To make a maximum rate turn, you need to turn at the highest angle of bank that can be sustained at the lowest possible airspeed – just above VS – that is why the stall warning is used to indicate maximum rate.

Maximum rate turns | aviation.govt.nz

to turn at maximum rate we need maximum centripetal force and maximum lift. The increased angle of attack means increased drag, so full power is used. As rate of turn is proportional to velocity, the limiting factor in a maximum rate turn is power.

Maximum rate turns | aviation.govt.nz
 

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Corner speed is an important factor of maximum turn performance. Corner speed is defined as

the minimum airspeed at which the maximum allowable g can be generated. At corner speed,

the aircraft can attain its maximum turn rate.

https://navyflightmanuals.tpub.com/P-821/Corner-Speed-200.htm

Load factor, n, (n = Lift/Weight) is what’s read on the g meter. In normal, 1-g equilibrium flight, lift equals weight. In 2-g turning or looping flight, the aircraft produces lift equal to double its weight. Some of that extra lift goes to generate a centripetal force that accelerates the aircraft toward the center of an arc. Flight at more than 1 g is always associated with a pitch rate

http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/8_Maneuvering.pdf

The Zhuhai air displays tells a lot about J-20 performance and specifications.

First since it lacks thrust vectoring nozzles it had no post stall capability, the flight display only  showed some vertical loops and horizontal turns and rolls, pretty very basic maneouvres, no post stall, no post stall means faster speeds to keep the minimun lift it needs to do not stall and fall from the sky.

J-20 flew with very high angles of banking, at sea level (Zhuhai is at sea level), at relatively low speeds, however its turn rate was unimpressive, since it was flying at very high angles of banking, J-20 was flying close to its max G over load, thus flying close to its corner speed at sea level generating its highest turn rate.

While the highlight of the show was the WS-10 engines fitted to the J-20, the flight performance did not show a nimble and an agile aircraft, hinting it still has low thrust to weight ratio, and WS-10 engines are not equivalent to the needed WS-15

 

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