Boeing 787 (partie 1)

By Jon Ostrower on June 24, 2009 5:59 PM |

Boeing yesterday announced it was postponing first flight of the 787 citing the need to reinforce structure where the wing box meets the center wing box at the side of body of the aircraft. FlightBlogger takes a closer look at exactly what the problem is and how Boeing came to yesterday's announcement.

Because of the need to go back into the detailed design phase for this fix, combined with the need to fabricate, install and test at component and at full scale levels, several sources with a direct familiarity to the situation estimate that the fix will take "months not weeks."

INSIDE:

•What is the problem?
•Historical Precedent
•Timeline
•The Fix
WHAT EXACTLY IS THE PROBLEM?
The issue centers around the wing-to-body join that mates the wing box (Mitsubishi/Section 12) and the center wing box (Fuji/Section 45/11). The center wing box is the combination of two pieces, the center wing tank (Section 11) and main landing gear wheel well (Section 45). The area of concern centers on the 18 points where Sections 11 and 12 meet.

Digging deeper, the 18 points in question on each side of the airplane (36 total) are located on the top panel of the center wing box and run port to starboard inside the structure of the center tank through to the other wing. These 18 'stringers' inside the center wing box are matched by 17 stringers on the wing box, which serve to stiffen the wing skin. The wing box has 17 stringers, but a source indicates they are designated 2-18, hence the reference to the 18 points that need to be reinforced.

The composite stringers, which give the wings its longitudinal stiffness, are cured during production when cooked in the autoclave and joined as a single bonded piece with the wingskins.

On the inboard side of the wing box where the 17 stringers end and connect to the center wing box, each has what is known as a 'stringer cap' that widens at the end and actually makes the hard connection between Section 11 and Section 12 on the side of body. The stringer caps on ZY997 sustained damage, albeit repairable, when the wings were flexed in late May.

Boeing confirms that small areas of the wing structure separated or "disbonded" from the wing skin, though declined to specify exactly where. Sources directly familiar with the situation say the shifting tension load from the stringer to fastener head also caused damage on the structure.

HISTORICAL PRECEDENT
In February 2006, nearly a year after A380 had begun its flight test program, Airbus was conducting testing on MSN5000, the static test airframe when the wing "ruptured" during ultimate load testing. The wing was being flexed to 150% of limit load when the wing broke between the inboard and outboard engines.

At the time, the wing was deflected 24.3 feet at 147% of limit load, below the 150% requirement for certification. Airbus said it designed the A380 wing to break just beyond 150% citing strict adherence to its weight reduction program. Airbus said it demonstrated the structural improvement, not through full-scale testing, but through further "finite element models to prove the adequacy of the structure on production aircraft."

Later that summer, Airbus was required to install a 66 lb wing strengthening package on the existing A380 fleet, starting with MSN003, the first superjumbo for Singapore Airlines that entered service in October 2007. The European airframer decided that wings delivered from MSN018 on would have the modifications incorporated prior to delivery to final assembly in Toulouse.

Airbus was able to verify the viability of the fix as a part of its certification documents supplied to the FAA and EASA for final analysis and approval.

TIMELINE - Updated

Late May
Boeing experiences the first signs of trouble on the static airframe. During that test, the wings of ZY997 were flexed and the strain measurements on the stringer caps were reading higher than predicted.

Previously, on April 21st, Boeing conducted the limit load test which saw the wings deflected over 17-feet and an equivalent of 120-130% of maximum load.

"We went in and did some inspections and saw a number of things indicative of what the strain gauges were saying," said Scott Fancher, vice president and general manager of the 787 program, said on yesterday's teleconference, implying that the test had left visible damage to the structure during the late May testing.

The 1G check out of the wing, which was conducted in late-March, would not have stressed the join hard enough to yield the same results. Previous rumors of delamination from December 2008 still stand as false and unrelated to the current situation which came directly from testing this past spring.

Early June
Preliminary analysis showed that the aircraft was still cleared for first flight, though with a reduced flight envelope. Sources indicate that the original plan was to fly ZA001 and ZA002 on their respective maiden flights to BFI as planned then park the aircraft while a fix, which was considered to be "relatively minor" at the time, was developed that would allow an expanded flight test envelope, though Boeing says this plan was never in consideration.

Scott Carson, CEO of Boeing Commercial Airplanes, said yesterday that "the airplane could enter flight test with a credible flight test envelope as [the company] worked relatively minor modifications."

