InstMadrat: since the J-31 is an F-35 analogue, its job is not to be a game-changer; the F-35 is never going to shoot down the F-22 and no one will expect it to be able to do that. It’s the J-20’s job to kill F-35s, not the J-31’s; whose job is closer to providing air support against a modern force with IADS.
InstLatenlazy: Your first two pictures have canards and the third has a Mig-29-style LERX. There’s no ascertaining whether it was CAC or SAC involved in it, although with the first two, they clearly look like SAC’s triplane canard-wing-tail configuration.
InstAmiga: At least give me some damn variety. Splice a LEVCON onto the F-35 airframe. Try to develop an F-35-class aircraft from the YF-23 direction instead of the F-22 direction; hell, the YF-23 lost to the YF-22 because of a lack of maneuverability and high costs; that’s not a problem for an F-35 equivalent! 😉
InstJ-31 isn’t the J-XX, however. It’s the F-35 in a Chinese hi-lo combo; it’s not even authorized by AVIC; it’s a private project paid for by SAC funds as an export product. It’s a late product and looks highly derivative; none of the decisions made were remotely original.
Su-27 might have been derivative of the F-14; you don’t know, but one is variable sweep and the other is not. You should also remember that the Soviets had their espionage network and weren’t aiming at cutting edge design; they were planning to be an N-1 army compared to the US military; 1-step behind cutting edge and greater numbers to compensate.
Eurocanards are not all copies of each other and are highly distinguished by their canard placement and size. Rafale and Gripen are close-coupled, Eurofighter is long-coupled, some of these have good radars, some of these have crap radars and are more A2G optimized.
YF-23 carries design lineage from the F-5 and F-20 Tigershark; both of which used a trapezoidal wing, which you can see is highly emphasized on the YF-23 in comparison to the F-22. There are significant departures from the F-5, though; the F-5 and F-20 has essentially no body lift aspects and are closer to wings attached to a tube, whereas the YF-23 is the exact opposite, which is essentially 3 tubes, one for the cockpit and radome, two for the engines, attached to a wing.
As far as the Flanker production experience goes, the Chinese flanker clones suck. They’re like the WS-10; it’s domestic and that’s great, but the Chnese flankers aren’t competitive with the Russian fighters; the J-11B lacks canards like the Su-30 or TVC like the MKI. It’s also in part supporting evidence for the J-31 is a F-35 copy argument; CAC has been innovative and has been able to pursue original planform designs with the J-10 and JF-17, but all SAC does these days is “Receive and Duplicate”. If they’ve been involved in “R&D” on the Flankers, why not “Receive and Duplicate” the F-35?
Yano what’s an even simpler answer? SAC either a) based the J-31 off their rejected J-XX proposal/some other in house design that never made it past models (companies experiment), or B) They simply decided to make a design that isn’t based on any of their previous ones. Impossible.
Show me the rejected J-XX proposal. We can establish a lineage for the J-20 on the J-12 and J-10 designs, but where’s the J-XX proposal? And as far as simply deciding to make a design that isn’t based on any of their previous models goes, “receive and duplicate”; we haven’t seen any significant design capability from SAC for a long time; the J-11B is worse than the Su-30 and is virtually a copy anyways.
InstMy argument is primarily based on lineage; which is to say, an aircraft does not come into existence ex nihilo, but is based on existing aircraft because existing aircraft provide aerodynamic and design research aspects that can be built on for cheaper than coming up with a completely new planform.
The J-20 comes from the J-10, the F-22 is a stealthified and improved F-15, the PAK-FA is a stealthified Flanker.
When you copy an aircraft, what you’re doing is that you’re taking someone else’s planform idea without descent from your own aircraft. It is very hard to copy because if you copy someone else’s aircraft, you don’t necessarily have the research data available to you so you don’t benefit from their lineage. But in the Chinese case, they’ve broken into Lockheed, so copying the J-31 off the F-35 is a lot more viable than a bunch of hicks in the middle of nowhere trying to replicate an F-22 from photographs.
The reason I think the J-31 is a copy of the F-35 and F-22 is because Shenyang has no lineage with the planform concept in the J-31; it’s traditionally worked with the J-11 and the J-31 doesn’t look anything like the J-11. Shenyang’s contender for the J-XX project was a triplane platform with canards, wings, and tailfins, and the J-31 doesn’t resemble that at all. The closest planes to the J-31 are the F-22 and F-35 fighters.
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The one other way to argue about it would be to say that the J-31 shows significant JF-17 lineage. The issue with that is that the JF-17 is Chengdu’s, not SAC’s, and I’m not sure how happy Chengdu would have been to transfer their old data on the JF-17 to their rivals in the Northeast.
InstRe: anticopyists:
Then what design elements are original in the J-31/21? The J-20 has an unique Canard – Lerx – Delta configuration thats shared only by the Rafale, and the Rafale doesn’t have the same V tailfins + anhedral dihedral mix, but the J-31 is really really close to copy-pasting a F-22 back onto a F-35 front + wings between F-35 and F-22 size.
ATD-X as far as being a copy goes is more similar to the J-20 in that it looks like a stealthified F-2 with less aggressive shaping compared to the true fifth-generation stealth aircraft.
And you really don’t have to complain about the J-31 being somehow inferior to the F-35 as a copy. Most real innovation is based on copying other people’s stuff and somehow getting it “wrong”, but when you get it wrong, you have to innovate to overcome your failings. The J-31 didn’t copy the F-35’s suboptimal design decisions where a lift-fan had to be integrated; and the design looks stealthier than the F-35 due to not having to design all these bumps because of not being able to meet an overly ambitious design spec.
Inst35*.9 = 31.5 rounded down
22*.9 = 19.8 rounded up
InstIt’s a copy because many many features of the plane are similar to that of the F-35. Not all the details are right, but the overall aerodynamic structure is similar, and we know the Chinese have broken into Lockheed and pilfered their design data.
This is not to say the Chinese didn’t do their own work on the aircraft, used their own supercomputers to run simulations, and made their own design decisions, but in large part this is an F-35 with twin engines, a larger wing, and better project management (although that’s not saying much).
InstThe Chinese have very poor engine technology; the first few instances will likely fly with Russian or outdated engines, and by having oversized engine compartments, they will be able to provide latitude if their final engine is oversize / overweight.
InstThis is pretty much an F-35 copy, but there are a few differences.
First, the wing loading on the J-21 is lower than on the F-35 A and B variants, although not the C variant, with a larger wing for its size.
Unlike the F-35, the J-21 does not have bumps on the bottom to optimize its aerodynamic characteristics. This should improve all-aspect stealth slightly, but we don’t know how good the Chinese are at stealth optimization in general.
The tailfins are larger on the J-21 than on the F-35, on a proportionate basis. This should increase stability somewhat, but will contribute to higher RCS.
With regards to complaints about rear-stealth, the great thing about the J-21 is that it’s a twin-engine design with the potential for optimization for all-aspect stealth. If you’re complaining about unstealthy exhausts, you can always swap them for 2D TVC once the technology is available.
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Also, inb4 Carlos Kopp complains that the J-21 is what the F-35 should have been.
InstDetection tracking range changes with the fourth root of power and RCS;
A 90% reduction in RCS approximately halves the range of radar, a 10-fold increase in radar power approximately doubles the range of radar.
The combined transmission and reception of the J-20 radar would have to be 10 times better than that of a F-22 or F-35 in order to compensate for an order of magnitude RCS inferiority.
Instwhat’s the aircraft in your RCS diagram?
InstFujitsu created a 100 watt T/R module, so a 20 watt GaN module isn’t anything interesting for the available technology. We also don’t know anything about the module sizes; a significant increase in per module energy at a cost of the number of modules will decrease range due to decreased resolution.
AFAIK, according to the radar range equations, you need a sixteen-fold increase in power to obtain a two-fold increase in range.
Since the J-20 is supposed to go into operation with 360kN of engine power at max and probably 200 kn of engine power without afterburner, it should have enough engine power to power the radar.
http://en.wikipedia.org/wiki/Boeing_E-3_Sentry
The E-3 sentry has 4 power generators mounted onto its engines, generating a total of 1 MW of energy. That’s with 93*4 kn. A J-20 using 2500 T/Rs at 100 watt peak a piece would be a 250kW peak power radar, which would easily be supplied by a similar apparatus and engines operating at 200 kN without afterburners.
As you mentioned, however, cooling and shielding emissions from enemy systems will remain a challenge.
InstWell, marble is about .0001, golf ball is .001.
This is an article on Chinese GaN X-band T/R module research. If it’s weaponized and it turns out the J-20 has a 2500 module AESA, then you have a 50 kw peak power AESA. Never mind that by the time the J-20 reaches operational status, the F-22 and F-35 will be on GaN AESAs as well.
InstOne other thing: no one has radome measurements? According to studies made on the J-20’s canards, the J-20’s RCS cannot be below 0.001 m^2 on the frontal sector because that’s the RCS contribution of composite radar transparent canards. This is an order of magnitude less than the F-35 and F-22, which means that for frontal RCS, the J-20 will be detected at twice the range it would be able to detect the F-35 or F-22 with comparable radar. Consequently, the radar of the J-20 would need to be significantly larger than the F-35 / F-22 radar to compensate.
In the case of the F-35, this can be relatively easy since the F-35 only has 1200 T/R modules. In the case of the F-22, however, the F-22’s APG-77v2 will have up to 2200 TR modules and it would be hard for the J-20’s radar to significantly outsize the F-22 to obtain equal detection ranges.
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