Development and Evaluation of a Thermal Based Failure Detection Algorithm for Use on Aviation Powerplant Gearboxes
Many light aircraft powered by automotive engines are equipped with a propeller speed reduction unit (PSRU). Often geared units, PSRUs lower the engine output shaft speed to allow the propeller to function at its most efficient rotational speed. Many of these units have no observable indicator of mechanical health, but some have lubrication oil temperature monitoring installed. One such temperature monitored gearbox experienced shaft spline damage requiring the operator to replace major components. While no abnormal temperatures had been observed on the cockpit temperature readout, recorded flight data has been processed to determine if a significant temperature deviation between the damaged and undamaged conditions could be found. A model was developed to simulate the oil temperature of a healthy PSRU based on a variety of conditions, and the measured temperature of the damaged PSRU was then compared with the model. No meaningful difference between the flights was found. The normal condition flights exhibited a 14.9 degree C maximum difference between the measured temperature and the model, while the damaged condition flights exhibited a 14.2 degree C maximum difference. Average differences vary insignificantly, with the normal condition averaging a 0.961 degree C difference between the measured temperature and the model, and the damaged condition averaging -0.728 degrees C. It is concluded that unless a more accurate model can be developed and proven, alternate equipment monitoring methods are recommended. Keywords - Aviation Gearbox, Condition Monitoring, Engine Health, Temperature Prediction.