J-20 5th Generation Fighter VII


Inst

Senior Member
Switching from WS-10 to WS-15 does not necessarily mean the intake area has to be drastically increased, or increased at all.

Yes, the thrust of WS-15 is much higher than WS-10, but that does not mean that WS-15's intaking air volume per unit time must be increased in the same percentage as thrust increase. Thrust increase is achieved by two main means. One is increasing intaking air volume as F-135 does with bigger fan. The other way is by increasing the temperature in the turbine, so the same amount of fuel and air can create more thrust. The limit to the second approach is the materials' ability to withstand the temperature. And we know that WS-15 (F119 as well) works on higher temperature than earlier generation engines. There is still a big room to increase the thrust without increasing air-flow so long as the material can improve until theoretical efficiency limitation of turbo jet takes over. In another words, new engines are improving their thermal efficiencies rather than wastefully sucking more air and burning more fuel.
It doesn't necessarily mean that the intake area will be increased, but that it's likely for it to be increased. To achieve thrust increases with only temperature increases is extremely difficult, first, and we know the WS-10 and AL-31 are banded within the J-20 engine compartment to account for the diameter difference between the WS-15 and interim engines.

The bigger question is whether the J-20 can achieve the WS-15's required airflow with just DSI mods, or whether the intakes would need to be adjusted and the entire airframe readjusted for the airflow.

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Well I don't think a strike variant J-20 makes much sense, that's why I said that if there wasn't a JH-XX, that buying more H-20s and J-20s would be a fine solution.

The idea of a strike variant J-20 would require the aircraft to have some rather significant modifications to make such a variant worthwhile to begin with, that it would end up basically being an entirely different aircraft.
And what's wrong with an entirely different aircraft that shares certain commonalities with its predecessor? This is basically what happened with the F/A-18E Super Hornet compared to the F/A-18 Hornet, but it meant that the Super Hornet had drastically improved development times compared to an old-growth variant.

Likewise, consider the Su-35 vs the Su-27. There's been tremendous weight growth, and the Su-35 is probably terrible on wing loading compared to the Su-27, and the structural airframe has changed tremendously with use of composites and internally enlarged fuel tanks. But the increased thrust with new engines should make the Su-35 either the equal or better of the Su-27.

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Basically, when you think of a strike J-20, the trade-offs are:

-A strike J-20 can likely dogfight as well or almost as well as a J-20A / J-20B.
-A strike J-20 will likely have a more limited maximum speed compared to a J-20A / J-20B, as with all strike aircraft, slightly weakening its interception ability.
-A strike J-20 can carry a significantly better air to air missile payload as well as an air-to-ground missile payload, possibly making a strike J-20 better than a J-20A / J-20B in the interception role due to its better missile loadings and better in the air-to-air role simply by carrying more air-to-air missiles.

We've mostly identified that the J-20 is anemic in terms of air-to-air missile load-out, the PL-15 will need to be modified just so the J-20 can carry 6 of them, and the modified PL-15 will be less capable.

A strike J-20 will likely be as capable or more capable than the current J-20A / J-20B in almost every way, just as the Su-30MK and F-15E outshone their "air superiority-only" variants.

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Basically, if the J-20 is redesigned to carry a Kinzhal-class missile, you'll have effectively double the air to air payload, or 150% if part of the payload is used for internal fuel tanks to further extend range. If you treat the rumors of the J-20 as around 100 million USD, and assume the F-35 drops to the equivalent of 50 million USD, you have a platform that's fully competitive with the F-35 in terms of strike capability for cost, as well as granting in further improved range if it's on a pure air superiority mission.

The weapons bay payload is the greatest weakness of the J-20; it's way better than the F-22 and better than that of the Su-57, but it can't compete with the F-35 for cost.

A redesigned "strike" J-20 would basically knock off the tailfins and move the engines to where the tailfin is right now, and if TVC is sufficiently mature there shouldn't be a significant loss in maneuvering ability and possibly even a gain with drag reduction from removal of tailfins and ventral fins. Likewise, the loss of 2-4 planes of planform alignment would further increase its stealth.

This would have the further advantage that Western commentators would immediately mistake it for a light bomber like the FB-22 or FB-23, instead of a strike platform using next-gen aerodynamics.
 
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taxiya

Colonel
Registered Member
It doesn't necessarily mean that the intake area will be increased,
This was my point, and the only point we can agree.

but that it's likely for it to be increased. To achieve thrust increases with only temperature increases is extremely difficult, first, and we know the WS-10 and AL-31 are banded within the J-20 engine compartment to account for the diameter difference between the WS-15 and interim engines.

The bigger question is whether the J-20 can achieve the WS-15's required airflow with just DSI mods, or whether the intakes would need to be adjusted and the entire airframe readjusted for the airflow.
All the above are based on your assumption that WS-15's diameter is bigger than WS-10. You DO NOT know that, unless you have information that we don't know. If you know that you would not have put the "whethers" in your reply.

