Aircraft Component Computer Design And Analysis
Transcript of 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
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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
9.2 Safety Factor 1.5
10. Case Study 3…………………………………………………………………………………. 48
10.1 FEM Analysis
10.2 Safety Factor 1.5
11. Modification…………………………………………………………………………………. 58
12. Conclusion…………………………………………………………………………………… 59
13. Photographs…………………………………………………………………………………. 60
14. References…………………………………………………………………………………… 62
Design and Development of Aero-Components and Processes
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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.
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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
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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.
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Design and Development of Aero-Components and Processes
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Design and Development of Aero-Components and Processes
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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.
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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”.
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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.
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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
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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.
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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
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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
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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
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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.
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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.
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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:
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Milling: Grinding:
Chip Formation:
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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.
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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.
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Standard Collet Fixture
Illustrated below is the configuration of a standard endmill fixtured in a knee-type milling
machine using a collet.
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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.
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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.
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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.
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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.
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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.
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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
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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
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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
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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
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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
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Front View of Stress Contour Plot with deformation
Design and Development of Aero-Components and Processes
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Side View of Stress Contour Plot with Deformation
Design and Development of Aero-Components and Processes
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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
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8.2 Safety Factor 1.5
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
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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
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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.
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9.1 FEM Analysis
The maximum torsion valve is 8.87 x 10 6 Nmm.
Constraint and Torsion Applied
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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
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Combination of Torsion and Forward Force Applied
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Stress Contour Plot w/o Safety Factor
Side View of Stress Contour Plot
Design and Development of Aero-Components and Processes
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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
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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.
Stress Contour Plot with Deformation
Design and Development of Aero-Components and Processes
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Side View of Stress Contour Plot with Deformation
Design and Development of Aero-Components and Processes
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9.2 Safety Factor 1.5
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.
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.
Stress Contour Plot with Safety Factor 1.5
Design and Development of Aero-Components and Processes
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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 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.
Front View of Stress Contour Plot with Deformation
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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
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Constraint and Hydraulic Force Applied
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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
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Stress Contour Plot w/o Safety Factor
Side View of Stress Contour Plot
Design and Development of Aero-Components and Processes
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Inner Wall View of Stress Contour Plot
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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
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Stress Contour Plot with Deformation
Inner Wall View of Stress Contour Plot with Deformation
Design and Development of Aero-Components and Processes
Landing Gear Component Design – Project 2
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Side View of Stress Contour Plot with Deformation
Design and Development of Aero-Components and Processes
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10.2 Safety Factor 1.5
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.
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.
Stress Contour Plot with Safety Factor 1.5
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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 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.
Front View of Stress Contour Plot with Deformation
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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.
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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.
Design and Development of Aero-Components and Processes
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13. PHOTOGRAPHS
Design and Development of Aero-Components and Processes
Landing Gear Component Design – Project 2
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Design and Development of Aero-Components and Processes
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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/