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Sealant Joints in Aircraft Integral Fuel Tanks Aerospace Engineering

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Sealant Joints in Aircraft Integral Fuel Tanks Aerospace Engineering a a Sealant Joints in Aircraft Integral Fuel Tanks João Pedro Róis Policarpo Thesis to obtain the Master of Science Degree in Aerospace Engineering Supervisor: Prof. Luís Filipe Galrão dos Reis Examination Committee Chairperson: Prof. Fernando José Parracho Lau Supervisor: Prof. Luís Filipe Galrão dos Reis Members of the Committee: Prof. Filipe Szolnoky Ramos Pinto Cunha Eng. Marco Frederico Espanhol November 2014 Acknowledgements I would like to express my gratitude to my Professor Luis Reis and my supervisor Engineer Marco Espanhol for their valuable advice, encouragement and availability throughout this research. I also would like to thank Engineers Carlos Rodrigues and Andreia Mendonça for their important input and time serving as well as valuable advice in performing experimental work. A special thanks to all my friends and teachers who directly or indirectly contributed towards this study. Above all, my sincere gratitude to my parents, family and my girlfriend for their encouragement, support, patience and love that arouses me each day to continue my investigation. i ii Abstract Leaks arising from aircraft fuel tanks have constantly represented a problem for aircraft manufacturers, operators and maintenance crews. The integral fuel tanks within aircraft structures are in general located within the wings and they rely on sealant materials to prevent leakage through joints and fasteners. However, aircraft integral fuel tanks are designed from a structural point of view first and as a fuel tank second. There are numerous potential leak paths for the fuel on these complex wing structures. The overall aim of the current research was to reduce the fuel leaks in the aircraft fuel tanks at the delivery. Following this approach a company background analysis was performed in order to find out the regions in the fuel tanks susceptible of fuel leaks. A Finite Element Analysis (FEA) of a critical structural member was done to investigate the structural behavior and propose structural improvements. A workcard with instructions to perform a nondestructive inspection (NDI) in the identified structural member was developed. A research and test of new sealants products was accomplished. The main goal was to initiate a research and test of potential sealants products in order to conduct a future proposal to the Lockheed Martin. A maintenance instructions manual was developed in respect to the procedure to inspect, clean and seal the fuel tanks. It was introduced simplified maintenance instructions to all the technicians in order to make possible an accurate sealing of the fuel tanks. Keywords: Aircraft, External Fuel Tank, Pylon Fitting, Structural Analysis, Sealants, Maintenance Instructions. iii iv Resumo As fugas provenientes dos tanques de combustível das aeronaves estão associadas a inúmeros problemas para os fabricantes, operadores e equipas de manutenção. Os tanques de combustível integrais compreendidos no interior da estrutura da aeronave são, geralmente, localizados no interior das asas e dependem de materiais selantes para evitar fugas através das articulações e elementos de ligação. No entanto, os tanques de combustível integrais são projectados primeiramente do ponto de vista estrutural e só depois como tanque de combustível, resultando assim em inúmeras possibilidades de fugas. O principal objectivo consistiu em reduzir as fugas de combustível nos tanques das aeronaves na fase de entrega. De forma a determinar as zonas dos tanques de combustível mais susceptíveis a fugas, efectuou-se uma análise ao histórico da empresa. Com base nesses resultados e de forma a investigar o comportamento estrutural e propor melhorias, foi realizada uma análise de elementos finitos (FEA) a um membro estrutural crítico. Foi também desenvolvida uma carta de inspecção com instruções para executar uma inspecção não destrutiva (NDI) no elemento identificado. Seguidamente realizou-se uma pesquisa e testes a novos selantes. Teve-se como objectivo iniciar uma investigação de potenciais produtos para propor futuramente à Lockheed Martin. Foi desenvolvido um manual de instruções de manutenção relativamente ao procedimento de inspecção, limpeza e selagem dos tanques de combustível. Nesse manual foram introduzidas instruções simplificadas de manutenção de forma a tornar possível uma selagem eficaz nos tanques de combustível. Palavras-chave: Aeronave, Tanque Combustível Externo, Pylon Fitting, Análise Estrutural, Selantes, Instruções de Manutenção. v vi List of contents Acknowledgements ...................................................................................................................................i Abstract.................................................................................................................................................... iii Resumo ....................................................................................................................................................v List of contents ....................................................................................................................................... vii List of Figures .......................................................................................................................................... xi List of Tables .......................................................................................................................................... xv Abbreviations, Acronyms and Nomenclature ....................................................................................... xvii 1. Introduction .................................................................................................................................... 1 1.1. Background .......................................................................................................................... 1 1.2. Purpose of Research Work ................................................................................................. 2 1.3. Aims and Objectives ............................................................................................................ 3 1.4. Thesis Structure................................................................................................................... 4 2. Literature Review .......................................................................................................................... 5 2.1. General Wing Design Considerations ................................................................................. 5 2.1.1. Structural Principles .................................................................................................... 5 2.1.2. Types of Structural Stress ........................................................................................... 5 2.1.3. Wing Construction ....................................................................................................... 6 2.1.4. Design Parameters ...................................................................................................... 7 2.2. Types of Fuel Tanks and Integral Fuel Tank Technology ................................................... 8 2.2.1. Types of Aircraft Fuel Tanks ....................................................................................... 8 2.2.2. Integral Fuel Tank Technology .................................................................................... 9 2.2.2.1. Principles ................................................................................................................. 9 2.2.2.2. Fuel ........................................................................................................................ 10 2.3. Theoretical Concepts concerning the Static Analysis ....................................................... 11 2.3.1. Introduction ................................................................................................................ 11 2.3.2. Stress Concentration Factor ..................................................................................... 11 2.3.3. Joint Failure Modes ................................................................................................... 12 2.3.3.1. Net Tension ........................................................................................................... 12 2.3.3.2. Tearing out ............................................................................................................ 13 vii 2.3.3.3. Bearing Failure ...................................................................................................... 13 2.3.3.4. Fastener Shear Failure .......................................................................................... 14 2.3.3.5. Transitional Failure ................................................................................................ 14 2.3.3.6. Requirements to Avoid Failure .............................................................................. 15 2.3.3.7. Correlation Method ................................................................................................ 16 3. Historical Analysis ....................................................................................................................... 17 3.1. Introduction ........................................................................................................................ 17 3.2. Presentation of the Lockheed C–130 ................................................................................ 17 3.2.1. Lockheed C–130 Specifications ...............................................................................
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