https://www.aerosociety.com/news/boxing-clever-chinas-next-gen-tailless-combat-aircraft-analysed/

Boxing clever? China's next-gen tailless combat aircraft analysed

On Boxing Day 26 December 2024, pictures and video emerged of a new Chinese stealth aircraft, featuring a unique configuration of three engines, diamond planform and no tail. Veteran aviation journalist and stealth expert BILL SWEETMAN assesses what we know so far.

Images of the flight were also remarkable as the mystery aircraft was accompanied by a twin-seat CAC J-20S. (via Chinese internet)

Fourteen years ago, Western aerospace people emerged from the festive fog and piles of wrapping paper to find an extra present from Yang Wei, the head of the design team at Chengdu Aircraft Industry Group: the revelation of China’s first stealth aircraft, the J-20.

Yesterday, he did it again, with a stealthy, supercruising medium bomber – that may be an indirect counter to the B-21.

Double surprise

Boxing Day 2024 saw images of CAC (left) and Shenyang (right) new stealth aircraft surface - both been flown openly in daylight. (via Chinese internet)

It’s been known for some time that China’s industry has been working on a larger stealth aircraft, sometimes referred to as JH-XX or H-XX. Rumbles around China-aerospace watchers indicated that there might be a post-Christmas event coming, but we’ve all been disappointed before.

Not this time. First, we saw the maiden flight of Chengdu’s new aircraft, chased by a twin-seat J-20S to provide scale; clearly large, crewed, supersonic, and stealthy, with a blended double-delta shape, no vertical stabilizer and (astonishingly) three engines, two with conventional underwing caret inlets and the third breathing through a dorsal intake.

And then came the debut of another stealth design, an apparently unmanned, smaller demonstrator from Chengdu sister company Shenyang. Some pictures were dated from a week ago, so this seems to have been an internal release rather than a necessarily public first flight from Chengdu.

For the moment I am going to focus on Chengdu’s newcomer. As of the evening of December 26, it has no name (as I write, one source is using J-36), but given the date, its likely mission, and Chinese history, I shall assign it the reporting name Boxer.

Let’s start with what is not happening. To call it a sixth-generation aircraft would be misleading, because, aside from the abuse that the 'generations' tag has been subjected to, you might think that Boxer is a fighter or some kind of analogue to the US Next Generation Air Dominance programme, whereas it’s something quite unique, and in no way a replacement for anything in service with the People’s Liberation Army – Air Force today.

Nor is it likely that (as some have speculated) there is any kind of competition between Chengdu and Shenyang. The Shenyang vehicle looks much smaller, and Boxer itself looks very analogous to the first J-20: not quite a pre-production aircraft in every detail, but a full-size prototype rather than a minimal technology demonstrator, to be followed by a low-rate production batch. This process worked well on the J-20 and on the aircraft based on Shenyang’s FC-31.

Unwrapping a mystery

The aircraft features an unusual configuration of upper and side intakes. Note dual main landing gear.(via Chinese internet)

With that in mind we can unpack some of Boxer’s features.

China’s armed forces and their equipment are designed to establish regional military dominance. From a Chinese perspective, the only important challenge to that dominance comes from U.S.-led air forces: the USAF and the Navy’s aircraft carriers, with allied support from Japan, Korea, Australia and others. (I hate to break it to the Marine Corps and the US Army but nobody in Beijing stays awake at night worrying about them.)

Boxer’s distinguishing attributes are stealth, speed, range, and weapons load. The J-20 does well at the first two, and does better at the third than other fighters, but it was designed to go after air targets – principally high-value air assets like airborne early warning and control aircraft, and intelligence and electronic warfare platforms – and its weapon bays are tailored accordingly.

Boxer is a chonky boi, eeerm, a large aircraft. It’s longer than the J-20 – about 75ft – but much broader. The blended double-delta wing spans 63ft, with more than 2,000 square ft of gross area. (Caution – these numbers are preliminary.) As I noted in my review of the Global Combat Aircraft Program’s Tempest design, large deltas accommodate massive quantities of fuel, leaving space in the body for weapons.