June 19
Boeing completes final detailed analysis on the stringer caps and decides to postpone first flight.

"The work done by the team through the week last week narrowed the envelope to the point where on Friday we determined that to fly would be such a small envelope for us that it would be an interesting exercise in having the airplane in the air but not particularly useful in terms of preparing the airplane for certification," Carson said.

June 23
Boeing makes a formal announcement of the first flight postponement. The change in first flight was unknown to many of those closest to the airplane. As late as the evening of Monday, June 22, sources indicated first flight had shifted to July 2nd at 10 am after holding at June 30th for more than a week before and during the Paris Air Show. Boeing says that the July 2nd date was never formally approved for first flight.

THE FIX
Boeing says it will be several weeks before it announces a new schedule for first flight and first delivery.

Several tasks have to be accomplished before 787 is cleared for first flight: 1. Develop the modification & concurrently repair ZY997. 2. Test the modification on a component level. 3. Install the modification on ZY997. 4. Conduct full-scale tests on ZY997. 5. Install the modification on ZA001.

"We have to give the team time to do time necessary to do this job," said Fancher. "While we will proceed with urgency, we will not compromise the process for the sake of schedule."

The fix, once identified, will be able to be installed on the aircraft in the factory, the flight line and at supplier partners without any anticipated schedule disruption.

Carson affirmed that the production plan will proceed as planned with a 10 aircraft/month ramp up targeted for 2012.

"At this point, that's our judgment that we will continue with the build up that we had previously anticipated."

FLIGHTBLOGGER: Understanding the 787 structural reinforcement
By Jon Ostrower

Boeing announced it was postponing first flight of the 787 on Tuesday 23 June, citing the need to reinforce structure where the wing box meets the center wing box at the side of body of the aircraft. FlightBlogger takes a closer look at exactly what the problem is and how Boeing came to yesterday's announcement.

Because of the need to go back into the detailed design phase for this fix, combined with the need to fabricate, install and test at component and at full scale levels, several sources with a direct familiarity to the situation estimate that the fix will take "months not weeks."

On his blog Jon Ostrower takes a deeper look at the issues surrounding the latest dalays to the aircraft programme ...

Ce problème -- le plus récent -- rencontré sur le B787 n’est nullement une surprise.
......
This pint-sized design mishap is, …., a big deal for Chicago-based Boeing Co. The new delay, far later in the development cycle than a major surprise should come, is raising more questions about the overarching ambition of Boeing's 787 and the global supply chain created to build it.

The parts to fix the design flaw will cover, altogether, no more than 72 square inches on the 787 airplane. A wing's surface alone on this composite jet covers more than 3,500 square feet.

But it's where those 72 square inches fall -- in two-square-inch increments along the line where the wings meet the fuselage -- that is giving Boeing fits.

Airlines and passengers have an acute interest in seeing wings attached securely to their airplanes. It's an understandable concern, especially with an untested design.

The 787 already is more than two years behind schedule. Current delays are costing Boeing several billion dollars. And now this: a delay that will last for Boeing-does-not-yet-know how long. To break down Boeing's latest scheduling calamity to its composite parts, here's what happened.

When Boeing conducted stress tests on a life-size model of the airplane -- putting pressure on the wings that exceeded what they would sustain in normal flight -- the plane's carbon-fiber composite showed more stress than expected.

Further ultrasonic testing yielded a most unwelcome result: The layers of plastic that make up the plane's fuselage had started pulling apart.

There is no known reason to believe that the 787 will be anything but safe. Composites have proved tough in fighter jets. They are used on wings and other high-stress parts of commercial airliners.

Even so, Boeing's 787 is the first aircraft to use composites so widely. Boeing already has faced unfounded concerns that the all-composite fuselage could not take a lightning strike. Now Boeing will have to address this additional safety question.

"Composites are the right choice for aircraft structure," said Scott Carson, president of Boeing's commercial aircraft division. It was a swear-on-a-stack-of-Bibles statement on an issue Boeing wanted settled long ago.

When a company sets out with the ambition of the 787 project, negative surprises are part of the deal.

When Boeing started the 787 project in 2004, it was designing the first all-composite airplane, lighter and more efficient than any of its size. It also was creating a lean, global manufacturing system by which partners in Japan, Italy, China and elsewhere would assemble wings, tails and fuselage sections, then ship them to Seattle for final assembly.

