By Rick Joe

China’s FC-31 is a twin-engine stealth fighter demonstrator, which includes two iteratively different flying airframes that have been under active flight test since late 2012 and late 2016, respectively. This aircraft has often incorrectly been dubbed the “J-31” and been given various other names over the years, such as “J-21.” None of these J-designations remain true to the aircraft’s current state. It is a self-funded technology demonstrator from Shenyang Aircraft Corporation (SAC) and AVIC rather than a project being actively developed by the People’s Liberation Army (PLA). Therefore the names “J-31” or “J-21” are incorrect.

However, for the last few years it has been accepted that the PLA Navy has selected an FC-31-derived airframe to be developed into its carrier-based fifth-generation fighter, resulting in an aircraft that will indeed receive a J-designation. The PLA watching community has often referred to this aircraft as “J-35”; however, such a designation would be quite a numerical jump from “J-20” and thus deviate from prior norms where aircraft designations were somewhat more sequential (see, J-10, J-11, J-15, J-16, all as fourth-generation fighters). It also seems rather on the nose, having the same number as the U.S. F-35. It goes without saying there is substantial room for confusion over this aircraft’s name alone.

The FC-31, China’s ‘Other’ Stealth Fighter

This piece will review the history and rationale of the FC-31 demonstrators, as well as consider the future of its carrier-based derivative, whose arrival is now expected sometime in 2021. For the purposes of this piece, the carrier-based fifth-generation fighter derived from FC-31 will be termed “J-XY/J-35,” in reference to the past “J-XX” name used for J-20, as well as to acknowledge the commonly circulated but yet to be confirmed “J-35” name.

FC-31 and Its Rationale

If the J-20 was the stealth fighter that changed PLA watching forever, it could be said that the FC-31 was a reminder that PLA watching still had the capacity to surprise.

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Unlike the J-20, there was no long accumulation of rumors leading up to the FC-31’s unveiling. While some hints of a possible medium-weight fifth-generation aircraft bounced around in the late 2000s, the J-XX/J-20 was considered a much more credible aircraft to expect. In September 2011, less than a year after the unveiling of J-20, a model of a twin-engine aircraft with a convention configuration similar to the F-22 and F-35 (popularized since then, by the likes of KFX, TFX, and AMCA), was seen under the 601 Institute/SAC group at a UAV Innovation competition in Beijing, with the name “F-60.” The relatively generic nature of the aircraft depicted, as well as how recently the J-20 had emerged, made much of the community dismiss the F-60 model either as an internal study or some sort of subscale remote-controlled drone.

Therefore, it was a surprise when photographs emerged in mid-2012 of a suspicious looking, partially disassembled airframe being transported along roads and highways in China, with only its silhouette and shape visible through its protective covers. Initially this aircraft was thought to possibly be a disassembled JL-10 trainer or some other, more conservative aircraft. However, photographs taken at SAC a few months later in September revealed the complete and assembled aircraft with serial number 31001, virtually identical in configuration to the previously dismissed F-60. This aircraft made its first flight on October 31, 2012, just over a year and a half after the first J-20 technology demonstrator airframe, marking a milestone for China as only the second nation at the time to be actively flying more than one stealth fighter design at the same time.

Somewhat astonishingly, at Zhuhai Airshow in November 2012, a model of the new aircraft was even shown at a display booth, implying the aircraft could be offered for export or might even be intended for export. Subsequently, it was confirmed that the official AVIC designation for the aircraft was FC-31 (appearing to be a continuation of the export designations of FC-1 for the JF-17 and FC-20 for the J-10A).

A second, more revised airframe was known to be under work from 2015 to 2016, and it made its maiden flight on December 23, 2016. This airframe retained the same overall configuration, size, and planform as 31001, but enjoyed revisions in its flight control surfaces and panel geometry. It also replaced the two-piece canopy with a single piece reinforced canopy, and replaced the first airframe’s engines (thought to be the RD-93 or WS-13A, distinctive by their smoke) with WS-13E engines that feature certain improvements in thrust and materials, as well as being visibly smokeless. This airframe was dubbed in the community as “FC-31V2” denoting it as “version 2” of the same aircraft. FC-31V2 was eventually painted by late 2019 with a low-profile grey color and given the serial number 31003, fueling suspicions that the missing 31002 was likely a static test airframe of FC-31V1.

