Since CAC prototype no. 2001 made its first flight on the 11th of January, 2011, the Chengdu J-20 has been a source of great speculation and discussion in the defence community and general media (Waldron, 2011). The emergence of what was clearly a large, stealthy fighter aircraft from a country not traditionally viewed as a serious high-technology military competitor to the United States prompted a range of reactions in western news media and defence experts, encompassing an extensive range of emotions from surprise and anxiety, to hostility and dismissal.
Interestingly, most reports of J-20 eventually came to speculate that its role and associated capabilities either revolved around that of a dedicated strike aircraft (Reed, 2011b; Trimble, 2011), or as a dedicated interceptor aircraft (Axe, 2011b). Needless to say, proper assessment of the J-20’s intended role is vital for an accurate projection of the future capabilities of the Chinese Air Force.
This entry intends to sample commentary and relevant news media of J-20’s potential roles as a striker, an interceptor, and an air superiority fighter, and critically examine the potential viability and sensibility of J-20’s design for those roles as well as the place of such roles in context of the Chinese Air Force’s potential requirements.
This paper is not intended to address J-20’s role in context of any substantive aerodynamic analyses given the complexity of aerodynamic design, and the inability to properly assess this without access to a wind tunnel, an accurate model, and a few experienced aerospace engineers.
J-20 as a striker:
J-20’s potential striker role has been emphasized greatly in the defence watching discourse, often in context of the larger perceived Chinese military doctrine of “Anti Access/Area Denial” or “Counter Intervention” capabilities (Barnes, Hodge, & Page, 2012). In many cases, J-20 is even described not only as a simple stealthy striker but also as a naval striker for specific targeted use against United States supercarriers (Reed, 2011b; Trimble, 2011).
There are compelling reasons to believe why the Chinese military may be interested in fielding a stealthy strike aircraft, and the requirement to counter United States carrier battlegroups are also well accepted. But whether J-20 is the plane to fulfil such a task is another question.
Any stealth aircraft intended for the strike role should optimally field a large diameter weapons bay to allow it to deploy a variety of munitions, including non-powered guided bombs or glide bombs, as well as powered guided weapons such as air launched cruise missiles, which are typically of a larger diameter than unpowered counterparts. For instance, the F-35 Joint Strike Fighter was designed from the outset with large diameter weapon bays (Figure 1.0), to accommodate powered guided weapons such as the Joint Strike Missile (Kongsberg). By comparison, the F-22 is limited to Small Diameter Bombs and 450kg class Joint Direct Attack Munitions as a consequence of having a weapons bay with less depth (Figure 1.1).
J-20’s weapon bay is shallower than that of the F-35, and from current picture evidence, it appears most similar to F-22’s weapon bay in dimensions as well as configuration (Figure 1.2). The configuration of J-20’s air intakes are also possibly indicative of the maximum depth of its main weapons bay: stealthy aircraft such as the J-20, F-22, and F-35 all feature air intakes which partially “overlay” their main belly weapon bays, restricting the maximum possible depth of the bays due to constraints of a minimum functional air intake/duct area to supply their engines. Other stealthy aircraft such as the Northrop YF-23 and Russian T-50 feature air intakes which do not overlay their belly weapon bays and instead run parallel (Figures 1.3 and 1.4), permitting the bays to potentially feature a substantially greater depth.
In the likely event that J-20 does lack a sufficiently deep weapons bay to field large diameter powered weapons, J-20 will be limited to deploying relatively short range glide bombs. Such glide bombs will also be limited in number, given the length of its weapons bay appears little greater than that of F-22. Modern glide bombs such as the SDB feature extended ranges of over 100km compared to legacy guided bombs, and supersonic deployment speeds may extend that range even further, but even then, the J-20 will be limited to deploying only a likely maximum of 12 SDB class weapons at a distance of far less than 200km from its target, which is inside the likely engagement envelope of future and some current surface to air missiles, not to mention lying well within airspace monitored by AEW&C and defended by combat air patrols. This therefore casts great scepticism over J-20’s potential role as a striker and whether the Chinese Air Force would consider development of such an expensive but inefficient strike aircraft in the first place
Of course, one may envision the Chinese Air Force seeking to procure a small diameter, powered weapon able to fit within J-20’s weapons bay, such as a reduced diameter JSM-esque weapon or a SPEAR III equivalent; or the folding wing Kh-58UshKE missile which some western media claim China has purchased from Russia (but for which there is no indication of in the Chinese military watching community). However such missiles would only make the best of a poor strike aircraft design, as they would be limited to small warheads and relatively short range compared to full sized powered weapons, and far inferior to missiles such as the new YJ-12 (Lin & Singer, 2014). Therefore if J-20 were to field even a token naval strike role, it would require development of a new generation of small sized powered missiles, of which J-20 can only carry a small number, whose efficacy against a well defended United States carrier battlegroup would very doubtful at best.
