A GVT (Ground Vibration Test) is a modal test conducted for the purpose of validating and improving a structural model describing the vibrating behavior of an airplane. The airplane structure is modeled in the tested configuration, including support system, fuel and payload mass properties, and with landing gear down. In the pre-test phase a test analysis model is used to assure that sensors and exciters are well located. In order to separate rigid modes from flexible modes, a soft support device was designed to lift the airplane above the floor on a soft air cushion, providing a free boundary condition in that way. The test strategy described here is to identify a linear 'small signal' model from multiple-input-multiple-output burst random frequency response functions (FRFs), and adjust it according to amplitude dependencies that are identified from selective stepped and 'swept' sine input testing. FRFs are measured using discrete stepped 'swept' sine at a few amplitudes, and a modal model is fit to these data. The backbones of individual modes are identified by fitting a linear SDOF model piece-wise to small sweeps for a few frequencies at each of many amplitudes. With increasing response amplitude, some mode frequencies drop, mode damping increase and most mode shapes are unaffected. Therefore, an important decision of the analyst is to select a nominal linear model to support the necessary predictions in the operating environment. The 'small-signal' model is validated by comparing its predicted modes with the modes identified by sine input testing. At least 20 modes correlate well.
Airplane ground vibration testing - Nominal modal model correlation
Grundschwingungsanalyse von Flugzeugen - Validierung eines linearen Strukturmodells
Sound and Vibration ; 36 , 11 ; 18-23
2002
6 Seiten, 23 Bilder, 25 Quellen
Article (Journal)
English
Airplane ground vibration test design method based on model driving
European Patent Office | 2025
|Testing device for ground turning performance of airplane
European Patent Office | 2023
|Results of Ground Vibration Tests on a YF-12 Airplane
NTIS | 1973
|