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China's Stealth Fighter Flies, But Does It Work By Ripping Off U.S. Tech?


China's now test-flying its new J-20 stealth fighter, coincidental with a visit to the nation by Defense Secretary Robert Gates. But exactly how does the Chinese aircraft stealth tech work?

Unlike the U.S.'s vintage SR-71, world's first stealthy aircraft the F-117 and the hugely impressive B-2, all developed under the utmost secrecy, the J-20 is having a particularly open development process (even more unusual when you consider China's normal habitual secrecy). Last week it was having taxi tests, and now it looks like it's flown for the first time:

You can bet your bottom dollar that American, European, Japanese, Russian, and who-knows-else security services have been training every space-borne radar, infra-red, and optical imaging system they can on the flight test zone, trying to learn how well the J-20 works.

But if you too are curious about how its stealth tech may (or may not) function, and how it compares to the F-22 Raptor, then read on. You'll be surprised, or possibly not, by how similar the aircraft are.

No flat surfaces

Flat surfaces are very good at reflecting radar—if you're using a dish far away to look at lots of flat surfaces, then lots of radar waves get sent back to you and you can tell where the target is. The original F-117 used lots of flat surfaces in its design, but each was carefully arranged so that the radar waves were bounced off in different directions. The new F-22 (like the B-2) avoids large flat surfaces, and uses a more aerodynamic shape, where blended curved surfaces bounce radar off harmlessly in directions away from the detecting dish. The J-20 looks like it uses very similar thinking—and the nose of the aircraft looks very familiar indeed.

Doors, edges

Doors, hatches, edges and even the cockpit edge on the F-117, B-2 and F-22 have complex "notches" cut into them, so that when they're open or closed there are no big give-away seams or straight edges that reflect radar well—similar to the avoidance of large flat structures on the plane. The J-20 seems not to incorporate this tech. But it is an early prototype.

Canted tail fins

A technique used on the SR-71 and F-117 to hide the large flat surfaces of the aircraft tails (vital for aerodynamics, control and combat maneuverability) was to cant them at an odd angle so that they don't reflect radar in directions that would give away the aircraft. The J-20 does this trick too.

Angular air intakes

The air intakes on the F-117 and B-2 are carefully shielded since their large scoop-like shape tends to create what radar scientists call corner reflectors—shapes that can reflect radar much more strongly than a flat plane. Hiding the air intake in the structure works to obscure it from enemy radar, but the F-22 uses a more advanced trick where the intakes are, like the tail fins, arranged at peculiar angles that avoid forming corner reflectors. The J-20's intakes look a lot like the F-22's.

Radar-absorbent materials

Metal is better at sending back radar waves than carbon fiber, plastic or fiberglass. That's why the F-117, B-2 and F-22 (and the European Typhoon) are made of large amounts of composite materials. As well as making them structurally strong, this lowers their radar signature—and can even affect its infra-red signature too. We have no idea what the J-20 is made of, but some of the larger box-like shapes of its body, and its all-moving tails (which need super-strength) make us think it's also made of advanced materials.

Infra-red signature, super-cruise engines

The F-117 and B-2 hid their engine exhaust from infra-red sensors (on missiles and other surveillance systems) by venting the jet plume through louvers and over the body of the aircraft. The F-22 can't do this trick, as its more powerful supersonic-capable engines make the effect harder. Instead it uses a slightly masked exhausts, and a technique called supercruise, which means it can break the sound barrier without needing the infra-red give away of reheat. This lowers its infra red signature a lot. The J-20 has been spotted running a couple of different engine variants—and all of them would seem capable of supercruise. But its big cylindrical engines are more of an infra-red give-away.

Thrust vectoring

This isn't a stealth tech per se, but is a mark of modern fifth-generation aircraft: They can lens and flex the engine exhaust petals to send the jet exhaust in different directions—meaning the aircraft can perform impossible "non aerodynamic" maneuvers. This trick can throw off following surveillance systems or possibly even fast-flying missiles. The F-22 uses door-like vectoring wedges, but the Chinese-made WS10-A and Russian AL-31F engines that seem to be in the J-20 also have thrust vectored addons in development.

To read more news on this, and similar stuff, keep up with my updates by following me, Kit Eaton, on Twitter.

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  • Ayer Ai

    Oh yea I see the resemblance now - two engines, two wings, a beak, and tail. Too bad birds couldn't patent themselves and the first man-made static-shaped objects called kites were not patentable in China. Since it's a copy, the U.S. should get the J-20s for a bargain and save itself from all the paint peeling off the F-22s in every flight in addition to $45,000 per hour flight, critical failures averaging every 1.7hours of flight, browning of the radome, and be able to fly it into a war zone for once without crashing at least twice - in L.A. and in Alaska. Seriously what has the F-22 done for the U.S.

  • Diggiti

    Seems like China is Built on a " Copy it If you cant Create It " society.
    They crush any attempts for their citizens to be creative & don't understand that Art Breeds Commerce.

    If there are any experts up here, Id like to know What have they actually CREATED in the last 20 Years?

  • Andrew Krause

    The question is "does it rip off US tech," and the answer is "of course." Just like the Soviet system of yore, engineers in repressive societies and emerging world powers have to play follow the leader. (And it makes sense: why waste your yuan to develop technology when the US already blew their dollar; just copy what they do and leapfrog ahead.)

    The important thing is not that the J-20 could be a gen 5 fighter, but that its made to appear to be a gen 5 fighter. China desires strongly to take its place on the world stage as a superpower - economically and militarily. It has worked hard to develop an ICBM capability under the thin guise of a manned space program. It has deployed a deepwater navy. What it lacks are (1) the power projecting capability of a super carrier, and (2) a Gen 5 fighter. So, it lets loose that it has developed the capability to take out a super carrier with a theater ballistic missile, and then it gladly boasts of its stealthy gen-5 fighter.

    In reality: China probably couldn't hit the broad side of a small island with a TBM, and this plane would probably show up like an airliner if it came near an allied radar station or AWACS. This is China putting the west on notice that it plans to dominate the Asian rim militarily as well as economically. They are the "sick man of Asia" no more.