Threat Analysis of Foreign Stealth Fighters: Shenyang J-31 Part I

Image 1: J-31 at Zhuhai airshow, 2014. Image Credit: Chen. 

The Shenyang J-31 made its official debut at the Zhuhai 2014 airshow earlier this month after images were first leaked of the aircraft in 2012. The combination of limited transparency of China's defense industry combined with frequent disinformation efforts by the Chinese Government makes obtaining verifiable information on the J-31 extremely difficult. This article's objective is to provide reliable information from reputable aerospace and defense publications on the potential domestic use, stealth characteristics, avionics, export prospects, and strategic ramifications of the Shenyang J-31. Any conjecture or educated guesses made by the author are noted. 

Domestic Prospects - PLAAF

The Chinese aerospace conglomerate, Aviation Industry Corporation of China (AVIC), maintains the J-31 is officially an export only aircraft and marketing materials at Zhuhai subsequently referred to the aircraft as the FC-31; fighter aircraft developed for the domestic market use the "J" designation in contrast to export aircraft which are assigned the "FC" designation such as the FC-1 fighter (Wong, 2014). However, given the limited transparency of the Chinese aerospace defense industry and the People's Liberation Army (PLA), its plausible that the aircraft could eventually enter service within the Chinese military. As Aviation Week observes, the People's Liberation Army Air Force (PLAAF) has consistently instituted a high-low mix fighter procurement strategy and either the 4.5 generation J-10B or the J-31 could hypothetically fulfill the low end spectrum with the J-20 serving as the high-end aircraft. The author is inclined to believe AVIC's remarks are legitimate given the separate public treatment between the J-31 and J-20. Under the assumption that the J-31 is an export only aircraft, the PLAAF must have a reason for choosing not to procure the J-31:

"What looks like a thoroughly modern stealth fighter is apparently not good enough to serve as China's next medium-weight combat aircraft...The J-20 was revealed in late 2010 and appears to have made its first flight in January 2011. It was not promoted at Zhuhai. And therein lies a key piece of evidence of the status of the J-31. The J-20 was not at Zhuhai because it is not for sale and because China does not want to reveal too much about it. It is intended for the Chinese air force. Conversely, because the J-31 was exhibited at Zhuhai and is promoted as an export product, the Chinese air force obviously does not want it."- Perrett, Hewson, Johnson, & Sweetman, 2014 

One possibility is that the PLAAF's existing 4th generation fighter force of hundreds of Su-27SK, J-10A, J-11B, and J-10B aircraft will be operational well into the late 2020s and likely 2030s; China is still replacing its hundreds of third generation fighters such as the J-7. Therefore, the PLAAF does not have an immediate need for a low end replacement fighter aircraft in the near future and might be more concerned with the development of the high end J-20. Feng from the China Air and Naval Power blog discusses the possibility that the current J-31 design may not meet PLA requirements and it is possible the design could undergo major changes before eventually entering PLAAF service several years from now. 

Domestic Prospects - PLANAF

The only operational J-31 demonstrator's nose landing gear features two side by side wheels, a common feature of carrier operated aircraft (Axe, 2014). Furthermore, a model J-31 was photographed on a Liaoning mock up in 2014. The combination of the nose wheels and the carrier mock up photographs has lead to speculation that the J-31 is being developed for the People's Liberation Army Navy Air Force (PLANAF).  

Image 2: J-31 model on Liaoning mock up flight deck, 2014. 

Given the current design of the J-31 demonstrator, the nose landing gear along with photographs of a model J-31 on a Liaoning mock up are insufficient to prove future PLANAF service. Carrier aircraft often feature a host of other design changes necessary for operating on a carrier deck such as foldable wings, arresting gear (tail hook), additional structural support to address the increased stress of carrier landings and take offs, protective salt water corrosion coatings, etc. Furthermore, given China's ongoing difficulty in the development of its first carrier operated fighter, the J-15 "flying shark", the concurrent development of a much more technologically demanding carrier based stealth fighter would be a poor management of risk. 

