By Taylor Marvin
Last Thursday images and video surfaced online showing a test flight of China’s second stealth fighter aircraft, the Shenyang J-31. This is a significant achievement for Chinese military aviation, though it is unclear if the design will ever enter service or whether it is designed to complement or compete with China’s other stealthy design, the Chengdu J-20. Also unclear is how original the aircraft actually is: there has been widespread speculation that the J-31’s design — which is visually similar to Lockheed Martin’s F-22 and F-35 aircraft — is partially a product of knowledge stolen
At The Diplomat, Trefor Moss speculates that the J-31 is a wholesale copy of the F-35 Joint Strike Fighter, built from stolen Lockheed Martin blueprints. Moss goes so far as to term the J-31 as “essentially an American stealth fighter with Chinese paintwork”, and furiously argues that lax computer security has allowed the PRC to secure a stealth fighter for much less than America:
“Speculation aside, the reality is that the F-35 program is presently slated to cost $395.7 billion. China has probably spent less than 0.1% of that developing the Fake-35. Ladies and gentlemen, you’re looking at the biggest free ride in the history of national security.”
I don’t buy it. China certainly has taken advantage of lax US information security, but Moss underestimates just how difficult it is to simply copy an advanced aircraft design. While the J-31 is certainly visually similar to Lockheed Martin 5th generation fighters, consider the necessary differences between it and the F-22 and F-35: different engines, an entirely different structural layout from the single-engined, STOVL-benchmarked F-35 family, and differing internal systems. These changes are not trivial. Even if Shenyang engineers possessed detailed LockMart blueprints they wouldn’t be of much practical value when it comes to designing the J-31 — while a valuable benchmark, there are simply too many different major systems. As Feng recently wrote at Information Dissemination, “it’s very hard for me to believe that SAC can reproduce F-35 from stolen files without access to the same engines or the material or the complicated computer code that controls the whole aircraft.”
Convergent evolution often leads competing air forces towards visually similar aircraft created for the same mission. Take the F-111 and Su-24, for example. Both low-level strike aircraft, introduced in the late 1960s and early 1970s, respectively, look remarkably similar: both possess variable geometry (swing) wings, a tall single tailfin, and a side-by-side cockpit, rare for a tactical aircraft.
The two aircrafts’ striking visual similarities led contemporary American observers to conclude that the Soviets had copied the F-111. Amusingly, as Greg Goebel notes in his excellent history of the Su-24, some Americans went so far as to be pleasantly surprised that the Soviets had tried to copy the then-notoriously troubled F-111 — if the US struggled to get the F-111 flying right, then surely the Soviets would as well. But while Soviet designers may have mined the F-111 for ideas, there’s little evidence any real copying was involved. Instead, given that both American and Soviet engineers were working with similar technologies towards the same goal, it isn’t surprising that they both landed on similar designs — just as American and Chinese engineers can be expected to do. Indeed, what was most surprising about the J-20 was how obviously different it is from anything in the American aircraft inventory.
However, there is reason to suggest that there’s more than simple convergent evolution behind the J-31’s external similarities to American 5th generation aircraft. An aircraft’s stealth is partially determined by the shape of the fuselage, was well as the surface coatings that absorb and diffuse radar waves. While China cannot know the details of American stealth coatings through anything but espionage, the low observability fuselage shapes of the F-22 and F-35 are obvious. Copying these elements — the F-22’s empennage, the F-35’s intakes — is an effective way to get some degree of stealth for less technically sophisticated developers. Given that the US has a two decades head start developing low observability aircraft, this is a smart trade for Shenyang engineers.
Does the J-31 owe aspects of its external fuselage to the F-22 and F-35: undoubtably. But this is far from saying that the J-31 is a naked copy of American aircraft. China still has a long way to go before a production aircraft derived from the J-31 enters service, if one does at all. That gives ample opportunity for delays and cost increases to pile up, degrading whatever lead the program has over the JSF, which it isn’t strictly comparable to anyway. The F-35’s STOVL benchmarked design makes it unique, and is reason enough to dismiss the idea that the J-31 is a cheap knockoff of the JSF. The J-31 will be a more affordable aircraft than the notoriously ill-conceived F-35, but that doesn’t automatically make it the deal Moss implies.