There are still many many questions about this bird not the least of all: what... or whose... engine are they using?
By way of comparison… The F-35A is rated a 31 ton, single engine fighter that is 15.7 meters (51.4 feet) long and with a 10.7 meter (35 foot) wingspan. The engine generates 12.7 ton (28,000 pounds) of thrust, or 19.5 (43,000) with afterburner.
The F-22 Raptor is rate at 21 tons that is 18.90 meters (62 ft 1 in feet) long and with a 13.56 meter (44 ft 6 in) wingspan. Its dual afterburning Pratt & Whitney F119-PW-100 turbofans incorporate pitch axis thrust vectoring, with a range of ±20 degrees. The maximum thrust is classified, though most sources place it at about 35,000 lbf (156 kN) per engine.Maximum speed, without external weapons, is estimated to be Mach 1.82 in supercruise mode
In contrast, the J-20 has two engines and appears to be 24 meters (75 feet) long and with a wingspan of 15 meters (46 feet). The engine for the J-20, the WS-15 is still in development. The prototype had afterburner thrust of 16.5 tons, although this was expected to hit 18.3 tons when development was complete. It is believed that the J-20 prototypes are powered by Russia AL31FU/117S engines, each with 14.5 tons of afterburner thrust. Two of these engines would give the 36-40 ton J-20 more power per ton than the F-35A.
China has yet to develop other F-35 technologies, like the AESA radar, highly efficient cockpit, stealth and software to tie everything together. Developing, or even copying, this tech is not easy. But the Chinese already know that, having decades of adapting stolen technology to their needs. Thus it appears that China is planning on having the J-20 ready for service by the end of the decade… 2018 or so. The key factor is their ability to develop or steal the needed technology by then. The J-20 appears to be less than an F-35 clone, and more of an F-35 type aircraft with pretensions to being an F-22. In any event, the J-20 is an attempt to develop some kind of 5th generation aircraft, complete with stealth.
Assume this bird flies… assume it is flight worthy now… today. They claim that they won’t be operational till 2018. Assume it’s really 2015.
We have 122 F-22s in service NOW… by 2015 we’ll likely have nex-gen (A, B, C variants) in service. Head to head… there would be no match… the F-22 would take it. The problem seen (by the Rand Corp among others) is getting the F-22 to the battle space. Logistics again will rule the day.
For those of you that don’t know…. The "first generation" jet fighters were those produced during World War II and through the late 1940s. The best examples of these are the U.S. F-86 and the Russian MiG-15. The second generation got going in the early 1950s, and produced aircraft like the U.S. F-104 and the Russian MiG-21. The third generation followed within a decade, producing the U.S. F-4 and the Russian MiG-23. The fourth generation arrived in the 1970s and 80s with the F-15, F-16, F-18, Russian MiG-29, Su-27 and French Mirage-2000. The fifth generation includes the F-22, F-35, and whatever the Russians and Chinese come up with. The Eurofighter and Rafale are often called Generation 4.5.
Russian fifth generation fighter developments were halted when the Soviet Union disintegrated in 1991. Actually, all development work on new fighters, by everyone, slowed down in the 1990s. But work on the F-22, F-35, Eurofighter and Rafale continued, and those aircraft became, in roughly that order, the most advanced fighter aircraft available today. This fifth generation may come to be called the "last generation," after they are replaced by the second generation of pilotless combat aircraft (counting armed Predators and the like as the first).