The J-31 is known to come from Shenyang because the company displayed a flyable model of a similar fighter last year with the designation F-60 and because a wrapped object that was presumably the real aircraft was trucked in June from Shenyang to Xian, where China has a flight-test center.
The designation “J-31” may be no more valid than the widely assumed but unconfirmed moniker “J-20” applied to a larger fighter from the Chengdu fighter works. The Shenyang aircraft is also sometimes called J-21—again, without any certain validity. The J-20 was revealed in late 2010 and appears to have made its first flight in January 2011. It was not promoted at Zhuhai.
And therein lies a key piece of evidence of the status of the J-31. The J-20 was not at Zhuhai because it is not for sale and because China does not want to reveal too much about it. It is intended for the Chinese air force.
Conversely, because the J-31 was exhibited at Zhuhai and is promoted as an export product, the Chinese air force obviously does not want it. Early production of a fighter intended for Chinese service would be reserved for the air force, as has been Chengdu's J-10, the current Chinese medium-weight fighter.
Why, then, has Shenyang developed it? There are a few possibilities. It could be a technology demonstrator funded by the military, one that the company's management thinks has good potential for full development as an operational fighter.
Alternatively, it could be an internally funded program for the export market, as the company seems to suggest, encouraged by the knowledge that not all countries have access to Western fighters. The J-31 would mainly be a competitor to Russian fighters—though Shenyang might also be calculating that buyers of Western equipment will want more choice as some U.S. and European types go out of production over the next decade or two. Importantly, the Chinese fighter should be cheap, as the JF-17 is, while offering at least the prestige of stealth technology.
Shenyang is working on China's ship-borne fighters, raising the possibility that the J-31 was at one time intended for the newly commissioned aircraft carrier Liaoning and its successors. If so, it probably is not now destined for such service, since the navy, like the air force, would not want to exhibit an aircraft that it intended to operate.
The difference in the sizes between the J-20 and J-31 indicates that they have probably not been designed for the same requirement. Moreover, Avic makes no mention of any domestic use for the aircraft.
A foreign aerospace executive with insight into Shenyang and the wider Chinese industry has perhaps the simplest explanation for the J-31's existence: “This is the program of a company that has more engineers than it knows what to do with.”
While a prototype or technology demonstrator is flying, a key question is whether much progress has been made in developing low-observability features that are easily maintained and do not encumber the aircraft with much weight. An even greater challenge for Shenyang and its suppliers to overcome is fitting the aircraft with electronic systems that merge the inputs from various sensors to give the pilot situational awareness. Avic's statement that the aircraft will offer capability “almost equivalent” to the latest U.S. fighter suggests that it aims to go some way in that direction.