J-20 5th Gen Fighter Thread VI

[Inst]

On the high-end, I'd estimate the J-20 to have around 17500 kg empty weight, including titanium weight reduction and larger sizes than the F-22. The fussing over MTOW is nonsense, however. Most aircraft will not fight in MTOW, nor will they even take off under MTOW conditions. MTOW usually implies that the aircraft is conducting a strike mission with all pylons filled with ordinance. The moment it sights an enemy fighter its escorts can't handle, it'll jettison its entire inventory to save the pilot and the plane. So MTOW is extremely unrealistic.

What you're actually looking for is loaded weight, which is the aircraft with full fuel + air-to-air missiles. The loaded weight is likely to be around 30000 kg with 17500 kg empty weight, or around 27500 kg with 15000 empty weight. Actual combat weight, or missiles + 60% fuel, comes out to around 22700 to 24700 depending on your preference for empty weight.

Also, in terms of comparisons, the J-20 is only about 5.5% larger in terms of cross-sectional area than the F-22. Scaling to volume as well, you'd get roughly 8% greater volume, and what's more, the J-20 lacks 2D TVC that adds roughly 800 kg. From that, you'd get roughly 20.5 tons based on mass alone.

That said, you'd get .98 T/W using the crappy WS-10 engines currently stationed.

I also don't see why we should doubt the WS-15 figures so much, when the current American state of the art is 190 kN with updates in the pipeline to 220 kN. Given that the WS-15 will reach maturity around the same time the updated F-35 engines are ready, it'd achieve 80% of the improved F-35's engine's capability, when the current WS-10B are around 70% of the current F135 engine's capability.

 

[siegecrossbow]

Skepticism is in order, but it wouldn’t be the first time we were given indication that significant effort was put into weight reduction for the J-20. As I mentioned earlier, I’m not sure we should dismiss a figure out of hand simply because it sounds incredulous. While we don’t know about the reliability of the original source to the 15 tonne claim, that source was also not typical of what we’d usually find in a transparently bad source.

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According to the documentary, usage of 3D laser printing reduced the structural weight percentage of the J-15 from 28% to 26.8%. Regardless of whether you believe the 15 tonne claim, you have to agree that weight saving from 3D laser printing alone couldn't have contributed to that much weight reduction.

 

[manqiangrexue]

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According to the documentary, usage of 3D laser printing reduced the structural weight percentage of the J-15 from 28% to 26.8%. Regardless of whether you believe the 15 tonne claim, you have to agree that weight saving from 3D laser printing alone couldn't have contributed to that much weight reduction.

Yeah, that's definitely not the only weight-saving measure. Something I just learned yesterday from you, though, is that titanium is only 20% in J-20 (vs 40% in F-22). So it greatly increased composite use. I'm no expert on composite weight savings, etc... but is there any way to take an educated guess at the impact of this? I know the Dreamliner says they saved 20% weight by composite use?

Of course there are other measures that shave weight off J-20 (lack of TVC for sure, no gun?, material upgrades, other things that its designers know that we don't) but I think that other than the TVC, it'd be hard for us to quantify those.

 

[siegecrossbow]

Yeah, that's definitely not the only weight-saving measure. Something I just learned yesterday from you, though, is that titanium is only 20% in J-20 (vs 40% in F-22). So it greatly increased composite use. I'm no expert on composite weight savings, etc... but is there any way to take an educated guess at the impact of this? I know the Dreamliner says they saved 20% weight by composite use?

Of course there are other measures that shave weight off J-20 (lack of TVC for sure, no gun?, material upgrades, other things that its designers know that we don't) but I think that other than the TVC, it'd be hard for us to quantify those.

You can't compare the 787 with the J-20 since the former is a passenger jet with much laxer structural requirements. Other weight saving measures on the J-20 include:

1) Smaller (proportionally speaking) net wing area and thinner wings.
2) Much smaller vertical stabilizers (even accounting for the ventral strakes).
3) DSI inlets (reportedly saved several hundred kilos on the F-35).
4) Fiber optic wiring instead of copper wiring.
5) Composite material (unsure how much is used).
6) Lack of gun + associated mechanism.
7) Use of simpler mechanism within the side bays compared with the F-22.

 

[manqiangrexue]

You can't compare the 787 with the J-20 since the former is a passenger jet with much laxer structural requirements. Other weight saving measures on the J-20 include:

1) Smaller (proportionally speaking) net wing area and thinner wings.
2) Much smaller vertical stabilizers (even accounting for the ventral strakes).
3) DSI inlets (reportedly saved several hundred kilos on the F-35).
4) Fiber optic wiring instead of copper wiring.
5) Composite material (unsure how much is used).
6) Lack of gun + associated mechanism.
7) Use of simpler mechanism within the side bays compared with the F-22.

I knew you couldn't directly translate weight savings from a passenger jet to a military jet but now that you mention it, if a passenger jet saved 20% weight off improvements to structure by 3D printing, composite use, etc... and the structuring on fighters is more dominant in the jet, then shouldn't those same techniques yield greater weight savings on fighters? 787 is 14% titanium, 50% composite. F-22 is 36% titanium, 24% composite (1). J-20 is 20% titanium, unknown composite... Do we have a lower limit based on something like J-10B or J-15/16?

(1)

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BTW, where did you get that J-20 is 20% titanium?

 

[latenlazy]

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According to the documentary, usage of 3D laser printing reduced the structural weight percentage of the J-15 from 28% to 26.8%. Regardless of whether you believe the 15 tonne claim, you have to agree that weight saving from 3D laser printing alone couldn't have contributed to that much weight reduction.

