The Sensitivity of Landing Gear Flexibility onGround Manoeuvring Simulations

UNIVERSITA` DEGLI STUDI DI PISA

Facoltà di Ingegneria

Dipartimento di Ingegneria Aerospaziale

Corso di Laurea Specialistica in Ingegneria Aerospaziale

Tesi di Laurea

The Sensitivity of Landing Gear

Flexibility on

Ground Manoeuvring Simulations

Relatori

Candidato

Prof.

Ing.

Eugenio

Denti

Lorenzo

Toninelli

Ing. Leonardo Vivarelli

Abstract

The present work has been carried out during a 12 months Internship in the

Landing Gear Centre of Competence, Design Analysis Team (ELYD) within

Airbus Operations Ltd at Filton, UK.

One of the main activities of ELYD is to provide results to Program ATA32

Integrators and Chief Engineers (ATA Chapter numbers provide a common

referencing for all commercial aircraft documentation and ATA32 is the

chapter regarding the Landing Gear) concerning aircraft performances during

ground operations.

Currently rigid Landing Gear models are used to simulate dynamic ground

manoeuvres using the software MSC ADAMS/View.

The aim of this thesis is to investigate how flexibility in Landing Gear can

affect aircraft performances on ground operations.

Two different ways of representing flexibility have been considered during this

work: Beam model and mnf model.

The comparison against the beam model has been done on the A350XWB. The

comparison against the mnf model has been done on A320. This is due to

model availability within Airbus.

Simulations show little differences in terms of turning performances. Flexible

models give a more accurate load transfer to the airframe, however they require

a much higher simulation time.

Acknowledgments

I would like to thank Prof. Eugenio Denti from Dipartimento di Ingegneria

Aerospaziale, Universita’ di Pisa for letting me know about this great

opportunity, moreover thanks to support me and let me develop my thesis

within Airbus UK.

Thanks to all the Landing Gear Design Analysis Team for making me feel a

team member and not just the last arrived. I wish that everyone could be

involved in teamwork like this at least once in a lifetime.

Thanks to Terry Frost that has always the right advice at the right moment.

Thanks to Luke Bagnall that taught me a lot of valuable skill, the best one is

thinking outside the box, he is always challenging me with something new and

always showing me interesting points of view in solving engineering problems.

I would like to thank also Ryan Davies, James Morris and Francesco Riso

whose are always ready to help me whatever I asked.

A special thanks goes to Leonardo Vivarelli that helped me with the structure

of this dissertation.

I also thank all the people that I have met in Bristol, everyone left me

something.

Thanks to my family that always support and believe in me.

Thanks to my Italian friends that make me feel not so far from home.

Last but not least I would like to thank Sabrina for being always at my side

when I try to follow my dreams, even if it is not easy. This means a lot for me,

I will always be there for her.

Contents

ABSTRACT ... I

ACKNOWLEDGMENTS ... II

TABLE OF FIGURES ... VI

LIST OF TABLES ... X

INTRODUCTION ... 1

1. OVERVIEW ... 5

1.2 A350XWB Rigid-Flexible beam model comparison ... 7

1.3 A320 Rigid-Flexible mnf comparison... 12

2. LANDING GEAR RIGID MODEL ... 15

2.1 Main Landing Gear ... 15

2.2 Nose Landing Gear ... 16

2.3 Shock absorber ... 17

2.4 Tyres ... 20

3. A350XWB FLEXIBLE BEAM MODEL ... 28

4. FLEXIBLE MNF MODEL ... 32

4.1 A320 Flexible mnf Main Landing Gear ... 32

iii

4.2.1 Configuration 1 ... 35

4.2.2 Configuration 2 ... 36

4.2.3 Configuration 3 ... 38

4.3 A320 Flexible models evolution... 41

4.3.1 Configuration 4 ... 41

4.3.2 Configuration 5 ... 42

4.3.3 Configuration 6 ... 42

4.3.4 Configuration 7 ... 43

4.4 A320 semi-rigid model: Configuration 8 ... 45

5. A320 FLEXIBLE BEAM SLIDING ... 46

6. RESULTS ... 48

6.1 A350XWB ... 48

6.1.1 A350XWB Rigid model ... 48

6.1.2 A350XWB Flexible beam model ... 51

6.1.3 Results comparison ... 53 6.2 A320 ... 54 6.2.1 Rigid model ... 54 6.2.2 Configuration 1 ... 56 6.2.3 Configuration 2 ... 59 6.2.4 Configuration 3 ... 61 6.2.5 Configuration 4 ... 63 6.2.6 Configuration 5 ... 66 6.2.7 Configuration 6 ... 68 6.2.8 Configuration 7 ... 70 6.2.9 Configuration 8 ... 72

