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J-31 (Jianjiji-31 Fighter aircraft 31)

The Chinese military leaked the first photos of long-rumored new stealth fighter, the second model revealed in China.The J-31 attracted wide public attention in June when some online pictures showed the cutting-edge fighter fully wrapped but with its futuristic shape still discernible. The J-31 fighter, named Falcon Eagle in Chinese, took its first flight at 10:32 am Beijing local time, Wednesday 31 October 2012, along with two J-11BS fighter jets from the runway of Shenyang Aircraft Corp, the producer and researcher of the fighter in Liaoning Province.

Shenyang Aircraft Industry Group (SAC), one of the leading aircraft design and manufacturing corporations of Chinas aviation industry, revealed the prototype of what might eventually become Chinese analog to the American F-35 Joint Strike Fighter. The new aircraft, said to be designated the J-31 or to have the codename F-60, has external characteristics that suggest to some that it could be used on future Chinese aircraft carriers. The J-31 prototype jet has the side number 31001, which is the origin of the J-31 nomenclature, since the first two J-20 prototypes had 2001 and 2002 side numbers, respectively.

Photos of a model labeled F-60 were posted online as early as September 2011. These images show only scaled-down models, not the real thing, with one notable difference being the single wheel in the model versus the paired nose-wheels in the real deal. This radio-controlled F-60 model had been built with the Shenyang University of Aeronautics and Astronautics [SUAA]. In June 2012 a photograph of a full scale airframe being transported on a truck trailer, obscured by netting, appeared online.

Though no characteristics of the prototype have been unveiled, one major difference is obvious: unlike its American relative, Chinas J-31 has two engines, as does the previously revealed J-20. The pictures of the Chinese technology demonstrator suggest that the engines the aircraft is currently equipped with do not have thrust vectoring nozzles. Possibly the prototype is at an early a stage of testing, and might be fitted with a more sophisticated and powerful propulsion package at a later date. The twin vertical tail and wide-spaced ram air inlets are reminiscent of these features on the Lockheed Martins F-22 Raptor.

The J-31 inlet design features diverterless supersonic inlet [DSI] similar in concept to that used on the American F-35. The F-35's diverterless inlet lightens the overall weight of the aircraft. Traditional aircraft inlets were comprised of many moving parts and are much heavier than newer diverterless inlets. The diverterless inlet also eliminates all moving parts. DSI moved from concept to reality when it was flown on a Block 30 F-16 in a highly successful demonstration program consisting of twelve flights flown in nine days in December 1996. Unlike the Russians and Indians, whose joint project to develop a fifth generation aircraft produced a single design, the Chinese military followed the American example and placed its bets on two horses: Chengdu Aircraft Corporation, which is already testing the J-20 fifth generation heavy combat aircraft, and Shenyang Aircraft Industry Group with its F-31/F-60 aircraft. It is unclear which America practice the Chinese have emulated. Possibly this is like the Advanced Tactical Fighter and Joint Strike Fighter programs, in which competing designs were flight tested before one was selected for production. Or possibly the J-31 and J-20 are not to be regarded as competitors, but as complementary pair such as the F-22 and F-35, because to some it appeared the aircraft may have different specializations.

The problem with the competitive fly-off explanation is that the first flight of the J-20 came in January 2010, nearly two years before the first flight of the J-31. This belies a competitive fly-off, absent a rather spectacular schedule delay in the J-31, or an extremely sedate development schedule in which such a two year discrepancy is insignficant in the long view. The complementary role explanation fails due to the apparent similarity in size. Unlike the large twin-engine air-superiority F-22 and smaller single engine air-to-ground F-35, both the graceful J-20 and the slightly shorter but visibly chunkier J-31 are twin-engined, presumably with the same WS10 Taihang engines. If the total weight of the shorter J-31 was signficiantly less than that of the J-20 [a fact not in evidence], either the J-31 would seem rather over-powered, or the J-20 somewhat under-powered.

China's J-31 stealth fighter may also be used on the carrier in future. The Liaoning would have about 40 fixed-wing aircraft on board. Possibly the complementarity lies in the J-20 being destined for land-based operations, while the J-31 is slated to go down to the sea in ships. Carrier based aircraft are normally twin-engined for safety reasons, and the Chinese might have decided that the greater structural strength needed for carrier operations would be wasted on a land-based J-20. The shorter J-31 would also make for easier handling on an aircraft carrier, where space is at a premium. The Chinese might also have decided that little was to be gained from trying to apply a common airframe to both the land and carrier missions. The F-4 Phantom succeeded in this effort, but the American F-35 was bedeviled by the requirements of being all things to all services.

The Chinese Military Review website published computer-generated images of the J-31 fifth generation fighter jet in action, with a variety of air to air missiles. On at least two images the aircraft is depicted with an extended tailhook that sea-based aircraft use to stop after landing on the deck of an aircraft carrier. The two-wheeled front rack chassis of the J-31 prototype also suggests the aircraft was designed for naval use, facilitating the attachment of the holdback device installed on the nosegear to the catapult, like sea-based versions of Dassaults Rafale in France, Lockheed Martins F/A-18 E/F Super Hornet and the Russian Su-33. There is no indications that the J-31 prototype is capable of short take off and vertical landing, a capability of the F-35B STOVL variant.

The current weak point of the J-31 - and the J-20, and the non-stealthy J-15 [also known as the Flying Shark, which is said to be a match for US F-18 Hornet fighters] - is its Russia-made Al-31 engines, which are less powerful than those of the American F-35 fighter. However, these fighters will be more competitive in future when the Chinese jets is equipped with more powerful Chinese engines, because the American F-35 has only a single engine.

As is well known, both Chengdus J-20 and Shenyangs J-31 face the problem of the lack of reliable Chinese-made jet engines with technical characteristics appropriate for a fifth generation fighter. Initially both may be fitted with Klimov RD-93 afterburning turbofans from Russia. China continues to buy Russian military jet engines. The WS10 Taihang, China's flagship jet fighter engine, remained seriously flawed after a quarter of century of development effort. The WS10 engine was intended to equip the new J-10 fighter, low-rate initial production of which was authorised in 2002. But at least the initial run of fifty J-10 aircraft were to be fitted with Russian AL-31F engines instead. The WS10 engine was reverse-engineered from the CFM-56 commercial turbofan, which in turn was a derivative of the General Electric F101 engine originally designed for the 1960s-era Advanced Manned Strategic Aircraft, which was eventually deployed as the B-1 bomber. That is to say, after nearly a quarter century development effort on a four decade old design, China remained unable to produce a viable high performance fighter engine. It is expected that eventually both the J-20 and J-31 will be fitted with the WS15 engine, but the core engine for the WS-15 engine was first tested in April 2005, suggesting a long road ahead.

China lacks the extensive electronic support [eg, RIVET JOINT, AWACS, etc] and aerial refueling capabilities that American stealth aicraft can rely upon. The J-31 might achieve an initial operational capability in the 2025 timeframe.

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