=military =aircraft =china
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
-
aerosociety
-
yahoo
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, and 2 smaller bays long
enough for the PL-15. 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, 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 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. 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.
Here are some relevant papers by the Chinese aircraft designers Yang
Wei and Wang
Haifeng. 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. 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" 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 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.