Looks like I've overestimated my capabilities... I actually don't have the power to do that. Thought that the new extended moderation feature would let me do it.
I think the typo names are endearing.
Because, as I pointed out further down in that post, 3D printing =/= weight saving - at least not necessarily:
"Same material, geometry which is achievable with traditional processes, likely somewhat inferior material properties which might require greater thickness in places than the conventional analogue to bear the same load."
I don't speak Mandarin, so I can't comment on the context of the Chinese claims (were the statements about weight savings a general comment or specifically about the bulkhead? I have no way of knowing), but the rest of the evidence doesn't add up IMHO. When they first pitched the Silent Eagle, Boeing liked to claim its head-on RCS was comparable to the F-35's... this may well in fact have been true for an arc so narrow as to be tactically irrelevant, but later they actually backtracked meekly on the statement. You have to apply common sense and check with some engineering judgement - not just with claims from Chinese manufacturers.
3D printing doesn't necessarily equal to weight savings, but the manufacture claimed both. Why believe the manufacture on one but not the other?
"As much as 40 percent of the weight can be reduced if the forged titanium parts on an American F-22 were made using the Chinese
, according to a a report on Chinese
Guancha Zhe."
"F-22的钛合金锻件如果使用中国的3D打印技术制造，在强度相当的情况下，重量最多可以减少40%。"
The Chinese says that if the F-22's titanium parts were made with China's 3D printing manufacturing process, in conditions of equivalent strength, they can reduce their weight by up to 40%. Pretty much in line with the ZDNet description. It doesn't specifically mention bulkheads, but most of the titanium used in the F-22 are for bulkheads and other large main structures, and earlier parts of the Chinese article specifically draws comparison between the F-22's forged and machined bulkheads and printing bulkheads with additive manufacturing, so I don't think it's a huge leap to consider that they're also referring to bulkheads.
As I've said consistently, I retain skepticism for the claim. However, we have no way of refuting it, and it is a reasonably well sourced one. I'd also add that "common" sense isn't always so "common". What you may regard as "common" is a reflection of what you find believable, which may or may not pertain to what is likely or possible. I agree about checking with "engineering judgement", but I think it might be a bit presumptuous to suggest that laymen like you or I, unless one of us is a manufacturing process or materials engineers, are genuinely qualified to say we have good "engineering judgment". Indeed, the manufacture is probably better positioned to making "engineering judgments" than we are.
I wouldn't compare Boeing's Silent Eagle marketing with AVIC Laser's claims. For one, the latter's claim is quite a bit more specific. Second, they may have very different motives at play. Boeing is trying to get buyers for an old airplane design, while AVIC Laser is either trying to improve its PR or burnish its credibility with manufacturing customers. Manufacturing customers are going to be quite a bit more stringent and discriminating about their judgments over product promise than buyers of a fighter jet might. Qualitative promises for jet fighter capabilities are quite a bit more ambiguous, while strength and weight claims for parts manufacturing are quite a bit more testable. Furthermore, the latter, to at least my knowledge, hasn't seemed to backtrack on the claim. This doesn't mean AVIC Laser's claims are unquestionable and indisputable, but without further elaboration and argumentation the credibility of one company's claims have no direct bearing on the credibility of another's.
The wing attachment bulkheads have to take the root bending moment of the wings (from a lift force totaling up to 9 times the aircraft's weight...) and the touch down loads from the landing gear (located in the vicinity due to cg considerations). In the aft fuselage, they carry the engines, take the associated thrust loads and those from the empennage. Count on it - bulkheads are among the most highly loaded parts in the entire airframe which is precisely why the manufacturers go through all that months-long manufacturing effort to make them out of single piece forgings in the first place
"Most highly loaded part" in a plane doesn't necessarily mean strongest part possible with forging.
This is an interesting excerpt I found while trying to dig up where I read that titanium can have cracking problems in the milling process. The F-22 *does* compromise on some strength properties for others, apparently.
It's the same with the first - they're both shown in the state after the final forging session, before machining (I think this also answers the question of whether they are welded or single piece...). After the latter, they will look just about the same as the 3D printed sample, which was my point. I am struggling to find good pictures of a finished F-22 bulkhead too but here's a "titanium fighter bulkhead" (shape strongly argues F-15, so very much legacy technology - this one *would* have to be welded to a corresponding top half):
Here's another example showing both forging and final part, from the F-35 (Al-Li material in this case, but the principle is the same):
If they look the same to you then ¯\_(ツ)_/¯. I did question much earlier in our discussion whether either of us have the qualifications to make confident visual judgments, so there was always going to be a limit to that point.
Interestingly enough, in the guancha article I linked, there *is* a picture of a finished F-22 bulkhead and, for what it's worth, I do think in this picture the F-22's looks a lot thicker than the J-31s.
Now that we've arrived at comparing parts pictures, I think it's worth saying that ultimately there are probably limits to how far either of us can go with looking at individual pieces while neglecting the overall structural design. You could argue pretty easily that if the F-22 used thicker titanium bulkheads but had fewer of them then the weight comparisons can be a total wash. We're probably fussing over details that don't
Yes, that's the kind of thing I meant. This type of structure would certainly provide a weight reduction (although that particular sample looks like plastic?). Thing is, to get a massive (as in something like 6t) reduction from 3D printing I'm pretty sure you'd have to take advantage of that technology at every opportunity you get, including bulkheads (leaving aside these, the heaviest parts in the airframe, means throwing away the biggest potential savings). I'm not sure all the bulkheads in an F-22 taken together even add up to all that much more than 6t!
Unfinished 3D printed parts can have a dull "plastic" look. I think I've read before that the F-22's titanium bulkheads are about 25% of its structural weight (don't take my word for this), which probably makes them about 4-5 tonnes, but if it's 40% titanium, then that means there are about 3 tonnes of titanium that aren't bulkheads. If that's actually the case, and if we presume that 3D printed bulkheads can't save that much weight, I think that probably makes the titanium weight savings claim stronger, not weaker. Why wouldn't China try to take advantage of that technology, if they had it, at every turn? Wouldn't printing bulkheads be a pretty strong indication that they already are?
Is the Chinese bulkhead like that inside? I guess this is just a case of extraordinary claims requiring extraordinary evidence to me - China having that kind of thing *flight-ready* by early 2013 qualifies as an extraordinary claim IMHO.
I doubt it, but it doesn't need to in order for them to use the manufacturing process to save weight?
As I said earlier, the claim is what it is. You can take it or leave it.[/QUOTE]
