Part 2 Design case study Catapult launcher for Unmanned Air Vehicles
(UAV) SESM2005: Engineering Design and Structural
Analysis Methods Group8
NaineshBumb;XenofonKalogeropoulos;AlexKelday;LeongWaiHou;LinXiao;HalilPortakalcioglu;JamesTagg;BugraTarazi
16/05/2012
The following report follows the design process of a UAV launcher specifically from conception to final design. The design process includes identifying the customer requirements, researching existing designs and constraint & cost analysis. Finally a des
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Table of Contents Abstract.....................................................................................................................................................................3
Introduction............................................................................................................................................................3
2.1OverallPerspective.................................................................................................................................3
2.2LiteratureReview....................................................................................................................................4
2.3CriticalReviewofdesignalternatives............................................................................................7
EngineeringCalculations..................................................................................................................................9
3.1BasicCalculations....................................................................................................................................9
3.11Stiffnessresearch..........................................................................................................................11
3.12Winchrequirements....................................................................................................................13
EngineeringDesignmethods.......................................................................................................................14
4.1Customerrequirements..........................................................................................................................14
4.2DesignConceptGeneration...................................................................................................................18
4.3DesignConceptSelection.......................................................................................................................27
4.31TheLaunchingsystem:...............................................................................................................27
4.32Thecradle:........................................................................................................................................30
4.33Thesupport:.....................................................................................................................................30
4.34TheFinalDecision.........................................................................................................................35
4.5DesignOptimisation.................................................................................................................................37
4.6CostAnalysis(VanguardStudio)........................................................................................................41
4.6.1TheOverallModel.............................................................................................................................41
4.6.2MaterialCosts.....................................................................................................................................42
4.6.3FixedCosts............................................................................................................................................43
4.6.4ProcessesCosts..................................................................................................................................44
4.6.5LogisticsCosts.....................................................................................................................................45
4.6.6CostversusMeritGraph............................................................................................................46
4.7 Finite Element Analysis..............................................................................................................................47
4.7.1SimulationoftheTrolley:.........................................................................................................47
4.7.2SimulationoftheRoll‐Bars......................................................................................................52
4.7.3Simulationofthewinchassembly:......................................................................................53
4.7.4Summaryforsimulationanalysis.........................................................................................56
4.7.5CalculationofFactorofSafetyforthetestedparts......................................................57
Summary................................................................................................................................................................59
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Conclusion.............................................................................................................................................................60
Futurework.........................................................................................................................................................61
References.............................................................................................................................................................62
Appendices...........................................................................................................................................................65
AppendixA:DesignMatrices..................................................................................................................65
A.1BlankBinaryWeightingMatrix.................................................................................................65
A.2CompletedBinaryWeightingMatricesandAveragedResults...................................65
A.3HouseofQuality...............................................................................................................................72
A.4CODA......................................................................................................................................................73
AppendixB:ProductionDrawings.......................................................................................................76
B.1BaseConnectingBar.......................................................................................................................76
B.2Cradle....................................................................................................................................................76
B.3WinchBase.........................................................................................................................................77
B.4EndLink...............................................................................................................................................78
B.5GroundSupport................................................................................................................................79
B.6LegBar..................................................................................................................................................80
B.7Link.........................................................................................................................................................81
B.8RollBar.................................................................................................................................................82
B.9Trolley...................................................................................................................................................84
B.10Wheel..................................................................................................................................................84
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Abstract
The following report follows the design process of a UAV launcherspecifically from conception to final design. The design process includesidentifying the customer requirements, researching existing designs andconstraint & cost analysis. Finally a design is selected and then modelled inSolidWorksforfiniteelementanalysis.
Introduction
2.1 Overall Perspective
UAVs (unmanned aerial vehicle) are aircrafts that are piloted withouthaving a human on board. Usually, they are controlled remotely althoughautonomoususeisincreasing.Asaresult,thevehiclestendtobemuchsmallerthan their manned counterparts with typical wingspans of just a couple ofmeters being able to provide a sufficient enough lift force to keep the UAVairborne. Although predominately used by the military, UAV’s are becomingpopularinasmallnumberofcivilapplications.
Figure1:ShowingthewiderangeofUAVintermofwingspanlength.[1]
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LaunchersallowtheUAVtobelaunchedinrelativelyshortdistances.This
isdesirablesinceitisn’talwayspossibletofindopenflatsurfacesthatcanactasrunways.UAVLaunchersallowtheusertolaunchthecraftvirtuallyanywhere.
Although UAV’s are mainly used by military for various uses such asreconnaissance and combat, applications in the civil sector are increasing.Thespecification of theUAV depends on its purpose. CombatUAVs can have hugesizeswhereonesusedforfilmingtendtobesmaller.
Figure2:Showingthepossibletypeoflauncher
usedinmilitary.[2]
2.2 Literature Review
Introduction
The literature review has been done to find the importance and the outline
the requirements for an Unmanned Air Vehicles (UAV) catapult launcher and to
investigate some different methods of solving the engineering challenge used in
different type of applications.
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Body
Unmanned Air Vehicles (UAVs) are also known as drones, which are
unmanned piloted aircraft. UAV are available in wide variety of sizes ranging from
small to large scale of 50 feet wing spans or more. For instance, RQ‐7 Shadow has 10
feet wing span and MQ‐9 Reaper has 66 feet wing span[3]. UAV are widely used in all
sort of areas, especially maritime as they allow the ships to defend themselves and
detect enemy threats autonomously from aerial vantage points. Furthermore, since
naval ships can be expected to operate in hostile environment and emergency
situations, it is important that the aerial platforms are also capable of being operated
under these conditions. For instance, the Manta UAV used to perform hyperspectral
imaging can be launch from the upper deck of the combat vessel “Stiletto” and Silver
Fox UAV mounted and launched from an 8m rigid hull inflatable boat (RHIB) boats
while they are in motion[4].
UAVs can be further divided down into few different categories such short‐
range, close‐range, medium range and stratospheric. Each UAV is assigned to
different type of mission depending on their endurance limit and payload capacity.
For example, the MQ‐9 Reaper is used for combat mission due to its high endurance
limit of 24 hour and high payload capacity of 3750 lb allowing it to carry 4 x 500lb
weapons. However, this massive UAV has to be launch using a runway due to its
weight. Furthermore, Scan Eagle is used in Marine Corps and Air Force for
surveillance by attaching a stabilized camera on to it for Electro‐Optical/Infra‐Red
imagery. Scan Eagle can be launched by a pneumatic catapult launcher which allows
operations from ships or from remote, unimproved areas [5].
The importance of UAV launchers in successful operations has given rise to
the challenges of designing and optimizing launchers for safety and operability in all
sorts of conditions; cost reduction by using a simpler and more effective launching
mechanism thus reduces the required manpower to operate and maintain. As a
result, most manufacturers aim to improve their designs in order to accommodate
what customer requires. For instance, the Pusher Prop launcher manufactured by
BAE system can launch a UAV at up to 44.8mph, it takes less than 12 minutes to
assemble and can be operated in remote locations with a battery pack. A more
handy UAV launcher such as the Tractor Prop Launcher by BAE System (shown in
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Figure 3 below) weighs less than 18kg and can packaged in one small container
152cm X 35cm X 40cm in size. Engineered Arresting Systems Corporation have
designed a expeditionary launcher which can mounted onto a HMMWV trailer for off
road mobility and can launch a UAV in less than 10 minutes with only two personnel.
These new types of launcher not only encourage all sectors to replace
expensive manned aircraft for suitable small operations, but also show the
convenience of using UAVs.
Figure3:Launcher[6]
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2.3 Critical Review of design alternatives
There are a various number of solutions for UAV launcher mechanisms that
depend primarily on the size and function of the UAV. Smaller UAVs, of 50kg or less
are suitable for bungee mechanisms. This is where a bungee cord is either winched
or cranked mechanically. The potential energy is stored in the bungee cord itself and
transferred to the mechanism cradling the UAV. They are used mainly in launchers
that are required to propel small UAVs because there relatively cheap compared to
other systems. The main drawback of a bungee launcher is the amount of potential
energy required to launch UAVs of larger masses. This typically results in higher
stiffness values that as are a function of the bungee’s cross sectional area. Hence
UAVs with greater masses require the bungee cord to have a greater area or bungee’s
arranged in parallel. However this affects efficiency and less energy can be
transferred to the bungee.
Figure 4: Pneumatic launcher. [7]
Pneumatics makes up the majority of the other launchers, usually used to
propel loads of 100kg or higher. They are usually self‐contained, compressed air
driven, stand‐off delivery systems capable of firing various projectiles to distances of
greater than 500 ft. The system consists of an air chamber, barrel assembly, braking
system, air compressor, and control panel. The air chamber is a cylindrical low
pressure vessel capped by spherical ends with airtight seals. The chamber has two
outlets: one provides inlet pressure to the air receiver, the other outlet links directly
to the projectile (this outlet would be capped in a UAV application). A firing
mechanism, air pressure equalizing tube, and barrel make up the barrel assembly.
When the firing mechanism is actuated, air pressure forward of the projectile
unseats the barrel cover and the resulting arterial force created helps pull the
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projectile along the barrel, while the air pressure behind the projectile
simultaneously propels the unit through the barrel, assisting in a smooth overall
acceleration due to a push‐pull effect. [8] They are very reliable and can deliver
remarkably consistent results. Given the wide range of pneumatics available, it’s
possible get the optimal sized pneumatics for your mechanism. Compared to the
bungee mechanism, the cost of pneumatic cylinder is higher and mostly the
pneumatic launcher comes in a huge size, thus creating problems in transportation.
Figure 5: Car top launcher. [9]
Car launchers – A cradle is attached to an automotive vehicle and the UAV.
The car then accelerates to the desired take off velocity at which point the UAV is
airborne. The advantage of such a design is the launch design itself is simple as all
the kinetic energy is provided by the car. The obvious draw back of the design
however is that fact that both a car and large open space are required.
Hydraulic Launch – The basic concept utilizes compressed gaseous nitrogen as
the power source for launch. The oil side of an accumulator is connected to a launch
cylinder, a piston connected to a moving crosshead of cable reeving with a 6:1 ratio.
The cable is routed over the launch rail and back to a launch shuttle designed to
"carry" the UAV. When proper launch pressure is reached, the release mechanism, an
electro‐mechanical device, is actuated to start the launch sequence. The system's
release mechanism is programmed with an actuation cycle which is designed to
lessen the rate of onset of acceleration. After release the shuttle is accelerated up
the launch rail at a near constant rate of acceleration. At the end of the launcher's
power stroke (10 to 12 ft.), the shuttle engages a nylon arresting tape, connected to
a water brake, the shuttle comes to rest and the UAV is launched. [10]
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EngineeringCalculations
3.1 Basic Calculations
After selecting the bungee catapult as a launching mechanism, the next step was
to calculate the necessary power required to launch the UAV. The main variables to
consider would be
Mass of UAV and launcher cradle
The aerodynamic drag
Resistance on wheel bearings
Angle of elevation
Stiffness of bungee
Figure 3.1 shows the forces on the mass at point where the mechanism is released.
As the UAV and cradle move vertically relative to the inclined ramp, the equilibrium
equation can be shown to be:
cos 0
cos
At the point of release, the mass is accelerating and therefore equilibrium
doesn’t exist. The force due to acceleration acting on the mass can be represented as
f0. Using Delbert’s principle the dynamic problem therefore can be considered static.
Equation 4.2 shows the forces acting parallel to the ramp.
Figure3.1
kx
R
mg
d
μ R
θ
Equation3.1
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sin
cos – sin
Where the symbols have their usual meanings, K represents the spring force
of the bungee, d represents the aerodynamic drag, x is the bungee extension and μ is
the co‐efficient of friction.
Although the drag force varies with velocity (and therefore at the point of
release will be zero), the maximum drag force has been calculated and assumed to
be constant throughout to simplify the equations. The maximum drag force is
worked out to be approximately 25 N as show in equation 3.3:
12
The resultant force that acts on the mass f0 can be equated to the change of
energy in the system ΔU, by integrating over the distance x, in which it acts. The
possible changes of energy are kinetic and potential, however since the equilibrium
equations are considered parallel and perpendicular to the inclined surface, the
potential energy changes are already accounted for in f0. Therefore the total energy
change can be given by equation 3.4
ΔU d
12
cos – sin d
12
12
– cos – sin
Rearranging for the bungee stiffness gives k to be
2
cos – sin
Using equation 3.4, a python based program was written to that plotted the
extension in bungee length against the bungee stiffness k.
Equation3.2
Equation3.4
Equation3.3
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From figure 3.2, we can see that the relationship between k and extension is
inversely proportional. Hence the bigger the bungee extension, a smaller stiffness is
required to propel to UAV.
3.11 Stiffness research
Quick analysis from the graph shows that for an extension in the interval of 3‐
5 meters, a bungee stiffness value is required in the range of approximately of 200‐
550 N/m. After researching bungee stiffness values on the Internet, it became
apparent that bungee cords are not sold by a specific k value. The reason is simple;
Where E is Young’s modulus, a material constant, A0 is the cross‐sectional
area of the material and L0 is the initial length of the cord. Therefore the stiffness
depends of the length of your bungee and that is likely to be the reason why bungee
cords are not sold with given k values. Therefore, since k and E are constants, a linear
relationship between the initial bungee length and cross‐sectional area develops.
Figure3.2
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Since Young’s modulus is given as
E StressStrain
percentageelongation
After contacting several retailers to find the Young’s modulus values, it was
suggested that the best way to find the numbers was to test some samples. An
experiment was devised to find the Young’s modulus of bungee rope by measuring
the extension of a cord. Weights were attached to a bungee cord via a hanger and
the extension measured. The results are shown below for a bungee with a diameter
of 14mm.
Mass (kg) Extension (ΔL/L0) Young’s modulus, E
7.5 6% 8.01 x 106
8.75 7% 8.00 x 106
9.75 7.4% 8.41 x 106
So the value on 107 Pa is a good
approximation for the Young’s modulus. The
number was checked and verified with
Professor P. Reed. Rubber has a modulus value
between 0.01 and 0.1 Gpa[11] so the value
seems reasonable.
As the design of launcher requires two
bungees to extend in parallel, the total stiffness
value is halved as for bungees acting in parallel;
the total k is the sum the individual cords. With
a given initial length it is now possible to
determine the required stiffness value, k to
launch the bungee at a velocity of 12 ms‐1.
Thus for an extension of 4m and an
initial length of 4m (8 meters when extended),
the required k value required is approximately 360 Nm‐1. Rearranging equation 4.5 in
Equation3.5
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terms of cross sectional area and substituting the values shows that an area of 1.4 x
10‐4 m2 is required. Thus the radius of each cord should be a minimum of 4.52 mm.
Given that it’s unlikely to find a cord on the market with such a specific diameter
(without having one especially made) a 5mm radius will be sufficient. This is
equivalent to a value of 420N.
3.12 Winch requirements The tensional force acting on the winch will be equal to the extensional force on
from the bungee. Hooke’s law as gives this force;
400 ∗ 4 1680N
Effectively this translates into a lifting force of approximately 170 kg. Electric winches
available to buy on the market have much higher values for lifting loads. Therefore
this gives room to maneuver in selecting a model which best suits the other
customer requirements.
The LT2000 ‘Superwinch’ was selected as the preferable mechanism. As well as
having a higher lifting load value of a 907 kg, it has a mass of only 5.4 kg and
therefore is extremely light. The equipment can be charged by connecting directly to
a car battery. However this requires use of an nearby automobile, which may not be
practicable in some environments. Therefore a 12V DC battery is supplied with the
launcher.
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EngineeringDesignmethods
4.1Customerrequirements
Based on the research, the most significant and important customer
requirements for the UAV launcher were listed in the customer requirements shown
below:
Compact size
Minimum weight
Setup quickly and easily
Safety
Low cost
Weather resistant
Suitable for special terrain
Consistent launch characteristics
Easy to operate
Easy to handle
Easy to repair
Durable
Reliable
Optimum take off distance
Optimum launch times
Aesthetics
Minimal personal requirement
Adjustable launch direction
Adjustable angle of launch
Multiple launches per day
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Compact size
As stated in the question sheet the size of the launcher needs to be small enough to
fit into a van. Furthermore, the smaller the size the better as the storage and
mobility is not a problem to any user.
Minimum weight
The weight will affects the stability and the ease of transport of the launcher from a
launching area to other launching area.
Setup quickly and easily
The time is precious. In order to achieve a successful operation, the launching has to
be fast and effective.
Safety
Safety is the most significant requirement of all customer requirements. This is
because to prevent any injuries and harm to the customer as wells as the
environment.
Low cost
Cost can manipulate the potential market of the launcher and the design as wells.
Low cost can attract more customers.
Weather resistant
The launching of UAV area varies. It can be done in anywhere any place with varying
weather and temperature. For example, the weather may change from time to time
and the launcher needs to cope with the changes.
Suitable for special terrain
The base of the launcher determines the effectiveness of the launch. In this case, the
launcher has to be flexible to fit for all kinds of terrain regardless of its place. For
example, the launching of the similar UAV can be done on a desert and on top of the
deck.
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Consistent launch characteristics
The consistency could determine the planning and timing of the launching the UAV
to the air thus affects the outcome of the operation.
Easy to operate
The use of a manual can be neglected if the operation for the launcher is user
friendly and easy. This has the advantage of giving the operator a quick
understanding of the launcher and encourages people with various machine
operating skill levels to use it.
Easy to handle
This can make the transportation of the launcher easier and user friendly.
Easy to repair
Minimizing the need for repairing and servicing equipment is very important in
business as it reduces manpower requirements and running costs. To ensure the
durability and effectiveness of launching, the launcher has to be easy to repair as
wells as service.
Durable
Durability determines the lifespan of the launcher. This can affect the customer
choice as all customers want products to last as long as possible.
Reliable
Reliability implies the amount of responsibility that can put on the launcher. For
example this will determine the amount of launches that can be performed on a
daily basis.
Optimum take off distance
The launching distance has a large effect on the performance of the UAV and its
successfulness in operation. Moreover, the distance available in which to launch a
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UAV is not always guaranteed to be the exact length a customer wants. So the take‐
off distance needs to be optimised in order to satisfy the customers.
Optimum launch times
The time taken to launch the UAV is considered fairly important as it determines how
many launches can be done in a given length of time.
Aesthetics
Aesthetics can affect the customer choice. This is likely to be important in a military
environment where camouflage is vital. Some customers may prefer a launcher to
match the UAV if, for example, it is being used in a public arena, such as the
demonstration of a UAV to potential customers.
Minimal personal requirement
The number of personnel required to launch a UAV can greatly influence cost and
work force allocation for the customer.
Adjustable launch direction
The conditions the UAV is being launched in may vary considerably, and due to time
or space constraints it may be impractical to relocate the launcher. For example, the
wind direction can affect the preferred direction of launching.
Adjustable angle of launch
The angle of the launch will determine the effectiveness and the performance of the
UAV. For example, 45 degree is the optimum launch angle to get the maximum
projection. However, this may vary depending on the wind conditions
Multiple launches per day
As stated in the case study description, the launcher needs to be used several times
in a day.
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4.2DesignConceptGeneration
The launcher is intended for a UAV of 3 meters wide and 2 meters long. It has
maximum weight 25kg and takeoff speed requirement of 12ms‐1.
Several primary concepts of the UAV launcher were generated based on the research
and are shown :
This launcher contains a cylinder with a little gap on it. And for this piston, it uses a
special piston which is fixed to the cradle so that when the compressor is connected
to the cylinder, the air will pushes the piston and so the UAV.
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For this one, it is quite similar to the previous one. But this one is using a spring to
accelerate the UAV and a motor is provided to pull the spring back to its origin
position after each launching process.
The spring stores maximum energy in the compressed position and its extension can
be controlled by the motor. So when the motor is turned on, it pushes the UAV with
the desired energy.
The design is simple and user‐friendly. It can be produced cheaply.
To meet the take‐off velocity, a large spring stiffness value is required increasing the
cost of the system. Also, this design does not consider the positioning of the
propeller of the UAV.
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A simple pulley block and cylinder is used in this case. The pulley block has an
elongation ratio 2:1. This means when the cylinder is fully extended, the rope will
pull the UAV to its critical position.
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This design is based on a crossbow design and it is using bungee to power the UAV.
An electrical motor is attached at the end of the launcher to pull the bungee back to
its initial position.
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A heavy mass is used in this design to store the potential energy. When it operates,
the energy in the mass is transferred to kinetic energy. Alternatively the motor in the
fulcrum could provide work.
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A big fly wheel is used in this design. In the preparation stage, the fly wheel is
powered by an electric motor and rotates in very high speed. In the launch stage, the
fly wheel is connected to a rope which pulls it.
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In this design, the UAV is accelerated by its gravity. The advantage of such a design is
that no power requirement is needed and increases the reliability of the system. The
main drawback is that by equating the required kinetic energy at the end of the ramp
the potential at the top, the required energy needed to launch the UAV at 12 ms‐1
requires a vertical change in displacement of over 7 meters.
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The belt drive is used in this case. And when the rotator is driven by electric motor or
gas engine, the UAV will reach its launch speed at the end.
The whole design consists of only 4 parts. Hence it can be produced cheaply.
The launcher would require a lot of force to meet the criteria of 12m/s take‐off
speed i.e. it would require a large battery to power it increasing the cost.
Another method to meet the criterion is to increase the distance between the gears.
This would increase the length of the belt again increasing the cost.
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This is the launcher works like a rail gun. The UAV is sitting in the middle attachment
which works like a clamp. And when the attachment is disconnected from the rail, it
splits into two parts as there is no additional force on either side of the attachment
and the releases the UAV.
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4.3DesignConceptSelection
For analysis, the UAV launcher is divided into three parts: the launching system, the
cradle and the support. And each part has several choices.
4.31 The Launching system: The pneumatic system: The pneumatic system is quite powerful and it is quite stable
and clean. However, it is relatively expensive and it is difficult to manufacture. Also
the weight of the pneumatic system can be relatively large and the storage for the
compressed air can be a problem.
There are two different types of pneumatic design which have different emphasis:
(The normal type cylinder)
This is a typical pneumatic system which using a pulley block. But this design is a bit
long so that fracture may easily occur during the launching process as there will be
more torque and momentum.
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(The cylinder with a gap)
In this pneumatic system, there is a small gap in the middle of cylinder which allows
the piston to push the cradle directly. This results in a shorter piston/cylinder and
therefore a more compact design. A loss of energy will occur due to air escaping
from the gap. This would need to be factored into the design or a seal would need to
be designed to prevent/reduce the escape of air. This would increase the complexity
and therefore the cost of the design as well as compromising its suitability to operate
in adverse weather conditions and environments.
The spring/bungee system: The spring/bungee system is very cheap, safe, easy to
manufacture and relatively light‐weight. The spring and bungee contribute a
decreasing force, not a constant force. This means the UAV has a maximum stress
initially but very low acceleration at the end of the rail. Usually these require two
winches to pull the system to its initial position.
(The spring launching system) (The bungee launching system)
(The crossbow bungee launching system)
The gravity/mass system: Systems using the gravity to store energy are reliable. The
gravity system is required to be quite large which means they are heavy, not a
compact size and difficult to assemble. For the size of the UAV and the mass of the
payload, a very large counterweight would be required. Also both of these systems
have a low acceleration and low efficiency.
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(Self‐gravity launching system) (The mass launching system)
The flywheel system: this system contains a flywheel to store kinetic energy. As a
result of launching, the flywheel would keep rotating for a while, and the energy
efficiency will be quite low. Also before the launching, the flywheel needs to reach a
required velocity which may take a long time. For a large flywheel the machine will
be massive.
(The launcher with a flywheel)
The electric system: The major concern with an electrical system is the generation or
storage of sufficient electricity while maintaining the light weight, compact design
philosophy to facilitate transport and flexibility. The rail gun system especially
requires prohibitively large currents. It is unlikely that a system with lower energy
requirements would have sufficient power to accelerate the UAV to the required
speed in an acceptable distance.
(The launcher with track) (The rail gun launching system)
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4.32 The cradle: The clamp cradle: this cradle will separate into two pieces so that it releases the UAV.
It has a quite large friction due it needs force from both sides to maintain occlusion
and it requires a high tolerance level in manufacturing. Due to its working function,
the stability of that cradle is also an issue.
Clamp (before launching) Clamp (after launching)
The holding cradle: this cradle holds the UAV and will have bump‐stops at the end.
The holding cradle may cause the UAV to stick at the top surface due to the upwards
force produced by the wings. There is a potential issue with collision with the tail of
the UAV when the cradle hits the bump‐stops.
(The holding cradle)
4.33 The support: Three points support: this three point supporting system uses a ball rolling
mechanism so that it can rotate 360 degrees and has multi launch angels. However, it
is unstable due to the size of the launcher. In addition, all of the stress is
concentrated on a single point which will require significant reinforcement to prevent
failure.
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(The three points support)
Multi‐points support: this is more stable than the three points support but it can’t
rotate naturally due to its structure. This could potentially be overcome by mounting
the system on wheel, but this would necessitate some method of locking the
structure in place.
(Different types of multi points support)
In summary, for the launching system:
Type of launching
system
Benefits Drawbacks
Pneumatic Powerful, stable, clean. Expensive, hard to
manufacture, not
assembled, difficult to
store
Spring/bungee Cheap, low weight, easy to
operate, clean
Property changes when
contact chemicals/at
critical temperature
Gravity/mass Relatively stable, clean High weight/large size
Electric Easy to operate, clean, high
energy efficiency
Low power
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a. Thenormalpneumatictypecylinderb. Thepistonlesspneumatictypec. Thespringlaunchingsystemd. Thebungeelaunchingsysteme. Thecrossbowbungeelaunchingsystemf. Self‐gravitylaunchingsystemg. Themasslaunchingsystemh. Thelauncherwithaflywheeli. Thelauncherwithtrackj. Therailgunlaunchingsystem
For cradle:
Type of cradle Benefits Drawbacks
Clamp cradle Simple structure High friction, high
manufacture tolerance
level, unstable
Holding cradle Easy to operate The structure may collide
with the UAV
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a. Theclampcradleb. Theholdingcradle
The support:
Type of support Benefits Drawbacks
Three points supporting 360 degrees launching,
multi slope launching
Unstable
Multi points supporting Stable Fixed degree of launching
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a. Threepointssupportingb. Multipointssupporting
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4.34 The Final Decision
In this case, the spring launching system, multi point supporting and a holding cradle
is finally selected. And the design is shown below:
After evaluating all the designs, the bungee mechanism was selected as the
mechanism launcher over a pneumatic design. For UAVs with a mass less than 50kg,
the research suggested that this was the most widely used launcher for UAVs of this
size. It’s generally accepted that the pneumatic launcher offers more reliability over
bungee cords, however with an additional price increase. Pneumatics cylinders
would require relatively large and expensive air compressors to generate to the
necessary force to launch the UAV. Hence the bungee mechanism is more simple.
Also the calculations required to work out the required take off velocity of the
UAV are simple and easy to calculate. This makes it easier to determine the neutral
points of such parameters as bungee stiffness, extension and initial length. The
design also has minimal moving parts, increasing the reliability of the system and the
decreasing the chances of system malfunctions.
OperationofthelauncherThe design of the mechanism is relativity simple, as explained in the concept
generation. The principle of the mechanism is to transfer potential energy from the
bungee cord to the UAV. Due to the Penguin B UAVs design, special consideration
was given on how to then transfer the kinetic energy from the trolley (or cradle) to
the UAV. Constraints such as propeller size and torque on the wheels had to be
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taken into account. The final design was to ‘cradle’ the wings above and below. The
cradle itself has groves to position the wheels.
A winch pulls the pulls a cable positioned on the undercarriage of the cradle
such that it doesn’t interfere which the UAV propeller. The Cradle itself has a total of
6 wheel bearings that slide into the rails on the ramp. Wheel bearings are
advantageous since they minimize the contact area and therefore friction with the
rail. When the bungee is fully extended to a length of 4m, the lynch pin is pulled to
release the winch from the cradle. The pin is connected to an inextensible cable and
therefore can be pulled at distance to increase the safety.
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4.5DesignOptimisation
Having determined the customer requirements, a binary weighting matrix
was constructed (appendix A.1). This was sent out to potential customers; the BBC;
ITV; Army Air Corps; RAF; Boeing; Lockheed Martin; and BAE systems in the hopes
we could obtain some input from potential users of UAV launchers. Unfortunately,
we received no responses. In order to generate weighted requirements the group
filled out the matrix individually and the resulting normalized scores were averaged
to give a set of weighted requirements we could use to optimise the design
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Fromthecombinedcustomerrequirements,itisclearlyshownthatthecustomerrequirement of safety is the highest with 9.30%. The second highestrequirementisreliabilitywith8.72%andthird,consistentlaunchcharacteristicswith7.56%.Themainreasonforthisisbecausesafetyplaysanimportantroleineverything thatpeopledo. Launching theUAVneeds tobe safe for thepeopleoperatingthelauncherandforpeopleinthevicinity.Ontheotherhand,reliableand consistent launch characteristics are very important in determining theoutcomeof theoperationas itwill determine the consistencyof launching theUAV.Besidesthat,therequirementofoptimumtakeoffdistance,anddurabilityhave the same percentage of 6.98%. Easy to repair, easy to operated andcompact size, all have the slightly lower percentage of 4.65%. The leastimportantcustomerrequirementistheaestheticswhichhasapercentageislessthan1%.
Having selected a concept design, a ‘House of Quality’ (HOQ) and ‘Concept
Design Analysis’ (CODA) [12] were used in order to optimise the design. The basic
engineering calculations above were used to determine both the feasibility of the
design and the parameter that would affect the optimisation. These calculations
also gave us baseline values for the relevant design parameters from which to start
the optimisation.
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Initially the HOQ was constructed (see appendix A.3) in order to identify
conflicting parameters. The HOQ shows that parameters which determine the
characteristics of the bungee were found to conflict. These are fundamental
properties and as such are not subject to change. Instead, a compromise between
these parameters will have to be found which will give the desired characteristics.
This will be done using the CODA. A further benefit of the house of quality is that it
gives a very user friendly, graphical interface to determine the strength of the
relationships between the customer requirements. This interface was utilized by
connecting it to the CODA and using the strength relationships from the HOQ in the
CODA.
The CODA (appendix A.4) was constructed using some of the baseline
parameters determined from the engineering calculations; for example bungee
characteristics, the required winch power, ramp length etc. Others parameters, such
as density of the ramp, were selected by common sense: for example ramp density
was chosen to be between that for Aluminium (2700 kg m‐3) and stainless steel
(7930 kg m‐3)[13]. The relationship functions were then considered individually and
neutral points/tolerances determined by basic calculations, rudimentary costing and
research as required. Once these elements were in place Solver was used to solve
the CODA and find the optimum design. The highest overall design merit possible is
54.06% customer satisfaction. The design parameters to achieve this design are:
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Design Parameter Value
Density of Ramp (kgm‐3) 2700
Length of ramp (m) 4.87
Cross sectional area of ramp (m2) 0.03
Initial bungee length (m) 6
Bungee stiffness (Nm‐1) 550
Bungee extension (m) 5
Bungee Area (cm2) 1.8
Take off velocity (ms‐1) 12
Winch power (kg) 300
Winch weight (kg) 38.2143282
Ramp recoil 3.00
Cradle density (kgm‐3) 1600
Cradle length (m) 0.01
Launch times (s) 10.65
Pin weight (kg) 0.005
Launch angle (º) 45
Pin size (m) 0.5
Wire length (m) 1
Co‐efficient of friction between ramp and cradle
0.0172672
Co‐efficient of friction between bungee and trolley
0.6
Number of bungees 2
An issue that the CODA raises is that one of the customer requirements ‘weather resistant’, is not addressed by these design parameters. However, the chosen design is inherently weather resistant. This will be improved by selection of weather/corrosion resistant materials where possible and, if necessary, a marginally increased maintenance schedule.
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4.6CostAnalysis(VanguardStudio)
The overall merit of the design was obtained using the CODA in the previous section. Even with a high merit, the launcher design could be rejected if it is very expensive to build. Hence, in order to evaluate the cost of manufacturing the UAV Launcher, Vanguard Studio software is used. The studio has a hierarchical tree interface which comprises of branches. Branches on the left are dependent on the ones to their right i.e. to solve a problem, the current branch is divided into two or more simpler components. The process is repeated until there is no further division of components. [14] The right most branches contains the design parameters used in the CODA and in this Vanguard can used in tandem with CODA to obtain the best value‐for‐money launcher by comparing the design merit to the cost.
4.6.1 The Overall Model For the UAV launcher, a cost analysis decision tree was designed to perform two tasks. The first task was to evaluate the optimum cost of the launcher by varying the design parameters and the second task was to relate the parameters with the overall merits. The basic Vanguard model of the UAV launcher is shown in figure 1.
Figure 1: Overall decision tree cost analysis of the UAV launcher.
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The model is a merger of two different modeling approaches:
1. Fixed Costs and Variable Costs:
In this approach, the cost is split into fixed costs and variable costs. The fixed costs are independent with respect to the production. In this model the wheel bearings, bungee cord, tooling items and the winch contribute to the fixed costs. The variable costs depend on the manufacturing process of the material at hand and the number of components manufactured. The material cost branch contributes to the variable costs.
2. Costs associated with physical manufacturing processes:
The model is based on the costs associated with the different stages involved in manufacturing a launcher. These stages can be defined as:
Processes costs
This branch includes the cost required to assemble the parts to make the product. It includes processes like fabrication and assembly costs.
Logistics costs
This branch describes the cost required to support the product. It includes the cost of transportation. It is a part of overhead cost as it is not directly related to the launcher itself.
4.6.2 Material Costs As mentioned before this section includes the cost required to manufacture individual parts. The components given in the table below were manufactured.
Manufactured
Ramp
Cradle
Base
Table 1: The table shows the components that were manufactured
The components to be manufactured have their cost depending on constraints such as the material of the part and its dimensions and so on. Consider the ramp for example. The cost of building an Aluminium ramp is broken
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down into the amount of Aluminium used for one ramp bar, the number of ramp bars and the cost of Aluminium per kg. The branch of the amount of Aluminium used for one ramp bar is broken down into the density of the bar and the volume of the bar which is further divided into the cross‐sectional area and the length of the ramp bar. It is convenient to build the ramp and cradle from the start as the prices of Aluminium and PVC are low for bulk quantities. [15][16]
Figure 2: Material Costs (variable) branch of the decision tree.
4.6.3 Fixed Costs This branch deals with the cost required to purchase a component.
Purchased
WinchWheel Bearings
ToolingBungee Cord
BatteryTable 2: The table shows the components that were purchased.
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The components in the above table make up the off‐the‐shelf purchases and hence have a direct cost associated with them. It is easier and more convenient to get these components from the market than manufacturing them. [17][18][19][20]
Figure 3: Fixed Costs branch of the decision tree.
4.6.4 Processes Costs The processes costs include all of the processes involved to assemble the launcher. These processes are: Fabrication‐ The processes of cutting, bending and welding of Aluminium
bars are included in fabrication. Each branch is further divided into the time
required to perform these tasks, the number of labourers performing the
task and the labour rate per hour.[21]
Assembly‐ It deals with the labour cost to assemble the product. [21]
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Figure 4: Processes Costs branch of the decision tree.
4.6.5 Logistics Costs For the launcher, logistics covers the transportation costs and packaging costs. The individual components of the model are going to be placed inside a Thermocole box. The Thermocole box is placed inside a wooden crate. The Thermocole is present to protect the launcher from damage in case of an accident.
Figure 5: Logistics Costs branch of the decision tree
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4.6.6 Cost versus Merit Graph By varying the design parameters in the CODA matrix, several values of merits and costs are obtained. Then, by plotting those on an excel spread sheet, a visual representation of the merit versus cost is seen. Hence, from the various plots, the best merit versus cost solution is chosen.
Figure6:Graphcomparingthecostandthemeritvalues.
Out of all the different merit‐cost combinations, the best result is the one noted in red (see figure 6). It is the cheapest and has the one of the highest merit value. Some of the designs have a higher merit value, but compared to the red dot design the cost does not justify construction of those designs. Having decided the parameters that provide the best merit and cost, the SolidWorks model can be finalized with these optimized values.
464748495051525354555657
0 1000 2000 3000 4000
Merit%
Cost$
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4.7 Finite Element Analysis
4.7.1 Simulation of the Trolley: Simulation of the trolley was made by defining the fixed geometry of the trolley
when assembled to the rest of the construction. Afterwards, two pulling forces
(1000N) were applied to the two sides of the trolley representing the pulling force of
the bungee when the trolley is located in the extreme position ready for release. The
material selected for the trolley bars was Aluminium 1060 alloy. After running the
SolidWorks simulation with these parameters the following results were obtained:
Figure1‐Deformationofthetrolleyduetobungeepullingforce(Scalex40)
From this simulation study the maximum displacement of the model was found to be
0.1487mm which is considered to be minimal. Furthermore, from SolidWorks
simulation the stresses within the trolley structure due to the bungee pulling force
when in the extreme position were plotted:
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Figure2‐Stressresultsplotduetobungeepullingforce(scalex40)
From this simulation study the maximum stress within the trolley is about
21.879MPa and it occurs in the side bars of the trolley as predicted, so Aluminium
bars are necessary for the trolley structure to maintain its structural rigidity during its
stress cycles. It should be pointed out that Aluminium can contribute to a heavy
weight construction if used solely even though it is considered one of the lightweight
metals it is much heavier and denser than many plastics such as PVC. For those
reasons it was decided that Aluminium should be used only in parts were the
stresses are concentrated and large. For this reason it was decided to make the
trolley form PVC material (which contributes to a lightweight construction) except for
the side bars that will be made from Aluminium 1060 alloy due to high carrying load.
To verify that PVC is a well suited material for the rest of the Trolley part some more
simulations were conducted, which are displayed below.
Firstly, the cradle was mounted on top of the Trolley and then another stress
simulation was conducted. The aim of this simulation was to examine how the cradle
responds to the reaction force applied to it from the UAV wings the moment when
the Trolley is released and has its maximum acceleration. The material used for
building the cradle was PVC, because it is a bulky part with complicated shape and
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building it out of a metallic alloy would be complicated as well as expensive and it
would result in a very heavy‐weight construction. The results of the simulation test
are shown below:
Figure3‐DeformationofthecradleduetoreactionforcefromtheUAVwingswhentrolleyreleased
(scalex20)
From this simulation the results obtained state that the maximum displacement of
the cradle compartment due to reaction from the UAV wings when having maximum
forward acceleration is 1.52mm in the x direction. Such a displacement is satisfactory
because it only occurs for a very short time. This is because as the trolley moves
forwards, the extension of the bungee cords is minimised and so does the reaction
force from the UAV wings to the cradle. Thus the 3.261 mm displacement will be
occurring very rarely in the whole time‐span of a take‐off. Next, the stresses within
the cradle and the frame were plotted:
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Figure4‐StressofthecradleandtheframeduetoreactionfromtheUAVwingswhentrolley
released.(Truescale)
From the results obtained, it is visible that the highest stresses occur in the bars
connecting the cradles with the trolley. The extreme stresses occur in the region of
the two back supports (wheel) which are made out of Aluminium with a magnitude
of 32.7MPa. After all, the choice of PVC for the cradle and the unstressed regions of
the trolley is a reasonable choice of material. Furthermore another stress test for the
trolley compartment was conducted. Its aim was to demonstrate how the lower free
(cantilever) part of the trolley which supports the front wheel of the UAV responds if
some of UAV’s is supported by this part. It should be pointed out that when
designing the trolley part, this lower cantilever was designed just to support the
UAV’s weight and not carry any of its weight. The weight of the UAV will be carried by
the cradles. Although in case of slight possible movement of the UAV during take‐off
some of its weight may be carried by the lower supporting part. Precautions should
be taken against large displacement of this part which may result in resonant
vibrations. The stress test was conducted with an arbitrary force of 100N was applied
to the free lower cantilever (roughly 1/3 of the UAV’s weight). The results obtained
were:
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Figure5‐Deformationofthelowercantileverpart,supportingthefrontwheeloftheUAV(scalex5)
paint
The results show that if the supporting part in the take‐off process happens to carry
about 30% of the UAV’s weight it will have a displacement of 8.7mm. It should be
pointed out that this is an extreme scenario which rarely may happen in case of
wrong attachment of the UAV on the cradles. Similarly the stresses carried by the
cantilever in this worst case scenario are plotted:
Figure6–Stressesinthelowerpartcantileversupport(scalex5)
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4.7.2 Simulation of the Roll‐Bars In this section, the simulation of the roll‐bars was carried out when the bungee cord
wrapped around them is stretched fully by the winch. The Bars are made out of
Aluminium since it is a light metal which high deformation resistance. The bars were
hollowed in an attempt to minimize the structure weight. The simulation results and
plots are displayed below:
Figure7‐Deformationoftheroll‐barduetobucklingloadfromthebungeewhenstretchedatits
extremeposition(scalex1000)
The results of the simulation show that the maximum displacement of the roll‐bar
part is 0.0189mm which is minimal. This shows that the Aluminium is a good
selection of material for the roll‐bar. It might be a heavier choice than a very
expensive alloy or a plastic material but it is crucial that the skeleton of the design
remains as rigid as possible when stressed. Next, the stresses in the roll‐bar were
plotted:
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Figure8‐Stresswithintherollbarwhenbucklingloadappliedbythestretchedbungee(scale
x1000)
The maximum stress obtained from the simulation is 4.839MPa. Its location is close
the point of application of the force. The maximum stress is very low compared to
the yield stress (27.6MPa). Thus from the simulations of the roll‐bars the application
of Aluminium material is justified.
4.7.3 Simulation of the winch assembly: The last simulation made was on the winch assembly. Its aim was to give an insight of
how the winch assembly will respond when the winch stretches the bungee cord to
its extreme position. The results of the simulation are shown below:
Firstly, the stress plot was carried out so see the levels of stress in order to select a
suitable material for the base flat plate of the winch assembly.
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Figure9‐Stresswithinthewinchassemblywhenbungeeisstretchedtoitsextremeposition(true
scale)
It was shown that the maximum stresses are in the region of 70MPa located in the
triangular bars connecting the base with the legs. Aluminium 1060 alloy has only
27MPa yield strength. Therefore Aluminium 1060‐H18 was decided to be used for
those two bars which have much higher yield strength of 125MPa. The material
selected for the base of the winch was selected to be PVC because of lightweight
properties and because the base does not carry any high value stresses. After that
the deformation plot was carried out:
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Figure10‐Deformationofthewinchassemblywhenbungeeisstretchedtoitsmaximumposition
(truescale)
From the simulation the largest displacement came out to be 2.125mm which is
minimal.
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4.7.4 Summary for simulation analysis
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4.7.5 Calculation of Factor of Safety for the tested parts. Factor of safety (FoS), also known as (and used interchangeably with) safety factor
(SF), is a term describing the structural capacity of a system beyond the expected
loads or actual loads. Essentially, how much stronger the system is than it usually
needs to be for an intended load.[22]
A simple formula for the calculation of the Factor of Safety of a component is given
from
ℎ
From the SolidWorks simulation we can work out the maximum stress that each
component experiences and knowing the material properties (Yield strength) we can
compute FoS for each stress tested part:
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Summary
The final design is shown below:
Its powered by bungee which runs from a winch to the UAV supporting
trolley via blocks in the end of the rails. The trolley is constructed of Aluminium
1060 and is attached to a PVC cradle in which the UAV sits. The trolley runs on
Aluminium 1060 C‐section which controls the launch trajectory of the UAV. Specific
parts of the structure which are subject to greater stress are made of Aluminium
1060‐H18 which has a higher yield stress. The result is a minimum factor of safety of
1.2. This has been deemed acceptable as during all calculations the worst‐case
scenario has been assumed so there is already an in‐built redundancy.
In order to keep the design compact the structure collapses and the rails split
into two so the largest piece is just over 2m in length, which will fit in a short wheel
base Ford Transit [23]. To facilitate an adjustable launch angle, the supporting legs
are adjustable. The construction is primarily of Aluminium and PVC so the design
will be both light‐weight and weather resistant. The electric winch will add to the
weight, especially if an additional 12V battery is required for remote use. These
were included in the design to make the launcher easy to use and reduce launch
times. If the launcher is required to be carried long distance or operate remote from
an electrical supply, it would be a simple matter to substitute a hand‐winch into the
design. In order to maximise reliability and minimise maintenance requirement we
have adhered to CL (Kelly) Johnson’s principle of KISS [24].
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As alluded to previously, the design is a compromise between
customer requirements, not least minimising cost. The design process that we have
employed ensures that we have met the customer requirements as fully as possible,
while minimising cost and ensuring safety and reliability.
Conclusion
This report demonstrates the design engineering process involved in making
an UAV launcher. Firstly the requirements of the customer were identified and then
weighted such that most important design aspects were focused on. The safety of
the user was identified as being the primary requirement with reliability being
second. From this, preliminary concepts ideas were generated from which a final
design was chosen. The design selected was a bungee catapult mechanism. The
design works by winching two bungee cords back and simultaneously releasing them.
The values for parameters such as bungee stiffness, extension and aerodynamic drag
were determined. As safety was the top requirement, the quick release mechanism
has designed to include a lynch pin that could be operated at distance. Analysis of
the CODA matrix showed that the best merit design to be 56.25%. The Price of the
final design is $870 which is relatively cheap when compared to commercially
available launchers of this type. This could be due to extra overheads in the design
process that have not been incurred in this process such as office rent, salaries and
tax.
The SolidWorks model is then built and a stress & displacement analysis
preformed. The Finite elements analysis shows the stress acting on the launcher is at
its maximum around at the point where the winch is attached to the ramp; the
material at this point was strengthened with a tougher aluminium alloy. To minimize
the weight and drag, the cradle was perforated. The lower stressed points such as
the assembly supports between ramp links were changed to cheaper lower weight
PVC.
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Futurework
Based on the customer requirements and further research into the
optimization of the launcher, the current launcher can be modified to increase
efficiency. Currently the angle of launch can be adjusted by varying the position of
the feet of the base. This adds an additional weight and size requirement. The design
would be better optimised if the back end on the rail could be adjusted and pivoted
about the front.
This technique not only can provide a launching angle by using the available
space underneath the launcher, but also shows the flexibility of the launcher in terms
of handling and operating. Besides that, the lowered ramp can provide a significant
improved in the stability as the center of mass is lower assuming the mass of the
ramp is larger than other parts of the launcher.
On the other hand, the solid ramp could be redesign to hollow in order to
save cost for the materials and weight. This is because the ramp does not generally
carry much weight and stress from the UAV, but the leg and the cradle of the
launcher.
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References
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8. Technology Option, Pneumatics, Launcher/Booster system Tradeoff Report (pdf), Jan 1995, Naval Research Laboratory. Available on http://www.google.co.uk/url?sa=t&rct=j&q=launcher%2Fbooster%20system%20naval%20research%20lab&source=web&cd=1&ved=0CFkQFjAA&url=http%3A%2F%2Fwww.dtic.mil%2Fcgi‐bin%2FGetTRDoc%3FAD%3DADA290066&ei=djiyT‐XwCImy0QXY_IyQCQ&usg=AFQjCNGI‐9YO2LPReZfq5PkYEh2T9cjRgg Accessed on 26/04/12.
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11. The Engineering ToolBox (website). Available on http://www.engineeringtoolbox.com/young‐modulus‐d_417.html. Accessed on 03/05/12.
12. Calvert JR, Farrar RA, An Engineering Data Booki, 3rdedition.PalgraveMacmillan,2008ISBN:978‐0‐230‐22033‐1
13. A Metric-based approach to Concept Design James Scanlan; Max Woolley; Hakki Eres; http://www.southampton.ac.uk/~jps7/Lecture%20notes/Student%20copy%20value%20based%20design.pdf
14. Visual Interface, Vanguard Studio, Vanguard Software Corporation. Available on http://www.vanguardsw.com/products/vanguard‐system/components/vanguard‐studio/ Accessed on 13/05/2012
15. Aluminium, metalprices.com. Available on http://metalprices.com/FreeSite/metals/al/al.asp Accessed on 14/05/2012
16. Plastic Prices, Worldscrap. Available on http://www.worldscrap.com/modules/price/index.php Accessed on 14/05/2012
17. Superwinch1220210LT2000UtilityWinch,amazon.com.Availableon
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http://www.amazon.com/Superwinch‐1220210‐LT2000‐Utility‐Winch/dp/B0015U6VLQ/ref=sr_1_fkmr0_1?ie=UTF8&qid=1337111478&sr=8‐1‐fkmr0 Accessed on 14/05/2012
18. 2 Bearing 6203ZZ 17x40x12 Shielded Ball Bearings VXB Brand, amazon.com. Available on http://www.amazon.com/Bearing‐17x40x12‐Shielded‐Bearings‐VXB/dp/B002BBOFG6/ref=pd_sbs_indust_5/191‐6039834‐3380561 Accessed on 14/05/2012
19. Bungee cord black (10mm), Bungee cord. Available on http://www.bungeecord.co.uk/bungeecordblack10mm.htm Accessed on 14/05/2012
20. Mobility battery 12v‐26Ah (AGM), Puredrive Batteries Limited. Available on http://www.puredrivebatteries.co.uk/golf‐trolley‐battery‐84‐12v‐26Ah‐7‐AGM‐Batteries.html Accessed on 15/05/2012
21. Wage and hour division (WHD), United States Department of Labor. Available on http://www.dol.gov/whd/minwage/america.htm#NewYork Accessed on 15/05/2012
22. Young, W: Roark's Formulas for Stress and Strain, 6th edition. McGraw‐Hill, 1989 ISBN:0‐07‐072542‐X
23. [23] Ford Transit Technical Specifications: http://www.fordtransitdirect.co.uk/newsales/newvans/transit/technicalspec.aspx Accessed 16/05/2012
24. 24. BIOGRAPHICAL MEMOIRS: CL (Kelly) Johnson The National Academies Press http://www.nap.edu/readingroom.php?book=biomems&page=cjohnson.html Accessed 16/05/2012
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AppendicesAppendix A: Design Matrices
A.1 Blank Binary Weighting Matrix
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A.2 Completed Binary Weighting Matrices and Averaged Results
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A.3 House of Quality
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A.4 CODA
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Appendix B: Production Drawings
B.1 Base Connecting Bar
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B.2 Cradle
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B.3 Winch Base
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B.4 End Link
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B.5 Ground Support
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B.6 Leg Bar
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B.7 Link
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B.8 Roll Bar
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B.9 Trolley
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B.10 Wheel