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


Equation

Lieutenant General
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!
It's obvious you're only interested in believing any sort of calculations that seem to result in a pleasing number to you. I'm as interested in J-20's numbers as anyone and I want them from Chengdu. I don't want amateur internet calculations by someone who's not even doing his best because he doesn't want to bother creating 3D models. If the weight of top secret fighter jets could be figured out like this, or if, even more amusingly, the fuel capacity could be determined to the gallon like this, there's no point in keeping anything classified. They might as well keep everyone updated on the exact numbers each step of the way LOL.


PS. It's not rocket science because it's harder than rocket science. Rockets were invented decades before 5th gen stealth fighters and today many countries with space programs cannot create stealth fighters. That you don't even comprehend how complicated the question is really highlights how little of a chance there is that you could answer it properly.
 

Tirdent

Junior Member
Registered Member
It could not be lighter by 6t (you mean 3.7t) if the aircraft were constructed purely by technology known to you.
You clearly have no idea what I mean, either deliberately (as I suspect) or due to genuine ignorance (in which case you might want to dial back the hubris).

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.
I'm aware of that snippet of info, but as you're so fond of caveats, you should know that an unqualified statement (or one taken out of context) can be completely worthless, no matter how credible the original source superficially is.

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.
There are tons of other possibilities, e.g. it refers to bare airframe structural weight (minus engines & equipment), it was is an developmental weight target quoted as a placeholder because the actual value is classified (this is precisely how the published F-22 OEW jumped from about 14t to almost 20t)...

And there sure are indications that something might be amiss, given that the figure is so conspicuously low when you compare to similar fighters - that should immediately prompt a healthy dose of skepticism. Feel free to disagree with the method by which I attempted to do a sanity check, but don't tell me to shut up, put words in my mouth or even accuse me of lying unless you have hard evidence of your own.

I guess it's ok to ignore caveats when you really like the 15t number...

(which is a lie because you just said you are capable of 3D modelling LOL)
I already spelled out the reasons why I didn't do a 3D model earlier. Are you a lawyer or something? Ok, for all the care I took in composing that summary I omitted one caveat, for people who insist on playing deliberately obtuse it should have read: "as best I can without jeopardizing real life commitments". In future I shall place a multi-page Terms & Conditions section in my signature just for your benefit :rolleyes:

A lie - seriously?

and you also noted that structural changes or improvements in technology will also have an unaccounted affect.
... and then discussed exhaustively why I personally don't think such a step change in technology is applicable. Another point you can feel free to disagree with of course (in case you were wondering, by that I do not mean accuse me of lying, telling me to shut up or twisting what I said :rolleyes:).

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.
Your total inability (or is it unwillingness) to entertain working assumptions and check plausibility is not anybody else's problem.
 

Equation

Lieutenant General
You clearly have no idea what I mean, either deliberately (as I suspect) or due to genuine ignorance (in which case you might want to dial back the hubris).



I'm aware of that snippet of info, but as you're so fond of caveats, you should know that an unqualified statement (or one taken out of context) can be completely worthless, no matter how credible the original source superficially is.



There are tons of other possibilities, e.g. it refers to bare airframe structural weight (minus engines & equipment), it was is an developmental weight target quoted as a placeholder because the actual value is classified (this is precisely how the published F-22 OEW jumped from about 14t to almost 20t)...

And there sure are indications that something might be amiss, given that the figure is so conspicuously low when you compare to similar fighters - that should immediately prompt a healthy dose of skepticism. Feel free to disagree with the method by which I attempted to do a sanity check, but don't tell me to shut up, put words in my mouth or even accuse me of lying unless you have hard evidence of your own.

I guess it's ok to ignore caveats when you really like the 15t number...



I already spelled out the reasons why I didn't do a 3D model earlier. Are you a lawyer or something? Ok, for all the care I took in composing that summary I omitted one caveat, for people who insist on playing deliberately obtuse it should have read: "as best I can without jeopardizing real life commitments". In future I shall place a multi-page Terms & Conditions section in my signature just for your benefit :rolleyes:

A lie - seriously?



... and then discussed exhaustively why I personally don't think such a step change in technology is applicable. Another point you can feel free to disagree with of course (in case you were wondering, by that I do not mean accuse me of lying, telling me to shut up or twisting what I said :rolleyes:).



Your total inability (or is it unwillingness) to entertain working assumptions and check plausibility is not anybody else's problem.

