I agree, however, I think for the sake of discussion it makes sense to err on the side of conservatism for this particular statistic
J-20 5th Gen Fighter Thread VI
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I agree, however, I think for the sake of discussion it makes sense to err on the side of conservatism for this particular statistic
manqiangrexue
Brigadier
Alright gents, Blitzo, Seige, Latenlazy... Brat as well, I guess... This just in:
https://www.sinodefenceforum.com/shenyang-fc-31-j-31-fighter-demonstrator.t5693/page-500#post-483264
This is a CCTV report interviewing Dr. Wu Bing of Shenyang who says that Shenyang was able to achieve a 26.8% reduction in aircraft weight through 3D printing and other advanced manufacturing techniques.
Right under it, I replied and noted the implications for J-20. If J-20 is 21 tonnes by size estimation with traditional manufacturing techniques and materials, a 26.8% reduction leaves it at 15.37 tonnes. This is assuming that Chengdu and Shenyang have comparable mastery over these techniques and while that's not a solid promise, they shouldn't be too far and it would be foolish for the CCP to allow keeping industry secrets at the expense of the effectiveness of its premier fighter...
https://www.sinodefenceforum.com/shenyang-fc-31-j-31-fighter-demonstrator.t5693/page-500#post-483264
This is a CCTV report interviewing Dr. Wu Bing of Shenyang who says that Shenyang was able to achieve a 26.8% reduction in aircraft weight through 3D printing and other advanced manufacturing techniques.
Right under it, I replied and noted the implications for J-20. If J-20 is 21 tonnes by size estimation with traditional manufacturing techniques and materials, a 26.8% reduction leaves it at 15.37 tonnes. This is assuming that Chengdu and Shenyang have comparable mastery over these techniques and while that's not a solid promise, they shouldn't be too far and it would be foolish for the CCP to allow keeping industry secrets at the expense of the effectiveness of its premier fighter...
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15T is totally possible but it's okay to remain skeptical of this despite some evidence supporting it. The issue is some people are all too certain about >20T. Brat is rarely personal or rude thought so that's something to keep in mind. Unlike a few others, even if certain people may be wrong and have misplaced confidence, as long as they approach the discussion with respect to others as well, they deserve tactful replies. Not saying you are not respectful or tactful most of the time though manqiangrexue.
While J20 structural weight savings (per similar undefined unit) are plausibly or even probably better than on F-22, fact remains J20 is a larger plane (I'm not talking about overall length).
Three more factors influence the structure and thus weight. One is the role of the plane, and thus relative forces that plane will have to withstand. Since role is similar, this factor is also likely similar.
Second is required lifespan. We know F22 was built to last until 2050s or so. If J20 is made to fly at similar hours per year but is designed to last 30 years instead of 40, for example, then its structure may be a bit less beefy. But by how much - who's to know.
Third factor is armaments required to be carried. F22 was not designed to haul around a lot of weight. it was not meant to be used as a strike platform really. J20 seems to be designed with decent air to ground secondary capability from the start. It also carries 4 underwing large tanks, while F22, even though initially planned for 4 tank capability, never went beyond 2 due to wing loading.
Last two factors could be MAYBE roughly guesstimated by looking at F15d and F15e difference. Its weight was increased by some 12%.
Also important to note - structural weight is one part of the empty weight of the plane.
Propulsion is second heaviest. Engines weigh up to 2 tons each, and there's usually 50-60% added weight in ancillary propulsion systems and fuel systems.
Skin is generally not part of the structure of the plane. Radar absorbing materials, be they cured into the skin or placed on top of it, add a lot, as they're quite voluminous and heavy if they're to cover a wide bandwidth. I am just guessing, but it could literally be hundreds of kg or even over a ton for a plane like J20.
Landing gear systems weigh several percent.
Electronics weighs hundreds of kilos, or probably a few percent.
Cockpit equipment weighs further several percent, and so on.
I'd say there are high chances that 7-9 tons of weight on F22 is not structural. Likewise on J20.
And structural weight savings on J20 may be largely mitigated by a larger airframe (again, not talking about length of the plane) while potential shorter lifespan may be mitigated by greater payload requirements.
In the end, I personally find it very unlikely J20's empty weight will be below that of F22. Probably it will be in the very low 20 ton range. But that's just a personal opinion and I can't expand on it nor can i really discuss it as it boils down to gut feeling, with all the arguments i made above just being general guidelines.
Three more factors influence the structure and thus weight. One is the role of the plane, and thus relative forces that plane will have to withstand. Since role is similar, this factor is also likely similar.
Second is required lifespan. We know F22 was built to last until 2050s or so. If J20 is made to fly at similar hours per year but is designed to last 30 years instead of 40, for example, then its structure may be a bit less beefy. But by how much - who's to know.
Third factor is armaments required to be carried. F22 was not designed to haul around a lot of weight. it was not meant to be used as a strike platform really. J20 seems to be designed with decent air to ground secondary capability from the start. It also carries 4 underwing large tanks, while F22, even though initially planned for 4 tank capability, never went beyond 2 due to wing loading.
Last two factors could be MAYBE roughly guesstimated by looking at F15d and F15e difference. Its weight was increased by some 12%.
Also important to note - structural weight is one part of the empty weight of the plane.
Propulsion is second heaviest. Engines weigh up to 2 tons each, and there's usually 50-60% added weight in ancillary propulsion systems and fuel systems.
Skin is generally not part of the structure of the plane. Radar absorbing materials, be they cured into the skin or placed on top of it, add a lot, as they're quite voluminous and heavy if they're to cover a wide bandwidth. I am just guessing, but it could literally be hundreds of kg or even over a ton for a plane like J20.
