designing an airship

Design Project

Design a lighter than air UAV

Frik van der Merwe 10139665

Study leader: Mr KP Grimsehl

Design Project MOX 41028 May 2014

FACULTY OF ENGINEERING, BUILT ENVIRONMENT AND INFORMATION TECHNOLOGY

Individual assignment

Cover page

Name of module Design Project

Module code MOX 410

Name of lecturer Mr. KP Grimsehl

Date of submission

Declaration:

1. I understand what plagiarism is and am aware of the Universitys policy in this regard.

2. I declare that my contribution to this assignment _____________report___________________ (e.g. essay, report, project, assignment, dissertation, thesis, etc.) is my own, original work.

3. I did not refer to work of current or previous students (excluding group members for this assignment), memoranda, solution manuals or any other material containing complete or partial solutions to this assignment.

4. Where other peoples work has been used (either from a printed source, Internet, or any other source), this has been properly acknowledged and referenced.

5. I have not allowed anyone to copy my work or those of my fellow group members.

Names of students (in alphabetical order) Student number Signature

Frik van der Merwe 10139665

Date received

Signature of administrator

Mark

Date

Signature of lecturer

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Summary

The aim of this project was to design a lighter than air UAV. This UAV would be used to follow rhinos in the Kruger National Park and would prevent poaching. A detailed literature study was done to determine some of the UAVs operating conditions. All the technical and functional requirements were specified in for the UAV. Concepts were drawn for the individual parts of the UAV and the best assembly selection was made. Detailed calculations were made done to acquire the governing dimensions of the UAV through an iterative process. From these calculations, detailed drawings were made for the airship. An analysis was done on manufacturing, maintenance, reliability and cost. Social, Legal, Health, Safety and Environmental aspects were considered and is discussed in this report. The total to manufacture the UAV will be R 53,246.76.

Keywords

Airship; UAV; Rhino; Anti-Poach; Kruger National Park;

Acknowledgements

A great deal of thanks to Mr. KP Grimsehl for his assistance during the project. Thanks to all the different suppliers for their friendly responses on my queries. Thanks to Mr. A. Van den Berg for his assistance with the Cost analysis. Lastly a great deal of thanks to Ms. K. Naud for her constant support and motivation.

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Contents Summary ............................................................................................................................................................................................iii

Keywords ...........................................................................................................................................................................................iii

Acknowledgements ............................................................................................................................................................................iii

1 Introduction ............................................................................................................................................................................... 1

2 Scope of work ............................................................................................................................................................................ 1

2.1 Problem statement.................................................................................................................................................................. 1

2.2 User Requirements ................................................................................................................................................................. 1

3 Literature Study ......................................................................................................................................................................... 1

3.1 Operating conditions .............................................................................................................................................................. 1

3.2 Airships workings .................................................................................................................................................................. 3

3.3 Following a Rhino ................................................................................................................................................................. 4

3.4 UAV Cameras ........................................................................................................................................................................ 4

3.5 Lowest safe Altitude (LSALT) .............................................................................................................................................. 53.6 Sound Production ................................................................................................................................................................... 6

3.7 Engines and Propellers ........................................................................................................................................................... 7

3.7.1Engine-Fuel system tradeoff study..................................................................................................................................... 7

3.7.2Selected engine-fuel system specifications ........................................................................................................................ 9

3.8 Ballonet pumps .................................................................................................................................................................... 10

3.9 Envelope and Ballonet Materials ......................................................................................................................................... 11

3.10 Dynamic force for an Engine-Propeller combination .......................................................................................................... 12

4 Functional Analysis ................................................................................................................................................................. 12

4.1 Functional Components ....................................................................................................................................................... 13

4.1.1Envelope .......................................................................................................................................................................... 13

4.1.2Rudder ............................................................................................................................................................................. 14

4.1.3Elevator ............................................................................................................................................................................ 14

4.1.4Ballonet ............................................................................................................................................................................ 14

4.1.5Engines ............................................................................................................................................................................ 14

4.1.6Gondola ........................................................................................................................................................................... 14

5 Technical Specifications .......................................................................................................................................................... 14

5.1 Requirements and Specifications ......................................................................................................................................... 15

5.2 Conclusion ........................................................................................................................................................................... 15

6 Concepts .................................................................................................................................................................................. 15

6.1 Concept Generation ............................................................................................................................................................. 16

6.1.1Envelope .......................................................................................................................................................................... 16

6.1.2Rudder and elevator concepts .......................................................................................................................................... 18

6.1.3Airship backbone ............................................................................................................................................................. 20

6.1.4Ballonet ............................................................................................................................................................................ 22

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6.1.5Engines for propulsion ..................................................................................................................................................... 25

6.1.6Gondola ........................................................................................................................................................................... 26

6.2 Concept Selection ................................................................................................................................................................ 28

6.2.1Airship Concepts.............................................................................................................................................................. 31

6.2.2Airship Concepts advantages and disadvantages ............................................................................................................. 33

6.2.3Concept selection matrix .................................................................................................................................................. 33

6.3 Detailed Concept design ...................................................................................................................................................... 35

7 Detailed design ........................................................................................................................................................................ 36

7.1 Calculations ......................................................................................................................................................................... 36

7.1.1Solving methodology ....................................................................................................................................................... 36

7.1.2Buoyancy Forces.............................................................................................................................................................. 37

7.1.3Speed of the airship and the air properties ....................................................................................................................... 37

7.1.4Size of the Airship ........................................................................................................................................................... 37

7.1.5Drag force from the envelope .......................................................................................................................................... 38

7.1.6Batteries ........................................................................................................................................................................... 38

7.1.7Motor size ........................................................................................................................................................................ 39

7.1.8Propeller dimensions ........................................................................................................................................................ 39

7.1.9Weight of the airship ........................................................................................................................................................ 39

7.1.10 Iterative solution .......................................................................................................................................................... 42

7.1.11 Discussion of results .................................................................................................................................................... 43

7.2 Detailed design sketches ...................................................................................................................................................... 43

8 Manufacturing Analysis ........................................................................................................................................................... 49

8.1 Gondola Case ....................................................................................................................................................................... 49

8.1.1Gondola Case Injection Molded....................................................................................................................................... 498.1.2Gondola Case Modular Method ....................................................................................................................................... 49

8.2 Connecting arm (ConnectorPlatePropPort) .......................................................................................................................... 509 Maintenance Analysis .............................................................................................................................................................. 52

9.1 Standard components ........................................................................................................................................................... 52

9.2 Envelope materials ............................................................................................................................................................... 52

9.3 Non-Standard Components .................................................................................................................................................. 53

9.4 Inspection ............................................................................................................................................................................. 53

9.5 Conclusion ........................................................................................................................................................................... 53

10 Reliability Analysis ................................................................................................................................................................. 53

10.1 System reliability ................................................................................................................................................................. 53

10.1.1 Probability of failure .................................................................................................................................................... 54

10.1.2 Severity of the failure ................................................................................................................................................... 54

10.1.3 Detection of the fault ................................................................................................................................................... 55

