Chapter 1: Introduction ......................................... 1
1.1 Motivation: Landing Gear Conceptual Design for an
Unconventional Aircraft Configuration ...................... 1
1.2 Solution Proposal: An Integrated Multidisciplinary
Optimization Process for the Conceptual Design of the
Landing Gear System of an Unconventional Aircraft .......... 3
1.3 Contents of the Thesis ..................................... 4
Chapter 2: Current State-of-the-Art in Landing Gear System
Conceptual Design ............................................... 7
2.1 Introduction ............................................... 7
2.2 Aircraft Landing Gear System: Function, Requirements and
Configuration .............................................. 7
2.2.1 Landing Gear System Function and Requirements ....... 7
2.2.2 Landing Gear Configurations ......................... 8
2.2.3 Landing Gear Layout Constraints: Operational
Requirements ........................................ 9
2.3 Landing Gear Energy Absorption/Transfer Component: The
Shock Absorber ............................................ 11
2.4 Conventional Landing Gear Design Process .................. 13
2.5 State-of-the-Art in Landing Gear Conceptual Ground Loads
Determination ............................................. 15
2.5.1 Landing Loads ...................................... 16
2.5.2 Ground-Handling Loads .............................. 17
2.6 State-of-the-Art in Landing Gear Conceptual Weight
Estimation ................................................ 18
2.6.1 Empirical Approach ................................. 18
2.6.2 Analytical Approach ................................ 19
2.7 Landing Gear Ground Load Effect on the Aircraft
Structure: Conceptual Design Level Perspective ............ 21
2.8 Shortcoming of the Conventional Design Process
Capabilities .............................................. 22
2.8.1 Shortcomings of Landing Gear Ground Load
Determination ...................................... 22
2.8.2 Shortcomings of Landing Gear System Weight
Estimation ......................................... 23
2.9 Simulation in Landing Gear Design ......................... 24
Chapter 3: Fundamentals of Multi-Body Simulation and
Multidisciplinary Optimization ................................. 26
3.1 Multi-Body Simulation ..................................... 26
3.1.1 Overview ........................................... 26
3.1.2 Fundamentals of Multi-Body Simulation .............. 27
3.1.3 Multi-Body System Coordinates ...................... 29
3.1.4 Multi-Body Simulation Algorithms ................... 30
3.1.5 Numerical Integration .............................. 30
3.1.6 MBS in Aircraft Ground Dynamics .................... 31
3.1.7 Methods of Modelling Aerodynamic Effects in MBS .... 31
3.1.8 MBS Simulation Tool: SIMPACK®, a Brief
Description ........................................ 33
3.2 Multidisciplinary Optimization, MDO ....................... 35
3.2.1 Optimization Task Definition ....................... 35
3.2.2 Type of Optimization Design Level: Sizing, Shape
and Topology Optimization .......................... 36
3.2.3 Overview of Optimization Methods ................... 40
3.3 MDO Aspects Concerning Landing Gear System
Conceptual Design ......................................... 42
3.3.1 Selection of the Optimization Algorithm for the
Landing Gear Configuration Design Problem .......... 42
3.3.2 Process Efficiency Improvement: a Pragmatical
Approach ........................................... 44
3.4 Evolutionary Algorithm .................................... 44
3.4.1 The Principle ...................................... 44
3.4.2 Components of Evolutionary Algorithm ............... 45
Chapter 4: An Integrated Multidisciplinary Optimization
Process for the Conceptual Design of the Landing Gear System
of an Unconventional Aircraft .................................. 51
4.1 Conceptual Design of Landing Gear Systems: A New Design
Opportunity for the BWB ................................... 51
4.2 Solution Proposal ......................................... 52
4.3 Implemented Process Formulation ........................... 55
4.3.1 Process Diagram .................................... 55
4.3.2 Shock Absorber Parameter Database: a 'Two-Mass'
Model Application .................................. 56
4.3.3 Aircraft Structural Model Representation:
Alternatives and Selection ......................... 57
