National University of Singapore

10

UAV DESIGN AND MANUFACTURE U067782B

ZHANG XUETAO

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Table of content

Summary 3

Introduction 4

UAV fuselage design 6

Aircraft shape and aerodynamics of fuselage 7

Aircraft structure analysis 12

Engine connection 12

Wing connection 16

Material selection 18

UAV Fuselage manufacture 22

Vacuuming forming 22

Conclusion 29

Recommendation 30

Reference 32

Appendix 33

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SUMMARY

The first part of the report is concentrated on UAV fuselage design. It consists three

sections: aerodynamics, stress analysis and material selection.

The fuselage shape must be such that separation is avoided when possible. That’s

where the aerodynamics of the fuselage design’s core. By designing the ratio and

shape of the UAV nose and tail cone, the ultimate goal is to reduce as much drag as

possible and provide lifts. We must be convinced that a manoeuvre always involves

acceleration, turning, deceleration, all of which will put the UAV under high loads,

that’s why the stress analysis is so important here. By referring to the thorough stress

analysis, theoretically the UAV is safe to fly under any conditions. Material is always

so important for aircrafts that in reality, all the aircrafts has been built by most

expensive industrial materials, like carbon fibers, carbon steels, nickels,

molybdenum, etc. For this UAV design, no much vibration, corrosion, noise would

be taken into consideration. What’s more, the stress involved is not as high as the real

commercial aircraft, so cheaper and realistic materials should be studied. In fact, after

a comprehensive study about wood, Styrofoam, plastics, steel and carbon fibers, PVC

is finally chosen as the main fuselage material.

The second part of the report mainly introduces an industrial process—vacuuming

forming and its implementation in this UAV fuselage design. Some advantages and

disadvantages are discussed in this part.

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Vacuum forming is one of the methods using thermoforming treatment. Besides the

fact that vacuum forming can make exact shape as the mould, it also take less pain to

build the station and take less time to produce one piece of prototype. However,

several disadvantages exist. The whole process should been monitored very carefully

since toxic gas would be produced if the plastic is overheated. Also in lab scale, it is

always very hard to build a station large enough for the overall design and the

prototype is very hard to modify as well.

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1. INTRODUCTION

The purpose of this project is to design and manufacture an Unmanned Air Vehicle

(UAV). As a group project, it requires four students to design and/or build wings,

fuselage, engine and optimization. This report is the final report for the fuselage

design and manufacture.

There are numerous interesting books on the history of aircraft development. This

section contains a few additional notes relating especially to the history of aircraft

aerodynamics along with links to several excellent web sites. (Refer to appendix 1).

However, there are very few topics relating to UAV design and manufacture. This

report gives students a comprehensive overview and understanding of UAV fuselage

design and manufacture.

According to the optimization, this UAV is designed to maximize the endurance. In

order to achieve the design goal, besides the wing and propulsion, the fuselage gives

great contribution as well. The following parts have two main sections: UAV

fuselage design and manufacture. In the design part, aerodynamics designs including

nose and tail cone together with stress analysis and material selection are elaborated.

In the manufacture part, a newly and practical industrial process—vacuum forming is

introduced and implemented.

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2. LITERATURE REVIEW

A search for “nose fineness ratio” produced 1240 journals from Engineering Village

and 480 from Web of Science. Further search for “aerodynamic nose fineness ratio”

produced 188 from Engineering Village. 80 out of these 188 journals have been

reviewed. Below are the summary of those researches.

Shu Xin-wei and Gu Chuan-gang (2006) did researches on “numerical simulation

on the aerodynamic performance of high-speed maglev train with streamlined nose”.

They indicated that with comparison and analysis of the results of the five different

configurations, regularity that its aerodynamic performance changing with its

aerodynamic configuration was drawn. When the other parameters are the same, the

aerodynamic drag and lift decrease with the length of the streamlined nose shapes

extending; when the length of the streamlined nose shapes is almost the same, the

aerodynamic drag of the front car of the protruding longitudinal profile is less than

that of the concave, while that of the rear car is the contrary; the aerodynamic drag of

the middle car varies within a small range, the aerodynamic lift of the rear car is

greater than that of the front one; and the total aerodynamic lift of the three cars of the

protruding longitudinal profile is greater than that of the concave.

Ota, Terukazu (1983) worked on the project of nose shape effects on turbulence in

the separated and reattached flow over blunt flat plates. He found that the nose shape

has a strong influence on the turbulence features in the separated and reattached

regions and even far downstream from the reattachment point.

