Delayed 747-8 Set For Pre-Flight Shake Tests

Despite earlier this week announcing a delay to first flight of the 747-8 into early 2010, Boeing is pressing ahead with preparations for the start of the flight campaign and expects to conduct key ground vibration tests on RC501, the first 747-8, on Sunday Oct 11.

The vibration test involves shaking the entire airframe and is used to determine if the structure is susceptible to any unsuspected aeroelastic characteristics. The evaluation supports the run-up to flight test by assisting in flutter test planning. It is also used to detect structural flaws and troubleshoot flight control dynamic problems. GVT is therefore a fundamental building block toward clearance for first flight, and is expected to be particularly significant on the 747-8 with its stretched proportions and larger GEnx-2B turbofans.
The test comes after engineers last week checked the cable runs to the flight control surfaces and discovered some areas where they needed to be tightened. This work is also set to take place next week, after completion of the GVT.
Boeing says the delay to first flight from a target date in early December to a more likely date in January cropped up because the "build-up of tolerances between structure designed with older tools and the new design tools has caused fit-up issues that have been discovered and are being resolved in the final assembly process." The 'fit-up' issues are thought to have concerned areas such as the doors for the drop-down ram air turbine, an emergency hydraulic power system not used previously on the 747, as well as the Kreuger leading edge flaps on the new wing.

source: aviationweek.com