Jura The idiot
General
at least didn't become "Mig29"
LOL
J-20 5th Gen Fighter Thread VI
- Thread starter siegecrossbow
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LOL
manqiangrexue
Brigadier
Well, this piece by Trident is the first analysis I've seen of why J-20 should weight 21t. Prior to that, it was just "my feeling." LOL
So the first thing I noticed is that he gave the engine thrust figures as 3.2 tons for F-22 and 2.5 tons for J-20. F119 are 156x2=312kN, which is roughly 31.3 tons (not accounting for rectangular nozzle reductions which I've heard to be from 3%-17%). Although the thrust for J-20's engines are not known, the best known AL-31X that was sold to China is AL-31FN3 with 137kN for J-10B. 2 of these is 274kN, which is 27.5 tons, not 25 tons. He's off by 10% on something that could be calculated as simply as that and that's ignoring the possibility that these are further upgraded AL-31X for J-20; for reference, the best AL-31 variant of the RuAF is FM3 with 145kN, but since there is no evidence that China got these, I used 137kN as the lowest figure possible, and he somehow went a full 10% lower. And for the Raptor, he rounded 31.3 to 32 instead of 31 or keeping the extra sig fig so based on that, I reserve my doubts for the rest of his numbers based on known inaccuracy and perceived bias towards the Raptor.
For some reason, he states the F-22 fuel capacity at 9.3 tons when it is 8.2 tonnes? Did he convert metric tons to American tons for this analysis??? Why? Is his analysis in tons or tonnes?
He took off 200kg for the DSI. Why? No explanation of why that number was used. Someone reported prior that the F-35 saved several hundred kg due to DSI.
He dismissed airframe composition as having any effect! It certainly is capable of having a big effect on weight; just because he's unable to calculate how much does not mean that it's nothing LOL J-20 heavily reduced titanium usage over F-22 (40% to 20% by weight), which indicates to me that big weight saving measures were put in place. Just because I can't begin to put a number on the overall effect does not mean that it's none. It could be huge just as bicycle frames can shed half its weight when using lighter material.
He gave 200kg off for the gun. I'd like to see him cite his source. We have to keep in mind that operationally, no gun means no ammo to carry as well but that is not considered in the empty frame calculation.
He does not see any weight reductions from the weapons bay. He could be correct as I also don't see any obvious weight reductions could come from but simpler indicates reduction of parts and thus lighter to me. Of course, you might be removing small light parts and replacing them with big heavy ones but does anyone have input on why some people say the bay mechanisms are lighter on J-20? I don't know about this.
He adds 100kg for EOTS on J-20. Where is that figure coming from?
He does not account for the know differences in engine weight between F-119 and AL-31X. Even the older AL-31F weighs 230kg less per engine than F-119. That's 460kg and that's not accounting for further weight reduction measures implemented in the modernization of the older 122.6kN AL-31F.
He does not account for the weight of the F-22's TVC. He mentions it but does not mathematically account for their weight. Someone else gave a figure of 800kg. I don't know if it's accurate but they look pretty big and bulky to me.
So the first thing I noticed is that he gave the engine thrust figures as 3.2 tons for F-22 and 2.5 tons for J-20. F119 are 156x2=312kN, which is roughly 31.3 tons (not accounting for rectangular nozzle reductions which I've heard to be from 3%-17%). Although the thrust for J-20's engines are not known, the best known AL-31X that was sold to China is AL-31FN3 with 137kN for J-10B. 2 of these is 274kN, which is 27.5 tons, not 25 tons. He's off by 10% on something that could be calculated as simply as that and that's ignoring the possibility that these are further upgraded AL-31X for J-20; for reference, the best AL-31 variant of the RuAF is FM3 with 145kN, but since there is no evidence that China got these, I used 137kN as the lowest figure possible, and he somehow went a full 10% lower. And for the Raptor, he rounded 31.3 to 32 instead of 31 or keeping the extra sig fig so based on that, I reserve my doubts for the rest of his numbers based on known inaccuracy and perceived bias towards the Raptor.
For some reason, he states the F-22 fuel capacity at 9.3 tons when it is 8.2 tonnes? Did he convert metric tons to American tons for this analysis??? Why? Is his analysis in tons or tonnes?
He took off 200kg for the DSI. Why? No explanation of why that number was used. Someone reported prior that the F-35 saved several hundred kg due to DSI.
He dismissed airframe composition as having any effect! It certainly is capable of having a big effect on weight; just because he's unable to calculate how much does not mean that it's nothing LOL J-20 heavily reduced titanium usage over F-22 (40% to 20% by weight), which indicates to me that big weight saving measures were put in place. Just because I can't begin to put a number on the overall effect does not mean that it's none. It could be huge just as bicycle frames can shed half its weight when using lighter material.
He gave 200kg off for the gun. I'd like to see him cite his source. We have to keep in mind that operationally, no gun means no ammo to carry as well but that is not considered in the empty frame calculation.
