EVERETT, Wash., Sept. 13, 2010 – Boeing [NYSE: BA] has begun fatigue testing on the structural airframe of the 787 Dreamliner at the Everett, Wash., site. Fatigue testing involves placing the 787 test airframe into a test rig that simulates multiple lifecycles to test how the airplane responds over time.
“Unlike static tests, where loads are applied to the airplane structure to simulate both normal operation and extreme flight conditions, fatigue testing is a much longer process that simulates up to three times the number of flight cycles an airplane is likely to experience during a lifetime of service," said Jim Ogonowski, structures vice president, Boeing Commercial Airplanes.
While the structural test program already has validated the strength of the airframe, fatigue testing looks at long-term, continued use. This is the natural progression of testing on a new airplane and part of the process to achieve U.S. Federal Aviation Administration certification.
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As he gazed at a 787 Dreamliner mounted in a metal cage and attached to hundreds of mechanical devices, Peter Brownlow recalled his childhood.
"Every kid's dream is to build something and then try to break it, right?," asked Brownlow, the fatigue testing conductor for the 787 program. "In essence, that's what we're doing. We take an airplane and we try to put it through its paces and try to break it at the end."
Brownlow and a team of engineers recently began an extensive program of twisting and tugging a 787 structural airframe. The ongoing punishment will simulate more than 100,000 flights.
Unlike static tests, which push the airplane to extreme loads to see how well it handles in once-in-a-lifetime emergencies, fatigue tests show how the structural integrity stands up to the day-in, day-out stresses that build up over thousands of flights spread out over decades.
"We're demonstrating the durability of the airplane," said Ray Clark, the 787 static and fatigue test director. "We're checking our structural maintenance procedures so we do them first on this airplane before an airline has to. And we validate that we do have inspection techniques where we can find any cyclical damage well before the fleet will experience it."
To simulate multiple flights, Boeing engineers direct mechanical devices to apply pressure to selected spots on the airframe's surface, from the leading edge of the wing to the tail fin to the fuselage.
"The devices impose loads typical of backing off the gate, taxiing out, taking off, climbing, cruise, experiencing a storm, descending, landing, taxiing back to the gate," said Clark. "So we mimic the ground-to-air-to-ground cycle of an airplane in service."
Since airlines will use the 787 on very different routes, stress analysts designed several flight profiles to recreate the range of conditions the airplane is likely to face over its lifetime.
The process continues seven days a week for three years as engineers push and pull on the control surfaces over and over again. When all is said and done, the airplane will have "flown" about three times the number of flight cycles a 787 is likely to face in its lifetime. It's part of the exhaustive program to certify the Dreamliner.
"It's certainly a long campaign," said Brownlow. "There's a lot of pride involved to be part of a program like this and to help usher it into the public and see people flying it safely." .
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