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

[Tirdent]

That is to say, the F-22 was originally expected to weight in the 15 tons class, so the increased airframe weight is very strange.

Nothing strange about it at all, it's much the same trap which later caught out the VTech students. Being among the first to develop a 5th generation fighter, LM was lacking decent historical weight data for more accurate estimates.

We are also looking at the F-22 alone, instead of using the Su-57 as a reference point for the J-20. The Su-57's dimensional area is 276.21 m^2, while the F-22 is 256.56 m^2 and the J-20 is 270.4 m^2. Yet the Su-57 weighs around 18 tons.

While it would definitely be nice to have more than one reference, the Su-57 is a poor choice for two reasons. Firstly, with its separate engines it is very different in fuselage configuration to the J-20 and F-22, so a comparison with the relatively crude tools at our disposal is going to be far more prone to error. Secondly, we do NOT have good weight data on the Su-57 - 18t is just somebody's guess, and pending confirmation no more credible (though perhaps a trifle more realistic) than 15t for the J-20!

That the J-20 is denser than the F-22 prototype.

That a combat-capable fighter is denser than a demonstrator which is not fitted for anything beyond a couple of specific tech demos should go without saying really. Again, the difference is due to a lot more than just adding RAM:

YF-22 to F-22 weight delta? That number comprises *a lot* more than just RAM (radar, EW, MAWS, data link, almost certainly beefed up structure for increased airframe life and external hardpoints, F119 was heavier & more powerful than YF119...)!

Here, you're accusing the Sukhoi engineer of dishonesty. Note that he was talking about TVC work in the late 1980s, when the modified airframe with 2D TVC flew in 1990. Moreover, the engineer is discussing the choice of 3D TVC over 2D TVC on the Flankers. If you're talking about the bomber TVC system, the Sukhoi engineer is comparing a 3D TVC, which was never discussed for the bomber, with 2D TVC. It stands to reason he's discussing TVC for the AL-31, not for the bomber engine.

Not at all, I suspect you are misinterpreting his comments - what in that article makes you so certain that he is talking about more than one flat nozzle design? He is not a Sukhoi but a Lyulka engineer, BTW.

Also, for size, please do take a look at the F-22's nozzles themselves, which are not insubstantial.

If you genuinely can't see how that is a lot smaller than the T-60S nozzle I guess I have no argument...

Compare this photo of a GE F110 to your F119 picture - I think you will find that, relative to the rest of the respective engine, the F119 nozzle is not much wider & taller as well as only slightly longer (mostly due to the triangular rear edge) than the axisymmetrical F110 counterpart.



Now compare the vanilla AL-31F on the other side to the one with the flat demo nozzle in the belly photo of the Su-27 test bed:

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Except that the F-22's development project was heavily delayed and its production variants had hypoxia issues, often lethal, for its pilots. But that's a dig and not really relevant, while your comment is an accurate correction, but it is not relevant to the fact that the YF-22 was more agile than the YF-23, and impressed evaluators, suggesting greater structural reinforcement

Well, the F-22 did push the envelope - not as much as the F-23 would have, but it was the first of its kind to be developed to maturity. And who's to say its competitor would not have proved every bit as troublesome and then some? For instance, as TerraN-Empire noted, the hypoxia issue isn't even specific to the F-22, so could have hit the F-23 in much the same way.

Your point about lesser airframe life on the YF-22 is accepted, but the other reasons for high structural weight are not. The YF-22 conducted high AOA flight, first, second, the YF-22 had a working weapons bay that would have added on weight. Only lesser airframe life would account for lesser structural weight on the YF-22, but this can't justify the 30% weight increase between the fighters.

Did the YF-22 have external hard points? Did it have a radar? An EW system? The larger, final F119 engines? A gun? What's not to accept there?

Basically, we're making an assumption that the light F-117 RAM paint reflects the light RAM on the F-22, when the F-117 is significantly less stealthy than the F-22 by -10 to -20 dBsm. RAM composites on the F-22 do not merely have to be paint.

An assumption which is vastly more plausible than believing that RAM accounts for all of the 4t difference between the YF-22 and F-22 and ignoring all the other differences that make up that total.

 

[Air Force Brat]

Nothing strange about it at all, it's much the same trap which later caught out the VTech students. Being among the first to develop a 5th generation fighter, LM was lacking decent historical weight data for more accurate estimates.