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Goodson, K. W (1958) wrote of journal named Effect of Nose Length, Fuselage

Length, and Nose Fineness Ratio on the Longitudinal Aerodynamic Characteristics of

Two Complete Models at High Subsonic Speeds. He discovered that the stability for

all model configurations showed substantially the same variation with changes in

forebody area moment. The forebody changes did not alter the angle of attack at

which an unstable break occurred in the moment contribution of the T-tail but did

alter somewhat the magnitude of the instability.

A search for “vacuum forming” produced 820 journals from Engineering Village and

210 from Web of Science. 40 out of these 1130 journals have been reviewed. Below

are the summary of those researches.

Campo, E. Alfredo (2008) wrote in his journal “Polymeric Materials and Properties”

that all PVC compounds require heat stabilizers to allow processing without

degrading and discoloring the polymer. Plasticizers are added to increase the

flexibility of the compound. They can also improve the heat stability or improve the

flame retardancy of the compound. Fillers are used to reduce the cost, improve

dimensional stability, stiffness, and impact strength. PVC is a recyclable commodity

thermoplastic material of large consumption by the building and construction

industry. PVC is popular because of its excellent impact, wear, chemical, and UV

resistance. PVC is used in a large variety of end products such as flooring, garage

doors, windows frames and profiles, siding, tubing, and connectors. These products

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are commonly available in standard sizes and shapes, low cost, and easy to work with

(weld, repair, and paint).

Fagence, S.W. and Garvin, W.Barry (1973) discussed the machines and their

operations (loading the sheets, clamping, heating, interlocking, drawing, pre-

stretching, etc); mold design; and mold cooling in the large piece of vacuum forming

process. He also stated that a definition of 'large sheet' could be a 'sheet in excess of

16 sq. ft'.

Wilhelm R (1971) stated in his report “Vacuum forming of thermoplastics”, that

although several materials can be used for the mold, for instance epoxies and silicone

rubber, metal forms were mostly used, particularly for long production needs.

Decoration and joining by adhesive bonding and HF welding of PVC vacuum formed

products were discussed.

Breuer, Heinz (1977) indicated in his journal “Importance of Vacuum Technology

for Extrusion of Plastics as Exemplified by PVC Processing” that the processing of

powdered thermoplastics - particularly PVC in the form of compounds including

common stabilizers - on twin-screw extruders was widely accepted quite some time

ago. The more recent development in the sector of PVC film for food packaging has

called the attention to compact extrusion lines with small sized calenders. Here,

however, single-screw and planetary roller extruders with sheering dies rather than

twin-screw extruders are used as plasticizing equipment. For improving the

profitability of these techniques as well as the quality of the finished products, the

extruders are fitted with vacuum-assisted feed hoppers. Apart from air and moisture,

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the vacuum technology from which the closed system of the vacuum type twin-

hopper venting unit with the extruder has been derived, also permits the removal of

other excess gases and vapors and, not last, the residual VC content from the PVC

melt.

Ian C. McNeill, Livia Memetea and William J. Cole (1995) discovered in their

study of “products of PVC thermal degradation” that PVC shows two stages of

degradation: during the first stage, between 200 and 360 °C, mainly HCl and benzene

and very little alkyl aromatic or condensed ring aromatic hydrocarbons are formed. It

was evaluated that 15% of the polygene generates benzene, the main part

accumulating in the polymer and being active in intermolecular and intermolecular

condensation reactions by which cyclohexene and cyclohexadiene rings embedded in

an aliphatic matrix are formed. Alkyl aromatic and condensed ring aromatic

hydrocarbons are formed in the second stage of degradation, between 360 and 500

°C, when very little HCl and benzene are formed. In this stage the polymeric network

formed by polyene condensation breaks down in the process of aromatisation of the

above C6 rings. The mechanism of benzene formation at different temperatures was

considered.

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3. UAV FUSELAGE DESIGN

The design of the fuselage is based on payload requirements, aerodynamics, and

structures. The overall dimensions of the fuselage affect the drag through several

factors. Hemida, Hassan and Krajnovic, Siniša (2010) Stated that fuselages with

smaller fineness ratios have less wetted area to enclose a given volume, but more

wetted area when the diameter and length of the cabin are fixed. The higher Reynolds

number and increased tail length generally lead to improved aerodynamics for long,

thin fuselages, at the expense of structural weight. Selection of the best layout

requires a detailed study of these trade-offs, but to start the design process, something

must be chosen. This is generally done by selecting a value not too different from

existing aircraft with similar requirements, for which such a detailed study has

presumably been done. In the absence of such guidance, one selects an initial layout

that satisfies the payload requirements.

