Russia is seeking ways to halt unauthorized Chinese production of Russian jet fighters. This has proven very difficult, especially since Russia and China are supposed to be allies these days. Earlier this year the extent of the problem was made quite stark when China refused to buy Su-35 fighters from Russia if a "no unauthorized duplication" clause was included in the contract. The Chinese wanted to buy the Su-35s but were not willing to sign a binding agreement to not copy the Russian design.
China is already producing unauthorized copies of the Russian Su-27, as the J11. They have since designed a two-seat fighter bomber version as the J16, a stealthy version (J17) and obtained an aircraft carrier version of the Su-30 (the Su-33) from Ukraine and are producing a copy (as the J-15). China insists these are all Chinese designs that just happen to bear some resemblance to Russian fighters. In response Russia has halted combat aircraft sales to China but will still sell jet engines for these aircraft. So far, China has been unsuccessful in building copies of these engines. The engine sales are too lucrative to pass up, as they enable the Russian engine manufacturers to continue developing new designs. The Chinese plan to steal these as soon as they figure out how to handle the exotic manufacturing skills required to build these engines.
The original J-11 entered service in 1998, but production was very slow and only a hundred were produced. It was during this process that the Chinese mastered all the technical details of building and modifying the Russian aircraft. Chinese officials were dismayed with the performance of the obsolete Russian electronics. After that, at least a hundred of the 33 ton J-11A were built. This model was equipped with modern, Chinese made, electronics and is capable of hauling eight tons of radar guided air-to-air missiles and smart bombs. Then came the J-11B, which was the same size and weight as the J-11A but had a more capable AESA radar and is intended to specialize in air-to-ground missions, while also being able to take care of itself in air-to-air combat.
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China is also working on a two-seat strike (like the U.S. F-15E) version of the J-11. This model, the J-16 would basically be a two-seat J-11B. There is also a stealth version of the J-11B, the J-17, with internal bomb-bays and changes in shape to make the aircraft less visible on radar.
There appear to be over 200 J-11s in service, with about 40 percent of them J-11Bs. This is deduced by the number of cell phone photos showing up, from different air force and navy air bases.
Over the last seven years China has been developing a carrier version of the Russian Su-27, calling it the J-15. There is already a Russian version of this, called the Su-33. Russia refused to sell Su-33s to China, when it was noted that China was making illegal copies of the Su-27 (as the J-11) and did not want to place a big order for Su-33s but only wanted two, for "evaluation." China eventually got a Su-33 from Ukraine, which inherited some when the Soviet Union dissolved in 1991. The Russians are not happy with this development. Russian aviation experts have openly derided the J-15, casting doubt on the ability of Chinese engineers to replicate key features of the Su-33. That remains to be seen, as the Chinese have screwed up copying Russian military tech in the past. But the Chinese have a lot of experience stealing foreign tech, so the J-15 may well turn out to be at least as good as the Su-33. Meanwhile, Russia itself has stopped using the Su-33.