The relatively open profile of the FC-31 at various air shows and arms expos, as well as promotion from AVIC for its export prospects, created an impression that the aircraft was primarily intended as an export-oriented fifth-generation fighter, both in mainstream defense media as well as partially in the PLA watching community. But over time, it became obvious that the export prospects for the FC-31 were limited, and any AVIC push for overseas interest was likely half-hearted at best.

As it was, the FC-31 airframes were certainly full-sized airframes with internal weapons bays and capable of being developed into proper fifth-generation fighter; however, producing such a fighter would require significant additional development work on the aircraft’s avionics suite and weapons suite; the development of maintenance and infrastructure facilities; and substantially more flight and systems testing, among others – all of which would involve significant amounts of money, time, and willingness to tolerate risk. At the time, the PLA had yet to express interest in the FC-31 (or an FC-31 derivative), therefore the project lacked PLA commitment and funding, and there were no foreign nations that had the money or commitment to fund development of the FC-31 into a proper mission ready fighter for export. Therefore, it is likely that there was never any serious desire from AVIC, SAC, or the Chinese government to push the FC-31 as a dedicated export fifth-generation fighter. However, without a doubt the FC-31 was likely useful in announcing AVIC’s potential for developing a future fifth-generation fighter that may be offered on the export market, as well as starting discussions with potential customers to assess interest.

That leaves the question of what the purpose of the FC-31 was, if not as an export fighter. In recent years, academic papers from SAC have suggested the FC-31 was primarily a technology demonstrator for certain new manufacturing technologies, including but not limited to additive manufacturing and new structural loading principles to reduce cost and weight. Rumors have also suggested the FC-31 may utilize improved stealth technologies to increase ease of maintenance and operation, relative to the J-20.

At the same time, the FC-31 was clearly a full-sized fighter with a weapons bay that could likely be adapted to an operational aircraft if so desired (i.e. more similar to the American X-35 or YF-22 rather than the Japanese ATD-X). The planform of the FC-31, its overall size, and configuration and landing gear spacing, also appeared appropriate for development into a carrier-based variant, and indeed there was initial speculation in 2012 that the aircraft was the prototype of a new carrier-based fighter (quickly proven to be false at the time).

Therefore, it is likely the FC-31 was developed by SAC primarily as flying technology demonstrators, while also providing a basis for a future medium-weight land-based or carrier-based fifth-generation PLA requirement. Ultimately, in the early to mid-2010s the J-20 was still in active development and the FC-31 airframes remained in early flight testing themselves; therefore there were few signs of clear PLA commitment to the FC-31 or a derivative of it. However, this changed when the PLA Navy’s requirements for a carrier-based fighter began to advance.

The Carrier Has Arrived

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By the mid to late 2010s, more concrete rumors surrounding the PLA Navy’s requirements for a fifth-generation carrier-based fighter started to emerge, with the two primary contenders being a navalized derivative of Chengdu’s J-20 versus a derivative of Shenyang’s FC-31.

For a couple of years, there was some swinging back and forth as to which aircraft the PLA would choose. Certain advantages and disadvantages existed for both options.

A J-20 derivative would be larger and enjoy greater range and payload as well as share greater commonality with the J-20 the PLA Air Force would induct. However, the larger size of a navalized J-20 would also impose restrictions on the number of aircraft that could be accommodated on the limited space of a carrier as well as on-deck maneuvering. A J-20 derivative would likely also need somewhat more extensive modifications to its control surfaces and wing size to enable better low speed handling. Furthermore, Chengdu had no prior experience developing and producing a navalized fighter compared to Shenyang, which might introduce greater relative risk.

