Tag Archive for: strike

China’s big new combat aircraft: an airborne cruiser against air and surface targets

The speed, agility, range and stealth of an individual aircraft type are still important, but they’re no longer the whole story of air combat. Advances in sensing, processing and communications are changing military operations.

The Chengdu J-36, the big Chinese combat aircraft that first appeared on 26 December, has been developed to exploit these changes and support China’s strategic goal: to establish regional dominance, including the ability to annex Taiwan by force.

If J-36s can fly supersonically without using afterburning, as the prototype’s shape suggests they will, each will be able to get into and out of battle faster and more safely than conventional fighters and bombers, which cruise subsonically. A high degree of stealth will greatly help J-36s in penetrating defences. Supersonic cruise would also mean each J-36 could fly more missions in a given period.

The design’s big main weapon bays are sized for considerable air-to-surface missiles, which J-36s could launch against such targets as airfields, aircraft carriers and air-defence batteries. With great speed and height, J-36s could also throw inexpensive glide bombs farther than other aircraft could.

The main weapon bays are big enough to carry unusually large air-to-air missiles for engaging aircraft at great range, including vital support units such as tankers and air-surveillance radar planes. Targeting data for this might come from other aircraft, ships, satellites or ground sources. The missiles might also be launched at fighters at ranges that keep J-36s safe from counterattack.

J-36s are themselves likely to be sources of targeting data for other aircraft and for ships, using large passive and active sensors that aircraft of such size can easily carry. They may command aircraft that fly with them. In all this, they’d use radio links that are hard for an enemy to detect.

To call the J-36 an airborne cruiser may not be far off the mark—and may call into question the West’s decision to prioritise development and production of fighters that are, by comparison, mere torpedo boats.

(An earlier article in this series technically assesses the design of the J-36. The type’s designation is likely but not certain.)

For the Taiwan mission, China’s principal opposing force is US-led air power, comprising the US Air Force and the US Navy’s aircraft carriers, with support from Japan, Australia, Taiwan and maybe South Korea and others. Air power from China’s opponents can hinder its maritime and amphibious operations, resulting in slower progress and higher casualties.

So, counter-air capability is crucial for China. This is what the US thinks of as China’s anti-access and area denial capability. It includes surface-to-air weapons, fighters, air-base attacks and the information realm.

To understand where the J-36 fits in, start by considering China’s current force, of which the Chengdu J-20 is the spearhead. The J-20 is fast and stealthy, with good range for a fighter, but its weapon bays are limited to short-range and medium-range air-to-air weapons. Like the F-35, it is more detectable outside its forward quadrant. That becomes a greater vulnerability in a networked environment, where a sensor platform on your beam may not be well placed to launch a weapon but will pass your track to one that is.

The long-range Xi’an H-6 bomber, used as a missile carrier, can launch attacks at air bases throughout the Western Pacific. But its effect is limited to the warheads of up to six costly missiles that must fly far enough to keep their vulnerable launch aircraft safe.

The J-36 combines speed and range with all-aspect stealth. Potential internal loads include such long-range air-to-air missiles as the PL-17, which the J-20 cannot carry internally. Heavier, air-to-surface missiles would be aimed at airfields and warships. It also probably supports the kind of mass-precision attacks made possible by accurate, more autonomous weapons, or—as autonomous technology advances—the carriage of loitering munitions and jammers.

The J-36’s smaller outboard weapon bays might accommodate defensive and support weapons, possibly on extending rails like the J-20’s side bays.

The large transparent side apertures in the forward fuselage could be wide-field-of-view passive warning and cueing systems. But there’s another possibility: if you wanted to integrate a high-energy anti-missile laser into an aircraft, with a hemisphere-plus field of fire but without unstealthy turrets, it might from the outside look like those transparencies. A single optical chain could feed left and right steerable heads under the conformal windows. Cue panic.

Speed is not just valuable for survivability, although it does erode missile engagement envelopes. Even Mach 1.8 supersonic cruise halves flight time and greatly increases sortie rate compared with a subsonic-cruise aircraft.

The US considered developing a supersonic strike aircraft in the early 2000s. But with 9/11 and the cost of the F-35 program, a high-speed project could not get funded. ‘Response time, and cost per target killed, were the two holy grails,’ a Northrop Grumman engineer commented in early 2001. The supersonic aircraft was big and complex, but the sortie generation rate was far higher than that of subsonic alternatives, and fewer aircraft were needed. And it could use cheap, unpowered glide weapons with a stand-off range estimated at 170km from a Mach 2 launch.

Speed on one side of a conflict is an important advantage. If the J-36 can penetrate to threaten bases in the second island chain, forcing the US to move B-21s, B-52s and other high-value assets further back, US strike sortie rate and effectiveness will diminish.