In this UAV fuselage design, the payload requires a fuselage being able to hold a

camera, batteries, servo, and targeting ball. Except the payload requirement, other

considerations are:

• low aerodynamic drag

• minimum aerodynamic instability

• ease of assembly and disassembly of fuselage

• structural support for wing and tail forces acting in flight, which involves

simple stress analysis for the entire fuselage

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3.1. Aircraft Shape and Aerodynamics of Fuselage

3.1.1. Aircraft Nose and Tail Cone Design

The fuselage shape must be such that separation is avoided when possible. This

requires that the nose and tail cone fineness ratios be sufficiently large so that

excessive flow accelerations are avoided.

The aircraft fineness ratios are defined as length divided by diameter, which including

nose fineness ratios and tail cone fineness ratios.

In all of the following nose cone shape equations, L is the overall length of the nose

cone and R is the radius of the base of the nose cone. y is the radius at any point x,

as x varies from 0, at the tip of the nose cone, to L. The equations define the 2-

dimensional profile of the nose shape. The full body of revolution of the nose cone is

formed by rotating the profile around the centerline (C/L). Note that the equations

describe the 'perfect' shape; practical nose cones are often blunted or truncated for

manufacturing or aerodynamic reasons.

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There are several shapes available: 3/4 Power, Cone, 1/2 Power, Tangent ogive,

parabolic, ellipsoid, etc. (Refer to appendix 2 for more details)

Liu Tang-hong, Tian Hong-qi and Wang Cheng-yao (2006) wrote in journal

“Aerodynamic performance comparison of several kind of nose shapes” that as speed

of the plane increases, the drag coefficient increase as well. Different type of fuselage

shape can give different drag coefficient as well. But as shown above, below Mach

number 0.5, the shape of the airplane does not give too much difference.

Except the shape of the fuselage, the nose and tail cone fineness ratio play an

important role in fuselage design as well. Below is a simulation graph: drag loss VS

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fineness ratio.

Not surprisingly, the elliptical shape has poorer performance than the other shapes,

but except from that, and perhaps the parabolic shape, the difference in apogee

between the other shapes is so small for the higher fineness ratios, that other criteria

may be taken into account when selecting the shape. A 2:1 fineness ratio may be

chosen over 3:1 for practical reasons. Also there are the thermal considerations in real

airplane consideration.

The profile of current designed shape is one-half of an ellipse, with the nose and tail

fineness ratio 2. R=4.5cm, L=18cm.

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In this UAV design, one of key factors in UAV fuselage shape design is the payload.

According to the payloads weights, centre of gravity as well as the attribution of the

different parts, the width, namely the aircraft lateral diameter is no less than 9cm. In

order to make sure the Centre of Gravity is behind the aerodynamic centre, which is

design to make sure of the aircraft stability and easily maneuverability, and based on

the fact that the tail of the plane is relatively high, the batteries and camera should be

put into the very front to counter the weight. As such, the nose should be designed so

as to have enough space to hold the payloads at the very front. That’s the main reason

of this design. Fineness ratio 2 is restricted by the overall length of the fuselage and

diameter of the fuselage. Any longer fuselage will increase the drag even more.

Besides all these considerations, the shape also depends on the manufacturability;

more details would be discussed in the UAV manufacturing part.

R=4.5cm

L=18cm

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3.1.2. Final UAV designed shape

The main function of this UAV fuselage is to protect the payloads during the flight

test and actually flying. So the priority of the design is to fulfill the payloads’

requirement.

The final design is as followed:

design parameters design value

fuselage length <36cm

nose length 18cm

tailcone length 18cm

main cabin length 0

cross section diameter 9cm

fuselage thickness 1mm

nose fineness 2

tailcone fineness 2

forward extra space 0.5cm

after extra space 0.5cm

Fuselage shape Ellipse R=4.5cm, L=18cm

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3.2. Aircraft Structure Analysis

The main concerns for this UAV design regarding to stress analysis are from

connections with engines and wings. The following are details of calculation for these

two parts.

3.2.1. Engine Connection

Engine: max thrust T=0.7*9.81=6.87N So there are two main force on steel plate T= 6.87Nand

M1=T*L1=6.87*0.04=0.275N.m.