Considering the above, it becomes difficult to envision J-20 as being designed primarily as a stealthy striker. Indeed, the reasons for suggesting J-20 was a striker rested on debatable logic in the first place. Some commentary have suggested J-20 may be a striker due to its supposedly large size (Figure 1.5), however later satellite analysis have shown that the J-20 is almost certainly under 20.5 meters in length (Figure 1.6), which is meaningfully smaller than early assertions of J-20 being in the same class as the 22.4 meters long F-111 (Axe, 2011b; Kopp & Goon, 2011).
However, this is not to suggest that J-20 cannot be a viable and capable strike aircraft. For instance, the F-22 has demonstrated that even though it can only carry a relatively light strike load of only JDAMs or SDBs, it can still provide a potent strike capability by leveraging supercruise, sensor fusion and a very low observable design. But F-22’s primary role is that of an air superiority fighter and it is equipped with a weapons bay designed to match that purpose. Therefore, it is most accurate to say F-22’s respectable strike capability arises despite the inherent limitations of the design of the actual airframe and its weapons bay dimensions rather than flourishing as a result of its design. In other words, if the Chinese Air Force truly desired a stealthy aircraft for strike and naval strike, there are a variety of other more sensible airframe designs and weapons bay configurations that could have been pursued first.
J-20 as an interceptor:
J-20’s other major role as speculated by mainstream defence media, is that of an interceptor. In such a role, it is suggested that J-20s would leverage their stealth, high speed, and long range to attack various United States airborne force multipliers such as vital tanker aircraft (Figure 2.0), airborne early warning and control aircraft, and electronic warfare aircraft (Axe, 2011a; Kopp & Goon, 2011).
Such actions, if successful, could cripple the ability of the United States military to conduct an effective air campaign in the western pacific, and the design of J-20 certainly does not rule out such a role for J-20 within an integrated offensive air campaign. However, as with the strike fighter debacle, the difficult question which arises is whether J-20 is designed primarily (or in other words, “only”) as a long range interceptor aircraft, or if its role as an interceptor is only one of many possible roles as a result of its design.
Dedicated interceptor aircraft were a common fixture of air forces during the early to mid Cold War, where the threat of massed nuclear bombers and the constant need to dissuade opposing reconnaissance aircraft, demanded fighters which could fly at high altitude with high speed with long range to reach and engage an opposing aircraft before it could launch its (potentially nuclear) payload. However, as the intercontinental ballistic missile succeeded the strategic bomber as the primary means of delivering nuclear weapons, the demand of the interceptor subsided.
Few air forces today operate dedicated interceptor aircraft, and those which do exist are typically increasingly obsolete and slated for replacement (such as China’s J-8II interceptors), or feature unique speed and range characteristics allow them to cross vast distances for countries with expansive geography (such as Russia’s Mig-31s). Today, any remaining dedicated interceptors may be upgraded with newer avionics and weapons systems in the air forces they serve in, however they remain a dying niche breed, and have been succeeded in the interceptor role by general air superiority aircraft (Figure 2.1), which are not only capable of aggressive air combat manoeuvring, but may also feature competitive performance in parameters such as speed, altitude, and range.
If dedicated interceptors are being almost internationally slated out, why is J-20 suspected of being a “dedicated” interceptor, rather than a general air superiority fighter which is also able to perform interceptor functions? (Note: with a few exceptions, it is generally a good rule of thumb that modern airframes designed for air superiority can be repurposed to make an effective strike aircraft or to perform interceptor functions, but an airframe designed for dedicated strike or dedicated interceptor duties will typically fare far worse as an air superiority fighter in comparison)
J-20’s possible role as an air superiority fighter will be addressed in the next section of this paper, so here we will consider the plausibility of J-20 being a dedicated interceptor in role.
