CONDITION MONITORING DIAGNOSIS METHODS OF HELICOPTER UNITS

Preventive maintenance is a significant cost associated with the use of helicopters. Recent efforts have focused on changing maintenance from periodic inspection to condition-based systems. In the past, various methods of vibration analysis have been used to detect faults in helicopter gearboxes. In this paper time-series quadratic detectors are used to establish a basis of comparison for new quadratic techniques. A shaft-rotation-synchronised quadratic detector is analysed to determine the important detection frequencies. These frequencies are utilised in smaller quadratic detectors that provide near-perfect performance, yielding a significant improvement over time-series detectors of identical length. Detection using standard spectral maxima provides a comparison. In most cases, the detector analysis frequencies yield better results than the spectral maxima. The use of instantaneous frequency (IF) to determine the pressure of localised faults is also discussed. Instantaneous frequency provides an intuitive measure of the angular acceleration. Increases in the acceleration due to gear faults appear detectable in the IF of the gear-mesh frequency.