# new chinese stealth aircraft

Recently, 2 Chinese military aircraft were seen flying for the first time. Some people wanted to read about my thoughts on them. In this post, I'll be referring to them as "Diamond" and "Dart" based on their shapes. Speculative designations being used elsewhere are:

- Diamond = Chengdu J-36
- Dart = Shenyang J-XS


## some articles

Instead of embedding photos here, I'll just link to some articles with pictures:

- [business-standard](https://www.business-standard.com/external-affairs-defence-security/news/china-flies-2-sixth-gen-stealth-jets-in-24-hrs-wake-up-call-for-india-us-124122700538_1.html)
- [aerosociety](https://www.aerosociety.com/news/boxing-clever-chinas-next-gen-tailless-combat-aircraft-analysed/)
- [yahoo](https://www.yahoo.com/news/china-stuns-heavy-stealth-tactical-125038888.html)



## what the photos show



### aircraft size

Diamond seems to be ~22m long, with a central weapon bay long enough for the PL-17 or [YJ-83](https://en.wikipedia.org/wiki/YJ-83) (6.4m), and 2 smaller bays long enough for the [PL-15](https://en.wikipedia.org/wiki/PL-15) (4m). It could probably carry glide bombs too. Its wing area is quite large for a fighter aircraft. The planform is similar to a [F-16XL](https://en.wikipedia.org/wiki/General_Dynamics_F-16XL), and scaling that up to 22m length would be ~50 tons MTOW.

Dart is smaller, and its bays seem big enough for the PL-15 but not the PL-17. So, it's meant to operate closer to its targets, but the PL-15 is still bigger and longer-range than current US air-to-air missiles.



### aerodynamics

Diamond has thin delta wings. Sweep is ~50°, quite high. It looks designed to go Mach 2 in a straight line at high altitude.

Dart has higher aspect ratio wings. It should have better turning at subsonic speeds, but probably has less range than Diamond at supersonic speeds and a lower max altitude. It should have significantly shorter takeoff distance than Diamond.


#### control surfaces

Both aircraft have no vertical stabilizer. Normally, those are important for preventing uncontrolled yaw to keep the aircraft pointed forwards.

Diamond has a lot of separate ailerons in the back, which could control yaw by increasing drag on 1 side. That's how the B-2 did things. Diamond also has thrust vectoring, as indicated by things including space between the exhaust nozzles; I suspect that's meant to be the main way Diamond controls yaw.

Dart has fewer ailerons, but has some funky protrusions on the wingtips - I wonder if those are exhaust nozzles for bleed air from the engines for yaw control. If the wingtip things aren't for controlling yaw, then Dart definitely needs thrust vectoring, but it seems designed for lower cost than Diamond and thrust vectoring does increase cost.


### stealth

I haven't done simulations or anything, but Diamond seems about as stealthy vs aircraft radar as the F-22, and more stealthy from above or vs low-frequency radar.

The advantage that the F-22 and F-35 have in stealth over the [J-20](https://en.wikipedia.org/wiki/Chengdu_J-20) comes from the US:

- having better supercomputers for simulations when they were designed
- being willing to spend more on manufacturing, and thus making fewer compromises about stealth

Those advantages are no longer applicable, so you shouldn't expect Chinese aircraft to be particularly worse in terms of stealth.

Aircraft are usually more stealthy from below than from above. So, high altitude is an advantage. Diamond should have a very high max altitude, higher than the F-22.

Radar reflections also depend on frequency. Removing vertical stabilizers has a bigger effect on low-frequency radar, which isn't usually used by fighter aircraft because it requires bigger antennas. It also reduces RCS from above more than RCS from below, since they're on the top of the aircraft.



### landing gear

The aircraft were seen with the landing gear left down, which might indicate an early test flight. (You test 1 thing at a time, and landing gear cycling is another potential failure.)

Diamond has tandem-wheel main landing gear, which indicates high max weight, possibly >50 tons.


### flight location

The flights were done over a populated area. The landing gear staying down points to an early test flight, but on the other hand, early tests are usually done where a crash won't hit people. It's possible that risk was outweighed by desire to show off something for Mao's birthday, or maybe testing has actually been going on for a while.


### engines

Video of Dart indicates 2 engines with afterburners.

Diamond seems to have 3 engines, since it has 3 nozzles. It might have been designed with 3 engines so it could cruise on 1 or 2 engines at subsonic speeds + low altitude without unbalancing thrust. If those engines are Shenyang WS-15 engines, it would have a pretty high thrust/weight ratio, which I'm guessing would be enough for a max speed between Mach 2.5 and Mach 3. Obviously heat becomes a problem at that point. Such high speed and T/W also implies a high max altitude, maybe ~22 km.

Most fighter aircraft have afterburners, but Diamond might actually not need them.

Chinese gas turbines are still not quite as good as new US ones, but based on recent power plant turbines, they're now using single-crystal nickel alloys with internal cooling channels and thermal barrier coatings, and are good enough for competitive aircraft if fuel efficiency isn't critical.