10.1.4 Risk of failure .............................................................................................................................................................. 55

10.2 Conclusions ......................................................................................................................................................................... 59

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11 Cost analysis ............................................................................................................................................................................ 59

11.1 Cost of standard components ............................................................................................................................................... 59

11.2 Cost of materials and Labor costs ........................................................................................................................................ 60

11.3 Total costs ............................................................................................................................................................................ 61

11.4 Conclusions ......................................................................................................................................................................... 61

12 Social, Legal, Health, Safety and Environmental Impacts ....................................................................................................... 62

12.1 Social Impacts ...................................................................................................................................................................... 62

12.2 Legal Impacts....................................................................................................................................................................... 62

12.3 Health Impacts ..................................................................................................................................................................... 62

12.4 Safety Impacts ..................................................................................................................................................................... 63

12.5 Environmental Impacts ........................................................................................................................................................ 63

12.6 Conclusion ........................................................................................................................................................................... 63

13 Conclusions and Recommendations ........................................................................................................................................ 64

13.1 Conclusions ......................................................................................................................................................................... 64

13.2 Recommendations ................................................................................................................................................................ 64

Appendix ........................................................................................................................................................................................... 66

Design Project Proposal ................................................................................................................................................................ 66Meeting Log Card ......................................................................................................................................................................... 70

Drawing for evaluation form ......................................................................................................................................................... 71

Table A: Available Batteries Above 4000 mAh ........................................................................................................................... 72

Table B: Available Quad Copter Motors ...................................................................................................................................... 72Table C: Available Quad Copter Propellers ................................................................................................................................. 77Iterative Solution Scrip File .......................................................................................................................................................... 80

Iterative Solution Function File (Volume) ................................................................................................................................ 81Iterative Solution Function File (Dim) ...................................................................................................................................... 81Iterative Solution Function File (Re) ......................................................................................................................................... 81Iterative Solution Function File (Cd) ........................................................................................................................................ 81Iterative Solution Function File (Drag) ..................................................................................................................................... 82Iterative Solution Function File (EngineWeight) ...................................................................................................................... 82Iterative Solution Function File (HullWeight) .......................................................................................................................... 88Iterative Solution Function File (ControlWeight) ..................................................................................................................... 88Iterative Solution Function File (RudderWeight) ...................................................................................................................... 89

References ......................................................................................................................................................................................... 90

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List of tables Table 1: Average Weights of white rhinos ......................................................................................................................................... 4

Table 2: Table of common sounds ..................................................................................................................................................... 6

Table 3: Engine trade-off study .......................................................................................................................................................... 8

Table 4: Car air compressor specifications....................................................................................................................................... 11

Table 5: Technical Specifications .................................................................................................................................................... 15

Table 6: Envelope, Concept 1, Advantages and Disadvantages ....................................................................................................... 16



Table 9: Rudder & Elevator, Concept 1, Advantages and Disadvantages ........................................................................................ 19

Table 10: Rudder & Elevator, Concept 2, Advantages and Disadvantages ...................................................................................... 19

Table 11: Rudder & Elevator, Concept 3, Advantages and Disadvantages ...................................................................................... 20

Table 12: Airship backbone, Concept 1, Advantages and Disadvantages ........................................................................................ 21

Table 13: Airship backbone, Concept 2, Advantages and Disadvantages ........................................................................................ 22

Table 14: Ballonets, Concept 1, Advantages and Disadvantages ..................................................................................................... 23

Table 15: Ballonet, Concept 2, Advantages and Disadvantages....................................................................................................... 24

Table 16: Engine, Concept 1, Advantages and Disadvantages ......................................................................................................... 25

Table 17: Engine, Concept 2, Advantages and Disadvantages ......................................................................................................... 26

Table 18: Gondola, Concept 1, Advantages and Disadvantages ....................................................................................................... 27

Table 19: Gondola, Concept 1, Advantages and Disadvantages ....................................................................................................... 28

Table 20: Concept Compatibility Matrix ......................................................................................................................................... 29

Table 21: Airship, Concept 1, Advantages and Disadvantages ........................................................................................................ 33

Table 22: Airship, Concept 2, Advantages and Disadvantages ........................................................................................................ 33

Table 23: Airship concept selection matrix ...................................................................................................................................... 34

Table 24: Example of Table A ......................................................................................................................................................... 38

Table 25: Example of Table B ......................................................................................................................................................... 39

Table 26: Iteration script values ....................................................................................................................................................... 42

Table 30: Probability of failure scale ............................................................................................................................................... 54

Table 31: Failure severity scale ........................................................................................................................................................ 54

Table 32: Fault detection scale ......................................................................................................................................................... 55

Table 33: FMEA for the airship ....................................................................................................................................................... 56

Table 34: Standard component costs ................................................................................................................................................ 59

Table 35: Material costs and estimated labour costs ........................................................................................................................ 60

Table 36: Total cost of the airship .................................................................................................................................................... 61

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List of figures Figure 1: Temperatures, Average and Extremes (Weather2, 2014) 2Figure 2: Precipitation Amount [mm] (Weather2, 2014) 2Figure 3: Wind Speeds [km/h] (Weather2, 2014) 2Figure 4: Airship Buoyancy Schematic (Stockbridge, et al., 2012) 3Figure 5: D-STAMP-HD reconnaissance camera. 5

Figure 6: Sound distance schematic 6

Figure 7: Working Quad Copter (Gajendran , 2012) 10Figure 8: Car compressor (Tosell, 2014) 11Figure 9: Airship functional components (IITB, 2010) 13Figure 10: Envelope, Concept 1 16

Figure 11: Envelope, Concept 2 17

Figure 12: Envelope, Concept 3 17

Figure 13: Rudder & Elevator, Concept 1 18



Figure 16: Airship backbone, Concept 1 21

Figure 17: Airship backbone, Concept 2 22

Figure 18: Ballonets, Concept 1 23

Figure 19: Ballonet, Concept 2 24

Figure 20: Engine, Concept 1 25

Figure 21: Engine, Concept 2 26

Figure 22: Gondola, Concept 1 27

Figure 23: Gondola, Concept 2 28

Figure 24: Example incompatibility check 29

Figure 25: Airship Compatible Concepts 30

Figure 26: Airship, Concept 1 31

Figure 27: Airship, Concept 2 32

Figure 28: 3D representation of the selected concept 35

Figure 29: The circle problem 36

Figure 30: Connecting arm, engine side detailed naming schematic 50

Figure 31: Connecting arm, gondola side detailed naming schematic 51

Figure 32: Schematic representation of milled rods 52

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Nomenclature list

UAV Unmanned Arial Vehicle

RPM Revolutions per minute

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1 Introduction

South Africa is home to the big five animals, the Lion, Elephant, African Leopard, Cape buffalo, and lastly the Rhino. These animals are the crown jewels in any game safari. Unfortunately, one of these animals is nearing extinction. Rhinos have been severely poached for their horns the past decade to the extent that new innovative ways have to be developed to monitor these animals. This project will focus on one solution, a lighter than air UAV, which will follow the Rhino and alert the ground patrols when a Rhino may be in danger of poaching.