Similar to the strike aircraft fallacy, initial estimates of J-20’s size vastly overshot its actual dimensions and helped propel a discussion that such a large aircraft of “over 22 meters” must surely be too cumbersome to properly function as a nimble air superiority fighter and therefore logically must be an interceptor (or a striker). Now that J-20’s length is determined to be only slightly greater than 20 meters, the prerequisite reasoning for its dedicated interceptor aerodynamic characteristics is significantly reduced. (Note: of course, a large aircraft does not mean it cannot manoeuvrable, after all, the Su-27 is one of the world’s largest modern fighter aircraft ever developed, but it is also regarded as very capable of air combat manoeuvres)
A subsequent argument for J-20’s dedicated interceptor role is related to its “relatively great length” and its “small wings”. While not described using such obtuse terms, this is effectively the base of many arguments, and is not itself illogical. Attempts to extrapolate J-20’s manoeuvrability based off estimating its weight, wing area, wing loading, thrust, have been made through numerous aviation and defence watching forums. But ultimately, the lack of anything as simple as definitive dimensions of J-20, let alone lack of access to a wind tunnel, a wind tunnel model, and the relevant computers and software (and engineers), will hamstring the credibility of virtually all armchair aerodynamic estimates of the aircraft’s performance from eyeballing the aircraft’s appearance. The Mig-25 is the classic lesson from history (Figure 2.2), warning observers to not use mere pictures to assess an aircraft’s aerodynamics, and just as the Mig-25 was suspected to be a manoeuvrable air superiority aircraft but turned out to be a cumbersome interceptor, it is hardly out of the question for J-20 to be suspected of being an interceptor but actually perform as an air superiority fighter (Figure 2.3).
At this stage, it is worth noting that certain publications have alluded to the possibility that J-20 may be intended for competitive air combat manoeuvring (Kopp & Goon, 2011; Sweetman, 2014). Such performance however, is rightly specified as contingent on J-20’s powerplant. As of August, 2015, all J-20 prototypes are suspected to be powered by a variant of the Russian Al-31 engine (Figure 2.4), possibly highly modified for greater thrust. Therefore if projections of J-20’s aerodynamic performance assumed the aircraft would be powered by an Al-31 variant, this may partially justify the limited scope of J-20’s predicted roles. Of course, for many years, Chinese military watchers have been aware of the WS-15 (Figure 2.5), a 17 ton class supercruise-capable turbofan which was intended to be the actual powerplant for J-20. A J-20 equipped with WS-15 would feature much enhanced thrust compared to an Al-31 acting as interim engines, and would have accompanying consequences for its aerodynamic performance and thus its roles. Therefore, it may be worth specifying just what kind of powerplant a J-20 is equipped with when speaking of its potential roles. For instance, a J-20 equipped only with Al-31s may well be less competitive in air combat manoeuvring and may be slated for “only” interception and strike duties, while a J-20 equipped with WS-15s may be far more competitive and excel as an air superiority fighter.
J-20 as an air superiority fighter:
Air superiority is a crucial possible role for J-20 which no western defence publication (to the author’s knowledge) has given meaningful consideration.
There are various possible reasons which may explain this glaring absence. One reason could be scepticism and hostility at the idea of the Chinese aerospace industry producing a fighter aircraft that may prove to be competitive with the western world’s “golden fighter” – the generation defining F-22 – indeed there have been many articles expressing dismissal of J-20’s design or speculating if its design was merely a “re-hash” of other fighters with superficially similar arrangements, such as J-20’s cockpit appearing similar to the F-22 (Lee & Johnson, 2012), or J-20 featuring a similar aerodynamic configuration to the Russian Mig 1.44 (Figure 3.0) (Reed, 2011a). This of course ignores despite the fact that the delta/canard/twin tail configuration had been tested by Chengdu Aircraft Company in the early 1970s as part of the VI variant of the J-9 project (Figures 3.1, 3.2 and 3.3), not to mention the logical fallacy of suspecting common heritage simply on the broad basis of aerodynamic configuration – otherwise the case could be made that Eurofighter Typhoon, Rafale, and Gripen must all be copies of each other due to their canard/delta wing/single tail configurations, despite each aircraft having their own unique and independent development paths.
Other reasons for doubting J-20’s role as an air superiority fighter may be related to the aforementioned engine question, where the aircraft’s potential differing powerplants may determine the aerodynamic performance in significant ways. Such a reason is logically sound and worthy of further observation and investigation.
But what of the support for J-20 being an air superiority fighter?
