EVERETT -- Boeing announced today it would make a decision on whether or not to break the wing of the static test aircraft in early 2009.
787 VP of Engineering and Technology Randy Harley said the decision will come early next year because, "we want to make sure you can learn as much as possible," before you test to failure.
Harley added that, "We've made provisions to test to failure if we decide to do so."
Boeing indicated that it expects the wing to deflect about 26 feet when 150% of maximum load is applied.
Blogged live from the 787 Final Assembly Line
Those are some pretty flexy wings.
For reference, the A380 wing broke at 147% and 7.4 m deflection (a bit over 24 feet). The 787 wing is 75% as long, but flexes even more (26 feet) under 150% limit load.
The question is if the applied test loads on a structure with such deflection are representative of the reality.
Is this not required *before* first flight?
Those in the know expect serious problem in the static test, and the FAA should dis-allow the test unless Boeing uses a production wingbox, not one specially modified that doesn't reflect the production design.
One would think that this test would be required, and it ought to use what will become production. So, the wait means that they do expect some feedback from flight testing.
What a difference in attitude? Were they really open and honest in your opinion, Jon? Were questions allowed or controlled?
> Those in the know expect serious problem
> in the static test, and the FAA should
> dis-allow the test unless Boeing uses a
> production wingbox, not one specially modified
> that doesn't reflect the production design.
Presumably "those in the know" have documented their concerns via registered letter to the local FAA inspections director, and have also submitted similar documents for the public record to the FAA certification board.
Signed with an X of course.
sPh
"Structures Guy," have you heard of equivalent stiffness? Are you saying that I can't replace an aluminum stringer that is loaded in tension with a titanium stringer with a cross-section that is 33% smaller?
If Rev. X (where X is the latest set) of loads determined that there was a buckling issue, then the designers and stress guys go and figure out what needs to be added to keep the section stable. It's not a new thing. Constantly changing loads are the stress engineer's biggest problem, they never seem to go down, but there are well-established techniques that all aerospace companies use to correct deficiencies and keep compliant.
"Structures Guy," have you heard of equivalent stiffness? Are you saying that I can't replace an aluminum stringer that is loaded in tension with a titanium stringer with a cross-section that is 33% smaller?
If Rev. X (where X is the latest set) of loads determined that there was a buckling issue, then the designers and stress guys go and figure out what needs to be added to keep the section stable. It's not a new thing. Constantly changing loads are the stress engineer's biggest problem, they never seem to go down, but there are well-established techniques that all aerospace companies use to correct deficiencies and keep compliant.
It's pretty easy to be confident when you don't have a clue about the dozens of serious problems currently undiscovered. Power-on will not go well, though Boeing won't spin it that way of course.
As for the wingbox comment - very interesting. I agree that the static airframe must use the production design and currently none of the airframes have the new wingbox design.
[quote ="Anynonmoose"] The question is if the applied test loads on a structure with such deflection are representative of the reality.[/quote]
Yes. They are.
[quote="Lambda"]Those in the know expect serious problem in the static test, and the FAA should dis-allow the test unless Boeing uses a production wingbox, not one specially modified that doesn't reflect the production design.[/quote]
The static test airplane uses a production wing box. You're confusing this test with the separate wing box test, which is currently being conducted at Boeing's Development Center at BFI. That partial wing box is a prototype which does not reflect the final production configuration. However, the test has provided valuable data that confirms Boeing's ability to model and analytically predict the behavior of a composite wing box under load.
Luke:
"Structures Guy," have you heard of equivalent stiffness? Are you saying that I can't replace an aluminum stringer that is loaded in tension with a titanium stringer with a cross-section that is 33% smaller?
Titanium stringers? Other than some possible exotic military applications, that's a new one on me. I'm trying to draw a mental picture of a long titanium stringer fastened to an aluminum skin. Here's what I see. First of all, titanium stringers would be prohibitively expensive. Then there's the issue of the different thermal expansion coefficients between the two metals, leading to induced stresses. How will aluminum behave galvanically in contact with titanium? Also, as you alluded, titanium is 50% stiffer (higher modulus of elasticity) than aluminum, but how do its yield and ultimate strengths compare? (Hint: depends on the heat treatment and other factors for the two metal alloys.) Oh, so many questions....
It was an example. Hypothetical even. Could have used Tootsie Rolls vs. White Pine, but it's the same net effect. Engineers the world over use equivalent stiffness every day, why is it so awful to use it on the 787?
The static test is merely to verify the structural modeling of it. If it behaves per the design model, you pass.
One only has to go to 150% and no further. Going past that to failure may gain more knowledge.
If it goes very far past 150%, that means it is overbuilt and you are carrying extra weight.
That wingbox is a production wing box from what I understand. It will deliver that way. It is just a different variation that incorporates a fix. Throughout the life of planes structures change. No big deal. One does not start from scratch for every change.
Have you ever wondered why every airplane derivative doesn't get its very own static test? Because they aren't required to. The 777 static test was on the basic -200 model. Results from that test were extrapolated to obtain certification for the later models.
The 787 static test configuration reflects the first six production airplanes. Test results will be tweaked to account for the structural differences on lines 7+. And eventually, for the -9, the -3, etc.