2 Scope of work

This will give a broad overview of what work has to be done during the design project. 2.1 Problem statement

Design a UAV rigid airship on which surveillance equipment can be mounted. The UAV can be used to patrol our national parks and should be able to track big game, such as rhino, for a period of at-least 24 hours.

The control system is not included in the design. Only focus on the mechanical design of the UAV.

2.2 User Requirements

Must stay in the air for at least 24 hours.

Must carry a surveillance camera, recording and transmitting equipment.

Must be able to withstand harsh conditions like those of the Kruger National Park.

Must be relatively inexpensive to manufacture and maintain.

3 Literature Study

This literature study will give a broad overview of what conditions and limitations the UAV should adhere to when operating. The literature study will also give an explanation of how an Airship works and what are its advantages and disadvantages.

3.1 Operating conditions

The UAV will first be implemented over the Kruger National Park. The Kruger National Park is a park that was founded to protect the limited amount of animals in the park. The park is situated just below Zimbabwe and left of Mozambique. This park, having luscious bushveld, is subject to high temperatures, low rainfalls and seasonal winds.

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Figure 1: Temperatures, Average and Extremes (Weather2, 2014)

Figure 2: Precipitation Amount [mm] (Weather2, 2014)

Figure 3: Wind Speeds [km/h] (Weather2, 2014)

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From Figure 1 it can be noted that the temperatures average between 9 C and 34 C. Taking into account the absolute maximums and minimums of Figure 1 with an added safety factor, it can be assumed that the UAV should be able to operate between the temperatures of -5 C to 70 C.

Looking at Figure 2, the precipitation amount on average is not very high. The UAV should thus be able to function in wet conditions but there will not be a need to design the airship for extreme wet

conditions.

Figure 3, show that winds speeds that can be expected in the Kruger National Park. The average wind speed per month is around 6 km/h. It can be noted that for every month there were some spikes in winds speeds, some ranging as high as 85km/h.

The elevation of the Kruger National Park varies from 140m above sea level to about 600m above sea level. As it can be seen, the Kruger National Park is fairly low compared to other regions in South Africa (Siyabona Africa, 2014)

3.2 Airships workings

Airships are also called lighter than air vehicles or LTAV for short. A LTAV works on the principle of using ballast, a lot like a submarine, to make it lighter or heavier than air. To make the balloon or hull of the airship light, a lighter than air gas is needed. Two of the most common gasses used in airships are Helium, having a lifting capacity of 1.02 kg/m3, and Hydrogen, which has a lifting

capacity of 1.1kg/m3. These lifting capacities are measures at sea level. Hydrogen, used in the early days of airship design, is highly flammable and is deemed unsafe to use.

Figure 4: Airship Buoyancy Schematic (Stockbridge, et al., 2012)

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Figure 4 show a schematic drawing of an airship with a cut made in the hull. Through the cut in the hull, it can be seen that there are two additional balloons in the hull called ballonets. Ballonets act as the ballast tanks for an airship, which are filled with air. To make an airship accent, the ballonets are deflated, expanding the constant mass of Helium and lowering its density. This creates a buoyancy effect that makes the airship lighter than air. To make the airship descend, the ballonets air inflated

with air, compressing the constant mass of Helium in the hull and increasing the density of the Helium, making the airship heavier than air. This is the basic principal of an airship (Freudenrich, 2014).

3.3 Following a Rhino

The main aim of the LTAV is to follow the Rhino in the Kruger National Park. Following a Rhino is

critical to the airships operation.

Table 1: Average Weights of white rhinos

Males 1800-2500 kg

Females 1800-2000 kg

Newborns 40-60 kg

Table 1 shows the average weights of a white rhino. Looking at the weight, these are fairly large animals and would be easy to spot. The average shoulder height of a full grown rhino is between 1.5m and 1.8m.

A daily activity of a rhino includes feeding and alternatively resting. In hot dry weather they routinely rest during the hottest part of the day. Much of the resting time is spent wallowing or rolling in dust. Rhino in general prefer long and short grass savannah areas.

When startled or threatened, a rhino can run up to 40km/h for short periods of time.

Concluding, a rhino can easily be spotted from the air as they prefer open areas and watering holes in hot and dry conditions. (Savetherhino, 2014)

3.4 UAV Cameras

A UAV camera should be light and should be able to rotate around its own axis to enable fast and efficient tracking of its target. The camera should rather rotate around its own axis, which will be fast, than waiting for the airship to change direction.

CONTROP designs and manufactures miniature, lightweight, electro-optical, stabilized, airborne sensors which are designed to be carries by a miniature UAV for tactical reconnaissance in daylight or

during night.

For the airship, it has been decided to use the D-STAMP-HD camera.

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Figure 5: D-STAMP-HD reconnaissance camera.

Figure 5 shows the D-STAMP-HD camera. This camera boast qualities that render it perfect for the airship:

Very lightweight for small UAVs. Weighs Low power consumption.

High performance image resolution and quality.

Low cost.

This camera will enable the UAV to be a distance of 1000m from the rhino, and still have clear visuals on the rhino. With thermal vision, it will be ideal to spot poachers when they are still a long distance away from the rhinos.

The camera is not part of the design, but the weight and functionality has to be taken into account. (Controp, 2014)

3.5 Lowest safe Altitude (LSALT)

The LSALT for a UAV is 1000 feet which is roughly (AMDT, 2010). This means that the UAV will hover in the air at. Raising the height of the airship will result in a broader outlook but if the airship is higher than, the camera will be rendered useless. Thus the optimal operation height should be between and. Having a camera range of and a LSALT of , calculated with Pythagoras, the airship can follow the rhino from about away. This will also maintains the peace in the resort and will not disturb the natural habitat of the rhinos.

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3.6 Sound Production

Keeping the sound down will be important to the functioning of the airship. An airship that produces a lot of noise, will disturb the natural habitat of the rhinos and any other animals living in the Kruger National Park. Sound is caused by pressure variations which moves in waves through a medium such as air. The further the sound has to move through the medium, the more the sound dissipates.

Table 2: Table of common sounds

dB Sound

0 Threshold of human hearing

10 Volcano Crater

20 Leaves rustling

40 Crickets at 5 meter

60 Conversation speech at 5 meter

80 Snow coach at 30 meter

90 Lawnmowers

100 Thunder

120 Military Jet at 100 meter

126 Cannon fire at 150 meter

Table 2 (National Park Service, 2014) is a table containing some common sounds that we may encounter to give reference of the decibels scale. The dissipation of sound over a distance can be calculated with the following formula:

Figure 6: Sound distance schematic

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(1.)

