An Initial Assessment of China's J-20 Stealth Fighter
Publication: China Brief Volume: 11 Issue: 8
May 6, 2011 05:31 PM Age: 5 days
Category: China Brief, Home Page, Featured, Military/Security, China and the Asia-Pacific
By: Carlo Kopp
The maiden test flight in January 2011 of China's J-20 stealth fighter prototype is an important strategic milestone in several different respects, and is part of an ongoing effort by China to develop advanced military technology [1]. The J-20 is the first combat aircraft developed by China that qualifies as "state of the art" by Western measures. It also shows that China has mastered "stealth shaping" technology—the essential prerequisite for developing stealth aircraft. Finally it shows that China has managed to integrate its strategic planning with the functional definition of a modern combat aircraft. Once fully developed, the J-20 has the potential to alter the regional balance in the Asian air power strategic game, by rendering nearly all regional air defense systems ineffective.
The People's Liberation Army (PLA) has yet to disclose any of the intended performance parameters of this fighter aircraft, or its intended avionic systems and weapons fit. As a result, analysts are left with one choice only, which is to apply analytical criteria such as size, shape and configuration to draw an estimate of the aircraft's characteristics. If applied with rigor, this technique can produce highly accurate results [2].
Scaling the dimensions of the J-20 against proximate ground vehicles of known types in photographs does yield very accurate dimensions, showing that the J-20 is a large fighter, in the size class of the United States F/FB-111 family of aircraft, or the proposed but never built FB-22A "theater bomber." This in turn indicates an empty weight in the 40,000 – 50,000 lb class, depending on construction technique used in the design, and an internal fuel load of up to 35,000 lb. Inevitably, this yields subsonic combat radius figures in the 1,000 – 1,500 nautical mile class, subject to the thrust specific fuel consumption of the production engine in subsonic cruise. The J-20 is therefore a fighter built for reach, and would be competitive in range performance against the F/FB-111 series, the F-15E Strike Eagle series, and the new Russian Su-35S Flanker series. The implications of this will be discussed further.
J-20 Capability Assessment
The shaping of the J-20 prototype has important implications from the perspectives of aerodynamic performance and stealth.
The delta canard configuration of the J-20 design is common to the earlier Chengdu J-10, the European Eurofighter Typhoon, the French Rafale and the prototype of the Russian MiG I.42 super cruise fighter. This configuration provides for high supersonic performance, excellent supersonic and transonic turn performance, and better short field landing performance than conventional delta wing designs. If equipped with suitable engines, a J-20 would be very efficient in supersonic cruise regime, with excellent close combat maneuver performance. The intended engine fit has not been disclosed, although there has been speculation that the prototype may be fitted with imported Russian Al-41F1S or Item 117S engines common to the Su-35S and T-50 PAK-FA prototypes. The Al-41F1 is an evolution of the supersonic cruise engine developed for the MiG I.42, with a more powerful Item 129 engine in development for the production T-50 [3].
There has been some media speculation about an indigenous engine for the J-20, designated the WS-15, but no substantial official disclosures to date [4].
The detail airframe stealth shaping design of the J-20 is clearly based on shaping design rules developed by the United States, and employed primarily in the F-22A Raptor, but with an engine inlet design closer to the F-35 Joint Strike Fighter. This is important insofar as most radar signature improvement in stealth designs is a result of shaping, with radar absorbent materials and detail design employed primarily to "clean up" unwanted reflections that could not be suppressed by shaping. Qualitative and quantitative analysis performed by the author indicates that the J-20 has the potential to yield much better stealth performance from the front and sides than the F-35 Joint Strike Fighter, and possibly as good as the F-22A Raptor, should Chinese designers master materials and detail design techniques adequately. The design has only two apparent weaknesses, which are the curvature in the slab side shaping, which provides broader reflection lobes than necessary, and the circular exhaust nozzle, a weakness common to the F-35 and T-50. Both may be artifacts of the prototype and may not be features of a future production aircraft.
The shaping design will be highly effective against radars operating above the 1 GigaHertz L-band, but much less effective below this band. This band coverage encompasses most surface based and airborne search, acquisition and fire control radars used by the United States and its allies in Asia.
A survey of twenty-six unclassified English language Chinese research papers on radar absorbent materials indicates a high level of research effort in the area, but mostly for materials not suitable for aircraft applications. Research in this area is usually not published in the West and there is no reason to believe China would do differently [5].
The available data supports the proposition that the J-20, once fully developed, will be a high performance stealth aircraft, arguably capable of competing in most cardinal performance parameters (i.e. speed, altitude, stealth, agility) with the United States F-22A Raptor, and superior in most if not all cardinal performance parameters against the F-35 Joint Strike Fighter.
The intended role of the J-20 has not been disclosed officially, and widely varying views have been expressed by various observers.
The suitability of this design for various roles will depend primarily upon what engines are installed, and whether faceted stealthy exhaust nozzles modeled on the F-22 design are employed, the latter being important for deep penetration through air defense systems.
If the engines deliver 40,000 – 50,000 lb class thrust performance, the J-20 will be viable as an air combat fighter, air defense interceptor and deep strike fighter. If thrust performance falls below this benchmark, the aircraft would lack the agility for close air combat, but still be very effective as an interceptor or bomber.
