Recently, on the test flight runway of Shenyang Aircraft Corporation in the aviation industry, a J-35 aircraft covered in green primer soared into the sky, marking the start of the "first flight of the new year" and the comprehensive launch of the year's test flight work. This is also the first time that the official has disclosed the J-35 flight footage with primer. Why is the J-35 test aircraft a "green skinned aircraft"? Firstly, it is necessary for anti-corrosion and basic protection. The body of the J-35 is made up of a large amount of metal and composite materials. During the initial stages of manufacturing, assembly, and flight testing, the surface of the aircraft is exposed to humid air, making it highly susceptible to electrochemical corrosion. The green primer contains chromate, which has strong anti-corrosion and anti rust functions, providing the most basic and important protection for metal bodies, just like the "moisture-proof putty" or primer applied to rough walls during house decoration to prevent internal damage. Secondly, for practical considerations of engineering flight testing. The core goal of the engineering team during the first and initial flight stages is to verify the basic qualities of the aircraft, such as flight performance, maneuverability, and structural strength. Maintain a simple "green skin" state for engineers to inspect, label, and repair the surface of the aircraft. The third issue is cost. Spraying expensive formal coatings before the design and condition are fully cured is a waste. Once the body structure needs to be modified, these coatings must be worn off and restarted. As the test flight progresses, the aircraft will gradually enter different stages of painting, and only when it reaches the mass production painting stage will it be painted with formal combat paint. In addition to green, there are also many cases in which Chinese military aircraft use yellow paint during test flights, affectionately referred to as "yellow skin aircraft" by military enthusiasts, which is also the "blank" state of the aircraft. Whether it is a "green leather machine" or a "yellow leather machine", it heralds the birth of new models or new capabilities. (New Society)