Boeing's New 787 Wings — Amazingly Flexible 564
An anonymous reader writes "Boeing is making the wings of its new 787 out of carbon fiber instead of metal. That means the wings are so strong and flexible that they could bend upward and touch above the fuselage — or come close. The company is expected to deliver the first 787 to All Nippon Airlines in May 2008. 'Boeing has completed static testing of a three-quarter wingbox, but engineers are still considering whether to limit testing of the full wing to a 150% load limit held for 3 sec. or to continue bending it to see when it breaks. 'There's a raging debate within the engineering team to see if we should break it or not,' says [787 General Manager Mike] Bair.'" They have come a long way in wing flexibility.
Why (not)? (Score:5, Interesting)
Re:I hope they test it! (Score:3, Interesting)
Re:I hope they test it! (Score:2, Interesting)
Design accommodations? (Score:1, Interesting)
Regardless, this should be a cheaper aircraft to operate. But are we going to be paying lesser for flights? I don't think so... But can they atleast put in smoking sections at airports or develop technology so that I do not have to remove my shoes everytime I want to smoke at a stopover?
Cheers!
Re:I hope they test it! (Score:4, Interesting)
You don't need to. You test to 150% of the rated load factor.
I think for for airliners it is +3 -2 Gs. It has been a few years since I needed to know it.
So you would test the wing to 4.5 Gs.
If it passes it is good to go.
Testing to destruction is good data to have but not required. If they get to to a 9 g load and the wing doesn't break I really think they could stop. Any airliner pulling a sustained 3 Gs will end up on the nightly news.
Old News: Flexible wings on the Boeing B-47 (Score:5, Interesting)
Re:missed the best part... (Score:2, Interesting)
747 Wing Flex (Score:4, Interesting)
Well... (Score:5, Interesting)
Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure. When a loading condition is prescribed in terms of ultimate loads, a factor of safety need not be applied unless otherwise specified
The three second requirement comes out of paragraph 305(b):
(b) The structure must be able to support ultimate loads without failure for at least 3 seconds. However, when proof of strength is shown by dynamic tests simulating actual load conditions, the 3-second limit does not apply. Static tests conducted to ultimate load must include the ultimate deflections and ultimate deformation induced by the loading. When analytical methods are used to show compliance with the ultimate load strength requirements, it must be shown that--
(1) The effects of deformation are not significant;
(2) The deformations involved are fully accounted for in the analysis; or
(3) The methods and assumptions used are sufficient to cover the effects of these deformations.
If our intrepid engineers manage to test to 200% for 3 second, then somebody is going to come along and say, "let's see if we can make the wings lighter"
Good thing or bad thing?....depends upon your point of view I guess.
As it turns out, validating airframe structures with respect to FAA airworthiness requirements is kinda what I do for a living.
Re:I hope they test it! (Score:1, Interesting)
Re:I hope they test it! (Score:3, Interesting)
Agreed, the Boeing engineers for this project may have no need to know what happens, but you never know...might that data prove useful for other applications of the material?
I am no engineer (software engineer doesn't count, I know), but I'd think you'd want to test things to failure, of course where practical (as in not with a new bridge or building). If for no other reason than you have to learn all kinds of interesting things from breaking things, no?
Maybe that notion falls apart (pun intended!) in the real, non-software, world. But if a programmer says "that'll never happen, no need to test that!" I guarantee you someone will break it once it goes to production. The only way to test software is to shake and break.
Re:While its great they are so flexible (Score:2, Interesting)
Re:While its great they are so flexible (Score:3, Interesting)
I mean who wouldnt want to see the 787 doing aerobatics at the next air show. I would definitely pay a ticket to see this. Maybe they could even get old Tex Johnston to fly it as well as he has some experience here...
Re:I hope they test it! (Score:5, Interesting)
Used to validate models (Score:3, Interesting)
First off the requirement is a 1.5 saftey factor, ie 1.5 times greater load on the wings then they would encounter during operations. In the past, wings were always broken on new planes. Not only is this fun (engineers do like breaking things, its true), but it provides very useful data to validate your computer models and test methodology. Not often does an engineer get to shatter such an expensive and large article! Predicting before hand when a wing will snap can be very useful on future airplane designs to optimize the structural layout. Remember, any load past the 1.5 saftey factor just means you made the wing too strong, and thus it has extra weight!
Now a days, the structural FEMs (finite element models) and load definitions from CFD (Computational Fluid Dynamics) have become so good, that its not necessary to validate the tools. They have been validated before, and there is a high level of confidence. Someone mentioned above me that these wings were different since they are composite, but in fact commercial airplanes have had composites in the wings for a long time. The military has been making nearly all composite airplanes for even longer.
