Interaction of Bootstrap Reservoir and Hydraulic Pump in Aircraft Hydraulic Systems

Abstract

This thesis focuses on studying system- and component-level phenomena in the fighter aircraft hydraulic power supply system in detail. The objective is to find out system-level root causes for premature failures of hydraulic pumps encountered in many modern fighter aircraft, and to study phenomena related to them. The thesis establishes a theoretically justified basis for understanding the interactions of the hydraulic system, bootstrap-type reservoir and axial piston hydraulic pump. It also presents a cost-effective and flexible method for studying system- and componentlevel phenomena in an aircraft hydraulic system by combining a theoretical approach with ground and laboratory testing.<br/><br/>The hydraulic pump and bootstrap reservoir are studied using computer simulations to find out how interactions in the system-level operation influence the internal loads of the pump. A hydraulic pump and bootstrap-type reservoir with pipework connecting them are modelled as analytical physical models. Other parts of the hydraulic system are modelled using empirical black box-type models. The models used are verified in the laboratory using a purpose-built test rig and field measurements made with a real aircraft. Root causes of failures and phenomena causing them are identified using simulations. On the basis of this, system and component design variables which affect these phenomena are determined. The results of the study prove that premature failures of the hydraulic pump encountered in certain types of high-performance fighter aircraft are related to hydraulic system design features and their service and maintenance practices. The thesis concludes with design recommendations for bootstrap-type reservoir and pump supply and drain lines.