Jan 3, 2011 
By Bill Sweetman
Washington

China’s first known stealth aircraft just emerged from a secret development program and was undergoing high-speed taxi tests late last week at Chengdu Aircraft Design Institute’s airfield. Said to be designated J-20, it is larger than most observers expected—pointing to long range and heavy weapon loads.

Its timing, Chengdu’s development record and official statements cast doubt on U.S. Defense Secretary Robert Gates’s 2009 prediction (in support of his decision to stop production of the Lockheed Martin F-22) that China would not have an operational stealth aircraft before 2020.

The debut of the J-20 was announced in a November 2009 interview on Chinese TV by Gen. He Weirong, deputy commander of the People’s Liberation Army Air Force. The general said a “fourth-generation” fighter (Chinese terminology for a stealth fighter) would be flown in 2010-11 and be operational in 2017-19.

The J-20 is a single-seat, twin-engine aircraft, bigger and heavier than the Sukhoi T-50 and the F-22. Comparison with ground-service vehicles points to an overall length of 75 ft. and a wingspan of 45 ft. or more, which would suggest a takeoff weight in the 75,000-80,000-lb. class with no external load. That in turn implies a generous internal fuel capacity. The overall length is close to that of the 1960s General Dynamics F-111, which carries 34,000 lb. of fuel.

The J-20 has a canard delta layout (like Chengdu’s J-10) with two canted, all-moving vertical stabilizers (like the T-50) and smaller canted ventral fins. The stealth body shaping is similar to that of the F-22. The flat body sides are aligned with the canted tails, the wing-body junction is clean, and there is a sharp chine line around the forward fuselage. The cant angles are greater than they are on the Lockheed Martin F-35, and the frameless canopy is similar to that of the F-22.

The engines are most likely members of the Russian Saturn AL-31F family, also used on the J-10. The production version will require yet-to-mature indigenous engines. The inlets use diverterless supersonic inlet (DSI) technology, first adopted for the F-35 but also used by Chengdu on the J-10B—the newest version of the J-10—and the Sino-Pakistani JF-17 Thunder.

The main landing gears retract into body-side bays, indicating the likely presence of F-22-style side weapon bays ahead of them. The ground clearance is higher than on the F-22, which would facilitate loading larger weapons including air-to-surface munitions. Chinese engineers at the Zhuhai air show in November disclosed that newly developed air-to-ground weapons are now required to be compatible with the J-20.

Features at the rear of the aircraft—including underwing actuator fairings, axisymmetrical engine exhausts and the ventral fins—appear less compatible with stealth, so the J-20 may not match the all-aspect stealth of the F-22. There are two possible explanations for this: Either the aircraft seen here is the first step toward an operational design, or China’s requirements do not place as much stress on rear-aspect signatures.

The major open question at this point is whether the J-20 is a true prototype, like the T-50, or a technology demonstrator, with a status similar to the YF-22 flown in 1990. That question will be answered by whether, and how many, further J-20s enter flight testing in the next 12-24 months.

Developing an effective multi-mission stealthy aircraft presents challenges beyond the airframe, because it requires a sensor suite that uses automated data fusion, emission control and low-probability-of-intercept data links to build an operational picture for the pilot without giving away the aircraft’s own location.

A rapid development program would be a challenge for China’s combat aircraft industry, which is currently busy: The J-10B, FC-17 and Shenyang’s J-11B and carrier-based J-15 are all under development. However, the progress of China’s military aviation technology has been rapid since the first flight of the J-10 in 1996, owing to the nation’s growing economy and the push by the People’s Liberation Army for a modernized military force in all domains. Before the J-10, China’s only indigenous production combat aircraft were the Shenyang J-8 and Xian JH-7, reflecting early-1960s technology from Russia and Europe.

Engine development has lagged airframe development, with reports that the Shenyang WS-10 engine, slated to replace Russian engines in the J-11B, has been slow to reach acceptable reliability and durability levels. That may not be surprising, given that high-performance engine technology is founded on specialized alloys and processes that often have no other uses. (The existence of the J-11B, essentially a “bootleg” version of the Su-27, has been a strain on relationships between the Russian and Chinese industries.)