It depends on what the technology is applied to. Remember, the 40% in titanium weight reduction claim came in part from 3D printed bulkheads. It doesn’t seem like that’s what they’re doing for the J-15.

 

[manqiangrexue]

It depends on what the technology is applied to. Remember, the 40% in titanium weight reduction claim came in part from 3D printed bulkheads. It doesn’t seem like that’s what they’re doing for the J-15.

Yeah, but if we were to believe that J-20 is 20% titanium then 40% of 20% is only 8% and that titanium likely isn't all bulkheads. Obviously, 3D printing can't be the only contributor to weight saving as I'm fairly certain that using advanced composites to replace titanium altogether is an even greater weight reduction method than 3D printing.

 

[latenlazy]

Yeah, but if we were to believe that J-20 is 20% titanium then 40% of 20% is only 8% and that titanium likely isn't all bulkheads. Obviously, 3D printing can't be the only contributor to weight saving as I'm fairly certain that using advanced composites to replace titanium altogether is an even greater weight reduction method than 3D printing.

If the J-20 were 20% titanium, but that 20% is after it shaved off 40% of some original titanium weight, its titanium weight would have otherwise been 33% of the current total weight but only 29% of the total weight of the aircraft pre weight savings holding the weight of all other materials used equal. The tricky part is that purely looking at percentage masks the degree of weight savings, because when you add in extra weight of one component you are adding to both the numerator and the denominator. For a 10,000 kg object that was 20% titanium, but that percentage was reached after a 40% reduction of some original weight in titanium, that would make the original weight in titanium 3,333 kg. However, the overall weight of the plane would have also increased to 11,333 kg. Or take an F-22 as an example. If we take an empty weight of 19,700 kg and 40% titanium composition, that would make its weight in titanium 7880 kg. Shave off 40%, and you get a titanium weight of 4728 kg. The weight reduced F-22 would be 16,548. That would make its titanium composition 28.5% of the new weight but 24% of the old weight. What we’re really interested in, if we want to see the effects of weight savings, is the percent reduced from the old weight, not the new percent composition of the new weight.

Anyways, as I recall the J-20 may only be about 25% composite, which is no different from the F-22. I’m somewhat doubtful that if the J-20 is around 15,000 kg those weight savings were attained through greater use of composites, unless those composites were also drastically lighter than their counterpart on other planes (which I think is unlikely, since I’ve never seen anything to indicate China’s composite manufacturing techniques are as advanced as the US’s). If the J-20 is only 25% composites and 20% titanium, then it may be over 50% aluminum, so maybe that’s where it could achieve weight savings, but for that to be true you’d need to somehow compensate for aluminum’s poorer weight to strength ratio, or else the high composition of aluminum might instead imply a heavier structural weight. If there’s any takeaway I want to leave in this comment it’s that there’s a limit to what percentage composition can tell us. If for example the J-20 just used less material structurally then it could come out with a lighter weight with the exact same composition of materials. Alternatively it could have the same composition of materials and use significantly more materials than its counterparts, which would then make it heavier. Composition only tells us relative amounts, but weight is an absolute figure.

 

[manqiangrexue]

If the J-20 were 20% titanium, but that 20% is after it shaved off 40% of some original titanium weight, its titanium weight would have otherwise been 33% of the current total weight but only 29% of the total weight of the aircraft pre weight savings holding the weight of all other materials used equal. The tricky part is that purely looking at percentage masks the degree of weight savings, because when you add in extra weight of one component you are adding to both the numerator and the denominator. For a 10,000 kg object that was 20% titanium, but that percentage was reached after a 40% reduction of some original weight in titanium, that would make the original weight in titanium 3,333 kg. However, the overall weight of the plane would have also increased to 11,333 kg. Or take an F-22 as an example. If we take an empty weight of 19,700 kg and 40% titanium composition, that would make its weight in titanium 7880 kg. Shave off 40%, and you get a titanium weight of 4728 kg. The weight reduced F-22 would be 16,548. That would make its titanium composition 28.5% of the new weight but 24% of the old weight. What we’re really interested in, if we want to see the effects of weight savings, is the percent reduced from the old weight, not the new percent composition of the new weight.

Anyways, as I recall the J-20 may only be about 25% composite, which is no different from the F-22. I’m somewhat doubtful that if the J-20 is around 15,000 kg those weight savings were attained through greater use of composites, unless those composites were also drastically lighter than their counterpart on other planes (which I think is unlikely, since I’ve never seen anything to indicate China’s composite manufacturing techniques are as advanced as the US’s). If the J-20 is only 25% composites and 20% titanium, then it may be over 50% aluminum, so maybe that’s where it could achieve weight savings, but for that to be true you’d need to somehow compensate for aluminum’s poorer weight to strength ratio, or else the high composition of aluminum might instead imply a heavier structural weight. If there’s any takeaway I want to leave in this comment it’s that there’s a limit to what percentage composition can tell us. If for example the J-20 just used less material structurally then it could come out with a lighter weight with the exact same composition of materials. Alternatively it could have the same composition of materials and use significantly more materials than its counterparts, which would then make it heavier.

Quite complex indeed LOL. Btw, what are the sources for J-20 being 20% titanium and 25% composite? Are they relatively reliable or rumors left unchallenged just because they sound standard?

 

[latenlazy]

Quite complex indeed LOL. Btw, what are the sources for J-20 being 20% titanium and 25% composite? Are they relatively reliable or rumors left unchallenged just because they sound standard?

The article that made the 15 tonne claim had some composition figures, and I saw another one within the last few months that I think said 25% titanium, but I’d have to do some digging to be sure.