When the Chinese J-20 stealth fighter was revealed nearly nine years ago, speculation was rife about its role and mission upon entering service in the People’s Liberation Army Air Force (PLAAF). In English language defense media, the most highly circulated and popular theories suggested it was a dedicated interceptor aircraft intended to destroy force multipliers like tanker aircraft or airborne early warning and control (AEW&C) aircraft, or a dedicated long-range strike aircraft akin to a modern F-111.
However, other similarly sized stealth aircraft like the U.S. F-22 and Russian Su-57 are widely accepted to be air superiority fighters with secondary interceptor and strike roles, and even aircraft like F-35 are intended to field serviceable air superiority characteristics. Some arguments backing up J-20’s interceptor/strike theory is doctrine driven, suggesting the J-20 was intended to specifically operate in the PLA’s so-called “anti-access, area denial” strategy. However, this is unconvincing, because such a doctrine would still hold a place for air superiority fighters.
Indeed, the primary argument surrounds the aircraft’s agility. Much commentary initially suggested J-20’s supposed length and its aerodynamic configuration made it poorly suited for aggressive air combat maneuvering (ACM). Therefore, J-20’s supposed limited agility and kinematic properties would place firm limits on its roles. Agility certainly does determine role; however, the aerodynamic performance of a modern, complex fighter aircraft cannot simply be eyeballed.
J-20 aircraft did make multiple appearances at
. This year, it performed longer and more aggressive flight displays than at Zhuhai 2016, and high-level individuals associated with the J-20 also revealed additional information. Taken together, Zhuhai 2018 finally provided clear, official statements regarding the intended role of the J-20 as well as the agility it is capable of. This piece will examine new developments and past documents and rationale to consider the J-20’s intended level of agility.
Why Care About Agility Anyway?
The agility of fifth generation fighter aircraft such as the F-22 and Su-57 outperforms past fourth generation aircraft in many flight regimes and loadouts. The F-35, designed from the outset as a multirole strike fighter, has often been criticized for being insufficiently agile; however, in recent years even the F-35’s agility has come around to be accepted as competitive against past fourth generation fighters, especially under similar combat and fuel loads.
In other words, competitive agility is important for any fighter aircraft intended to face opposing fighters, even in a secondary role. Furthermore, there are few clear indications as to what future fifth generation versus fifth generation air battles may look like, and it would be foolhardy for any air force to dismiss agility in such confrontations. Indeed, in stealth versus stealth engagements, one could even make the case that equal advancements in stealth, sensors, networking, electronic warfare, and weapons systems may end up cancelling out each side’s advantages and cause beyond visual range engagements to transition into within visual range combat where the importance of ACM is further elevated.
Following this, one may naturally assume that the J-20 would feature at least competitive agility. However, many proponents of the interceptor/striker position do not consider air superiority to be a primary mission that the PLAAF would have required the J-20 to fulfill. A commonly insinuated premise is that the Chinese aerospace industry was not capable of producing a fifth generation air superiority fighter, and would have to “settle” for a less technically challenging interceptor or striker instead. Such a position has often been articulated in two parts; one reflecting the J-20’s inherent aerodynamic design, and the other in relation to the J-20’s powerplant. We will now consider both parts in closer detail.
Dr Song’s Paper and the Limits of Eyeballing
Public commentary surrounding the J-20’s aerodynamic design has been of dubious quality, at best. Past assertions primarily revolved around the J-20 being “too large” to be agile, despite being shorter than a Flanker. Occasionally, estimates of the J-20’s wing loading seek to extrapolate its agility in relation to other fighters. However, such eyeballing comparisons are simplistic and potentially dangerously flawed, as they do not provide a holistic picture of the additive effects of various design features where the whole may be greater than the parts. The infamous Cold War misattribution of the Mig-25 as an agile fighter aircraft demonstrated how visual estimates alone were unreliable when ascertaining an aircraft’s kinematic performance.
More legitimate estimates can be made if one has experienced aerospace engineers, a wind tunnel, and accurate, representative models of the aircraft in question. Fortunately, the results of such an investigation for the J-20’s aerodynamic configuration exist, thanks to Dr. Song Wencong.
Song, who passed away in 2016, was a Chinese aerospace engineer and aircraft designer, and chief designer of the single seat J-10 aircraft, as well as mentor to Yang Wei, who was chief designer of the JF-17 and subsequently the J-20. In 2001, Song published a
titled “Aerodynamic configuration study of a small aspect ratio, high lift aircraft,” which investigated a future fighter aircraft’s configuration intended to resolve design conflicts between stealth, high maneuverability, supercruise, transonic performance, and high angle of attack performance.
An English
of the paper has been available online for a few years now, provided by PLA forum-goer “Siegecrossbow,” and is recommended reading for anyone interested in the J-20’s aerodynamic background. The paper describes Song’s proposed aircraft in great detail; however, we will only examine the concluding remarks:
The proposal employs lift-body LERX canard configuration. It is unstable in both the lateral and yaw directions. The proposal employs small aspect ratio wings with medium back sweep angle, relatively large dihedral canards, all moving vertical stabilizers far smaller than those on conventional fighter aircraft, and S-shaped belly intakes. According to our assessment, the proposed aircraft will have excellent supersonic drag characteristics, high AOA lift characteristics, high AOA stability and controllability, and excellent stealth characteristics.
Needless to say, this configuration almost perfectly reflects the J-20’s aerodynamic features and overall design. Considering Song’s past leading role in Chengdu Aerospace Corporation as well as his work with Yang Wei, it is overwhelmingly likely that Song’s study became the basis for what would became the J-20. Therefore, the quality and depth of analysis shown in this paper and its English translation should serve as a minimum benchmark that any opposing theories of the J-20’s aerodynamic configuration should meet.
