I suppose both of these are copies of the Su-30.
optimized for long-endurance missions at high altitude, the aircraft features an unusual tandem, joined wing platform.Except for the wing, the Xianglong is similar in appearance and mission to the Northrop Grumman RQ-4 Global Hawk operated by the United States Air Force.
Attention to the angular, faceted features of the design, comparing them to the F-117 Nighthawk (J-XX)
We all are aware about the hacking from chinese to US and other defense Provider server and downloading the design data of planes.
Moreover the J-XX is too big to be hide from radar, and its cross section only will came to know when it fly outside which we can hardly know because we know it won't because china don't have just enough real technical edge that it can show to world.
Once can judge from the fact that while you able to copy the SU 30 russian Engines easily but can't make your attack helicopter engines why? because the requirement of the attack Help engine is different and till now no country have provided you that configuration engine which can be used in your Attack Helos and you didn't able to copy that's why you didn't have the engine.
Composites are used extensively on the T-50 and comprise 25% of its weight and almost 70% of the outer surface.[49] It is estimated that titanium alloy content of the fuselage is 75%. Sukhoi's concern for minimizing radar cross-section (RCS) and drag is also shown by the provision of two tandem main weapons bays in the centre fuselage, between the engine nacelles. Each is estimated to be between 4.9-5.1 m long. The main bays are augmented by bulged, triangular-section bays at the wing root.
T-50 has been designed to be more maneuverable than the F-22 Raptor at the cost of making it less stealthy than the F-22. One of the design elements that have such an effect is the Leading Edge Vortex Controller (LEVCON).
So you understand the designing part now?