That's the point, that's why Russia was neither shocked, nor even surprised by the Chinese fighter developments, since they most likely was well aware of them, be it in fighter design, radar or engine fields.
I doubt that the Russians had any inkling on which of their stuff the Chinese used as a foundation for a Chinese 'stealth' fighter, let alone a fighter whose sophistication -- at least by appearances -- is on a par with theirs. In this competition for 'stealth', it is between the Russians and the Chinese, no longer US, and the Chinese does not need to produce any conceptual/theoretical and/or engineering breakthroughs, they just need to either meet the Russians or near their standards, to gain respect as an aviation power and we can reasonably assume that the Russians never believed that China, who have been a steady customer, to actually produce something like the J-20.
They succeded in re-producing what they got from other sources and I have praised their capabilities in the production field often enough, but wrt to own developments, they still struggle, which is evident by the fact that they remain to be dependent on Russia for radar and engine techs. The J20 might look like a NG fighter, but unless it gets a NG radar, engine and avionics, it isn't!
It is still not confirmed if J11B has an AESA, or what kind of radar J10B gets, recent reports hints on delays possibly caused by the difficulties they have with own radar as well as engine developments.
I don't critisize that they copy, they hardly have another choice, just like to spend huge ammounts of money, but they are technically still not on a level with the Russians now.
I bet sub-systems developments are concurrent with airframe. Am not saying that all started at the same time and may be they were, but if the Chinese were willing to risk much money in trying to have their own 'stealth' fighter, they would be willing to live adapting existing level of avionics into the new J-20 until truly indigenous avionics development caught up. The Chinese do not need to achieve everything at once.
The angled faceting is the same for any stealth fighter and is even similar to US stealth fighters.
Not as prominent today. Basically, the world has learned that while the technique works, too much sacrifices are needed in other areas, notably agility, in order to have stable flight. The US explored and largely eliminated that technique as primary for a flying low radar observable body.
Also how is J20 evolutionary from existing designs, it it's a mix of the Mig 1.44 and the F22?
Not F-22. My contention is that the J-20 is an evolutionary design of the 1.44.
That would have been the case if they have further developed the J10 design to a stealth fighter (as early speculations suggested), but that obviously wasn't the case and that is the difference of their current capabilities, compared to Russian or US. The later have existing knowhow to base such NG developments on, China will only have it in the coming years and decades, but they will go there way.
The J-10 has a single vertical stab. Sorry, but that alone disqualified the J-10 as candidate for RCS reduction measures ala 'Silent Eagle'.
But then you have the answer why Russia is behind and that it doesn't have anything to do with their general capability to develop things like this.
The break up of the Soviet Union compounded the consequences of when the Soviets rejected Ufimtsev's work.
Speculate that the Soviet Union did not break up. What this mean is that the F-117 and B-2 would have been produced in larger quantities. Then when the F-22 and F-35 designs are under manufacture, there would have been no reduction in purchase quantity. Probably the F-35 would not be available for partners, or to very limited partners. Back during the Cold War, the Soviet Union was already behind US in vital areas like electronics and metallurgy, so would the Soviet Union in this speculation be able to build an F-117 equivalent when the Americans would be rolling out the F-22? Not likely. When Ufimtsev's work was rejected, it became legal for Ufimsev to publish his work in the open. Even if this Soviet Union draft Ufimtsev to build a Soviet 'stealth' aircraft, the methodology cat is already out of the bag and we ran with it for at least one generation. With the pressure of the communist threat, budget for a mostly 'stealth' air combat fleet will not be much of a problem in the US Congress. Without a 'war on terror', low radar observable UAVs will be built in droves and stationed throughout Western Europe without the Warsaw Pact the wiser on where. The Soviet Union was already economically depressed to start, MIG and Sukhoi will not be able to catch up.
