Three-dimensional erosion rates of bionic coating of V-type at impact speed of 220 m/s.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Value [kg/(m\({}^{2}\)s)]**} & \\ \hline  & 70 m/s & 150 m/s & 220 m/s \\ V-type & \(0.28\times 10^{6}\) & \(0.29\times 10^{6}\) & \(0.31\times 10^{6}\) \\ VC-type & \(1.07\times 10^{6}\) & \(1.09\times 10^{6}\) & \(1.13\times 10^{6}\) \\ \hline \hline \end{tabular}
\end{table}
Table 8: Average erosion rates of the two types of bionic coatings at different impact speeds.  
writing--review and editing, Y.Y., Z.H. and J.Z.; supervision, Y.Y.; project administration, S.Z. and J.Z.; funding acquisition, Y.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China, grant number 2018 YFA0703300, Joint Fund of Ministry of Education for Equipment Pre-research, grant number 6141A02022131, the National Key R&D Program of China, grant number 2017 YFC0602000, and Science and Technology Development Project of Jilin Province, grant number 20190303061 SF.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.