Chinese engines are anaemic in comparison – so much so that many Chinese fighters still fly with imported Russian engines. It was a big deal when, a few years ago, a Shenyang engine-maker reverse-engineered the Franco-American CFM56 engine into a Chinese variant, the WS-10, which produces 15 tons of thrust at peak power.

The Chinese fighter engine industry is currently at work on the new WS-20, an evolution of the WS-10 with slightly greater thrust. This engine is already powering newly built J-20s. 

It’s possible the J-36 has three WS-10s. That should produce enough thrust to accelerate the heavy fighter to high supersonic speeds even when it’s carrying a heavy payload. But sheer thrust might not be the only purpose of the three-engine design. Modern warplanes need electrical power. And they tend to get their power from their engines. 

The J-36 may be particularly hungry for electricity. The Chinese air force, like the US and many allied air forces, is determined to operate its newest manned fighters in conjunction with unmanned fighters. This so-called manned-unmanned teaming may involve a human pilot issuing commands to drone wingmen. 

The manned jet at the centre of a mixed manned-unmanned formation is, in effect, a flying command post sending and receiving signals to accompanying drones. It’s a potentially power-hungry mission profile, especially when you add the radar and other sensors plus the electronic-warfare systems that every modern fighter requires.

Then there’s the prospect of directed energy weapons, a stated aspiration for most sixth-gen fighter programmes. A DEW – a raygun, in essence – might emit focused beams of microwaves that could fry enemy circuitry in the same way the electromagnetic pulse following a nuclear explosion does. It might even be powerful enough to heat its targets up and burn or damage them that way. Alternatively it might be a high-energy laser, able to blind enemy sensors or even melt holes in its targets. Whatever form DEWs take, they will be very power hungry.

In short, Chengdu may have broken the fighter-design mould and added a third engine to the J-36 because the Chinese expect the new fighter to generate a lot of power – and the power-generation of two WS-10s just wasn’t going to cut it. In that way, the three-engine design could reflect both the promise and the limitations of Chinese fighter technology.