And yet that could all be far away. There is a world of difference between, on the one hand, flying an aircraft that from the outside looks like a fighter and, on the other, building an operational combat aircraft. The F-35 will go into service almost 20 years after the first flight of its X-35 technology demonstrator. Similarly, Shenyang may so far have little more than a bare aircraft that an “export” customer would be expected to help fully develop, or at least fund, as Pakistan has with the JF-17.

Avionics immaturity may be the reason why the J-31 is an export-only aircraft, even though it seems well-sized as a successor to the Chinese air force's J-10 and as a cheaper, large-production complement to the J-20. The air force may well have decided that Chinese industry has enough of a challenge in improving the J-10 and integrating systems for the J-20. But yet another possibility is that Shenyang or Chengdu is cooking up something more advanced than the J-31. With no clear answer, that probably remains the key mystery about the J-31: Why does the Chinese military not want it?

Reviewing the J-31's configuration, it appears that the designers have aimed for an aircraft that has stealth but also conventional fighter versatility, and they are not trying to achieve supersonic flight without afterburning, as the F-22 does. The choice of a quad aft-tail arrangement—two horizontal and two vertical stabilizers—indicates the designers wanted to combine low radar reflectivity with high angles of attack and therefore easier handling in combat, which that would have been hard to do with a canard configuration.

The aft-tail layout also puts hard points close to the center of gravity, probably making the carriage of stores easier and thereby promoting versatility. Photographs of the aircraft at an airfield in September revealed the doors of a large ventral weapons bay.

The model has only moderate sweep on the leading edge of the J-31's wing. To minimize radar reflections, air inlets for the engines have no boundary-layer diverter plates. The nose volume is not large, leaving room for only a modestly sized radar antenna.

For all its habitual secretiveness, the Chinese military displayed two recent attack helicopters at Zhuhai for the first time. One of these was the Z-10 (or WZ-10), which Chinese media suggest is sized between the Eurocopter Tiger and Boeing AH-64 Apache. It is a product of the Changhe works of Avic rotary-wing specialist Avicopter.

The other was the Z-19, an adaptation of the Z-9 and, ultimately, Eurocopter AS352 Dauphin, but with a new fuselage and tandem seating. As a Dauphin derivative, the aircraft should have a gross weight of 4-5 tons, making it somewhat smaller than the Z-10. Harbin Aircraft, also part of Avicopter, builds the Dauphin derivative. It did so originally under a license that Eurocopter says has expired.

Both attack helicopters are powered by Chinese engines, says Avic. The Z-10, at least, has reportedly been fitted with foreign engines during development.

Harbin has also developed an attack version of the Z-9 that retained the bulky cabin of the original utility helicopter. The Chinese army allowed rare close inspection of a recent version, the Z-9WZ in July.

Bradley Perrett, Robert Hewson and Reuben Johnson Zhuhai, China and Bill Sweetman London