Ground Vibration Testing
The ground vibration test (GVT) system is necessary to assure the aeroelastic and aeroservoelastic stability of new and modified aircraft. These GVT data are used to validate analytical vibration and flight control models by measuring flight control transfer functions and structural frequency response functions. The GVT supports flight test activities by assisting in flutter test planning and resolving in-flight aeroelastic related anomalies. It is also used to detect structural flaws and troubleshoot flight control dynamic problems. The GVT system consists of state-of-the-art equipment including aircraft soft-support, structural excitation, vibration sensors, and data acquisition and analysis tools.
Soft-support systems are used to simulate the free-free (unconstrained) boundary conditions that an aircraft experiences during flight. Three soft-support systems are available to test aircraft ranging from small remotely piloted vehicles to aircraft weighing up to 45 metric tons (50 english tons). The F-18 High Alpha Research Vehicle (HARV) is shown mounted on a soft-support system.
Structural excitation is realized using up to 14 electrodynamic shakers. Four shakers provide peak forces of 670 N (150 lb), 8 provide peak forces of 220 N (50 lb), and 2 smaller shakers provide 44 N (10 lb) of force. Programmable signal generators provide a variety of random and deterministic waveforms.
Accelerometers are used to measure the response of the structure. More than 300 accelerometers are available to measure the response of a test vehicle adequately. High-temperature and noncontacting measurements can be done using laser vibrometers.
The computer-based data acquisition and analysis system is the heart of the GVT capability. It can acquire 200 channels of response data simultaneously and provides a large variety of data processing functions including parameter identification, spectral analysis, and test/analysis correlation. The system can generate finite element models and perform vibration dynamics analyses. It also has a sophisticated graphics display capability for visualizing static and animated information. The GVT system is networked to support correlation of analyses with other engineering disciplines.