Photos of advanced prototype posted amid speculation over imminent test

China is said to be planning the maiden flight soon of the upgraded version of the J-20 stealth fighter.

A number of photos recently taken by aviation enthusiasts at an unidentified base, and widely circulated on websites that follow the Chinese military, show a prototype of the twin-engine, fifth-generation aircraft with the serial code "2011" painted on both sides of the cockpit.

Active members on cjdby.net and fyjs.cn, the two most-visited sites that cover the Chinese military, said the first test flight of the prototype aircraft is imminent.

The flight is expected to take place in Chengdu, where the aircraft's developer, Chengdu Aircraft Industry Group, is headquartered.

An employee of the Aviation Industry Corp of China, parent company of the Chengdu industry group, speaking on Wednesday on condition of anonymity, said that he could neither confirm nor deny the rumors.

Recent media reports about China's military hardware testing have confirmed many of the rumors published by Chinese military enthusiasts. Many of the followers claim to have a great deal of knowledge about weapons, and sources with defense contractors.

The newest J-20 is the stealth fighter's third prototype since the aircraft's debut three years ago.

In January 2011, the J-20's first prototype made its maiden flight at an unidentified airfield in Chengdu. The 15- minute flight made China the third nation in the world to "develop and test-fly a full-size stealth combat aircraft prototype", after the United States and Russia, according to Western media outlets.

China launched its stealth fighter programs in the late 1990s. It is also developing a single-engine, radar-evading fifth-generation jet fighter called the J-31. That aircraft has undergone several test flights.

China reportedly conducted test flights of a second J-20 prototype in Chengdu in May 2012. Pictures of a J-20 prototype firing from its side weapons bays surfaced in March 2013. It's unclear which prototype was tested in March.

Chinese aviation enthusiasts said a series of improvements have been made to the stealth fighter. It reportedly has a new air intake design, shorter engine nozzles and a sensor technology that helps pilots detect and track enemy aircraft or missiles in every direction simultaneously.

An upcoming test would indicate that its engineers and designers have made remarkable strides to finalize the J-20 project, said Wang Ya'nan, deputy editor-in-chief at Aerospace Knowledge magazine.

"Most of the changes made to the third prototype seem to be about its aerodynamics," he said. "I think the upgraded version will have better avionics, stealth capability and stronger survivability in combat."

But Wang emphasized that it is too early to tell if the aircraft's design has been finalized, pointing out that the United States spent many years on its jet fighters and adopted numerous changes.

"China only has a short history of developing advanced aircraft. There is still a long road for us before our aircraft can compete with others," he said.

Frank Kendall, the US under-secretary of defense for acquisition, technology and logistics, recently told The Wall Street Journal that US defense officials "expect the Chinese to have export versions of the equipment that they have built".

Kendall said China is expected to put the J-20 into active military service in the next few years and added it could export the aircraft to other nations.