Boeing 787 Dreamliner - Mark Wagner [79]
For the full-scale tests, Boeing planned two airframes: a static test unit designated ZY997, and a fatigue airframe, ZY998. Although structurally complete, neither would ever fly, and both were doomed to a life of torture. In the case of ZY997, destined to be enclosed in a metallic prison made up of 1.5 million pounds of steel in the 40-23 Building, the static airframe would ultimately be flexed and stretched to destruction.
The static test airframe ZY997, enclosed within 1.5 million pounds of steel beams, was used initially to clear three preconditions needed for first flight, including a “high blow” overpressurization of the fuselage to 14.9 pounds per square inch, and dynamic actuation tests of the leading edge slats and trailing edge flaps. Mark Wagner
Although structurally complete, ZY997 did not incorporate simulated payloads or systems installations. The wings supported some representative control surfaces and high-lift devices, as well as engine pylons and weights, while a welded steel structure in the aft fuselage simulated the horizontal stabilizer. The static airframe was used to test eleven design-limit load conditions before the ultimate load testing, which was expected to see the wing bent upward by twenty-six feet. The airframe is pictured surrounded by towers and reaction fixtures, and was tested as a free-floating body with a ballasted load system to compensate for the deadweight. Mark Wagner
Pictured at Hamilton Sundstrand’s APSIF test facility, the company’s APUs APS5000 goes through its paces. The 787 APU was designed solely with the intent of generating electrical rather than pneumatic power and therefore did not have either a load compressor or a bleed system. Rated at 1,100shp and driving dual 225kVA generators through a large gearbox, the APU was started electrically using a starter/generator for the first time on October 31, 2005, at Hamilton Sundstrand’s power systems facility in San Diego, California. The APU used an electrical control system similar to that developed for the APS2300 used on the Embraer 170, and incorporated a single-stage centrifugal compressor with a pressure ratio in excess of 8:1, and a two-stage power turbine section. Hamilton Sundstrand
Static tests were designed to validate that internal and external stresses matched design predictions as well as to demonstrate the 787’s ultimate load capability. They included taking the airframe to the design limit load, the highest possible load expected to be experienced under extreme flight or ground conditions, without sustaining permanent structural deformation. Strain and stress test data also would be key to determining the growth potential of the structure for future versions of the 787, particularly the proposed “double-stretch” 787-10 variant.
Described by Harley as the “graduation event for the 787,” the static test program gradually ramped up in intensity. “We will test eleven conditions to design limit load, and then do the ultimate load testing when we expect a twenty-six-foot vertical displacement of the wing,” he said. Ultimate load tests took the structure to 150 percent max load or beyond, and was vital not only to determine the strength of the basic structure but also to discover if the airframe was overdesigned or had previously unknown areas of weakness.
The closer the final point of destruction came to 150 percent load, the better. During static tests on the 777, for example, the twinjet’s wing deflected twenty-four feet, reaching 154 percent maximum load point, before finally breaking with explosive force in January 1995. A final test to take the 787 wing to the point of failure was due at the completion of static work in 2009.
The static airframe was surrounded by towers and fixtures and raised to allow room