J-20 - physical parameters and other overflow from main thread

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The RD-93 isn't a scaled down F135 though The latter is 25 years more modern in technology, achieving a 30% higher pressure ratio with 40% fewer compressor stages. All else needs to be equal, as I said (it was a thought exercise to address the argument that more engines = more weight).
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Scaled down F-135 doesn't exist, brah; you're imagining things. RD-93 is the real engine on the J-31 now unless WS-13 replaces it and we have no numbers on that.

I realize that, but even 16t is hardly any more credible than 15t. Anything substantially below 21t requires a step change in airframe structure technology and/or compromises in capability (e.g. lower g-limit).
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Every part of your analysis for why J-20 must be around 21 tons comes with a caveat and that's, "to the best of my design ability." So if your knowledge of aircraft design is somewhat less than the knowledge of the design team of the J-20, then your assumptions would not hold true.

From the F-22, but being significantly larger than the Raptor, a J-20 built with approximately the same technology level will be heavier (around 21t), so realistically you need to take that figure as the basis, as I said.

Please don't talk about J-20 being larger (or how much larger) than F-22 anymore without providing 3D modelling computer calculations for volume. Eye-balling the volume of (extremely) complex shapes is not acceptable without numerical evidence. And also, assuming that they are built to the same technological level is obviously false because there are known techniques used on building J-20 that were not available at the time of F-22's build.

The Flanker (and the MiG-29, for that matter) are 4th generation fighters - they are not accurate benchmarks for 5th generation fighter weights, else why is the F-22 heavier than the Su-27?

I wasn't comparing 4th gen to 5th gen weight LOL. It was Brat, who was saying J-31 should be same weight as MiG-29 with no evidence at all as usual, so I was using his logic. And I dunno why F-22's so heavy. I didn't design it. Su-57 is longer, has a greater wingspan, and is rumored to be 18 tons. F-22's not the only thing in the world we have to compare J-20 to and if it is, then we have a problem in sampling error.

 

[Tirdent]

Scaled down F-135 doesn't exist, brah; you're imagining things.

I didn't say it existed.

As for imagining things, what part of "it was a thought exercise to address the argument that more engines = more weight" or the "FYI" in the original post did you miss? All I'm saying is that more engines need not equal more weight per se - the point was more general and not necessarily aimed at the J-31.

Every part of your analysis for why J-20 must be around 21 tons comes with a caveat and that's, "to the best of my design ability."

First of all, my analysis on the J-20 does NOT say it must be around 21t, only that to be significantly lighter than this, it needs to leverage a step change in structural design/materials or compromise on capability.

Second, while my analysis does naturally come with the caveat "to the best of my ability", a 15t OEW is so exceptional a claim that it doesn't take terribly accurate methods of estimation to conclude this would require some rather extraordinary evidence to believe.

Please don't talk about J-20 being larger (or how much larger) than F-22 anymore without providing 3D modelling computer calculations for volume. Eye-balling the volume of (extremely) complex shapes is not acceptable without numerical evidence.

Please don't tell me what to say unless you can actually prove my point wrong. At least I did provide some numerical data, but a 3D model is out of the question unless somebody pays me a hefty sum of money - been there, done that and for me at any rate it is way too time consuming to do for free. Censoring arguments is not acceptable without hard evidence.

And also, assuming that they are built to the same technological level is obviously false because there are known techniques used on building J-20 that were not available at the time of F-22's build.

There are indications that techniques were used in building the J-20 which were unavailable to the F-22, but no confirmation. And even less evidence that those techniques could plausibly shave no less than 6t off its weight - IIRC the F-35 includes up to 900 3D printed components yet it didn't seem to help very much. Anyway, this argument has been basically discussed to death by latenlazy and myself, so I'm not going to recapitulate the arguments.

Su-57 is longer, has a greater wingspan, and is rumored to be 18 tons. F-22's not the only thing in the world we have to compare J-20 to and if it is, then we have a problem in sampling error.

Using the Su-57 would indeed require a 3D model for an acceptable level of accuracy because unlike the F-22 its fuselage configuration is very different from the J-20. However even supposing somebody made a model, what would it tell us, given that we have nothing more than unfounded rumours about its weight? Regrettably the F-22 is the only *sensible* thing in the world we have to compare the J-20 to (with reasonable effort) - does that mean the estimate is prone to sampling error? Sure, and I acknowledged as much earlier, but that doesn't necessarily mean it is in fact wrong.