It’s important to keep in mind that the J-36 will be part of a family of systems and a network of capabilities. The appearance over the holiday season of the KJ-3000 airborne early warning and control system, based on the Xi’an Y-20 airlifter, is significant.

China has produced five different airborne radar systems since 2003, more than any other nation, all based on the technology of active electronically scanned arrays (AESAs). It has expanded their role beyond that of forward-passing adversary track data to fighter aircraft. AESA radars can update tracks much faster than a rotating-antenna radar, so these systems can provide guidance-quality midcourse updates to missiles.

Compared with the propeller-driven KJ-500, the KJ-3000 can be moved faster and farther forward to support an operation, and it can fly higher for greater sensor range. Working with a KJ-3000, the J-36s could launch missiles while remaining radar-silent.

If its speed and stealth allow it safely to get close to the enemy, a J-36 itself will be able to provide targeting data to other weapons, such as missiles launched by H-6s that prudently stay well behind it. It will also be the command and control hub for other aircraft, crewed and uncrewed. If it is a two-seater, the second crew member will likely be a force manager.

As for how to classify the J-36, too many people have rushed to call it a ‘sixth-generation fighter’.

The ‘fifth-generation’ term, invented in Russia, was picked up by Lockheed Martin as a marketing tool in the early 2000s. What Lockheed Martin would call 5-gen fighters combine supersonic speed and maneuverability with some degree of stealth. The Chengdu J-20 fighter is fifth-generation by that standard.

But this ‘generation’ taxonomy misleads more than it informs, because combat aircraft designs need not and do not fall into discrete sequential groups of characteristics.

And ‘fighter’, ‘bomber’ and ‘strike’ definitions are getting less clear. Most Boeing F-15s, nominally fighters, have been built as strike aircraft, and the fighter-derived Sukhoi Su-34 is another step down the same path. Designed against air and land threats, the J-36 is even larger than the Su-34. Its size and flight performance put it into its own category, for which there is no name. Maybe ‘airborne cruiser’ will catch on.

China’s big new combat aircraft: a technical assessment

China’s aircraft industry celebrated Mao Zedong’s birthday in style, unveiling three aircraft developments that will comprise an air warfare family of systems for the 2030s and beyond. One, from Shenyang, looks like a demonstrator for a fighter-size aircraft with next-generation stealth, possibly carrier-compatible. Also new was an airborne warning and control variant of the Xi’an Y-20 airlifter, the latest in an unparalleled air-surveillance line-up.

The most spectacular debutant, making its maiden flight on December 26 was from Chengdu Aircraft Industry Group: a stealth combat aircraft that various anonymous commenters on the Chinese internet identify as the J-36. It is the largest combat aircraft designed and developed in China, and the second-largest to fly anywhere in 35 years.

The J-36 (if that really is its name) is designed to combine supersonic performance with all-aspect stealth. That’s also the goal of the US Next Generation Air Dominance program, currently stalled by budget and policy issues. (A second article in this series looks at the J-36’s roles.)

There may be more. Anonymous Chinese internet commenters with better records for accuracy than others say that the new arrivals are part of an air warfare ‘tea set’ and that we have not yet seen the ‘teapot’—the long-expected H-20 stealth bomber; this will probably be an analogue to the Northrop Grumman B-21. Nonetheless, the J-36 alone has given observers enough to chew on.

Its revelation followed the pattern as the appearance of the J-20 fighter exactly 14 years earlier. No technical details have been released officially, and it’s unlikely that any will be soon, but a prototype for the design flew in daylight from an airfield in a dense urban area, and the Chinese government permitted images to be released.

The aircraft was chased by a two-seat J-20B, giving a good indication of its size. It’s longer than the J-20—about 23 metres—and its double-delta wing spans an estimated 19 metres, with around 200 square metres of wing area. (The F-22’s wing area is 78 square metres.) As I commented on the Global Combat Aircraft Program’s Tempest design, large, moderately swept deltas can accommodate a lot of fuel and are very useful if the designer is looking for long range.

The tandem-wheel main landing gear units point to a big aircraft, since single wheel, tyre and brake units are inadequate at weights above about 35 tonnes. The main weapon bay, about 7.6 metres long, and supplementary side bays for smaller weapons also suggest considerable size. A 55-tonne take-off weight is a reasonable guess, two-thirds more than the J-20 and compared with an estimated 82 tonnes for the Northrop Grumman B-21.

The J-36 planform unequivocally speaks of stealth and supersonic speed. It is a modified version of the Hopeless Diamond, the first shot by Lockheed’s Skunk Works at all-aspect stealth, which got that name because it could not be made to fly with 1970s technology. Another variation on the planform was tried in 2003 with Northrop Grumman’s X-47A Pegasus unmanned combat aircraft demonstrator, which did fly. Once.

