The WS-15 engine is finally expected to be operational in 2025. This marks a turning point for China’s J-20, with supercruise, increased stealth, and reliability issues.
Summary
For more than a decade, China’s J-20 has suffered from a persistent suspicion: that of a fifth-generation fighter jet hampered by an unsuitable engine. Using Russian AL-31 engines and then improved WS-10 engines, the aircraft failed to meet the expected standards in terms of thrust, supercruise, and thermal management. In 2025, several corroborating sources indicate that the WS-15, a domestic engine developed by China, will finally enter operational service. If this information is confirmed, it marks a major strategic shift. The WS-15 does not only represent a gain in performance. It determines infrared stealth, range, long-range air combat capability, and Chinese industrial credibility. The debate now focuses less on the engine’s existence than on its actual reliability, a parameter that remains unclear but is central to assessing the J-20’s true value.
The J-20’s long-standing engine handicap
An advanced aircraft penalized by its propulsion
Since its public debut in the early 2010s, the Chengdu J-20 has been presented as a direct competitor to the Western F-22 and F-35. Its stealth airframe, carefully designed air intakes, internal fuel tanks, and modern avionics placed China in the select circle of powers capable of producing a fifth-generation fighter. However, one element was missing: the engine.
The first production J-20s were equipped with Russian AL-31F and then AL-31FN engines, originally designed for the Su-27. These engines provide approximately 123 kilonewtons of thrust with afterburners (approximately 12.5 tons), which is insufficient to fully exploit a heavy aircraft estimated to weigh more than 25 tons at maximum mass. Above all, they do not allow for supercruise, i.e., supersonic flight without afterburners.
China then introduced the WS-10, a domestic engine conceptually derived from the AL-31. Despite gradual improvements, this engine has long lagged behind in two critical areas: turbine blade life and high-temperature stability. These limitations have fueled recurring criticism that the J-20 was advanced on paper but incomplete in reality.
The WS-15, a strategic program under intense pressure
A decade of difficult development
The WS-15 is no ordinary engine. It is the first Chinese turbojet engine designed from the outset for a fifth-generation fighter jet. Its stated objective is clear: to deliver more than 180 kilonewtons of thrust with afterburner (approximately 18 tons), while maintaining sufficient dry thrust for supercruise.
However, its development has been chaotic. Several test incidents were reported indirectly during the 2010s, including turbine failures and material problems. The main difficulty lies in metallurgy. Producing single-crystal blades capable of withstanding temperatures above 1,600 degrees Celsius is a challenge that only a few countries have fully mastered.
China has had to catch up with decades of Western advances in thermal coatings, manufacturing precision, and quality control. This delay explains why the WS-15 was announced long ago, then postponed. The silence surrounding the program was not insignificant: a public failure would have dealt a severe blow to China’s technological credibility.
Entry into service in 2025: what we really know
Converging clues but few official confirmations
In 2025, several reports from open sources, satellite analysis, and indirect statements suggest that J-20s equipped with the WS-15 are now operating within certain PLAAF units. Images show aircraft without the visual signatures typical of previous engines, particularly at the nozzles.
No detailed official announcement has been made, fueling speculation. This silence is consistent with Chinese doctrine: the integration of a strategic engine is only confirmed once its capability is deemed stable. Nevertheless, it is accepted that the WS-15 is at least in initial operational capability, which is already a significant milestone.
Caution is needed. Entry into service does not mean complete maturity. The first series may be limited in lifespan or reserved for specific use cases. But the mere fact that the Chinese Air Force has agreed to use them indicates that the engine has passed a critical milestone.
Supercruise, a major tactical change
Why this capability transforms the J-20
Supercruise is often presented as a luxury. In reality, it is an efficiency multiplier. Flying at Mach 1.3 or Mach 1.5 without afterburners drastically reduces fuel consumption and thermal signature. An afterburner engine generates extremely high temperatures, which are easily detectable by modern infrared sensors at distances of tens or even hundreds of kilometers.
With the WS-15, the J-20 could maintain extended supersonic speed while remaining undetected. This improves penetration into monitored areas, increases the effective range of air-to-air missiles, and reduces exposure time to enemy defenses.
By comparison, the F-22 is capable of supercruise at around Mach 1.8 depending on the profile. If the J-20 can even reach a stable Mach 1.3, the operational impact is significant. This allows it to control the initiative in combat, choose when and where to engage, and withdraw more quickly.
Infrared signature and overall stealth
The engine as a key factor in stealth
Stealth is not limited to the shape of the airframe. The engine is a key element of the infrared signature. Outlet temperatures, hot flow management, and nozzle design directly influence detectability.
The WS-15 is supposed to incorporate better thermal management, with materials capable of operating at higher internal temperatures while reducing the heat emitted at the rear. Combined with optimized nozzles, this makes detection by enemy IRST systems more difficult.
In an environment where low-frequency radars are advancing, infrared is becoming an increasingly critical sensor. Reducing this signature gives the J-20 a tangible advantage in beyond-visual-range combat, especially against adversaries with advanced passive sensors.
The central question of reliability
Chengdu’s best-kept secret
All of the WS-15’s theoretical performance is based on one condition: reliability. A powerful but fragile engine is a handicap. The time between overhauls, resistance to speed variations, and tolerance to foreign objects determine the actual availability of the fleet.
On this point, information is virtually non-existent. This is deliberate. China has every interest in concealing any initial limitations. Historically, the first batches of Chinese-made engines have often suffered from shorter lifespans than their Western counterparts, sometimes less than 1,000 hours before major overhaul.
If the WS-15 achieves standards comparable to modern Western engines, i.e., several thousand hours with controlled maintenance, then the J-20’s status will change. Otherwise, the aircraft will remain high-performing but costly to operate, with a direct impact on the number of aircraft actually available in times of crisis.
Strategic implications for China
Enhanced industrial and military credibility
The entry into service of the WS-15 goes far beyond the J-20. It means that China now masters one of the most complex industrial segments in the world. The engine is the heart of the aircraft, and historically, this is where emerging powers have failed.
Militarily, this strengthens the credibility of China’s air deterrence. A fully operational J-20, capable of supercruise and low thermal signature, complicates adversarial planning in the Asia-Pacific. It forces greater investment in passive detection, space surveillance, and rapid response capabilities.
Industrially, it paves the way for derivatives. The WS-15 could serve as the basis for other programs, including next-generation aircraft or heavy, high-performance drones.
What the WS-15 really reveals
The debate surrounding the WS-15 is not just technical. It reveals a simple strategic reality: China has understood that military credibility requires complete mastery of the technological chain. For years, the J-20 was seen as a promising but incomplete aircraft. If the WS-15 delivers on its promises, this view will have to be revised.
Caution remains the order of the day. The performance figures must be confirmed over time. But one thing is certain: the engine is no longer the obvious weak link in the J-20. And in the field of modern air combat, this detail changes much more than it seems.
Sources
Reports from the International Institute for Strategic Studies
SIPRI analyses of the Chinese aerospace industry
Specialized publications on military aircraft propulsion
Public statements and communications from the PLAAF
Comparative studies on supercruise and infrared signature
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