Progress with avionics may be indicated by the advent of the J-10B, with new features that include a canted radar bulkhead (normally associated with an active, electronically scanned array antenna), an infrared search-and-track system, and housings for new electronic warfare antennas.

One question that may go unanswered for a long time concerns the degree to which cyberespionage has aided the development of the J-20. U.S. defense industry cybersecurity experts have cited 2006—close to the date when the J-20 program would have started—as the point at which they became aware of what was later named the advanced persistent threat (APT), a campaign of cyberintrusion aimed primarily at military and defense industries and characterized by sophisticated infiltration and exfiltration techniques.

Dale Meyerrose, information security vice president for the Harris Corp. and former chief information officer for the director of national intelligence, told an Aviation Week cybersecurity conference in April 2010 that the APT had been little discussed outside the classified realm, up to that point, because “the vast majority of APT attacks are believed to come from a single country.”

Between 2009 and early 2010, Lockheed Martin found that “six to eight companies” among its subcontractors “had been totally compromised—e-mails, their networks, everything,” according to Chief Information Security Officer Anne Mullins.

The way in which the J-20 was unveiled also reflects China’s use and control of information technology to support national interests. The test airfield is located in the city of Chengdu and is not secure, with many public viewing points. Photography is technically forbidden, but reports suggest that patrols have been permitting the use of cell phone cameras. From Dec. 25‑29, these images were placed on Chinese Internet discussion boards, and after an early intervention by censors—which served to draw attention to the activity—they appeared with steadily increasing quality. Substantial international attention was thereby achieved without any official disclosures. 

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By David A. Fulghum, Bill Sweetman, Bradley Perrett, Robert Wall Washington, Washington, Beijing, London

China’s newest combat aircraft prototype, the J-20, will require an intense development program if it is going to catch up with fast-moving anti-stealth advances.

In fact, anti-stealth will bring into question all stealth designs: How much invulnerability will current low-observability techniques offer as air defense systems adopt larger and more powerful active, electronically scanned array (AESA) radars? From the early days of AESA development, a key goal was to build a radar that could detect very small objects—such as a cruise missile at a distance great enough to target and shoot it down—or a larger object like a fighter with a very low-observable treatment.

Airborne detection of stealth aircraft may already be an operational capability. In a series of tests at Edwards AFB, Calif., in 2009, Lockheed Martin’s CATbird avionics testbed—a Boeing 737 that carries the F-35 Joint Strike Fighter’s entire avionics system—engaged a mixed force of F-22s and Boeing F-15s and was able to locate and jam F-22 radars, according to researchers. Raytheon’s family of X-band airborne AESA radar—in particular, those on upgraded F-15Cs stationed in Okinawa—can detect small, low-signature cruise missiles.

Moreover, Northrop Grumman’s lower-frequency, L-band AESA radar on Australia’s Wedgetail airborne early warning and control aircraft is larger and potentially more capable of detecting stealth aircraft at longer ranges.

Lockheed Martin also hinted at a JSF anti-stealth capability in 2009 in a reference to combat with sophisticated, foreign aircraft. “The F-35’s avionics include onboard sensors that will enable pilots to strike fixed or moving ground targets in high-threat environments, day or night, in any weather, while simultaneously targeting and eliminating advanced airborne threats,” said Dan Crowley, then-executive vice president and F-35 program general manager.

Better images emerging from China point clearly to the J-20’s use of stealth technology, but major uncertainties and questions remain unresolved.

The overall shape resembles that of the F-35 and F-22, which have a single “chine line” uniting the forebody, upper inlet lips, and wing and canard edges with a curved surface above that line and flat, canted body surfaces below it. The wing and canard edges are aligned: The wing and canard leading edges are parallel and the trailing edge of each canard is aligned with the opposite wing’s trailing edge. The same basic philosophy also has been adopted in British, Swedish and Japanese studies for stealth fighters.