As part of China's broader effort to reduce US influence in the Western Pacific and implement an anti-access area denial strategy, its future carrier air wings do not have to be as large or powerful as their American counterparts. Bryan McGrath and Seth Cropsey both observe that the purpose of China's carriers would be to weaken the US network of alliances in the Asia-Pacific rather than take on the US Pacific Fleet:   

"China is building the capability to project power from the sea in order to build its strength relative to its neighbors, primarily those with whom it has ongoing territorial seas claims (including Vietnam, the Philippines, and Japan). China does not need to build a navy as large or as powerful as the U.S. Navy in order to create fear and uncertainty among its neighbors. It only needs to build a navy with the credible means to project power over those neighbors’ shores.'...the strategic target of the PLAN in building a carrier force is not the U.S. Navy, but the network of alliances that longstanding U.S. economic and security interests in the region aim to preserve. Creating uncertainty and doubt in the minds of regional governments that the United States can continue to assure their security is at the heart of China’s desire to see the U.S. diminished in the region." - Bryan McGrath & Seth Cropsey, 2014 

Image 3: Chinese carrier group in January of 2014 consisting of 12 ships including: Type 051C destroyers, Type 052C destroyers, one Type 071 LPD, Type 054A frigates, Type 093 SSN and a Type 094 SSBN. Note the lack of fleet replenishment oilers or logistics ships. 

In the near term, Chinese carrier groups with the J-15 would be sufficient to pressure US allied or sympathetic countries in the Western Pacific. In the event of hostilities, Chinese naval forces would require substantial land based missile and air support to mitigate which would be available within the first and second island chains.  Furthermore, the addition of carrier based stealth fighters would not address the most significant threat to Chinese naval assets the Western Pacific, US attack submarines.  Thus, China's broader strategic goals do not require stealth carrier based aircraft in the near term and the developmental risks of the concurrent development of the J-15 with a much more technologically demanding J-31 naval variant would be exceedingly high. As with the PLAAF, there is a remote possibility that the J-31 design could be adapted or be used as the basis for a new design for a future aircraft that would serve on China's yet to be constructed super carriers several years from now, but the probability that an aircraft similar to the current design will enter PLANAF service a few years from now is slim. 

Stealth & Airframe Characteristics

Image 3: Frontal aspect of J-31 demonstrator, note the intense smoke generated from the Russian RD-93 engines. The RD-93 is a variant of the RD-33 which was originally developed for the Mig-29 in the 1970s. The smoke from the rear of Mig-29 made it easier to track in visual range combat exercises between between Polish, German, and US forces after the end of the Cold War. 

The J-31 design makes use of planform alignment, the orientation of flight surfaces at a common angle to reflect incoming radar waves away from the source, to lower its radar cross section (rcs). The angle of the diverterless supersonic inlets (DSI) matches the angle of its vertical canted tails. Similarly, the 35° wing angles  match those of the horizontal stabilizers. The use of planform alignment and DSI within the J-31 airframe strongly resembles rcs reduction techniques used on the Lockheed Martin F-35. The current J-31 demonstrator does not incorporate sawtooth engine nozzles or other forms of rcs reduction measures on the exposed RD-93 engines. Given that none of the four more technologically mature J-20 prototypes incorporate sawtooth engine nozzles or specially shaped thrust vectoring nozzles, as used by the F-22A, it is possible China does not value rear aspect stealth. Bill Sweetman explains the exposed engine nozzles for both the J-20 and Russian T-50: 

"The rear-aspect view of the aircraft is not as stealthy, a feature also seen on the Sukhoi T-50. This is clearly an intentional trade, eliminating the heavy 2D nozzles of the F-22. In this respect, both the T-50 and J-20 reflect the philosophy behind the pre-1986 Advanced Tactical Fighter studies that preceded the F-22, based on the theory that a fast, high-flying, agile aircraft is relatively immune from rear-quarter attacks." - Bill Sweetman, 2012

