Boeing's New 787 Wings — Amazingly Flexible

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.

Comments

I hope they test it!

[chris098]

From the article:

No one's ever really tried that before, so testing is critical.

Since this seems like such a new concept (please correct me if I'm wrong; I don't follow plane technology too much), it would just seem prudent to try bending the wings until they break... how can they make accurate judgments and calculations without knowing exactly how much stress the wings can take before snapping?

Re:I hope they test it!

[stoolpigeon]

I was wrong - 777. and the video is here - what a wonderful age we live in.

Re:I hope they test it!

[nelsonal]

It's potentially more dangerous than an alumnium wing, 150+% of design load has to be a substantial amount of energy stored in the wing, and while aluminum will deform in failure (converting most of the energy to heat) carbon fiber seems more likely to shatter.

Re:I hope they test it!

[secPM_MS]

There is no need to do so. As you bend the wings enough you are going to loose lift. You need to test to a good safety factor. The testing would be very expensive. You would want the thing heavily instrumented. The amount of mechanical energy would be very large and you would have to clean the mess up afterwards.

My doctorate is in Mechanical Engineering - Materials, in this case fracture mechanics. The fact that the wing is so strong suggests that it may be being over-designed. My graduate structures professor, who worked on the 747, point out that airplanes are designed for what might be called simultaneous mode failures -- there is no point in having the wings significantly stronger than the fuselage, as once the fuselage breaks the wings don't do you any good, you have just been carrying too much material in the wings. The same is true for all sub-systems. Hence, you have to do a very exhaustive analysis of the expected situations and make sure that all of them are appropriately covered, then you add a safety factor.

Typically, fatigue cracking has been the limiting factor in aircraft structures, and has caused numerous crashes. With the experience that has been gained in military programs, we should now know enough to use these composites properly.

Re:I hope they test it!

[MonorailCat]

What a huge distraction, I just went on a 30 min youtube binge watching destructive testing of aircraft parts... Back to work!

Re:I hope they test it!

[Shadow Wrought]

It was in the summary!!!

Pfffft. Real slashdotters only need a headline.

Re:I hope they test it!

[steveo777]

What I think will happen is that tips will meet. They'll try to compress the wings vertically, but before any definitive results are in, there will be a very loud "SPROING" in which case, the wings will be freed from their restraints. They will smash toward ground, propelling the plane into the air. As they bounce back to equilibrium the wings will flap carrying the plane roughly 1000km in the direction it was pointed. Eliminating the need for any fuels on short trips. Carbon Fiber FTW!

Re:I hope they test it!

[TheRaven64]

A deformed wing may not be aerodynamic enough to fly with, but it may slow your descent enough to turn a fatal crash into a near-fatal crash. A shattered wing is unlikely to do any good at all.

Re:I hope they test it!

[pyrbrand]

Haven't you learned anything from Mythbusters? Since when do we not test things just because we don't need to know the answer? Get Jamie and Adam on it and the build crew will clean up the mess!

Re:I hope they test it!

[LWATCDR]

Well Aircraft unlike computers are only operated by trained professionals.
Since you can not make the wing infinitely strong you you put operating limits in it.
One "neat" trick they use involves airspeed. When you start pulling Gs your stall speed goes up. Once a wing is stalled it stops generating lift so it unloads.
Back in the day your airspeed indicator had arcs. The green arc means that your wing will stall before it breaks.
The Yellow arc means that yes you can break the wing if you try.
The Red line means bad things are going to happen.
So when flying into storms the pilot can slow the the top of the green arc and be safe.
BTW a stall at altitude isn't a terrible thing. It is better than breaking the wing.

With this wing it may have an all Green arc.

As to breaking the structure to learn things. Yes but that kind of testing is expensive. If the wings of the 787 pass with a bigger than average margin then I would much rather see them do repetitive tests to see how it does with multiple over stress conditions.

The thing about some of the composites I have dealt with is some don't fail gracefully. I have parts of aircraft deform from stress but not totally fail. In other words it will get you home but she isn't going to fly again without A LOT of work.
I have seen carbon fiber get a good scratch in it and the next thing you know it is in a million part small parts.

Re:I hope they test it!

[timeOday]

Typically, fatigue cracking has been the limiting factor in aircraft structures, and has caused numerous crashes.

That is the issue. It doesn't really matter whether the wings can bend until they touch when they are brand new. What matters is whether they will hold up after billions of tiny deflections, especially if there is a defect deep inside or as they get chipped, etc.

Re:I hope they test it!

[Dare nMc]

while aluminum will deform in failure (converting most of the energy to heat) carbon fiber seems more likely to shatter.

of course their is a downside to most changes.
by deform, you mean yield so, yes if you exceed the limit of carbon fibre you likely have snapped, where as aluminum, you have destroyed the structure of the frame. So if they both exceeded this limit at the same load, the aluminum may allow you to make it through one event.

For this to be obviously safer, you need:
      1) the yield points would have to be very close.
      2) it must be a single yield event (not repeated yield points, leading to a quick fatigue failure)
      3) you must know the event occured so that you will replace the yieldied aluminium part, before the next event.
      4) the yield event would still have to be in the yield strength of the aluminum, and not exceed it to the point of failure.

I think that is the issue, all of these are false. Carbon fibre has a much higher yield point, the aluminum wings constantly need inspected for fatigue cracks, and with each cycle they become closer to the point of failure.

With the carbon fibre, as the wing bends, it is probably designed to self limit the load. Since the aluminimum cannot survive the same amount of movement, it cannot self regulate (it bends, which makes it hot, which makes it softer, which makes it bend more which makes it hotter and softer,...)

of course it takes alott of energy to bend carbon fibre also, so it is releasing energy as heat as well. Granted aluminum is a much better heat conductor, so it would naturally transfer that heat better. But carbon fibre is known to stay stronger at high temperatures than aluminum.

Re:I hope they test it!

[Firethorn]

Yes, but from my reading, it's likely that the carbon fiber wing will still be intact after suffering forces that would have reduced the metal wing to a twisted, useless mess.

So, while some failure modes might be worse than traditional aluminum wings, it's also likely to be better in others.

Then it becomes a matter of risk assessment and minimization. A good example would be seatbelts - there is the occasional accident where you'd be better off without the belt, but in the vast majority of accidents you're far better off with it on.

Re:I hope they test it!

[Anthonares]

Composites are significantly different from metal structures in that their primary failure modes are not fatigue related microfractures, but a phenomenon called delamination in which static and dynamic loading can cause the layers of alternating orientation fibers to separate. It could very well be that in order to design a wing that was not susceptible to delamination, the wing turned out to be incredibly flexible.

It sounds as if Boeing uses a "factor of safety" of 1.5, where the maximum anticipated load is multiplied by the factor of safety to determine the design strength of the wing. The factor of safety is calculated based on the earliest failure mode of the part, so it could simply be that other failure modes than wing deformation and buckling (as seen in the youtube video) are what determines the factor of safety with this new carbon fiber wing.

Re:I hope they test it!

[NeilTheStupidHead]

While this sounds good, looking at the video of the 777 wings, I doubt they would hold up under windspeed after that kind of damage. The aluminium panels buckled and ripped free of the rivits and the way the aircraft sagged as they did suggests that the panels are a signifigant structural component of the wings. This 150% number they keep throwing around is 150% greater than the maximum load the aircraft wings would be expected to face (which probably has it's own safety margin thrown in). Given that aircraft can and have been flown into hurricanes, and hurricanes can have maximum sustained winds of over 300 kph, I don't think I'll be worrying about the wings failing the next time I get on a Boeing aircraft.

Re:I hope they test it!

[fosterNutrition]

Pfffft. Real slashdotters only need a headline. Some of us only need a category Oh come on, who needs categories? We all know what to say anyway:
Does it run linux?
Imagine a Beowulf cluster of those!
In Soviet Russia, aeroplane wings break you!
etc, etc, etc.

Clearly, you must be new here.

Re:I hope they test it!

[kryten_nl]

Fly the new 787 - It's so strong, you only need one plane for two towers.

If this doesn't bring my karma down .....

Re:I hope they test it!

[binarybum]

because if Chuck Norris were on an aluminum airplane he could go out on the bent wing and bend it back, but if he were on a carbon fiber airplane he would just shout, "I've got nothing to work with here assholes!" shoot everyone on the plane, jump out the window, knit a parachute out of his sweater on the way down and land topless on a throng of adoring Laotian women.

Re:I hope they test it!

[Lorkki]

Your ideas are intriguing and I wish to subscribe to your newsletter.

Re:I hope they test it!

[Mithrandir]

In a previous life, I did a lot of work on major structural repairs to composite fibre airframe structures - and more specifically on sailplanes. I had several qualifications for inspection and maintenance on them, and worked in a shop that did everything up to and including spar repairs. There's actually less requirements for inspections on any form of composite structure than metal or wooden frame. And when there was inspections, it was much simpler. For example, the spar is tested simply by taking two identical tuning forks, placing one on one end of the spar, ringing the second one, placing it on the other end of the spar. If the other one rang in sympathy, things were fine. The wing surface itself is very easily checked for delamination by simply tapping and listening. When you're more experienced, you can feel it in the way your tapping object responds to the impact. That's far easier that some of the x-ray type inspections we had to do on the metal aircraft. That sort of level of inspection was only done once a year, or every 200 hours, whichever came first. Given the rest of the aircraft industry inspection schedules, I highly doubt that anything will change for the 787.

You are correct that microfine stress fractures are impossible to see in a pure carbon structure. To work around that, every object has a very fine fibreglass layer (070 or thinner) on the outside surface. When stress is applied, the fibreglass shows the stress marks and you can then visually see that something is wrong.

The biggest issue with C/f structures is design life. At the time when I was last working in the industry (mid 90's), they weren't even sure what the maximum life was. There was no data anywhere in the world. The sailplane factories were stating that 10K hours was the minimum and they would test after that (metal airframes were 30K hours before EoL). There were studies being done at Melbourne's RMIT (Australia). The last I heard there was they got to 17K hours before failure of one wing. Given the absurd number of hours a commercial airliner does compared to a sailplane, I would hope and expect that they have done some lifetime studies beyond that. I haven't yet seen any numbers from Boeing about expected airframe life for their pure composite structures.

Why (not)?

[borizz]

You could, instead of downright trying to see how much it will take, try to get it up to 200% (or something, I'm not an aerospace engineer) and see for how long it can hold up to extremes like that. Might be more valuable data. Maybe someone more in the know can elaborate.

The 787

[kannibul]

The 787 will be the envy of "tuner" kidz everywhere with it's carbon fiber wings.

If only one could find a 4ft diameter chrome exhaust tip...

Must resist onomatopoeic humor...

[powerpants]

Pull them back, let them go, and... BOEINNNNG!

Re:missed the best part...

[kannibul]

Enter the flapping apparatus! It'll make the passengers feel more comfortable, having their plane flap it's wings!

Slashdot Poll

[chill]

If any article screams out for a Slashdot poll, this one is it.

1. Chicken out and don't break 'em
2. See how far they go and post it to YouTube
3. Orinthop mode! Pull 'em back and let 'em flap!
4. Cowboy Neal

Shopping for planes has never looked more fun

[ajenteks]

Airbus: Care for some metal wings?
Boeing Client: No, thank you, I take them flexible, like my women.

While its great they are so flexible

[N3WBI3]

Does it really matter if, because of how they are bent, you lose lift?

Re:Nothing new

[Cobalt Jacket]

You are joking, right? Assembly of the first A350 won't even begin for about 5 years. It's not at design freeze. The 787 is about to roll out, and first flight is in a few months.

Re:Nothing new

[Hays]

Both companies have been using carbon fiber. The 787 uses an unprecedented amount of it. You can't say it's nothing new by citing an Airbus project that doesn't have a scheduled delivery until 2013. http://en.wikipedia.org/wiki/Airbus_A350

One year ago? How about twelve?

[peacefinder]

"They have come a long way from even just a year ago."

The linked video may have been uploded about a year ago, but it cites as its source a PBS production from 1995. (Which, incidentally, is discussing an entirely different airplane, the 777.)

Re:I really don't see the big deal

[Cobalt Jacket]

The point of the 787 is to fly further, more cheaply. So while costing less to fly, it is also supposed to do to the Pacific what the Boeing 767 did to the Atlantic market. That is, the 767 brought in a revolution of being able to connect mid-sized cities on both continents, rather than forcing people to go through hubs on larger aircraft such as the 747 or DC-10.

Old News: Flexible wings on the Boeing B-47

[G4from128k]

Thin flexible wings date back to the Boeing B-47. Up until this plane appeared in 1947, planes tended to have thick rigid wing structures. Advances in aeronautics, fluid dynamics, and structure design enabled engineers to create thin flexible swept wings that offered lower drag at high speed without flutter or breakage. The wings of B-47 (and B-52) were so floppy, they needed outrigger wheels to keep the wings from dragging on the ground during landings and take-offs.

Don't break it

[Broken scope]

A bit of wisdom from a Retired Boeing exec who I forgot the name of.

The story was about one of the earlier Boeing's, they had stressed the wing to like 10 times any theoretical force that could be possibly placed on it during a rather publicized testing of its strength. They test folks were all about trying to break it.

During the process of doing this an exec asked them what they were doing. "Breaking the wing" they replied.
The exec said No, stop the testing.

Why? the testers asked.
Because the headline won't read ,

"Boeing wing breaks at 40 times the stress encountered during possible flight conditions",

Instead it will read

"New wing of new Boeing Jet Breaks".

Please note Its been awhile since I heard that story, but I think the point is pretty clear.

Well...

[StressGuy]

The actual requirement from Title 14, Code of Federal Regulations, Part 25, Subpart C, paragraph 303 is where ultimate load definition comes from:

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:Well...

[georgewilliamherbert]

Engineering ethics dictate that we take reasonable precautions to preserve human life, balancing extreme cases with the economic viability of producing the product in the first place.

What reasonable is, depends on which field you look at. The same standards do not apply to structural engineering (buildings), civil engineering (bridges, dams), aerospace engineering (aircraft), electrical power engineering (building wiring, electrical distribution systems), etc etc.

The FAA standards are, they set a specific limit load condition calculation for classes of aircraft (light aircraft are different from jet transports carrying people, etc). That's based on performance, operational usage, and the number of people typically carried. There are load cases for limit loads for gust loading (suddenly hitting a headwind when you're already pulling Gs), wind shear, emergency pull-ups, etc. A speed is established, called maneuvering speed, below which nothing you can do to the aircraft is credibly likely to ever cause the aircraft to exceed the limit loads.

Then, you add a 50% safety factor on top of those loads (failure load >= 150% of design limit load), and demonstrate to the FAA's satisfaction that the aircraft meets that ultimate load. For jet transports carrying people, the demonstration requires that you take it out to the 150% load limit and see if it breaks there.

Now, that ultimate load can be expected to cause permanent damage to the wings. Pretty much any aircraft exceeding the design limit load (100%) will get grounded, and anything approaching 150% is guaranteed to have damage. Since the test to 150% damages the test structure for any aluminum aircraft, the usual assumption is that it's a good idea to just keep testing past 150% until it breaks.

But you just need to prove that it meets the 150% for the FAA to be happy.

Designers try to make the failure point slightly, but not too much, past 150% of design limit load. Because adding weight is expensive (operations costs), and as others have mentioned it doesn't do any good for the wing to be stronger if the fuselage breaks first, etc. The loads are all balanced; it's inefficient for things to fail at different points.

These standards are reasonable, for transport aircraft. We know that because large jets are not falling out of the sky due to wing failures. I can't offhand think of the last one that wasn't due to some external cause (collision, etc). There closest incident recently was the American Airlines 587 crash in 2001 (http://en.wikipedia.org/wiki/American_Airlines_Fl ight_587), where a possible gap in the maneuvering conditions / load conditions / stress analysis the FAA requires and airplane manufacturers design to led to an A300 jetliner to lose its tail in flight.

Re:Design accommodations?

[mustafap]

>Or you could, you know, give up a disgusting habit that is poisoning you.

What? Give up slashdot? Never. I'll die first.

YMCA

[everphilski]

I want to see the 787 do the Y-M-C-A :)

Re:Nothing new

[badasscat]

You are joking, right? Assembly of the first A350 won't even begin for about 5 years. It's not at design freeze. The 787 is about to roll out, and first flight is in a few months.

Yeah, it kind of reminds me of when Airbus called Boeing's composite barrel design "old fashioned"!

Bearing in mind that nobody has produced such a design yet, including Airbus. Until Boeing did it a couple of weeks ago, that is.

The A350 was designed in direct response to the 787, which surprised Airbus in the amount of interest it received (they had at the time placed their bets on the now-troubled A380 program, which may never break even). Saying the 787 copied any of the A350's design or construction methods is getting it completely backwards.

What?

[msauve]

The engineers at Boeing are smart enough to design the wing for optimal performance under normal conditions. That includes whatever wing bending occurs under nominal conditions.

If the aircraft is experiencing extreme conditions which are bending the wing excessively, then you _want_ to lose lift, rather than stress the wing and airframe more. Kind of like how sailors change to smaller sails during storms.

This is your captain...

[Taimat]

Ladies and Gentlemen, this is your captain speaking... If you take a look out the windows on the left side of the plane, you will notice our right wing....

787 is a revolution in design and manufacturing

[Thagg]

The fact that the 787 is a "plastic airplane" will get a lot of play, and having wings that bend, potentially to the point that they will tough, is just the most obvious and mediagenic manifestation of that. But it is just the tip of the iceberg of the innovations.

1) Yes, it's almost completely carbon fiber. This means that the plane can (and is) lighter, so it will be more fuel efficient. Also, it's easy to make complex curved shapes, so the wings and fuselage are slightly more aerodynamic. Because carbon fiber structures are so strong, the windows can be larger, and the plane can be pressurized to a lower altitude (it will be pressurized to 6000' instead of the typical 8000' of today's fleet). There is no corrosion, and little worry about fatigue in composites.

2) The plane is not built in Seattle, although that's where the final assembly takes place. All of the building takes place in multiple facilities around the globe, each producing parts to Boeing's plans. These parts will "snap together" in the Everett plant. The first 787 is being assembled right now, and will roll out on 7/8/7 (just over a week from now.) Apparently the left wing was off by 2 thousands of an inch or so, the right wing was absolutely perfect. Boeing converted three 747's to be gigantic cargo transporters to move all the parts from around the world to Everett.

3) The plane has almost completely electric, without the high-pressure pneumatic systems that older planes had. In particular, the AC systems are electric. This will be somewhat more efficient, and safer.

4) The plan for certification of the plane is borderline insane. The final assembly started a couple of weeks ago, and the plane will be rolled out in a week, the first flight will be in a couple of months, and the first delivery will be in Q2 2008. This is a tiny fraction of the time this process required on previous airplanes -- maybe 1/4 the time of the 777 and even less than that of the latest Airbus. This would be remarkable, even if the plane wasn't revolutionary in every other way, too!

5) Aviation Week and Space Technology visited the final assembly line recently, and were surprised to find that it was almost an empty building. That's not because they weren't ready -- that's because there are almost no tools needed to assemble the plane. They snap together the pieces, install the landing gear, and roll it down the building on its gear installing the various subassemblies. Boeing intends to assemble a plane every three days once they get going, a remarkable and unprecedented schedule.

Anyway -- there are so many revolutions in this airplane that I would have thought it was a scam if it was any other company than Boeing. It remains to be seen if they can meet their goals, but so far things are going remarkably according to the plan they laid out a few years ago.

Thad

Re:Who cares if they bend

[AK Marc]

Sorry, I didn't realise that you could shrink the downward pull of gravity. I am fairly certain that it stays at about 9.81 m/s^2...

No, I think that the "pull" of gravity is mass times the acceleration due to gravity. When you "pull" on something, you are talking about the force, not the acceleration. Not only are you a pedantic ass, but you are also wrong.

It's probably designed to different criteria

[Solandri]

The fact that the wing is so strong suggests that it may be being over-designed.

It's probably not be overdesigned per se. Composites tend to exhibit much more strain (deflection under stress) than traditional materials. So a lot of times, the maximum deflection becomes the prevailing design criteria, not the maximum sustainable load. Most likely, the specifications for how much the wing is allowed to deflect under normal load is a more stringent criteria than how much load the wing can support without breaking. So they have to add more material to reduce the deflection, which adds strength as a side effect. (They could probably put additional stringers inside or switch to a sandwich structure to gain stiffness without additional material, but that could complicate fuel capacity and inspections.)

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:missed the best part...

[arivanov]

Comfortable? Forget it. I hate flying on any of the new Boeings. Have you flown on a 777 in a storm? You can actually see the fuselage bend and buckle and the luggage compartment above the central seats move by nearly a foot left and right. While the engineer in me knows that this way it is actually more likely to survive through turbulence and load, the little scared mammal in the depth of my brain (which everyone has) screams "run for your life". No thanks, had that twice and enough is enough. From there on I try to chose long haul flights by Iberia or one of the other airlines which operate "boeings and dogs not allowed" policy and use A340 on transatlantic routes. It is considerably more comfortable.