While it would definitely be nice to have more than one reference, the Su-57 is a poor choice for two reasons. Firstly, with its separate engines it is very different in fuselage configuration to the J-20 and F-22, so a comparison with the relatively crude tools at our disposal is going to be far more prone to error. Secondly, we do NOT have good weight data on the Su-57 - 18t is just somebody's guess, and pending confirmation no more credible (though perhaps a trifle more realistic) than 15t for the J-20!



That a combat-capable fighter is denser than a demonstrator which is not fitted for anything beyond a couple of specific tech demos should go without saying really. Again, the difference is due to a lot more than just adding RAM:





Not at all, I suspect you are misinterpreting his comments - what in that article makes you so certain that he is talking about more than one flat nozzle design? He is not a Sukhoi but a Lyulka engineer, BTW.




If you genuinely can't see how that is a lot smaller than the T-60S nozzle I guess I have no argument...

Compare this photo of a GE F110 to your F119 picture - I think you will find that, relative to the rest of the respective engine, the F119 nozzle is not much wider & taller as well as only slightly longer (mostly due to the triangular rear edge) than the axisymmetrical F110 counterpart.

View attachment 44039

Now compare the vanilla AL-31F on the other side to the one with the flat demo nozzle in the belly photo of the Su-27 test bed:

Please, Log in or Register to view URLs content!

Well, the F-22 did push the envelope - not as much as the F-23 would have, but it was the first of its kind to be developed to maturity. And who's to say its competitor would not have proved every bit as troublesome and then some? For instance, as TerraN-Empire noted, the hypoxia issue isn't even specific to the F-22, so could have hit the F-23 in much the same way.



Did the YF-22 have external hard points? Did it have a radar? An EW system? The larger, final F119 engines? A gun? What's not to accept there?



An assumption which is vastly more plausible than believing that RAM accounts for all of the 4t difference between the YF-22 and F-22 and ignoring all the other differences that make up that total.

Amen to each and every point! in addition if somebody would post a cut-a-way drawing of the F-22 structures? (I saw a very good one recently, maybe on one of your links), you would understand that the J-20, as a more than likely 9+ G air superiority platform, is far more dense than you could imagine, being familiar with general aviation aircraft construction, even those intended for aerobatics, (6+ to 10+ Gs), have far less internal structure...

It will make you take a step back and reevaluate all your thinking,, the supporting structure of the F-22 and J-20 is far more numerous and dense than what you would imagine. The J-20 as an F-22 competitor will have a very similar internal superstructure, and there is far less room for equipment and fuel than might be imagined...as I have stated before, a 20 ton airframe at 9 G's, actually weigh's 180 ton's, its not make believe, it is the law of gravity and physics at work..

To make this real, all you need to do is hitch a ride, hey come ride with me,,,,, I'll show you what 4.2 Gs feels like even in our old 172, if you weigh 200 lbs, I can quadruple your weight to 800lbs with a simple "pull" on the stick? Conversely, I can push on the stick and float you right out of your seat and stick your butt on the top of the cabin, even if you weigh 400 lbs!

In the real world of fighter aircraft, 4 G's are nuthin, nuthin, go to 5 G, 6 G, most SDFer's would be greyed out to blacked out,,, G's will break an airplane any day, it takes a heck of lot of structure to carry those load's,,, that's what the 15 ton dreamers don't care to realize.. Carbon Fibre, even Titanium 3D printing isn't magic, even though you might realize some weight savings, on the other hand, a machined forging might actually save you weight, and yes I do know what I'm talking about!

 

[Equation]

Amen to each and every point! in addition if somebody would post a cut-a-way drawing of the F-22 structures? (I saw a very good one recently, maybe on one of your links), you would understand that the J-20, as a more than likely 9+ G air superiority platform, is far more dense than you could imagine, being familiar with general aviation aircraft construction, even those intended for aerobatics, (6+ to 10+ Gs), have far less internal structure...

It will make you take a step back and reevaluate all your thinking,, the supporting structure of the F-22 and J-20 is far more numerous and dense than what you would imagine. The J-20 as an F-22 competitor will have a very similar internal superstructure, and there is far less room for equipment and fuel than might be imagined...as I have stated before, a 20 ton airframe at 9 G's, actually weigh's 180 ton's, its not make believe, it is the law of gravity and physics at work..

