Abstract
The article describes the vibration measurement technology used for light aircraft and some results obtained during the prototyping process. The aim of researches was to determine the resonant frequencies and natural modes of an aircraft or its selected structural components. Ground Vibration Testing is an essential dynamic structural test necessary to carry out before the aircraft certification. This test should be performed on the aircraft example which is predicted to test in flight. The measuring system used in the Institute of Aviation Technology of the Military University of Technology consists of a multi-channel LMS SCADAS analyzer, a set of piezoelectric accelerometers, two vibration exciters equipped with impedance heads and a computer with the Test.Lab Software. The aim of the article is to present the methodology of performing GVT tests. Using the equipment applied to an aircraft or its airframe component, key vibration characteristics corresponding to resonant points can be determined. Not only completed aircraft can be tested, but also its isolated fragments (wings, stabilizers, tail units) or just empty airframe. Testing separately supported components allows to examine their aeroelastic properties at early stage of prototyping. As examples of the use of vibration measurements in various stages of the prototyping process, three examples are presented herein. The isolated strut-braced wing from of the light reconnaissance aircraft OSA, the airframe of a light jet FLARIS LAR, and the light drone ATD JET-2 intended to be an aerial target for some anti-aircraft artillery sets. Some exemplary results obtained from testing these objects were presented. At the end, some observations and conclusions were noted in the context of usefulness of conducted researches.
Highlights
Aeroelastic phenomena may be divided according to the triangle scheme of aeroelasticity (Fig.1)
Static aeroelastic phenomena that exclude inertial forces are characterized by the unidirectional deformation of the structure, whereas dynamic aeroelastic phenomena that include inertial forces are typical in their oscillatory property of structure deformation
During the measurements the following characteristics and parameters are determined: - adapted harmonic excitation force distribution corresponding to the tuned form, - amplitude-frequency spectrum of sensor responses, - matrix of spectral transition functions (Frequency Response Functions), - resonant modes and frequencies of - determined according to the applied tuning criterion, - coefficients of generalized mass, stiffness and damping coefficients
Summary
Aeroelastic phenomena may be divided according to the triangle scheme of aeroelasticity (Fig.). The main objective of a Ground Vibration Testing is to experimentally determine the low-frequency modes of the whole aircraft structure for validating and improving its structural dynamic model as part of the flutter clearance process [1]. During the measurements the following characteristics and parameters are determined: - adapted harmonic excitation force distribution corresponding to the tuned form, - amplitude-frequency spectrum of sensor responses, - matrix of spectral transition functions (Frequency Response Functions), - resonant modes and frequencies of - determined according to the applied tuning criterion, - coefficients of generalized mass, stiffness and damping coefficients. Generalized coefficients refer to isolated resonance treated as vibrations of the model equivalent system with one degree of freedom. The experimental determination of at least one of the coefficients: guarantees the calculation of the other two
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