All aspect stealth is critical when disabling an enemy's surface to air missile (SAMs) systems within an integrated air defense system (IADS). If an aircraft with only a forward stealth capability turns after missile release, it exposes its less stealthy rear aspect to enemy radars and it subsequently becomes vulnerable to SAMs. Russia and China field the largest respective SAM forces in the world including the S-300, HQ-9 and S-400 systems as part of their anti-access area denial strategies. Conversely, with the exception of the Patriot PAC-2, the United States mostly relies upon its fighter force to defend air space. Therefore, rear aspect stealth could be of less value to China and Russia relative to the United States given the comparatively few number of US SAM systems. The FC-31 model displayed at Zhuhai does incorporate sawtooth engine nozzles among other slight airframe and design changes from the J-31 demonstrator: 

"The airframe and control surfaces of the two aircraft are similar, comprising the low aspect ratio design and chined fuselage, with forward-swept engine intakes, 35° sweptback trapezoidal planform wings, and similarly-shaped tailplanes. However, the outward-canted twin vertical fins and rudders have now been updated, terminating in tips that are diametrically angled compared with the current design's flushed tips." - Kelvin Wong, 2014

Image 4: Sawtooth engine nozzles on FC-31 display mock up at Zhuhai. Image Credit: Defense Update, 2014. 

As for estimates regarding the rcs of the J-31, no credible figures exist. Without the use of an identical J-31 mock up with rcs reduction treatments and a radar testing facility, its unlikely figures posted online can be verified. In the case of the PAK FA, patent documents filed by Sukhoi indicated the aircraft had a much larger rcs than previously estimated by numerous online sources at between 0.1m^2 and 1m^2; The 1m^2 figure likely refers to the rear of the aircraft and the 0.1m^2 the comparatively more stealthy frontal aspect. In comparison the F-22A has a frontal rcs of 0.0001m^2 or - 40 dBSM and the F-35 has a frontal rcs between 0.005m^2 and 0.001m^2 or - 30 dBSM (Global Security & Kopp, 2011). Given the relative secrecy of Shenyang, its unlikely that similar patent documents will be available within the public domain. However, there is good reason to be skeptical of assessments which assert the J-31 is as stealthy or stealthier than the F-35; Shenyang still has difficulty with basic quality control on its fourth generation production fighters. Low observability is notoriously hard to maintain as small manufacturing discrepancies that undermine planform alignment or the radar-absorbent material coatings can negate rcs reductions. 

"Quality control, in general, could undermine the J-31’s biggest apparent selling point: its ability to evade radar. 'The potential problem with Chinese- and Russian-construction stealth fighters is that if there’s a bolt out of place, it shows up on a radar signature...Russian and Chinese construction is typically much looser.'”- Robert Farley, 2014 

A US intelligence official reporting to Defense News indicated China's domestic built copy of Russia's Su-27SK fighter, the J-11B, has experienced numerous crashes due to manufacturing issues (Axe, 2013). Furthermore, China's efforts to illegally obtain US aviation grade carbon fiber also suggests the Chinese aerospace industry is experiencing ongoing difficulties in the production of high quality aircraft materials. 

This is not to say the J-31 or FC-31 is not a low observable aircraft, but one should be skeptical of extraordinarily low J-31 rcs estimates. As a caveat, its also worth noting that the J-31 does not need to match US 5th generation low observability qualities to be a significant threat to US or allied forces. US fourth generation aircraft, specifically the legacy hornet and F-16C (after the cancellation of the CAPES upgrade program) would likely have significant difficulties in detecting the J-31 from the frontal aspect. Furthermore, as Part II will discuss, many of the countries interested in potentially acquiring the FC-31 would be satisfied with a moderately reduced rcs aircraft. Part II will also discuss the avionics and strategic ramifications of the Shenyang J-31

PART II 

Related Articles 

China's Anti Access Strategy Part II: Air Power

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