 

[plawolf]

All this incredulity about the J20’s rumoured 15t weight and volume analysis argument against that fails the most basic sense check when one only need to look at the 14.9t empty weight of the FY22.

If the FY22 and F22 can have pretty much the same external shape and dimensions, yet are so much different in weight, it pretty much rules volume analysis out as a credible technique with so much unknown about the materials used and internal structures of all the planes used as both the benchmark and ultimate target.

The FY22 proves that 15t ballpark weight was possible with 1980s technology for a tech demonstrator.

The 20-30 years’ worth of technological advancement in supercomputer processing power (allowing for more accurate calculations of forces and structural strength to allow excessive safety margins to be reduced without compromising performance or safety); material science (lighter, more durable materials); manufacturing tools (things like 3D printing that allows parts to be crafted much closer to theoretical perfect shapes and dimensions thereby cutting down on flash waste) etc, and it’s not out of the question that a 15t ballpark weight is achievable today for a production plane.

Before anyone gets their underwear in a twist extrapolating the lower weight to performance or national technology capabilities, remember the golden rule: Designs are driven by requirements and specifications.

Give the same designer the same materials and technology but give him different specifications and he will give you very different design choices with different weights and other key characteristics because of those different criteria.

If weight saving was deemed a critical requirement, does anyone here seriously doubt the US could not have controlled the F22’s weight more, so that it was closer to the FY22’s 14.9t rather than the F22’s 19.7t?

Design is all about trade-offs.

For the US, weight saving wasn’t a top priority because they know they have those monstrously powerful F119s to play with.

But for China, they know engines have always been a weakness, so how would it make sense that they could make the same trade-offs as the F22 team and not instead focus more on weight management?

If the J20 does turn out to be 15t or thereabouts, that doesn’t automatically make it better than the F22. It only means the J20’s designs made different choices as to what their priorities are.

The J20 may well have a lot of designed for but not yet built in features and capabilities that will only be ‘unlocked’ with the introduction of the WS15.

The most obvious and easy thing to take out is fuel capacity and TVC.

Just because it has the designed space for massive fuel tanks does not mean they need to actually fill or even install some of those fuel tanks.

I would not be surprised if the J20’s weight does jump by a fair few tons after the WS15 becomes available and CAC gets to add in all the things they had to leave out to achieve the weight needed to allow the J20 to reach its performance benchmarks with its current engines. Although it make still enjoy unusually good TWR even after all the weight gain.

 

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I didn't say it existed.

As for imagining things, what part of "it was a thought exercise to address the argument that more engines = more weight" or the "FYI" in the original post did you miss? All I'm saying is that more engines need not equal more weight per se - the point was more general and not necessarily aimed at the J-31.



First of all, my analysis on the J-20 does NOT say it must be around 21t, only that to be significantly lighter than this, it needs to leverage a step change in structural design/materials or compromise on capability.

Second, while my analysis does naturally come with the caveat "to the best of my ability", a 15t OEW is so exceptional a claim that it doesn't take terribly accurate methods of estimation to conclude this would require some rather extraordinary evidence to believe.



Please don't tell me what to say unless you can actually prove my point wrong. At least I did provide some numerical data, but a 3D model is out of the question unless somebody pays me a hefty sum of money - been there, done that and for me at any rate it is way too time consuming to do for free. Censoring arguments is not acceptable without hard evidence.



There are indications that techniques were used in building the J-20 which were unavailable to the F-22, but no confirmation. And even less evidence that those techniques could plausibly shave no less than 6t off its weight - IIRC the F-35 includes up to 900 3D printed components yet it didn't seem to help very much. Anyway, this argument has been basically discussed to death by latenlazy and myself, so I'm not going to recapitulate the arguments.



Using the Su-57 would indeed require a 3D model for an acceptable level of accuracy because unlike the F-22 its fuselage configuration is very different from the J-20. However even supposing somebody made a model, what would it tell us, given that we have nothing more than unfounded rumours about its weight? Regrettably the F-22 is the only *sensible* thing in the world we have to compare the J-20 to (with reasonable effort) - does that mean the estimate is prone to sampling error? Sure, and I acknowledged as much earlier, but that doesn't necessarily mean it is in fact wrong.