About "increasing temperature alone is extremely difficult". We all know it is difficult, that is the reason the F119 and WS15 are called "new generation". Take F-15 and F-22 for comparison. F-22 has much higher thrust than F-15, do you see F-22's intake bigger than F-15? You can't say just because car engines in the 1940s are not efficient, so engines in the 2000s have to be double sized to be double powerful.
 

Inst

Senior Member
This was my point, and the only point we can agree.


All the above are based on your assumption that WS-15's diameter is bigger than WS-10. You DO NOT know that, unless you have information that we don't know. If you know that you would not have put the "whethers" in your reply.

About "increasing temperature alone is extremely difficult". We all know it is difficult, that is the reason the F119 and WS15 are called "new generation". Take F-15 and F-22 for comparison. F-22 has much higher thrust than F-15, do you see F-22's intake bigger than F-15? You can't say just because car engines in the 1940s are not efficient, so engines in the 2000s have to be double sized to be double powerful.
Information given here is that the AL-31s/WS-10 have bands to allow them to fit inside the J-20 snugly.

IIRC, when I measured the F-22, it roughly had a .88-1m^2 inlet size. This is within DSI modification for the WS-15; i.e, the WS-15 would have to have 160kN thrust for such a thing to be possible.

And yes, I can remeasure it, but likely the F-22 has an inlet size that's greater than that of the F-15. The F-35, per engine, has a greater inlet size than the F-22's.

And rumors mentioned here state that the WS-15 has a lower turbine temperature than the F119 or F135.

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What's going on here is basically our antipathy for Minnie Chan clouding our judgment. She's unreliable, no one denies that, but that doesn't mean that whatever she says is false, it just means that what she says is possible and requires outside corroboration for it to be true. The J-20B claim was wrong in terms of what engine was being used, but we know from other sources that a J-20B with TVC exists.

Likewise, we have other sources stating that there's consideration for the J-20 being developed into a striker, and the J-20 being developed into a carrier variant. We need further corroboration of these claims to know that the J-20 will be developed into a striker and a carrier-based aircraft, but it seems a no-brainer for me for the J-20 to get a substantially improved internal weapons bay with WS-15 maturity.
 
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taxiya

Colonel
Registered Member
Compare and constrast: AL-31 vs WS-10.

I wonder why the engine compartments are shortened. The AL-31 version has the engine fully covered except the moving flaps, while the WS-10 version has the grey part exposed. Is the grey part of WS-10 movable?
 

gelgoog

Senior Member
Registered Member
...
The WS-15 being equivalent to the F119, let's put it this way, even the Izdeliye 117 engines aren't equivalent to the F119, with substantially increased thrust (160 kN class vs 170-180 kN class). If you say the WS-15 is equivalent to the F119, you're saying the WS-15 is a crap engine.
...
Sigh. The best way to compare military engine generations isn't by looking at the total thrust of the engine. It is to look the thrust to weight ratio of the engine. Sure the Izdeliye 117 has less total thrust than the F119 but it is also lighter than it. The Izdeliye 117 has a wet thrust to weight ratio of 9.3:1 supposedly. That makes it have around the same or more thrust to weight ratio than the known figures for the F119.
Now the issue with the Izdeliye 117 is that it has worse thrust to weight ratio than more modern engines like the F135. That supposedly has a thrust to weight ratio of 11.47:1. For this the Russians are developing the Izdeliye 30 engine.

Both aircraft, the Su-57 and the F-22, have a thrust to weight ratio over unity (1.0). This means they are highly agile.
An aircraft with thrust to weight ratio over unity can basically hover on the air with engine power alone. That's how agile it is.

The F-35 has thrust to weight ratio under unity. The airframe is heavy like heck. It's like an albatross around the engine.

The J-20 has thrust to weight ratio also under unity but between the F-35 and F-22. Plus it has canards which should enhance maneuverability. Once WS-15 engines become available it should have thrust to weight ratio over unity.
 
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Bltizo

Lieutenant General
Staff member
Super Moderator
Registered Member
What's going on here is basically our antipathy for Minnie Chan clouding our judgment. She's unreliable, no one denies that, but that doesn't mean that whatever she says is false, it just means that what she says is possible and requires outside corroboration for it to be true. The J-20B claim was wrong in terms of what engine was being used, but we know from other sources that a J-20B with TVC exists.
Nope, as I wrote over on a different forum...

"The problem is that her articles often have one or maybe two claims which are plausible, but is hampered down by many other inaccurate statements which are not corroborated by other sources or some of which are outright illogical.

Just off the top of my head, the J-20B article she wrote that you refer to suggests:
- the idea that J-20 "mass production" was ever limited by engine availability or waiting for WS-15 (latter of which she has a terrible track record of)
- the idea that J-20s in production will be fitted with Al-31 engines but with ??Chinese TVC nozzles?? All of this keeping in mind that all photos of new production J-20s since last year show J-20s with WS-10s??
- the very designation of J-20B is controversial as well, given if we were going to receive a new J-20 "variant" with a full on designation change, it definitely would've been noticed by the community -- not least because the J-20B designation has been floated as the name of J-20 for when it would receive its intended spec WS-15s
- the author also has a strange set of criteria what "qualifies" a jet as a "true fifth generation fighter jet"


The only "useful" thing from that article (if you want to call it that) is it does suggest a J-20 with some kind of TVC engines may be in production in some form...
But that is something we didn't need to read her utter failure of an article to know, because that same information was conveyed from the grapevine in about the same time period.

