The Chinese Chengdu J-20 stealth aircraft took to the sky a second time this past weekend from an airfield in Chengdu. What appears to be a second test flight (after the initial January 11th 18-minutes flight) also coincided with the 60 years anniversary of China’s aviation industry. The 85 minutes flight took place in front of crowds of people allowing more photographic images of the aircraft to emerge. The plane stealthy look is undisputed although it appears remarkably bigger (probably as long as 75 feet) than the US F-22. Experts now concede that it is a an actual prototype of a fifth generation fighter aircraft and not a technology demonstrator. Here are some of our observations.

American ‘Heritage’

The Chinese have learned very well their lessons on American Stealth technology from the F-22 and F-35 programs, but are also celebrating their heritage of 60 years aerospace industry. Stealth is primarily provided by careful shaping of control and fuselage surfaces as well as internal carrying of weapons as articulated by mature American stealth designs on the B-2, F-117, F-22 and F-35. The ability to appropriately deflect incoming radar beams is increased when weapons bay and landing gear doors edges show the characteristically stealthy saw-tooth shapes. The sleek F-22 forward fuselage section, nose and even canopy are incorporated to the Chinese design. The horizontal bi-section of the fuselage along the chine that extends from the J-20 canard roots to the nose are direct incorporation of the F-22 design except that on the F-22, the chine actually extends from the wing root to the nose. The result is the diamond shaped fuselage structure and frontal cross-section of the aircraft which -just like the F-22, offers a greatly diminished radar cross section. The air intakes seen frontally again have maintained the trapezoidal shape similarity with the F-22. And this is where the F-35 engine air intake design also comes into play: the air intake lateral edges are sweeping slightly forward maintaining the jagged ‘stealthy’ look. The J-20 also seems to have ‘cannibalized’ other parts from the F-35. The aft fuselage all-moving twin dorsal fins/vertical tails are very short and have with a pronounced sweep backward identical to the F-35.


The Indigenous Fighter Programs

Despite the air intake similarity of look with both the F-35 and F-22, the J-20 air intake shows the presence of Divertless Supersonic Inlet DSI which are ‘bumps’ on the fuselage adjacent to the air intake edges. They provide adequate air flow separation to the engines during maneuvering in order to prevent engine compressor stalls. Their presence on the indigenous JF-17 fighter aircraft produced in large number for Pakistan is also the tell-tale sign of the WS-13 Taishan family of engines developed from Russian technology.

The Chinese built JF-17 with Pakistan Air Force with the DSI fuselage 'bumps' at the engine air intake

 

The flight control surfaces except for the vertical fins which -we have seen, originate from the F-35 are derived from another successful Chinese program, the Chengdu J-10. The Chengdu J-10 employs both the delta-shaped canard design and double-delta wing design. This double-delta wing design had first been adapted to the F-7 Chinese production of the Russian MIG 21 sold to Pakistan, Nigeria, Zimbabwe etc. For the J-20, these control surfaces guarantee very high agility in flight maneuvers. On the J-10 the combination delta-shaped canards plus double-delta wings led to a highly maneuverable, high angle of attack, Mach 2 capable multi role fighter. The aft fuselage ventral fins providing additional control during aircraft roll are present on both J-10 and J-20 designs.

The indigenous J-10 delta shaped canard and double-delta shaped wings

 

Finally the exhaust nozzles of the J-20 are anything but stealthy. The large metallic circular nozzles are both electromagnetic and infra red signature prone to detection. A pair of pictures suggested that they were tilting in flight. If that is the case we are seeing Thrust Vector Controlled nozzles whose non-stealthy attributes suggest their interim presence for purely testing purpose. This also makes clear that the engines currently involved in the J-20 are the WS-10B Taihang engines developed from the Russian Lyulka Saturn AL-31FN. The Saturn engine was part of the J-11 program that locally manufactured the Russian Sukhoi-27 for the People Liberation Army Air Force. The Saturn has been further developed into the WS-10A Taihang for the Chengdu J-10. The WS-10B Taihang on the stealth prototype delivers up to 30,000 lbs and implements Thrust Vectored Control and digital engine control technology (similar to western engines FADEC Full Authority Digital Engine Control) but its circular nozzles makes it an unlikely candidate for an operational stealthy aircraft. We maintain thus that the J-20 is employing those engines as an interim measure until the better 35,000 lbs thrust-vectored WS-10G Taihang engines implementing stealthy shaped nozzles outlets become ready.

Overall the J-20 materializes the big and dominant aircraft that the a frustrated Chinese Defence Establishment always fantasized about, which at some point was embodied by the powerful MIG 31 aircraft that the Russians never let them acquire. But clearly the J-20 is much more than fulfilling a dream of grandiosity. We are seeing emerging stealthy capability from a Chinese Aerospace industry which has struggled for 60 years to achieve world recognition. Its activities for the main part of its history have been restricted to reverse-engineering Russian designs and building large number of locally built clones or hybrid aircraft like the F-7 and J-8/F-8 interceptors. Its ability to produce very large numbers of aircraft at very low unit cost could compensate the total absence of state-of-the-art technology and dubious quality control processes. However tremendous advances with programs implemented since the early 90’s (the J-11/ Sukhoi-27, the J-10 indigenous fighter, the JF-17 with Pakistan) seem to pay off. The J-20 latest flight confirms that we are indeed witnessing a bona-fide prototype testing program now gathering even more momentum. The J-20 is not a technology demonstrator. The aircraft design features shows that stealth and maneuverability (thrust-vectoring) are primary goals. We do not believe that Super Cruise capability will be significant in this current design, at least not in the way that the American F-22 is able to perform (sustained cruise to Mach 1.7 without using afterburners) even though powerful engines with digital engine control will be available. The stealth attributes as implemented along the lines of American stealth philosophy are valid. Achieving a real fifth generation fighter aircraft will take China a few more years as mature multiple sensor integration and integrated data communication networks are necessary. But already the prospects of a stealth aircraft likely to appear in very large numbers will tip the balance in the region.



The Divertless Supersonic Inlet (DSI) 'bump' on the fuselage visible at the engine air intake

 


The all-moving swept twin vertical tails similar to the US F-35

 

 

The J-20 thrust-vectored controls as derived from the J-11/Su-27 family of aircraft

The angled nozzles adapted from the thrust vectored J-11/Sukhoi-27

 

 

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