The idea was bold. It was brash. It had zero room for error.

"It's the kind of risk that a truly competitive organization will take," said Richard Lewis II, executive director of the Lean Advancement Initiative at the Massachusetts Institute of Technology. "They will do everything they can to minimize the risk, but sometimes, that's not enough."

John Quelch, a marketing professor at Harvard Business School, posits that Boeing underestimated the challenges baked into the 787 program in 2004 when it set up such a complex industrial structure and an untested use of materials, both at the same time.

"I don't believe the complexity costs were adequately recognized at the time," Quelch said.

Yet another delay for the 787 will not materially diminish the program. Boeing's airline customers, facing combined losses expected to top $9 billion this year, may even welcome the news. Few airlines have the cash right now to begin payments on planes that list for $190 million each.

The 787 program has faced so many delays, they do not feel like a surprise anymore. At this point, it would be a surprise if there are no more surprises.

Rasta' a écrit:Effet domino, quoi...

Vector a écrit: Pourrait-on m'expliquer ce qu'il y a de si complexe et risqué à modifier une voilure dont les performances et la structure sont depuis longtemps modélisées et vérifiées. Est-ce qu'on parle de profil, de caractéristiques de formes en plan, de raccordement au fuselage? Il est évident qu'une remotorisation est beaucoup plus complexe, même sans changement de l'aile.

Vector a écrit: J'aurais crû naïvement que les logiciels de simulation et de CAD/CAM, permettaient de prévoir avec une certaine précision les effets d'une modification incrémentale.

Vector a écrit: Est-ce qu'on parle d'un redesign majeur dans le cas de l'A340-600?

sevrien a écrit:Investir dans une aile nouvelle ? En sus des moteurs, avec de nouvelles nacelles ? Pour vendre combien d'avions? Et apporter combien de potentiel de retour sur investissement, ...accru,.... pour les "airframer", motoriste et opérateurs ?

Vector a écrit:Pour le 787, il semble que la rigidité de la voilure aux efforts verticaux est assurée par la résistance du fuselage en compression latérale et que c'est là où le bât blesse.

Peut-être que Boeing aurait dû opter pour l'approche "cadres plus panneaux", ... comme Airbus !

sevrien a écrit:Poncho, j'avance respectueusement que John OSTROWER ne reçoit plus que ce que Boeing veut bien lui donner comme informations, et pour cause.

Ce que je vous ai avancé est bien plus fiable, dans ce sens que c'est un ingénieur, spécialisé en composites, qui est à la base de la communicartion.

Et, encore, il ne doit pas tout dire !

Jeannot a écrit:Rentrant d'une journée harassante à l'étranger je vous lis et je cite Sévrien

Peut-être que Boeing aurait dû opter pour l'approche "cadres plus panneaux", ... comme Airbus !

Pourtant Airbus a été critiqué par certain pour cela. Non ?

Jeannot a écrit:Rentrant d'une journée harassante à l'étranger je vous lis et je cite Sévrien

Peut-être que Boeing aurait dû opter pour l'approche "cadres plus panneaux", ... comme Airbus !

Pourtant Airbus a été critiqué par certain pour cela. Non ?

Admin a écrit:

sevrien a écrit:Poncho, j'avance respectueusement que John OSTROWER ne reçoit plus que ce que Boeing veut bien lui donner comme informations, et pour cause.

Ce que je vous ai avancé est bien plus fiable, dans ce sens que c'est un ingénieur, spécialisé en composites, qui est à la base de la communication.

Et, encore, il ne doit pas tout dire !

Merci Sevrien,

Donc, il y a enfumage ?

Admin a écrit: Le problème est bien plus complexe ?

Vector a écrit:
Si j'en crois les posts ci-dessus, on n'est pas près de "louer la clairvoyance" d'Airbus pour n'avoir pas sauté sur le char du tout-composite.
!

Jeannot a écrit:Bonsoir cher Vector

Vector a écrit:
Si j'en crois les posts ci-dessus, on n'est pas près de "louer la clairvoyance" d'Airbus pour n'avoir pas sauté sur le char du tout-composite.
!

Bien au contraire mon intervention allait dans le sens de souligner que Airbus n'avait pas suivi Boeing dans la technologie du "Full Barrel" et avait même été critiqué pour cela.