The Astonishing Supersonic Maneuverability Difference Between 4th and 5th Generation Fighters.
I have again and again emphasized the importance of Supersonic Cruise and Supersonic Maneuverability to 5th Gen. fighter. Without ability to do Supersonic Cruise, there could be no Supersonic Maneuverability.
Here is the picture that illustrate the astonishing difference between Supersonic Maneuverability of F-15, F-35 and F-22. Supersonic Maneuverability is a measure of how agile of a plane is in Supersonic Speed at various height. Because the air density at different height, the Maneuverability will be greatly affected.
Here is the 5G Maneuver Envelope. The Maximum Speed of a plane able to maneuver at 5G at various height.
As we can see, F-15, one of the most agile 4th gen. fighter in the world, could only pull a 5G Maneuver at Mach 0.8 at sea level, and at 32,000 ft, only Mach 0.7. No Supersonic Maneuverability at 5G over Mach 0.8. Basically, it could only fly pretty much in a straight line with a huge turn radius at higher speed.
Whereas, F-22 could pull 5G at nearly Mach 2 at the Maximum altitude of 65,000ft. At sea level, it could still able to reach Mach 1.3 while pulling a 5G turn.
Basically, sustained Supersonic Maneuverability is determined by Aerodynamics of the airframe, Power of the engine and structural strength of the airframe.
If you don't have outstanding Aerodynamics design, your air speed will quickly drop below supersonic during high G maneuvers. If you don't have a powerful engine in the first place, you can't do Supersonic Cruise without afterburner. If you turn on your afterburner in order to go supersonic, you will quickly run out of fuel. If your airframe isn't strong enough, your plane will fall apart at high G during Supersonic Maneuvering. If you have a very tough airframe, but a weak engine, you will be overweighted. And if you have a very powerful engine, but overweighted and have a lousy aerodynamics design, you will end up being clubbed like baby seals like F-35.
As if we can see, even the mightily powerful F-15 don't have much Supersonic Maneuverability, it is useless to talk about that for 4th Generation fighters, instead they concentrate on subsonic maneuverability. But Supersonic Maneuverability is such an awesome ability. F-15 and F-16 pilots said whenever F-22 goes into Supersonic, the fight is over. They can't follow it into those Supersonic speed without turning on the afterburner, and if they did, they would run out of fuel in minutes.
The result: The F-15 and F-16 can't out run and can't fight the F-22. They always lost.
So without Supersonic Cruise, there is no way for J-20 to determine its vitally important Supersonic Maneuverability flight envelope at various height and speed.
And you said that's no problem, that could always be determined, later, after WS-15 is ready, and in the mean time, lets put J-20 into LRIP and even mass production?
Lockeed Martin started the production of F-35 way before all tests were done. Ask them how they are doing with F-35.