Redesign and stress analysis of simplified landing gear
Junghoon Suh
Final Report
ECM3101/ECM3102
Title: Redesign and stress analysis of simplified landing gear
Date of submission: 01/05/2014
Student Name: Junghoon Suh
Programme: BEng Mechanical Engineering
Student number: 600060234
Candidate number: 030412
Supervisor: Philippe G Young
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Abstract
This project was carried out with the aim of redesigning the tricycle main landing gear based
on the reference data of a Boeing 777 aircraft under the landing conditions. In particular, the
redesign of a safe and durable target landing gear considering a Boeing 777 aircraft should
withstand the maximum landing loading of 1016196.52N and ensure the completion of
10,000 lifecycles. To achieve this, an in depth understanding of the landing gear system,
theoretical design and 3D visualisation and stress analysis have been performed. In addition,
the main part of the landing gear, shock strut, originally incorporated an oil-pneumatic type
shock absorber, but was replaced by a spring shock absorber to verify its feasibility as an
alternative solution. Comparisons between the two types of shock absorbers were made by
using vibration equation to theoretically compare the differences in terms of landing gear
weights and sizes with different shock struts. However, the usage of a spring shock absorber
resulted in an increase of shock absorber dimensions and weight. The height increased from
4.27m to 12m and the weight increased from 4,536kg to 39,000kg, with much of the weight
increase caused by the spring. The design of the spring shock absorber was carried out based
on three different materials: alloy spring steels, stainless spring steels and copper-base spring
alloys, and alloy spring steel. These materials were all selected to be used in the shock
absorber as fatigue rate of spring was found to be the slowest with the lowest concentration of
stress. Although the weight increased with varying levels, durability of the landing gear was
verified from stress analysis which showed the results of maximum concentration of 733MPa
out of yield strength of 745MPa of landing gear material of titanium 5553, and 10,000 times
of life cycle was assured.
Keywords: landing gear, main strut, shock absorber, deflection, spring, SolidWorks, ABAQUS, Stress analysis,
materials
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Acknowledgment
I am fully appreciated to my supervisor Philippe Young who enabled me to successfully
accomplish completion of the project with a number of supports and advices under all the
conditions, and to deepen the level of analysis performed during project duration.
Moreover, I dedicate this project to my family and friends who always back up and
encourage me to carry on my project.
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Table of Contents
Abstract .......................................................................................................................................
Acknowledgment ........................................................................................................................
1. Introduction .......................................................................................................................... 1
2. Background Theory ............................................................................................................. 2
2.1 Research methodology .................................................................................................................. 2
2.2 Structural analysis ......................................................................................................................... 2
2.2.1 Nose landing gear ........................................................................................................................................................ 2
2.2.2 Main landing gear........................................................................................................................................................ 3
2.2.3 Troubleshooting of present landing gear ............................................................................................................... 5
2.2.4 Safety .............................................................................................................................................................................. 5
2.3 Mechanical analysis ...................................................................................................................... 5
2.3.1 Boeing 777 reference data ......................................................................................................................................... 6
2.3.2 Static load balance ...................................................................................................................... 6
2.4 Design of shock absorber ............................................................................................................ 11
2.4.1 Spring shock absorber ............................................................................................................................................. 11
3. Methodology ....................................................................................................................... 17
4. CAD Design ........................................................................................................................ 18
4.1 Shock absorber ............................................................................................................................ 18
4.1.1 Spring design ............................................................................................................................................................. 18
4.1.2 Shock absorber ........................................................................................................................................................ 18
4.2 landing gear ................................................................................................................................. 19
5. Results and discussion ....................................................................................................... 20
5.1 ABAQUS analysis ....................................................................................................................... 20
5.1.1 Spring shock absorber ............................................................................................................................................. 21
5.1.2 Landing gear .............................................................................................................................................................. 26
6. Design and quality of research and innovation in research process.............................. 28
7. Sustainability ...................................................................................................................... 29
8. Conclusions and recommendations .................................................................................. 30
References ............................................................................................................................... 31
Appendix ................................................................................................................................. 33
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Appendix A Vibration data sheet ....................................................................................................... 33
Appendix B ABAQUS analysis figures ............................................................................................ 34
Appendix C Spring material variation............................................................................................... 35
Appendix D Project management...................................................................................................... 36
Appendix E Health and Safety risk assessment ................................................................................ 37
Appendix F Preliminary report.......................................................................................................... 38
Redesign and stress analysis of simplified landing gear
Junghoon Suh
1. Introduction
This project was conducted with the aim of investigating the applied mechanics of the
current landing gear (Boeing 777). Throughout the analysis, the ensured safety of the landing
gear is the priority whilst seeking the feasibility of design modifications to obtain higher
levels of durability, and green sustainability during the landing process under assumptions
considered in the simplified design model.
The landing gear is one of the major parts critical to the safety of passengers, as it should
fully support the aircraft weight and absorb impact generated during landing. Before
commencing the analysis and design modification, the target landing gear, Boeing 777, was
extensively investigated. The Boeing 777 incorporates a tricycle landing gear, which consists
of a single nose gear positioned at the front and two six wheel bogie type main landing gears
positioned at the rear side. [4] Six wheel bogie type main landing gears are built in the Boeing
777 and successfully enable it to sustain higher level of loads from the aircraft body, as
landing loads of 201,840kg are distributed over six wheels.
This report contains an investigation of the landing gear system, analysis, calculation, 3D
design and virtual testing for durability of landing gear redesigns. In the first section, the
landing gear system in the Boeing 777 aircraft is described, design guidelines for components
sizing and positioning, and justification of target landing gear choices are made with a brief
statement of target landing gear malfunctions and problems identified. During the analysis
section, assumptions and limits of the project are explained, followed by an explanation of
the required formulas used for the redesign of the landing gear. Furthermore, a deeper level of
troubleshooting studies for defects of target landing gear has been performed. The design
section includes the 3D target landing gear model, which was designed based on the
information and calculated with approximations taken for the few parts where information
was not available. The redesigned landing gear had a target of 10,000 life cycles and not to
weigh more than five times the original landing gear. These are then compared and
component modifications are explained with 3D design illustrations. Finally, a case study has
been conducted in order to compare the cost variance and environmental factors of materials
of landing gear components, both of which are major factors when selecting the optimum
redesign model among prototypes.
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
2. Background Theory
2.1 Research methodology
As this project was focused on analysis and visualization of landing gear through the
simulation utilising CAD tools by hand works and computers, any experiments in university
workshop were not required. However, an immense amount of research and support were
vital for forming the successful redesign of the landing gear.
Research and supporting background work was carried out in the following forms:



Research using online sources due to the ease of data collection and immense quantity of
information available.
Through the Exeter e-library, Google scholar and Journal of aircraft provided
dissertations and literature that served as a framework for this project.
Alternatively, offline research, such as paper books and journals, sourced primarily from
the library which provided an excellent source of technical information.
2.2 Structural analysis
The landing gear in a Boeing 777 has a highly sophisticated system to ensure steering and
stabilisation during take-off, landing and taxing. Tricycle type landing gear in a Boeing 777
has two types of gears. First, the nose gear positioned at the front, and secondly, two main
gears positioned on the rear side of the aircraft.
2.2.1 Nose landing gear
The nose landing gear is located at
the front of the body of the plane and
provides
steering
and
shock
absorption. It consists of a shock strut,
drag strut assembly, lock link
assembly, torsion links and tow
fitting. [18] Starting with the shock
strut, it utilises a forged steel air-oil
shock absorber at the same time as
the landing gear, but has relatively
smaller amount of forces to withstand
in comparison to the shock absorber
of the main landing gear. Torsion
links are connected to the shock strut
to prevent spins of outer and inner
cylinders which cover the shock
absorber inside. [22] Drag strut
assembly is located above the fitting
of the shock strut and its function is to maintain the
shock strut in a retracted or extended position. Lock
link assembly of front and after links fixes the nose landing in both the retracted and stretched
positions alongside the drag strut assembly, and is connected by lock springs that maintain
Figure 1: nose landing gear structure [22]
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
the lock links in locked position, and hinge.
2.2.2 Main landing gear
The main landing gear is located at
the rear side of the aircraft. As each
main landing gear is connected to the
wing, each time the aircraft takes off
it retracts into side parts of fuselage
and comes out from fuselage during
the landing. The main gear also
contains the main strut which consists
of a shock strut, drag strut and wheels.
[19]
The shock strut is vital part of
the landing gear as its primary
function is to support the aircraft from
loadings. It contains oil oleo
pneumatic shock absorber which is
[6]
filled by oil and nitrogen. In
Figure 2: Main landing gear structure
comparison to light type of jets, large
transporting aircraft incorporate pneumatic shock absorber as it offers great shock absorption
and higher rates of efficiency. Hence, it also offers immense size and weight reductions in
contrast to the light weight jets. In case of drag, the strut functions as a stabiliser when the
aircraft is landing. The main strut is connected by reaction links to the side fuselage. Torsion
links play a considerable role in preventing internal rotations of outer and inner cylinder and
holding each cylinder. Axle assembly from truck beams normally attaches wheels and brakes.
2.2.2.1 Main shock strut
Boeing 777 incorporates a steel air-oil
pneumatic shock absorber. When the aircraft lands,
landing loads are absorbed into shock absorber and
transmitted to the end of truck beam to the wheels. It
is consisted of inner cylinder, which is expanded and
retracted inside the outer cylinder. [23] Torsion links
connect both the outer and inner shock absorber in
order to prevent rotation between two cylinders
under the landing loading and to support them in
horizontal line. Torsion links which nose landing
gear is rotated by, are supported by the actuator. In
The
terms of the principle of shock
absorption, both compressed nitrogen
gas which is located in the upper part of main strut and oil which is located in
the lower part, flows into the shock strut that is located in the middle of main
strut.
In most cases, the aircraft shock strut incorporates two types of absorption
types, spring and pneumatic absorption. Light weight aircrafts use shock
spring absorber rather than oil pneumatic as a suspension system, although
Figure 3: oil-pneumatic shock absorber [14]
3
Figure 4: section view of spring shock absorber [21]
Redesign and stress analysis of simplified landing gear
Junghoon Suh
pneumatic suspension system bring higher rates of efficiency. Therefore, as part of the project,
spring shock absorb was designed to replace pneumatic absorption system in the target
landing gear, and evaluation will be conducted between original landing gear with oilpneumatic shock absorber and redesigned landing gear with spring shock absorber in terms of
sizes and weights to check whether usage of pneumatic type is much efficient as shown in
figure 5. Comparisons between the results of the model in terms of weight, sizes and prices
were made. In addition, three of different spring materials was compared and tested to be
chosen for redesign.
Graph 1: Comparison of efficiency of several type of shock absorption [28]
2.2.2.2 Drag strut
During landing as the main strut moves downwards, it becomes extended, with the drag strut
supporting main strut to prevent it from becoming excessively stretched. The upper part and
lower link, hinged in centre, are components of the drag strut. There is a connection between
upper drag strut and nose wheel side, whereas the outer cylinder is connected to the lower
link of drag strut. Retraction of the main strut is allowed by the drag strut, which will fold
during retraction and extension. [22]
2.2.2.3 Torsion link
Torsion links prevent internal rotation between the outer cylinder and inner cylinder of the
main strut. During steering, force is applied with the torsion link allowing the struts to be
rotated. Normally, torsion links allow vertical movements to occur and are located in the
outer cylinder and inner cylinder of the main strut. [22]
2.2.2.4 Brake system
The brake system is one of the essential parts in the landing system, as it should stop the
airplane in certain distances from landing against the exerted drag. Hydraulically powered
brake systems are used for landing gears. [3]
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
2.2.3 Troubleshooting of present landing gear
The main issue of the current landing gear is the overhaul of the landing gear. In particular,
the squat switch problem is believed to be the major associated problem with the landing gear.
[11]
Therefore, following several repair and maintenance operations should occur to ensure the
safety of the landing:

No sign of landing gear warning
The operation of the horn should be checked under the extracted and extended positions of
landing gear. Moreover, connecting wires from landing gear to the control monitor in pilot
control system room should be checked to verify whether it is broken from fatigue.
Malfunction of throttle and squat switches should also be inspected. [27]
2.2.4 Safety
Safety is the first priority when designing a landing gear, as it is integral to a flight that a safe
landing and planned stop of the aircraft occurs. There are several safety systems present in
order to prevent landing gear from failure:
1. Alternate extension system: Is an emergency function when the absence of hydraulic
pressure in the brake or vertical extension does not occur. This system is activated by an
electric motor which allows extra hydraulic fluids to flow into the brake system. Furthermore,
unlocking pin is overridden by this motor to extend the landing gear from extracted position. [11]
2. Ground locks: When the landing gear is on the ground, ground locks assist the landing gear
with stability, preventing the landing gear from collapsing. A Pin or spring is installed in the
landing gear to support landing structure from the occurrence of falling back. [12]
2.3 Mechanical analysis
In this section, general explanation of exerted forces during landing were carried out to help
understand the functions and systems of the landing gear of the Boeing 777 alongside the
calculations for the transmitted forces and energy in order to generate the redesign of the
landing gear.
