It took 4 years to produce three prototypes of the J–11B multirole fighter,
and another 2 years to build the twin-seat J–11BS variant. Sources in the Chinese
defense industry report that the J–11B is based on roughly 90 percent Chinese-
designed parts and subsystems, including the Type 1474 serial radar system,
3-axis data system, power supply system, emergency power unit, brake system,
hydraulic system, fuel system, environment control system, and molecular sieve
oxygen generation systems.117 The J–11B/BS is also fitted with indigenous PL–12
air-to-air missiles. There have been several cases since 2008 of Russian authorities
in the Transbaikal region arresting Chinese citizens for attempting to smuggle
spare Su–27 parts into China.118 This might suggest that China is not able to
design 90 percent of the original fighter’s parts and subsystems (the 10 percent gap
in design capability alluded to presumably refers to engines, avionics, and radar
304 SAUNDERS AND WISEMAN
which were not among the smuggled items). The engine is the only major subsystem
China has openly acknowledged it has yet to master, relying on the imported
Russian AL– 31F turbofan for both the J–11 and J–10 fighters.119 Shenyang Liming
Motor Corporation has produced a turbofan engine in the WS–10A Taihang
(likely the product of substantial reverse engineering) that approaches the performance
of the AL–31F, but takes twice as long to “spool up,” or obtain the same
thrust output, as its Russian counterpart.120 This lag time could have life or death
consequences for a pilot needing to restart his engine.
http://www.ndu.edu/press/lib/pdf/books/chinese-air-force.pdf
This PDF gives more information also its well worth a read