The Hong Kong-based South China Morning Post reported on Monday that a new model of China’s Chengdu J-20 stealth fighter, the J-20B, is entering “mass production” with sophisticated new thrust-vector controls that significantly enhance maneuverability so as to “meet the original criteria.”
According to an anonymous source cited by defense journalist Minnie Chan, commencement of production was celebrated in a ceremony on July 8 attended by the vice-chairman of China’s Central Military Commission.
The twin-engine J-20A “Mighty Dragon” entered service in 2017, and today remains the only operational stealth jet designed outside the United States. Around 50 are believed to have been built so far.
However, the Post reports the J-20B will continue to rely on Saturn AL-31F M2 turbofans imported from Russia rather than higher-thrust domestic WS-15 engines China is still struggling to refine for production.
Tilting Nozzles, Supermaneuverable Jets
Chengdu Aviation Corporation has reportedly set up four production lines each capable of producing one J-20B per month, and the Chinese military is supposedly sufficiently satisfied with the model’s refinements to place a large order. However, Chan’s article details only one major new technology.
Thrust Vector Control (TVC) allows a pilot to tilt the exhaust nozzles of a jet engine to redirect thrust, allowing aircraft like the F-22 Raptor and Russia Su-35S Flanker to perform jaw-dropping maneuvers at very high angles of attack, meaning the aircraft’s nose is pointed at an angle greatly exceeding the plane’s current vector.
Such maneuvers may grant a pilot an edge when evading a missile or seeking an advantageous position in within-visual-range air-to-air combat.
However, many cutting-edge jet fighters do not use thrust-vector engines. For one, maneuvers leveraging thrust-vectoring drain an aircraft’s energy very rapidly, leaving it in a low-energy state vulnerable to follow-on attacks. This was allegedly a downside exploited by U.S. F-15 jets in a Red Flag exercise against thrust-vectoring Indian Air Force Su-30MKI jets in 2008.
Furthermore, U.S. air combat doctrine emphasizes maintaining a high-energy state, and executing stealthy, beyond-visual range missile attacks.
Therefore, Western designers have mostly deemed the added weight and complexity of thrust-vector controls to not be worth the added cost outside of the pricey air-to-air specialized F-22 Raptor, or jump jets like the Harrier or F-35B Lightning, which primarily exploit thrust-vectoring for short or vertical takeoff-and-landing capability.
However, thrust vectoring controls are common in modern Russian jet fighters.
Interceptor or Air Superiority Fighter?
If true, the decision to install thrust-vectoring on the J-20B hints at the intended role of the Chinese stealth fighter.
Initially, Western analysis of the J-20 estimated that it was a fast and hard-hitting—but not highly maneuverable—interceptor or strike fighter optimized for hit-and-run attacks rather than an air-superiority fighter designed to engage enemy fighters while performing tight air combat maneuvers.
Chan’s article notes Western reports of the J-20A’s ‘lack of maneuverability’—although whether the PLAAF concurred with that assessment is unclear.
This limited concept of the J-20’s intended role and capabilities has received push-back in recent years from some analysts which now seems merited.
In December 2016, China struck a deal to import 24 Su-35S fighters—an order widely speculated to be primarily aimed at procuring the thrust-vector-capable Russian jets for study by Chinese technicians.
Then in 2018, a J-10C fighter outfitted with thrust-vectoring controls was showcased at the Zhuhai airshow, revealing Chinese development of the technology.
The Post’s report that the J-20B will use thrust-vectoring controls, if accurate, indicates the PLAAF does want to enhance the maneuverability of the J-20. That in turns implies intent for the J-20 to perform in a traditional air superiority role of engaging and defeating agile enemy fighters.
To be clear, low-observability on radar and long-range missiles and sensors would likely remain the J-20’s primary asset in air-to-air combat. However, an air superiority fighters ideally need to be able to hold its own within visual range, particularly if pitted against advanced fighters capable of eluding long-range sensors and/or missiles.
China’s Engine Woes
Unfortunately for the PLAAF, an arguably more important puzzle piece to unlocking the J-20’s intended performance remains stubbornly out of reach according to Chan’s article: a domestically built WS-15 turbofan engine capable of generating 44,000 pounds of thrust. The AL-31F M2 engine currently in use generate 32,600 pounds of thrust.
Refining the WS-15 will finally make it possible for the J-20 to improve its currently subpar thrust-to-weight ratio. It could also eventually free Chinese manufacturers from their dependence on Russian-built jet engines.
Severe quality-control issues have dogged China’s attempts to mass-produce domestic Shenyang WS-10 Taihang turbofans for years, leading to their frequent substitution with Russian engines. The Xian WS-15 Emei turbofan will necessarily need to overcome these problems while pushing the performance envelope further.
Chan’s source claims WS-15 development is progressing “quite smoothly” and that it may be ready in “one or two years,” at which points the J-20B would be able to swap WS-15s in place of AL-31 engines. However, such estimates have been wrong before, and it is surely disappointing for the PLAAF that the second production model of the J-20 fighter must enter service still using lower thrust stop-gap engines.
To be fair, Russia too is using a stop-gap turbofan engine on its troubled Su-57 stealth jets until a higher thrust model is ready later in the 2020s.
These issues aside, the reports of the J-20B model suggests the continued maturation of the J-20 platform, and add to the evidence that it is intended serve as a air superiority fighter capable of holding its own against agile enemy fighters.
This in turn could imply new challenges to the air superiority doctrine of countries like India, Japan and the United States competing with China in the Indo-Pacific.