Where is the sound level and is the distance from the source of the sound to the point of interest. From the above text, we determined that the airship has to be more than in the air when operating. We can also assume that we do not want the sound on the ground to be more than. Solving the equation gives:

!" #$%

From the above calculations, it was determined that the airship should not emit sound loader than

& '"when standing from the airship. In comparison, the sound emitted from the airship should not be louder than a lawnmower when standing from the airship. The engines will be the main source of sound production so a silent engine has to be chosen. (Sengpielaudio, 2004)

3.7 Engines and Propellers

The engines of the airship will be used to turn the propellers which will create thrust. With the thrust created from the propellers, the airship can be moved. The engines will be the main source of power for the airship. The engines will use a type of fuel, and convert the fuel into kinetic energy which will be used to rotate the propellers. Looking at the above mentioned paragraphs, it can be concluded that the engines should be light, should not emit relatively loud noise and should not be too complex to maintain the buoyancy while using fuel.

3.7.1 Engine-Fuel system tradeoff study

For this, a tradeoff study was setup to compare different engine systems. This tradeoff study will only take into effect the engines and the type of fuel they use. Four types of engine-fuel systems were selected for this tradeoff study. A petrol engine, a hybrid engine, an electric engine powered by batteries and lastly an electric engine powered by solar panels.

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Table 3: Engine trade-off study

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Table 3 shows the tradeoff study between different engine-fuel configurations. The tradeoff study looks at different aspects, giving them a score with the highest score being the best. The first aspect that has to be taken into account is the airborne aspect. This looks to weather this engine-fuel combination can be airborne for 24 hours as the technical specifications specify. The second aspect is sound. This looks at the sound produced by the engine, with quietness being the aim, as this will function in a National Park. The third aspect is the buoyancy-fuel compensation which has to be taking into effect. As the airship uses fuel, the airship becomes lighter which means the control system has to constantly adjust the buoyancy of the airship to compensate for this. The last aspect is the weight of the engine-fuel system. The lighter the airship is, the smaller it can be which will reduce the production costs of the airship. The weight of each aspect is shown by the amount of points that can be awarded for the aspect.

The petrol engine will be able to be airborne for 24 hours without refueling as the airship will carry the needed fuel with it. Petrol engines are notoriously loud engines when operating. This engine will use petrol, which when used, will decrease the weight of the airship, which the airship then has to compensate by filling the ballonets more. The total weight of this engine-fuel system will be relatively small as the amount of fuel needed to produce the needed power will be small.

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The hybrid engine will be able to be airborne for 24 hours without refueling as the airship will carry the needed fuel with it. This system will consist of a petrol engine, a generator and an electric engine which will turn the propellers. Petrol engines are notoriously loud engines when operating. This engine will use petrol, which when used, will decrease the weight of the airship, which the airship then has to compensate by filling the ballonets more. The total weight of this engine-fuel system will

be relatively small as the amount of fuel needed to produce the needed power will be small. This will still be heavier than the above mentioned petrol engine as this will have a generator included into the system to produce electricity.

The electric engine with batteries will be able to be airborne for 24 hour before the batteries will have to be recharged. With this being a complete electric system, it will be virtually inaudible. The battery weight will not change as they become discharged, so no buoyancy-fuel compensation has to be taken into effect. The weight of the batteries will be very heavy, needing for the airship to have an increase in size just to carry the weight of the batteries.

The electric engine with solar panels will not be able to be operational for 24 hours. During the night the solar panels will not be able to charge, leaving the engines powerless. With this being a complete electric system, it will be virtually inaudible. The will be no weight change when the system is operational, so the buoyance-fuel compensation does not need to be taken into effect. Because this system will not have the added weight of heavy batteries, this system will be very light.

From Table 3 it can be noted that for this airship, the best engine-fuel system will be an electric engine with batteries. This system outperformed the rest in the tradeoff study.

3.7.2 Selected engine-fuel system specifications

Determining the exact engine and batteries needed for the airship will be virtually impossible if the drag force of the airship is unknown. This part of the literature study will only show what will be needed for the system to work, as well as possible components that can be used. The best configuration of components will be chosen in the detailed calculations, after the drag has been calculated.

The components chosen for the airship will be that of an ordinary quad copter. The reason for this is because of the recent worldwide interest in quad copters, the components for them are easily acquirable. There is also a lot of knowledge gained over the years from experts which help facilitate the design of the airship propulsion system.

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Figure 7: Working Quad Copter (Gajendran , 2012) Figure 7 shows an image of a working quad copter. The principle of the quad copter is to generate lift using four electric motors to rotate four individual propellers which creates enough lift to fly.

An airship produces lift with its envelope, but the same motor that produces lift for the quad copter can be used to propel the airship. Batteries, a control system, electric motors and the propellers are what are needed to create a complete propulsion system. Because the control system for the airship is not part of the design, only the battery, electric motors and propellers will be chosen for the airship.

In the appendix, Table shows a list of off-the-shelf batteries and their specifications. Table is a list of available quad copter motors that can be used to rotate the propellers. Table is a list available quad copter propellers that can be used for the airship. The best combination of batteries, electric motors and propellers has to be chosen for the airship according to the drag that the airship produces.

3.8 Ballonet pumps

The ballonet pump will be the pump which inflates the ballonets in the envelope to increase the density of the Helium, making the airship heavier. The pump will have to be powerful enough to compress the Helium, but also be lightweight and be able to operate with the available battery power provided above. The optimum pump would be a car compressor. This will not only enable the pump to operate with the available power, but also be able to compress the Helium in the airship enough to make the airship descend. The pump chosen for this project is the following:

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Figure 8: Car compressor (Tosell, 2014) Figure 8 shows the selected air compressor that will be used for the airship. This is a very small air compressor which is ideal as the air throughput can be accurately stopped. The air compressor has the following specification:

Table 4: Car air compressor specifications

Specification Value Description

Pressure 20.78 Bar This compressor can reach a pressure of 20 times the atmospheric air pressure at sea level.

Voltage 12 V This can be powered from the batteries of the propulsion system as they operate at 11.1 V

Weight 246 g This is a very small, lightweight compressor weighing a quarter of a kilogram

Size 165x85x127 mm This shows that the air compressor is very small.

Table 4 shows that this compressor should be able to compress the Helium enough by inflating the ballonet. This compressor will not be used to its full potential as a pressure of 20 Bar will easily burst the envelope. For the design a compressor is used as the pump system will be a design project on its own. This is not the best pump for the operation of the airship but this pump will be able to sufficiently inflate the ballonets and increase the density of the Helium.

3.9 Envelope and Ballonet Materials

The envelope and ballonet materials selected should satisfy a range of requirements. These requirements are:

Should be able to last a vast amount of time without weathering.

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Should have a low Helium permeability.

Should be able to deform without shearing.

Should be able to easily be joined, be it adhesive or clamps.

A study was done into the most ideal material for an airship envelope (Khoury & Gillett, 1999) where two materials where discussed and a conclusion was made on two different materials. These materials are as follows:

Polyvinyl fluoride, or more commonly known as PVF has a very low Helium permeability. PVF is resistant to fungal growth which would be ideal when using it in a tropical area. PVF was also found to have a life cycle of 15-20 years with no maintenance the material.

Polyurethane, or more commonly known as PUR, is a material which also has a low Helium

permeability. PUR has a good crease resistance making it ideal to use in constantly deforming balloons. PUR has a 5 year life cycle with modest maintenance, having to soften the outside layer to prevent cracking. PUR is very easy to join with either adhesives or by heat bonding.