- I'm talking about real live aircraft here so I said 2xRD-93. I had no idea that you just drifted into make believe scenarios with "aircraft in general." LOL OK, whatever you say. Not what I'm talking about.


- No problem. Previously you did acknowledge that your methods were crude, untested, and very possibly unreliable. Let's be reminded of that.


- So you want people to pay you to prove your own point? LOL OK I think I'll have to keep my money and leave your argument without support then. And you want to use freedom of speech to defend your right to make assertions without evidence? OK, well that works both ways then. I don't agree with your size estimate. J-20 looks smaller than F-22 to me and I think we can start it off at 18 tons on the same technological level. I've got as much evidence as your 21 then.


- So anyway, your argument can be summed up with this:
"I think that by eyeballing, or if J-20 was made with the best design capabilities that I could come up with, then J-20 would be about 21 tons."


- I have no problems at all with that statement.

PS. 19.7-16 = 3.7, not 6.

 

[Jura The idiot]

I'm not guessing the weight; I'm saying we should remain open-minded about the possibilities, especially those that are published in semi-reliable sources that claim to have gotten their info from Chengdu.

The only people who are actually guessing the weight are those who claim it has to be heavier than F-22 or place a number like 20 or 21 tons based on nothing except their own eye-balling of volume and assumptions of density, in other words, making up numbers when you don't have them.

If anyone was halfway serious about this, the least he should do is develop/use a program to render 3D models of both jets, enter the relatively known data for length and wingspan, and use that to actually get in silico calculations for volume of both aircraft. That would be a very basic start. Just get the volume numbers. Even then, you couldn't definitively draw weight conclusions because you don't have density data. I don't understand how anyone could be so delusional as to think that they could arrive at a number doing this with eyeballing and guesstimating.

Of course we will! (our team knows with-in a 1,000 lbs what the J-20 weighs), this isn't rocket science, and its unlikely that China will ever divulge the J-20s weight willingly,,, like I said, who really cares what the J-20 weighs, but its a known quantity.. more importantly, we know how well it performs.. We know its thrust, we know its weight,, no doubt we know within a few gallons how much fuel it carries, and exactly what will be in those weapons bays when the doors close, oh and don't forget we know about the radar, the ejection seat, and how many hours they can reasonably expect to get out of those Russian AL-31FN's

Truth be told, this discussion is NOT about weight, but about intellectual honesty!

and for the record, I've NEVER been in the military, other than having a very early USAF part and serial number stamped at the TOP of my right butt cheek,, Govt Issue #1 Son, serial # 000000056-1,,, that pleasant looking gentlemen in the picture is my dear old Dad,,, I can tell he's having a great day by the smile on his face!

remember, "imitation", remains the sincerest form of flattery"

and with the Russian's flying their SU-35's in Syria, we know the numbers on that score as well!

I thank both of you, as I said: take it easy
I now unsubscribe from this thread LOL

 

[Tirdent]

All this incredulity about the J20’s rumoured 15t weight and volume analysis argument against that fails the most basic sense check when one only need to look at the 14.9t empty weight of the FY22.

If the FY22 and F22 can have pretty much the same external shape and dimensions, yet are so much different in weight, it pretty much rules volume analysis out as a credible technique with so much unknown about the materials used and internal structures of all the planes used as both the benchmark and ultimate target.

The equipment and other differences between the YF-22 and F-22 have been discussed right here at great length - suffice it to say that it's an apples to oranges comparison.

The FY22 proves that 15t ballpark weight was possible with 1980s technology for a tech demonstrator.

Correct, but not for a combat capable fighter - the YF-22 lacked even the most basic sensor suite and other essential features of an operational aircraft which the F-22 does have. Sorry, comparing a combat-ready fighter to a proof of concept that is not fitted for anything beyond the limited scope of its intended tech demos is frankly disingenuous.

Before anyone gets their underwear in a twist extrapolating the lower weight to performance or national technology capabilities, remember the golden rule: Designs are driven by requirements and specifications.

Yes, you could conceivably get a decent weight reduction by consciously accepting a somewhat lower g-limit than 9g for example and designing the structure for the resultant lower loads. I dare say being combat-capable with a radar, EW system and other essentials is among the non-negotiable requirements and specifications for an operational fighter though.

If weight saving was deemed a critical requirement, does anyone here seriously doubt the US could not have controlled the F22’s weight more, so that it was closer to the FY22’s 14.9t rather than the F22’s 19.7t?