Landing gear systems weigh several percent.
Electronics weighs hundreds of kilos, or probably a few percent.
Cockpit equipment weighs further several percent, and so on.
I'd say there are high chances that 7-9 tons of weight on F22 is not structural. Likewise on J20.
And structural weight savings on J20 may be largely mitigated by a larger airframe (again, not talking about length of the plane) while potential shorter lifespan may be mitigated by greater payload requirements.
In the end, I personally find it very unlikely J20's empty weight will be below that of F22. Probably it will be in the very low 20 ton range. But that's just a personal opinion and I can't expand on it nor can i really discuss it as it boils down to gut feeling, with all the arguments i made above just being general guidelines.
There have been reports over the last few years that 3D printing and advanced manufacturing have allowed new aircraft like FC-31 and J-20 to achieve a reduction in weight.
However, I've always considered such claims to be doubtful at best. While I definitely will not rule out the possibility of J-20 having an empty weight that is similar is in the 15 ton class, I am very hesitant in using that empty weight for discussions about what J-20's potential kinematic performance may be like.
Simply put, it seems almost too convenient a solution for J-20 using less powerful engines.
All very important considerations, but the point of inventing new manufacturing techniques that reduce structural weight is to get the same mechanical tolerances with less mass, so it’s not inconsistent to be able to get lighter structural weight *with* greater carriage capacity rather than have greater carriage capacity neutralize lighter structural weight. *That* said, I’m not convinced at all that the J-20 was designed with significantly greater A2G capabilities than the F-22 in mind. I don’t see anything definitive in the design that would suggest it. As we’ve come to note consistently the J-20’s bays are not signicantly larger than the F-22’s or particularly deep and an EOTS placed below the nose is not solely or even always primarily useful for A2G functions.
Let’s take, for the sake of a mental exercise, the 7000 kg figure for non structural weight you submitted. For a 19,000 kg plane, that would make its structural weight 12,000 kg. A 25% reduction of that would be 9000 kg, which would make the total weight for this reduced structural weight design 16,000 kg. *If* the J-20 would have shared the same structural weight as the F-22 (I’m not saying it does) in absence of the claimed benefits from 3D printing, you could get very close to the original 15 tonne claim assuming the same savings in structural weight claimed by SAC carried over.
Specifically on the point about fuel tanks, I’m not sure how that suggests anything about intended structural tolerances. The J-20 carrying 4 fuel tanks could just as easily be a decision to compromise wingloading for range because it fits with longer range mission profiles where engagement is expected to be further out from bases. Likewise the F-22 only carrying two fuel tanks could just as easily reflect the lack of need rather than the lack of structural capability.
I’m going to leave the point about volume alone. I think I’ve already made my views about volume comparisons abundantly clear in other posts, and will spare everyone of the repetition.
Maybe it looks “too convenient” because it reflects a deliberate and calculated intention? It’s not like the PLAAF arrived at the J-20’s design in a blind vacuum. They know exactly what their situational context is and how their needs fit into it, and it would be shocking if they didn’t make design decisions specifically to address that situational context. This is not to suggest, if the 15 tonne figure is real, that the J-20 could get away with such significant weight savings completely without penalty, but does it really seem so unreasonable that the PLAAF may choose to eat some costs along other dimensions in order to optimize for and acquire capabilities that can more timely address their most pressing needs for the design? If they’re making other sacrifices to get around thrust deficiencies, we could easily see the J-20 put on weight to reverse those sacrifices when it acquires a more powerful engine, rather than live with limited capabilities in one of its primary roles while waiting for better engines. (If you were the PLAAF would you really choose to preserve either longevity of the airframe or some strike capabilities for the J-20 if sacrificing that meant you could mitigate some of the impact on air superiority from weaker engines?)
I think a good sanity check is to simply ask, holding the same structural strength requirements the same, if the F-22’s entire structural design and manufacturing process was revised from the ground up with today’s manufacturing technology, would it be conceivable for it to achieve the same weight savings? I don’t think it would be outlandish to say yes. If Lockmart made these sorts of claims would we be nearly as hesitant to buy it? This is what I mean when I say perhaps we shouldn’t dismiss the claim out of hand simply because it sounds incredulous. It might be more a reflection of latent availability or anchoring biases than any well grounded reasoning.
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by78
General
About 3D printing and weight reduction, could someone take a look at this video, starting around 12:53 mark and ending 13:27?
I'm interested to know if the cited figure of 26.8% is the ratio of internal structural weight to empty weight; or is it the ratio of empty weight to max takeoff weight; or is it internal structural weight to max takeoff weight?
I'm interested to know if the cited figure of 26.8% is the ratio of internal structural weight to empty weight; or is it the ratio of empty weight to max takeoff weight; or is it internal structural weight to max takeoff weight?
Hah. If I’m hearing this segment right I think we have a false alarm on our hands. As I understand it, the segment is saying that typically the structural weight of the aircraft is usually about 30% of the aircrafts takeoff weight (they don’t say max, so I suspect this is standard), with exceptional cases able to reduce this down to 28%. With 3D printing SAC has been able to reduce the structural weight to take off weight ratio down to 26%. The interviewer even asks if this reduction might be trivial. I think it’s also implied, given how the narration and interview is spliced together, that they’re talking about the J-15, not the J-31.
broadsword
Brigadier
So the 15 tonne figure is beyond reach!
If they’re talking specifically about the J-15, then perhaps not. There’s only so much you can do with a baked in legacy design after all. Plus, the margin for weight reduction will be much smaller for a more mechanically demanding carrier fighter.
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