Aircraft Component Computer Design And Analysis

School of Mechanical Engineering

Aerospace Technology

Project 2

Landing Gear Component Design

By

Chong Chern Hao Francis (S10026545H)

Chiang Teck Chuan (S10026825E)

T3T2

For

Mr Peter Liang

School of Mechanical Engineering

4th February 2008

Design and Development of Aero-Components and Processes

Landing Gear Component Design – Project 2

Ngee Ann Polytechnic – Aerospace Technology 2

CONTENT

1. Introduction……………………………………………………………………………………. 3

2. Development of Landing Gear………………………………………………………………… 5

3. Objective………………………………………………………………………………………. 9

3.1 Analysis Criteria

3.2 Undercarriage Loadings

4. Materials……………………………………………………………………………………….. 10

4.1 Aluminum Alloys

4.2 Titanium Alloys

4.3 Magnesium

4.4 Aluminium Bronze

4.5 Beryllium

4.6 Composite

4.7 Steel

4.8 Selection of Material 300M

5. Manufacturing Process………………………………………………………………………... 16

5.1 Manufacturing Methods

6. Design Drawing……………………………………………………………………………….. 27

6.1 Schematic Drawing

6.2 3D Model

7. Design Considerations………………………………………………………………………… 29

7.1Mesh Design

7.2 Constraints

8. Case Study 1…………………………………………………………………………………… 31

8.1 FEM Analysis

8.2 Safety Factor 1.5

9. Case Study 2…………………………………………………………………………………… 38

9.1 FEM Analysis


10. Case Study 3…………………………………………………………………………………. 48

10.1 FEM Analysis


11. Modification…………………………………………………………………………………. 58

12. Conclusion…………………………………………………………………………………… 59

13. Photographs…………………………………………………………………………………. 60

14. References…………………………………………………………………………………… 62




1. INTRODUCTION

Development of the landing gear design has progressed in all areas after the War World II:

the threshold of general acceptance for the tire design is now radials after moving through

many of the designing stages; developing of better materials for the brake system which

include beryllium and carbon; the controls of the skid control system had been converted to

fiber-optic; Accessible of super-high-strength steels and stress-corrosion-resistance aluminum

alloys coupled with better understanding of the intricacies of highly efficient shock

absorption allow major improvement of detail design of the landing gear.

Landing gear designers are faced with the problems of keeping pace with the aircraft designs

as the form of engineering was getting more sophisticated in the last 30 years or so. A

satisfactory compromise had to be reached between the sometimes conflicting demands of

structures engineers, aerodynamicists, runway designers, and operational personnel. Weight

of the transport aircraft had also increased dramatically – the Boeing 747 is more than twice

as heavy as the 707-320C and nearly 28 times as heavy as the DC-3. Therefore, in order to

fulfill the requirement given by the airframe designers and aerodynamicists, they had to

create a design with minimum effect on the basic airframe structure and aircraft drag.

Moreover, they also had to ensure that the high-density operations of the heavy aircraft does

not break or damage airport’s runways during landing.

Landing gears could be classified on the basis of whether they are retractable or not

retractable landing gear was developed to eliminate as much as possible, the drag caused by

the exposure of the landing gear to the airflow during flight. A landing gear would be

designed to be retractable if the additional weight and cost involved in designing it to be

retractable offsets the drag penalty in having it extended into the air stream.

Therefore a landing gear is designed to be retractable if it is a highspeed aircraft where the

drag penalty in having the gears exposed is substantial. On smaller and low speed aircraft

however it may not be economical to have a retracting system and therefore they are made

fixed with provision for streamlining the airflow around the gears to reduce the drag imposed

by having them projected in to the air stream.

A generally used means of reducing the drag on fixed landing gears is to contain the wheels

in what is called wheel pants shown in the diagram. Fixed landing gear may have bracing or

it may be of the cantilever type without any additional bracing.

Retractable landing gears are designed to be retracted in different directions depending on

whether it is the nose gear or the main gear and also on the type of aircraft. On some

airplanes the retraction is towards the rear and on others it is inwards toward the fuselage and

on still others it folds outward. toward the wing tips. Usually nose gears are retracted along

the length of the aircraft either forward or rearward.




The retraction extension system is normally accomplished with hydraulic or electrical power.

In addition to the normal operating system an emergency system is provided to ensure that

the gears can be extended in case of a main system failure.

Emergency systems may consist of a back up actuating system of either stored gas or

accumulator pressure that can be directed into the actuating cylinders or a mechanical system

that can be operated manually or a free fall gravity systems.

The landing gear of an airplane serves a number of very important functions. Some of these

functions are:

It supports the airplane during ground operations

Dampers vibrations when the airplane is being taxied or towed

Cushions the landing shocks

Provides a mounting surface for the brakes

Allows the execution of ground manoeuvres such as taxing, steering, towing and

parking etc

Takes up loads during cross wind landing/ take-off

The main landing gear buildup assembly is made from the major component parts that follow:

The oleo component assembly and the truck beam assembly

The wheel and tire assemblies

The brakes and the truck positioner actuator

The main gear steering actuator and the main gear retract actuator

The drag brace and the side brace

The hydraulic tubing and the electrical wiring

Other than essential intermediary between the aeroplane and catastrophe elements listed

above, these following items are also included in the landing gear design:

Tail bumpers

Arresting hooks

Jacking, mooring, and towing attachments

Landing gear doors and their operating equipment

Layouts to show ground clearance at various aircraft attitudes and with varying

degrees of strut/tire inflation

Calculations to show compatibility with airfield surface




2. DEVELOPMENT OF LANDING GEAR

Similar to the designing of the aircraft itself, before the establishment of a formal contract,

the concepts of the landing gear had to be first prepared. A need for a new or modified

aircraft will be determined by the marketing organizations. The results are gathering through

market surveys, discussions with potential customers, or close attention to deliberations being

made by various airlines or military organisations. The basic requirement will then be

established after discussion between the marketing and preliminary design department. This

is follow by preparations for basic concepts.

Maintenance of the complete documentation is extremely important throughout the whole

designing process. The very minimum of each aircraft configuration should at least consist of

a listing of its assumed weights and geometric data in the landing gear files– and attached to

it is the summary of the basic essentials of the gear by the designers. The configuration

and/or the complexity or distinctiveness of the landing gear involved will affect the depth of

the summary.

In the concept formulation phase, the main focus is to determine the location of the landing

gear on the airframe, the number and the size of the wheels. The former is, at this time, a

function of center-of-gravity location and general structural arrangement. The weight of the

aircraft, braking requirement and flotation requirement (if specified) will determine the

number and the size of the wheels.

In the project definition phase, the preliminary design activity begins to focus on the detail as

well as analysis of the design as the general configuration has been decided. At the end of this

phase, proposal preparation usually takes place and as much detail and credibility must be

provided. Able to sell the product is the main objective of the proposal so it should convince

the customer that proposed aircraft design is able to meet his requirement and overcome all

other competitor’s product. This explain the need for detail and analysis as it is able prevent

argument regarding it’s capability.

Certain design changes may be requested by the customer at this point which may be due to

influence of a competitor’s proposal and this will directly affect the cost, weight and

performance of the landing gear if it were being implemented.

Illustrated below is a picture of the summary of the preliminary design activity. The second

picture shows the post contractual design activity through Critical Design Review.




The following tasks are to be performed before the Critical Design Review (CDR):

Tire and wheel selection or design is concluded, load/speed/time data revised, and

vendors established.

Brake energy requirements are updated, vendors selected, and the design finalized.

Shock absorber details and support structure are sized to be compatible with the

revised loads.

Electrical and hydraulic power requirements are defined for retraction, extension, and

steering.

Flotation analyses are updated again to reflect changes in loading on the landing gear.

Installation and space envelope drawings are prepared to facilitate determination of

stowed landing gear clearances and to provide appropriate information to the airframe

designers.

Tests and models may be used in this phase to acquire confidence in the proposed

design, to gain a better understanding of problem areas, to display complex

kinematics, and to evaluate the locking mechanisms.

The entire design is then documented for presentation at the CDR.

Before the first flight, various tests are being carried out. Failure Modes and Effects Analysis

(FMEA) is one of the many conducted. This analysis is essential as it could assess if any

failure would occur in any parts in the overall landing gear system and what effects it had on

the aircraft. The timings for this analysis are usually made such that any changes in the

design would not affect the schedule of the first flight as some deficiencies may be uncover

by the analysis.

In the last 2 decades, in

acknowledgement for the growing

demand for increased readiness of

mission as well as improved

economics, it became a must for

reliability and maintainability

analysis to be carried out. Therefore,

emphasis on life cycle costs and

durability had been increased.

Methods and measures had also been

improved to minimize maintenance

man-hours required per flight hour.




3. OBJECTIVE

In this project, we are required to reverse engineer a design based on a physical landing gear

component, the inner cylinder shock strut, starting with taking direct measurements on the

physical part and transferring these measurements into physical drawings with the use of

ProEngineer. We will have to apply their knowledge of manufacturing processes, engineering

design, strength of materials, design for failure prevention, basic principles for creating shape

and size, and the guidelines for material selection, in the process of completing this project.

3.1 Analysis Criteria

The main requirement is to ensure that the design has a factor of safety of 1.5from

YIELDING failure. The challenge is to keep the factor of safety as close as possible to the

requirement so as not to over-design or under-design. To do this, students must perform stress

analysis using NASTRAN 4D to ensure the maximum loading condition on their component

does not exceed the design limit.

3.2 Undercarriage Loadings

A number of different loads had been created by the undercarriage and the structure which

the undercarriages is attracted to must be able to carry all the loads. Forces that can be a few

times the weight of the aircraft are created during landing and the kinetic energy is absorbed

by the main undercarriages. At the point when wheel come in contact with the ground, the

velocity of the wheels had to match the ground velocity therefore resulting in a load in the

opposite direction. If cross winds are experienced during landing, the aircraft may side slip

and generate side loads. During landing and taxiing the nose-wheel can also experience high

shock loads. However, the loads experienced during taxiing are smaller but due to the

unevenness of the ground, the loads generated will vary. Even when the undercarriage is

retracted during flight, loads is still generated on its mounting as there had weight and inertia.

The undercarriage can be loaded in quite a number of different ways. The simplest form of

load is a concentrated force which result from the weight of an object times the acceleration

due to gravity. Tension or compression depending on the direction is generated when a force

is applied to the side of a piece of structure. Bending moment which will cause the structure

to bend is generated when a force is applied at right angle to a piece of structure. Finally,

torsion or twisting of the structure is generated when a force is offset from the line of a beam.

This brings us to an important point, equilibrium. Equilibrium is “the state in which all forces

and moments are exactly in balance”. Newton’s Third Law says that “for every action there

is an equal and opposite reaction. For every force or moment acting on a structure, there is

another force or moment holding the structure steady”.




Any structure subjected to stress will also experience strain since it is impossible to separate

this two. Each form of load will need a different type of structure to carry it most efficiently.

For tensile loads, the area of materials under stress is the only critical factor. Therefore, it is

the cross-section area instead the shape of the cross-section which affect the magnitude of the

stress. For compressive loads, it is similar except that the structure will bend away from the

line of action if the applied load.

4. MATERIALS

A high strength to weight ratio materials must be used in the construction of the structural

areas for the landing gear. Other than high strength to weight ratio, stiffness is equally

important for the materials and there are other factors to be considered as well:

The properties of the materials used must be consistent and predictable. However,

there will be slight different in the basic properties so an appropriate factor of safety

should be implemented (1.5 for aerospace industry) during the designing process.

This ensures that the material properties will not be worse than the specified

properties.

It should be ideally have the same properties in all parts and in all directions, although

the way a particular material is processed may mean this is not possible.

It should be non-flammable or of low flammability. It should present no other safety

hazard, such as toxicity, in use, manufacture or repair.

It should be readily available and at reasonable cost, and should be suitable for

manufacturing using standard processes. Where a material’s properties are

particularly useful, new processes can sometimes be devised to make its use more

practical.

It should not be highly susceptible to fatigue, or must be used at stress levels low

enough to ensure an acceptable life.

It must have good stiffness for a given weight.

It must retain adequate strength at the temperatures to which it will be subjected,

particularly with materials used in certain regions of the aircraft.




4.1 Aluminum Alloys

Reviewing the commonly used materials, 7079-T6 should not be used in the extruded, forged,

or plate form. Until a few years old, 7075-T6 was widely used because of its higher strength;

however, it is very subject to stress corrosion and has been replaced by 7075-T73. This is

virtually immune to stress corrosion immunity of 7075-T73. Other materials that are often

used are 7049-T43 and 7050-T736.

Advantages of aluminum alloys:

High strength-to-weight ratio

A wide range of different alloys, to suit a range of different uses

Low density, so greater bulk for same weight means they can be used in a greater

thickness than denser materials, and thus are less prone to local buckling

Available in many standard forms

Aluminum alloys are easy to work after simple heat treatment

Can be super-plastically formed

Disadvantages of aluminum alloys:

Prone to corrosion, so need protective finishes

Many alloys have limited strength, especially at elevated temperatures

No fatigue limit

4.2 Titanium Alloys

Alloy Ti-6Al-6V-2Sn can be used effectively where tube buckling or stiffness is significant.

Increase, wall thickness can be provided using this alloy, without increasing weight, and it

does not require corrosion protection. The minimum design ultimate strength in the solution

heat treat and age (STA) condition is 170 ksi (150 ksi in the annealed condition). The

advantages of this material are a high strength/weight ratio, high un-notched fatigue

strength/density, and elongation. However, the cost of the material is relatively high.

Advantages of titanium alloys

High strength-to-weight ratio

Maintains its strength at high temperatures

Higher melting point and lower thermal expansion than other materials

Can be super-plastically formed and diffusion bonded

Very high resistance to corrosion, especially from salt water




Disadvantages of titanium alloys

Expensive

Can be difficult to work, especially machining

Poor electrical and magnetic screening

Very had scale forms on the surface at high temperatures

4.3 Magnesium

Magnesium used to be used for some aircraft wheels, but it is now generally regarded as an

unacceptable material for landing gear usage. The causes for this rejection are the fire hazard

and its susceptibility to corrosion.

4.4 Aluminium Bronze

This is a widely used and extremely satisfactory material for supper and lower shock strut

bearings.

4.5 Beryllium

Beryllium is widely used as a brake heat sink material, and as a brushing material. It has a

higher bearing stress than aluminium bronze, but care must be taken in the design to insure

that sharp steel edges do not impinge upon beryllium-copper flange corners. Such an

impingement has caused the flanges to crack.

4.6 Composites

Composites material is spreading rapidly. They offer weight savings, but their cost is

relatively high. Boron-epoxy was used for the A-37B main landing gear parts, including the

outer cylinder, piston, side braces, and torque arms. Weight savings were 2-40% depending

upon the component. Tests showed that filament-wound composites were reliable and

sustained the required loads. They also showed that further work was required in these areas:

fabrication of thick-walled parts, development of suitable liners and coatings for hydraulic

cylinders, and analysis and design of attachments and joints.




4.7 Steel

The most common landing gear steels are 4130, 4340, 4330V, and 300M. where stiffness for

minimum cost is important, 4310 is used. For maximum strength/weight ratio 4340 and

300M are used, the former primarily in the 260-280 ksi range and the latter in the 280 – 300

ksi range. In the last few years, 300M has been used with great success for such items as

bogies, pistons, braces, and links. It has about the same fatigue properties as 4340, excellent

ductility at very high strength; also, because the material can be interrupted quenched,

distortion due to heat treat is greatly reduced. The maximum section size appropriate to heat-

treated 300M (280 ksi) is approximately twice the size at which 4340 can attain 260 ksi.

Although air-melt material has been widely used, vacuum-melt material should be used in all

high-heat-treat applications.

Advantages of steel alloys:

Cheap and readily available

Consistent strength

Wide range of properties available by suitable choice of alloy and heat treatment

High strength useful where space is limited

Some stainless steels are highly resistant to corrosion

High-tensile steels have high strength-to-weight ratio

Hard surface is resistant to wear

Suitable for use at higher temperatures than light alloys

Most steels easily joined by welding

Very good electrical and magnetic screening

Shows a fatigue limit

Disadvantages of steel alloys:

Poor strength-to-weight ratio except high tensile alloys

Dense, so care must be taken not to use very thin sections, or buckling may result

Most steels very prone to corrosion




4.8 Selection of Material 300M

Our group has selected 300M as the material for our component based on the criteria stated

above. As 300M has a lot of variant, our group have decided to use a variant manufacture by

Latrobe Specialty Steel Company (www.latrobesteel.com). Below provide some basic

properties and information of the steel we selected.

LESCALLOY 300M-HS VAC-ARC steel is a modified 4340 steel with added silicon allowing

for use of a higher tempering temperature. The steel has high hardenability and strength with

good ductility and toughness in heavy sections, which make it suitable for aircraft landing

gear, flap tracks, and other structural components. This variant has been developed for

applications requiring 287 ksi (1979 MPa) minimum tensile strength through stringent

control of chemistry and processing parameters. The enhanced properties of Lescalloy

300M-HS VAC-ARC permit the design of lighter aircraft components that exhibit equivalent

load carrying capacities compared to standard 300M components. Vacuum arc remelting

(VAR) is used to provide optimum cleanliness and preferred ingot structure.

– adapted from http:www.matweb.com

Typical Composition

Carbon Chromium Vanadium Manganese Molybdenum Nickel Silicon

0.42 0.80 0.07 0.75 0.40 1.80 1.65

Physical Properties

Density: 7.84g/cm3

Thermal Conductivity: 37.49 W/mK

Specific Heat: 448 J/KgK

Mean Coefficient of Thermal Expansion (-17.8 – 93°C): 11.34 x 10-6

mm/mm°C

Mechanical Properties

Ultimate Tensile Strength: 2055 MPa

Yield Strength: 1731 MPa

Modulus of Elasticity: 205 GPa

Poissons Ratio: 0.28

Shear Modulus: 80.0 GPa

http://www.latrobesteel.com/




Machinability

Machining is best accomplished with the alloy in the normalized or normalized and tempered

condition. Final machining to finish tolerances is done by grinding with care due the hardness

of the heat treated alloy (Rockwell C 55). It is important to do a stress relief anneal at 550 F

after finish grinding.

Forming

Formability by conventional methods is good in the annealed condition. The alloy behaves

much like AISI 4340 steel.

Welding

300M can be welded by fusion methods or by flash resistance welding. Approved procedures

must be used for fusion welding, including pre and post-heating practice, because the alloy

will air harden due to heat input from welding. Following welding it is essential to re-

normalize or re-normalize and temper prior to the final hardening heat treatment.

Heat Treatment

300M must be normalized at 1700 F before hardening. After the normalizing treatment the

alloy is hardened by heating to 1600 F and oil quenching. Tempering is then done last.

Cold Working

In the annealed or normalized condition the alloy has good ductility and can be readily cold

worked by conventional methods.

Annealing

Anneal at 1550 F and slow furnace cool at a rate of less than 50 F per hour down to 600 F.

From there it may be air cooled.

Tempering

Temper at 600 F to give a nominal 300 ksi strength




5. MANUFACTURING PROCESS

Physical and mechanical properties together with shaping the engineering materials into

useful components in an economical and timely manner will determine its overall valve. The

performance of the components will be affect without the necessary shape, and without

economical production, the material selection should be further refined by considering the

possible fabrication processes and the suitability of each “prescreened” material to each

process.

It is necessary for the designer to be familiar with various manufacturing alternative and had

knowledge of the associated limitations, economics, product quality, and surface finish,

precision and so on. The types of materials used will influence the types of processes used for

manufacturing. Before performing certain fabrication processes, it is necessary to compare

the distinct ranges of product size, shape and thickness of the process with the requirement of

the product. Each process has its characteristic precision and surface finish. Secondary

operations such as machining, grinding, and polishing can add costs to the manufacturing

process since it require the handling, positioning, and processing of individual parts.

Therefore, it is good when there are few secondary operations in the whole manufacturing

process. In addition, there are still many other overhead costs such as production rate,

production volume, desired level of automation, and the amount of labor required, especially

if it is skilled labor which will directly affect the cost of fabricating the product. Constraints

may also be implemented which will affect the design of the components so that it will be

able to suit the requirement of existing equipment or facilities.

Geometric details of a component design such as the presence of cored holes, the magnitude

of draft allowances, or the recommended surface finish can obstruct certain process.

Therefore, designer had to communicate properly with manufacturing experts before

implementing this features. Change in design should be made when appropriate to make

manufacturing process more simple.

After some research, we discovered that the materials normally used for manufacturing

landing gears are 6061-T6 aluminum alloy and 300M steel. Between these two materials, we

decided to go with 300M as the choice for the inner cylinder shock strut. The reason are the

strength of aluminum alloys are much lower than steel and it is way too expensive to use

titanium alloys for landing gears.




5.1 Manufacturing Methods

Available to us are a wide range of manufacturing processes and each of these process are

suitable for producing a specific kinds of structure and often influence the materials selected.

Material forming and joining are 2 main types of process which make up most manufacturing.

However, not all of the products required both types of process and both of the processes can

be combined in some forms of manufacturing.

Many methods are available to form metals:

Bending, pressing, rolling and drawing

Casting

Forging

Extrusion

Machining

Heat treatment

Surface finish

Paint work

Machining, forging, heat treatment, surface finish and painting are the process we are looking

into as our component is manufactured using 300M steel.

Forging

Forging is the process in which heat is applied on the metal and applying suitable

compressive force to shape the metal by plastic deformation. Power hammer or press is

usually used to deliver the compressive force.

The grain structure can be refines at and physical properties of the metal improved after

forging is performed. With proper design, the orientation of the grain flow can be in the

direction of the principal stress encountered during use. Grain flow is the direction of the

pattern that the crystals take during plastic deformation. Comparing a forged metal to a base

metal, the physical properties of the forged metal are better as the crystals of the base metal

are randomly oriented.

No porosity, voids, inclusions and other defects will be present after forgings as the process is

consistent from piece to piece. Therefore no voids will be exposed by finishing operations as

there are none in the first place. Little preparations is needed for coating operations due to a

good surface.




In the design of aircraft frame members, forgings yield parts are often used due to its high

strength to weight ratio.

Machining

In manufacturing, the most important process is machining. The definition of machining is

the removal of materials from a work-piece in the form of chips. For metallic materials, the

term used is call metal cutting. Low set-up costs are involved for most machining compared

to forming, molding and casting processes. However, it is more expensive to machine high

volumes of work-piece. When tight tolerances on dimensions and finishes are needed,

machining is used to achieve it.

The Machining section is divided into the following categories:

Drilling: Turning:




Milling: Grinding:

Chip Formation:




We will be focusing on milling only for our component.

Milling is as fundamental as drilling among powered metal cutting processes.

The accuracy of milling is less than turning or grinding as its set up had many degrees of

freedom. However, it can be improved with the implementation of rigid fixture.

As expected from such a general process, there are a range variety of milling tools. For the

tools shown below, the term “end mill” is used. Horizontal and vertical surface can be cut

using these tools and they are the most common type of milling cutters.

Below are illustrated two types of solid milling arbor cutters.




Illustrated below is the detailed nomenclature for a solid milling arbor cutter.

To hold the work piece and allow for easy release, the collet of a mill is critical. Illustrated

below are three types of collets and a cut-away of a collet.




Standard Collet Fixture

Illustrated below is the configuration of a standard endmill fixtured in a knee-type milling

machine using a collet.




Horizontal Collet Fixture

Illustrated below is the configuration that allows flats to be cut at specified angles on a

cylindrical part. The collet had to be fixed horizontally for this purpose.

Boring Bar Milling Fixture

Illustrated below is the boring head for fixing a boring bar tool on a mill. The accuracy of

using a mill for boring a hole is not as less than when it is on a lathe, which is dedicated to

machining solids of revolution.




Fly Cutter Fixture

Illustrated below is the fixture for a fly cutter. To carry out milling to flatten a surface rapidly,

fly cutters are used. Often, fly cut marks will be left behind on metal stock after being milled

to shape.

Slitting Saw Fixture

Using a slittering saw for milling deep, narrow grooves is better than an endmill. Illustrated

below is a slitting saw with an angle head. For the same application, using a endmill is too

dangerous as it is long and thin.




Heat Treatments

The properties of 300M may be altered by heat and it is common in many of the processes

employed in forming and joining materials involve heating. Therefore, heat treatment is

normally performed after any process involving heating so that the correct strength and

fatigue properties can retain by the 300M steel. Wide variety of properties for the steel alloy

can be achieved by different states of heat treatment.

The definition of heat treatment is to alter the physical and/or mechanical properties if metals

with controlled heating and cooling without changing the product shape. In manufacturing,

heat treatment is sometimes performed unintentionally due to process that required heating or

cooling such as welding or forming.

Increasing the strength of materials is often associated with heat treatment. However, certain

manufacturability objectives such as improving machining and formability, restore ductility

after a cold working operation can also be achieved with heat treatment.

Steel is very responsive to heat and the quantity of steels used for commercial purpose

exceeds many other materials, therefore are particularly suitable for heat treatment.

Under the term “annealing”, there are many heat treatment operations. . These maybe

employed to reduce strength or hardness, remove residual stresses, improve toughness,

restore ductility, refine grain size, reduce segregation, or alter the electrical or magnetic

properties of the 300M inner cylinder shock strut. The materials being treated and the

objectives of the treatment determine the temperature, cooling rate, and specified details of

the process.

Surface Treatments

The processes of surface treatments, more formally surface engineering, tailor the surfaces of

engineering materials to

control friction and wear,

improve corrosion resistance,

change physical property, e.g., conductivity, resistivity, and reflection,

alter dimension,

vary appearance, e.g., color and roughness,

reduced cost.




Ultimately, improvement can be made in the functions and/or service lives of the materials

For our component, hardening is the only purpose of performing surface treatment. The

hardness of steel are commonly increase by shot peening. The dimensions of the steel will not

change significantly using this hardening treatment. The depth of hardening can have a wide

range of variety from 250Jm to the whole section depth. Rapid cooling of the materials is

required and to achieve this for large work-piece will be difficult. Therefore the section must

be thin, usually less that 25 mm to achieve hardening of the whole depth of the section. For

this reason, only the surface can be hardened for most large section work-piece.

Alloy Steel AISI 4340 is another term used for 300M steel.

Materials Hardness (RC)

Cast Iron

class 30 45 - 55

class 45 55 - 62

ductile 80-60-03 55 - 62

Carbon Steel

AISI 1025 - 1030 40 - 45

AISI 1035 - 1040 45 - 50

AISI 1045 52 - 55

AISI 1050 55 - 61

AISI 1145 52 - 55

AISI 1060 60 - 63

Tool Steel

AISI O1 58 - 60

AISI S1 50 - 55

AISI P20 45 - 50

Alloy Steel

AISI 3140 50 - 60

AISI 4140 50 - 60

AISI 4340 54 - 60

AISI 6145 54 - 62

AISI 52100 58 - 62

Recently, the discovery of “low plasticity burnishing” process for 300M steel allow

significant progress for mitigation of stress corrosion cracks and fatigue damage in high

strength steels. This new process is comparable to the conventional shot peening in term of

results.




From test conducted, persistent compressive residual stresses are imparted in 300M steel

surface using low plasticity burnishing. This tested steel show signs of being able to

withstand fatigue, foreign object damage and stress corrosion cracks more effectively.

It is predicted that the steel used for manufacturing aircraft components can be more durable

follow continued research efforts.

Greater depth and stability as well as higher performance than conventional shot peening are

some advantage of low plasticity burnishing. Low plasticity burnishing can be performed

together with the manufacturing process thus able to eliminate the time and costs for

performing conventional shot peening in other locations/sections

6. DESIGN DRAWING

With the physical inner cylinder shock strut handled over to our group, measurements of the

structure were taken as accurately as possible. Due to the structure’s complexities, problem

arises as few dimensions seemed to be unobtainable with the tools available. Thus,

simplifying assumptions are required in order to obtain a manageable solution to the problem

of determining these dimensions. At the same time, our group had also ensured that these

simplifying assumptions are considered carefully over and not result in reflecting the

performance of the real inner cylinder shock strut.

6.1 Schematic Drawing

Below show the schematic drawing of the inner cylinder shock strut.




6.2 3D Model

Below show the 3D model of the inner cylinder shock strut in the Nistran 4D.

Front View of Inner Cylinder Shock Strut

Back View of Inner Cylinder Shock Strut

Wheel Installed

Towing Lugs

Fixed End of Axle

Inner Cylinder Piston

Axle Head of Inner Cylinder

Shock Strut




7. DESIGN CONSIDERATIONS

7.1 Mesh Design

After completing the physical modelling of the component with the aid of ProEngineer, it is

essential to put the structure through vigorous testing with safety limit and ultimate loads.

The safety limit is added in order to comply with the airworthiness requirements. Due to the

complexion of the inner cylinder shock strut, just with the use of Strength of Material Theory

alone is not accurate enough to evaluate stress experience by the component. Thus, Nastran

4D software was used to carry out FEM analyses in order to obtain accurate results of

displacement and the critical stress points.

For Nastran 4D to carry out investigation of the inner cylinder in the case study of this report,

the structure was being break down smaller and simpler pieces call finite elements connected

with each other at nodes. The assembly of the elements and nodes is call finite element model.

The smaller the number of mesh size chosen for the structure, the more the number of finite

elements in the structure.

The quality of the solution increased with smaller mesh size chosen for the structure.

However, the computing time will increase as more calculation is needed to solve for the

solution.

Therefore, we had decided on a mesh size of 3 with the refinement option selected so that the

result achieved is of certain quality without too much computing time spent.

Mesh Design for Landing Gear Inner Cylinder Shock Strut




7.2 Constraints

As shown in the picture, we have two critical constraints applied on the component. The first

which is at the bottom of the tube full X, Y and Z , which Nastran4D will interpret as that

whole area being unable to move at all and that all movement will be relative to that point.

This point is chosen because in reality the movement of this particular point is restricted by

the movement of the hydraulic fluid by the orifice from the inner cylinder to the outer

cylinder, in order to give the damping effect of the landing shock impact.

The second constraint is added at the lug as shown in the picture. This would be a more

realistic example as from our research that portion is a torsion link connection point to the

outer cylinder to help in operation on the ground, to maintain stability, and to prevent the

inner cylinder and outer cylinder from turning out of its aligned position. We had both Z and

radial constrained for these two areas.

Constraint Applied for Inner Cylinder Shock Strut




8. CASE STUDY 1

We shall start out the stress analysis with the most fundamental one where the aircraft is in it

stationary position or parking. When designing an aircraft, the Maximum Take-Off Weight is

a very important parameter as this will affect the design of the landing gear. Landing gear

cannot be over-designed as the weight penalty will be too significant.

In stationary, we could determine the maximum deformation of the axle in the y-axis which is

fully caused by the weight of the aircraft. In the landing gear system, the weight of the

aircraft, which is a single downward force at the Centre of Gravity, will be translated into a

rotary pressure force around the axle where it contacts the wheel.

However, in this analyse, we did not include hydraulic pressure acting on the inner cylinder

wall as the pressure is at the minimum and will not cause failure of the inner cylinder shock

strut component as long as the maximum weight do not exceed and provided the component

is in good condition. No doubt, the inner cylinder must have sufficient buckling resistant due

to the length and the enormous weight acting on it.

8.1 FEM Analysis

To simulate this, pressure forces 5.5 x 108 Pa were applied at the four locations on the axle

where the wheel bearing contacts and while the component is fully constraint in x, y, and z

axes directions and z-radial direction.

Constraint and Force Applied




From the FEM analysis in Figure above, both the top and bottom of the axle experiences

equivalent stresses of 5 x 108 Pa to 7 x 10

8 Pa represented by cyan shades region and green

shades region overlapping, and yellow and red shades regions concentrating at the connection

point of the axle and the head of the inner cylinder shock strut, and the inner portion of the

axle.

Stresses are experienced on the top and bottom of piston due to a tensile and compressive

effect produced by the weight of the aircraft. Also, from background knowledge, one of the

causes to stress concentrations is where a solid and hollow part connects together. In addition,

the axle connection point to the head experiences the greatest bending moment at the fixed

point. Hence, it could be concluded that the connection regions is the main contributing factor

to experiencing a maximum von Mises value of 1.15 x 109 Pa.

Stress Contour Plot w/o Safety Factor




Front View of Stress Contour Plot with deformation




Side View of Stress Contour Plot with Deformation




With deformations shown in FEM analysis, significant bending deformation occurred on the

axle, as shown clearly in figure above. This matches our initial assumption as there is a

upward bending on the axle as the weight is acting downwards at the centre of the inner

cylinder, then translate to the axle and finally the wheel. With reference from Figure of the

front view, it explained the tensile and compressive effects it has on the top and bottom of the

axle due to the downwards force, weight, acting in a single y-axis direction. At the same time

as bending force is overcome by the component, it provides a solution in determining the

piston’s bending strength before yielding takes place.

Stress Contour Plot with Deformation





In order to ensure safe and reliable operations, a safety factor of 1.5 must be applied to the

prescribed limit load for all foreseeable operating conditions. This is in accordance to the

mandatory requirement for design safety factor as stated in JAR 25 Subpart C – JAR 25.303.

To simulate this, pressure forces 3.53 x 108 Pa were applied at the four locations on the axle

where the wheel bearing contacts and while the component is fully constraint in x, y, and z

axes directions and z-radial direction. The design stress was reduced before as compared

above due to the additional of the safety factor 1.5.

Stress Contour Plot with Safety Factor 1.5




The FEM analysis in above with safety factor 1.5 produces a matching result as the one

without safety factor imposed in terms of deformation pattern and locations of stress regions

occurring on the axle.

In the previous study without safety factor, stresses experienced on axles are of 5 x 108 Pa to

7 x 108 Pa. However, since a safety factor of 1.5 is now taken into consideration, stresses

experienced are now reduced to a smaller value of 3.45 x 108 Pa to 4.83 x 10

8 Pa. It also

meant that deformations are less severe as shown in above.

In general, a smaller maximum von Mises value of 1.15 x 109 Pa is experienced compared to

the maximum von Mises value in the previous study without safety factor.

Front View of Stress Contour Plot with Deformation




9. CASE STUDY 2

The next study we will be a critical condition of an aircraft landing gear component on the

ground occurs when taxiing where the forward force is greater than the backward force in

order to overcome the ground friction. In this case, we could also study the speedy rolling

(approximately 250 knots) effect on the landing component right after the first contact of the

gear with the runway and applying brake at the full force.

Take note that in this analyse, the forward force is greater than the backward force which is

suited for the taxiing condition. In the event of braking the backward force will be greater

than the forward force in order to overcome the momentum effect of the landing speed and

the mass of the aircraft.

However, in this analyse, we did not include hydraulic pressure acting on the inner cylinder

wall as the pressure is at the minimum and will not cause failure of the inner cylinder shock

strut component as long as the maximum weight do not exceed and provided the component

is in good condition. No doubt, the inner cylinder must have sufficient buckling resistant due

to the length and the enormous weight acting on it. The impact for the hydraulic pressure will

be study in the latter case.

Also, in this analysis, the steering effect is not taken into consideration.

To simulate this, the component is fully constraint in x, y, and z axes directions and z-radial

direction and the stress analysis will be broken into two parts and then combine into one. In

reality, the axle will experience a torsion force and a greater axial force in one direction,

which is forward in our study, due to the translating of the frictional force up to the axle axis.

However, our group had decided to only add in direction force (which is the bigger force)

rather than two forces in different direction with one bigger and the other smaller in order to

reduce the complexity of the analyse. In fact, if the bigger direction force did not fracture the

material, the small force will not fracture the material. Thus, this analysis will determine the

bigger forward force.

Firstly, the pure maximum torsion force and the pure maximum forward force are determined

separately.




9.1 FEM Analysis

The maximum torsion valve is 8.87 x 10 6 Nmm.

Constraint and Torsion Applied




The maximum forward force is 4.2 x 107 Pa.

When combining the two forces together, we have to fix one of the smaller forces and reduce

the other one in order to determine the combine forces. Thus, torsion force of 8.87 x 10 6

Nmm and a axial force of 2.88 x 107

Pa is applied, as shown in the picture, in order to

simulate the maximum taxiing speed or braking force this particular inner cylinder shock

strut can withstand.

Constraint and Forward Force Applied




Combination of Torsion and Forward Force Applied





Side View of Stress Contour Plot




From the FEM analysis in Figure above, stresses from 4 x 108 Pa to 6 x 10

8 Pa are more or

less evenly distributed represented by cyan shades region, except for the joints at the head of

the inner cylinder strut as shown in Figure above.

From the above figures as shown, slight yellow shades region overlapping the green shades

region stresses from 8 x 108 Pa to 1.1 x 10

9 Pa make up the critical stress points of the whole

inner cylinder strut. These critical stresses developed are mainly due to compression and

tension effect as mentioned in Case Study 1 upon stationary. In addition, torsion effect can be

seems in the figure above where the critical stress is in the axle where the torsion is acting

within the axle due to the translation of friction force from ground to the axle.

Out of these three critical points, it could thus be concluded that the inner of the axle

experienced the most stress, resulting in a maximum von Mises stress value of 1.73 x 109 Pa.

Critical Point at the Inner of the Axle

Critical Points at the Fixed Ends of the Axle




With deformations shown in FEM analysis, deformations occurred on the axle as shown in

the figures under this section. The compression and tension effect in the x-axis had naturally

resulted in a bending on the axle due to the frictional force and the momentum of the aircraft

while moving. There is also expansion and shrinking effect of the thickness of the axles due

to torsion force.

The deformations matches our assumption as the analysis shows that the fixed end of both

axles and the inner part of the axles are experiencing higher stress than other points/parts of

the inner cylinder shock strut. Thus, with higher stresses also meant that both the axles will

experience bending in the x direction. The thickness of the axles is very important due to the

additional torsion force which will cause twisting and complication to the existing axial force.

As a result, it will provide a solution in determining the critical points on the inner cylinder

strut operating in reality.









After applying the safety factor 1.5, the design limit stress is 1.91 x 107 Pa for pressure acting

on the axle and 5.91 x 106 Nmm for the torque acting on the axle.








In the previous study without safety factor, stresses experienced on axle are of 8 x 108 Pa to

1.1 x 109 Pa. However, since a safety factor of 1.5 is now taken into consideration, stresses

experienced are now reduced to a smaller value of 5.52 x 108 Pa to 7.59 x 10

8 Pa. it also

meant that deformations are less severe as shown in above.

In general, a smaller maximum von Mises value of 1.15 x 109 Pa is experienced compared to

the maximum von Mises value in the previous study without safety factor.





10. CASE STUDY 3

In case 3, we will be studying the loads transmitted between the contact surface of the ground

and the rotary pressure force around the axle where it contacts the wheel during the landing

of the aircraft on the runway. In this situation, we included the hydraulic pressure acting on

the inner cylinder wall as the impact of the landing is absorbed by the hydraulic structure.

However, the landing gear structure must still be able to withstand part of the loads.

To simulate this, pressure forces were applied at the four locations on the axle where the

wheel bearing contacts and while the component is fully constraint in x, y, and z axes

directions and z-radial direction. In addition, pressure forces were applied at all locations of

the inner cylinder wall.

Firstly, the pure maximum pressure force on the axle and the pure maximum hydraulic

pressure force are determined separately.

The maximum pressure force on the axe is 5.5 x 108 Pa.

Constraint and Force on the Axle Applied




Constraint and Hydraulic Force Applied




The maximum hydraulic force is 1.21 x 108

Pa.

When combining the two forces together, we have to fix one of the smaller forces and reduce

the other one in order to determine the combine forces. Thus, hydraulic pressure of 1.21 x 108

Pa and pressure force on the axe of 1.41 x 108 Pa is applied, as shown in the picture, in order

to simulate the maximum landing force this particular inner cylinder shock strut can

withstand.

Combination of Force on the Axle and Hydraulic Force Applied





Side View of Stress Contour Plot




Inner Wall View of Stress Contour Plot




From the FEM analysis in Figure above, stresses from 2 x 108 Pa to 4 x 10

8 Pa are more or

less evenly distributed represented by cyan shades region along the axle of the landing gear.

For the FEM analysis of the inner cylinder piston, stresses from 4 x 108 Pa to 5 x 10

8 Pa are

more or less evenly distributed along the piston’s surface. This evenly distribution pressure is

mainly due to the cylinder allowing a direct load path without any obstruction. This can

prevent bending occurring at any one point as it was the objection of the designer to produce

a uniform stress distribution.

However, one critical point can be identified from the analysis. This critical point is located

on the upper part of the inner cylinder piston where the key seat in the key slot. This is

properly due to the thinner cross-section area compared to the other area on the piston and

resulted in a much higher concentration of stress. The maximum von Mises stress is 1.5 x 109

at that point.

When the key is inserted into the key slot properly, it will reduce the stress concentration in

that area dramatically and provide a uniform stress distribution along the entire piston.

With deformations shown in FEM analysis, bending occurred on the axle and the piston as

shown in the figures under this section. When the aircraft land, large amount of the force is

absorbed by the hydraulic structure in the inner cylinder and this resulted in high pressure

acting on the inner cylinder wall causing the inner cylinder to expand. Furthermore, the high

pressure in turn resulted in a compression and tension effect on the piston causing it to bend.

The compression and tension effect in the y-axis had naturally resulted in a bending on the

axle due the weight of the aircraft and the landing force occurring in contact with the ground.

The deformations matches our assumption as the analysis shows that the bending occurred at

fixed end of both axle and the lower part of the inner cylinder piston.

Critical Point on the Piston at the Key Slot





Inner Wall View of Stress Contour Plot with Deformation








The new design limit stress, for safety factor 1.5, is hydraulic pressure of 8.07 x 107

Pa and

pressure force on the axe of 8.66 x 107 Pa.








In the previous study without safety factor, stresses experienced are of 2 x 108 Pa to 4 x 10

8

Pa on the axle and 4 x 108 Pa to 5 x 10

8 Pa on the inner cylinder piston. However, since a

safety factor of 1.5 is now taken into consideration, stresses experienced are now reduced to a

smaller value of 1.38 x 108 Pa to 2.76 x 10

8 Pa on the axle and 2.76 x 10

8 Pa to 3.45 x 10

8 on

the inner cylinder piston, it also meant that deformations are less severe as shown in above.





11. MODIFICATIONS

Modifying existing aerospace components especially critical components, like inner cylinder

shock strut, is virtually impossible. As weight is a very important factor in aircraft design

consideration and if the product has being successfully launch, the product should be at its

optimized performance.

For our component, inner cylinder shock strut, lazy materials have been removed till it

maximum based on the performance needed. For example the axle of our component has

different diameter at various places and the partial portion of the axle is made hollow. The

head of the inner cylinder shock strut have also holes and weird curvatures.

If a further modification is needed, the most possible modification is the change of the core

material of the component. With new development of existing or new material, the

performance of the component can be enhanced in term mechanical and performance

properties like strength to weight ratio and stress corrosion, shorter manufacturing time, or

cost.

The next possible modification is a further reduction of weight of the inner cylinder shock

strut through hollowing the whole axle if the performance of the new design still permits

the existing flight conditions. As seems in some other type of inner cylinder shock strut, the

axle is hollowing, definitely with certain thickness to withstand the shearing and bending

stresses. Another possible method to this modification is to have the axle separated from

the inner cylinder shock strut as compared to one structure. As the axle is experiencing

much greater stress than the inner cylinder and with the separated axle and inner cylinder,

the axle and the inner cylinder can be manufactured of different materials. Thus the axle

could be made of stronger material which might be heavy and the weight will be

compensated by the cylinder which is made of weaker material that might be lighter.

However this might cause difficulty in maintenance jobs.

The last possible modification is the removal of the key for the locking of the bearing on the

axle. With the key and key slot, it induces unnecessary stresses and problems in term of

performance and maintenances. A small component like a key will tend to fracture first. The

contacting surfaces of the key to the key slot must be perfect, if not stress will not be

uniform. Thus changing the method of locking the bearing to the axle is suggested.




12. CONCLUSION

In this project, our basic sciences and computational skills from mathematics are being taxed

on when predicting the critical zone of the inner cylinder shock strut when carrying out the

analysis on Nastran 4D. Nastran 4D allows us to predict the performance or behavior of the

design and reinforce the critical zone to prevent re-formula a whole design from scratch

which time consuming.

In modern times, the designers of aircrafts can preview the strain developed on their design

with the use of FEM analysis. The designer can simulate their design in Nastran 4D, and get

the prediction result in a short period of time and verify with the calculated stresses done by

the design engineers. This would help in reducing the times and costs of the design process as

they do not had to construct prototypes to test out the accuracy of their calculation of stresses.

This will greatly reduce the time for a landing gear component development. As a designer,

there are many things to be taken into consideration before a component can be manufactured

and be introduced to the market. In the design phase, there has to be mission requirement,

that’s leads to conceptual design and then preliminary design. Then the preliminary design

undergoes several computational simulations.

Technology like the CNC machine has also assist design engineers to have a preview of the

process of how the products and components would be manufactured. To allow effective and

efficient manufacturing process of a product, it is very important for designers to know the

different manufacturing processes.

To minimize product development expense, product development teams must be well-

organized. They must do it right the first time because engineering change orders are

expensive and redesigns are even more costly.

Thus, FEM analysis can help to ensure that the design would be able to meet the need/request

of the customers and do it right the first time so that customer will be satisfy with the end

products.

In conclusion, this project gives us a glimpse of what it is like to be a designer in the future

and allows us to understand briefly the advantage of FEM analysis. However, compare to the

real process taking place in the industry, what we had done is a tip of an iceberg. For most of

the project, we mainly concentrate on analyzing the strain developed when loads in applied

without taking into consideration of the designing and manufacturing process, and the after

maintenance and repair jobs. But, it provides us with the experience we need in the future and

it could be useful in a few years time when we step into the industry ourselves.




13. PHOTOGRAPHS




14. REFERENCES

1. Norman, S. Currey (1988). Aircraft Landing Gear Design: Principles and Practices. S.W. Washington D.C.:

American Insitute of Aeronautics and Astronautics, Inc.

2. Tanner, John A., Emerging technologies in aircraft landing gear . Warrendale, PA : Society of Automotive

Engineers, c1997

3. http://www.efunda.com/home.cfm

4. http://www.suppliersonline.com/

http://www.efunda.com/home.cfm

http://www.suppliersonline.com/

Aircraft Component Computer Design And Analysis

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