POWER PLANT RELIABILITY ISSUES AND WEAR MONITORING IN AIRCRAFT PISTON ENGINES. PART I: ENGINE WEAR AND TBO REAL-TIME EXTENSION

This paper introduces a method to prepare an engine for very long flights without maintenance. It also gives criteria to estimate time between overhaul by using the sensor data to have an estimation of the engine condition. In-flight refueling has introduced new challenges to UAV (Unmanned Aerial Vehicle) propulsion systems. It is now possible to run continuously an UAV without landing for long periods. For this task, it is necessary to carry a quantity of lubricant sufficient for at least one month (approximately 800h). For extremely long flights, diesel piston engines are better than spark ignition ones due to extremely low fuel consumption. A selection in the assembly line individuates those engines that are suitable for long endurance flight. This is possible because automotive engines are manufactured in thousands per day and many quality controls take place in the assembly process. Moreover, mass produced automotive engines pass several tests during the assembly process including a very short run. The results of these tests are useful for an initial selection. Then, a 25-hour trial with a very thin lubricant is sufficient to forecast the oil consumption up to 1,000 hours. The 25 hours run corresponds to the time necessary to stabilize the oil consumption rate. In addition, during the 25 hours run also the electronic infancy failures are detected. In modern engines, the electronic on board diagnosis, the full redundancy of vital sensors, electronic control units and batteries/generators, make it possible to fly safely without emergencies with random electronic failures of components and wiring. Another major requirement is to forecast the engine failure or an unacceptable deterioration in terms of mechanical performance. This paper introduced a method to evaluate the state of wear of the engine starting from a digital monitoring system. A wear model of the engine based on the real duty cycle is proposed. It is then possible to prolong the life of the engine and to increase the time between overhaul. It is also possible schedule the overhaul operation