The cross section Area of the steel plate is: 0.5cm*4cm=2cm^2=0.0002m^2

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The equation for thin walled structure is as follow:

For this problem, since the section is symmetric about both y and z axis, Iyz=0.

Since Mz=0. So 𝜎𝜎𝑥𝑥 = 𝑀𝑀𝑦𝑦𝑧𝑧

𝐼𝐼𝑦𝑦𝑦𝑦

𝐼𝐼𝑦𝑦𝑦𝑦 =1

12 ∗ 40 ∗ 53 = 417𝑚𝑚𝑚𝑚4

Z=2.5mm

M=0.275N.m=275N.mm

So 𝜎𝜎𝑥𝑥=275*2.5/417=1.65N/mm^2=1.65×106𝑁𝑁𝑚𝑚2 = 1.65𝑀𝑀𝑀𝑀𝑀𝑀

Γ=F/A=3.5×104𝑀𝑀𝑀𝑀=0.035MPa

Mohr’s Circle Let’s suppose we know all the stresses in the normal (x, y, z)-coordinate system.

When we shift the coordinate system, the normal stresses and the shear stresses

change. The way in which this occurs is described by Mohr’s circle. Mohr stated that

if you plot the direct stresses and the shear stresses, you would get a circle. Such a

circle is shown in figure below.

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𝜎𝜎𝑥𝑥 = 1.65𝑀𝑀𝑀𝑀𝑀𝑀.𝜎𝜎𝑦𝑦 = 0. Γ=0.035MPa.

Use the Java applet(4, aoe) to draw the Mohr’s circle:

Max normal stress in tension is 1.65MPa, in compression is 7.42MPa

Max shear stress is 0.826MPa

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In aircraft structure design, one of the most important factors is safety factor. Each

design of aircraft has its own V-n diagram. Here we use the diagram the same RV-9.

According to the V-n diagram below,

Since the airspeed is no more than 25 kts, a safety factor of 1.5 is given.

So the max stress is 2.48MPa.

For steel, the stress strain curve is shown below.

According to the calculation, the max stress is 2.48MPa=360 psi, is far smaller than

the upper yield point for steel, so this steel is safe to use.

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3.2.2. Wing Connection

Now we are going to calculate the structure stress due to wing loading. According to

Shaoming’s analysis, the max lift is 30N in total. Each wing contributes 15N. Since

there are two rods attached to each wing, the load for each rod is 7.5N. If the longer

rod can bear the loads, the shorter one can as well. We should calculate the longer

rod. The length of the rod is 5cm.

M2=7.5N*50mm=375N.mm r=5mm

𝜎𝜎𝑥𝑥 = 𝑀𝑀𝑦𝑦𝑧𝑧𝐼𝐼𝑦𝑦𝑦𝑦

𝜎𝜎𝑥𝑥=1.9MPa Γ=0.0095MPa

The Mohr’s circle is as follow.

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The max normal stress is 1.9MPa. The max shear stress is 0.955MPa.

Adding safety of factor in 1.5, the max stress is 2.85MPa.

Stress strain curve for carbon fibre is as follow.

The max stress is far less than yield strength. So the aircraft structure is safe by using

carbon fibre rod at the wind area.

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3.3. Material Selection for Fuselage

3.3.1. General Selection

Choice of materials emphasizes not only strength/weight ratio but also:

• Nose transparency for camera function;

• Comparably large strength allied to lightness;

• Strong stiffness and toughness for the rear rod;

• Low cost and weight for all parts.

• Fracture toughness

• Crack propagation rate

• Stress corrosion resistance

• Exfoliation corrosion resistance

Today, the main material used is aluminum alloys for all kinds of aircraft, which is

pure aluminum mixed with other metals to improve its strength. In the real world of

aircraft, Cui Degang (2008) conventional stiffened fuselages (skin/frames/stiffeners),

sandwich fuselages, double walls (skin with an interior panel), insulation blankets in

between the skin and the interior panels, application of damping improving visco-

elastic layers, application of piezo electric elements for active noise control, etc, are

designed and launched to strength the fuselage. Since the UAV does not need too

much strength, only the skin with basic holding structure would be enough.

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Below is a comparison of material property comparison for different kinds of possible

materials for aircraft fuselage, aluminum sheet, wood, Styrofoam, plastics, and

carbon fibers.