For the airship envelop, the material that will be used is PVF because of its durability, while the material for the ballonet will be PUR, as the ballonet will constantly be deforming.

3.10 Dynamic force for an Engine-Propeller combination

The force that an Engine-Propeller combination produces is mainly dependent on the RPM at which the propeller is turning, the diameter of the propeller and pitch of the propeller. Determining the thrust accurately is dependent on the form of the propeller as well as the density of the fluid it moving though, but for simplicity the thrust force can be determined with the following formula derived by Gabriel Staples (Staples, 2013):

( ")

* +, * -./ * 0"1

.3456 ") * +7 * -./ * .3456 (1.)

This formula will give the thrust in Newton where the -./ is the Revolutions Per Minute the engine is turning at, is the diameter of the propeller measured in inches and .3456 is the Pitch of the propeller measured in inches. It can be noted that this is just an approximation of what the thrust will be and has been proven to be a conservative formula. The above formula will underestimate the thrust

produced by 89. This formula was chosen because of its conservative nature and simplicity.

4 Functional Analysis

The functional analysis consists of breaking the airship up into its most basic parts needed. This will enable the student to do a more detailed design of the airship by designing each component as a

whole.

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4.1 Functional Components

An airship consists of a set of basic functioning components that, when combined, creates a lighter than air vehicle.

Figure 9: Airship functional components (IITB, 2010) From Figure 9 we can see that an airship consists of a lot of components with the Envelope or Hull being the main component. The most basic components are as follows:

Envelope or Hull.

Rudder.

Elevator.

Ballonet.

Engine for propulsion.

Gondola or basket.

4.1.1 Envelope

The envelope is the main component of the airship. The envelope will contain the gas needed to make the airship lighter than air. Because of this, the airships envelope size will be a function of the weight. The large the weight of the total airship, the larger the envelope will become. As it can be seen in Figure 9, the envelope contains the Ballonets. The envelope will have a constant volume of gas inside of it.

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4.1.2 Rudder

The rudder will control the direction the airship is flying in. Upon changing the rudder direction, one can make the airship turn port (left) or starboard (right). A rudder will no likely be more than an flat plate of metal, than will be used to manipulate the airflow over the airship.

4.1.3 Elevator

The elevator has the same basic function as the rudder, but instead of controlling the port and starboard movement, the elevator will control the up and down movements of the airship. This will also in its most basic form be a flat plate that will manipulate the airflow over the airship.

4.1.4 Ballonet

Ballonets are used to control the ballast of the airship. Changing the volume of the ballonets, will in effect compress or decompress the gas in the envelope, making the airship lighter or heavier than air. The ballonets will have a changing volume of gas inside of it. The volume of gas will be controlled by the control system. Because the envelope has a constant volume of gas, but the ballonets has a changing volume of gas, the envelopes mass of gas contained will change, but not the volume. This basic principle is what makes the airship more buoyant or less buoyant.

4.1.5 Engines

The engines of the airship are what will propel the airship, or make it hover on a constant position if

there is a light breeze blowing. The aim of the engine is to be as light as possible and still be powerful

enough to overcome the drag forces created by the large envelope.

4.1.6 Gondola

The Gondola is a basket containing all the small components that are needed the control the airship. The Gondola typically sits on the bottom center of the airship. For this airship, the gondola will

contain the following:

Fuel for the engines.

The control system.

The camera.

The pumps for the ballonets.

5 Technical Specifications

Technical specifications deal with the specifications that the final product will be measured by. The design of the airship has to be able to satisfy all the technical specification. This will also show the importance of the technical specification to the design of the airship.

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5.1 Requirements and Specifications

Table 5 is a table with the technical specifications for the airship:

Table 5: Technical Specifications

Nr. Specification Not Important Relatively Important

Very Important

1. Operate at a height between 300m and 1000m above ground level.

2. Can be airborne for a time of 24 hours without landing.

3. Can fly at a speed of 40km/h for a time of 2 hours and still have enough fuel to stay in the air for the remaining 22 hours

4. Can stay airborne for a complete cycle of 24 hours on one specific spot.

5. Operate in a temperature range between -5 C to 70 C

6. In the case of extreme weather conditions, be able to land on any surface to prevent being blown away.

7. Be silent to not disturb the peace in the national parks.

8 Be able to operate in wet conditions where there is light rainfall.

5.2 Conclusion

In Table 5, all the technical specifications with their importance to the project can be noted. The importance was assigned in the manner to best protect the rhinos, while moving the self-preservation of the airship to a lower priority.

6 Concepts

In the concepts part of the report, the concept generation will take place for all the functional parts of

the airship. Concepts will include location, as well as any other important information needed to explain the concept.

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6.1 Concept Generation

During concept generation, concepts will be generated for each functional part of the airship. Concepts do not include measurements or dimensions, just basic forms with advantages and disadvantages of those particular concepts.

6.1.1 Envelope

The envelope has to be designed to have the least amount of drag, being able to carry the needed amount of weight with the least amount of internal forces.

6.1.1.1 Envelope, Concept 1

Figure 10: Envelope, Concept 1

Figure 10, shows a concept for the envelope where the length of the envelope has two times the diameter of the envelope.

Table 6: Envelope, Concept 1, Advantages and Disadvantages

Advantages Disadvantages

The envelope, with the above shape, will have a fairly low drag force.

No sharp edges, to minimize stress concentrations

Continuous shape, so deformation will be minimal when subjected to internal pressures.

Because of the long shape, there will be internal bending moments that have to be taken into effect.

As can be seen in Table 6, concept has a lot of advantages compared to the disadvantages.

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Figure 11 shows an envelope in the shape of sphere. This concept will have minimal internal bending moments but because of the shape, it will have increased drag.



No sharp edges, to minimize stress concentrations.

Continuous shape, so deformation will be minimal when subjected to internal pressures.

Minimal internal bending moments.


Not optimal shape to minimize drag forces.

Table 7 shows that this concept has more disadvantages. Because the speed of the airship is critical and the drag forces are directly proportional to the airspeed, it can be assessed that this concept is not in the best interests for this design.



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Figure 12, showing concept 3 for the envelope, gives a shape where the length of the envelope is four times that of the maximum diameter. This shape will have decreased drag when moving through the air, but will have high internal moments caused by the long shape of the envelope.



The envelope, with the above shape, will have a very low drag force.

No sharp edges, to minimize stress concentrations


Because of the long shape, the airship may deform when subjected to large internal pressures.

Very large internal bending moment produced by the long shape of the envelope.

Form Table 8, it can be noted that an envelope with a long length does indeed have a negative impact on the design of the envelope. This being said, it will be recommended that the envelope length be less than four times the diameter of the envelope.

6.1.2 Rudder and elevator concepts

The rudder will be used to steer the airship and manipulate the airflow over the airship to stabilize its movement while the elevator will also be used to stabilize the movement but will not play as large of a role as the rudder will. Most of the lift will be generated from the envelope and not with forward movement as a plane generates lift.

6.1.2.1 Rudder and elevator, Concept 1

Figure 13: Rudder & Elevator, Concept 1

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Figure 13 shows a concept where the elevator will be fixed. The rudder will be fixed as well but will have a moving piece which moves relative to the rudder plate. This rudder will be similar to that of an small airplane.

Table 9: Rudder & Elevator, Concept 1, Advantages and Disadvantages


Known to work as this type of tailfins are what aircrafts use

Simple concept

Elevator can be replaced or left out altogether if a good working ballonet system is implemented.

Having the rudder move independently from the airship, additional controls are needed to operate the rudder.

Rudder might not have enough power to control the airship

Airship needs to move relative to the air for rudder to work

Table 9 shows that this is the fool proof method of creating a tailfin for the airship, but for the use of the project, it might not be the best concept. This concept limits the manoeuvrability of the airship and needs a lot of extra components to work.

6.1.2.2 Rudder and elevator, Concept 2


Figure 14 shows the concept where the rudder will be rigid with no moving parts, but instead will have an extended rudder with an individual propeller in the rudder. The elevator fin will also be rigid without any moving parts.



Airship will be very manoeuvrable using the rudder propeller to turn.

Elevator can be replaced or left out altogether if a good working ballonet

For an additional motor, the battery size has to be increased to compensate for the power consumption.

Envelope volume has to be increased to

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system is implemented.

Less moving parts, which makes this a more simple solution

compensate for the increase in battery weight.

Table 10, shows that this is a good concept for making the airship more manoeuvrable, but might add significant weight and volume to the airship. Because the volume of the airship increases, it can be assumed that the drag will also increase, which will in effect need a larger battery to compensate for the additional power losses for the engines having to work harder.

6.1.2.3 Rudder and Elevator, Concept 3


Figure 15 shows the concept with three rigid air fins, evenly spaced from one another. The air fins will not have any moving parts on them. This concept will only act as a stabilizer.



Light tailfin concept, while still maintaining basic function.

No moving components which lower the chance of failure.

This concept will not act as a rudder or elevator but rather like stabilizers.

Needs an additional mechanism to make the airship manoeuvrable.

Table 11 shows that this is a good concept in the sense of its simplicity. It will have no moving parts. This tailfin will only act as a stabilizer. Unfortunately for this tailfin to act as a rudder, an additional mechanism will be needed to make the airship manoeuvrable.

6.1.3 Airship backbone

The tailfins, being the rudder and elevator, of the airship will have a relatively heavy weight as they will be made from rigid materials. The envelope of the airship will be made from a type of fabric which will not be able to carry the weight of the tailfins without deforming. The backbone of the airship will act as a load bearing mechanism that will connect to the gondola to the tailfins. This will

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make the airship a semi-rigid airship. These concepts also tried to reverse the effect of the bending moment created by the tailfins.

6.1.3.1 Airship backbone, Concept 1

Figure 16: Airship backbone, Concept 1

Figure 16 shows a concept for the backbone of the airship. This concept illustrates the gondola being connected directly to the tailfins of the airship by means of the backbone. The backbone will be an array of beams. These beams will be fixed to the gondola and tailfins by means of ordinary fasteners.

Table 12: Airship backbone, Concept 1, Advantages and Disadvantages


Lightweight design.

Strong structure to make the airship semi-rigid.

Simple structure.

The tail will create a moment around the centre of mass, making the airship lean backwards.

Table 12 shows that this concept has more advantages than disadvantages. Looking at the disadvantages, it shows that the airship will lean backwards because of the moment caused by the tailfin. This moment can be cancelled out by moving the gondola forward in the airship, creating a lightweight and stable backbone for the airship.

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6.1.3.2 Airship backbone, Concept 2

Figure 17: Airship backbone, Concept 2

Figure 17 shows the alternative concept for the backbone of the airship. This concept will have an added water tank inside the front of the airship. With the added weight of the water tank, the backbone will cancel the moment of the tailfin.

Table 13: Airship backbone, Concept 2, Advantages and Disadvantages


Gondola will not to move from the centre of the airship.

The airship will be stable and not lean backwards.

Heavier design, meaning a drastic increase in envelope size.

Increased moment of gyration.

Table 13 shows that this concept boast advantages as well as disadvantages. The main disadvantage will be increase in envelope size to compensate for the increase of weight from the water. This is not a recommended concept for the backbone of the airship.

6.1.4 Ballonet

Ballonets are the components that control the buoyancy of the airship. Inflating the ballonets increases the weight of the airship, making it descend. Deflating the ballonets will decrease the weight of the airship and in effect make it ascend. The ballonets should also be able to control the pitch of the airship, controlling if the airship points upward or downward.

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6.1.4.1 Ballonets, Concept 1

Figure 18: Ballonets, Concept 1

Figure 18 shows a concept for a ballonet system. For this concept, two ballonets are used which can be independently controlled. Controlling the ballonets independently will enable the control system to change the pitch of the airship by inflating one ballonet more than the other.

Table 14: Ballonets, Concept 1, Advantages and Disadvantages


Can accurately change the pitch of the airship.

If one ballonet fails, the airship will still be able to descend using the other ballonet.

Very complex system with either two individual pumps for the individual ballonets on one pump with a control valve.

From Table 14 it can be noted that this is a complex system, which might increase the cost of the project as a whole. The price of this concepts ballonet will be rewarded with being able to change the airships pitch very accurately.

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6.1.4.2 Ballonets, Concept 2

Figure 19: Ballonet, Concept 2

Figure 19 is a concept where there is only one ballonet inside of the envelope. The bottom side of the ballonet will be fixed to the gondola and the top side of the ballonet will be able to move. This free movement will be governed by a string that will pull the ballonets forward to the nose, or backwards to the tail of the envelope. By moving the ballonet inside of the envelope, the pitch of the airship can be changed. Moving the ballonet forward, moves the excess Helium to the back, creating more lift at the back.

Table 15: Ballonet, Concept 2, Advantages and Disadvantages


Simple system with an easy control system.

The system can be simplified even more to be only adjustable on the ground as a calibration mechanism of the pitch.

Cheap to manufacture

The ballonet will have limited movement as one end of the ballonet is fixed and will rely heavily on deformation for moving.

Because of excessive stretching, the ballonet may fail, causing contamination of the helium.

Table 15 shows that this concept will be very simple to operate. This can be simplified to a concept that can be only used on the ground to calibrate the pitch of the airship. This will have a low cost to produce with still a high sense of accuracy. Because the airship will be a very small ship with very small moment of inertia. The need for the control of the pitch will be very limited.

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6.1.5 Engines for propulsion

Engines are used to propel the airship forward, or make the airship hover on one place if there is a breeze from the front. Engines can also be used to rotate the airship to be placed correctly.

6.1.5.1 Engine for propulsion, Concept 1

Figure 20: Engine, Concept 1

Figure 20 shows a concept where two engines are used, one on each side of the gondola. This will create a shared forward thrust. The engines will be spaced from the gondola by means of solid rods which extend from the gondola. The rotation direction of each engine will be independent of the other.

