The J-31 on its debut flight. Photo: via China Defense Mashup

China’s newest stealth fighter prototype reportedly took off on its first test flight over the Shenyang Aircraft Company airfield in northeastern China on Wednesday morning. The 10-minute aerial debut of the twin-engine Falcon Eagle represents a huge leap forward for China’s ambitious stealth warplane program.

But more than a month after the Falcon Eagle first appeared in blurry photos apparently shot and posted online by Beijing’s army of sympathetic bloggers, there are still more questions than answers about China’s second stealth fighter model.

Is the Falcon Eagle, apparently designated J-31 and not J-21 as we originally reported, a competitor to the larger J-20 stealth prototype that first flew in January 2011? Or is the newer plane meant to complement the J-20, the third copy of which recently appeared outside the Chengdu Aircraft Industry Corporation factory in southwest China?

Is the J-31 destined to operate off of China’s first aircraft carrier, the Liaoning, which has been undergoing testing near the port of Dalian since July 2011 but has yet to launch or land a fixed-wing plane? Or is the new fighter strictly land-based?

We don’t know. Nor do we know the state of the Falcon Eagle’s engine, avionics and weapons development. The origins of the fighter are equally murky, although superficial similarities to the U.S. F-22 and F-35 have fueled speculation in the West that Beijing based the J-31′s design on blueprints reportedly stolen from the servers of at least six American aerospace subcontractors in 2009.

In any event, China is now testing two separate stealth warplane designs, placing the rising Asian power just behind the U.S., which has three F-35 stealth models in development, and ahead of Russia with its 3-year-old T-50 and Japan with the ATD-X stealth demonstrator still being assembled.

Fortunately for Washington, the acceleration of Beijing’s stealth program comes just as the U.S. Air Force is restoring its beleaguered F-22s to full service amid problems with their oxygen systems — and as the delayed, over-budget and technically troubled F-35 is finally showing some testing progress. In recent weeks the F-35 has refueled mid-air, released a missile and flown at night with its finicky helmet sight.

If the J-20 and China’s other new warplanes are any indication, the J-31′s flight testing will ramp up slowly over a period of years. In time, additional copies of the new plane will join the test program. When the J-31 might enter frontline service is anyone’s guess.

Of course, the same can be said of the U.S. F-35 and every other stealth fighter in development.