I was wondering if anyone could highlight the main physical differences of the two-seaters for newbies like me? I can tell the difference between canards and no canards but most other things look quite similar!
Well, I do not know how much it will help, but here's the best explanation I can give you about the five different aircraft.
The two-seat Su-27UBK is the export version of the SU-27UB two-seat trainer built by the Russians. The Chinese signed three seperate contracts with Russia for SU-27s which included forty-two Su-27SKs, which were the export version of the Su-27S in Russia, and 34 of the Su-27UBK trainers. So there were a total of 76 Su-27s acquired from Russia.
The Chinese produced the Su-27 in a license build mode and named those aircraft the J-11. Around 100 of these aircraft were built, taking on the designations of J-11 and J-11A as the Chinese made some improvements in the sensors and equipment in the aircraft.
Ultimately, China reverse engineered the license built J-11 aircraft and built the entire thing indegenously, using composites, Chinese sensors and Chinese weapons systems...removing the requiremnt to use Russian sensors, systems, and weapons entirely. This became the J-11B.
The J-11BS is the two-seat, trainer version of the J-11B. Like the SU-27UBK is the two-seat trainer version of the SU-SK in Chinese sevice.
The two-seat SU-30MKK is the export version of the Russian SU-30M, which is a super-manueverable strike fighter variant of the SU-27M. The Chinese SU-30MKK is a two-seat, multi-role strike fighter, not a trainer. 134 of these were purchased from Russia starting in the year 2000.
The two-seat J-16 is a new, indegenous, multi-role, longer range version of the J-11BS. It is not meant to be a trainer, but like the SU-30MKK, it is a long range strike fighter conparable to the F-15E Strike Eagle. This puts China in a position to build its own long-range strike fighters and not rely on Russian sensors or weapons...just like they accomplished with the J-11B over the J-11 and SU-27S. The J-16 in essence accomplished the same thing with the SU-30MKK...except newer and with even more advanced Chinese sensors.
The two-seat J-15S is a two-set version of the J-15, which was a Chinese development that used an older Ukrainian Su-33 prototype and the J-11B to develop an indegenous Chinese strike fighter for their aircraft carrier(s). The J-15S is a prototype two-seat version of that aircraft. It is not thought to have gone into production yet. It is thought that it will be a platform that the Chinese will use to develop a more capable attack, and electronic warfare variant of the single-seat J-15 like the two-seat F/A-18F and EA-18G do for the single-seat F/A-18E Super Hornet in US Navy service.