siegecrossbow
PDF THINK TANK: ANALYST
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If J-20's empty weight is 22 tons (2 more than F-22) and carrying only 4 tons of internal fuel for the demo, than it's flying weight would be 26 tons, that is 8.8 tons (or 51.2%) more than the military thrusts (17.2 tons) of two WS-10 or AL-31 engine.
At such a load on the engines, not only their AB must be turned on, but it must be turned on to near full blast, and a long red hot flame must be definitely visible, in a cloudy overcast day.
There is no visual evidence, that J-20's AB was even turned on, during the vertical climb demo, much less, turned on to full blast.
A su-27 equipped with Al-31 engines, turned on afterburner in full blast.
View attachment 422012
That's not how vertical climb works though. You don't necessarily need a thrust to weight of over one to perform a vertical climb since you can channel a portion of the plane's forward momentum into a climb. The J-20 didn't go into a climb immediately after take off, so it probably built up some momentum before the climb.