Table 16: Engine, Concept 1, Advantages and Disadvantages


The two engines can be used by rotating in opposite directions, to rotate the airship. This concept will make the airship very manoeuvrable.

Two engines are used to share the thrust, which will reduce the strain on the individual engines.

Because two engines are used, a more complex control system has to be used.

Might need addition fuel to propel two individual engines rather than one.

Table 16 shows that this concept is highly manoeuvrable. This in effect can be used in cooperation with a less manoeuvrable tailfin system to keep the costs down, but still maintain the manoeuvrability of the airship.

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6.1.5.2 Engine for propulsion, Concept 2

Figure 21: Engine, Concept 2

Figure 21 shows a concept where the engine is mounted at the back of the airship. The engine will be fixed to the rudder and elevator of the airship.

Table 17: Engine, Concept 2, Advantages and Disadvantages


Only one engine will be needed to propel the airship.

Might need less fuel as only one engine is used.

Only controls to forward and backwards movement of the airship.

Additional weight at the back end of the airship, to make it even more heavy, creating a larger moment around the centre of mass.

Because of the position of the engine, it may have to operate in turbulent conditions, which can cause spikes in the power consumption and can cause control system failure.

Table 17 shows that this concept has to be used in cooperation with a tailfin system that make the airship manoeuvrable. This will increase the weight at the back end of the airship and create an even

larger moment around the centre of mass.

6.1.6 Gondola

The gondola is the package of the airship. In the gondola, all the components of the airship will be placed so that the gondola acts as its own unit. The gondola should contain the Camera, Control

System, Batteries and the pumps for the ballonets.

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6.1.6.1 Gondola, Concept 1

Figure 22: Gondola, Concept 1

Figure 22 shows a concept depicting the layout of the gondola. The layout from the front will be the camper, control system, batteries ant the ballonet pump. In this concept, the gondola is also hanging below the airship

Table 18: Gondola, Concept 1, Advantages and Disadvantages


The control system will be between the batteries and the camera, separating the power cables from the camera visual cables. This will reduce the induction created from the power cables.

The batteries, being the heaviest compared to the other components of the gondola, will be place far back. This will create a moment around the centre of mass.

Because of the gondola hanging outside of the airship, an additional drag force will be imposed.

Table 18 shows that this concept will function normally and will have no effect on the performance of the airship, but may cause internal moments.

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6.1.6.2 Gondola, Concept 2

Figure 23: Gondola, Concept 2

Figure 23 shows a concept where the batteries have been moved forward in the layout of the gondola. This also shows that the gondola will be placed inside of the envelope, en will be visible on minimal places outside of the envelope.

Table 19: Gondola, Concept 1, Advantages and Disadvantages


Because a major part of the gondola is hidden inside of the envelope, the drag caused by the gondola will be minimal.

With the batteries moved forward, the weight of the batteries will cause a moment, that can cancel out the moment caused by the tailfins

Because the gondola is hidden inside of the envelope, and the camera being part of the gondola, the camera might have limited visuals.

Table 19 shows that this concept can solve the problem of having residual internal moments, but might cause the camera to have limited visuals.

6.2 Concept Selection

The concept selection will look at the best combination of sub-system concepts to create the best concept for the airship. A compatibility matrix was set up to see which concepts are compatible with which concepts. After the compatibility test, the remaining sub-system concepts will be combined to create the complete concepts of the airship. These complete concepts will be evaluated using a concept evaluation procedure which will determine the best concept for the airship.

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Table 20: Concept Compatibility Matrix

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Table 20 shows which concepts are compatible with which concepts. Compatibly for this instance can be defined as checking to see whether the concepts would logically be able to work together. The greyed out area in the table would contain data already in the table because of symmetry of the table.

Having the concept compatibility checked, the incompatible sub-system concepts have to be eliminated. A tree diagram was used to do this, looking at the end result to see if anything was incompatible.

Figure 24: Example incompatibility check

Looking at Table 20, a simple figure like Figure 24 can be created. From the above figure it can be noted that these sub-system concepts are not compatible with each other. When checking the table it

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30

can be noted that Envelope Concept 1 is not compatible with Rudder Concept 1. Rudder Concept 1 is also incompatible with Gondola Concept 1. This means that a combinations of the above sub-system concepts will not be able to exist.

Doing a compatibility check for all the possible concepts, the following figure was generated:

Figure 25: Airship Compatible Concepts

Figure 25 shows a tree diagram of all the compatible sub-system concepts. There are now only two airship concepts in total. Using a concept evaluation method, these concepts will now be tested to determine the best concept, which will be taken into further development.

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6.2.1 Airship Concepts

Figure 26: Airship, Concept 1

Figure 26 shows the first airship concept. The envelope in the concept is transparent. The concept shows the estimate positions of all the predetermined concepts.

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Figure 27: Airship, Concept 2

Figure 27 shows another complete airship concept. The envelope of the airship is transparent in this concept. This concept boasts a single ballonet which is controlled by an adjustment wire.

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6.2.2 Airship Concepts advantages and disadvantages

Table 21: Airship, Concept 1, Advantages and Disadvantages


Light design

Very Manoeuvrable

Change airship pitch.

Minimal drag and internal moments.

Advanced pump system needed for the ballonets.

Table 21 shows that this concept has many advantages making it a great concept for the purpose at hand. Some simplicity is needed for the pump system but otherwise this is a good concept up for possible consideration.

Table 22: Airship, Concept 2, Advantages and Disadvantages


Light design.

Very Manoeuvrable.

Changeable airship pitch.

Minimal Drag and internal moments.

Possible fatigue of the ballonets rubbing against the backbone can cause ballonet failure and contamination of the helium inside the envelope.

Table 22 shows the advantages and disadvantages of the second complete airship concept. It can be noted that is a simplified concept from the first airship concept. This simplicity possesses its own problems as fatigue now becomes a problem. As the ballonet will have minimal movement, the fatigue threat will also be minimal.

6.2.3 Concept selection matrix

The better of the two individual concepts have to be selected to be taken into further production. For this, a final concept selection has to be done. This concept selection will be done by setting up a matrix with individual criteria to which the airship concepts have to be measure by. These criteria is set up by

34

taking into account the technical specified earlier in the report. The main aim will still be protect rhinos in the wild. Each of the individual criteria has a specified weight which is directly relative to the importance of protecting the rhinos.

Table 23: Airship concept selection matrix

Airborne (100): The possibility of the airship to be airborne for a time of 24 hours.

Maneuverability (50): The ability of the airship to stay be easily maneuvered.

Complexity (20): The less complex the concept is, the easier it will be to maintain, receiving a higher score.

Silence (30): Being able to operate silently is important to the functioning of the airship.

Total (200):

Airship Concept 1 90 50 16 30 186

Description: In extreme weather conditions, where wind is higher than expected, the airship will need to be recharged before the end of 24 hours.

With the positions of the engines in the concepts, the airship will be very maneuverable.

This concept will make use of a complex pump system. Furthermore the rest of airship will be fairly fixed.

Making use of an electric propulsion system, the airship will emit very low levels of sound, making it virtually inaudible when operating in the sky.