Yes, I doubt it. If they could have, why did they not simply do so (according to you, having done so on a demonstrator means they could have done so on the production model...)? Makes no sense.

- No problem. Previously you did acknowledge that your methods were crude, untested, and very possibly unreliable. Let's be reminded of that.

Crude untested and very possibly unreliable, but almost certainly not 6t worth of crude untested and very possibly unreliable. It's not a binary thing, you know.

- So you want people to pay you to prove your own point?

Nope, just pointing out why I took a different route, even though a 3D model would clearly be preferable and I actually have the skills, tools and experience to make one.

And you want to use freedom of speech to defend your right to make assertions without evidence? OK, well that works both ways then. I don't agree with your size estimate. J-20 looks smaller than F-22 to me and I think we can start it off at 18 tons on the same technological level. I've got as much evidence as your 21 then.

Between the two of us, the only one who's making assertions completely out of thin air is you, so for you of all people to accuse me of doing so is a bit rich. You know I worked off measurements derived from imagery and compared with a similar, well-documented design - that's rather more than eyeballing it. Not as good as a 3D model, but it beats supplying nothing at all, like you have, any day. Until you can put up something of more substance which proves my points wrong, you're the last person who has any justification in telling me to shut up - just making that clear.

- So anyway, your argument can be summed up with this:

"I think that by eyeballing, or if J-20 was made with the best design capabilities that I could come up with, then J-20 would be about 21 tons."

Since you know better already I suspect you don't care, but for the record a decent summary of my argument could be:

"My J-20 estimate is based on finding the difference in volume to the well-documented F-22 based on the best imagery available (accounting for parts where the J-20 has more or less volume as best I can) and any quantifiable equipment differences (gun, EOTS, engines, ...). Density (weight per volume) I assumed to be the same - based on this, i.e. similar structural design/materials, I get an OEW of 21t for the J-20. Anything substantially lower than this would require a step change in structures technology and/or compromises in capability."

PS. 19.7-16 = 3.7, not 6.

Starting with 19.7 again - if you must play the pedant, at least do so stringently and get 5. Not that it matters.

 

[Air Force Brat]

The equipment and other differences between the YF-22 and F-22 have been discussed right here at great length - suffice it to say that it's an apples to oranges comparison.



Correct, but not for a combat capable fighter - the YF-22 lacked even the most basic sensor suite and other essential features of an operational aircraft which the F-22 does have. Sorry, comparing a combat-ready fighter to a proof of concept that is not fitted for anything beyond the limited scope of its intended tech demos is frankly disingenuous.



Yes, you could conceivably get a decent weight reduction by consciously accepting a somewhat lower g-limit than 9g for example and designing the structure for the resultant lower loads. I dare say being combat-capable with a radar, EW system and other essentials is among the non-negotiable requirements and specifications for an operational fighter though.



Yes, I doubt it. If they could have, why did they not simply do so (according to you, having done so on a demonstrator means they could have done so on the production model...)? Makes no sense.



Crude untested and very possibly unreliable, but almost certainly not 6t worth of crude untested and very possibly unreliable. It's not a binary thing, you know.



Nope, just pointing out why I took a different route, even though a 3D model would clearly be preferable and I actually have the skills, tools and experience to make one.



Between the two of us, the only one who's making assertions completely out of thin air is you, so for you of all people to accuse me of doing so is a bit rich. You know I worked off measurements derived from imagery and compared with a similar, well-documented design - that's rather more than eyeballing it. Not as good as a 3D model, but it beats supplying nothing at all, like you have, any day. Until you can put up something of more substance which proves my points wrong, you're the last person who has any justification in telling me to shut up - just making that clear.



Since you know better already I suspect you don't care, but for the record a decent summary of my argument could be:

"My J-20 estimate is based on finding the difference in volume to the well-documented F-22 based on the best imagery available (accounting for parts where the J-20 has more or less volume as best I can) and any quantifiable equipment differences (gun, EOTS, engines, ...). Density (weight per volume) I assumed to be the same - based on this, i.e. similar structural design/materials, I get an OEW of 21t for the J-20. Anything substantially lower than this would require a step change in structures technology and/or compromises in capability."



