Take it to the limit

We’ve had an overwhelming response and a good conversation going on in the comments to the Tanker posts, and we will be following that issue as we go forward.

But I wanted to take a moment catch up on some other news. We just wrapped up a series of tests on a 787 Dreamliner fuselage barrel. And the tests couldn’t have gone any better. When I allude to “take it to the limit,” like the old Eagles song, I’m not kidding.

Turns out the barrel did better than expected under a condition with more than two-and-a-half times the force of gravity - at 200% limit load.

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The composite barrel is completely enveloped by the test rig equipment during the structural testing for the 787 Dreamliner in Everett.

In Everett, Boeing engineers have been putting the composite technology, design, and construction through a series of static stress testing scenarios beginning late last year. The tests were done on a Section 46 (mid-fuselage) barrel as part of Boeing’s certification efforts for the 787.

During stress tests, parts of the airplane are pushed, pulled, and twisted by hydraulic jacks. This series of tests concluded last week with what’s called “destruct sequences.”

The tests were incremental. First, they put the barrel to “limit load.” This is a test that simulates the most extreme conditions expected in the life of the airplane.

Then, they went even further – putting the barrel at 150% of limit load. This is called “ultimate load,” and it’s the level required for certification.

Well, turns out the barrel showed no signs of damage after these tests. So they pushed the barrel past what’s known as “ultimate load.” Well beyond ultimate load. It’s a destruct-condition, and as I mentioned, it’s beyond two and a half times the force of gravity. And obviously well above even the most extreme conditions an airplane would experience.

At this point, the team observed audible indications of damage but the piece did not reach the point of destruction - even at this extreme load.

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An array of monitors and screens inside the “control room” provided the team with plenty to focus on as data and video images of the barrel were displayed during testing. You may notice in the bottom photo, team members sporting retro flattop haircuts, starched white shirts, narrow ties, and horn-rimmed glasses - it’s their way of honoring the history and contributions of their predecessors - the pioneers of their field.

You might be interested to know that the tests put the barrel through a variety of scenarios simulating both standard and extreme flight conditions:

  • Maneuvers at two and a half times the force of gravity without structural failure
  • Maneuvers at negative gravity forces
  • Maneuvers to simulate abrupt elevator up and elevator down conditions
  • Emergency landings
  • Engine out response conditions
  • Performance during normal loads with the presence of visible damage to the composite materials
  • Emergency landing at six times the force of gravity
  • Extreme maneuvers with unrestrained cargo

These tests are all essential to clearing the Dreamliner for first flight. Now, the next step for engineers is an extensive inspection of the barrel and a study of the test results in detail – with an eye toward optimizing the 787 design.

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The 787 barrel testing team. They put in a lot of long hours – including over the holiday break – and did an exceptional job to achieve these test results.

We’re going to be doing some additional testing on the composite barrel section, to learn more for our own background. And then there will be additional static testing required, which we’ll do on a full airplane structure before first flight. That test airplane is in final assembly in the factory right now.

Comments (14)

Reece Lumsden (Everett, WA):

It's great to hear that the barrel met all of the certification requirements. Just talking out loud here, it'd be interesting to see the extra cost incurred to design the barrel to withstand beyond the certification limit.

In other words, is the cost to make the barrel able to withstand 200% limit load way higher, much higher or about the same than getting it to withstand 150%? Was there an ultimate end in sight with respect to the loads or did we just design it to stand up to some extremely high figure which will only later be reduced once we analyse data from the test aircraft (I assume gathering this kind of data will be part of the flight tests)?

Ultimately, is the design gold plated or is it focused on meeting the requirement?

Steve (Siggnethal Station, Switzerland):

Congratulations to the Composite Barrel Engineering Team!

With these large margin results, and your comment about optimizing the design, it appears that the team went with a conservative low risk approach, to compensate for the "unknowns" of this new application for CFRP.

Though obviously the correct thing to do, does this now mean that there may be efforts made to reduce the weight of the structure by eliminating some of the extra margin? In the past, with the standard aircraft materials, having a 2.0+ safety factor would have resulted in excessive weight, is this not also the case with CFRP?

Or is it too late to modify the 787 structure, and thus the knowledge will be utilized on the next CFRP design, such as a 777NG-CFRP?

Norman (Long Beach, California, United States):

The carbon-fiber composite fuselage barrel looks to be an outstanding proof of concept that works, this means a better chance of surviving very severe turbulence, a crash landing, and a sudden change of direction mid-air to avoid striking an errant aircraft in the sky.

Destructive testing is the genuine article that must be made to prove the real strength of an aircraft in which computer systems cannot fully and entirely simulate the way destructive testing can.

With the success of this test I hope Boeing will reconsider the wing bending test in a protected environment if Boeing has not reconsidered it already.

Gravity force tests, pressurization tests, wing bending tests, flight cycle tests, and maximum weight rejected takeoff tests as well as other tests are all vitally important especially for the B787 since it is the first airliner of it's type with a majority carbon-fiber composite airframe.

The 787 looks to be a outstanding airliner and a robust one at that.

G (France):

It's nice to see those old and young engineers working together.

lucklucky:

2.5G's? How is this compared to other planes and the maneuverability limits of military planes like F16 that an go to 9G? Is this the same thing?

LIGHTWEIGHT (Fance):

Did Boeing replicate the choice done with the 737NG?
737NG-600/700 slightly heavier that they could have been (empty weight), to standardize building process of the four fuselages length.

That mean, like the 737NG, stretching one time (787-9), and a second time (787-10) will add only the weight of barrel and seating added(if the wing is barrel like sturdy.

Minimum weight increase for -9 and -10, without reenforced zones to keep only 8 wheels for the heaviest 787...

Birgit (Germany):

Your comment that "the barrel did better than expected under a condition with more than two-and-a-half times the force of gravity - at 200% limit load." is a little confusing.

Certification regulations put ultimate load requirements at 150% of limit load. Limit load for commercial airliners usually is two-and-a-half times the force of gravity, or 2,5g. The makes the ultimate load that needs to be demonstrated 3,75g.

In contrast, the "200% limit load" you achieved equals a whopping 5,0g! From the perspective of safety, a 5.0g capability sounds really nice. But against a certification requirement of 'only' 3,75g the barrel seems to be designed with quite conservative load assumptions. In other words, it looks like there's a potential for future weight reduction!

sPh (Midwest US):

I have been reading the "2.5g" report various places and I am a bit confused. I thought commercial airliners were certified to +2.5g/-1.5g, which would make the ultimate load +3.75g/-2.25g. Or am I misunderstanding something about this test?

Phil (Wokingham UK):

Excellent news for the team and it endorses the quantum leap Boeing was so bold to take in the further utilisation of composites in commercial airframes.

Given the original over ambitious time scales the announced delays are hardy surprising at this juncture with the challenges presented in the airframe and associated systems, I am sure more announcements in terms of delays will be forthcoming, repeating myself, it's hardly surprising with this style of project.


It would be good to see the hanger doors opening sooner rather than later, let us hope power up is uneventful and that the flight test programme is equally so.

Ron B Mesa, AZ, USA:

That is just great to hear about the strength of this new section 46 mid-fuselage barrel! Are there any videos available to the public, that show this testing?

So much for the testing, how is the rest of the 787 program coming along? Reading comments from various analysts, they are indicating that Boeing is again having problems with estimating the time to assemble the first aircraft so that the delivery date will once again get pushed out. If that is the case, then this will not be good news for those launch customer expecting to have them soon rather than later.

anon (washington):

Did anyone else notice a distinct lack of pocket protectors for the picture of them in white shirts? :(

Chris C (South Africa):

Thanks for sharing this stupendous information regarding the recent 787 fuselage barrel testing Randy!! The fuselage test speaks volumes about the sheer superiority of the super-efficient 787 airframe design! Looking forward to power-on...soon!

Will we see the 1,000th 787 order this year? Absolutely.

Kevin K (Canada):

Wow Randy, with test results like that you may have a different type of problem on your hands. Since carbon fiber does not corrode like metals and with an over built fuselage giving it a really long fatigue life how exactly are you going to convince air carriers that they need to buy new airplanes?

Let me be the first to congratulate Boeing on building the DC-3 of the jet age. As it may turn out you all might have done your jobs a little to well.

Alan Crandell (Sunriver, OR):

Congratulations, from a former 777 test engineer.

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