Thus, certain more aggressive projections of J-20 performance, such as a top speed of Mach 2.5, may be premised on engines that have yet to be fully developed.
In January 2011, the maiden flight of a large, dagger-like grey jet announced that China had developed its first stealth aircraft—the Chengdu J-20 “Mighty Dragon.” Six years later, after several substantial revisions, J-20s entered operational service with the People’s Liberation Army (PLA) Air Force.
(This first appeared several months ago.)
As radar-guided missiles from fighters and ground-based launchers threaten aircraft from dozens, or even hundreds of miles away, stealth capabilities are increasingly perceived as necessary for keeping fighter pilots alive on the modern battlefield.
But just how good is the J-20? And what is its intended role? After all, America’s first stealth fighter, the F-117 Nighthawk, was not even really a fighter and lacked any air-to-air capability whatsoever.
The PLA has, true to custom, kept its cards close to the chest, and has not shared performance specifications to the public. Thus, there are broad estimates of the J-20’s top speed (around Mach 2), and considerable-seeming range (1,200 to 2,000 miles), but those remain just that—estimates. For years, analysts even over-estimated the aircraft’s length by two meters. It’s broad but relatively shallow weapons bay can accommodate four to six long-range missiles or bombs, though not munitions with especially heavy warheads.
International observers generally concluded the large twin-engine jet possessed high speed and long operational range, but that the Mighty Dragon lacked the maneuverability necessary to prevail in close engagements with enemy fighters. Relatively modest aerobatic displays in the Zhuhai 2016 and 2018 airshows (you can see some of the latter here) reinforced the narrative in certain quarters that the J-20 isn’t optimized for gut-wrenching air combat maneuvers.
Given the above premises, observers mostly speculate the J-20 would either serve as long-range supersonic strike plane, or a hit-and-run interceptor used to slip past fighter screens and take out vulnerable supporting tanker and AWACS planes.
However, Rick Joe of The Diplomat argues these theories of the J-20’s supposedly specialized role might be a case of group-think, ignoring both design features and statements by Chinese sources suggesting the J-20 was intended as a multi-role fighter with “competitive” dogfighting capability.
For example, a brochure distributed at Zhuhai 2018 explicitly stated the J-20 was capable of “seizing & maintain air superiority, medium & long range interception, escort and deep strike.” In other words, a multi-role fighter.
“A commonly insinuated premise is that the Chinese aerospace industry was not capable of producing a fifth generation air superiority fighter, and would have to “settle” for a less technically challenging interceptor or striker instead,” Joe argues.
He points out that the lengthy J-20 is still shorter than the Russian Su-35 Flanker-E, one of the most maneuverable jet fighters ever designed. He further cites a 2001 study by Song Wecong, mentor of the J-20 designer Yang Wei, which you can read translated here. Wecong wrote that stealth aircraft “must have the capability to supercruise and perform unconventional maneuvers such as post-stall maneuvers.”
Song concluded the ideal stealth fighter would incorporate canards (a second, small set of wings close to the nose of the plane), leading-edge root extensions (or “strakes,” a thin surface extending where the wing emerges from the fuselages), and S-shaped belly intakes, in order to balance stealth, speed and maneuverability. These are all design characteristics evident in the J-20.
While details on the J-20’s radar remains elusive (presumably a low-probability of intercept AESA radar), it also mounts arrays of electro-optical and infrared sensors with 360-degree coverage, reportedly designed to fuse sensor data to form a common “picture” and even share it with friendly forces via a datalink—technology seemingly modeled on the advanced sensors found on the American F-35. Such sensors could be particularly useful for detecting radar-eluding stealth aircraft.
J-20 pilots also are equipped with helmet-mounted sights that allow them to target high-off-boresight PL-10E heat-seeking missiles within a 90-degree angle of the plane’s nose simply by looking at the target. The short-range missiles are stored in small side-bays but can be cunningly rotated outside prior to launch, as depicted here.
These by no means unprecedented capabilities nonetheless suggest that the J-20 may be designed to hold its own in a close-range encounter, not just sling long-range hypersonic PL-15 missiles from its fuselage bay from dozens of miles away. Particularly when engaging agile fighters, short-range missiles (which might still threaten targets over a dozen miles away) have a much higher probability of a kill—by some estimates, up to 80 percent.
Chinese designers have also expressed interest in incorporating vector-thrust engines in the J-20. These have moving exhaust nozzles to assist in pulling off tight maneuvers. The PLAAF recently acquired Su-35 fighters from Russia with vector-thrust engines, and also reportedly tested domestic vector-thrust turbofans on a J-10B two-seat fighter.
Despite the awesome maneuvers enabled by vector-thrust engines, they are far from being automatically included in modern fighters. This is because they significantly add to weight, cost, and difficulty in minimizing radar cross section (RCS). Moreover, when vector-thrust engines are over-used in combat, they can bleed off energy rapidly, leaving the aircraft sluggish and vulnerable to enemy fighters (as occurred in one exercise in Nevada pitting U.S. F-15s against Indian Air Force Flankers). For this reason, few Western fighters incorporate vector-thrust technology, the F-22 being a notable exception. China’s interest in thrust-vectoring again suggests it sees relevance in agility.
The J-20’s short-range capabilities naturally lead to the question—what exactly happens when two stealth fighters clash? If their stealth qualities are robust, both aircraft may only be able to detect each other within 50 miles or less—at which point air combat maneuvers could prove important. As U.S. stealth aircraft are one of the chief military threats to China, it seems reasonable to assume the J-20 would be designed to have a fighting chance against them.
While the J-20 would likely remain outclassed by the F-22, it could potentially prove a dangerous adversary to the F-35, which is not as optimized for within-visual-range engagements. However, both the F-22 and F-35 are believed to have a significantly lower all-around RCS than the J-20, though the Chinese fighter still appears to be significantly stealthier than the Russian Su-57.
A 2011 analysis by Australian aviation expert Carlo Kopp concluded that J-20 probably had strong stealth from a frontal aspect, but a larger radar cross section (RCS) when scanned from the side or rear—a limitation also found in the Russian Su-57 stealth fighter.
But as the extent and type of the radar-absorbent materials used affect RCS, visual analysis alone cannot determine how stealthy an aircraft is. This has not dissuaded the U.S. Marine Corps from a building a full-scale mock-up of a J-20 in Georgia for study and training purposes. The Indian Air Force has boasted its Su-30 Flankers have tracked J-20s on radar, but as stealth fighters often employ emitters called “Luneburg Lens” to enlarge their RCS on routine flights, and thus conceal their true capabilities, it’s difficult to infer much from this either.
Another issue confusing analysis of the J-20 is that it doesn’t yet have the high-thrust WS-15 turbofans the PLAAF envisioned for them, and are making do with Russian AL-31F engines instead. Even China’s fourth-generation jets have been frustrated by deficient jet engines. The WS-15 generates 23 percent more thrust than the AL-31FN, and would enable the J-20 to super-cruise, or sustain supersonic speeds without resorting to fuel-gulping afterburners. Thus, certain more aggressive projections of J-20 performance, such as a top speed of Mach 2.5, may be premised on engines that have yet to be fully developed.
As long as the PLAAF has only a few dozen J-20s in service, it may make sense to reserve them for hit-and-run tactics and special deep strikes. But as the article in the Diplomat points out, there’s ample evidence the J-20 may be intended to grow into a capable all-rounder that can hold its own in a dogfight.
Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring.