AIRCRAFT DEFECT IDENTIFICATION BY VIBRATION PARAMETERS IN OPERATION
The article considers the problem of identification of operational defects in the airframe and aircraft systems which can be detected by vibration parameters. These defects include, for example, a loss of structural integrity, looseness of unit attachment and gaps in joining points, backlashes in mechanical systems of force or movement transfer, increased coulomb friction in the deflecting surface supports, the resonant vibration modes of airframe components and systems. The existing methods of structure vibration inspection are based mainly on the fact that due to damages there appear changes in frequencies, forms and damping of mechanical system self-vibrations. To implement these methods, a linear design model of the initial system is constructed, and locations and values of arising damages are determined by changes in dynamic characteristics of the undamaged structure. Monitoring of these changes is usually based on the results of vibration tests of the objects of verification under ground-based conditions. Studies of the influence of defects on the aircraft dynamic response carried out in the present work helped to determine identification characteristics of typical defects to control them during operation. Thus, amplitude-frequency characteristics and power spectrum densities of random vibrations recorded by an acceleration sensor are identification signs of cracks and damages in structures, looseness of unit attachment and presence of gaps in joining points as well as the occurrence of vibration resonant modes of structural elements. It is proposed to use distortions of forced vibration portraits to identify control linkage backlashes and coulomb friction in the deflecting surfaces supports. Flight conditions in which operational defects can be identified are also revealed.