## 6 Conclusions  
We performed acoustic measurements of large-scale and small-scale landing gear models, which have identical simplified geometry and differ only by their scales. The tests of the full-scale generic landing gear were performed in the large anechoic facility FL-17 CARDC (Mianyang, China), whereas the small-scale landing gear models were tested in an anechoic chamber with flow, AC-2 TsAGI (Moscow, Russia).  
The large-scale landing gear models are simplified and lack small geometric details, which for the first time allows their results to be directly compared with those for small-scale models of the same geometry. It is shown that the normalized spectra for broadband noise of the landing gear models of different scales are in a good agreement with each other. This conclusion implies that the small-scale tests can be reliably used to search for broadband noise reduction solutions, at least for the low-frequency region of full-scale noise spectra. One can mention the technology of truncated cylinders for landing gear noise reduction [21], which was initially developed for small-scaled cylinders and landing gear models and then successfully validated for low-frequency noise reduction at the full scale. Such studies can be continued with respect to other low-frequency noise reduction technologies. Small-scale tests can also be used for refinement of semi-empirical models of broadband noise prediction for different landing gear elements.  
On the other hand, development of noise reduction technologies for high-frequency parts of the spectrum based on small-scale models seems problematic, because it requires high-fidelity reproduction of fine details of the landing gear, measuring the noise spectra up to very high frequencies, and introduction of large corrections due to sound refraction by the flow and sound attenuation in the atmosphere.  
The present study also corroborates the conclusion that small-scale tests are ill-suited for tonal noise investigation for full-scale models due to high sensitivity of the tones to the parameters of flow and model geometry. This is not a significant drawback, however, because the tonal noise of full-scale landing gears should be effectively reduced with a number of noise reduction methods, both for Aeolian tones and cavity tones; thus, realistic landing gears have their tonal noise suppressed, so that their aerodynamic noise is essentially broadband in nature [2]. This means that investigations of broadband noise of landing gears in small-scale tests can be of practical interest.  
Conceptualization, V.K. and K.Z.; methodology, V.K.; software, I.B. and K.Z.; validation, M.Z.; formal analysis, M.Z.; investigation, I.B.; resources, V.K. and K.Z.; data curation, I.B. and M.Z.; writing--original draft preparation, I.B.; supervision, V.K. and K.Z.; project administration, V.K. and K.Z.; funding acquisition, V.K. and K.Z. All authors have read and agreed to the published version of the manuscript.  
This research was partially supported by the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2022-1023) within the program for the creation and development of the WCRC \"Supersonic\". The small-scale tests were carried out on the basis of the TsAGI facility \"AC-2 Anechoic chamber with flow\" modernized with the financial support of the Ministry of Science and Higher Education of the Russian Federation under agreement No. 075-15-2022-1036.  
Not applicable.  
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.