He does not see any weight reductions from the weapons bay. He could be correct as I also don't see any obvious weight reductions could come from but simpler indicates reduction of parts and thus lighter to me. Of course, you might be removing small light parts and replacing them with big heavy ones but does anyone have input on why some people say the bay mechanisms are lighter on J-20? I don't know about this.
He adds 100kg for EOTS on J-20. Where is that figure coming from?
He does not account for the know differences in engine weight between F-119 and AL-31X. Even the older AL-31F weighs 230kg less per engine than F-119. That's 460kg and that's not accounting for further weight reduction measures implemented in the modernization of the older 122.6kN AL-31F.
He does not account for the weight of the F-22's TVC. He mentions it but does not mathematically account for their weight. Someone else gave a figure of 800kg. I don't know if it's accurate but they look pretty big and bulky to me.
HEH! HEH! of well, just proves we're all human, even those of you who are smart guys,,, like I've told some of my buds, it better be accurate, or it will haunt you forever on the "interwebs"..
You should probably take this with a ton of salt considering the fact that Zhang Zhaozhong was responsible for this analysis. Although he formerly served as a rear admiral in the PLAN, there is little to no credence to many of his wild theories, which include:
1) Using kelp farms to tangle the propellers of foreign submarines in the South China Sea.
2) PM 2.5 can minimize the effectiveness of American laser weapons.
3) The J-20 (before it came out) was nothing more than a stealth version of the J-10.
Zhang Zhaozhong is kind of like the "anti-credibility" official as far as public PLA personalities go.
I.e.: anything he says should be disregarded and if anything the opposite should be assumed lol
Haha, AFB, although I have no opinion on future of PLAN's naval aircraft developments, I like this analogy alot
!Have a nice day guys!
Assuming that the J-20’s internal structure isn’t significantly lighter than the F-22’s I’d more or less agree with Trident’s analysis. I do have minor quibbles with how he approached his assessment of volume like, for example; how both the F-22 and J-20 have a wingtip twist, but what makes many of us think the J-20’s wings are indeed thinner isn’t the overall thickness of each wing in the front view but at least perceived difference in thickness at their leading edges; how even if the combined surface area of the ventral strakes and vertical stabilizers was comparable to the surface area of the F-22’s vertical tails the F-22’s vertical tails would still have to be thicker just by function of needing more mechanical support for the wider and taller structure; and some concerns about how he determined cross section (but Trident himself admits his estimates are rough). Even so though, I don’t think those differences alone would cause drastic estimate differences, perhaps at most in the range of maybe 1-3 tonnes of difference, which would put the J-20 in the ballpark with the F-22.
Where I withhold certainty is with the other factor of the weight question, which is density. Density can’t be eyeballed. If the J-20 were to be significantly lighter than the F-22 that’s the side of the equation where it’d have to be different. It’s not completely unfathombale either, to be honest. The X-35 was only 9 tonnes, the YF-22 was only 15 tonnes, and the YF-23, despite being a dimensionally larger plane than the YF-22, was only 13 tonnes. Of course these are clean sheet prototypes, so you can only stretch this point so far, but I think it carries a very strong point, which is that this weight disputed is not purely a matter of spatial dimensions. If the PLAAF and CAC really wanted to, they could come up with a 15 tonne J-20. It would have to involve some mix of remarkable ingenuity and trade offs but it’s not a completely unreasonable supposition. For what it’s worth I really think it makes sense for the PLAAF to drop some requirements if it can save weight in order to can prioritize air superiority if they’re waiting on better engines. It won’t be the first time China has done significant modifications to a design in its production midlife. I’m not saying this is reason to believe for sure the J-20 must be 15 tonnes, but you can reason your way somewhat plausibly to that outcome.
Edit: I’d like to add one addendum. Just because the J-20 has a smaller percent composition of titanium that doesn’t necessarily mean this is from weight savings. It could just mean that for whatever reason (cost, manufacturing capability, structural design, alternative or better fitted materials) the J-20 uses less titanium while being just as heavier or heavier than its peers.
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Jura The idiot
General
OK LOL
would be an asset in the pub which I visit
manqiangrexue
Brigadier
So to summarize what you said, it doesn't look technically impossible to make J-20 15-16 tonnes though whether that is the case can't be proven either way right now. It also highly depends on whether Chengdu chose to prioritize weight or having a ton of system (like the gun). Density of the aircraft is a major determinant of that answer (you can't get density at all by looking at volume). Yeah man, I'm with you. I've agreed with that all along. I'm just arguing against the "J-20-lighter-than-F-22-is-IMPOSSIBLE" theory.
Yeah, half the titanium content technically may or may not make the aircraft lighter but as I see it, titanium has the greatest strength to weight ratio of any metal and China is superb at 3D printed titanium (likely the best in the world). If they choose not to use titanium, that indicates to me that they decided to sub it with something lighter than even the most intricately 3D printed titanium for that particular area. In other words, the results of expanding the 20% titanium to the 40% titanium of the F-22 (or more) would easily be doable for China but they decided not to because that would make the airframe needlessly heavier. So by reducing to 20%, they most likely but not definitively made the airframe lighter and less dense than if they used the same composition of the F-22. That's just an indication for me; by no means it it proof.
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