Hydraulic pumps are among the most complex and responsible units from the point of view of aircraft flight safety. One of the most important scientific and technical problems in improving the reliability of hydraulic pumps is to understand the physical nature of the cause of damage in them and on this basis to develop measures and recommendations to ensure their reliability. The article discusses the characteristics of hydraulic piston pairs of hydraulic pumps according to the kinematics of their movement and load conditions. Selected actual damages of axial piston pumps are discussed. The paper presents a simplified 3D solid model of the cylinder-piston assembly and the mechanism for adjusting the inclination of the piston cylinder block, the axial hydraulic pump, and the model of breaking loads for selected elements of this pump. The digital solid model and element load analysis were developed in SolidWorks Simulation.

Methods of diagnosing technical condition of aircraft hydraulic systems have been analysed. Associated precision pairs of aircraft hydraulic systems have been presented. The most essential features of operating conditions and the loads that affect distributor components of sliding pairs have been identified. The structure of BU intensifier with a sliding distributor has been illustrated. Equation for internal leakages for a precision hydraulic pair with a concentric annular gap (clearance) has been presented. Illustrated and discussed are instances of examining internal leakages occurring in hydraulic systems (with direct methods applied). Findings of research into these issues have been presented as based on measurements taken on the hydraulic system of the Su-22 operated by the Air Force of the Republic of Poland. The technique of examining the problem consists in taking and recording measurements of the drop in pressure in the hydraulic system. The relationship between time of pressure-drop and total leakage for hydraulic systems of particular Su-22 aircraft has been illustrated. The results of research direct and indirect methods have been presented and analysed. Both methods have been compared from the aspect of assessing technical condition of the aircraft hydraulic system. Potential factors that could affect measurements with a given method have been identified.

Defects in an aircraft can be caused by design flaw, manufacturer flaw or wear and tear from use. Although inspections are performed on the airplane before and after flights, accidents still result from faulty equipment and malfunctioning components. Determining the causes of an aircraft accident is an outcome of a very laborious and often very long investigation process. According to the statistics, currently the human factor has the biggest share within the causal groups. Along with the development of aviation technology came a decline in the number of accidents caused by failures or malfunctions, though such still happen, especially considering aging aircraft. Discovering causes and factors behind an aircraft accident is of crucial significance from the perspective of improving aircraft operational safety. Effective prevention is the basic measure of raising the aircraft reliability level, and the safety-related guidelines must be developed based on verified facts, reliable analysis and logical conclusions. This article presents simulation tests carried out by finite element method and constitutive laboratory tests leading to the explanation of the direct cause of a military aircraft accident. Computer-based simulation methods are particularly useful when it comes to analysing the kinematics of mechanisms and potential stress concentration points. Using computer models enables analysing an individual element failure process, identifying their sequence and locating their primary failure source.

The article presents a methodology for the implementation of preliminary and state tests on the example of the project entitled “Jet air targets with a programmable flight route” conducted by the Air Force Institute of Technology. The experience in the field of maneuvering aerial targets has allowed for implementation of an aerial jet target set. The further stages of research necessary to implement the set for operation have been presented. Investigations of the aerial jet targets were carried out based on the regulations in force in the Polish Armed Forces.

Throughout previous practice, estimating the life of aviation hydraulic drive assemblies has been utilizing a variant, which requires conducting long-lasting studies of the drive assemblies until they move to the unfitness state. Such studies, which enable estimating life a posteriori, are costly and long-lasting. Hence the need to look for new strategies for estimating life. The article presents a method of estimating the durability of a hydraulic drive assembly based on the control of its change in technical condition. Inspection of the technical condition enables timely detection of the condition before the emergency hydraulic assembly. The novelty of the method is to use, to detect the condition before the emergency team, the principle of determining the pre-emptive control parameter tolerance. Pre-emptive tolerances are a set of control parameter values between threshold levels and pre-emergency (allowable) levels. The intensity of depletion of durability (intensity of aging, wear) is random. The paper presents a stochastic description of the control parameter change and the resulting empirical relationships between the control parameter verification time probability density (verification periodicity) and the control parameter value change probability density. The inter-relations between these two functions were described. It also presents empirical relationships enabling the determination of the permissible value for the control parameters and the periodicity of the control parameter checks after exceeding the limit value. An example of estimating the life of a hydraulic piston pump on-board an aircraft operated in the Polish Air Forces was shown. The permissible values and the time for the first control parameter verification after exceeding the limit value were determined for selected control parameters of the hydraulic pump. The proposed method binds life (fitness time) with the physical wear mechanisms concerning the assemblies. It can be applied in work aimed at determining the resource life of technical equipment. Furthermore, it enables utilizing technical equipment according to a technical state strategy with monitoring the parameters.