Chinese J-20 stealth fighter testing progresses

In January 2014, the third prototype of the Chengdu J-20 stealth fighter bearing serial number ‘2011’ was spotted undergoing testing in China. This aircraft features a number of significant changes from earlier prototypes, indicating that the design and development of the airframe is still being refined.

Most noticeably, the engine air intakes have been heavily reshaped and now feature prominent diverterless supersonic intake (DSI) ‘bumps’ on the inboard edge, making them very similar to the smaller Shenyang J-31, which itself mimics the intake configuration of the F-35 JSF. DSI designs are both lighter and less complex than conventional means of regulating airflow, such as intake ramps or inlet cones. As an added benefit, DSIs are stealthier than conventional variable intakes, although less so than stealth-optimised variable intakes such as those on the F-22 Raptor.

Another less prominent but arguably more significant change is the addition of an electro-optical targeting system (EOTS) under the nose. The EOTS provides capabilities in line with contemporary dedicated targeting pods and IRST sensors, but in a conformal (and stealthy) housing.

The canopy has received an embedded detonating cord for low-level/low-speed ejection and has also been internally braced, although it remains a single-piece bubble. Small intakes, likely for cooling, have been incorporated at base of each vertical fin and fairings for the wing-mounted control surface actuators have been made more compact.

The aircraft is reportedly still using a variant of the Russian AL-31 engine, as the Xian WS-15 afterburning turbofan is still not ready for integration with the airframe although it has been spotted being flight-tested on an Il-76 testbed operated by the China Flight Test Establishment (CFTE).

It is not entirely clear why the aircraft carries the serial number ‘2011.’ Considering the two preceding aircraft were ‘2001’ and ‘2002,’ the third aircraft should have carried the number ‘2003.’ However, a likely theory is that 2001 and 2002 belong to the first (0) batch of prototypes, whereas 2011 begins the next (1) batch. This second lot of prototypes incorporates design changes that have resulted from programme development as well as flight-testing results from the first batch.