Off-Highway Powertrain Services (OHP Services) was asked by an airship manufacturer to investigate problems on failure-prone motor drive shafts. In the context of a development project the dynamics of the propulsion and the root cause of the failures was to be studied. After an extensive exchange of information regarding the operational conditions OHP Services recommended an analysis of the torsional vibration behavior and the torque.
For the measurement three different shafts were applied with strain gauges in the OHP Services lab. The telemetry, used to transfer data from the rotating to the nonrotating measurement system, was mounted on site. The measurements were carried out on different operational points that can be associated with different movements of the airship. The preliminary works and the measurements were carried out and monitored by a certified vibration expert of OHP Services.
The data acquisition and analysis was done on a data logger, specially configured by OHP Services to measure the torsional vibrations and the torque with the necessary precision and sampling frequency.
From the measured data Campbell diagrams were calculated for the most relevant operational points. With the Campbell diagram, which shows the Eigen frequencies in relation to the speed, the certified specialist of OHP Services could investigate the resonances of the drive configuration in the different operating points.
The analysis of the data demonstrated that no resonances in the operating points occurred, so they could not be the root cause of the problems. Further investigation of the data showed that two of the three investigated shafts had peak loads caused by the driving motor. The customer was advised to take measures to eliminate the influence of the driving motor. These measures could be performed by OHP Services too.