Airship Concept 2 90 50 18 30 188

Description: In extreme weather conditions, where wind is higher than expected, the airship will need to be recharged before the end of 24 hours.

With the positions of the engines in the concepts, the airship will be very maneuverable.

This concept will make use of an simple pump system, furthermore the rest of the airship will be fairly fixed

Making use of an electric propulsion system, the airship will emit very low levels of sound, making it virtually inaudible when operating in the sky.

From Table 23, it can be noted that according to the proposed concept selection, the best concept is Airship Concept 2. The deciding factor for this concept was its low level of complexity. For all the other criteria, the concepts will neck in neck. Airship Concept 2 will now be taken into further development.

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6.3 Detailed Concept design

Figure 28: 3D representation of the selected concept

Figure 28 shows the pre-design-calculation representation of the selected concept. The sizes of all the relative components will be determined in the detailed calculations.

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7 Detailed design

The detailed design will include all the calculation for all the parts of the airship. These calculation will give answers such as the governing dimension for the airship. With the information acquired in the detailed design calculation, the detailed design can be drafted.

7.1 Calculations

The calculation for the detailed design will solve all the unknowns of the airship. This includes the materials used, the airship dimensions and the various assumptions that were made to solve the

unknowns.

7.1.1 Solving methodology

The largest part of the design calculations is to determine the size of the envelope. This poses a problem as the envelope size is dependent on the weight of the airship. The weight of the airship is

mainly governed by the amount of batteries used. The amount of batteries used is determined by the motors used, which in co-operation with propellers has to overcome the drag force of the envelope. The drag force of the envelope is dependent on the size of the envelope.

Figure 29: The circle problem

There are too many variables for the equation to be solved algebraically. Thus, the weight of the airship will be assumed and an iterative solution will be used to solve to remaining variables.

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7.1.2 Buoyancy Forces

Helium inside the envelope has a lower density than the air around it. This will in effect create a buoyancy force, meaning the airship will want to ascend. This is the key to the workings of an airship. The buoyancy force can be calculated with the following formula:

(: ; ? ;@AB=CDEF@=G ? HF@=G (2.)

where (: is the Buoyancy force created by the change in densities of the different gasses. As the airship ascends, the air density will decrease. During the assent the density of the Helium in the airship envelope stays the same. The implication of this is that the buoyancy force decreases as the height of the airship increases. This also means that the airship has a fixed maximum height it can fly, which is referred to as the ceiling height. When the airship is flying at its ceiling height, the buoyance

force (: 0I. For simplification and later consideration, a constant buoyancy force is assumed which is a function of the volume of the airship:

(: 10.0062N/m0 (3.)

This is an accurate assumption if the airship is close to sea level.

7.1.3 Speed of the airship and the air properties

The speed at which the airship should be able to move is largely governed by the speed of the rhinos it has to follow, as well as the expected wind speeds. For the literature study it can be noted that the

airship will on average not have to face a wind speed of more than10/6. For the iterative process, it is assumed that the airship will have to be able to maintain an airspeed of 40/6 for a time 36NOP and should be able to overcome a wind speed of 20/6 for a time period of246NOP.

7.1.4 Size of the Airship

From the concepts generated, the best form factor for the airship is a 2:1 form factor. This means that the length of the airship will be twice the diameter of the airship. The volume of the airship will be a function of the weight it has to lift, as well as the lifting force from the Helium. The lifting force can

be determined as follows:

(QABC=D (:9.81 1.02/0

(4.)

The mass will be determined in a later section. The volume of the airship can be determined as follows:

EF@=G F@=G/(QABC=D (5.)

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This will give the volume of the airship. Having the volume of the airship, the length and the diameter can be solved iteratively using the following formula:

EF@=G 43RST (6.)

These will form the governing dimensions of the airship.

7.1.5 Drag force from the envelope

To calculate the drag force of the airship which is moving through air, some constants have to be calculated first. The basic formula for the drag force of an immersed body is as follows:

(U>

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battery pack produces. The weight of the battery is how heavy the battery is. Unlike a petrol system fuel tank, the weight of the battery will not decrease as it becomes discharged.

7.1.7 Motor size

A list of possible motors that may be used is shown in Table in the Appendix. An example from the table is as follows:

Motor

Kv

YZ[\ ] R

(ohm)

Kt

^_. `ab

No Load Current

(A)

No Load Volt

(V)

Max Current (A)

Motor Weight

(g)

1 Above All 2813-18 1200 0.075 1.127 1.2 8.2 25 55

Table 25: Example of Table B

Table 25 is a single line from Table B in the Appendix. These are the set values for the specific motors that are available on the market. The cd value is a constant. To calculate the RPM at which the motor will be rotating the formula -./ cd * E

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7.1.9.1 Propulsion system weight

Various formulas where used to calculate what combination Batteries, Motors and Propellers has to be

used in accordance to overcome the drag force (U of the airship moving through the air. This was an iterative process in itself. First a combination of a Battery, Motor and Propeller was selected. The static force from the combination of hardware would produce was calculated with the following formula:

(FjmG0.1.3456 * 4.233 * 10

+7 * -./ * .3456

Where SG>mG is the diameter of the propeller in Inches and the .3456 is the pitch of the propeller in inches. The above formula was calculated for all the possible combinations of the hardware in Tables A, B and C. If the force calculated was smaller than the drag force produced by the airship envelope, the combination of hardware was ignored. For all the combinations of hardware that produced a force that could overcome the drag force of the airship, the amount of current that that combination would consume was calculated with the following formula:

ikmnFCDA 2 * co * SG>mG7 * .3456 * cd0 * Epq (9.)

Now that the amount of current the hardware combination consumes is known, the amount of batteries can be calculated by looking at the time the airship has to stay in the air versus the amount of time the battery can produce the needed current. This was done for all the remaining hardware combination. These combinations weights were tallied and the combination that could produce the needed force with the minimum amount of weight was the combination that was selected.

7.1.9.2 Envelope Weight

The envelope weight is a function of the surface area of the airship. The material that would be used

for the airship envelope is PVF which has a density of ; 140/0. For simplicity, the thickness of the hull was assumed to be 0.2 thck. The weight of the envelope material can be approximated as follows:

HAnrABmGA XF * 0.0002 * 140 (10.)

This would give an approximation of what the envelope material would weigh.

7.1.9.3 Control System Weight

For this, values were assumed in accordance to what each component is expected to weigh. The control system weight takes into account the weight of the Camera, Control System, Ballonet Pumps the Gondola Casing and an addition contingency weight. These weights were assumed to be:

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Hk< 1 Hkmnj>FqF 2 Hp

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7.1.10 Iterative solution

To solve all of the above equations, an iterative solution was needed. The equations were set up in Matlab, and was solved to give the best possible answer. An initial weight for the airship was selected of 30kg for the complete airship. The calculations were also done to determine the specifics of an

airship that needed to fly at 40/6 for a time of 36NOP. This will also be a conservative measure taken to ensure that the airship will be able to maintain a speed of 20/6 for a time period of 246NOP. The script used in Matlab can be seen in the Appendix und

designing an airship

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