The aim in all cases is to endow a practical, agile fighter configuration with a “bow-tie” radar signature, with the smallest signature around the nose and the greatest (still much lower than that of a conventional aircraft with curved or vertical-slab sides) to the side. The fighter’s mission planning system, using a database of known radar locations, then derives a “blue line” track that weaves between radars and avoids exposing the side-on signature to those radars more than transiently.

The “diverterless” supersonic inlet avoids a signature problem caused by a conventional boundary layer diverter plate. For example, the F-22 has a conventional inlet, which is likely to require extensive radar absorbent material (RAM) treatment.

The biggest uncertainty about the Chinese design concerns the engine exhausts, which as seen on the prototype are likely to cause a radar cross-section (RCS) peak from the rear aspect. One possibility is that a stealthier two-dimensional nozzle will be integrated later in the program; however, the nozzles on the current aircraft show some signs of RCS-reducing sawtooth treatment, suggesting that the People’s Liberation Army has accepted a rear-aspect RCS penalty rather than the much greater weight and complexity of 2D nozzles.

Other features are less clear. Stealth development has been dogged by detail-design challenges. All the antennas on the aircraft have to be flush with the skin and covered with surfaces that retain stealth properties while being transparent in a specific frequency. Maintainability becomes a complex tradeoff: Some systems requiring frequent attention will be accessed via landing gear and weapon bays, and others by latched and actuated doors that can open and close without affecting RCS—but the latter involves a weight penalty.

Perhaps the toughest hurdle is managing radio-frequency surface currents over the skin. Early stealth designs used heavy, maintenance-intensive RAM. The F-22 introduced a much lighter surface treatment, but it has proven unexpectedly difficult to maintain, causing corrosion issues. Lockheed Martin now asserts that the F-35 will be robust and affordable to maintain in service, with a combination of a high-toughness, sprayed-on topcoat and a conductive layer cured into composite skin panels.

The Chengdu J-20 design has struck many analysts and observers as familiar and somewhat different from the F-22, F-35 or Sukhoi T-50.

“The J-20 is reminiscent of the Russian MiG-1.42 both in terms of planform and also with regard to the rear fuselage configuration,” says Douglas Barrie, senior fellow for military aerospace at London’s International Institute for Strategic Studies. “The most obvious difference is the greater forward fuselage shaping as the basis for low-observable characteristics, along with the different engine intake configuration. The MiG program was canceled by the Russian government around 1997,” he notes. However, the similarity to the MiG concept may suggest some collusion with the Russian aviation industry.

The J-20 made its first flight shortly before 1 p.m. Beijing time on Jan. 11. The flight ended three weeks of anticipation that began in late December when the new design started taxi tests.

The discussion about the program will now shift to the aircraft’s mission (fighter or, more likely, long-range strike), sensors (strike missions would require a high-resolution, long-range radar) and communications (which would demand high-speed data links and sophisticated integration).

Conventional radars have only one-half to one-third of the range of an AESA radar. Moreover, the movement of a conventional, mechanically scanned radar antenna provides a tell-tale glint of radio-frequency reflections to enemy aircraft with advanced radars. Such reflections undercut the effectiveness of a stealth airframe. China is known to be pursuing newer radar technology.

“It’s too early to tell the true status of the Chinese AESA program,” says a Washington-based intelligence official. “We’ve seen lots of press and air show information on the program, but that doesn’t automatically translate into a robust development or give us an accurate look at where [China] is as far as fielding one anytime soon.

“Like the [high-performance] engine, it’ll be a challenge to take the step from older radars to one designed for a fifth-generation fighter,” he says. “Again, though, the J-20 is just the first or second—depending on whom you believe—prototype in a very long development program.”

If the Chinese conduct a few months of flight tests and there are no more aircraft involved in the program, this might indicate that the J-20 is a proof-of-concept or technical demonstrator. If there are several aircraft eventually, a prototype program would be a more likely conclusion.

The flight occurred during a visit to China by U.S. Defense Secretary Robert Gates, who says Chinese President Hu Jintao confirmed the event to him in talks. However, Gates still believes the U.S. will retain a preponderance of stealth fighters through 2025. 

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