Or just another rumour?

by Sébastien Roblin

In a 2018 Zhuhai airshow in China, a specially modified Chengdu J-10B single-engine multi-role jet wowed audiences with a series of jaw-dropping manoeuvres including the famous Pugachev’s Cobra and the Falling Leaf, in which the diving aircraft spun laterally on its horizontal aircraft as it seemingly floated lazily towards the ground. You can see the stunts in this video.

Like its American counterpart the F-16 jet, the J-10—dubbed the Vigorous Dragon, or the Firebird by NATO—is a quite agile fourth-generation jet with an aerodynamically unstable airframe that has to be regulated by its flight control computer. But such manoeuvres would have been impossible for a regular plane relying entirely upon conventional flight controls.

The secret-sauce in the J-10B at Zhuhai was its power-plant: instead of the usual Russian AL-31F(N) turbofan, it boasted a WS-10B Taihang engine normally reserved for use on the larger twin-engine Chengdu J-20 Mighty Dragon stealth fighter. 

More importantly, this particular Taihang (labelled the WS-10G in some sources) was modified with three-dimensional Thrust Vector Controls (TVC) allowing the pilot to redirect the engine’s thrust by tilting the exhaust nozzles side by side as well as up and down.

This enhances the jet’s ability to adjust pitch, roll and yaw, granting the J-10B super-manoeuvrable flight characteristics, in which the pilot retains control of the aircraft during a stall, unlike for a conventional plane.

Aside from various test beds, the United States only operationally deploys a single TVC-equipped fighter, the super high-performing F-22 Raptor air superiority stealth fighter equipped with two-dimensional TVC. Lockheed did not incorporate TVC in the later F-35 Lightning attack-oriented stealth jet.

Russia has adopted TVC engines on a larger-scale in the fourth-generation Su-30MK, Su-35S and MiG-35 fighters, as well as its Su-57 stealth fighter. China’s purchase of 36 Su-35 fighters in 2016 likely gave it access to technology it used to inform the TVC-equipped WS-10.

The ability to perform tight manoeuvres is obviously slick card for pilots to hold up their sleeve in a within-visual range dogfight, potentially allowing them to outmanoeuvre nearby foes and possibly dodge an incoming missile.

But the value of incorporating heavier and more expensive TVC engines remains debated in Western aviation circles, because performing such extreme manoeuvres drains away the jet’s energy in terms of speed and altitude that can be traded for speed. That means that a tight manoeuvre may pay off against an immediate threat, but then leave the TVC-equipped jet in question a ponderous state in which it would struggle to evade follow-up attacks.

It’s alleged that over-reliance on thrust-vectoring led to the defeat of Indian Air Force Su-30MKI fighters which duelled American F-15C jets in a Red Flag exercise in 2008. 

Another issue is that the advent of high-off-boresight missiles like the American AIM-9X and Russian R-73 missiles and helmet-mounted sights on the latest fourth-generation fighters allow pilots to launch short-range air-to-air missiles at targets without having the nose of the plane pointed at them (though being so positioned remains desirable due to the added momentum.) This reduces, but hardly eliminates, the advantages granted by superior manoeuvrability.

The Troubled Taihang

Photos have revealed additional J-10Bs and more advanced J-10Cs modified as WS-10B testbeds, both with and without thrust-vectoring. in November 2019, photos emerged of a yellow composite-skinned J-10C with production model serials equipped with higher-thrust non-TVC WS-10B turbofans.

Furthermore, a J-20 stealth fighter test bed equipped with a thrust-vectoring engine is also known to exist.

China has for years struggled to get its indigenous WS-10 turbofans, particularly their metallurgy and single-crystal fan blades, to perform to the specifications and reliability required of them. Reportedly, early WS-10s had to be returned to the factory for refurbishment after only a few dozen flight hours. 

For that reason, its J-20 stealth fighters often make do with lower-thrust Russian AL-31F engines, and so the beastly stealth jet has yet to attain its full projected performance characteristics.

A Chinese Thrust-Vector engine design

After years of refinements, J-10 and J-20 manufacturer CAIG hopes the WS-10B model marks a more consistent step up in thrust and performance while China completes the development of a much higher-performance WS-15 turbofan. 

The WS-15 is projected to generate 40,000 pounds of thrust, possibly boosting J-20 speeds to the point it can super cruise—fly supersonic in level flight without using fuel-gulping afterburners. The WS-15 is also speculated to feature three-dimensional thrust vectoring.

The question that emerges, therefore is whether the multiple J-10 TVC test beds indicate China intends to build a higher-thrust, and possibly thrust-vectoring J-10D production model to succeed its very respectable J-10C fighter (detailed further in a companion article).

Or do the tests instead indicate CAIG’s focus on making thrust-vectoring J-20 stealth fighters? Dr. Andreas Rupprecht, author of the Modern Chinese Warplanes series of books, told Defence News earlier in 2019 it’s more likely that the J-10 engine test beds are being used to test capabilities that will make their way into new WS-15 engine planned for the J-20.

The predominant theory in western circles is that beefy J-20 is exhibiting high-speed but inferior manoeuvrability, making it best suited for hit-and-run style attacks. But China’s evident sustained interest in testing agility-enhancing TVC engines may support a counter narrative that the J-20 is intended to evolve into a more well-rounded jet once upgraded with new engines, one that could more than hold its own in within-visual range combat.