There does exist a small – but arguably credible – base of literature which may suggest that J-20’s design is intended to be aerodynamically competitive in air combat manoeuvring.
One source is from a Chinese Air Force officer, Colonel Daixu, who was quoted by a Global Times state media article in 2009 as saying the “Chinese 4th generation aircraft” will feature “4 S characteristics” (Deng, 2009), one of the “S” being super-manoeuvrability. Super-manoeuvrability is a term that has been applied to various highly manoeuvrable aircraft ranging from the Su-27 family to the F-22. (Note, in Chinese parlance, “4th generation” is equivalent to the rest of the world’s “5th generation” and Chinese “3rd generation” is equivalent to the rest of the worlds “4th generation”. E.g.: an F-22 would be described as “4th generation” in Chinese articles and an F-16 would be described as “3rd generation”)
While Chinese state media is not always a reliable source for Chinese military matters, in this author’s experience, when state media write original articles surrounding certain Chinese military subjects, there is a good likelihood of authenticity especially if there are other corroborating new facts. In this particular news release, the new generation of fighter aircraft is said to enter service within 8-10 years (from time of its publishing in 2009), logically placing its inevitable first flight sooner rather than later. Less than two years after this date, J-20 made its first flight.
Another valuable source that may shed light on J-20’s intended role, is from a paper published in 2001 by Dr. Song Wencong (Song, 2001) (Figure 3.4), a Chinese aircraft designer responsible for the J-10’s design and who mentored Yang Wei, the designer of JF-17 and J-20. In this paper, Dr. Song illustrates the configurations a fighter aircraft may field if it sought to achieve significant radar cross section reduction (radar stealth), as well as supercruise, high manoeuvrability and unconventional manoeuvres such as post-stall manoeuvres. The paper settled on an aerodynamic configuration with delta wings, canards, leading edge root extensions, and lifting body and all moving vertical stabilizers (Siegecrossbow, 2012). This of course, is almost a word for word description of J-20’s exact aerodynamic configuration.
Altogether, these two sources are not irrefutable proof that J-20 is an aircraft with excellent or competitive manoeuvrability, however in this author’s opinion, they do together provide strong indication that J-20 was designed with intention to be aerodynamically competitive at the very least. Whether its performance will match its design goals is another matter entirely and that performance is not one which can be judged at this time.
A final thought which must be seriously considered, is that when the requirements for J-20 were first established, the Chinese Air Force almost certainly recognized the F-22 would be the most dangerous combat aircraft their pilots would face if they ever had to contest air superiority against the United States Air Force. Therefore it is worth pondering if the Chinese Air Force would have requested an aircraft that could directly compete with the F-22 rather than merely seeking to strike at the support elements of the F-22 (such as tanker aircraft). Putting it bluntly, one has to ask if the Chinese Air Force would have accepted that their future high end fighter aircraft would have to run if it encountered the F-22 (or any other opposing stealth fighter for that case), or if it should be able to hold its own and have the ability to win in a confrontation as well.
There is a sensible case to be made that a confrontation between opposing stealth fighters may be decided at within-visual-ranges, where elements of classic dogfighting and close in air combat manoeuvring may apply. Therefore if one does entertain the possibility that Chinese Air Force brass required their next generation fighter to be capable of competing against opposing stealth fighters, then it is natural to ask whether the performance necessary for dogfighting would be part of its demands. Of course, the logical answer to the question should be a resounding yes.
It is worth noting, that if J-20 is a capable air superiority fighter, it would also be capable of performing the interceptor role and acting as a striker as well, which dramatically broadens its utility in potential conflict scenarios if the aircraft were merely an interceptor or striker.
This entry has briefly summarized the western defence media’s commentary regarding the J-20’s possible combat roles. It is concluded that there is little evidence and little logic to support popular notions that J-20 is designed or intended to function a dedicated strike aircraft or a dedicated interceptor aircraft, although it is acknowledged that J-20’s manoeuvring capability will be dependent upon its final powerplant.
Furthermore, this paper suggests that J-20 may instead be designed and intended to be an air superiority fighter due to various credible Chinese sources, as well as the logical requirement for a next generation fighter aircraft to be capable of performing air combat manoeuvres.
This entry does not make any claims about J-20’s aerodynamic performance relative to other specific aircraft beyond the suggestion that it is likely intended to compete with other air superiority aircraft in the air combat manoeuvring domain.