Just pondering, did J-9 evolve into J-20 decades later? Just like YF-17 evolved into FA-18.
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CAC started off as a division of SAC which was responsible mainly in theoretical research iirc. That meant that what later became CAC was responsible for designing and testing a huge array of different aerodynamic models, and the theories and models they developed in those early years had a profound impact on the design of the J10 and then the J20.
Chinese engineers and designers have long lamented that China was never really that far off the pace in terms of theoretical research, and what was holding them back was China's manufacturing capabilities in turning those theories into reality.
The close resemblance between the J9 model and the J20 is a vindication of those views, and a testate to just how advanced Chinese theoretical aerodynamic research was even back then. Had China had the ability to make the J9 a reality and fully up to spec, I believe it would have been one of the best fighters of it's time.