We investigated three fan-shaped jets observed above sunspot light bridges or nearby sunspot regions. The study aimed to explore the dynamics and physical properties of jets’ features that appear as blob-like structures at the tips of the jets, which we call ‘dark blobs’. A transparent region is observed beneath the dark blobs, creating a visible gap between the dark blobs and the trailing body of the jets. These phenomena were studied in chromospheric and transition region imaging and spectral high-resolution co-observations from the Visible Imaging Spectrometer of the Goode Solar Telescope at the Big Bear Solar Observatory and the Interface Region Imaging Spectrograph (IRIS), together with data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We analyzed the jets’ morphology and fine structure. We obtained the spatial scale and the dynamics of the dark blobs that are seen mostly in the wings of the Hα line and have a cross-section of about 0.2′′–0.3′′. The dark blobs and the transparent regions are seen bright (in emission) in the IRIS slit-jaw 1330 Å, 1400 Å, and AIA 304 Å images. The IRIS Si iv 1394 Å spectrum of the brightenings showed blue-shifted emission of about 16 km s−1 with non-thermal velocities of up to 40 km s−1. We also estimated the electron density of the blue-shifted brightenings to be 1012.1±0.2 cm−3. Our findings likely suggest that we detect the observational signatures of shock waves that generate and/or contribute to the evolution of fan-shaped jets.

The paint removal of fighter jets is just as important as the painting, because perfect paint removal ensures the quality of the exterior painting on the aircraft. However, the current conditions for paint removal work of the ROKAF’s are poor. It is identified that the painting process currently implemented by the ROKAF is not only exposed to harmful compounds such as harmful dust and hexavalent chromium, but also consumes a lot of water. Thus, the introduction of advanced facility is considered. This study compares the fighter jets painting removal process currently applied by the Korean Air Force with the improved laser coating removal process of the US Air Force, and conducts an incremental analysis to perform economic analysis for the introduction of advanced facility. Four scenarios were envisioned on the premise of an increase in the number of fighters in the future, incremental analysis shows that laser coating removal method is advantageous in all scenarios. In addition, it is recommended that paint removal cycle keeps the current 12-year and the outsourcing amount to civilian depot is reduced.

The Korean Air-Force aircraft maintenance depot paints the exterior of various aircraft, including high-tech fighters. Aircraft exterior painting is a maintenance process for long-term life management by preventing damage to the aircraft surface due to corrosion. The de-painting process is essential to ensure the quality of aircraft exterior paints. However, because the Korean Air-Force’s de-painting process is currently done with sanding or Plastic Media Blasting (PMB) method, it is exposed to harmful dust and harmful compounds and consumes a lot of manpower. This study compares the de-painting process currently applied by the ROK Air-Force and the more improved process of the US Air Force, and performs economic analysis for the introduction of advanced equipment. It aims to provide information that can determine the optimal time to introduce new facilities through Cost-Volume-Profit (CVP) analysis. As a result of the analysis, it was confirmed that the sanding method had the most economical efficiency up to 2 units per year, the PMB method from 3 to 21 units, and the laser method from 22 units or more. In addition, in a situation where the amount of de-painting work is expected to increase significantly due to the increase in fighters in future, BEP analysis was conducted on the expansion of the existing PMB method and the introduction of a new laser method. As a result of the analysis, it was confirmed that it is more economical to introduce the laser method when the amount of work exceeds the PMB work capacity(18 units per year). The paper would helpful to improve the productivity and quality of the Korean Air Force Aircraft maintenance depot through timely changes of facilities in the workplace in preparation for expansion.