Other indicators of Boxer’s true size include its tandem-wheel main landing gear units, something seldom found today on any military aircraft under 100,000lb take-off weight, and a fully bomber-sized weapon bay, 25ft long and more than 7ft wide. Plus two side bays, sized for defensive AAMs or anti-radiation missiles.

It would not be at all surprising if a fully loaded Boxer weighed 120,000lb or even a little more – at that weight, the wing loading is a modest 60 pounds/sq ft, similar to the Saab Draken, which Boxer somewhat resembles in planform and the location of its side inlets. A clean fuel fraction above 0.4 is attainable.
Sweep angles and inlet shapes point to a max Mach number around 1.8 (see F-22). Supercruise capability will depend on non-afterburning thrust, and we will return to that point.

The stealth shaping is similar to the J-20, with canted plane surfaces. It has six planform-edge alignments. Extreme low observables it is not – unless China has made a breakthrough in materials, which can’t be ruled out – but this is also a stand-off, supersonic aircraft, and ELO is less necessary to survivability.

Where Boxer diverges from previous supersonic designs is in the absence of vertical tail surfaces, bringing all-aspect stealth into the high-speed realm. It has five control segments on the trailing edge of each wing, of which the two outer elements (at least) are split to act as brake/rudders. They seem to have been wide open for the duration of the first flight, a position that gives them maximum authority. However, as on the B-2 and B-21, those surfaces must stay closed in stealth mode and directional control must be provided by other means.

Northrop Grumman used differential thrust on the B-2, and likely on the B-21 as well. It is possible that Boxer uses a similar technique, and this may have a connection to its unique propulsion layout.

Three-engined beast

This image shows the aircraft clearly has three engines. (via Chinese internet)

Why three engines? There has to be some very important benefit to justify the complexity of the Boxer configuration, with a completely different inlet design for the center engine, which also sees different aerodynamic conditions. The simplest explanation is that there is no extant Chinese engine large enough for a twin, but would that justify such a drastic impact to the shape?

The one image seen so far of Boxer on the ground shows three large-diameter exhausts opening just ahead of the trailing edge, and other shots show what appear to be movable trailing-edge segments behind the exhausts – giving some ability to vector thrust.

But Yang Wei’s team has almost certainly bought some nasty thermal issues if those engines have full afterburning: the trench exhausts on the YF-23 were a nightmare. (I was a consultant on the resulting lawsuit between Northop and Allison, which had supplied its Lamilloy thermal protection system.)

But how do you match thrust supply and demand over a wide subsonic and supersonic flight regime? It’s possible that the Boxer designers have done this by using the center engine mainly for take-off, initial climb and supercruise – leaving two symmetrically disposed engines to provide differential thrust and vectoring for stealthy flight control.

If the designers wanted to be extra double sneaky (and be hated by logisticians) there’s no physical reason why the center engine needs to be the same as the outers. It could have a lower bypass ratio and overall pressure ratio (like a big Eurojet EJ200) and hence better performance in supercruise – providing Boxer with the benefits of variable-cycle propulsion without the same complexity and risk. Three engines in the 22,000 lbs. thrust class, with some use of afterburning boost for takeoff and transonic acceleration, should be adequate.

Supercruising striker

The aircraft has a huge-bomber-sized weapon bay. (via Chinese internet)

Operationally, what does this add up to? As noted above, counter-air is the main mission. Boxer can carry air-to-air missiles, but the big main weapons bay means larger weapons for larger targets – aircraft carriers and air bases. Alternatively, Boxer could launch swarms of loitering munitions against air bases, including more distant ones hosting long-range B-21s.

That brings up an advantage of supercruise and a limitation of the B-21. A supercruiser, operating at long range, can achieve much higher sortie rates than a subsonic missile carrier like the H-6. Conversely, if a relatively slow subsonic bomber is forced to use more distant bases because of the risk of air attacks, its sortie rate will be much lower and it will need more tanker support; and if the adversary uses large supercruisers with air-to-air weapons, the tankers themselves will be at risk even if they are more than 1,000 miles from adversary bases.

Timing? The first J-20 appeared in December 2010, the pre-production aircraft in around 2014. So this beast could be approaching production by the end of the decade.

We may have a problem on our hands.