Chapter 5: Simulation Model .................................... 60
5.1 Introduction .............................................. 60
5.2 Aircraft Modeling for a Multi-Body Simulation ............. 60
5.2.1 Aircraft as a Multi-Body System .................... 60
5.2.2 Landing Scenarios .................................. 62
5.2.3 Landing Simulation and Aerodynamic Force Routines .. 62
5.3 Landing Gear Modeling for a Multi-Body Simulation ......... 64
5.3.1 Modeling of a Rigid Landing Gear Model ............. 64
5.3.2 Force Elements in the Landing Gear Model ........... 67
5.4 An Analytical Landing Gear Conceptual Design and Weight
Estimation ................................................ 69
5.4.1 Introduction ....................................... 69
5.4.2 Tool Capability and Limitation ..................... 70
5.4.3 Static Load Calculation ............................ 71
5.4.4 Ground Maneuver Stability Margin of Safety
Calculation and Landing Gear Length Design ......... 71
5.4.5 Tire Selection and Wheel Weight Calculation ........ 72
5.4.6 Dynamic Loads Calculation .......................... 73
5.4.7 Resolution of Ground Loads into the Structure ...... 75
5.4.8 Stress Analysis, Structural Sizing and Mass
Calculation ........................................ 76
5.5 Landing Gear Two-Mass Model: Generation of the Shock
Absorber Parameter Pre-Designed Database .................. 78
5.5.1 Introduction ....................................... 78
5.5.2 Shock Absorber Parameter Optimization .............. 78
5.6 Aircraft Landing Gear Bay Structure Modeling for
Conceptual Weight Estimation .............................. 83
5.6.1 Introduction: Review of the Current Proposal for
the BWB Structural Concepts ........................ 83
5.6.2 Implemented BWB Landing Gear Bay Conceptual FEM .... 85
Chapter 6: Applications and Results ............................ 89
6.1 Introduction .............................................. 89
6.2 Process Generation: Integration under an MDO Platform ..... 89
6.3 Validation of the Landing Gear Analytical Design Tool ..... 91
6.3.1 Landing Gear Component Weight Validation ........... 92
6.3.2 Landing Gear Component Structural Stability
Validation ......................................... 94
6.4 Validation of the Overall Landing Gear System Design
Process ................................................... 95
6.4.1 Verification Design Case: Conceptual Re-design of
the Future Mass Transport Aircraft Landing Gear .... 95
6.4.2 Verification Results ............................... 96
6.4.3 Discussion of Result ............................... 98
6.5 Process Application: Conceptual Design of the Landing
Gear System of a Blended Wing Body Aircraft ............... 99
6.5.1 Application Aircraft ............................... 99
6.5.2 MLG Position Topology: Results and Discussion of
Results ........................................... 103
6.5.3 MLG system Mass, MLG Bay (Aircraft Structure)
Mass and Total System Mass: Results and
Discussion of Results ............................. 108
6.5.4 MLG System Mass Trend: Results and Discussion of
Results ........................................... 111
6.5.5 Optimization Process Flow: Result and Discussion
of Result ......................................... 113
Chapter 7: Conclusion ......................................... 118
7.1 Summary .................................................. 118
7.2 Contributions ............................................ 119
7.2.1 A Proposal for the Number of MLG and the MLG
Location for the BWB .............................. 119
7.2.2 Conceptual Ground Loads Determination of the BWB .. 119
7.2.3 Main Landing Gear System Mass Prediction for the
BWB Aircraft ...................................... 119
7.2.4 Ground Loads Effects on the Blended Aircraft
Structure of the BWB Aircraft ..................... 120
7.3 Outlook .................................................. 120
Bibliography .................................................. 122
Appendix A: Aircraft Tire Database ............................ 127
Appendix B: Process Formulation Alternatives .................. 129
Appendix C: The Analytical Landing Gear Conceptual Design
Tool Input and Output ............................. 132
Appendix D: The Ground-Handling Loads Calculation ............. 134
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