The smaller footprint of a FC-31 derivative compared to the J-20 would enable a greater number of aircraft to be accommodated, and might prove easier to adapt for the navalized role by virtue of its more conventional configuration and existing landing gear arrangement. Shenyang also enjoyed experience in developing and producing the J-15 family of navalized fighters. However, a navalized FC-31 would also be more limited in range and payload than a navalized J-20, and would share less commonality with the PLA Air Force’s J-20.

Around 2018, a chorus of credible rumors strongly implied a navalized FC-31 had been chosen as the PLA Navy’s fifth-generation carrier-based fighter, now widely called “J-XY/J-35.” It remains unclear how much modification the J-XY/J-35 will undergo compared to the standard FC-31. It is expected the J-XY/J-35 will pick up from the FC-31V2 airframe, and include obvious modifications to enable carrier operations, including strengthened structure and landing gear, catapult compatible nose gear, a tailhook, folding wings, and corrosion resistance for operating in a maritime environment. It is also expected that the initial J-XY/J-35 prototypes and airframes will be powered by the 9-ton thrust WS-13E engine, to be succeeded by the more modern, 10+ ton thrust WS-19 currently under development. Notably, the development of the WS-19 may see a faster pace of work than the larger WS-15 being developed for the J-20, despite starting work later. That’s partly because the WS-19 is expected to take advantage of key technologies and advancements made as part of the WS-15’s development to begin with, as well as because the WS-19 sits in a smaller thrust category than the WS-15, with potential corresponding benefits for things such as yield and production of monocrystalline fan blades of smaller size.

What is not known is whether the J-XY/J-35 will undergo modifications in its wing size and control surface size, or changes to its overall size in general. As it stands, the FC-31 is not a small fighter; however, a carrier-based fighter may benefit disproportionately more from having a larger internal fuel load and internal weapons bay size. AVIC has shown promotional material indicating the FC-31 has an internal fuel combat radius of 1,200 km and a maximum takeoff weight (MTOW) of 28 tons. While the conditions of these numbers are not known, a slight increase of these parameters might benefit the overall flexibility of the aircraft, especially for carrier-based operations where greater range is always desirable. One past rumor had suggested the J-XY/J-35 might see a slight enlargement in size and weight up to an MTOW approaching 30 tons.

More intriguing is the ultimate size and geometry of J-XY/J-35’s weapons bay. The aircraft will likely retain the same main ventral bay configuration as on the FC-31 (which in turn is similar to that of the J-20 and F-22), while lacking dedicated side weapons bays. Given the geometry of the aircraft’s fuselage, it is unlikely that the J-XY/J-35 will enjoy as deep of a weapons bay as the F-35’s large diameter outboard stations. That said, the J-XY/J-35 might still field a sufficiently voluminous weapons bay to field powered strike weapons – the same source had suggested the aircraft might field the same weapons bay loadouts that the ventral bay of the J-20 can accommodate, raising an interesting prospect that the J-XY/J-35 might have the same main weapons bay geometry as the J-20.

In terms of sensors and avionics, it is very likely that it will be equipped with derivatives of the same suite that the J-20 enjoys. In fact, given the J-20 and J-XY/J-35 will likely enjoy a significant period of overlapping production, both aircraft may end up employing common subsystems in general. The usual suite of an AESA radar, passive electronic support measure systems and passive electro-optic detection systems, an electronic warfare system, an electro-optic chin mounted sensor, and robust datalinking capability with emphasis on networked warfare are all expected. It will be interesting to see if the initial J-XY/J-35 prototypes will be more similar to the J-20 project’s 200X technology demonstrators, or the more refined and more production representative 201X prototypes.

At time of writing in early February 2021, it is tentatively projected that the J-XY/J-35 may be unveiled sometime around mid-2021, but the effects of the global pandemic and overall global stability are confounding factors. But assuming a first flight sometime in 2021, development of the aircraft will likely take at least four to five years, implying the earliest the aircraft could see initial production would be 2026. However, this might be expedited slightly if the aircraft is able to exploit the many years of prior flight testing that the FC-31 airframes have enjoyed from 2012 to 2021, as well as utilizing existing, mature subsystems already employed on the J-20. The initial years of J-XY/J-35 production will be powered by the WS-13E, with the WS-19 potentially becoming available for production around the mid to late 2020s.