To make this real, all you need to do is hitch a ride, hey come ride with me,,,,, I'll show you what 4.2 Gs feels like even in our old 172, if you weigh 200 lbs, I can quadruple your weight to 800lbs with a simple "pull" on the stick? Conversely, I can push on the stick and float you right out of your seat and stick your butt on the top of the cabin, even if you weigh 400 lbs!

In the real world of fighter aircraft, 4 G's are nuthin, nuthin, go to 5 G, 6 G, most SDFer's would be greyed out to blacked out,,, G's will break an airplane any day, it takes a heck of lot of structure to carry those load's,,, that's what the 15 ton dreamers don't care to realize.. Carbon Fibre, even Titanium 3D printing isn't magic, even though you might realize some weight savings, on the other hand, a machined forging might actually save you weight, and yes I do know what I'm talking about!

So...wait let me get this straight by your logic is that J-20 needs to be 20 tons in order to support a 20-ton (empty) air frame turning at 9Gs? You cannot assume that your point is true in order to prove that it's true; that's called circular logic. Here's an example: Spiderman exists because his life is detailed in the comics and the comics are true because they are written about someone who exists: Spiderman. That's the circular logic you're using.

By your logic, J-20 could be 15 tons because lightening it by 5 tons means that's 45 tons lighter during a 9G turn, thus requiring less supports. Nobody says aircraft have to be 20 tons to support 9G's; Eurofighter is 11 tons. Nobody even says that heavy fighters have to be 20 tons to support a 9G turn; Su-27 is 16 tons and pulls over 9G. And guess what? It's made with 1980's Russian manufacturing, is longer than J-20, and has a greater wingspan than J-20 meaning it endures great torque during the turn... all at 16 tons empty.

When you give numbers, you need to actually connect them mathematically. Why is 15 tons too light for 180 tons but 20 tons is sufficient? (By the way, this number doesn't make sense either because a loaded jet is closer to 27-32 tons depending on empty weight and you don't fight empty.)Where is the math? You can't eyeball numbers as proof (or even evidence). There needs to be calculations that arrive at a number between 15 tons and 20 tons for the weight of the supports of a fighter of the J-20's dimensions for you to say that 20 is enough but 15 is too low.

What does your tossing a 400 pound man around in an old prop plane have to do with J-20's weight?

And nobody has ever been convince by "... yes I do know what I'm talking about." You think you know. I'm just saying.

 

[Air Force Brat]

So...wait let me get this straight by your logic is that J-20 needs to be 20 tons in order to support a 20-ton (empty) air frame turning at 9Gs? You cannot assume that your point is true in order to prove that it's true; that's called circular logic. Here's an example: Spiderman exists because his life is detailed in the comics and the comics are true because they are written about someone who exists: Spiderman. That's the circular logic you're using.

By your logic, J-20 could be 15 tons because lightening it by 5 tons means that's 45 tons lighter during a 9G turn, thus requiring less supports. Nobody says aircraft have to be 20 tons to support 9G's; Eurofighter is 11 tons. Nobody even says that heavy fighters have to be 20 tons to support a 9G turn; Su-27 is 16 tons and pulls over 9G. And guess what? It's made with 1980's Russian manufacturing, is longer than J-20, and has a greater wingspan than J-20 meaning it endures great torque during the turn... all at 16 tons empty.

When you give numbers, you need to actually connect them mathematically. Why is 15 tons too light for 180 tons but 20 tons is sufficient? (By the way, this number doesn't make sense either because a loaded jet is closer to 27-32 tons depending on empty weight and you don't fight empty.)Where is the math? You can't eyeball numbers as proof (or even evidence). There needs to be calculations that arrive at a number between 15 tons and 20 tons for the weight of the supports of a fighter of the J-20's dimensions for you to say that 20 is enough but 15 is too low.

What does your tossing a 400 pound man around in an old prop plane have to do with J-20's weight?

And nobody has ever been convince by "... yes I do know what I'm talking about." You think you know. I'm just saying.

no Equation, its NOT "circular reasoning", its linear reasoning,,, and since you're NOT a PILOT, nor a MECHANIC, nor even an engineer,,,

The J-20 and the F-22 will carry a very similar payload, at a very similar G factor, the AirFrame must be able to sustain those 9 G loads, both airframes will accelerate to a very, very similar top speed, and perform a very similar mission..

no doubt in my mind that those two aircraft are less than a ton or two difference in weight, and the FC-31 will be very close to the Mig-29.. so when and if that weight ever becomes a known factor?? you can remember who told you the truth! and if it turns out the J-20 is 15 tons empty by an official report, I will give you and everyone else on this forum an official AFB, PUBLIC APOLOGY, so you decide who cares about the truth!