I know what you you mean; you can't fathom how such a large weight reduction could be achieved. Not problem since it's not your job to know, nor are you properly equipped. I'd be shocked if you actually could figure it out because take the capability difference between 1 amateur (who doesn't want to bother with 3D models) vs a national top design team with supercomputers at their disposal; if even the amateur could figure out how to drop 5 tons, then those guys had better be able to figure out how to drop 12 just to keep their jobs LOL. So... you can't see how 16 tons could be done = totally natural. Means nothing to the situation in Chengdu.



I don't know if you can read Chinese, but it's not taken out of context at all. It compares J-20's 15 ton class weight directly to F-22's 19 ton class weight. It specifically said that the weight was controlled to that limit. The entire article is about the J-20 as it is today. That it means anything else is an off chance to be considered, which I have. But that weight is J-20 without engines?? That weight was some random placeholder? LOL Where do you come up with these? What's next? Maybe the weight didn't include the wings, right? Or maybe 15 tons is just the fuselage LOLOL That's all you trying to bend a foreign language backwards hoping it might say something you want to hear. I've already touched upon the largest realistic caveat and that's the small chance that the reporter mistook a prototype weight for an LRIP weight. Other than that, read the black and white: it says J-20's empty weight is 15-16 tons just like F-22's is 19-20.



Right, you demonstrated why you didn't think the upgrades in tech were applicable. I understand that; that's why I said everything is to the best of your ability, not the ability of Chengdu's professional design team.




Your total inability (or is it unwillingness) to entertain working assumptions and check plausibility is not anybody else's problem.
As for entertaining your assumptions, I'm of the thought that it's better to have no conclusion than to have a wrong one. You demonstrated that you used crude measurements of 2 complex objects and you ended up with a difference of less than 6.6% (21/19.7) so I'm going to have to say that that's well within the range of error.
 

Klon

Junior Member
Registered Member
I don't intend to get back into this debate, so just this post. In my first post here, I asked about the source of the 15 tonnes figure. Here are three replies I received.
"Yes, we did, and the short and thin of it is simply that we don't know enough about the source to know for sure how reliable it was. On one hand, the claim was from a trade magazine, so it's atypical of the usual bad sources we're used to, but on the other hand it's not a source we've seen before so we have no history of claims to make judgments with and no context for how reputable, well sourced, connected, and diligent the publication is."
"However, the source that it came from is more legitimate than normal so, based on what we know and can know, the probability of the claim's being true is now firmly out of "negligible" territory."
"It came from a trade magazine called 兵工科技 (Military Tech)."
(Not using the quote function because it doesn't particularly matter who posted what.)
Some points that I should have brought up then but didn't:
1) I don't think the source or it's credibility had (or have) actually been talked about (this is from memory as I haven't rechecked the close to 100 pages of the thread)
2) the magazine looks to be closer to popular instead of trade (although I say this without any certainty, just going by the vague online description).
In my opinion, there's a lot of room for a discussion of the source for anyone interested. Like I said, not me.

@Tirdent What was the ratio of J-20 and F-22 volumes that you found (revisiting a previous question)?
 

Equation

Lieutenant General
The source itself is neither one that is considered highly credible, nor incredible. I take this as a positive sign because while many sources like Global Times, Yahoo, etc... are considered clearly not credible, there are no sources that come to mind that are regarded as definitely credible on classified Chinese military information (except maybe official announcements from Chengdu). In that respect, the inability to eliminate something as not credible is already quite a nod to its trust-ability. But of course that does not make it certainly true.

Upon analyzing the article itself, it lacks any signs of being a hack. It claims that its data is from speaking with Chengdu and does not contain any obviously false information, which is usually seen in articles of poor credibility. The tell-tale signs that the reporter just needed to write an article but did not know what he was talking about are very common and easy to spot in hack articles, for example, saying that J-20 is currently mounted with WS-15, J-20 is 75 feet and can only be an interceptor, China's building a 200,000 ton catamaran aircraft carrier, etc... The article does not present any clearly false information.