Some people are saying one engine of Diamond is a ramjet, but that doesn't make sense for the overall design. I think all the engines of Diamond and Dart are low-bypass turbofans, but it's possible the center engine of Diamond has a different bypass ratio.


### sensors

As articles have noted, Diamond seems to have some big sideways-pointed AESA radars, and a big optical sensor that's probably an [IRST](https://en.wikipedia.org/wiki/Infrared_search_and_track). Dart seems to have smaller and less expensive sensors, but I'm sure it still has a decent AESA radar.

China is pretty good at making GaN AESA radars now. They're still not quite as good as new American ones for a given size and power, but not enough to outweigh significant size differences, and the Chinese are getting a lot more radar per cost - which is part of why they're putting AESA radar in AA missiles.


## cost

The different manufacturing methods for modern military aircraft have similar costs. I'd expect Diamond to cost about as much per mass as a F-35. That's $100M for 30 tons, so Diamond might be $170M if it was made in the US, but China can often make military stuff for 1/3 the nominal cost in the US. For aircraft, I suspect the cost multiplier is closer to 1/2, and the J-20 nominal cost is ~$60M. So Diamond might be ~$85m, maybe a bit more because it seems premium, while Dart might be a bit less per mass.


## strategic purposes

I previously wrote a bit about Chinese air strategy; see "chinese strategy" in [this post](https://bhauth.com/blog/military/destabilizing%20weapons.html).

Here are some relevant papers by the Chinese aircraft designers [Yang Wei](https://hkxb.buaa.edu.cn/CN/10.7527/S1000-6893.2020.24377) and [Wang Haifeng](https://hkxb.buaa.edu.cn/CN/10.7527/S1000-6893.2024.29978). Yang Wei is someone I'd previously noted as a possible modern Mikhail Gurevich.


### Diamond

Based on the aircraft size, the main purpose of Diamond is to carry big long-range missiles, such as the PL-17 and YJ-83. It looks expensive, and those are expensive missiles. It's also not possible to target something stealthy (like a F-35) at very long range. So, Diamond is meant to attack high-value non-stealthy targets such as military ships, tanker aircraft, and AWACS.

Based on extrapolation from existing aircraft, I'm guessing it's designed for a combat radius of ~1600 km without refuelling. That's long-range for a fighter, but short for a bomber.

It has a long takeoff distance, so it's definitely land-based. It's too expensive and short-range for strategic bombing.

Diamond has some big sideways AESA radars. I suspect it's meant to act as AWACS sometimes, making it sort of a...stealthy supercruising missile-bomber/AWACS. It could fire, turn 90°, use one radar for detection and the other radar to send data to friendly craft, then turn off its radar and lose any incoming attention by being fast and stealthy.

The other goal apparent in the design of Diamond is competing directly against F-22 stealth by sacrificing maneuverability and production cost. It's hard to beat the stealth of a F-22 from below vs aircraft radar, so the plan would be:

1. Use ship-based low-frequency radar to detect a F-22.
2. Use a big IRST on Diamond to track it.
3. Have high speed to chase down the F-22.
4. Fly almost directly over it, and get a missile lock first by being at higher altitude and seeing the less-stealthy top side.



### Dart

Compared to Diamond, Dart is smaller and more maneuverable, so it'd be used more like existing fighters than Diamond, with fast turning being relevant for the same reasons. Usage would be similar to a F-35.

It seems a lot cheaper, so it's meant to be made in larger quantities than Diamond to increase total aircraft numbers. Takeoff distance seems much shorter so it might be designed for use on carriers.


### other possible new aircraft

China has been working on a stealthy subsonic long-range bomber, the [H-20](https://en.wikipedia.org/wiki/Xi%27an_H-20). That's slower but longer-range than Diamond; it fills a similar strategic role to the US B-21. It hasn't been seen publicly yet, and the actual program status isn't clear.

I suspect China is also working on a stealthy tanker aircraft for refuelling its fighters.

The US has been working on "[loyal wingman](https://en.wikipedia.org/wiki/Loyal_wingman)" UAVs, which would fly together with a manned aircraft to carry more weapons for it, while being cheaper because they're smaller & subsonic & don't have good sensors. China seems to be working on something similar, which'd probably end up with similar specs to a [XQ-58](https://en.wikipedia.org/wiki/Kratos_XQ-58_Valkyrie) by convergent evolution.


## Taiwan timelines

Do these Chinese aircraft programs indicate anything about if and when China will go for Taiwan?

Developing large new military aircraft is expensive, so maybe it doesn't make sense for China to have 4+ such programs going and start a war shortly before they go into full production. Waiting until 2-3 years after mass production starts would make more sense.

For several years now I've been expecting China to go for a blockade of Taiwan, and earlier than most estimates, around 2025-2027. That was based largely on Chinese industrial activity and resource stockpiling indicating preparation for trade by ship stopping; their military buildups are much more opaque. These aircraft programs could line up with 2027-2028, but I think they're an indication China won't go for Taiwan in 2025. In retrospect I was underestimating the leeway the Chinese gov wanted for finding alternatives to failed projects and expanding successful ones, so 2025 was too early. Good thing I didn't decide to hold Intel stock, eh?