Forced to vibrate
A ground vibration test is an important milestone in the final stages before a new aircraft type is approved. Its purpose is to reveal
whether the first built sample of the aircraft will indeed behave in the way its engineers want it to and the simulation models predict.
So engineers engage in a series of experiments to determine the prototype’s actual vibration properties, hence permitting a mathe-
matical description of vibration responses and providing validation of the simulation models the engineers applied. In turn, these
validated models can deliver computational predictions of how the aircraft will respond in certain operating conditions, for instance
when encountering a wind gust, if the pilot initiates abrupt flight manoeuvres or under shock loads when the undercarriage touches
ground during landing.
The DLR Institute of Aeroelasticity in Göttingen is a world leader in the field of ground vibration tests. To meet the stringent
requirements of the contracting entity, in this case Airbus, with regard to test duration, deployment of human resources and test
equipment, the French Aerospace Lab ONERA requested DLR’s cooperation to put the A350 XWB through its paces. The engineers
installed 530 acceleration sensors throughout the machine to ensure precise detection of the complex, dynamic deformation.
Different states of vibration were deliberately induced at 25 points in the aircraft, while the 530 sensors
measured how the aircraft responded to stimulated vibration. With the results from the ground vibration test,
the experts reviewed the computational model of the A350 XWB. Subsequent aeroelastic analyses simulate
how the vibration characteristics will change across different flight conditions. Flutter analysis is used to
predict whether the surrounding flow field can induce vibration during flight. To get certification, it must be
demonstrated that the A350 XWB possesses a sufficient margin with respect to any critical ranges of induced
vibration (fluttering) across the entire flight envelope for which it was designed.
More information:
Image: AIRBUS S.A.S. 2013 – photo by e*m company / A. Doumenjou
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