I have faith in Chinese engine development. However, you have to addmit that 117S is currently Russia's best engine ( it is still more realiable than the 117 !)
China does not have an engine that is as good as the 117S. WS-10B has 135Kn of thrust, FADEC, and better life and more realiable. However, WS-10B does NOT have 3D TVC, and 117S has 142Kn which is still more than the WS-10B.
The fact is that China will not have an engine that is as good as the 117S for at least another 5 years !
Buying 117S will be an insureance for the J-20, and will also help the Chinese getting familar with 3D TVC !
WS-15 will not come online until 2020 the earliest, so 117S server a good interim engine for J-20. J-20 can use the WS-10B or even AL-31FN but it will not be as good as using 117S !!
Therefore, buying a small batch of SU-35 might worth it.
Yes, 117S is a good engine, it
might be the best engine in Russia now... However from experience, I don't think Russia would export the best of them out to a foreign country, especially one that is so close to her unless she already had something in the pipeline and is very far into development that by the time the 'best' thing got exported, the system is already out.
And, as plenty of argument was already out there and I am not going to actually get into such a borrrrrring argument without risking certain member from coming in and damage this otherwise fine thread again, that TVC was actually not an answer to everything and lack of TVC does not actually meant that an aircraft would be sitting duck (not accusing you of every stated that in the first place). So China do not actually be putting too much effort in TVC technology.
Also, what is 5 years to China? Is China getting into a war right away? Or is China in a dire threat that her current aircrafts couldn't support? So if China is going to get an engine as good as 117S in five years time or somewhere later, I think the Chinese might find that acceptable, at least they do not need to be reliance to outsiders, and from many of China's experience, over relying on outsider almost always not bode good in the end.
Finally, it is kind of silly to just get a batch of Su-35 which China had absolutely no uses of, just to get the engines that are fitted to the back of the aircraft. What is the Chinese going to do? Tear those multi-million dollar aircraft apart, take out their engines and fit them to J-20 or J-31? The airframe of the J-20 and J-31 might not even be designed to fit in the 117S, so a redesign is needed.
However, with the WS-15 already in the pipeline and assuming that it was already deep into development, J-20 might already been designed for the WS-15, if a redesign was done on the J-20 airframe to fit the 117S, does it also mean that a redesign must again be done when the WS-15 was ready, or if WS-15 should be redesign so that it can be fitted into the J-20, and that would definitely means a delays to the WS-15 again.
Plus if two types of engines are used and they might not be interchangeable in future to the J-20, then we will be seeing two different airframe, which again might mean nightmares for the Chinese supply chain and logistic, also nightmares to the Chinese engineers.
That is why I believe the deal will not come through... but that is just my opinion.