6.2.10 A320 Flexible beam sliding model... 73

6.2.11 Results comparison ... 74

7. CONCLUSIONS AND FURTHER DEVELOPMENTS ... 78

iv

BIBLIOGRAPHY ... 80

REFERENCES ... 80

APPENDIX A: FUNDAMENTAL OF MULTIBODY SIMULATION ... 81

APPENDIX B: CONSTITUTIVE EQUATIONS FOR BEAM MODEL IN

ADAMS ... 86

APPENDIX C: BACKGROUND OF FLEXIBLE BODIES IN ADAMS . 89

Table of Figures

Figure 0.1 - Modelling process ... 3

Figure 1.1 - U Turn manoeuvre ... 5

Figure 1.2 – How to measure Turning Radius and Turn Width ... 6

Figure 1.3 – Rigid model, simulation script ... 7

Figure 1.4 – Flexible models, simulation script ... 7

Figure 1.5 - Comparison between A350XWB-900 Rigid and Flexible models. ... 8

Figure 1.6 - A350XWB Flexible model setup ... 9

Figure 1.7 – Dialog box for selecting thrust, steering input ... 10

Figure 1.8 – Dialog box for selecting brakes input ... 10

Figure 1.9 – A320 Flexible model setup ... 12

Figure 1.10 – Comparison between A320 Rigid and Flexible models. ... 13

Figure 1.11 – Flexible .mnf model Torque calculation ... 14

Figure 2.1 - A350XWB-900 Wing Landing Gear ... 16

Figure 2.2 - Nose Landing Gear ... 17

Figure 2.3 – Shock absorber ... 18

Figure 2.4 – Design of a Michelin tyre[3] ... 20

Figure 2.5 - Tyre forces[2] ... 21

Figure 2.6 – Tyre forces in ADAMS ... 22

Figure 2.7 - Vertical force vs deflection tyre curves [3] ... 24

Figure 2.8 - Drag force curves [3] ... 25

vi

Figure 2.10 – Self Aligning Torque curves [3] ... 26

Figure 2.11 – Contact-Patch Tyre Axis System[2] ... 26

Figure 3.1 – A350XWB-900 Main Landing gear, flexible beam model ... 28

Figure 3.2 - Rigid bodies connected by beam element ... 29

Figure 3.3 - Beam element dialog box ... 29

Figure 3.4 - Flexible beam model, top main fitting joint ... 30

Figure 3.5 - Bushing dialog box ... 31

Figure 4.1 - Flexible .mnf parts ... 33

Figure 4.2 – A320 Left MLG, flexible mnf main landing gear constraints ... 33

Figure 4.3 - How to swap a rigid/flexible body ... 34

Figure 4.4 – Flexible mnf model overview, configuration 1 ... 36

Figure 4.5 – Right Landing Gear, configuration 2 ... 37

Figure 4.6 – Right Landing Gear, configuration 3 ... 38

Figure 4.7 – Asymmetric Tyre Side Forces during the initial straight phase ... 39

Figure 4.8 – Turn Width calibration, Left U-Turn ... 39

Figure 4.9 – Turn Width calibration, Right U-Turn ... 40

Figure 4.10 - Right Landing Gear, configuration 4 ... 41

Figure 4.11 - Right Landing Gear, configuration 5 ... 42

Figure 4.12 - Right landing gear, configuration 6 ... 43

Figure 4.13 - Flexible mnf model overview, configuration 7... 44

Figure 4.14 - A320 configuration 8 overview ... 45

vii

Figure 5.2 - Sliding Tube Drawing ... 47

Figure 6.1 - A350XWB-900 MLG Tyres numbering convention ... 48

Figure 6.2 - A350XWB-900 Rigid model: Turning Radius and Turn Width ... 49

Figure 6.3 - A350XWB-900 Rigid model: Tyre Side Forces; case 1 ... 50

Figure 6.4- A350XWB-900 Rigid model: Tyre Side Forces; case 6 ... 50

Figure 6.5 - A350XWB-900 Rigid model: Left and Right Landing Gears Torque ... 51

Figure 6.6 - A350XW-900 Turning Radius and Turn Width comparison ... 51

Figure 6.7 - A350XWB-900 Beam model: Tyre side forces, case 6 ... 52

Figure 6.8 – A350XWB: Tyre 1 Side Force comparison, case 6 ... 52

Figure 6.9 – A350XWB: Left Landing Gear Torque comparison, case 6 ... 53

Figure 6.10 - A320 MLG Tyres numbering convention ... 55

Figure 6.11 - A320 Rigid model: Turning Radius and Turn Width, Left turn ... 55

Figure 6.12 - A320 Rigid model: Tyre side forces, Left turn ... 55

Figure 6.13 - A320 Rigid model: Left and Right Landing Gears Torque, ... 56

Figure 6.14 - A320 configuration 1: Left and Right Turn Width comparison. ... 56

Figure 6.15 - A320 configuration 1: Tyre Side Forces, Left turn ... 57

Figure 6.16 - Tyre Side Forces Config 1 vs Rigid ... 57

Figure 6.17 - A320 Config 1: Left and Right U-Turn Tyre Side Forces ... 58

Figure 6.18 - A320 configuration 2: Left and Right Turn Width ... 59

Figure 6.19 - A320 configuration 2: Tyre side forces, Left turn ... 59

Figure 6.20 - A320 Tyre Side Forces config 2 vs config 1 ... 60

viii

Figure 6.22 - A320 configuration 3: Left and Right Turn Width ... 61

Figure 6.23 - A320 configuration 3: Tyre side forces, Left turn ... 62

Figure 6.24 - A320 Tyre Side Forces config 3 vs config 2 ... 62

Figure 6.25 - A320 configuration 3: Left and Right turn inboard Tyres Side Forces ... 63

Figure 6.26 - A320 configuration 4: Left and Right Turn Width ... 63

Figure 6.27 - A320 configuration 4: Tyre side forces, Left turn ... 64

Figure 6.28 - A320 Tyre Side Forces config 4 vs config 1 ... 64

Figure 6.29 - A320 configuration 4: Left and Right turn inboard Tyre side forces ... 65

Figure 6.30 - A320 configuration 5: Left and Right Turn Width ... 66

Figure 6.31 - A320 configuration 5: Tyre side forces, Left turn ... 67

Figure 6.32 - A320 Tyre Side Forces config 5 vs config 2 ... 67

Figure 6.33 - A320 configuration 5: Left and Right turn inboard Tyre Side Forces ... 68

Figure 6.34 - A320 configuration 6: Left and Right Turn Width ... 68

Figure 6.35 - A320 configuration 6: Tyre side forces, Left turn ... 69

Figure 6.36 - A320 Tyre Side Forces config 6 vs config 3 ... 69

Figure 6.37 - A320 configuration 6: Left and Right turn inboard Tyre Side Forces ... 70

Figure 6.38 - A320 configuration 7: Left and Right Turn Width ... 71

Figure 6.39 - A320 configuration 7: Tyre side forces, Left turn ... 71

Figure 6.40 - A320 configuration 7: Left and Right turn inboard Tyre Side Forces ... 72

Figure 6.41 - A320 configuration 8: Turning Radius and Turn Width... 72

Figure 6.42 - A320 configuration 8: Tyre side forces ... 73

ix

x

Figure 6.44- A320 Flexible Beam Sliding: Tyre side forces, Left turn ... 74 Figure 6.45 - A320 Turn Width vs configuration ... 74 Figure 6.46 - Turning Radius vs configuration ... 75 F



igure 6.47 - Right LG Tyre Side Forces vs configuration ... 77

List of Tables

Table 6.1 - A350WXB-900 results comparison ... 54

Introduction

The landing gear is one of the basic aircraft systems, which plays a dominant

role during ground manoeuvres. It is required to brake and steer the aircraft

according to manoeuvrability requirements. The structure must support the

aircraft weight and the landing and take-off loads the aircraft experiences. It

must provide a safe, comfortable ride for the passengers or cargo on board.

The design of an aircraft landing gear also has difficult maintenance and

fatigue requirements. It is one of the most exposed components when on

ground and must be designed to withstand the operational environment of an

aircraft runway.

The system must survive thousands of touchdowns over the aircraft lifecycle.

Hence, it is critical that the system can be easily maintained and checked to

ensure safety.

Simulation can be defined as the act of imitating some real life process or

system, building and developing a model that reflects its real life behaviour

using physics, mathematics and software tools. Modelling the aircraft landing

gear allows validating the system design and ensuring that the system meets all

technical requirements prior to being deployed on the real aircraft. These

models help to ensure the landing gear can be integrated effectively into the

final aircraft.

The Design Analysis team in the Landing Gear Centre of Competence (CoC) is

responsible for the simulation and modelling of Landing Gear systems on

many Airbus aircraft, currently including the A380 and the A350XWB.

It is a group of dynamic people that developed into a multi-disciplinary team

which covers a wide range of subjects: it has world-class skills from the design

of models to define and validate technical requirements, to the validation and

verification of the Landing Gear system design, using a wide range of

simulation techniques and analysis methods.

The Design Analysis team also delivers models to other Airbus teams to help

support the integration of Landing Gear systems. The team is split in four main

areas: Aircraft Systems, Avionics System, Physical Systems and Simulation

and Modelling [1].

Currently rigid landing gear models are used to simulate dynamic ground

manoeuvres using the software MSC ADAMS/View.

ADAMS is a family of interactive motion simulation software developed by

Mechanical Dynamics and is owned by MSC Software. It is a motion

simulation solution for analyzing the complex behaviour of mechanical

assemblies. ADAMS allows the user to test virtual prototypes and optimize

designs for performance, safety, and comfort, without having to build and test

numerous physical prototypes.

Core packages of the ADAMS family are ADAMS/View, ADAMS/Solver, and

ADAMS/PostProcessor. ADAMS/View is the graphical user interface of

ADAMS, which gives the user the opportunity to build the models from

scratch, or offers basic predesigned models in the library.

The ADAMS/Solver is provided in FORTRAN and in C-code and is the

numerical analysis application of ADAMS. It solves the equations of motion

for kinematic, static, quasi-static, and dynamic simulations.

ADAMS/PostProcessor supports the user in analysing the results of the

simulation [2].

The modelling is an important part of the engineering process; a model which

represents all system components in a very detailed way it is not necessarily

the best model. A high detailed model results in high computational time and

high complexity, which makes the analysis more costly. If the model is too

simple, important information could be missed. It is necessary to identify the

most important systems which have to be modelled, in order to capture the

model requirements. The goal is to build a simple and fast model that fulfils

analysis criteria.

2

The modelling process, illustrated in figure 0.1, starts with the identification of

the model requirements and it is an iterative process. The purpose of this

process is to build and test small elements or subsystems of the model before

building the entire model. It starts by building sets of components with low

level of detail. After the components are built they are tested to make sure that

there is no error in the model. The following review gives the input for the

improvements which were decided in the review. Once the model at this level

is adequate, the process starts again with a higher level of detail.

Figure 0.1 - Modelling process

The purpose of this thesis is to understand what are the benefits in taking

flexibility into account and how complex is to set up the flexible model for

ground manoeuvrability.

The flexibility has been taken into account initially with two different

approaches, one based on a flexible beam model for the Airbus A350XWB-900

and the other one based on a flexible .mnf model of the Airbus A320.

A third approach comes from a results review, it is a model composed by a

rigid main fitting and a flexible beam sliding tube.

The key parameters used to measure the added value of flexibility are:

1. Turning Radius

2. Turn Width

3. Tyre Side Forces

4. Torque between the main fitting and the strut

5. Computational time

In the first chapter there is an overview about the way flexibility effects have

been evaluated, the simulated scenario and which comparisons have been done.

In the second chapter there is a brief description about the current rigid model

and the assumptions done for building it.

The third and the fourth chapters describe the flexible beam model, and the

flexible .mnf model, how to integrate flexible parts in the existing ground

manoeuvrability models.

In the fifth chapter there is a description about the third approach, which comes

out merging the two previous models.

Results are included in the chapter six followed by conclusion and possible

further developments.

4

Theoretical background about multibody simulations, flexible beam theory and

flexible bodies’ background in ADAMS can be found in the appendixes.