Fri, Jul 24, 2009
Structural Problems More Difficult To Repair Than Originally
Thought
Two engineers with knowledge of the
situation say that the structural issues with the B787 Dreamliner
are more complex than originally described by Boeing, and the
maiden flight of the aircraft could still be months or more in the
future.
The engineers told The Seattle Times that the issue involves an
area where the wing joins the fuselage, caused by high stress loads
at the ends of the stringers in the upper skin of the wing. As the
wings flex during flight, the stress loads could cause the
composite stringers to delaminate from the skin. This condition
occurred during wing flex tests. The engineers said while
this is not likely to lead to a catastrophic failure of the wing,
it would require constant and expensive monitoring and repair over
the aircraft's life.
The repair as described to the paper by the engineers is
extensive, and involves someone inside the wing of the
aircraft first relieving and then reinforcing the stress
points. They said the repair would need to be completed on the
non-flying test aircraft before proceeding on to the flight-test
models.
The delamination showed up during the maximum load test of the
wing, which the engineers said is 50 percent higher that is
expected in normal operation, though it is unknown if it began at
lower stresses and was masked by titanium components in the wing.
The repair will have to be monitored at every stress level during
subsequent tests.
The engineers told the Times that Boeing's focus now is on
repairing the current Dreamliners so testing can resume, and that
it has not been determined at what point in the production process
a permanent fix would be implemented.
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