The A380 from Airbus ran into trouble a few years ago, as they designed the wing for 1.5 load factor, but on testing it only made it to 1.48. Hence they had to add extra weight and strengthen it. But being that they aimed for 1.5 and got to 1.48 shows you how accurate the tools have become.
There might also be a cost element in this decision. I believe Boeing could potentially use that model for some other purpose, whether it be passenger escape tests, wing fuel fire tests, wing fatigue tests, or maybe even just for a model to sit in a hanger somewhere and generate PR. Personally, im hoping to see a great video on YouTube of those wings splintering into pieces!
The reason for the debate is.... (Score:2, Interesting)
Re:787 is a revolution in design and manufacturing (Score:3, Interesting)
Re:I hope they test it! (Score:4, Interesting)
Up until you get something that exceeds their theoretical load limit - either they misguessed or something else happened. There's a reason for the 150% requirement.
Personally, I'd test it up to 2-300%, just so they can slap it up as a 'safety' feature; Wings that are stronger than ever before. Twice as strong as FAA requirements!
Has nobody seen the fuselage pictures yet? (Score:4, Interesting)
Now I am an engineer at an aircraft MRO. Once these things hit more than 15 years old, there are going to be a million problems with this fuselage. Carbon fibre is a very different beast to aluminium, or even fibreglass. For one, the carbon is a conductor of electricity, which can lead to galvanic corrosion (the circumferential frames are still aluminium, there are still metallic fasteners going through the skin to attach them). Also, repairs are going to be an absolute bitch.
Twice in the last month, we have had to fix large holes in the side of aircraft due to trucks driving into the side of them. These incidents happened at outstations (where there were no major repair facilities) and we had to send out a small team to assess and repair the damage. In both instances these were done by a repair engineer, inspector and a couple of sheet metal workers in a couple of days. They took a sheet of metal, an air compressor and a bucket of rivets.
Currently, composites are used on a number of components on almost all aircraft. Invariably they are removable components, like flight control surfaces, or fairings. In order to repair them, they are usually removed from the aircraft and repaired in a composites shop, where temperature and humidity can be controlled - preferably in an autoclave.
Now, how the hell is anyone going to remove a fuselage section to drag it into a shop?
Re:I hope they test it! (Score:2, Interesting)
That is correct... (Score:4, Interesting)
Re:I hope they test it! (Score:4, Interesting)
It's probably designed to different criteria (Score:5, Interesting)
The first time this was really driven home to me was in undergraduate school in '88. A classmate was working on a portable carbon-fiber bridge project for the Army. It had to support the weight of a main battle tank crossing it. In the full-scale test demo, the general overseeing the project commented that you'd get one and only one tank crew to cross the bridge. He felt that after the other tank crews saw how much the bridge flexed, there was no way they'd want to drive on it.
Re:I hope they test it! (Score:3, Interesting)
Personally, I'd be in favour of much more testing. Yes, the wings are more flexible, but is that necessarily a good thing? A Boeing is not in the same league as the round-the-world-nonstop aircraft, where wing flexibility has been paramount. Nor is it under the same stresses as a fighter aircraft. Optimizing for one variable may de-optimize another, so it is important that the right one is picked.
I'd also want to see much more data collected on these new wings. Again, fighters are probably scrutinized very carefully, and RTW aircraft generally only fly once. How much data has been gathered on fatigue? Were ultrasound or IR sensors used to pick up where stress was building, allowing for direct comparison between computer models and the tested system? Can the wings take being repeatedly stressed to that degree, or will faults rapidly develop?
Fuel is stored in the wings, so the wings become lighter as the aircraft flies. That fuel is pumped between the tanks under the aircraft and the wings in both directions, so wing loading will be non-linear with time. If the wings are highly flexible, will this affect lift or other characteristics?
We can assume Boeing has all the answers to these questions, but that's all we'd be doing. Unless you work there, you don't know for a fact what data they have, all you know is what they say they have, which may be entirely different.
Of course, with the rise in popularity of Blended Wing Bodies and Waveriders, there is the question of why Boeing is even sill using the tube-with-wings design. It's inefficient, it's likely more prone to failure, and a good BWB airframe should be able to land more passengers on smaller runways, greatly increasing the number of people who could buy them.
