You are welcome.
Precisely because this is a publicly available forum and that not everyone is proficient in English, I stay away from overly complex technical language and if there are any acronyms, I make efforts to explain not only what the letters stands for but also any ideas behind them. Those who know -- anything about any subject of interests -- owe at least that degree of consideration for the many silent readers and interested laymen out there.
As for the J-20's engine problem...Keywords search for you: 'operational tempo'
https://ssi.armywarcollege.edu/pubs/parameters/articles/99autumn/castro.htm
China have no choice but to work on the engine until success. There is no turning back. The J-20 is essentially finished with only Propulsion as the limiting factor regarding the planned operational tempo of a J-20 squadron.
I am USAF veteran. F-111 and F-16, so I will speak on the air operations aspect of OPTEMPO.
The J-20 -- based upon best known information -- is supposed to be a long range interceptor. The engine for this platform must have durability as primary consideration.
An intercept at peace time is not the same as an intercept while on a war footing.
For starter, a peace time intercept is usually an identification and escort mission. This will require visual contact with an unknown target, establish communication, and escort the target to a different location. A peace time intercept is normally of a non hostile scenario, or to put it in legal language, innocent until proven guilty.
On the other hand, a war time intercept is always premised that the target is hostile, or to put the scenario as guilty until proven innocent.
In both scenarios, speed is important. We want to meet the target, peace time or war time, as far away from us as possible. So the apparent assumption is that the engine must be capable of Mach so-and-so. That is not true.
A low durability engine have a negative effect on OPTEMPO regardless of how fast it can make the jet go. Accidental incursions by ignorant and/or lost aircrafts are unplanned. Neither are attempts at air defense penetration by hostile air forces. In both scenarios, the low durability engine requires higher degrees of support elements such as extra whole engines, manpower, and assorted parts. If any of these elements are lacking, the interceptor will not be able to fly as much as these unplanned events occurs. An intercept that is closer to home base is better than no intercept at all. This is the reality that every squadron lived with since the beginning of air combat. The worst possibility is that the low durability engine increased the odds of combat losses because the engine may fail in-flight.
A high durability engine have less demands on support elements, the squadron's tactical utility is increased due to geographical deployment flexibility because of the lower demands on logistics, decreased preparation time for any deployment, and increased combat survivability because the pilot will not hesitate to use the engine to its maximum potential. Another benefit is that of deterrence. Since the high durability engine contributes to the higher OPTEMPO per aircraft, the squadron as a whole have a higher deterrent factor in the enemy's calculations.
Air Dominance. The ability of an air force to compel other air forces to rearray themselves, often into subordinate postures.
Air Superiority. The ability of an air force to achieve control of contested airspace, repeatedly if necessary, and if there are any losses, those losses would not pose a statistical deterrence to that ability.
Air Supremacy. He flies, he dies. In other words, control of airspace is absolute and unchallengeable. If the enemy flies, he dies.
All of the above is not possible without endurance. Air superiority is not possible without persistence of presence, it means you must be able to return again and again, and you must be able to do so at your tactical convenience. Air power is more possible with persistence of presence than of attainable speed.
Most people thinks that air refueling is about extending range. But if there is enough fuel to fly longer in distance, then why not use the fuel to fly longer in time. That is persistence of presence made possible by air refueling.
An interception mission is not about flying as fast as possible to point X, shoot one or maybe a few missiles, then fly home. Even if you scared of the intruders without firing a shot, an interception mission requires your continuous presence over that area of violation for as long as your fuel can hold in order for you to determine your mission is successful. A high durability engine make this possible.
The J-20 have a very high standard to meet -- US. Not Russia, but US. If you see any Chinese boasting of how fast the J-20 can fly with WS-whatever-designator-number, ignore it. US airpower, of all branches of services, is based more upon persistence of presence, and less on speed. The PLAAF generals understand this better than the Internet Chinese.