Reference data, mainly taken from Boeing technical information page, is introduced to show
the range of values to be used during the investigation. After that, the results are narrowed
down from weight distribution of entire aircraft to specific components, mainly considering
the main strut and tire.
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
2.3.1 Boeing 777 reference data
Figure 1 below shows the obtained reference data available from the technical information
page of Boeing website that is utilized for the usage of analysis. In the cases where values
and conditions were not available, several assumptions were made for the redesign of the
landing gear.
Name
Symbol
Maximum landing weight [5]
Mmaz landing
Approach speed [25]
Vapproach
Thrust
Fthrust
Value
Units
201,840 kg
136 kias
77,000 lb*2
Table 1: Table of reference value [4]
Furthermore, several assumptions have been set for the factors that cannot be identified, and
for the simplification of calculations:



Landing process occurs in an extreme situation, so, maximum landing mass is used,
hence the maximum vertical velocity that the aircraft should sustain, is calculated.
Centre of gravity is located in the middle of the aircraft.
Landing angle is assumed to be 3 degree nose up. Therefore, forces of drag, lift and
thrust shall be 3 degree tilted during landing. [11]
2.3.2 Static load balance
2.3.2.1 Force distribution on two landing gears
Working on the weight exerted on the landing gear offers a good start to estimating the size
for the components, such as the dimension of main strut and wheel sizes. Figure 2 shows the
vertical force distribution of the aircraft.
During landing, the force that is exerted from
maximum landing mass is applied downward.
As single nose and two main landing gears
sustain the aircraft mass, the equation for the
forces around the aircraft can be made
underneath.
Fy = F(max landing weight) - 2F1 - F2 - (1)
Figure 5: Distribution of forces over landing gears
Level of loads, applied to the nose gear (F1) is
normally 14% and 86% of landing weight
applied to 2 main landing gears, where each
main landing gear accounts for 43%. Therefore,
the equation can be rewritten for simplifying
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
the calculation for finding gravitational force:
F (max landing weight) = 50/7 F2
F2 (nose landing gear) = 7/50 F
F1 (single main landing gear) = 43/100 F
Mass proportion on M1 = 7/50 M, therefore, mass on nose gear 28257.6kg
Mass on each main landing gear 86791.2kg
In order to work out the forces during the landing, iteration works are performed to find the
displacement of landing and the acceleration from vibrating parts.
From part 3, it was found that required time to the maximum compression is 1.3182 seconds.
In addition to this, the amount of force that each main strut in the main landing gear should
sustain under the maximum landing mass is calculated to be 1016196.52N.
Therefore, viscous shock absorber which is the spring shock absorber is designed to sustain
1016196.52N of force.
2.3.2.2 Landing gear positioning
Before designing the landing gear, the location of landing gears should be demonstrated in
order to assure static balance and proper stress transmissions. [20] Figure below shows the side
view of the aircraft. The distance of A between the tip of head and nose gear is approximated
to be 4m, and whole length of airplane is 63m. [2] The distance between two type of landing
gears were found to be located the main landing gear at the position that could sustain
transmitted force from the landing impact.
Figure 6: Side view of the aircraft
Sum of Fy
Wtotal = 0.14W + 0.86W
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
Sum of Moment
M = -0.14WE +0.86WC
The distance of E can be found as centre of gravity locates in the centre of the airplane and A
is 4m.
= -0.14*(1016196.52N)*(31.5m-4m) + 0.86(1016196.52N)*C
= -3.85m +0.86*C
=> C= 2.99 m = 3m
=> B = E + C = 31.5m + 3m = 35m
Therefore, the distance of E, between the center of gravity and nose gear, is 27.5m, distance
of C, between the center of gravity and main landing gear, is 3m, and the distance between
nose and main gear was found to be 35m.
2.3.2.3 Specification of forces on landing gear
The landing gear when landing should be conducted under the static balance of the aircraft.
Therefore, an investigation was conducted into 4 different types of forces around the landing
gear during landing, drag, lift, thrust and gravitational forces. [3] Among different kinds of
forces, the values for thrust and maximum landing mass were found.
- Thrust: Boeing 777 has 2 engines which are capable of generating the maximum thrust of
154000 lbs (=77,000 lbs *2), which is equivalent to 69,853.2kg. The amount of thrust is
685,259.892N. The safe landing cannot be done with maximum thrust. The percentage of
thrust for the landing is 40% of the thrust (40% N1), as stated in the manual, which leads to
the necessary thrust of 274,103.9568N. [9]

Maximum landing mass: Landing operation can be safely conducted when the landing
mass is equal or less than maximum landing mass. For the analysis, maximum design
landing mass is used for the calculation of static balance, which value is 223,198kg.
From vibration equation, the gravitational for during landing was found to be
1016196.52N. (3)
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
Figure 7: 3 Degree nose-up landing view
From the (2.3.1), 3 degree of nose-up is shifted during landing was set, hence, figure below
shows the directions of forces acting upon 3 degree shifted-up plane.
Actual landing occurs with 3 degree of nose up as depicted above, so calculations for forces
were derived as below:
Sum of Fy
Flift*cos(3°) + Fdrag*cos(87°) + Fthrust*cos(87°) - Fgravitational =0
Sum of Fx
Fthrust *cos(3°) + Flift *cos(87°) - Fdrag *cos(3°) = 0
For the ease of calculation, landing angle is assumed to be tilted 3 degree above to reduce
trigonometry calculations. Therefore, equations can be newly derived as below:
Fgravitational : 1016196.52N
Fthrust : 274,103.9568N
Sum of Fy
Flift + Fthrust *sin(6°) - Fgravitational *cos(3°) = 0
Flift + 274,103.9568 * sin(6°) - 1016196.52 *cos(3°) = 0
Flift = 986152.2N
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
Sum of Fx
Fthrust * cos(6°) + Fgravitational *sin(3°) - Fdrag = 0
274,103.9568 * cos(6°) + 1016196.52 * sin(3°) - Fdrag = 0
Fdrag = 325786N
2.3.2.4 Calculation of vertical velocity during landing
Since it is assumed that aircraft touches down with 3 degree nose up and reference data of
approach speed of 136 KIAS (=69.69m/s). The vertical speed during landing can be found as
follows:
Vvertical = Vapproach * sin (3°)
= 69.96m/s * sin (3°) = 3.66m/s
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
2.4 Design of shock absorber
2.4.1 Spring shock absorber
Figure 8: 2D Modelling of spring shock absorber and free body diagram of forces
Design of the landing gear should consider the maximum deflection that shock strut needs to
be compressed and maximum landing force shock strut should withstand. From applying
vibration equation, maximum deflection and maximum force under the vertical speeds and
maximum landing mass of the aircraft. In addition, the following equations were constrained
to deflection of shock strut without deflection from the tire.
These vibration equations were used in order to find exerted force in the maximum
compression and requiring stiffness of spring and damping constant for steel spring shock
absorber. [10]
Equation from free body diagram F = ma
−kx − c
x
x
= m 2
dx
dx
Damping ratio is assumed to be 1 which implies that the aircraft landing with the least
oscillation from the landing gear, it leads to the definition of critical damping.
Therefore, initial conditions need to be set to find the maximum displacement of landing
gear with displacement equations below:
x(t) = (𝐶1 + 𝐶2 ∗ 𝑡)𝑒 −𝑊𝑛𝑡 - (1)
𝑥̇ (𝑡) = 𝐶2 𝑒 −(𝑊𝑛𝑡) − Wn(𝐶1 + 𝐶2 𝑡)𝑒 −𝑊𝑛𝑡 - (2)
Initial conditions are defined in order to solve equations by using spring-force equation, to be
used in calculations:
K∗x= m∗g
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
mg
k
Using this, initial conditions for first equations can be set (when fully stretched before
compression):
x=
x(0) = −(
mg
k
)
- (3)
𝑥̇ (0) = V vertical (max displacement occurs when V=0)
- (4)
Apply initial conditions of (3) and (4) into displacement equations of (1) and (2) to find out
C1 and C2.
x(0) = (𝐶1 + 0)𝑒 −𝑊𝑛∗0
=> 𝐶1 = − (
mg
k
)
𝑥̇ (0) = 𝐶2 − Wn (−
mg
)
k
=> 𝐶2 = 𝑥̇ (0)(= 𝑉𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙) + Wn (−
mg
k
)
Now, apply known C1 and C2 into displacement equations again to obtain appropriate
equations.
Therefore, two equations can be derived:
mg
mg
x(t) = (− ( ) + (𝑉𝑣𝑒𝑟𝑡 + Wn (− )) 𝑡) 𝑒 −𝑊𝑛𝑡
k
k
𝑥̇ (𝑡) = (𝑉𝑣𝑒𝑟𝑡 + Wn (−
mg
mg
mg
)) 𝑒 −(𝑊𝑛𝑡) − Wn ((− ( )) + (𝑉𝑣𝑒𝑟𝑡 + Wn (− )) 𝑡) 𝑒 −𝑊𝑛𝑡
k
k
k
Simplifying x/dt (t)
𝑥̇ (𝑡) = (1 − Wnt)Ae−Wnt + 𝑊𝑛 (
Putting 𝑉𝑣𝑒𝑟𝑡 + Wn (−
mg
k
mg
𝑥̇ (𝑡) =
k
𝑘
) 𝑒 −𝑊𝑛𝑡
) back into A
𝑥̇ (𝑡) = (1 − Wnt) (𝑉𝑣𝑒𝑟𝑡 + Wn (−
By replacing Wn (−
𝑚𝑔
) to
g
mg
𝑚𝑔
) ) e−Wnt + 𝑊𝑛 ( ) 𝑒 −𝑊𝑛𝑡
k
𝑘
, this can be rewritten as:
Wn
𝑔 −𝑊𝑛𝑡
g
g
𝑒
+ (V −
) 𝑒 −𝑊𝑛𝑡 − (V −
) 𝑊𝑛𝑡𝑒 −𝑊𝑛𝑡
𝑊𝑛
Wn
Wn
As maximum displacement can be determined once 𝑥̇ (𝑡) = 0
Equation of 𝑥̇ (𝑡) can be again simplified to find maximum time to find maximum
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
displacement:
0=
𝑔
g
g
𝑒 −𝑊𝑛𝑡 + (V − Wn) 𝑒 −𝑊𝑛𝑡 − (V − Wn) 𝑊𝑛𝑡𝑒 −𝑊𝑛𝑡
𝑊𝑛
This can be derived in terms of t:
=> t =
1
g
1
(1 + Wn ∗ (
𝑊𝑛
𝑣−
𝑔
𝑊𝑛
))
Using the equation of t when 𝑥̇ (𝑡) = 0, maximum time can be calculated following by
maximum displacement by varying stiffness of k.
Stiffness value was set as 700000N/m, and following equations were used to find maximum
deflection and forces:
t=
=
1
1+
700000 1/2
(
)
3.66𝑚𝑠−1
1
g
1
(1 +
∗(
𝑔 ))
𝑊𝑛
Wn
𝑣 − 𝑊𝑛
9.81
700000 1/2
(
)
3.66𝑚𝑠−1
∗(
1
3.66𝑚𝑠 −1 −
(
9.81
700000 1/2
(
)
3.66𝑚𝑠−1
)
= 1.318seconds.
)
Maximum deflection was calculated by substituting t of 1.318 seconds:
mg
mg
x(t) = (− ( ) + (𝑉𝑣𝑒𝑟𝑡 + Wn (− )) 𝑡) 𝑒 −𝑊𝑛𝑡
k
k
1
= (− (
86791kg∗9.81
700000N
m
𝑚
) + (3.66 ( ) + (
𝑠
700000 2
)
3.66𝑚𝑠−1
∗ (−
86791kg∗9.81
700000N
m
)) ∗ 1.318𝑠) 𝑒
−(
1
700000 2
) ∗1.318𝑠
3.66𝑚𝑠−1
= 1.411m
Value of stiffness was iteratively performed in order to obtain the target range of maximum
time between 1 second to 1.5 seconds and maximum deflection between 1.2 meters and 1.5
meters. Consequently, using stiffness of 700000N/m, maximum compression time of 1.318
seconds and maximum deflection of 1.411 meters were obtained.
Detailed table of values and methodology of using spreadsheet can be found in appendix A.
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
Graph 2: Changes of original lengths over time
Checking the validity of the equations and calculations of previous works, the graph of
compression against time was plotted. As time passes, it can be clearly noted that the
compression exponentially decreases over time. In other words, deflection increases over
time. Also, from the point where time passes 1.4 seconds, the compressions slows down and
significant level of deflections would not be expected to occur in comparison to the period of
first 1.4 seconds. This again proves that usage of maximum time of 1.318 would be
appropriate.
Graph 3: Changes of damping and spring forces over time
This graph shows the changes of the level of two different forces, damping force and spring
force. As observed, while the level of spring force increases, damping force falls. This could
be interpreted that as the immense amount of deflection occurs, spring force increases with
the increase of deflection, but damping forces decreased due to the fact the level of oscillation
caused by landing impact falls over the same period. In addition, due to the setting of
damping ratio of 1, damping force line was plotted smoothly without any fluctuation.
Therefore, this graph demonstrates that the calculations were appropriate and results were
successful. For the maximum force, it was calculated to be 1016196.519N where the
maximum deflection occurs.
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Redesign and stress analysis of simplified landing gear
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2.4.1.2 Spring design
Spring design is an important phase of modeling the landing as the spring is a major part
which absorbs the impact of landing. As the shock absorber in the main landing gear is a
spring, which stores the exerted impact from the landing, the properties and dimensions of the
spring should be identified. Spring material was used with Chromium Vanadium (ASTM
A231), as it is most commonly used for spring shock absorber. For the design criteria, the
spring was designed to withstand the maximum deflection of 1411mm and ultimate loads of
1321055.476N, which was multiplied by 1.3 of safety factor from maximum landing force of
1016196.519, factor of safety for spring of 2, and spring index of 9 were assumed to be used
in the equation. [24]
Figure 9: Section views of spring [24]
It is already given that 𝜏𝑦 = 690𝑀𝑃𝑎 𝐺 = 79340𝑀𝑃𝑎
Diameter of wire
𝜏𝑦
Shear stress
𝜏=
Wahl’s stress factor
𝑘=
Spring Index
𝑐=
𝐷
𝑑
2
690𝑀𝑃𝑎
2
=
4𝑐−1
4𝑐−4
+
0.615
𝑐
= 345𝑀𝑃𝑎
=
(4∗8−1)
4∗8−4
0.615
)
8
+(
= 1.1621
=9
=> D =9d
Using equation of shear stress, standard diameter of wire was calculated.
𝜏=
8𝐹𝐷𝑘
𝜋𝑑3
By substituting D=9d and known values into equation, equation can be newly derived
72𝐹𝑘
72 ∗ 1321055.476𝑁 ∗ 1.1621
𝑑=√
=√
= 336.623𝑚𝑚
𝜋𝜏
𝜋 ∗ 345𝑀𝑝𝑎
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
𝐷 = 9 ∗ 𝑑 = 3029.613𝑚𝑚
Standard diameter of wire is calculated to be 336.623mm.
Diameter of coil
Mean diameter of 3029.613mm
Outer diameter of coil is 3366.237mm (3029.613mm + 336.623mm)
Inner diameter of coil is 2692.989mm (3029.613mm - 336.623mm)
Number of turns
Using the equation of deflection, number of coils in use can be clarified.
y=
8FD3 i
Gd4
This can be rearranged in terms of active coil, i.
i=
Gd4 y (79340MPa ∗ 336.6234 mm ∗ 1411mm)
=
= 4.873
8FD3
8 ∗ 1321055.476N ∗ 3029.6132 mm
Therefore, active coil turn number is 5.
Free length
Free length of the entire spring could be calculated using the equation of free length of helical spring
𝑙 ≥ (𝑖 + 𝑛)𝑑 + 𝑦 + 𝑎
Clearance, a, was assumed to be 25% of maximum deflection. In terms of n, ends of the spring, it
was not added as this spring was modeled to withstand great level of maximum landing force, and
fittings to maintain spring compression in vertical line were added in CAD designs.
Putting all the values into equation:
𝑙 ≥ (5 + 0)336.623𝑚𝑚 + 1411𝑚𝑚 + (0.25 ∗ 1411𝑚𝑚)
𝑙 ≥ 3340.249𝑚𝑚
Pitch
𝑝=
𝑙 − 2𝑑 3340.249𝑚𝑚 − 2 ∗ 336.623𝑚𝑚
=
= 553.400𝑚𝑚
𝑖
5
Mass[13]
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
M = Volume ∗ Density = (3.14 ∗ D ∗ i ∗ (3.14 ∗
d2
7.861kg
)) ∗ (
∗ (10−6 )) = 33,260kg
4
m3
As a result, the spring to withstand the ultimate force of loading, 1321055.476N, was
designed theoretically, and will be represented visually with aid of CAD, Solidworks. The
design is based on the following dimensions:
Weight of spring = 33,260kg
Standard diameter of wire: 336.623mm.
Mean diameter of coil: 3029.613mm
Number of turn: 5
Free length: 3340mm
Pitch: 553.400mm
3. Methodology
Redesign of target landing gear proceeded from looking at the functional requirement from
research performed, with forces and stresses analysis around the aircraft, mainly focused on
main landing gear from handworks and CAD tools. From the investigation of structural
analysis, construction of nose and main landing gear was acknowledged in order to analyze
realistic forces and stresses around the landing gear during landing process. After
understanding of the landing gear system, exerted forces in association with landing and
stress proportions in each component in landing gear were theoretically calculated by far
through the researches and hand works.
CAD modeling and FEA analysis were performed in order to validate and optimize to the
final model of the landing gear obtained.
In the CAD modeling, SolidWorks were used to visualize the redesign from theoretical
calculations. Apart from spring shock absorber, all the other parts were sized randomly as
first modeling, but were then able to achieve final modeling through the optimization process
of checking in competency of the model under the loading and stress analysis.
FEA analysis by ABAQUS enabled the investigation of the location of the maximum stress
concentration where it is anticipated to deteriorate relatively quickly, and the level of
deflection of the model. Variation of the dimensions and materials were made in order to
compare different designs of landing gears and generate the final model.
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
4. CAD Design
Using SolidWorks, landing gear was modeled in a logical manner. Starting from the spring
design, the spring shock absorber was created, and then the landing gear which incorporates
outer and inner cylinder, torsion links, and wheel truck were built.
4.1 Shock absorber
4.1.1 Spring design
The spring was designed in a helical shape in order to
incorporate it into the cylindrical shape of the landing
gear main strut. It has a good advantage in reducing
the nominal compression under the load in
comparison to the wire shaped spring for shock
absorption. It has dimensions of height of 3440mm,
width of 3366mm, and pitch is 553mm. In the shock
absorber, fitting for the spring shall be modeled in
order to ensure the nominal compression apart from
deflections in other directions.
Figure 10: Spring design
4.1.2 Shock absorber
Spring shock absorber was then designed based on
the dimensions of the spring. The damper was
safely designed for the unexpected over
compression above 1.4m, it empties the height of 2
meters. Furthermore, it is designed to function as
fitting for the spring that width of upper part of
damper is 3100mm in order to encourage the
spring to be compressed in one direction. The
shock absorber has dimensions of 8 meters height
and 3.4 meters of width. Two mounts were
designed to be connected with each outer and
inner cylinder of main strut.
Figure 11: Spring shock absorber design
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
4.2 landing gear
Figure 13: Section view of landing gear
Figure 12: Landing gear redesign
The landing gear was modeled successfully after the designs of spring and spring shock
absorber were created. The outer cylinder was designed to protect shock absorber from
external hazards and environmental danger. Additionally, torsions links are connected to the
inner shell in order to prevent rotations of the landing gear under the landing impacts. In case
of torsions links, they were designed to enable outer cylinder move downwards for 2 meters
in comparison to maximum feasible compression of 1.4 meters from spring in order to
prevent unnecessary collision with inner cylinder. The outer cylinder is robust and fixed with
the shock absorber by linkage axle on the top of shock absorber. The inner cylinder is fixed
with bottom parts of shock absorber and truck parts for wheels.
With these models, stress analysises were conducted to iteratively optimise the model in
an efficient and economical way. After the stress analysis, optimisation process of solid
works modelling was to generate the final model of the landing gear.
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Redesign and stress analysis of simplified landing gear
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5. Results and discussion
5.1 ABAQUS analysis
Based on the SolidWorks models of the original spring shock absorber and landing gear,
FEA analysis of model was conducted by ABAQUS. Through the FEA analysis, the
concentration of maximum stress and maximum deflections were identified, enabling the
redesign of the original landing gear with various materials and dimensions.
The analysis was divided into two sections, the analysis of spring shock absorber, and the
landing gear. Both analyses were set up by 1.4 seconds of time periods when maximum force
is exerted and with a damping ratio of 1. All parts were assigned separately and boundary
conditions were assigned on the bottom of each spring shock absorber and landing gear as in
real landing situations. Consistency of units was in Pa, N and m.
First, spring shock absorber was analysed in order to ensure the maximum force of
1321055.476N, which was utilised to theoretically design the spring and damper. After that,
different materials were separately incorporated to determine the best materials in terms of
weight and cost in order to maximise the economy and sustainability. Upper parts and lower
parts used aluminium and spring materials, which were varied from the original alloy spring
steel, stainless spring steels and copper-based spring alloys.
Second, the original landing gear was tested in two stages, basic stress analysis and fatigue
testing to check redundant fittings and excessive material usages, and ensure the durability of
the landing gear under the maximum landing mass.
Table 2 shows the types of materials used in testing and each property.
Types
Usage
Name
Modulus of
elasticity (MPa)
Poisson's ratio
Alloy Spring
Steels[17]
Spring test
Chromium
Vanadium
Stainless Spring
Steels
Spring test
Stainless Type
302
Copper-Base Spring
Alloys [15]
Spring test
207000
193000
128000
103000 [6]
0.31
0.3
0.2
0.31[16]
Table 2: Table of mechanical properties of materials
20
Phosphor Bronze
Titanium
landing gear
titanium type
5553
Redesign and stress analysis of simplified landing gear
Junghoon Suh
5.1.1 Spring shock absorber
In the original design, an Alloy spring steel (Chromium Vanadium, ASTM A231) was used
for the spring for the shock absorber. On the other hand, several materials were selected as
candidates which could replace the original alloy spring for the better durability of spring
shock absorber, which are Stainless Spring Steels and Copper-Base Spring Alloys.
Figure 14: Pressure areas
For the analysis of shock absorber, equivalent pressures
to the ultimate landing load of 1321055.476N were
calculated to be applied in the model. The linkage part
of top was excluded to assist with calculations for
pressures. It is not anticipated that significant
differences in accuracy will occur as result of this
exclusion, as the transmitted forces from landing evenly
propagates throughout the landing gear. Total pressures
were calculated in a simple way, which is shown
below.
𝑃=
𝐹
𝐴
1321055.476N/ (1.22 m2 ) ∗ 3.14= 292165.4892Pa
1321055.476N/( (1.72 − 1.32 m2 ) ∗ 3.14)= 350598.587Pa
1321055.476N/ ( (1.32 − 1.22 m2 ) ∗ 3.14)= 1682873.218Pa
5.1.1.1 Mesh convergence
Graph 4: Mesh convergence
Since the model was designed in 3D, a number of elements should be multiplied by eight in
order to double the resolution. For processing mesh refinement, due to the size and
complexity of the model, it was not possible to achieve resolution-doubled meshes, but
21
Redesign and stress analysis of simplified landing gear
Junghoon Suh
meshes with doubled number of elements were acquired from controlling global sizes and
elements sizes. The figure below shows the finer meshes, 1691, 3162, 6140 and 11235
elements, but finer meshes than 20000 nodes were not feasible because of the restriction of
student licensed product. As a result, the finest mesh of 11235 with stress of 6.077MPa
succeeded obtaining the highest stress value, but it was presumed that higher stress value
could be achieved at the mesh elements around 4000. Eventually, 6.794MPa of stress was
found by analysing 4073, and it was used to conduct stress analysis and material replacement.
With the 4073 elements, meshing was done with
tetrahedron mesh element shape and shows good
dimensions. As helical in spring has complicated
issues, this part requires additional mesh elements
compared to the upper and lower parts of shock
absorber. These were set differently to assign
different number of meshes. Appendix B.1
showed the shape changes of the mesh models
depending on the number of mesh elements.
Figure 15: Meshed model
5.1.1.2 Stress analysis
Using von-mises stress analysis, an
investigation of stress was carried out. The
location of the highest stress point was at
damping pins. [8] This is an expected
phenomenon in which the damping forces
over deflection increases require higher
level of force to stabilise growing oscillation.
With regard to the high concentration of
stresses over the damping bars, the thickness
of it could be increased to expand the
pressure area in order to slow down future
fatigue around this highly stressconcentrated area.
Figure 16: Concentration of stresses
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
Graph 5: Stress against strain graph
Having performed the stress analysis, a graph which shows the table of stress changes over
the strain, was plotted from the data of analysis. Alloy spring steel was tested under the two
conditions, elastic property and elasto-plastic property to identify any permanent deflection
occurrences until the time reaches when maximum landing loads have been exerted. As a
result, the alloy spring steel was proved to be recoverable under the landing loads.
Furthermore, it could be demonstrated that the maximum stress of 6.794MPa does not reach
average yield stress of 320MPa of shock absorber, this model could be used for landing.
However, judging from the significant differences between maximum stress and average
stress, it could be anticipated that unnecessary materials could be reduced so as to optimise
the process in sizing.
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
5.1.1.3 Deflection analysis
As pressure is applied to the top of the shock
absorber, the shock absorber also displays shape
change in terms of deflection. In z axis, vertical axis,
pressures were applied as landing loads acting in
same direction, and it could be clearly seen that the
shock absorber deforms with gradual deflection of
the spring over the period of time. More accurate
phases of deflection changes can be found in
appendix B.2. Thus, this model could now be
validated to be used for a landing gear as the spring
compresses with consistent rate of deflection
changes. As can be seen from the figure 17, location
of the highest deflection was found to be in the
centre of the string, and taking account of forces
which exerted from x and y axis, failure of the
centre of spring could be suspected. Therefore,
Figure 17: Concentration of deflection
optimisation was done in a way that landing could
be applied to only single direction z axis and minimising the effects from x and y direction as
much little as possible. This will lead to prevent deterioration of spring in long term
perspective, moreover, downsizing of the volume of top parts and lower parts of shock
absorber that has allowable deflection could result in reduction in cost from decreasing
thickness of the part.
5.1.1.4 Material replacement
Graph 6: Changes of deflection against force increase
The spring used in the shock absorber was replaced with three different materials that can be
incorporated for shock absorption, in order to select the best material. With regards to general
24
Redesign and stress analysis of simplified landing gear
Junghoon Suh
results, it can be seen that most of materials have similar values of deflection. Among
materials, stainless spring steels shows the increase of high deflection changes over the
landing force increases, whereas alloy spring steels showed the least deflection.
The table of Graph 5 and 6 were derived from the spreadsheet (Appendix B.3) that organised
and divided the values according to the materials and type of values.
Graph 7: Changes of stresses over time increase
In case of stress comparison, copper-base spring alloy showed the highest rise in stresses
among three materials, whereas current spring material, alloy spring steels, resulted in the
second highest stress increases with only small differences from stainless spring steels, which
demonstrates the reason alloy steel has been widely preferred as a spring absorption material.
This also means fatigue at the point where maximum stresses occur will have the slowest rate
in comparison to springs with alloy spring steel or copper-base alloys.
Summing up the results from both analyses of material replacements, it could be said that
the three materials demonstrate similar results, particularly considering the alloy spring
ranked the best in material in terms of the lowest deflection where replacement of material
does not seem to be vital. This reason could be backed up by the mechanical properties of
each material. Alloy spring, Chromium Vanadium, has relatively higher resistances to the
impact loading and fatigues of the parts, whereas rest of materials also have property of good
tensile strength but even in comparisons of expected weights of spring, alloy spring steel
showed the lowest weight at 33,000kg. [15] (Appendix C).
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Redesign and stress analysis of simplified landing gear
Junghoon Suh
5.1.2 Landing gear
5.1.2.1 Stress analysis
Figure 18: Concentration of stress over landing gear under the loading
Stress analysis on the landing gear was performed throughout the model. The titanium 5553
type was assigned to be material of the landing gear. The maximum von mises stress value
was 730MP in comparison to the yield strength of 745MP the titanium 5553. It showed that
present model of landing gear would not break or fail due to the loads. Relatively higher
stress concentrations were found around the areas where vertical motions occur from outer
cylinder and inner cylinder. Weight of the model was 44560kg, and in comparison to original
weight of target landing gear of 6,636kg, it resulted in a significantly higher weight. It is
expected result that oleo pneumatic offers high shock absorption than spring shock absorption
in terms of weight and sizes, but this redesign of landing gear incorporated the spring as
suspension within the gear, leading to a large increase of the overall general weight.
26
Redesign and stress analysis of simplified landing gear
Junghoon Suh
5.1.2.3 Final design
From the optimisation process of different sizes of landing gear, it was possible to utilize a
spring material, alloy spring, which has a small shock absorber volume and could still sustain
the landing load. Additionally, the dimension of the landing gear could be downsized as well.
In the final model, the volume of the truck beam was shrunk by a factor of 0.8 and upper and
lower parts of shock absorber became smaller as maximum stresses did not reach the overall
yield strength of the shock absorber. After all, maximum stress over the landing gear was
found to be 733MPa, and model weight decreased to the 39000kg.
Figure 19: Concentration of stress over final landing gear
Figure 20: Final model of landing gear
27
Redesign and stress analysis of simplified landing gear
Junghoon Suh
6. Design and quality of research and innovation in research process
Research of the specification and materials used in the landing gear design were based on
aircraft related websites. Core information, such as dimensions and landing mass information,
related to the target landing gears were extracted from the Boeing technical information
section of the company website. Furthermore, the large amount of research in literatures and
technical documents enabled an in depth analysis and the generation of the final model of the
landing gear.
The design process proceeded in a logical manner with the understanding of landing gear
structure, theoretical designs of landing gear, visualization, analysis and generation of final
model. The understanding of the structure of the landing gear occurred prior to the modelling
of the landing gear, hence related papers and books from library offered a variety of
opportunities to become familiar with the landing gear system. In particular, unanswered
questions or unclear information from literatures were again personally clarified from
aviation forum and email correspondences from Boeing Company. The theoretical design of
the landing gear was assisted by the lecture notes from Solid Mechanics lecture and materials
lectures. As a spring shock absorber located in a real landing gear can be designed from
principles of vibration study, this allowed for the design of the spring and damper, with the
lecture slides from university making a great contribution to achieve theoretical design of the
landing gear. Regular supervisor meetings were of great benefit, particularly as the supervisor
was the lecturer of solid mechanics module meaning that the theoretical design of landing
gear was accurate and reliable. Material lecture notes provided a great resource with the
selection of materials for the spring for spring shock absorber and information from the notes
assisted with the analysis of the fatigue and failure of landing gear. Visualization of landing
gear was largely helped by Solidworks forums and guidebook from the web, as level of CAD
model was advanced than the curriculums, used in lectures. Finally, the analysis of the
landing gear using ABAQUS and SolidWorks tools were assisted by a research fellow, who is
very competent with ABAQUS.
28
Redesign and stress analysis of simplified landing gear
Junghoon Suh
7. Sustainability
In terms of life cycle, 100,000 times
of life cycles of the model was
achieved with respect to the objective
of 10,000 cycles. This brought down
the fact that landing gear could sustain
for maximum landing load of
1016197N.
Figure 21: Life cycle of landing gear
Sustainability should be another consideration in designing the aircraft and landing gear.
Materials should be either reusable or manufacturable with less energy consumption. For
example, two major leading airplane manufacturing companies, Boeing and Airbus, have
developed lighter and stronger carbon-fibre composites parts in comparison with titanium
which has been used more frequently, resulting in a significant reduction in carbon emissions.
Boeing shows the statistical results that increased energy discipline and increased usages of
carbon-fibre composites into aircraft parts, has enabled an achievement of carbon emissions
of 24.4 percent from 2002 to 2008.[4] Moreover, EU ETS (EU emission trading system)
strengthened the level of emission law, and anticipated of saving of 176 million tonnes of
carbon dioxide emission by 2015, which will boost aircraft manufacturers develop energyefficient parts to reduce amount of required fuels for flight.[26]
29
Redesign and stress analysis of simplified landing gear
Junghoon Suh
8. Conclusions and recommendations
Investigation and analysis of the landing gear was finalized with the generation of the final
model which incorporates the spring shock absorber. Structural analysis of the landing gear
was carried out with significant amounts of research to boost 3D visualization of the landing
gear. After that, vibration equation successfully enabled us to evaluate the target maximum
deflection of 1.411m, and from optimization of work to find appropriate spring stiffness, the
stiffness value was found to be 700000N/m. Based on theoretical redesign, CAD tools,
SolidWorks was used to design a 3D model of landing gear, able to withstand the landing
loads. Stress analysis was flawlessly proceeded to check the fatigue of redesign and as final
model showed the 730MPa of maximum stress in comparison to yield strength of titanium
5553 of 747MPa, durability of the redesigned landing gear was assured. Through the
sustainability investigation, methods and actions of reduction in carbon emission were
explored to manufacture landing gear in much greener ways.
With regard to the future continuation of work, modelling of landing gear was performed
entirely by using the principles of solid mechanics for sizing and analysis. Moreover, several
parts of the landing gear were intentionally excluded due to the irrelevancy or low level of
correlation to the core of project. However, realization of redesigned landing gear needs more
specific steps until the manufacturing phase, as stated below:

Thermodynamics – During the landing, as outer cylinder slides downward over the inner
cylinder, heat is generated. Due to the heat, corrosion of the joint part is expected to be
boosted, but since this project was focusing on solid mechanics, forces and stresses, this
area could not be covered. However, thermodynamics is also another part should be
considered for landing gear design.

Oil-pneumatic shock absorber – The actual target landing gear uses the oil-pneumatic
shock absorber, but designing of this type required the much of time due to the
complexity of the model apart from its aesthetic. It needs to concern about landing force
that shock absorb should withstand, but the flows of both nitrogen and oil should be
appropriately designed. Therefore, from the plenty of researches from solid mechanics
and thermofluid, the deeper understanding and appropriate application of knowledge
would be expecting to generate more appropriate comparison between spring and oil –
pneumatic types.

Missing landing gear parts – In this project, size of landing gear was begun sizing with
approximation and optimized. However, since most of the parts were size with
approximation, the appropriate amount of materials for each part could not be specified
as well. Moreover, this part was to design the simplified landing gear under the landing
conditions, redesigned landing gear only incorporated few parts which only needed to
absorb impact. As continuous work, what requires to be continued are designing missing
parts, such as drag strut and lock links, which requires for steering or taxiing apart from
landing and more precisely calculation of the dimensions of each part of landing gear.
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Redesign and stress analysis of simplified landing gear
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POLITECNICO
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MILANO.
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ABSORBER.
Available:
ftp://ftp.uni-
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Appendix
Appendix A Vibration data sheet
33
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Appendix B ABAQUS analysis figures
1. Mesh convergences (1691, 3162, 6140 and 11235 numbers of mesh elements from left to the right)
2 Animation of deflection changes ( 0 second to the 1.4 seconds with increment of 0.2 seconds)
3. Table of values from analysis (shock absorber)
Materials->
time
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
Alloy Spring Steels
stress(Pa) force(N)
deflection (m)
0
426656
853312
1279970
1706620
2133280
2559940
2986590
3413250
3839900
4266560
4693210
5119870
5546530
5973180
0
77216.8
154434
231650.8
308868
386084.8
463300
540520
617736
694952
772168
849388
926604
1003820
1081036
0
0.0942005
0.1884005
0.282601
0.376801
0.4710015
0.5652
0.6594
0.7536
0.847805
0.942005
1.036205
1.130405
1.224605
1.318805
Stainless spring steels
stress(Pa) force(N)
deflection (m)
0
416561
833121
1249680
1666240
2082800
2499360
2915920
3332490
3749050
4165610
4582170
4998730
5415290
5831850
0
77376.4
154752.8
232129.2
309505.6
386882
464260
541636
619012
696388
773764
851140
928516
1005892
1083268
34
0
0.101207
0.202414
0.3036205
0.4048275
0.506035
0.60724
0.70845
0.809655
0.91086
1.01207
1.113275
1.214485
1.31569
1.416895
Copper-base spring alloys
stress(Pa) force(N)
deflection (m)
0
454125
908251
1362380
1816500
2270630
2724750
3178880
3633000
4087130
4541250
4995380
5449510
5903630
6357760
0
77112.8
154226
231338.8
308452
385564.8
462676
539792
616904
694016
771128
848244
925356
1002468
1079580
0
0.0959905
0.1919815
0.287972
0.3839625
0.4799535
0.575945
0.671935
0.767925
0.863915
0.959905
1.055895
1.15189
1.24788
1.34387
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Appendix C Spring material variation
35
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Appendix D Project management
36
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Risk item
Effect
Cause
1
Insufficiency
of mesh
elements in
ABAQUS
Student license
of software
2
Calculation
error
Stress analysis
will not be able to
work for the best
and most accurate
result
CAD tools are
unable to be used
for analysis
3
Inaccurate
design
of
landing gear
4
Simulation
error
in
solidworks
5
Exact weight
of
redesign
landing gear
could
be
impossible
Original
dimensions of
landing gear
cannot
be
achieved
CAD
programmes
did not work
on campus
6
7
FEA
analysis
cannot be used to
unreliable
solidworks design
Fatigue
testing
cannot be done
Comparison with
weight of original
landing
gear
could not be
possible.
Comparison
in
dimensions
cannot be done
Analysis
and
Design of landing
gear could not be
carried out for a
week
High
Importance
ID
Severity
Likelihood
Appendix E Health and Safety risk assessment
Action to minimise risk
M
L
Request of professional
version or seeking alternative
ways for reliable analysis
Ask for postgraduate in
research
area
of
aerodynamics
or
solid
mechanics and ask for the
help to professor
Redesign of landing gear or
get support from solidworks
supervisor
Complexity of
applied
mechanics in
landing gear
Low
M
L
Occurrence of
design error in
Solidworks
Medium
L
H
Imprecise
entities
or
overlapping of
surfaces
Downgrade of
quality
of
evaluation of
new
landing
gear.
Classification
of landing gear
values
from
company
H
M
H
ABAQUS
was
simultaneously used for the
error in solidworks
M
L
L
SolidWorks has feature of
measuring sizes and weights
of the part.
H
M
M
Approximation of sizing was
done and optimisation was
proceeded.
License of each
programme and
my university
account
had
crashed each
other
L
H
H
Went to meet technician to
fix the problem. Spent extra
time
for
revision
of
theoretical results
37
Redesign and stress analysis of simplified landing gear
Junghoon Suh
Appendix F Preliminary report
38