An entry into service in 2026 or 2027 would be a few years later than when the catapult equipped carrier 003 is expected to enter service; therefore at this stage it is expected that a catapult compatible J-15 family will be produced in the next few years, exploiting the flexibility and size of the Flanker airframe. It is unknown if the J-XY/J-35 will be designed with the ability to also take off from ski jumps, which would allow it to operate from the existing carriers Liaoning (CV-16) and Shandong (CV-17) as well as the future catapult carriers. It goes without saying that equipping the Liaoning and Shandong with the J-XY/J-35 will greatly enhance their combat potential. The stealthy nature of the J-XY/J-35 means the aircraft may be able to reliably take off from a ski jump under most conditions with a “light” load of full internal fuel and weapons, as such a weight would still only be a fraction of its MTOW.

An Air Force and Export Future?

The full-fledged development of the FC-31 into the J-XY/J-35 also presents an opportunity for the J-XY/J-35 to in turn be leveraged into a land-based fighter. A hypothetical land-based variant of the J-XY/J-35 would be capable of leveraging all of the development and subsystems work as part of the standard carrier-based aircraft, with removal of carrier-relevant details such as folding wings, structural enhancement, catapult nose gear, and tailhook, among others. Such modifications would not only reduce the weight of the aircraft, resulting in slightly improved kinematic performance, but also would be far less time consuming and complex than doing the reverse.

A land-based J-XY/J-35 could prove an attractive proposition for the PLA Air Force as a medium-weight fifth-generation fighter to complement the larger J-20, and if pursued might be production ready just a few years after the standard J-XY/J-35. However, an alternative medium-weight fighter may be a single engine aircraft powered by the WS-15. Holding all else equal, a single engine WS-15 powered fighter would enjoy benefits in operations cost by virtue of its single engine nature; however such an aircraft would likely have to be a clean sheet design compared to a land based J-XY/J-35, and there are also questions as to how the production of WS-15 can be scaled up to meet such demands.

Therefore, it remains an open question as to whether the PLA Air Force will commit itself to a land-based J-XY/J-35 variant, with some compelling arguments in favor of it. If such an aircraft is developed, it would certainly enjoy a rather convoluted development pathway, though there are some similar historical parallels. The YF-17 was a demonstrator fighter that competed with the YF-16 for the U.S. Air Force’s Lightweight Fighter competition, ultimately being declined in favor of the YF-16 (which became the widely used F-16). Meanwhile, the YF-17 was chosen by the U.S. Navy and developed into the F/A-18 as a carrier-based fighter – but interestingly, the F/A-18 was also developed into the F/A-18L, a land-based derivative of the aircraft for potential export. Ultimately, the F/A-18L did not result in any orders and was cancelled as a project, but interesting parallels exist, between the development path of the FC-31, J-XY/J-35, and a potential land-based J-XY/J-35, with that of the YF-17, F/A-18, and F/A-18L, respectively.

Furthermore, a land-based J-XY/J-35 would likely prove to be a viable export fifth-generation fighter, as such an aircraft will have been fully developed and adopted by the PLA. Such an aircraft might only emerge as a viable export product in the late 2020s, and therefore would likely be aimed at nations which desire a fifth-generation capability but are unable to purchase F-35s due to geopolitical alignment and/or cost. The most likely customer could be the Pakistani Air Force; however, Pakistan is currently also actively pursuing a fifth-generation capability dubbed Project Azm, whose stage of maturity is unknown, let alone what degree of indigenous industrial effort will be involved.

In summary, the role and capability of the FC-31 may have been questioned and even dismissed in the early years of its existence; however, a significant level of confirmed and potential development now lies ahead. The most significant development on the horizon is the emergence of the first J-XY/J-35 prototype, followed by careful waiting to catch any hints of PLA Air Force interest in a land-based J-XY/J-35 variant.

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