On the J-36, the diamond is stretched into a double-delta to reduce transonic and supersonic drag. It has a leading-edge kink, a change in sweep angle. That’s not ideal from the standpoint of radar cross-section but, as Northrop Grumman’s cranked-arrow designs have shown, it can be lived with. There is an unbroken edge and chine line around the aircraft, and all sensor apertures are inside it (not the case with the J-20 and other fighters). That is the foundation of all-aspect stealth.

There are no vertical tail surfaces and no visible control surfaces other than the wing trailing edges, with five moving panels on each side and one behind each engine; such surfaces are called ‘elevons’. (It’s possible that there are flight-control effectors that we have not yet seen, such as inlaid panels in the upper surface of the wing.) The hinge lines of trailing-edge surfaces appear to be covered by flexible skins. The outer pair of surfaces are split horizontally to form brake-rudders, as on the B-2 and B-21, and were fully open in all pictures of the first flight.

Elevons have reliably provided pitch and roll control since the 1950s, but dispensing with the vertical tail is a challenge, and more so with a supersonic aircraft. The J-36 can rely on its brake-rudders when it is not close to an enemy. But, for stealth in a threat zone, it will need to keep them closed and use both aerodynamic and propulsive effects to keep the pointy end in front—which brings us to another almost unique feature.

J-36 has three engines, side-by-side at the rear of the broad centre-body. F-22-like inlets of caret shape, with swept and canted lips, under the wing leading edge, supply the left and right engines, and the center engine is fed by a diverterless supersonic inlet above the body.

The three engine exhausts are ahead of and above the trailing edge, which comprises what appear to be articulating panels. Full turbofan reheat boost would impose scary thermal and acoustic loads on the trailing edge structure. (The trenches at the rear of the Northrop YF-23 into which its engines exhausted did not endure the environment as well as expected.) This tends to support the idea that the J-36’s engines are either non-afterburning or have limited afterburning used for transonic acceleration.

Some commentators have suggested that the J-36 has three engines because China does not have an engine design large enough to power it in a twin installation. This doesn’t seem likely. Even if your available engines were delivering only two-thirds of the thrust required for a production-size twin-engine aeroplane, you could build an 80 percent linear-scale demonstrator with two-thirds the wetted area, and it would be both easier to develop and more representative of the final configuration.

There has to be a good reason to justify the added complexity. One possibility is that the two outer engines provide enough thrust for subsonic flight, while operating at full thrust and peak efficiency, and the third cuts in for supersonic cruise.

A variation on this theme would be to have a center engine optimized for supersonic flight, which would deliver some of the advantages of a variable-cycle engine without its complexity and risk (I can hear the logisticians screaming, 12,000km away) but in a configuration that could be fitted later with a VCE.

One former combat aircraft designer suggests that the trijet arrangement could be influenced by stability and control considerations, allowing for symmetrical thrust vectoring in pitch with one engine inoperative.

The trailing edge flaps would provide thrust vectoring in pitch when used symmetrically and in roll with the outer engines’ exhaust deflected asymmetrically (while still using the center engine for pitch). It is entirely possible that fluidic control (injecting fan-stream air asymmetrically into the nozzle) could be used in the yaw axis.

Three engines in the thrust class of 22,000 lb (10,000kg or 100-kilonewtons) should be enough to make the J-36 a supercruiser—an aircraft that can fly supersonically without using fuel-guzzling afterburning. Its sweep angles point to doing this at Mach 1.8 to Mach 2.0 (1900km/h to 2200km/h, depending on altitude). The key is not so much achieving enough static thrust but building the engine to withstand the high temperatures at the exit of its compressor. China’s engine technology has been headed in this direction.

Agility? High maneuverability is in opposition to combining supersonic cruise and range—the F-22 being deficient in the latter—because it demands large control forces and high installed thrust (and the weight it brings). Physics are a limitation: the J-36’s trailing-edge controls and thrust-vectoring systems must provide all the control force for the aircraft, unassisted by vertical stabilizers, canards or pitch-recovery devices like the Sukhoi Su-57’s movable leading-edge root extensions.

As for the need for maneuverability by a supersonic stealth aircraft packing a heavy weapon load and long-range sensors, the reader is referred to the classic movie short, Bambi Meets Godzilla.

We will learn more about the J-36 as it follows the pattern of the J-20 through a pre-production and service test phase. There are other puzzles about the design: apparently large electro-optical sensor windows on either side of the nose, and a dark-tinted canopy that wouldn’t be road-legal in many US states. But one thing can be said firmly: those who accuse Chengdu chief engineer Yang Wei and other Chinese designers of being copyists need to take a seat.