Possible "Initial Operational Capability" (IOC) for the J-20 Mighty Dragon may occur in the 2017-18 timeframe

In November and December 2014 two additional prototypes of the Chengdu Aircraft Corporation's (CAC) J-20 fifth-generation fighter emerged, advancing its development towards a possible initial operational capability (IOC) of 2017-18. The J-20 programme currently features six known prototypes. Two are early technology development articles (serial numbers 2001 and 2002) that emerged in 2009 and 2010, while four are modified versions closer to operational prototypes (serial numbers 2011, 2012, 2013, and 2015) that all emerged in 2014.

Chinese aircraft spotters responsible for early internet photos report that the latest J-20 prototype, 2015, made its maiden flight from the CAC airfield on 18 December. Source: Chinese internet

No prototype numbered 2014 has yet to appear and may not, given the traditional Chinese view that four is an unlucky number. Chinese aircraft spotters responsible for early internet photos report that the latest prototypes, 2013 and 2015, made their maiden flights from the CAC airfield on 29 November and 18 December 2014 respectively. Both have most of the refinements seen on aircraft 2011, which emerged in February 2014: cropped canards and vertical stabilisers, a modified air intake, modified wing leading-edge extensions, and a new electro-optical targeting system (EOTS) under the nose. 

A view of the latest J-20 prototype, 2015, which made its maiden flight from the CAC airfield on 18 December. (Chinese internet)

 However, 2013 and 2015 lack the nose-mounted pitot tubes that featured on the earlier prototypes. In addition, number 2015 has longer and sharper-shaped rear-fuselage horizontal strakes. Although this aft surface does not appear to be movable, it may contribute to aircraft stability, as a similar - though movable - surface did for the Grumman X-29 technology demonstrator.

A detail of the strakes on the latest J-20 prototype, 2015. (Chinese internet)

 Early internet-sourced images have also emerged of the J-20's retractable refueling probe, placed on the upper starboard of the nose. The development status of an indigenous Chinese turbofan for the J-20, often referred to as the WS-15, remains unknown. There is speculation that early J-20 examples may use a version of the Russian Saturn AL-31 turbofan.