Experience of aircraft defects monitoring by vibration parameters

The problem of aircraft defects identification for the reason of changes induced by them in the dynamic characteristics of objects under control is being addressed. Such defects as a loss of structural integrity, attachments loosening and occurrence of gaps in joining places, backlashes in mechanical systems of forces or movements transfer, increased Coulomb friction in the deflecting surface supports, the resonant modes of vibrations of airframe components and systems, insufficient efficiency of hydraulic dampers as a part of the flexible airframe are considered. Monitoring can be realized at the level of qualitative or quantitative evaluation of one or more defects. The results of studies on the defects influence on the aircraft dynamic response allowed the defect identification characteristics determining. Thus, changes in the amplitude-frequency characteristics and the spectrum density of the random vibration power are the identification signs of cracks and damages, attachments loosening and presence of gaps in joining places, occurrence of resonant vibration modes of structural elements. It is proposed to use distortions of Lissajous figures and forced vibrations portraits to identify control circuit backlashes and dry friction in the deflecting surfaces supports. The research into the causes of the hydraulic dampers low efficiency was made using the nonlinear mathematical model of the aircraft controls, the parameters of which were determined by the dynamic tests results. An open spacecraft defects monitoring technique has been suggested, which contains three stages of research. At the first stage the exploratory tests are performed with the low intensity of vibrational loading and registration of the structure responses by accelerometers. At the second stage, according to the exploratory tests results a normalized safe loading mode is calculated. Tests upon this mode are conducted on the vibration testing machine and in the acoustic chamber. At the third stage the exploratory tests are repeated, the results of which are compared with the results of the first stage. By the vibration parameters deviations the defect location and nature are determined.