The reason why Minnie Chan's articles are almost always categorically dismissed, is because it's not worth to identify and disqualify all of the many incorrect premises she writes in her articles, just for the purpose of identifying one premise that might be plausible or half true at best.
Especially because it's so much easier to get the same information from the PLA watching community without having to hash through a mess of nonsense."


Minnie Chan's articles basically never offer anything that we didn't already know from the standard PLA watching grapevine, but her contributions are crippled by the fact that her articles always includes multiple incorrect premises or interpretations.

The fact that her articles offer no exclusive information at all, and the fact they are virtually always accompanied by multiple instances of incorrect information, means her current approach to writing does not deserve any defense or justification.
No one's judgement is "clouded" by the dismissal of Minnie Chan's articles -- her articles offer nothing that we didn't already know from the tried and true PLA watching methodology that's been practiced for over a decade now.
 

gongolongo

New Member
Registered Member
We've mostly identified that the J-20 is anemic in terms of air-to-air missile load-out, the PL-15 will need to be modified just so the J-20 can carry 6 of them, and the modified PL-15 will be less capable.

Honestly I think it's pretty well established that the J-20 has plenty more room for missiles and that a 6 PL-15 loadout isn't out of the question.
 

siegecrossbow

Brigadier
Staff member
Super Moderator
Honestly I think it's pretty well established that the J-20 has plenty more room for missiles and that a 6 PL-15 loadout isn't out of the question.
Weight wise it is no problem, space-wise it is. PL-15 is thicker than the AIM-120D and has wider fins. Even when stacked there isn't enough space in the main bays for 6 missiles.
 

Inst

Senior Member
Nope, as I wrote over on a different forum...

"The problem is that her articles often have one or maybe two claims which are plausible, but is hampered down by many other inaccurate statements which are not corroborated by other sources or some of which are outright illogical.

Just off the top of my head, the J-20B article she wrote that you refer to suggests:
- the idea that J-20 "mass production" was ever limited by engine availability or waiting for WS-15 (latter of which she has a terrible track record of)
- the idea that J-20s in production will be fitted with Al-31 engines but with ??Chinese TVC nozzles?? All of this keeping in mind that all photos of new production J-20s since last year show J-20s with WS-10s??
- the very designation of J-20B is controversial as well, given if we were going to receive a new J-20 "variant" with a full on designation change, it definitely would've been noticed by the community -- not least because the J-20B designation has been floated as the name of J-20 for when it would receive its intended spec WS-15s
- the author also has a strange set of criteria what "qualifies" a jet as a "true fifth generation fighter jet"


The only "useful" thing from that article (if you want to call it that) is it does suggest a J-20 with some kind of TVC engines may be in production in some form...
But that is something we didn't need to read her utter failure of an article to know, because that same information was conveyed from the grapevine in about the same time period.

The reason why Minnie Chan's articles are almost always categorically dismissed, is because it's not worth to identify and disqualify all of the many incorrect premises she writes in her articles, just for the purpose of identifying one premise that might be plausible or half true at best.
Especially because it's so much easier to get the same information from the PLA watching community without having to hash through a mess of nonsense."


Minnie Chan's articles basically never offer anything that we didn't already know from the standard PLA watching grapevine, but her contributions are crippled by the fact that her articles always includes multiple incorrect premises or interpretations.

The fact that her articles offer no exclusive information at all, and the fact they are virtually always accompanied by multiple instances of incorrect information, means her current approach to writing does not deserve any defense or justification.
No one's judgement is "clouded" by the dismissal of Minnie Chan's articles -- her articles offer nothing that we didn't already know from the tried and true PLA watching methodology that's been practiced for over a decade now.
Basically re: Minnie Chan, the issue is that you don't dismiss things out of hand because she's said something, you just assign it the value of "Minnie Chan said it" and wait for other corroboration.

In the case of the strike variant, we have reports from other sources that Chengdu is interested in creating other variants of the J-20.

It's a natural progression as the US is providing newer technologies to change the regional balance of power (NGAD, B-21 EO AEW&C, micromissiles) and the J-20 platform needs to change in order to keep up with the times.

The idea that the J-20 is static and is married to a Su-57-style dogfight uber alles paradigm is basically asking for the PLAAF to lose.

***

The difference between us is that I constantly expect the PLAAF to adapt to fight the wars of the next generation, instead of simply seeing the USAF as a static target so that the PLAAF will try to fight Iraq and Afghanistan, when the US wants a new paradigm for enemy military planners to (hopefully not) grapple with. Having novel capabilities, paradigms, and designs is the only real way to compete with the United States.

Therefore, the J-20 platform needs to be constantly modified and improved instead of simply being "hay, we have an air superiority fighter with WS-15" and calling it a day. Doing that is asking to get slaughtered.
 

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