So... short of an actual statement from Chengdu, that's about as close to reliable as it gets in my opinion. And as I voiced before, my main concern is whether the reporter and the interviewee understood each other perfectly when discussing the weight number as there is no ambiguity in the way that it's written.
 

latenlazy

Colonel
  • Thread Starter Thread Starter
  • #86
I don't intend to get back into this debate, so just this post. In my first post here, I asked about the source of the 15 tonnes figure. Here are three replies I received.
"Yes, we did, and the short and thin of it is simply that we don't know enough about the source to know for sure how reliable it was. On one hand, the claim was from a trade magazine, so it's atypical of the usual bad sources we're used to, but on the other hand it's not a source we've seen before so we have no history of claims to make judgments with and no context for how reputable, well sourced, connected, and diligent the publication is."
"However, the source that it came from is more legitimate than normal so, based on what we know and can know, the probability of the claim's being true is now firmly out of "negligible" territory."
"It came from a trade magazine called 兵工科技 (Military Tech)."
(Not using the quote function because it doesn't particularly matter who posted what.)
Some points that I should have brought up then but didn't:
1) I don't think the source or it's credibility had (or have) actually been talked about (this is from memory as I haven't rechecked the close to 100 pages of the thread)
2) the magazine looks to be closer to popular instead of trade (although I say this without any certainty, just going by the vague online description).
In my opinion, there's a lot of room for a discussion of the source for anyone interested. Like I said, not me.

@Tirdent What was the ratio of J-20 and F-22 volumes that you found (revisiting a previous question)?
You can reverse engineer it pretty easily. He assumed the same density, so the ratio of volume is identical to the ratio of mass.
 

Tirdent

Junior Member
Registered Member
Yup, though the pure volume ratio is best obtained by taking the J-20 OEW figure in the table (i.e. before I account for equipment changes), adding 400kg (which I subtracted for the AL-31F being lighter than the F119, so really an equipment change too) and comparing that to 19.7t.
 

Klon

Junior Member
Registered Member
You can reverse engineer it pretty easily. He assumed the same density, so the ratio of volume is identical to the ratio of mass.
Yup, though the pure volume ratio is best obtained by taking the J-20 OEW figure in the table (i.e. before I account for equipment changes), adding 400kg (which I subtracted for the AL-31F being lighter than the F119, so really an equipment change too) and comparing that to 19.7t.
I knew there was additional weight reduction mentioned (e.g., gun).
The reason I ask is because the masses seem to differ by a lot less than one might expect considering the J-20 is supposed to have quite a bit longer fuselage with a larger cross section, while the weight difference is under 10%.
 

Tirdent

Junior Member
Registered Member
I don't know if you can read Chinese, but it's not taken out of context at all. It compares J-20's 15 ton class weight directly to F-22's 19 ton class weight.
I don't read Mandarin unfortunately. Nonetheless, apples and oranges comparisons by nominally credible sources which should have known better and that even this "amateur" was able to catch have actually happened before. You may not be able to fathom that, but it is what it is.

It specifically said that the weight was controlled to that limit. The entire article is about the J-20 as it is today. That it means anything else is an off chance to be considered, which I have.
"It" said - does that mean the interviewer (you indicated earlier that it was an interview of sorts) said so, or is the Chengdu official quoted verbatim? Is the official named and his function revealed?

But that weight is J-20 without engines?? That weight was some random placeholder? LOL Where do you come up with these? What's next? Maybe the weight didn't include the wings, right? Or maybe 15 tons is just the fuselage LOLOL
All of these are not unusual, I was not pulling them out of thin air (quit projecting your own modus operandi on others). As I indicated, F-22 OEW was widely quoted as ~14t (which is what the public domain developmental target was) until the actual figure was declassified a few years ago. Bare airframe weight without equipment & engines is often the basis for those handy structural materials percentage figures you see for various aircraft.

Again, just because you were not aware of it doesn't mean it doesn't exist or that it's nonsense.

Other than that, read the black and white: it says J-20's empty weight is 15-16 tons just like F-22's is 19-20.
Given the ignorance and attitude that you've displayed toward me in this discussion, forgive me for not taking your word for anything without actual evidence or corroboration from more trustworthy individuals...

Right, you demonstrated why you didn't think the upgrades in tech were applicable. I understand that; that's why I said everything is to the best of your ability, not the ability of Chengdu's professional design team.
Are you Chengdu's professional design team? They have not supplied proof that is in any way accessible to me, so while I would much prefer to hear their input, I'm regrettably stuck with arguing among amateurs - and you certainly haven't provided anything which would change my appraisal either.
 

latenlazy

Colonel
  • Thread Starter Thread Starter
  • #90
All of these are not unusual, I was not pulling them out of thin air (quit projecting your own modus operandi on others). As I indicated, F-22 OEW was widely quoted as ~14t (which is what the public domain developmental target was) until the actual figure was declassified a few years ago. Bare airframe weight without equipment & engines is often the basis for those handy structural materials percentage figures you see for various aircraft.
If I recall correctly, at least part of the weight gain came from changing requirements, primarily structural changes needed to expand ordinance carriage for attack roles.
 

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