Starting with 19.7 again - if you must play the pedant, at least do so stringently and get 5. Not that it matters.

and with this Brother, lets let it rest, obviously the other team is just toying with us? and has no real desire for the honest weight of the J-20,, and with one final point,,, those canards are very large, and they are "full thow" with what appears to be 180 of travel, pitch positive to negative, there has to be a massively strong underlying architecture to support the weight and massive airloads in the far forward fuselage,,, that's why the center of gravity is actually fairly normal!

the J-20 is a beautifully designed, well balanced aircraft, my compliments and admiration for Dr. Song and his design team once again!

and for you guys wishing for a 15 tonne J-20,,,, Happy New Year!, yes it will be upon us very soon, and perhaps Chengdu will gift us with 3 or 4 more J-20 in the early new year, maybe 7 or 8 by late summer and 11or 12 by this time next year!

excellent points Master Trident, and welcome to SDF!

 

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The equipment and other differences between the YF-22 and F-22 have been discussed right here at great length - suffice it to say that it's an apples to oranges comparison.



Correct, but not for a combat capable fighter - the YF-22 lacked even the most basic sensor suite and other essential features of an operational aircraft which the F-22 does have. Sorry, comparing a combat-ready fighter to a proof of concept that is not fitted for anything beyond the limited scope of its intended tech demos is frankly disingenuous.



Yes, you could conceivably get a decent weight reduction by consciously accepting a somewhat lower g-limit than 9g for example and designing the structure for the resultant lower loads. I dare say being combat-capable with a radar, EW system and other essentials is among the non-negotiable requirements and specifications for an operational fighter though.



Yes, I doubt it. If they could have, why did they not simply do so (according to you, having done so on a demonstrator means they could have done so on the production model...)? Makes no sense.



Crude untested and very possibly unreliable, but almost certainly not 6t worth of crude untested and very possibly unreliable. It's not a binary thing, you know.



Nope, just pointing out why I took a different route, even though a 3D model would clearly be preferable and I actually have the skills, tools and experience to make one.



Between the two of us, the only one who's making assertions completely out of thin air is you, so for you of all people to accuse me of doing so is a bit rich. You know I worked off measurements derived from imagery and compared with a similar, well-documented design - that's rather more than eyeballing it. Not as good as a 3D model, but it beats supplying nothing at all, like you have, any day. Until you can put up something of more substance which proves my points wrong, you're the last person who has any justification in telling me to shut up - just making that clear.



Since you know better already I suspect you don't care, but for the record a decent summary of my argument could be:

"My J-20 estimate is based on finding the difference in volume to the well-documented F-22 based on the best imagery available (accounting for parts where the J-20 has more or less volume as best I can) and any quantifiable equipment differences (gun, EOTS, engines, ...). Density (weight per volume) I assumed to be the same - based on this, i.e. similar structural design/materials, I get an OEW of 21t for the J-20. Anything substantially lower than this would require a step change in structures technology and/or compromises in capability."



Starting with 19.7 again - if you must play the pedant, at least do so stringently and get 5. Not that it matters.

It could not be lighter by 6t (you mean 3.7t) if the aircraft were constructed purely by technology known to you.



If you're going to do it, then do it right with a 3D model. Attempting to parse highly complex structures into simple shapes to get an elementary measurement is not acceptable as it is susceptible to swings of many percent; it may even be worse than eyeballing because when you eyeball, people know you're not serious but when you so this, some might be fooled into thinking you're getting the correct number when you're just using slightly more complex methods to get the same wrong number number as eyeballing.


You accused me of supplying nothing but actually, behind my argument is an actual source! Someone actually interviewed with Chengdu and claimed that they said the aircraft weight was controlled to 15 ton range (which is up to just under 16 tons). An actual Chinese source with ties to Chengdu is really worth more than any amount of calculating you can do. At this point, my biggest doubt in the source would be if they misunderstood each other and the interviewee was talking about a prototype while the reporter thought he was talking about an LRIP, but there is no indication of this.



I'm OK with your summary sentence. Caveat of assuming similar materials, similar density, volume gauged as best you can (which is a lie because you just said you are capable of 3D modelling LOL), and you also noted that structural changes or improvements in technology will also have an unaccounted affect. I think we're on the same page on this one... the only people who aren't are those who really like your 21 number and take it as fact, ignoring all your caveats.



Starting with 19.7 cus I've no reason to start at 21... well, technically, I have no reason to start at 19.7 either cus I can't just assume their volume is the same. I guess it'll just have to be X.