2. Group Report 2013 2
Abstract
This report explains the process from design to
implementation of a landing gear actuator as well as
the hydraulic system within a Cessna Citation Jet.
Also within this report, the manufacturing processes
are identified as well as areas for improved
productivity as well as the design.
I. INTRODUCTION
The group coursework is based around the design of an
actuator from an aircraft of our choice. The aim of the
task is to analyse the actuator as well as the hydraulic
system from the aircraft and make changes to it to
improve perhaps the materials, the number of
redundancies in the hydraulic system or the pressures,
which the actuator works at. The actuator we are doing is
the trailing link actuator in the undercarriage system.
With this piece of work, multiple programs were used
in-order to complete the task. Programmes that were
used were Multisim, Simulink and Solidworks to make
changes to the design of the hydraulic system as well as
the actuator. Calculations were used to explain our
reasoning for the dimensions of the actuator as well as
the operating pressure with no assumptions made, as the
information was available. The communication for this
project was key and this was achieved through social
networks, emails and texting. Each member of the team
was informed with a clear role they had within the group
and knew the tasks that they had to complete.
II. PLAN
A. The Aircraft and its Hydraulic Components
The aircraft that we have chosen was the Cessna Citation
Jet, this aircraft is not too large on a scale compared to
most commercial aircraft such as a Boeing 747. Another
reason for choosing this aircraft is that the hydraulic
system schematics, which we found via smarkcockpit
which give a detailed outline of the system and showing
every individual component in it. The system itself was
also smaller than if we had chosen a larger aircraft and
may have had a less detailed schematics of it and maybe
less information about it.
Fig. 1. Cessna Citation Jet- 525 (Pingstone, 2008)
The basic components of the hydraulic system are made
of a reservoir, actuators, pumps, accumulator, valves and
fluid. The hydraulic system is show in Appendix 1 and
2.
• Hydraulic system is a system composed of
using hydraulic fluid to drive components such
as an actuator and is used in this case in aircraft
when the pilot cannot perform a task that is
impossible to complete due to the amount of
work needed, and so the system aids them with
this.
• Reservoir: This is where the fluid is stored and
from this point it is distributed throughout the
system.
• Pump: This is a mechanical device that provides
a force that then in turn gives the fluid motion
around the system.
• Accumulator is another storage component but
instead of fluid it stores the pressure for the
hydraulic fluid as it a non-compressible fluid
and this is achieved by the means of an external
force.
• Valves are sections between components of the
hydraulic system. The reason there valves as
they act as a safety measure if the pressure
becomes too high then it can stop the flow of
fluid or even be a limiter to prevent the pressure
of the fluid becoming too high.
Cessna Citation Jet, Hydraulic System Analysis
and Actuator Life Cycle
M.Etienne, J.Heath, D.Gachie, H.Bansal C.Hewitt, H.Ismail, O.Salah
Coventry University
3. Group Report 2013 3
• The fluid is non-compressible as it is a liquid
and the type of hydraulic fluid used in
commercial aircraft is Skydrol.
• Actuator is a component that changes the energy
of the fluid flow to a mechanical force.
B. EASA Requirements
Although the Cessna Citation jet is an American aircraft
it is still required to meet EASA requirement to fly in
Europe, and also must follow Airworthiness directives,
which there as been several published since 2007.
The 'Cessna Citation Jet (CJ1-2)' is classed under the
regulations for 'Aeroplanes Multiple Turbine Engine'.
This is due to two factors, first that the total take off
weight is less than 5700Kg and second, the aircraft is
powered by two turbofan turbine engines (FJ44-1A) that
are provided by Williams International. As for noise
regulations the citation jet follows the ICAO annex 16,
volume 1, edition 4-amendment 8 certification basis.
[EASA, 2012]
When taking into account solely hydraulic systems there
are certain requirements, which must be met, some of
examples of these are:
1) The design, each hydraulic system must be designed
to meet the following:
2) a) Each component must be able to support the
structural pressure as well as the hydraulic
pressure
3) b) If a hydraulic system as two or more primary
functions then an appropriate indicator of the
pressure must be displayed to the crew
4) c) The total pressure in the systems, including the
surge pressure will not exceed the safety
limitations on the given system.
TABLE 1
These are the EASA requirements for the Cessna
Citation Jet landing gear system [EASA, 2012]
C. Plan
Michael who led the project with the help of rest of his
team members carried out risk assessments weekly,
which looked at the risks, and opportunities that were
highlighted as well as looking at the actions. The risk
assessments were provided online. Examples are
provided (Appendix 3).
Some of the Examples of the Risks, Opportunities and
Actions:
Risks:
• Personnel – People were unable to attend to
meetings or lectures associated with this project due to
illnesses
• Design - the design failed to work first time via
Simulink meaning alterations had to be made
• Infrastructural – Lack of ICT facilities available to
use certain software such as Simulink which can be
used for designing the system
• Information flow – Communication of what people
are doing or researching about for the hydraulic
system.
Opportunity:
• Personnel – Reschedule tasks set by team leader or
assign different roles for every team member’s
strengths.
• Design – The design might be simplified for the
4. Group Report 2013 4
actuator or the hydraulic system it is part of.
• Infrastructure – ICT facilities may be better for this
type of project as well as the programmes that can be
used, in this case would be the computers in
engineering building. Software available on these
includes Matlab and Simulink.
• Information Flow – Some cases that could occur is
having more people assigned to one section of the
work than needed meaning less work is being
completed and duplicates are being made.
Action:
• Capture risk information on the one-page form,
which could be done daily or weekly at meetings
within the group members. Generate a list of all the
risks within the project and then prioritise which ones
will have the greatest impact on the work.
• Perform the actions and regularly review the risk.
Update the forms and register. Add any new risks
when they occur and keep track of how your risk
changes over time so that you are able to adapt to the
situation and able to make any changes to the plans.
III. DESIGN
The hydraulic architecture has been modelled in
SIMULINK to identify the output of the system and
possible areas for improvement. All details input into the
model have been selected accordingly for the particular
aircraft as interpreted from the hydraulic system in
appendix 1.
Fig. 2. Hydraulic Circuit Diagram for the Cessna
Citation Jet.
Once the general structure of the hydraulic system was
determined. The CAD of the actual actuator began. It
started out with determining the force required to move
the landing gear both releasing and retracting it. This
involved research of the weight of the Cessna citation jet
landing gear. However, this was limited due to
manufacturer privacy and therefore further research was
carried out to estimate the actual weight of the aircraft. It
was finally determined that the force required to move
the actuator was 4% of the take off weight. With this
essential information the effective length, maximum
stroke length, rod diameter and supporting factor were
easily determined enabling the initial design of the
actuator using Solidworks. Using the pre-installed
wizard in Solidworks, the bore, clevis type, operating
pressure and stroke length were then keyed in. However,
due to the function of the selected actuator, the stroke
length not only had to be directly influenced by the force
to be produced but also by the distance needed for the
landing gear to be fully retracted and released. Refer to
section C of the report for calculations and appendix 4
for diagrams and images.
A. Architecture
The SIMULINK model includes all components
required in the actuator of the landing gear extension and
retraction system. The input is via a step input via a sine
wave to identify a continuous maximum and minimum
displacement and response to the solenoid input.
The mass of the actuator was estimated from the size of
the component and the mass of the materials used.
Because of this the actual mass of the actuator may be
different from the calculated value, leading to possible
errors in the information displayed on the scope
B. Test Plan
After the manufacture of the actuator parts, they are
then tested carefully for the following reasons: the parts
need a safety certification, so that the actuator shows it
has met the specification and safety requirements. The
other reason being the life of the product, there should
be an idea of how long the product will last. The final
reason is that all the design errors are correct so the
product has no faults.
Tests included varying the hydraulic fluid type of which
this did not have any major effect on the output. This is
shown with the basic test of the actuator response with
5. Group Report 2013 5
respect to time and displacement (Fig.3.).
Fig. 3. Actuator Response with respect to time and
displacement
Fig.4. Actuator over compensating
From the test, it shows (Fig.4) that our design of the
actuator over compensates as shown by the ripple at the
bottom of the response curve. This indicates the
response time of the actuator is more than adequate thus
efficient but reducing the life cycle of the actuator.
C. Actuator Requirements
The calculations below show how the actuator
dimensions were acquired and this was done using the
pressure of the system as 1000-1500psi of which the
bore size was determined using a graphical method.
The bore size in this instance was 10.68mm
Weight of landing gear is 4% of the take-off weight.
4717kg/2 (2 actuators) = 2358.5
0.04 x 2358.5 = 94.34kg
94.34 x 9.81 = 925.475N
A=F/P
= 925.475/ (10.34 x 106
)
= 8.950 x10 -5
m
A = π r2
R = 5.34 mm
D = 10.68mm
Piston Rod D = 4mm
Bore = 10.68mm
Support factor = 1.2
416.66 x 1.2 = 500mm max stroke length.
Design is a forked clevis.
D. Materials
The components that are found in an actuator as well
as the material that is used:
“
• Head & Cap- rolled steel plates
• Cylinder barrel- steel stubbing
• Gland bushing- bronze
• Piston rod- alloy steel
• Tie rod and nuts- steel
• Barrel seal- fluorocarbon
• Cushion seal- bronze
• Piston seal- glass & bronze
• Rod wiper- polyurethane but can be replaced by
fluorocarbon
• Cushion plunger- mild steel
• Piston- steel
• Seal and packing- double urethane “
[MOOG, 2013]
The standard actuator is comprised off components
mostly constructed from steel such as the piston and
cylinder barrel. While the seals and other parts are made
from bronze, as it is a good sealer as well as having a
low friction between two metals when they are in
contact. The areas of an aircraft where it can cope with
the demand are in the undercarriage pivot components,
engine mounting and wing root attachments as these are
places where there are high tensile strength, resistance to
wear and stiffness. But the reason it has not be replaced
by any other material with similar properties is due to
the cheaper costs but the expenses are within the
manufacturing of the raw material, weight as well as
rusting when in contact with moisture. This means that
steel parts of an actuator have to be coated with a seal to
prevent the moisture rusting parts.
Carbon Steel is a specific material that is used in aircraft
parts and structures as it can withstand high tensile
strengths, high stiffness and high resistance to wear. It
would be suitable as a material for actuator parts as this
is the type of forces that are found in the undercarriage
6. Group Report 2013 6
system.
Fig. 5. Selected Actuator Materials
IV. IMPLEMENT
This section looks at the process and tools used for the
manufacture of the raw materials, which are transformed
into parts for the actuator system
A. Tools and Techniques for Manufacture
For the manufacture of the actuator, each individual part
identified in the previous section all goes through the
same process of fabrication. Fabrication is the process in
which the metal is:
“
• Acquisition of the raw materials
• Cutting and burning
• Forming
• Machining
• Welding
• Final Assembly “
[Wikipedia, 2013]
In the scenario with steel or any other raw materials
there acquired from the mining facility and taken to
factory facility where it is processed to either become an
alloy or be cut to specific sizes used in products. The
cutting and burning process would be where the
customer has given the manufacturer the dimensions in
which the material has to be cut for manufacture. An
example of machining is the piston inside the actuator
can be manufactured is by, “skiving and subsequent
roller burnishing inside a tubular work piece. Skiving
uses a set of carbide blades positioned around the
diameter of a tool to slice away chips and create a
geometrically round bore. Roller burnishing, a cold-
working process, and uses multiple rollers to compress
the peaks of material left behind after skiving to generate
an extremely smooth surface finish. Burnishing also
introduces a residual stress layer into the cylinder wall,
which improves cylinder fatigue life. “ [Collins, 2013].
This process can be quite time consuming with all the
different steps involved in this process but the results
produced do enable the product to having a longer life
and reduce the need for maintenance on this part.
The end result is a composition of the alloy, which is not
only light and strong but has a high corrosion resistance,
meaning no layer is needed. This can reduce the overall
costs of manufacture of the actuator.
B. Project Plan
The project plan is put in place, so there are guidelines
of how the outcome of the project should be, the project
plan would also contain the times and dates of different
deadlines for a section of the project to be completed, it
is put into place so that the tasks can be completed and
the product can be made in time for use. The project plan
will also include the list of names of people working on
it, and the allocated roles they have within the project.
Some of the things included in the project plan are:
• Quality control standard: is a list of actions that
are set so that the criteria is matched
• Tractability of parts
• Improvements in productivity
• Staff certifications
• Risk assessment forms
C. Test for Failure
After the manufacture of the actuator parts, they are then
tested carefully for the following reasons: the parts need
a safety certification, so that the actuator shows it has
met the specification and safety requirements which
allows the aircraft to become airworthy. The other
reason being the life of the product, there should be an
idea of how long the product will last and this can be
related with the type of maintenance required to either
extend the life or the need to remove and replace it. The
final reason being all the design errors can be corrected
before the product is manufactured with computer
simulations as well as physical testing with manufacture
of test models. This reduces overall the number of faults
or the likelihood of a fault occurring.
These tests can be carried out in different ways such as
running the model of the actuator in this case in
simulations such as stress testing as well as thermal and
pressure changes to see what the effects they have on the
7. Group Report 2013 7
performance of the component. As well as this 3D
models can be produced using 3D painting as an
example. This type of method is becoming popular with
manufacturing companies due to reduction of costs as
the materials are not as costly as actual ones used in the
product and these can be tested again with similar tests
used in the computer software.
V. MANAGE
Aircraft maintenance is:
“The overhaul, repair, inspection or modification of an
aircraft or aircraft component.” [Collins, 2013] The
European Aviation Safety Agency (EASA) is regulatory
body that regulates the European civil aviation industry
and has a series of legislation materials that companies
and engineers have to follow or meet the requirements of
to ensure maximum safety and reliability of aircraft and
there parts. Some of the regulations engineers and
companies must follow are:
• Part 147: Training Organisation
Requirements: This section covers the
requirements of an organisation or the company
for the training of staff for the maintenance of
aircraft and components.
• Part 66: Certifying Staff: Each engineer within
the company will be required to have a type
rating certificate which is a document saying
that they are fully trained to work on a specific
type of aircraft, and that they are working are on
the correct ones.
• Part M: Continuing Airworthiness
Requirements: It is a regulation that specifies
that the conditions to be met by companies
involved in the continuing airworthiness
management or maintenance of the aircraft
• AD-: Airworthiness Directive: This is a
regulation that is found if any faults that occurs
with the aircraft. The only AD to occur with this
aircraft was the lithium-ion batteries due to fires.
This led to some of the batteries being replaced
or modified to prevent this type of event in the
future.
A. System Documentation and Support Services
Preventative maintenance is a type of maintenance
performed to prevent failures of parts of an aircraft, the
need to manufacture unnecessary parts and failing to
comply with regulations that are set by EASA, which
could result in the aircraft being grounded, as it is not
airworthy. It is also a type of maintenance that can
extend the life of parts as well. With this type of
maintenance there are a number of checks, which are
performed, as different parts of an aircraft require
maintenance because of different life cycles. There are
four types of checks and each one is explained as well as
the parts of the aircraft that fall into each category.
• A Check: This is a check that is performed
approximately every 500 - 800 flight hours or
200 - 400 cycles, which the aircraft completes.
The aircraft then requires around 20-100 man-
hours and this is usually performed overnight
at an airport gate or in a maintenance hanger.
B Check: This type of check is performed
approximately every 4–6 months. This
requires more man-hours at about 150hours
and this requires up to 1–3 days working on
the aircraft in an airport hangar.
• C Check: This is check is performed roughly
every 15–21 months or a specific amount of
actual Flight Hours (FH) as set out by the
manufacturer after it has manufactured the
part which is being checked. The time needed
to complete such a check is generally 1–2
weeks as it covers large majority of aircraft.
• D Check: Check D or also known as heavy
maintenance is the most demanding and
comprehensive check out of all of them. This
type of check occurs every 5 years and this
involves the whole aircraft being taken apart.
The amount of man hours required for this is
around 40,000 hours which means this can
take up to 2 months to be completed with the
aircraft being grounded for that entire period
of time.
In this case with the hydraulic system this would be an
A check as the system would be checked for leakages,
corrosion of the pipes as well as fluid changes if needed.
The materials that can be changed form the original
actuator would be the steel and then use a stronger alloy,
which is carbon steel. Not only can withstand high
tensile strength but as well as high loads applied. This is
essential for the actuator, as it will experience high loads
when the aircraft lands. However, the change in material
has a notable/significance increase in mass as making
the actuator lighter reduces its strength and fatigue life.
Testing/ implementing the changes into Simulink, a very
significant change in the response of the actuator was
noted as not only did the actuator reduce its response
time, but the operating pressure had to be changed and
furthermore the scope had multiple zero crossing that
resulted in errors. Therefore it was advisable to retain the
mass as calculated or designated by the manufacture and
was therefore retained in our final design of the actuator.
8. Group Report 2013 8
Evolution of the Design:
Using the SIMULINK model we changed elements of
the systems to improve the response and reduce
redundancy by removing parts rather than adding or
changing inputs this was done by check valve 3 or 4
could be removed to reduce the total number of the
components in the system, reducing the total weight,
cost and build time. Alternately removing fixed-
displacement pump 1, Check valve 1 and check valve 3
to further simplify the system.
The system was tested after these components had been
removed and the performance was not affected, showing
that it would be a potential improvement for the design,
which still met the specification matrix you made at the
start.
Fig.6. Improved design of the actuator system
Fig.7. Output after design improvement
Recycling and Retiring of the Product:
Sustainability is defined as “a process or commodity
that can be maintained at a certain level” (Harrison,
2013). A lot of the components of the actuator are
manufactured from steel and this is the most recycled
material in the world with over 105% of cars
manufactured from steel are recycled. Parts such as the
piston rod, piston, tie rod and nuts as well as the cushion
plunger can be melted down and manufactured into
similar actuator parts or for new products. The raw
materials would marginally be extracted from wales
where it can be refined and constructed into blocks of
steel ready for manufacture. The carbon impact this
would have is the transportation of the materials from
the factories in wales to plants such as Bristol where it
can be manufactured into parts for the actuator.
VI. CONCLUSION
Overall the actuator design for the Cessna Citation Jet
is limited in areas due to the material use as when you
change the mass it affects the output. This was shown in
our report using Matlab where it led to a delay in the
response time of the device. But with design there are
improvements in the testing of the component to
increase the standards of the product as well as overall
safety.
The areas of improvement would be however
productivity of the manufacturing of the actuator with
using different technologies to test and manufacture.
With this another area would be the environmental
efficiency with using more environmentally methods of
acquisition, manufacture and shipment of the actuator as
well as using materials, which are less harmful to the
environment through similar processes. This can be done
with more funding into research and development by the
government for aerospace companies such as Meggitt.
10. Group Report 2013 10
APPENDIX 3
Risk/Opportunity Register
Programme: Hydraulic System Construction via Simulink
Group: L
Title:
Redesign the Hydraulic System
on Simulink
Current Score (PxI): -5
Potential score (P2xI2): -1
Description:
Using the original hydraulic system already constructed on Simulink to then alter to make it
more efficient and maybe remove or add redundancies to the system.
Assuming this risk occurs then:-
Best case: 1 weeks delay to redesign hydraulic system – no further effect.
Worst case: 3 weeks delay to redesign hydraulic system.
Current Score – Risks negative, opportunities positive.
Risk: High -3, Med -2, Low -1, Opportunity: Low +1, Medium +2, High +3
What is the probability (P) that this will happen (1 to 3): 2
What is the impact (I) if this happens (±1 to ±3): -3
Mitigation
Reduce Probability: -
1. Deliberately over-estimate the retraction system sizing to have spare capacity. Refine
the design later if time allows.
2. Provide additional team support to aid in the calculations and designing with system as
the work load can be broken down meaning less stress on team members to complete it.
Reduce Impact: -
1. Set up the calculations electronically via software such as Matlab to be easily re-worked
to follow design changes that may occur
2. Consider maybe leaving it for sometime and come back later if it is becoming time
consuming when other parts of the hydraulic system such as the actuator could be
worked on.
Potential Score – What will the score be if we carry out the mitigation
What will the probability (P2) become (1 to 3): 1
What will the impact (I2) become (±1 to ±3): -1
11. Group Report 2013 11
APPENDIX 4
BS8888 Standards for the technical drawings down via Solidworks
13. Group Report 2013 13
ACKNOWLEDGMENT
Acknowledge the individuals in this group for the
completing this work with every member contributing their
own part.
REFERENCES
• Adrian Pingstone (2008) Cessna Citation Jet
[Online] available from <
http://en.wikipedia.org/wiki/File:Cessna_525_cit
ationjet_g-seaj_arp.jpg > [10 March 2013]
• EASA (2012) EASA standards and requirements
for the Cessna Citation Jet [Online] available
from <
http://www.easa.europa.eu/ >[20 March 2013]
• Coventry University (2013) A085 Series Servo
actuators booklet [online] available from <
http://cumoodle.coventry.ac.uk/mod/resource/vi
ew.php?id=17181> [20 March 2013]
• Wikipedia Page (2012) Manufacturing and
Fabrication Processes [Online] available from:
http://en.wikipedia.org/wiki/List_of_manufactur
ing_processes [20 Feb 2013]
• Smart Cockpit (2013) Cessna Citation Jet
Hydraulic Systems [Online] (Appendix 1 & 2)
available from <
http://www.smartcockpit.com/aircraft-
ressources/Cessna_Citation_Jet-Hydraulic.html
>[25 February 2013]
• Coventry University (2013) Methods of
Machining [online] available from <
http://cumoodle.coventry.ac.uk/course/view
.php?id=4719
>
[20
March
2013]
• Coventry
University
(2013)
Definition
of
Maintenance
[online]
available
from
<
http://cumoodle.coventry.ac.uk/course/view
.php?id=4719
>
[20
March
2013]