 

[Equation]

Just saying it's linear doesn't make it linear. It is factually and demonstrably circular because you assumed that your point was true in order to prove that it's true. You don't even know what qualifies for linear and circular reasoning??

Being a retired pilot or a mechanic doesn't qualify you to judge cutting edge designs made decades after your time. And neither of us is an engineer. Brat, nobody is intimidated by your resume so please don't bring it up again. It's not convincing and it makes you look desperately out of reasoning when you resort to that kind of stuff.

Very similar in mission and capability still leaves +/- 10% or more possible differences in all parameters and as technology advances, we can achieve the same with less weight/cost. We all know that. That's not any sort of evidence that 2 machines need to weigh the same.

It's interesting that you think that FC-31 is MiG-29 weight, which is 11 tons, or roughly a 17% reduction in weight over the even lightest F-35 despite the FC-31 having 2 engines instead of 1. No one even made any claims about that and you believe it for some reason?? And you abjectly dismiss the possibility that J-20 can achieve something similar even though it was published. We all know that the PLAAF is very happy with the J-20 and not happy enough with J-31 to even fund it.

You can give an apology or not; nobody's on this forum are interested to hear that. But your track record does not merit your current confidence. Last time you thought China could not have purchased Su-35, you gave an apology and last time you said that Dr. David Dao would be arrested, your knowledge of aviation law failed you again as he was awarded an undisclosed settlement ($140 million by the accounts on the Chinese internet), United apologized profusely and the officers who grabbed him were suspended. So I would remind you to leave room for uncertainty when you make your statements, especially when they were known to be wrong time and time again before. I'm just saying not trying to be a smart Alec or anything.

 

[Deino]

In order to keep the other J-20-thread free from such very much technical discussions and leave the original one for news, developments and so on, so please continue here and I will try to move as much of the older posts since some of them are interesting but not really strictly related to the J-20

Best,
Deino

 

[Air Force Brat]

Just saying it's linear doesn't make it linear. It is factually and demonstrably circular because you assumed that your point was true in order to prove that it's true. You don't even know what qualifies for linear and circular reasoning??

Being a retired pilot or a mechanic doesn't qualify you to judge cutting edge designs made decades after your time. And neither of us is an engineer. Brat, nobody is intimidated by your resume so please don't bring it up again. It's not convincing and it makes you look desperately out of reasoning when you resort to that kind of stuff.

Very similar in mission and capability still leaves +/- 10% or more possible differences in all parameters and as technology advances, we can achieve the same with less weight/cost. We all know that. That's not any sort of evidence that 2 machines need to weigh the same.

It's interesting that you think that FC-31 is MiG-29 weight, which is 11 tons, or roughly a 17% reduction in weight over the even lightest F-35 despite the FC-31 having 2 engines instead of 1. No one even made any claims about that and you believe it for some reason?? And you abjectly dismiss the possibility that J-20 can achieve something similar even though it was published. We all know that the PLAAF is very happy with the J-20 and not happy enough with J-31 to even fund it.

You can give an apology or not; nobody's on this forum are interested to hear that. But your track record does not merit your current confidence. Last time you thought China could not have purchased Su-35, you gave an apology and last time you said that Dr. David Dao would be arrested, your knowledge of aviation law failed you again as he was awarded an undisclosed settlement ($140 million by the accounts on the Chinese internet), United apologized profusely and the officers who grabbed him were suspended. So I would remind you to leave room for uncertainty when you make your statements, especially when they were known to be wrong time and time again before. I'm just saying not trying to be a smart Alec or anything.

Actually being a pilot and mechanic do qualify me to have an educated opinion, educated by experience,,, really Byron, this is rather disrespectful coming from you Brother....you disagree with my "learned opinion" and wish to interject your own opinion? on an unvetted internet source that stated something that you would very much like to be true???

I'm neutral, I really don't care if the J-20 only weighs 10 tonnes, and if that were indeed true?? I would be expressing my total and absolute awe! I have been flying quite a bit lately, I completed a flight check less than 2 weeks ago! so your observation that I am retired is simply untrue, nor have I ever, ever, stated I was retired.. I have keys for an aircraft in my flight bag, that I am free to take, anywhere, anytime, day or night..

