The Chinese, with their current state of technology, opted to have a fighter jet with three engines, doing Mach 2.5(marginally better then the J-20), but significantly larger size with significantly longer range and quantum leap in power generation and avionics as well as the ability to carry much larger weapon in its internal weapon bay. At first look, I find it a very smart move. It has a huge impact on their entire network of systems and it bypass some of their weakness, for example in engine tech. In fact, with the three engines system, they can optimize for two different flight regimes. For example, the middle engine could be tuned to optimize for lower Mach numbers where as the two side ones for higher speed.
This thing isn't a fighter. It may weigh around 26-30 tons empty and have an MTOW of around 48-52 tons, which are not fighter numbers at all. If the weight and size issue isn't enough, the fact that the middle engine's intake is on top of the fuselage (Which was probably done this way to allow for larger center weapon bays) is a dead giveaway to me that thing doesn't plan on executing any fighter type maneuvers, at least with that engine in the middle not stalling. One thing I don't understand is why the side engines have their intakes on the bottom.
Regarding power generation. This was never a limitation in modern military planes. Military turbofans can push multiple tens of thousands of shaft horsepower easily without breaking a sweat, so even if the plane was a twin engine, it would not be that difficult to draw a megawatt out of them via generators and constant speed drives. Also I don't see how much electricity a plane of this size requires. It carries a bunch of radars and electro-optics and I'm assuming the one at the nose would be the most power hungry, and even that thing would not consume anything beyond 30-40kw. That is literally less than 60hp, which is nothing to even a single engine, let alone three. The three engine configuration of the J-36 is most certainly due to the need of higher thrust, and has absolutely nothing to do with "next generation power requirements".
Now for optimizing different engines for different flight regimes. This basically means different bypass ratios, which means the engine with the higher bypass ratio would generate drag at higher speeds, while the low bpr engines would not be working at their peak efficiency at lower speeds. The other issues that I see is higher bpr engines push higher maf at lower jet velocities, so with three engines sitting so close to one another ejecting air at different speeds rubbing up on one another, would cause even more losses. In my opinion, having identical engines would be the best solution here, but I'm open to discussions regarding this.
Since the J-36 has 3 engines and assuming the engines are similar to the J-20 (WS-10 or WS-15 or similar dimensions), and if it were to travel at the same speed and have the same drag as the J-20's, it would need to carry 1.5 times the fuel in order to go as far. If we assume the J-36 is designed to have higher speeds than the J-20, then we can safely assume the J-36 will need to carry more than 1.5 times the fuel of the J-20 in order to travel the same distances, which my gut tells me is unlikely, especially since it is supposed to carry larger sensors and obviously larger weapons, but we will have to wait for clearer photos and more info.
