Diagnostic methods and tools for condition-based maintenance of aircraft drives

The helicopter ground-airborne health and usage monitoring system (HUMS) presented in the paper illustrates the basic methods of determining the technical condition of aircraft drives by a set of signals received in operation. These algorithms can be realized using the kinematic scheme of a rotor unit with information about the number of teeth in gears, the number of splines in spline connections, the design parameters of the bearings as well as the presence of synchronization signals that are recorded in parallel with vibration signals. The presented methodology for the estimation of vibration parameters of multi-shaft units takes into account the fluctuation of specific frequencies in the real operating conditions of the gearbox. Hardware requirements are formed on the basis of vibration models of gears and gearboxes. The operating frequency envelope of vibration sensors is to include specific frequencies of all gears, spline connections and rolling bearings. The dynamic range is determined based on the vibration activity of the gearbox and units in the places where the sensors are installed. The requirements to the equipment of data accumulation and pretreatment are presented and validated. A method of balancing helicopter classical and coaxial rotors is presented.  The method is based on the analysis of the effect of varying the values of the adjustment parameters of rotor blades (balance weight, assembly swash plate, tab angle) on the values of amplitudes of vibration harmonic components. The main goals of the support center concerning the technical condition of helicopter drives and its cooperation with the operator are stated.