In the past I worked for an AI,,, I do not have an A&P, but my work was done under the supervision, and under the signature of the AI who manages and owns, Klem's Aero Repair, I was the "night shift",, all of the aircraft I worked on were returned to service, certified as airworthy by my AI.

I am familiar with steel, aluminum, magnesium, fibre glass,carbon fibre, and even wood... all of those materials have properties which are unique, failure patterns that are quite distinct, and repair procedures that are unique to each material, so once again, believe whatever you heart desires??

I'm sure you'll want the last word, I do hope that you will be more considerate of our friendship, for what its worth, I've always done my best to express sincere and heartfelt respect toward you personally, that's all I ask in return please??

 

[Equation]

Actually being a pilot and mechanic do qualify me to have an educated opinion, educated by experience,,, really Byron, this is rather disrespectful coming from you Brother....you disagree with my "learned opinion" and wish to interject your own opinion? on an unvetted internet source that stated something that you would very much like to be true???

I'm neutral, I really don't care if the J-20 only weighs 10 tonnes, and if that were indeed true?? I would be expressing my total and absolute awe! I have been flying quite a bit lately, I completed a flight check less than 2 weeks ago! so your observation that I am retired is simply untrue, nor have I ever, ever, stated I was retired.. I have keys for an aircraft in my flight bag, that I am free to take, anywhere, anytime, day or night..

In the past I worked for an AI,,, I do not have an A&P, but my work was done under the supervision, and under the signature of the AI who manages and owns, Klem's Aero Repair, I was the "night shift",, all of the aircraft I worked on were returned to service, certified as airworthy by my AI.

I am familiar with steel, aluminum, magnesium, fibre glass,carbon fibre, and even wood... all of those materials have properties which are unique, failure patterns that are quite distinct, and repair procedures that are unique to each material, so once again, believe whatever you heart desires??

I'm sure you'll want the last word, I do hope that you will be more considerate of our friendship, for what its worth, I've always done my best to express sincere and heartfelt respect toward you personally, that's all I ask in return please??

Yeah, you can state and restate all of your "qualifications" but when you're proven wrong on multiple occasions, and demonstrate that you doesn't understand the difference between linear and circular logic, none if it means anything. You're not an active member of the USAF and you've never been a member of any engineering/design team of Boeing, Lockheed Martin, Northrup Grumman, etc... So although you're slightly more qualified than the average person on the street, you're still not anywhere in the ballpark of being qualified to judge a 5th gen design. Although a 2nd grader might be better in math than a first grader, they're both completely unqualified to solve a multi-variable calculus problem and it's very dangerous when the 2nd grader pretends to be qualified, using his second grade education to intimidate the first graders into thinking he has to be right. In any case, I'd ask you to stick purely to arguments and not fall back on your past to try to make people accept your points without proper reasoning.

I've noticed that you've ignore all the facts I've presented (in both my prior posts) and defaulted completely on what your career was for your current reply. I don't want to continue that senselessness with you.

It's fine to express your "learned opinion" and I'm happy that you've admitted it as such. It's your opinion. It's not proven fact, so you should respect other opinions, and refrain from calling them nonsense or dreams. It is for this reason that I must make it clear to you that your position is in the same category: an opinion, except the 15 ton claim at least has a semi-trustworthy source behind it while yours has nothing.

Our friendship is based on mutual respect of each others' opinions and the ability to converse civilly, pointing out the faults in each other's arguments/logic with facts. It is not based on reverence for your experience with 30 year old aircraft or blind acceptance of your unsupported claims.

 

[Jura The idiot]

noticed this thread as anonymous a moment ago LOL no idea how a J-20 weighs, am just hoping you two will take it easy

Actually ...

Yeah...

you're my inner circle ROFL

 

[Tirdent]

It's interesting that you think that FC-31 is MiG-29 weight, which is 11 tons, or roughly a 17% reduction in weight over the even lightest F-35 despite the FC-31 having 2 engines instead of 1.

I don't believe it will be appreciably lighter than a F-35, but FYI: all else equal, 2 scaled-down engines with the same total thrust will end up slightly lighter than one big engine (broadly speaking thrust scales with cross sectional area, i.e. with the second power of linear dimension - weight with volume, i.e. the third power). In the case of the F-35, there is also the fact that its engine has a relatively high bypass ratio, making for voluminous intake ducts.

BTW, a 15t J-20 would be a ~25% reduction over the F-22, let alone it's expected weight when extrapolating for size, so that goes a good bit further than even assuming 11t for the J-31.