Here is a size comparison between Mig-25 and J-20. Mig-25 was a 1960's era Soviet high speed, high altitude interceptor, capable of reaching the speed of Mach 3.2 and the incredible atitude of 35,000 metres (115,000 ft).
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It's enormous speed and size was very impressive to anyone who saw it. It's length was 19.75M or 67ft, and wingspan of 14.01m or 45ft.
The dimensions are almost identical to J-20, with J-20 being slightly longer, 72ft or 21.9m in length, and smaller wingspan, 44ft or 14m.
No wonder many people were convinced that J-20 was built as a interceptor. This was no mere coincident. J-20 was based on the cancelled, 1970's era, J-9 interceptor designed to the achieve Mach 3, and altitude of 30,000m, the same as Mig-25.
J-9 designers must have studied the Mig-25 carefully, in the 1970's, for inspirations to reach those lofty goals.
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J-20 and the iconic Mig-25 have the near same length and wingspan.
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The long and slender shape of J-20 is optimized for Supersonic speed and the canards are for maneuverability. It is interesting to see if J-20 can match the Mig-25's incredible top speed of Mach 3.2.
Mig-25's engine max thrust is "only" 100kN, while J-20's thrust is reportedly greater than 180kN, possibly > 210kN as I have speculated.
The mighty F-15 could reach Mach 2.5 with two max thrust 105kN engines.
Powerplant: 2 ×
Pratt & Whitney F100-PW-100 or −220 afterburning
turbofans