Seung Self-Induced Fault of a Hydraulic Servo Valve

A Possible Cause for Hidden Malfunction of Aircraft's Systems
1. Auflage 2019
ISBN: 978-3-030-03523-5
Verlag: Springer International Publishing
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 74 Seiten

Reihe: SpringerBriefs in Applied Sciences and Technology

This report describes recent trouble-shooting results in aircraft engineering concerning a self-induced fault mechanism of a hydraulic servo-valve. It presents a possible root cause for past aircraft accidents and as such helps to avoid such malfunction and its fatal consequences in the future.

Dr.-Ing. Seung is an Aircraft Engineer with emphasis on Aerodynamics, Flight Mechanics, System Technology and Hydraulics. He is also a Public-Funding Manager for Aeronautics Research Programs of the German Federal Ministry for Economic Affairs and Energy.

Autoren/Hrsg.

Seung, Taehun

Inhaltsverzeichnis

1;Acknowledgements;6
2;Contents;7
3;Abbreviations;9
4;Introduction;10
4.1;Topics and Arrangement of This Report;12
5;1 Occurrence and Suspicion;13
5.1;1.1 Occasion for Investigation, Brief Description of the Occurrence;13
5.2;1.2 Appraisal and Fundamental Contemplation for a Pressure-Controlling Servo Valve;14
5.2.1;1.2.1 Design Shape/Working Principle of the Hydraulic Valve;14
5.2.2;1.2.2 Characteristic Diagram—Static and Dynamic Demanding and the Signal Answer;15
5.2.3;1.2.3 Significant Influence Factors and Fault Sources of a Servo Valve;18
5.2.3.1;1.2.3.1 Particle Contamination of the Fluid (—A Widespread Superstition);18
5.2.3.2;1.2.3.2 Robustness of the Torque Motor (First Stage);19
5.2.4;1.2.4 Fault Potentials and Parameters in the Spool and Sleeve Assembly (Second Stage);19
5.2.4.1;1.2.4.1 Dormant Fault Potentials Hidden in Design Shapes;19
5.2.4.1.1;Dimensional Tolerances at the Spool and Sleeve Assembly;19
5.2.4.1.2;Importance of the Balancing Grooves for Spool’s Working Ability;21
5.2.4.2;1.2.4.2 Significant Parametric Circumstances Whilst Operating;25
5.2.4.2.1;Changing of Actual Friction on the Sliding Surface Area Whilst Operating;25
5.2.4.2.2;Internal Leakage and Gap Tolerance as a Significant Influence Factor;25
5.2.4.2.3;Air/Temporary Vacuum in the Hydraulic Circuit;26
5.2.5;1.2.5 Fault Potentials/Possible Circumstances in a Solenoid Valve (First Stage);27
5.3;1.3 Existence of a Self-induced Fault of a Two-Stage Servo Valve—Hypothesis;29
6;2 Survey and Supposition;31
6.1;2.1 Experimental Investigation—Test Execution and Results;31
6.1.1;2.1.1 Test Set-Up and Test Method;31
6.1.2;2.1.2 Measurement Data Analysis and Interpretations;33
6.1.2.1;2.1.2.1 Abnormality in the Pressure Response and Interrelations;33
6.1.2.2;2.1.2.2 Stability of the Pressure Signal Answer and Mobility of the Spool;33
6.1.2.3;2.1.2.3 Switching-Off Dynamic of the Spool;36
6.1.2.4;2.1.2.4 Feedback Intensity in the Water Hammer Effect;43
6.1.2.5;2.1.2.5 Fluid Dumping Behaviour at the Control Circuit;44
6.1.2.6;2.1.2.6 Hegemony Loss of the First Stage, Completion of the Self-induction;50
6.1.2.7;2.1.2.7 Development of a New Drainage and the Loss of Command Ability;51
6.2;2.2 Reconstruction of the Entire Fault Working Mechanism—Interim Conclusion;52
7;3 Supplements and Inference;53
7.1;3.1 Additional Reflections/Supplementation of Contemplation;53
7.1.1;3.1.1 Basic Working Mechanism of a Spool and Sleeve Assembly/Homologous Model;53
7.1.1.1;3.1.1.1 Mobility of a Spool/Equilibrium at a Working Point;53
7.1.1.2;3.1.1.2 Confinement of the Spool’s Freedom Grade/Guided Sliding of the Spool;54
7.1.1.3;3.1.1.3 Equilibrium and Meta-Equilibrium in the Second Stage;55
7.1.2;3.1.2 Origin of the Fault/Interlock Mechanism;60
7.1.2.1;3.1.2.1 Order of the Fault Induction/Origin of the Fault;60
7.1.2.2;3.1.2.2 Self-stabilization of the Flapper/Interlock of the Entire Servo Valve;61
7.1.2.3;3.1.2.3 Danger of the Flow Separation on the Flapper Body and the Timing;61
7.1.3;3.1.3 Initializing, Propagation and Escalation of the Blemish/Reason for Blemish;64
7.1.3.1;3.1.3.1 Degradation/Collapsing of the Lubrication Film—‘Dry Friction’;64
7.1.3.2;3.1.3.2 Holistic Consideration Incl. The Reaction of the Control Loop;65
7.1.4;3.1.4 Arbitrariness of the Fault—Russian Roulette Effect;66
7.2;3.2 Conclusion and Summary;68
7.2.1;3.2.1 Conclusion;68
7.2.2;3.2.2 Summary;70
8;Epilog;71
9;References;74