Analysis of an aircraft engine start-up process on the example of the PZL-130 TC-II „Orlik” training aircraft

The paper discloses the analysis of processes that take place during the start-up operation of the driving unit for the training aircraft of the TZL-130 TC-II Turbo-Orlik type. The aircraft is designed for selective and initial trainings at the Air Force School of “Little Eagles” in Dęblin. The driving unit comprises the PT6A-25C turbo-propeller engine from Pratt & Whitney combined with the four-bladed airscrew from Hatzell. It is specifically mentioned that data for the analysis were sourced from the S2-3a on-board recorder of flight parameters manufactured by the Air Force Institute of Technology (AFIT). The analysis was carried out both during ground and flight tests. The paper briefly outlines general structures and operation principles of typical start-up systems with the focus to their key components. Attention is paid to how important it is to select an appropriate start-up system to match the specific aircraft type and the guideline parameters for selection that should be adhered to are specified. Also there are disclosed the key mathematical relationships that are indispensable to design start-up systems and to find out their basic characteristics. It is emphasized that the start-up operation must be considered as a non-stationary process that lasts from the standstill state of the engine until the moment when the minimum required rpm is reached, sufficient to generate necessary power of the engine. In addition, the attention is paid to the fact that the value of the engine acceleration is crucial to the achievable start-up time that is deemed as one of key parameters for all start-up systems. It is demonstrated that to achieve the required level of acceleration, it is necessary to secure the so called overhead of the engine power which needs constant flow offuel and air into the combustion chamber of the engine. The last part of the paper comprises selected characteristic curves that were obtained from the analysis of the engine start-up processes both on ground and in flight. The final conclusions emphasize that the start-up system for the presented driving unit is really efficient and guarantees correct operation of the engine under any conditions.