## 7 Conclusions  
To date, the technology supplied by the manufacturer of Mi helicopter blades has not included instructions for the repair of leading edge deformations in field conditions. Therefore, a technology was developed and described in this paper, which presented the leading edge design of Mi helicopters. A number of factors may contribute to blade damage, as the frequency of damage is related to the intensity of operation. Based on an analysis of literature, operation, and technical documentation, the mechanical loads of blades were characterized and the environmental conditions affecting blades were determined: temperature range \(-40:50\)\({}^{\circ}\)C and maximum humidity of 80%. Due to the lack of data on the materials used in production, tests were carried out to identify the material properties relevant to the operation and repair technology. Spectroscopy was used to determine that a titanium alloy was used for the shield. This affected the selection of appropriate sandblasting parameters for surface treatment prior to bonding.  
DCS analysis was performed to check the thermal stability of the polymer materials used on the leading edge. This information was useful in the development of the technological process related to detaching the damaged section of the leading edge. Knowledge of the thermo-physical properties was essential for initially selecting the bonding systems for further research.  
Using the designed assembly device, a repair demonstrator and the samples for testing were produced.  
The reference samples produced for non-destructive testing were used for the validation of the tap-test method as a service diagnostic method. The verification confirmed that the repair was carried out correctly.  
The strength tests showed that the repaired bonded join was 30% weaker in comparison to the factory-made join.  
Differences in strength between the factory bonding samples and samples after the proposed repair technology may be due to the residual stresses, introduced during the repair process. This phenomenon requires further research and will be studied in the future. The environmental impact on the strength properties of the repair was negligible.  
The Polish Air Force approved the considered technology for supervised operation at the end of 2019. Within two years, the Air Force has not reported any problems with the repaired rotor blades.  
Conceptualization, M.S.; methodology, M.S., P.S., A.L. and R.K.; software, not applicable; validation, E.S., V.H. and A.B.; formal analysis, M.S., K.P. and A.L.; investigation, M.S., K.P., A.L., P.S., K.O., D.G. and R.K.; resources, M.S.; data curation, M.S.; writing--original draft preparation, M.S. and A.L.; writing--review and editing, K.O. and K.P.; visualization, E.S., V.H., D.G.  
Figure 21: Non-destructive testing: (**a**) Method of tap-test with an inspection hammer; (**b**) Trajectory of the tap-test.  
and A.B.; supervision, M.S.; project administration, M.S.; funding acquisition, M.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Director General of the Air Force Institute of Technology, Research task for 2018-2020.  
Not applicable.  
**Data Availability Statement:** Library of Air Force Institute of Technology, Report SP-70/58/20219, ID 2698/I. According to the policy of the Air Force Institute of Technology, all the raw data supporting plots and figures are not publicly available.  
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.