After years of having their military technology blatantly stolen by China, Russia is no longer selling them much of anything. In addition, the state controlled Russian media is now featuring lots of pundits deploring the low performance of the Chinese arms industry, and how poorly they have copied Russian military technology. A recent flurry of reports disparaged Chinese attempts to copy the Russian Su-33 (an aircraft carrier version of the Su-27). This all rings hollow when you consider how the Chinese have already caught up with a lot of Russian military manufacturers, and are driving them out of business in some areas.
For example, using stolen Russian technology, China is driving Russia out of the low-end weapons business. In turn, Russian attempts to maintain their status as a major developer of military technology are fumbling, largely because of the sales stolen by China. Increasingly, China is undercutting Russian sales efforts with similar weapons containing lots of stolen Russian technology. The Chinese won't invest as much in developing new technology, and the Russians can no longer afford to. So the second tier weapons markets slide further into mediocrity.
Through most (1960s-80s) of the Cold War, Russia (Soviet Union) had a well financed arms industry. Many innovative weapons were developed, but all this effort was hobbled by the fact that the Russian economy as a whole was very inefficient, and Russian industry could not build high tech as well, or reliably, as Western firms. Thus Russian high-tech gear always came in second to Western counterparts.
When the Cold War ended, so did the lavish spending on the Russian defense industries. Many, actually over half, of these weapons manufacturers went bankrupt, or converted to non-military production. Those that survived, did so by exporting weapons. Throughout the 1990s, the Russian armed forces could not afford to buy much new stuff. China came to the rescue in the 1990s, and over the next decade, bought nearly $20 billion in Russian arms. But China also began to blatantly copy lots of the Russian tech, and build their own. Thus, not surprisingly, for the last five years, Chinese orders have shrunk, while production of copies of Russian tech have increased. In some cases, Russia has simply refused to sell China high tech stuff, to avoid having it copied.
In the 1990s, Chinese manufacturing capabilities were so far behind that Russia believed their lead would never disappear. But with Russian military manufacturing largely stalled for the last two decades, and the Chinese economy booming (over 10 percent growth per year), the Russians are horrified to realize that the Chinese are catching up, and fast. For example, China believes it will be free from dependence on Russia for military jet engines within the next five (or so) years. Currently, China imports two Russian engines, the $3.5 million AL-31 (for the Su-27/30, J-11, J-10) and the $2.5 million RD-93 (a version of the MiG-29s RD-33) for the JF-17 (a F-16 type aircraft developed in cooperation with Pakistan.) But in the meantime, Chinese engineers have managed to master the manufacturing techniques needed to make a Chinese copy of the Russian AL31F engine. This Chinese copy, the WS10A, is part of a program that has also developed the WS13, to replace the RD-93.
China has long copied foreign technology, not always successfully. But in the last decade, China has poured much money into developing a jet engine manufacturing capability. The Chinese encountered many of the same problems the Russians did when developing their own engine design and construction skills. But China has several advantages. First, they knew of the mistakes the Russians had made, and so were able to avoid many of them. Then there was the fact that China had better access to Western manufacturing technology (both legally and illegally). Finally, China was, unlike the Soviets, able to develop their engine manufacturing capabilities in a market economy. This was much more efficient than the command economy that the Soviets were saddled with for seven decades.
It is true, as the Russians like to point out, that the Chinese have taken a long time to develop some of their latest high-tech weapons (like the J-10 and JF-17 jet fighters, jet engines and many missile and electronic systems). But that's because the Chinese regarded these projects as learning exercises, and have not produced the resulting aircraft in large numbers. The Chinese use what they have learned for the next project, and they have made a lot of progress in two decades. China has already demonstrated an ability to build (and copy) world class technology. They now have the largest automobile industry on the planet. China can build things, and build them well. They learn from their mistakes, and they are surpassing their long time Russian mentors. The Russians know this is true, but they don't want to admit it.