What this suggests is that if Chinese engine technology has not matured enough by the latter half of this decade, when IOC is planned for the J-20 [6], early variants could be employed as strike aircraft, or interceptors, with later variants "growing" into the air combat role as more powerful engines become available.
China has deployed or developed a range of new guided weapons suitable for internal carriage by the J-20. While no imagery as yet exists showing the configuration of the J-20 internal bays, the aircraft layout could permit a similar arrangement to the F-22A, but with a longer and deeper fuselage bay capable of carrying larger bombs, or even more weapons.
Richard Fisher at the International Assessment and Strategy Center has detailed a number of Chinese 5th Generation Air-Air Missiles, including evolved variants of the PL-12, modeled on the United States AIM-120 AMRAAM, the ramjet powered "PL-13" modeled on the European MBDA Meteor, and the agile thrust vectoring PL-ASR/PL-10, modeled on the A-Darter and Iris-T missiles [7].
Guided bombs suitable for strike against surface targets are also abundant. At the Zhuhai and CIDEX 2010 arms expos, Luoyang/CASC (China Aerospace Science and Technology Corporation) displayed a range of new guided bomb designs. These include the "Lerting" (Thunderbolt) LT-3, which is modeled on the US GBU-55/56(V)/B Laser JDAMs, the FT-1, FT-3 and FT-5 modeled on the U.S. GBU-32/35/38 JDAM satellite aided bombs, and the winged FT-2, FT-4, FT-6 and LS-6 planar wing glide bomb variants, broadly modeled on the Australian JDAM-ER glide bomb family. The LS-6 family also includes 50 kg and 100 kg small bombs, modeled on the U.S. Small Diameter Bomb series, but with cruciform strakes rather than planar wings [8].
The heavy emphasis placed by Luoyang/CASC on glide bombs is important, as these can be released by stealth aircraft from ranges well outside the detection range of the aircraft itself, which can thus remain unseen through the whole delivery maneuver, effecting complete surprise.
The strategic impact of a mature production J-20, even if limited to strike roles alone, would be profound. With sufficiently good stealth performance to defeat air defense radars in the L-band through Ku-band, the aircraft could easily penetrate all air defense systems currently deployed in Asia. Even should the aircraft be tracked by a counter-stealth radar, the high altitude supersonic cruise penetration flight profile makes it extremely difficult to engage by fighter aircraft and Surface to Air Missiles. The only fighters deployed in the Pacific Rim with the raw performance to reliably intercept a supersonic J-20 are the F-22A Raptor and Russian MiG-31 Foxhound.
The size of the J-20 and resulting fuel fraction indicate that the aircraft will be able to cover the "First Island Chain" without aerial tanker support, and with tanker support, reach targets across the "Second Island Chain" on subsonic cruise profiles. Nearer targets would be accessible on supersonic cruise profiles [9].
The Impact of the J-20
There can be no doubt at this time that a mature production J-20 with fully developed stealth and supersonic cruise capability would qualify as a "game changer" in the Asia-Pacific region.
The J-20's combination of stealth and supersonic cruise—the cardinal design feature of the F-22A Raptor—provides the capability to defeat nearly all extant Integrated Air Defense Systems. Defeat is effected by denying detection, and should detection occur, by kinetically defeating launched missiles, which cannot close with the target before it exits radar tracking range. Even without stealth, high altitude supersonic aircraft are challenging targets for all but the largest and longest ranging Surface to Air Missiles. Interceptor aircraft without a capability for sustained supersonic flight are typically ineffective against high altitude supersonic targets.
The development of the J-20 around the combination of stealth and supersonic cruise results in a design, which will be undetectable at range by almost all air defense radars operated by the United States and its numerous allies in the Asia-Pacific region. In practical terms, this results in the "block obsolescence" of most Asian air defense systems.
Another important consideration is that the J-20 is a large fighter and therefore, if flown on fuel efficient subsonic cruise profiles, will be able to reach targets at ranges of around 1,000 nautical miles without aerial refueling tanker support.
If flown from PLA airbases along the eastern seaboard of mainland China, the J-20 will thus be able to comfortably reach any target within China's "First Island Chain," unrefueled. These targets include airfields in Japan, South Korea, and former US Air Force airbases in the Philippines.
With modest aerial refueling support, the J-20 will be able to reach most targets situated along China's "Second Island Chain," including the strategically critical Guam facilities.
The strategic choices available to the United States and its allies for dealing with the J-20 are very limited; such is the potency of all aircraft combining stealth and supersonic cruise capabilities. These distill down to the deployment of large numbers of F-22A Raptor fighters in the region, and the development and deployment of "counter-stealth" radars operating in the HF, VHF, and UHF radio-frequency bands. Funding for the production of the F-22A was stopped in 2009, following an intensive political effort by Secretary of Defense Robert M. Gates. There is no program to fund the development and volume production of "counter-stealth" radars.
The incumbent U.S. Administration has thus committed itself politically to a path in developing air power for the U.S. armed services and allied air forces, predicated wholly on future opponents operating obsolete Soviet era air defense weapons and fighters. The unveiling of the Russian T-50 PAK-FA and Chinese J-20 over the last two years has not produced any significant changes in U.S. planning, which may challenge the United States and its Pacific Rim allies’ strategic advantage in conventional air power.