Re:While its great they are so flexible (Score:3, Interesting)
Also, just because an aircraft can take the G loading does not make it a good aerobatic aircraft. In fact, the Extra 300 is one of the best aerobatic aircraft out there and is perfect for doing snap rolls, but flying it from airshow to airshow is a bear... Dang thing is annoyingly too unstable and likes to roll too much...
wrong and wrong (Score:3, Interesting)
Your comments about holes in planes ("ramp rash") are also off base. Boeing has two patch kits, one which can be applied in a very short time, the other which takes something like 36 hours to cure. Boeing has shown to the airlines that fixing small holes from collisions with trucks won't be a problem.
Re:Methinks misguided article! (Score:3, Interesting)
What the heck are you talking about?
Nothing about the wing flexing causes a loss of lift, aileron effectiveness, or engine intake efficiency unless the wing flexes in such a direction to it.
You can also flex in such a way as to increase lift, aileron effectiveness, or engine intake efficiency.
Wing flex is actually a good thing from a turbulence and sudden control input perspective. But you're right in saying the infrastructure in the wing would have to tolerate the flexing as well.
Re:I hope they test it! (Score:3, Interesting)
You too?
I only got caught twice..
I liked the one with all the wheels on fire (aborted takeoff simulation). Full speed, full throttle down the runway with a fully loaded 777, and then stand on the brakes til it stops.. Very pretty.
Re:Well... (Score:2, Interesting)
Re:While its great they are so flexible (Score:3, Interesting)
It's great that the wings can flex that much, but I hope it still requires just as much force to bend them 10 degrees out of normal as it currently does with a metal wing.
Photos of the first 787 (Score:3, Interesting)
787 Photos [airliners.net]
Carbin Fiber flex? (Score:3, Interesting)
Re:I hope they test it! (Score:3, Interesting)
Re:I hope they test it! (Score:2, Interesting)
Well, while it's true that brittle materials are frequently stronger than tough materials like aluminum, it's much more difficult to tell when they will fail under cyclic loading. Unless, that is, they're operating under such low stresses that no damage is ever done (unlikely).
Nowadays, a huge amount of work goes into inspecting the fuselage and wings for microcracks, because there is a maximum length that a crack can be before it expands rapidly. A great example of this is the DeHavilland Comet aircraft of the early 1950's, of which two disintegrated in midflight. There are lots of ways to figure out what that maximum length is, though I'm personally more familiar with the methods for materials that work harden like aluminum. However, I am 90% sure that carbon fiber engineered in a similar spec to the aluminum would be able to deal with a much smaller maximum crack length before failing catastrophically.
But, I can say with confidence that the engineers at Boeing certainly know all about this. The thing to be worried about is probably damage done to the wing due to cyclic loading, because that damage builds up until it reaches the critical threshold when it propagates uncontrollably. It'd just be a matter of either making absolutely sure that the strain is below the threshold where it causes any damage (which it sounds like they might have done), or to have cool new technologies with which to detect the microfractures that will form.
Um... IAAMS... that was probably way too much information.
Re:I hope they test it! (Score:1, Interesting)
To address galvanic corrosion, we used some pretty nasty sealant anywhere that aluminum and composites were joined together.
Some anecdotes about the composite wings we built...
1. Even tho the engineers swore up and down that the glue used in the stringers was more than enough to hold them to the skin, the final plans still called for just a handful of traditional fasteners. We refered to them as "Chicken Fasteners". Someone was chicken and didnt trust the engineers.
2. The 777 rear empanage was "25% overbuilt" according to results from testing per one of the engineers in my building. This means that more material is being used than is needed, and as a result, the parts weigh more than they need. Its a cascade of events after that. If the rear wings were built "just right", then other supporting parts could be made lighter. Net result is less weight, cheaper airplane, better return on investment for buyer. Also such things as greater cargo, or longer range.
And just for bragging rights, my dad was one of the main mechanics who did all the legwork to make that 777 final destruct happen. Him and his team were responsible for all the structure, load cells, spreader bars, wires, cables, you name it. He was on the floor with an engineer just a couple yards from the wing behind a plexiglass/lexan whatever shield. Even better seats than the company president!
Re:missed the best part... (Score:5, Interesting)
Re:missed the best part... (Score:3, Interesting)
As far as the 'new Boeings' part, it's not really a new thing. If you sit in an aisle seat far back in a 747 and sight down the seat line, you can see the fuselage bend. As far as I know, there has never been an inflight structural breakup of a 747 that was due to turbulence. They've had passengers killed by turbulence (UA over the Pacific), engines thrown in turbulence (Anchorage), but never has one come apart due to turbulence that I'm aware of.
Still, I can see that it would make some people nervous. Fly whatever you enjoy the ride on.