Imagery emerged on the Internet last weekend showing China’s latest stealth fighter in prototype form. With fifth-generation characteristics, it bears a distinct resemblance to the Lockheed Martin F-22A Raptor and F-35A/C Lightning II stealth fighter designs, and appears to be similar in size to the latter. Photos of the twin-engine aircraft on the ground at an unidentified airfield–possibly Xian-Yanliang airbase–were leaked the day before U.S. Secretary of Defense Leon Panetta started a three-day visit to Beijing. Could this be mere coincidence? China’s earlier stealth design, the Chengdu J-20, made its first flight just before former Defense Secretary Robert Gates visited China in January 2011.

Rumors of a stealthy, JSF-sized aircraft being developed by Shenyang Aircraft have been in circulation for some time. Models of such aircraft were displayed at an exhibition in Beijing last year. A few weeks ago, photos emerged of a tarpaulin-shrouded airframe being trucked from Shenyang by low-loader on public roads, fueling speculation that the fighter would be revealed imminently.

With these photos and some computer-generated imagery (CGI) also posted online, it is possible to make some general assessment of the aircraft, although there has been no official recognition of its existence, or any firm details for that matter. The designation J-21 was initially mooted, while the model display suggested that it was the F-60, although this is most likely the designation for any future export version. The airfield photos show an aircraft serial-numbered 31001, and it is therefore now assumed that the designation is J-31.

The J-31 is smaller than the Chengdu J-20, and would appear to complement it rather than compete with it. Unhampered by the need to provide a common airframe that could incorporate STOVL capability, the J-31 differs from the Lockheed Martin F-35 by having much longer and larger weapon bays and by being powered by twin engines. The CGI shows four hardpoints under each wing, with the inner two carrying heavy missiles. It also shows an arrestor hook deployed, suggesting carrier capability.

It has been assumed that the aircraft would be powered by the Guizhou WS13, and possibly in the future by a new-generation powerplant currently dubbed “WS-XX.” However, examination of the nozzles of the new aircraft suggests that, initially at least, it is powered by the Klimov RD93. This engine is a version of the MiG-29’s RD33 developed specifically to power the Chengdu JF-17 and has been supplied to China in some numbers for that production program. The inlet design is diverterless, a feature of the F-35 but not the F-22.