
We know that the Al-31 cannot provide sufficient thrust at altitude for the Su-27 with its variable inlets. The drag estimated for about 35,000 FT to at the Mach barrier is about 20,000 lbs. To reach Mach 1.4, you'd need about 25,000 pounds. The AL-31, at best, can do something like 60.5 kN with 2 engines (13,500 pounds) at that altitude and at Mach 1.1.
Is it possible that the Al-31 / WS-10 can do so at altitude given larger inlets (greater initial airflow), longer inlet length (greater space for the diffuser to do its work), as well as bypass ducts (as on the F-22) to bleed off low-speed excess airflow?
The total inlet length, ignoring geometry, is around 8-8.5 meters on the J-20, vs about 5 meters on the F-22.
Suspected bypass ducts on the J-20:

https://www.quora.com/What-are-these-op ... of-an-F-22
Known bypass ducts on the F-22:
