spherical vtol uav structure and aerodynamics

ME 4101 BACHELOR OF ENGINEERING DISSERTATION

Spherical VTOL Unmanned Aerial Vehicle

(Structures and Aerodynamics)

Project AM31

Faculty of Engineering

Department of Mechanical Engineering

Submitted By: CHIA YONG HAN TIMOTHY

Matriculation Number: A0073919U

Session 2012/2013

Page i

SUMMARY

The objective of this project is to design, build and test fly a Spherical-shaped

Vertical Take-Off (VTOL) Unmanned Aerial Vehicle (UAV). This is a 2-men

project which consists of 5 components, namely Propulsions, Electronics, Control

System, Aerodynamics and Structures. This thesis will only cover the

Aerodynamics and Structures components, and a the rest of the components will

be covered in Project AM30.

This newly shaped UAV allows the propellers to be encased within spherical-

shaped struts, which enables the UAV to fly into obstacles without damaging the

propeller. This also makes it safe for the pilot, as well as, anyone in the vicinity.

Running only on a single propeller-motor configuration, the UAV is able to hover,

climb vertically, and transit into translation flight, which is similar to that of a

helicopter.

Apart from that, this UAV boasts a new concept of take-off and landing, which is

not commonly seen in most of the other UAVs. During landing, the UAV rolls

onto the ground until it comes to a standstill. It can then be piloted to an upright

orientation before taking-off again. With a built-in wireless camera, the UAV is

able to navigate within tight spatial constraints, suitable for urban surveillance

operations. The camera is able to provide aerial view of live video footage during

flight.

A total of 3 prototypes were constructed where Prototypes 1 and 2 were

constructed to investigate and study the aerodynamics and structural components

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of the UAV. Only after undergoing thorough experimentation and analysis to

optimise the various component designs, Prototype 3 was finally constructed.

The aerodynamics component of the UAV was first dissected by using equations

to prove the pitch, roll and yaw motion. The control surfaces were optimised

using Computational Fluid Dynamics software during the design stages, and its

results were confirmed by various experiments and flight tests conducted.

The structural component of the UAV was mainly the study of the structural

integrity of the body of the UAV to ensure that it is able to withstand impact

loads. This was done using a simulation software, which provided useful

information of its effects when experiencing an impact load. Similarly, this was

confirmed by experiments which were conducted after the prototypes had been

constructed.

The final product is only made possible by integrating the electronics, control

system and propulsion components.

Page iii

ACKNOWLEDGEMENT

This author wishes to express his sincerest appreciation to A/Prof Gerard Leng for

his patience and guidance throughout the course of this project, as well as, staffs

of the Dynamics and Vibrations Laboratory for their administrative and logistical

support.

I would also like to extend my heartfelt thanks to my project partner, Andrew

Ong, who is working on the Electronics and Propulsion portion in Project AM30.

His hard work and sheer dedication to the project allowed for the timely

submission of this project. I would also like to express my gratitude to Andrew,

for all time and sacrifices that he had put in to ensure the success of this project.

Page iv

TABLE OF CONTENTS Page No

1) Introduction ................................................................................................................. 1

2) Literature Survey ......................................................................................................... 2

3) Stages and Objectives .................................................................................................. 3

3.1) Flowchart Process ............................................................................................................. 3

3.2) Project Goals ..................................................................................................................... 4

3.3) Objectives .......................................................................................................................... 5

4) Flight Dynamics .......................................................................................................... 6

4.1) Definition of Motion ......................................................................................................... 6

4.2) Propeller Slipstream .......................................................................................................... 9

4.3) Forces and Moments ....................................................................................................... 11

5) Design ........................................................................................................................ 16

5.1) CAD Modelling ............................................................................................................... 16

5.2) Center of Gravity ............................................................................................................. 16

5.3) Structural Simulations ..................................................................................................... 17

5.4) Flow Simulation .............................................................................................................. 19

5.5) Control Surfaces Optimisation ........................................................................................ 20

6) Prototyping ................................................................................................................ 21

6.1) Material Selection ........................................................................................................... 22

6.2) Prototypes Comparison ................................................................................................... 23

6.3) Manufacturing process .................................................................................................... 25

7) Experiments ............................................................................................................... 29

7.1) Thread Test...................................................................................................................... 29

7.2) Bench Test ....................................................................................................................... 30

7.3) Actual Drop Test ............................................................................................................. 31

8) Actual Flight Tests ..................................................................................................... 31

8.1) Indoor Flight Test ............................................................................................................ 32

8.2) Outdoor Flight Test ......................................................................................................... 34

9) Results and Discussion .............................................................................................. 35

9.1) Aerodynamics ................................................................................................................. 35

9.2) Structures......................................................................................................................... 36

9.3) Stability and Control ....................................................................................................... 38

10) UAV Performance ................................................................................................... 43

11) Conclusion ............................................................................................................... 44

12) Recommendations for Further Work ....................................................................... 45

REFERENCES ................................................................................................................. .

APPENDICES .................................................................................................................. .

Page v

LIST OF FIGURES Page No

Fig 1 Japanese Spherical UAV (left) and Fixed-wing VTOL UAV (right) ...................................................... 2

Fig 2 Final UAV Prototype SolidWorks Model ............................................................................................... 6

Fig 3 Yaw Motion ............................................................................................................................................. 7

Fig 4 Pitch Motion ............................................................................................................................................ 7

Fig 5 Roll Motion ............................................................................................................................................ 8

Fig 6 Propeller Slipstream .............................................................................................................................. 9

Fig 7 Hover Front View (Left) and Top View (Right) ................................................................................ 11

Fig 8 Pitch while Hovering, transit to Translational Flight Front View .................................................... 13

Fig 9 Flaps Orientation during Translational Flight Top View ................................................................. 13

Fig 10 Finding Center of Gravity using SolidWorks ..................................................................................... 17

Fig 11 Structural Deformation Front ......................................................................................................... 18

Fig 12 Stress Concentration Lower Struts (Left), Octa Plate (Right) ......................................................... 18

Fig 13 Flap Sizing ........................................................................................................................................... 20

Fig 14 UAV Materials ................................................................................................................................... 23

Fig 15 Prototype 1 ......................................................................................................................................... 23

Fig 16 Prototype 2 ......................................................................................................................................... 24

Fig 17 Prototype 3 ......................................................................................................................................... 25

Fig 18 Constrution Process ........................................................................................................................... 26

Fig 19 Octa Plates ......................................................................................................................................... 27

Fig 20 Central Unit ......................................................................................................................................... 28

Fig 21 Thread Test ......................................................................................................................................... 29

Fig 22 Bench Test .......................................................................................................................................... 30

Fig 23 Actual Drop Test ................................................................................................................................ 31

Fig 24 Wall 'Sticking' .................................................................................................................................... 32

Fig 25 Take off by hand ................................................................................................................................. 33

Fig 26 Stairs Flight ....................................................................................................................................... 33

Fig 27 Outdoor Flight Path ........................................................................................................................... 34

Fig 28 Fracture at lower struts ..................................................................................................................... 38

Fig 29 Longitudinal Stability Zoom Out ..................................................................................................... 38

Fig 30 Longitudinal Stability Zoom In ....................................................................................................... 39

Fig 31 Longitudinal Stability with Disturbances Zoom Out ....................................................................... 40

Fig 32 Longitudinal Stability with Disturbances Zoom In ......................................................................... 40

Fig 33 Directional Stability - Zoom Out ........................................................................................................ 41

Fig 34 - Directional Stability - Zoom In ........................................................................................................ 42

Fig 35 Directional Stability with Disturbance - Zoom Out ........................................................................... 42

Fig 36 Directional Stability with Disturbance - Zoom In .............................................................................. 43

Page vi

LIST OF TABLES Page No

Table 1 - Project Phases and Objectives ......................................................................................................... 4

Table 2 Drop Test Conditions ....................................................................................................................... 18

Table 3 Flaps Optimisation ........................................................................................................................... 21

Table 4 Materials Ranking ............................................................................................................................ 22

Table 5 Airflow Velocity (m/s) at different locations ..................................................................................... 35

Table 6 Structural Simulation Results ........................................................................................................... 37

Table 8 UAV Performance ............................................................................................................................ 43

Table 9 Technical Properties (Depron, 2012) .............................................................................................. 2

Table 10 SolidWorks Material Input ................................................................................................................ 2

Table 11 Total Material Costs for Prototype 3 Structures .............................................................................. 3

Table 12 Total Costs Spent on Prototype 3 ..................................................................................................... 3

Table 13 Flow Simulation ................................................................................................................................ 1

LIST OF GRAPHS Page No

Graph 1 Cl vs AOA ........................................................................................................................................ 19

Graph 2 Cd vs AOA ....................................................................................................................................... 19

Page vii

LIST OF SYMBOLS

Angle of Attack (AOA) , rad

Flap Deflection, rad

Rudder Deflection, rad

Drag, N

Lift, N

b Wing span, m

Moment about CG

Xb Body Axis, X-Axis

Yb Body Axis, Y-Axis

Zb Body Axis, Z-Axis

Xe Earth Axis, X-Axis

Ye Earth Axis, Y-Axis

Ze Earth Axis, Z-Axis

T Thrust

Tmotor Motor Torque

Vi Induced velocity of air, accelerated across the propeller

Ve Induced exit velocity of air

Cl Lift Coefficient

Cd Drag Coefficient

SPHERICAL VTOL UAV (STRUCTURES AND AERODYNAMICS)

1) Introduction

The evolution of UAVs started mainly for military purposes during World Wars I

and II. The need to gain aerial superiority at that time led to quick advancements

of unmanned aircrafts, as it meant that no lives were risked during reconnaissance

or sabotage missions. Then in recent years, after the invention of helicopters, the

race to develop fixed wing fighter jets capable of VTOL began to emerge as this

will allow fighter jets to take-off and land using shorter runways, which are also

found on-board aircraft carriers. This capability is also known as short take- off

and landing (STOL). In order to take advantage of both of these capabilities, a

hybrid VTOL UAV was created, with many variants that are currently researched

around the world.

This thesis will discuss the aerodynamics of the UAV which includes the forces

and moments equations governing the pitch, roll and yaw motion of UAV. This is

followed by the design process which includes CAD modelling, structural

analysis using SolidWorks and SolidWorks Motion Simulation. Computation

Fluid Dynamics using SolidWorks Flow Simulation was also done to analyse the

flow behaviour and optimise the control surfaces, before discussing the

manufacture and construction the actual prototype. Experimental data obtained

from the flight tests would be used to confirm the theoretical studies. Finally, a

more intensive date collection of the final prototype would be done to provide

information of the performance and capabilities of the UAV. The portion of

propulsion, electronics and control system is done by Andrew Ong, A0073979H,

project AM30 (AY2012/2013).

2) Literature Survey

There are two types of VTOL UAVs currently available in the market that are of

interest to this project, which sparked the ideas of the prototype designs. The first

is the spherical UAV which was invented by in Japan. In October 2011, research

engineer, Fumiyuki Sato, working at the Defence Ministrys Technical Research,

presented the worlds first flying spherical UAV in a press conference. It runs on a

single propeller motor and hovers like a helicopter. The spherical UAV is also

claimed to reach speeds of up to 60 kilometres per hour when transiting into

translation flight. Costing about US$1,400, the latest prototype was made merely

from parts bought from a local consumer electronics store in Japan.

Fig 1 Japanese Spherical UAV (left) and Fixed-wing VTOL UAV (right)

The second UAV mimics a fixed wing aircraft capable of VTOL. Similar to the

Japanese spherical UAV, it is propelled by a single rotor which is usually placed

at the tip of the UAV. It is also capable of hovering as well as transiting into

translational flights which looks like a normal fixed wing aircraft.

During the design and prototyping stages, this project aims to investigate the pros

and cons of both designs and finally come up with a final prototype to achieve the

best possible configuration to achieve the objectives which have been set up.

3) Stages and Objectives

This section describes the initial planning, and a brief summary of the process of

designing before arriving at the final prototype. This is followed by a list of

objectives to define the scope of the project.

3.1) Flowchart Process

Prior to the start of the entire project, the team has developed a flowchart process

to systematically tackle the various objectives, through a series of stages, to be

achieved before arriving at the final prototype.

Figure 1 - Flowchart Process

1) Design/Re-design

2) Prototyping

3) Flight Tests and Troubleshooting

4) Manufacturing of Final Product

5) Final Testing

6) Post Data Processing

3.2) Project Goals

Below summarises the main goals during the different phases of the entire project:

Table 1 - Project Phases and Objectives

Phase Project Goals

1) Design Structures and Aerodynamics

- Dimensioning/ CAD Modelling

- Structures

- SolidWorks, SolidWorks Motion Simulation and

SolidWorks Flow Simulation

Propulsion and Control

-Sizing of Motor and Propeller Selection

-Calculating required current drawn and selecting

suitable battery

-Integrating Flight Control System with Flight

Controls

2) Prototyping - Integrating flight control electronics system with

UAV structure

3) Flight Tests and

Troubleshooting

- Testing of effectiveness of flight control surfaces

- Systematic Tuning of PID control settings

4) Re-Designing - Final modification of the structural, propulsion and

control designs

5) Manufacturing of

Final Product

- Consolidating modified designs

6) Final Testing - Make final adjustments to the control settings

7) Post Data Processing - Verify that all objectives are met

3.3) Objectives

This thesis mainly focuses on the structures and aerodynamics of the UAV and

the objectives are as follow:

1) The overall costs for the entire project must be kept below SGD 500.

2) The material used must be lightweight to reduce the all-up weight of the

UAV, so as to increase flight endurance and allow for possible payload.

3) The design of the struts must able to withstand impacts when landing or

due to accidental collision against possible obstacles within an enclosed

Build-Up Area (BUA).

4) The flaps and rudder sizes must be optimised to achieve the highest lift-to-

drag ratio.

5) The final prototype of the UAV must successfully achieve the following

during the test flights:

a. Stability and Control

b. Ability to fly up a flight of stairs.

c. Withstand wall collisions and ability to stick on the surface of the

wall before returning to normal and stable flight.

d. Landing and rolling, followed by a successful take off from the

ground.

4) Flight Dynamics

This section of the thesis will first introduce the various parts of the UAV and it

will be followed by the response on the motion of the UAV when the relevant

control surfaces are activated. The propeller slipstream theory will also be

explained and finally a theoretical derivation of the motion using equations of

forces and moments.

4.1) Definition of Motion

Typically, for a fixed wing aircraft, the pitch, roll and yaw motions, in the 3 axes,

are controlled by three different sets of control surfaces elevator, aileron and

rudder respectively. However, for the spherical UAV, the motions can be

simplified to 2 axes. This will be further explained in the following sub-section.

Fig 2 Final UAV Prototype SolidWorks Model

Propeller

Flaps (x4)

Rudders (x4)

Central Unit

Struts (x8)

Median Strut

Xe

Ze

Ye

Earth Axes

Xb

Zb

Yb

Body Axes

Octa-Plates (x4)

4.1.1) Yaw

The yaw motion is controlled by four sets of rudders which have been

programmed to move concurrently when the signal is received. The torque effect

from the counter-clockwise motion of the propeller causes the body of the UAV to

rotate anti-clockwise (about the Z-axis), causing the UAV to yaw. In order to

counter the inherent yaw motion due to the moving propellers, the rudders must

be activated at an angle at its default trim position.

4.1.2) Pitch

Flaps (x2)

Rudders (x4)

Xe

Ze

Earth Axes

Xe

Ye

Earth Axes

Fig 3 Yaw Motion

Fig 4 Pitch Motion

Rudders (x4)

The pitch motion (about the Y-axis) is controlled by two out of four flaps and four

rudders, which have been programmed to activate in a specific orientation to

cause the motion, as shown. With the Center of Gravity (CG) on the midline of

the UAV, the top two flaps move in opposite directions to the bottom rudders to

create a torqueing effect, thereby allowing the UAV to pitch in the desired

direction.

4.1.2) Roll

Fig 5 Roll Motion

Since the UAV is symmetrically constructed in each quadrant, the roll motion is

similar to the pitch motion, but the coupling moment is about the X-axis. The

pitch and roll motions are essentially describing the same movements. Therefore,

this motion will be defined by pitch in the subsequent sections of the thesis.

Ye

Ze

Earth Axes

4.2) Propeller Slipstream

Assuming Conservation of Energy, where no loss of kinetic energy is experienced

within the control volume,

Fig 6 Propeller Slipstream

Applying Bernoullis Equation,

Since ,

From Regions (0) to (1): p

V

g p

V

g (4.3.1)

From Regions (2) to (3): p

V

g p

V

g (4.3.2)

Assuming incompressible flow and constant density of air across the propeller,

conservation of mass can be applied,

From Regions (1) to (2):

V A V A (4.3.3)

Since A1 and A2 are the area of the propeller which is represented by the disc, it is

the equal, A1 = A2 = Ad,

V0 (0)

(1)

(2)

V1

V2

V3 (3)

V V V Vi (4.3.4)

Where Vi, is the induced velocity of the air which is accelerated across the

propeller.

Thrust produced from the propeller disk is due to pressure difference between

regions (1) and (2),

T (p p

) Ad (4.3.5)

Since V3 = V0 + Ve, where Ve is the induced exit velocity of air, and p3 = p0, and

also substituting (4.3.3), (4.3.4) and (4.3.5),

From (4.3.1); p p

V

V

From (4.3.1); p

V

p

V Ve

p

V

p

V

V

V Ve

T

Ad

V

V Ve

T

Ad

V

V

VeV Ve

T

Ad

VeV Ve

T

Ad VeV V

Using Quadratic equations to solve, the exit velocity can be determined by

V V V

T

Ad (4.3.6)

For hovering flight, since V0 = 0,

V T

Ad (4.3.7)

T

AdV

(4.3.8)

4.3) Forces and Moments

This sub-section of the thesis will explain the response of the control surfaces on

the UAV theoretically, using forces and moments. The following are the

assumptions made:

1) The axial direction of flow of Ve is always parallel to the symmetrical axis

of the UAV body, and the normal velocity, Vn, is negligible because Ve >>

Vn.

2) The direction of airflow is smooth and uniform and is vertically

downwards in the -Zb-direction.

3) The control surfaces are completely submerged in the induced exit airflow,

Ve.

4.3.1) Hover Flight

During hover flight, the velocity of airflow on the control surfaces is the induced

exit velocity of the air produced by the propeller, Ve, because Ve >> V0.

Fig 7 Hover Front View (Left) and Top View (Right)

Ve

T

W

Xe

Z

Earth Axes Xe

Ye

Earth Axes

FD,rudders

FL,rudders

Vn

FL,rudder4

FL,rudder2

FL,rudder1

FL,rudder3

r

During hover flight, there is an inherent yaw motion as mentioned in Section

4.1.1). Therefore, all four rudders must be in the orientation shown above at

neutral position to counter the clockwise rotation of the UAV body.

Sum of forces in Ze-Axis;

T W FD,rudders = m . w

Since w = 0;

T = W FD,rudders

Moments about Ze-Axis; (Taking counter-clockwise to be +ve)

Mcg,r = Tmotor - FL,rudders . r

where FL = Ve2 CL S and CL = 2 (for flat plate)

In order for the UAV to yaw in the CCW direction, Tmotor > FL,rudders . r , and for

the UAV to yaw in the CW direction, Tmotor < FL,rudders . r . This can be achieved by

controlling the amount of deflection of the rudders, r. The larger the the

deflection, the greater the FL,rudders.

4.3.2) Translational Flight

During hover flight, the velocity of airflow on the control surfaces is the induced

exit velocity of the air produced by the propeller, Ve, because Ve >> V0.

Fig 8 Pitch while Hovering, transit to Translational Flight Front View

Fig 9 Flaps Orientation during Translational Flight Top View

During translational flight, the UAV must first pitch as shown in the orientation

above. When the pitching moment reaches equilibrium, the UAV will translate in

the resultant direction.

From left picture in Fig 8, the UAV achieved hover flight first,

Sum of forces in Ze-Axis;

Xe

Ze

Earth Axes

RESULTANT

T

T

V

Xe

Ye

Earth Axes

Ve Ve

FL,rudders

FL,rudders

FL,rudders

FL,flaps

FL,flaps

FL,flaps

FD,frontal

f

r

W

T - W - FD,rudders - FD,flaps - FDstruts + FL,rudders + FL,flaps + FL,struts = m . w

Since w = 0;

T + FL,rudders + FL,flaps + FL,struts = W + FD,rudders + FD,flaps + FD,struts

However, from Fig 8, after reaching equilibrium when pitching,

Summation of forces in Ze-Axis;

T sin - W - FD,rudders - FD,flaps - FDstruts + FL,rudders + FL,flaps + FL,struts = m . w

T sin - W - D + L = m . w

For the same throttle setting, T, when the UAV achieved hover flight, there will

be a decrease in the overall thrust of T.(1 - sin ), due the change in resultant

thrust vector direction.

Since both (T sin ) and W are constants, the resultant increase or decrease in w is

dependent on D and L which is based on the Lift-to-Drag ratio, dependent

of the angle of attack , for a given Ve and V.

Summation of forces in Xe-Axis;

T cos - FD,struts - FD,rudders - FD,flaps = m . u

T cos - FD,frontal = m . u

where FD,frontal = (Ve + V) 2 Cd S

Moments about Ye-Axis;

Mcw, Flaps & Rudders = Lf,z-axis . (FL,flaps cos f) + Lr,z-axis . (FL,rudders cos r)

Mccw, Flaps & Rudders = Lf,x-axis . (FL,flaps cos f) + Lr,x-axis . (FL,rudders cos r)

Mcw by Propeller = Lp,x-axis . T cos

Mccw by Propeller = Lp,x-axis . T sin

where FL = (Ve + V) 2 CL S

(Taking counter-clockwise to be +ve)

Mcg = {[ Lf,z-axis. (FL,flaps cos f) + Lr,z-axis . (FL,rudders cos r) ] + [ Lp,x-axis . T cos ]}

- {[ Lf,x-axis. (FL,flaps cos f) + Lr,x-axis . (FL,rudders cos r) ] + [Lp,x-axis . T sin ]}

Theoretically, it is difficult to achieve straight and levelled flight during pitching.

However if L is able to overcome W and D, it will result in an increase in

altitude, which is more ideal. Therefore, it is concluded that the UAV should

flown at a high enough thrust which must be decreased proportionally to

compensate for the increase in Lift at high velocity to achieve a successful

translational flight. This hypothesis will be further elaborated in Section 5.4) Flow

Simulation.

5) Design

In order to make a fair comparison with the Japanese Sphere, some specifications

of the prototypes were based on the limited knowledge of the Japanese

specifications released. A total of 2 prototypes were made, before arriving at the

final prototype and the diameter of the UAV is fixed at 42 centimeters for all three

prototypes.

5.1) CAD Modelling

The prototypes were modelled using Computer Aided Software SolidWorks, to

speed up the design process by allowing the user to visualise the designs before

manufacturing the actual product. Each parts of the UAV were designed

individually and assembled using the software.

Apart from designing the prototypes to meet the technical specifications, the

design considerations also encompass the manufacturing process. A step-by-step

assembly procedure must be taken into consideration to ensure smooth assembly

as some of the steps require permanent adhesion which is irreversible.

5.2) Center of Gravity

To ensure that the centre of gravity is as close to centre of the sphere as possible,

all the electronics are modelled into individual parts and assigned their individual

masses, which were weighed using an electronic weighing machine. These parts

are then assembled to achieve the desired CG location, at the centroid of the

sphere.

Fig 10 Finding Center of Gravity using SolidWorks

5.3) Structural Simulations

Before manufacturing the actual prototype, the CAD model is meshed before

undergoing simulations to test the structural designs. The simulation software

used was SolidWorks Motion Simulations.

To ensure that the struts are able to withstand the impact forces due to improper

landing or accidental collisions into obstacles when flying indoors, the UAV is

simulated to undergo a drop test. This provided useful visual aids to identify

locations where high stress concentrations exist, which may lead to possible

fractures. Changes to the designs can be made instantly to improve the structural

integrity of the struts.

5.3.1) Drop Test

The drop test is to simulate the sudden vertical decent of the UAV (in the Ze-

Axis) either due to loss of battery power or during improper landing at 3 different

height of 0.2, 0.5, 1.0 meters. The objective is to find out the location of the UAV

which receives the most stress through the simulation. The following were the

boundary conditions applied:

Table 2 Drop Test Conditions

Conditions Inputs

Material: Depron Foam Refer to Appendix A: Depron Foam

Connections Global Contact (Bonded)

CG located at Center of Sphere 600g

Gravity in the Ze-Axis 9.81 m/s2

Fig 11 Structural Deformation Front

Fig 12 Stress Concentration Lower Struts (Left), Octa Plate (Right)

Based on the maximum normal stress criterion, the highest stress concentration

can be observed at the centre of the octa plates as shown in Fig 13. The results

also showed that high stress concentrations, represented by the red/orange regions,

are observed at the lower portion of the struts in Fig 13. The calculated shape of

deformation can also be observed in Fig 11. A more detailed discussion can be

found in 9.2) Structures.

5.4) Flow Simulation

SolidWorks Flow Simulation is used to investigate the lift and drag forces at Ve of

13.2m/s while varying the AOA. The highest Lift Coefficient, Cl, can be observed

at approximately 42 degrees, from Graph 1 Cl vs AOA. Also, from Graph 2 Cd vs

AOA, it can be observed that Cd increases with AOA.

Graph 1 Cl vs AOA

Graph 2 Cd vs AOA

To further explain the hypothesis from 4.4.2) Translational Flight, it can be

concluded that at AOA of less than 42o, there will be enough lift force to cause a

resulting increase in altitude since the drag experienced is also lower at smaller

AOA.

0

0.05

0.1

0.15

0.2

0.25

0.3

0 10 20 30 40 50 60 70 80 90

Co

eff

icie

nt

of

Lift

, Cl

AOA, (o)

Cl vs AOA (o)

0

0.1

0.2

0.3

0.4

0 10 20 30 40 50 60 70 80 90

Co

eff

icie

nt

of

Dra

g, C

d

AOA, (o)

Cd vs AOA (o)

5.5) Control Surfaces Optimisation

To achieve the highest lift-to-drag ratio, the size of the flaps and rudders must be

optimised. This will ensure that enough lift force is generated by both the flaps

and the rudders to provide sufficient pitching moment for translation flight, and

the size of the rudders is sufficient to counter the inherent yaw motion caused by

the propeller.

5.5.1) Flaps Optimisation

The objective of the flap optimisation is to find the suitable chord length to

provide the highest lift-to-drag ratio. For a fixed spherical UAV diameter of

420mm, the maximum chord length of the flap is 58.5mm. The velocity of

airflow, Ve, just below the propeller, is taken to be 13.2m/s at throttle setting of

50%, which is the approximated cruising speed. Below are the assumptions and

boundary conditions that were applied:

Span = 355

Chord Length, c

Ve = 13.2m/s

Fig 13 Flap Sizing

Table 3 Flaps Optimisation

Assumptions/ Boundary Conditions Values

Density of air @ 300K, 1.17714 kg/m3

Dynamic Viscosity of air @ 300K, 1.56E-05 kg/m s

Velocity of air, Ve 13.2 m/s

Span, b 0.355m

AOA, 42o or 0.733 rad

Using SolidWorks Flow Simulation, a parametric study was setup by varying the

chord length between 40mm to 58.5mm.

Results showed that for a smaller chord length, there was only a slight decrease in

the lift-to-drag ratio. However, the resulting Lift force is reduced, compromising

on the resulting pitching moment, which is undesirable. Instead, the maximum

allowable chord length of 58.5mm produced the highest Lift-to-drag ratio.

Therefore, the most suitable chord length of the flap is limited to the diameter of

the sphere at 58.5mm.

In addition, it can be observed that from Appendix C, as AOA increases from 0 to

40 degrees, the simulation results showed that the air flow is still sticking onto

the surface of the flap. However, at 50 degrees onwards, flow separation is

starting to occurs. Therefore, it can concluded that the maximum pitch angle

should not be more than 42 degrees as observed from the Graph 1, as it is the

angle at which the maximum lift force can be generated.

6) Prototyping

There are limitations to how much each prototype can be simulated using software

simulations, and the prototyping stage only begins after intensive simulations

have been done. This is where the manufacture and assembly of the prototypes

took place. This section will first describe the key considerations for the material

selection and how each prototype is evolved. This will be followed by a brief

description of the construction process.

6.1) Material Selection

Table 4 Materials Ranking

Materials Cost Ease of fabrication Strength-to-weight

ratio

Depron Foam

(3mm)

Low 1 Very Easy 1 Low 4

Depron Foam

(6mm)

Low 2 Very Easy 2 Low 3

Plywood Medium 3 Easy 3 Medium 2

Carbon Fibre Very High 4 Very difficult 4 High 1

There are various considerations that had to be made when selecting the most

appropriate material to manufacture the struts, which will experience the highest

impact loads.

Since the objective of the project is to keep costs low, costs was the highest

priority and thus Depron was selected over plywood and carbon fibre, which have

the highest strength-to-weight ratio.

Due to time constraint, the time taken for the construction was the next on the

priority list. Depron foam is the easiest choice of material to work with as it can

be cut easily with simple tools pen-knife or foam cutter. Therefore, it was

selected over all the other materials. Below are the materials used for the different

parts of the final prototype:

Fig 14 UAV Materials

6.2) Prototypes Comparison

This subsection aims to describe the structures and aerodynamics characteristics

for the first two prototypes and explain the pros and cons of each model, before

arriving at the final prototype.

6.2.1) Prototype 1

Fig 15 Prototype 1

The key difference between Prototype 1 and the two later models is the

construction of the central unit. It is made of a 1.5 litre water bottle which was cut

to a suitable height, and its cap was used to mount the propeller. Since the bottle is

Depron Foam

5.0x0.6mm Carbon Strips

6mm Carbon Rods

Octagonal- Shaped 3mm Plywood

shaped similar to that of an aircraft fuselage, its smooth and streamline body

allowed for better airflow. Its advantages and disadvantages are further explained

in 6.3.2. After thoroughly flight testings, the UAV was unable to achieve any

control or stability when the Ardupilot flight control board was installed.

6.2.1) Prototype 2

Fig 16 Prototype 2

Prototype 2 was designed based on the fixed wing VTOL UAV, which was

introduced in 2.1) Literature Survey. During the research, such fixed wing VTOL

UAVs in the market had shown to have high stability during hovering flight. The

construction of Prototype 2 was also much easier and much faster to construct.

It served as a stepping stone to test out the new KK2 Board flight control board

while Prototype 3 was being designed. The larger surface area at the central unit

also contributed to the increase in structural strength of the struts.

The KK2 Board was able to provide stability for the UAV, however, during

subsequent flight testings, it was observed that the UAV was too stable. The

increase in surface are resulted in an increase in front drag during translation

flight, which was undesirable.

6.2.1) Prototype 3

Fig 17 Prototype 3

After many design considerations and optimisations from its predecessors,

Prototype 3 was finally constructed. It was installed with the KK2 Board, and

stability was achieved with minor tuning. The strut design was a hybrid of

Prototypes 1 and . It was more hollow at the central unit as compared Prototype

1, to decrease the front drag during translational flight. At the same time, the

assembly of the 8 struts makes up the central unit to install all the electronics. The

circumference of the struts was lined with carbon strips using epoxy as adhesives

to further increase the structural integrity of the UAV. The analysis of the entire

thesis is based on the Prototype 3.

6.3) Manufacturing process

This sub-section aims to briefly describe the process of constructing the

prototypes where similar processes were done for all three prototypes.

6.3.1) Struts, Median Strut and Octa Plates

Fig 18 Constrution Process

Using SolidWorks, the part files can be converted into drawing files, which allows

the drawings to be printed in 1:1 scale. The template is then cut out and traced

onto Depron Foam sheets, which are cut by hand using a pen-knife. Slots are

specifically designed and cut to assemble the struts with the octa plates and

median struts, in a jig-saw like manner to properly distribute the stresses. All parts

are then assembled and epoxy is used as the adhesion for those assemblies that

require permanent bonds. The octa plates are laid with fibreglass cloth and cured

using epoxy resin to increase the structure strength as it experiences the largest

stress concentration seen in Fig 19.

1 2

3 4

Fig 19 Octa Plates

6.3.2) Central Unit

The central unit is the middle structure of the UAV where all the electronics are

mounted on. Apart from having to withstand torsional loads from the moving

propeller, the central unit must be designed to allow the electronics to be mounted

sturdily.

For the first prototype, an indigenous idea of using a bottle for the central unit

struck the team. The motor fits perfectly on the bottle cap and the torqueing

direction of the propeller tightens the cap further which enhances the design

safety. The cylindrical body of the bottle is ideal for taking torsional loads, and

the electronics can be contained within it. Despite its advantages, a lot of time is

spent on creating brackets for the electronics and fitting them into the bottle. In

addition, holes and slits have to be cut to access the electronics which decreases

the structural integrity of the body. Therefore, the idea was scraped in the

subsequent designs.

Fiberglass cloth with epoxy

Fig 20 Central Unit

In the second and third prototypes, the central unit is made from the assembly of

all eight struts. This will allow greater stress distribution of the struts thereby

increasing the structural integrity of the struts. The final improvement to the struts

is seen in the third prototype, where mm carbon fibre strips are stuck onto the

circumference of the struts, using epoxy, to increase the strength of the struts.

7) Experiments

This section describes the main experimental test flights which were done after

each prototype was constructed, followed by an actual drop test to validate the

structural integrity of the UAV. The results and discussion will be done in Section

9 of the thesis.

7.1) Thread Test

To investigate if the boundary layer is laminar or turbulent on the control surfaces

and inner surfaces of the UAV, flight threads were attached to the respective

surfaces to observe the behaviour of the threads. If the threads flap in a smooth

and uniform downward direction, it can be concluded that the flow is laminar. If

the threads flap erratically, there is a possible flow separation on the particular

surface has occurred, resulting in turbulent flow in the region.

The throttle setting was increased at intervals from 13.2m/s to 16.8m/s, while

observing the behaviour of the flight threads at 3 different surfaces of the UAV, as

V3 (3)

Flaps

Internal Wall

Rudders

V0 (0)

(1)

(2)

V1 V2

Mid-Section

Fig 21 Thread Test

Flaps

Internal Wall

V2

shown in Fig 21. An anemometer was carefully placed just beside the surfaces to

observe the airspeed at the various throttle settings.

7.2) Bench Test

Before the actual test flight, the UAV needs to first attain dynamic stability under

a controlled environment. Dynamic stability refers to the dampening of

oscillations caused by disturbances back to the original equilibrium position, with

time.

In order to prove the forces and moments were valid for the pitching motion, the

Bench test was set up to restrict the UAV to just one Degree of reedom about

the CG. The controller is then activated by the pilot to test if the activation the

correct sets of control surfaces will result in a coupling moment, causing it to

pitch in the desired direction.

Fig 22 Bench Test

Using the same test rig and set-up, but now with the flight control board activated,

a series of P-I-D settings was tested to investigate the effects of the increase or

decrease in the input gain of the P-I-D settings on the response of dampening the

oscillations of the UAV, when disturbed at an angle.

The gain values in this experiment were predicted to be overestimated as there are

frictional forces acting at the contacts where the UAV is being hung. However, it

provides useful information of the effects on the change in P-I-D settings which

will reduce the time taken to trim the settings during actual flight tests.

7.3) Actual Drop Test

Fig 23 Actual Drop Test

As mentioned in the design process of the drop test in 5.3.1 Drop Test, and actual

drop test was done for the Final Prototype to test out the structural integrity of the

UAV in the event of a motor failure. The objective of this test is to ensure that the

internal electronics and control surfaces are protected within the spherical struts.

Similar to the simulation done using SolidWorks Simulation, the UAV is released

at 3 different heights of 0.20m, 0.5m and 1m.

8) Actual Flight Tests

Once the UAV was able to achieve decent stability using the bench test, the

UAV will then undergo the actual indoor flight test. The original P-I-D settings

derived from the bench test were no longer valid, as the dampening effect was

accelerated due to the kinetic coefficient of friction at the contact points where the

UAV is pivoted about its CG.

However, since the effects of each setting have been thoroughly investigated

during the bench test, the process of trimming was sped up during the actual test

flight. This was done by Andrew Ong, and the results were collated in Project

AM30. This section will describe the indoor and outdoor flight tests to prove its

capabilities, followed by numerical findings to describe the performance of the

UAV.

8.1) Indoor Flight Test

The objective of the indoor flight test was to test fly the UAV under no wind

conditions, and to execute different the various manoeuvres to exhibit the unique

characteristics of the UAV. In addition, the longitudinal and directional stability

was also tested and it will be discussed in section 9.3 of the thesis.

Fig 24 Wall 'Sticking'

1) Unlike most UAVs in the market, this spherical UAV is able to stick

onto walls, and return to normal flight. This is because the propellers are

encased within the spherical struts which protect the propellers and the

electronics. Furthermore, the struts have been designed to withstand

impacts loads as it may be crash into obstacles within constraint areas.

Fig 25 Take off by hand

2) There are two ways which the UAV can take off and land. One is by

holding onto it as shown in Fig 25, and the other, on the ground. However,

the unique capability of this UAV is that it is able to land by rolling onto

the ground, and take off again. This is a critical feature, as it gives UAV

the versatility to take off or land in most conditions. Similarly, the struts

have been designed to withstand impacts loads when landing at heights of

up to 1m, as proven during the drop tests.

Fig 26 Stairs Flight

3) The UAV is also able to translate easily up flights of stairs without the

pilot having to increase the throttle. This proved the above hypothesis in

5.4) Flow Simulation. Since the lift force was able overcome the drag

force at that particular angle, resulting in a gentle climb during translation

flight.

8.2) Outdoor Flight Test

Fig 27 Outdoor Flight Path

Although the primary role of the UAV is to fly within constraint areas, the

outdoor flight test was done and the flight path was recorded using a GPS at low

wind conditions. With a larger aerial space, there was more room to manoeuvre

the UAV.

The objectives were to test fly the UAV with a planned flight path, as shown in

Fig 27, and test the endurance of the UAV, to find the maximum flight time. The

pilot will manoeuvre the UAV in a V-shaped path, for as long as the battery can

last and the flight time was recorded when the battery ran completely flat. With an

accuracy of about 3 meters, the GPS will record the latitude, longitude and

altitude co-ordinates in real-time and these can be plotted onto Google Maps,

during post processing of the results. The output values of the pitch, roll and yaw

motions are also recorded with time. With this information, the behaviour of UAV

can be studied.

9) Results and Discussion

This section aims to compare results from simulations and actual testing and

prove if the initial hypothesis concurred with the experimental results. The

discussion consists of 3 sub-sections Aerodynamics, Structures and Stability.

9.1) Aerodynamics

9.1.1) Thread Test Results

Table 5 Airflow Velocity (m/s) at different locations

Throttle Settings

Surface Locations 50% 60% 70% 80% 90% 100%

Flaps 13.4 13.9 14.6 15.3 15.9 16.6

Mid-Section 13.4 13.8 14.7 15.3 15.9 16.7

Rudders 13.0 13.5 14.3 15.0 15.7 16.4

Internal Wall 6.1 6.2 6.5 6.7 7.0 7.5

From the Thread Test, it was observed that at maximum throttle setting, the flight

threads continue to flap in a uniform and smooth downward direction in the -Zb

direction, depicting laminar flow on the surfaces. This concurs with the

simulation results in 5.4 Flow Simulation, where the UAV was simulated to

experience an airflow velocity from 13.2m/s to 16.6m/s to observe the flow

behaviour.

Another observation made was the change in the velocity of airflow at the four

different locations. When the anemometer was placed just below the propeller, at

the top flaps, the readings observed were similar to the Motor testing readings.

However, there was a slight decrease in velocity when the anemometer was placed

further downstream, at the mid-section and the bottom of the UAV, just below the

rudders. This is due to a loss of kinetic energy of the air as it travels further away

from the propeller, as some of the air escapes into the surroundings.

The internal wall, on the other hand, gave much lower readings, and the flight

threads do not flap as much but still remains smooth and laminar. This is because

airflow at this region does not lie within the exit velocity of the propeller as

shown by the control volume defined in the propeller slipstream.

From the thread test, it can be concluded that the assumptions that were made in

4.2) Propeller Slipstream theory were valid.

9.2) Structures

9.2.1) Drop Test Simulation Results

According to Coloumbs criterion, also known as the maximum normal yield

stress criterion, the effective stress can be defined as:

= MAX ( | | , | | , | | )

The simulation calculates the effective stress when subjected to impact loads at

various drop heights, and compares it with the yield stress of the 3mm depron

foam, y, which was defined when initialising the material properties.

Since the likelihood of an engine failure is low, and the pilot has ample time to

react by throttling up when the UAV is flying to low, thereby cushioning the

impact of the descent. If the UAV starts to lose lift too quickly at heights of more

than 1m above the ground, the resultant catastrophic impact would be inevitable.

The team has decided that a safety factor, X, of 1.5 was sufficient. The safety

factor is given by:

= y

1.

2.33 MPa

Therefore, the maximum effective stress must not be greater than 2.33 MPa.

Table 6 Structural Simulation Results

Drop Height (m) Max Effective Stress (N/mm2) or

(MPa)

Possible Failure

0.2 0.7 No

0.5 1.2 No

1.0 2.6 Yes

From Table 6, SolidWorks Motion Simulation showed that the maximum

effective stress experienced during a 1.0m drop height was 2.6MPa, but it has not

failed because it is below the yield stress of depron. However, due to a safety

factor of 1.5, there is a possibility of a failure which may occur at the struts.

9.2.2) Actual Drop Test Results

The results of the actual drop test showed that at heights of 0.2m and 0.5m, there

were no signs of cracks or fractures on the struts of the UAV and the electronics

were completely kept intact. However, when the UAV was released at 1m, one of

the struts experienced brittle fracture, resulting in delamination of the carbon

strips which were originally attached to it. There were no damage to the rudders,

and the electronic components were untouched.

The location of the fracture is similar to the simulation results, where high stress

concentration was observed at the lower portion of the struts, depicted by the red

regions, as seen in Fig 28. This shows the congruence in both experimental and

simulation results.

Fig 28 Fracture at lower struts

As mentioned during the drop test simulation, the likelihood of the UAV

experiencing a free fall is extremely low as the pilot will instinctively increase

throttle when the UAV starts to decent too quickly, thereby cushioning the free

fall impact. Therefore, it can be concluded that it is safe for the UAV to drop at a

height of 1m.

9.3) Stability and Control

9.3.1) Longitudinal Stability

Fig 29 Longitudinal Stability Zoom Out

Longitudinal stability refers to the UAVs ability to return to its equilibrium due

the pitching motion. The first test was to investigate the time taken for the UAV to

return to its trim position at 0o after the UAV has been manually displaced by the

pilot. This was done by deflecting the relevant control surfaces of the UAV to

bring it to approximately 45o pitch angle, and holding it for approximately 2.8

seconds before releasing the control stick to allow the UAV to return to

equilibrium. An interval of 5 seconds was given between the activation of the

control surfaces.

Fig 30 Longitudinal Stability Zoom In

From the above results, it was observed that at approximately 39 seconds, the

control surfaces for pitching were activated and it took about 1.1 seconds before

the UAV maintained at a pitch angle of about 42o. Subsequently, when the control

surfaces were deactivated, the UAV took about 1.4 seconds before returning to its

trim point. From the sinusoidal graph, it can be observed that the system is

underdamped and the oscillations are exponentially decaying, therefore the

damping ratio is between 0 and 1.

9.3.2) Longitudinal Stability with Disturbances

Fig 31 Longitudinal Stability with Disturbances Zoom Out

The next test was to test the longitudinal stability with disturbances. This was

done at hover flight, where the UAV was subjected to sudden displacements

which caused the UAV to pitch in a small angle. The pilot will not input any

controls to bring the UAV back to equilibrium, instead, the flight control board

will sense the sudden change in pitching angle and autonomously send signals to

the relevant control surfaces to counter the disturbances. This test was done to

investigate the time taken for the flight control board to react and finally bringing

the UAV to equilibrium.

Fig 32 Longitudinal Stability with Disturbances Zoom In

From the above, it can be observed that at the point of disturbance at 53.1

seconds, it caused the UAV to pitch at an angle of 44o. The UAV was brought

back to equilibrium in 1.4 seconds. This concludes that the system is stable in the

longitudinal direction.

9.3.3) Directional Stability

Fig 33 Directional Stability - Zoom Out

Directional stability refers to the UAVs ability to return to equilibrium due to the

yawing motion. However, unlike the pitching motion, the UAV is unable to return

to 0o or its original position. This is because the UAV does not have a Heading

Sensor, thus when the flight control board senses that the yaw motion of UAV

comes to a standstill, it will stop sending signals to the rudders to compensate the

yaw motion. The experiment was carried out by deflecting the rudders to cause

the UAV to move approximately 180o from its starting position, before releasing

the control stick to allow the UAV to return to equilibrium. An interval of 5

seconds was given between the activation of the rudders in opposite directions,

causing the UAV to yaw in counter clockwise and clockwise directions during

each interval.

Fig 34 - Directional Stability - Zoom In

It can be observed that at the starting position of about -90o, the rudders were

activated and it took approximately 1.8 seconds before the UAV reaches about

90o. However, the inertia of the yaw motion caused the UAV to travel to 100

o

even after the control stick was released, and it only reached equilibrium after 2.0

seconds later.

9.3.4) Directional Stability with Disturbance

Fig 35 Directional Stability with Disturbance - Zoom Out

Similarly, the UAV was subjected to a disturbance force, at hover flight, with

each disturbance alternating between clockwise and counter-clockwise directions.

This is to investigate the response of the flight control board to bring the UAV to

equilibrium when a sudden disturbance force causes the UAV to displace in a yaw

direction, without the pilots control.

Fig 36 Directional Stability with Disturbance - Zoom In

From the graph above, it can be observed that at the original position of 150

degrees, the UAV was displaced due to an external force at 89.1 seconds, causing

the UAV to yaw towards the 0o yaw angle. However, the rudders were able to

react and counter the yawing motion, bringing the UAV to equilibrium at 35

degrees, within 1.9 seconds. This concludes that UAV has directional stability.

10) UAV Performance

The initial objectives of the UAV were set based on some of the capabilities of the

Japanese Sphere and Prototype 3 was used to make comparisons with it.

Table 7 UAV Performance

Description Initial Objectives Prototype 3

Dimension 42cm diameter 42 cm diameter

Maximum All Up

Weight

Under 600 grams 551 grams

Flight Endurance 8 minutes 7:10 minutes

Target Cost Under SGD 500 SGD 445.43

Target Payload 150 grams 150 grams achievable with good

performance

Others Surveillance Capabilities 5.8 GHz wireless camera

surveillance System

From Table 7, it can be observed that Prototype 3 met most of the quantitative

objectives. With an initial estimate of just SGD 500 for the total costs of

constructing a spherical UAV in this project, which was way below the US$1,400

used for the Japanese Sphere, only SGD 445.43 was spent on Prototype 3.

The Maximum All Up Weight was 49 grams lesser than the initial objective

which increase the total allowable payload. The 5.8 GHz wireless camera

surveillance system selected was lightweight and provided surveillance

capabilities which allows for possible reconnaissance or during search and rescue

missions.

Although Prototype 3 fared well most objectives, the flight endurance of the UAV

fell short by 50 seconds. The initial estimate of 8 minutes was calculated based on

the specifications of the motor and battery and the all up weight of the UAV. The

estimated all up weight was increased because of the ArduPilot and extra battery

which were mounted to collect data of the flight test, resulting in a decrease in the

total flight endurance.

11) Conclusion

In conclusion, all the objectives of the project have been met. Through both

theoretical and experimental studies of the aerodynamics and structural

components of the UAV, it can be observed that most of the results concur and

this provides useful information of VTOL UAVs.

This uniquely spherical shaped UAV is definitely a class of its own as it has many

characteristics which sets itself apart from most other UAVs currently in the

market.Running only on a single propeller-motor configuration, the UAV is able

to hover, climb vertically, and transit into translation flight, which is similar to

that of a helicopter. Apart from that, this UAV boasts a new concept of take-off

and landing, which is not commonly seen in most of the other UAVs. During

landing, the UAV rolls onto the ground until it comes to a standstill. It can then be

piloted to an upright orientation before taking-off again. With a built-in wireless

camera, the UAV is able to navigate within tight spatial constraints, suitable for

urban surveillance operations. The camera is able to provide aerial view of live

video footage during flight.

12) Recommendations for Further Work

Majority of the body of the UAV is made up of Depron Foam. It is light weight

but has low strength-to-weight ratio. Further work can be done to construct the

UAV using CFPR which has much higher strength-to-weight ratio. However, its

only limitation is the costs and manufacturing of the product.

Page A1

REFERENCES

1. Daniel Moll, J. N. (2008). VTOL UAV A Concept Study. Linkping.

2. Depron, i. d. (2012). Depron Foam Technical Information. Retrieved March 15, 2013, from Depron Foam Web site:

http://depronfoam.com/depron-foam/resource/Depron-White-Technical-

Data-Sheet.pdf

3. Nelson, R. C. (1998). Flight Stability and Automatic Control. McGraw-Hill .

4. Zhao, H. W. (2009). Development of a Dynamic Model of a Ducted.

Page A2

APPENDICES

Appendix A: Depron Foam

Table 8 Technical Properties (Depron, 2012)

3mm 6mm

Compressive Stress (@

10% foam deformation):

0.10MPa 0.15MPa

Tensile Stress (@ break,

length direction):

1.30MPa 0.90MPa

Tensile Stress (@ break,

transverse direction):

0.70MPa 0.90MPa

Elongation (@ break,

length direction):

9% 10%

Elongation (@ break,

transverse direction):

12% 12%

Table 9 SolidWorks Material Input

Page A3

Appendix B: Material Costs for Prototype 3

Table 10 Total Material Costs for Prototype 3 Structures

Description of

Items Qty Unit Price (SGD)

Total Amount

(Include GST) (SGD)

Carbon Rod Flat

5x0.6x1200mm 8 3.00 25.68

Carbon Rod Solid

3x1200mm 2 3.80 8.13

MUMEISHA/

Epoxy 5 Min 1 8.50 9.10

Velcro Peel and

Stick Adhesives

(100x200mm)

1 5.50 5.89

Depron Foam

1500X1000X3mm 1.5 5.75 8.63

Total 57.43

Table 11 Total Costs Spent on Prototype 3

S/N Item

Item Weight

(Grams) Quantity Cost (SGD)

1

Prototype 3 Material

Structures (From Table 8) 217 1 57.43

2 Motor Assembly 76 1 24

3 Propellor 8 1 3

4 Electronic Speed Controller 23 1 18

5 Receiver 8 1 30

6 Battery Eliminator Curcuit 13 1 24

7 Servos 9 6 78

8 kK2 Flight Control Board 22 1 33

9 Wiring 5 1 0

11 Counter Balance Weights 20 1 0

12 Battery 82 1 48

13

Camera System (Incl

Cables) 23 1 130

Total: 551 445.43

Page A1

Table 12 Flow Simulation

0 Degrees 10 Degrees 20 Degrees 30 Degrees 40 Degrees

50 Degrees 60 Degrees 70 Degrees 80 Degrees 90 Degrees

Max Velocity (m/s)

0 m/s

Appendix C: Flow Simulation Results

spherical vtol uav structure and aerodynamics

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