Considering all the factors listed at the beginning of this section, including stress

factors, cost, manufacturability, weight-to-stress ratio, and resistant to corrosion or

stress concentration, etc, plastics are the best choice, and vacuum forming method is

chosen for plastics’ manufacture.

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3.3.2. Selection of Plastics

For the UAV fuselage, from all the possible plastics, PVC is chosen. It has strong,

tough thermoplastic with good transparency in thinner gauges, good chemical and fire

retardant properties and highly resistant to solvents. Thicker materials are rigid with

good impact strength ideally suited to outdoor industrial applications.

In the following table, a comparison of various plastics is listed, including PS, ABS,

PP, PE, PVC and PC. A scale from zero to three is given to each of the four

properties, heating time, cost, formability, and strength. For each material property,

four percentages are given, which are 10%, 10%, 40%, and 40% respectively. The

final scores are calculated for each plastic and we get PVC has the first position

which get a score 2.60 (full score is three).

Materials Heating

time(S)

10%

Cost

10%

Formability

40%

Strength

40%

Total

Score

Ranking

PS 60

3

2.5 3 1.5 2.35 3

ABS 80

2.5

2 2 2 2.05 5

PP 100

1

2.5 1 3 1.95 6

PE 100 2.5 1 3 1.95 6

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1

PETG 60

3

1 3 2 2.40 2

PVC 60

3

3 3 2 2.60 1

PC 120

0.5

1 2 3 2.15 4

• The standard thickness for the heating is 2mm.

More details about vacuuming forming of PVC would be discussed in the

manufacturing section of the later part.

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4. UAV Fuselage Manufacture

4.1. Vacuum forming

The whole fuselage requires vacuuming forming as a tool to manufacture two parts:

aircraft nose and the tail cone.

Vacuum forming is one of the methods using thermoforming treatment. Vacuum

forming has generally been promoted as a ‘dark art’ and best left to companies with

sophisticated processing equipment that is able to supply the facility and service. By

using this method, moulds, plastics, vacuum machine and heaters are commonly

being used.

In its simplest form the process consists essentially of inserting a thermoplastic sheet

in a cold state into the forming clamp area, heating it to the desired temperature either

with just a surface heater or with twin heaters and then raising a mould from below.

The trapped air is evacuated with the assistance of a vacuum system and once cooled

a reverse air supply is activated to release the plastic part from the mould.

Although this force is quite limited, about 15 PSI maximum, this is the most common

process used for high volume thin gage products. In this process the heated sheet is

placed over a cavity mold. Contact is made between the sheet and the mold creating a

seal. The air in the cavity is evacuated and atmospheric pressure forces the sheet

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against the contours of the cavity. Most vacuum forming machines include a surge

tank which is first evacuated so the forming can occur very quickly in the process.

The followings are some key dimensions of this vacuum forming stations with

pictures.

Vacuum box Vacuum cleaner

Frame 25*20cm Plastics 0.5mm for testing

1mm

manufacturing

Oven 30*25cm Temperature 240 degrees

Effective working

ratio

1:1.5 Time needed 1minutes for

0.5mm

3minutes for 1mm

Max mould length 18cm Max mould

diameter

9cm

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4.1.1. Advantages

Firstly, by using vacuuming forming method, as shown below, we could make the

exact shape as the moulds, which is one of the key factors in this UAV design. Since

the design of the fuselage has very restricted requirements, there are only two

possible economic ways to do that: clamping and vacuum forming. For student lab

scale, it would be practical to design and build the vacuum forming station.

Secondly, it is relatively easy to use vacuum forming method for fabrication,

although there are some minor defects. The practical vacuum forming station is built

by a vacuum cleaner, vacuum table, oven, and a frame. Some other tools are being

used during the fabricating as well. The working station is shown below.

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Thirdly, it is not a very time-consuming process. Once the station is settled, the all

process for one part would be approximately 10 minutes without assembly.

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4.1.2. Disadvantages and Solutions

Despite all these advantages about vacuuming forming process, there are some

disadvantages needed to be taken into accounts.

4.1.2.1. Toxic gas

Firstly, it is toxic if the plastics are being heated too much. The temperature plays a

crucial part here. The purpose of heating the plastics is to soft the plastics, not to melt

them. If the plastics are overly heated, it would be dangerous for the operator.

By experiments, the setup time for the oven to heat up to the desired temperature is 5

minutes. Then by different materials, heating time is different. (Refer to the appendix

for industrial heating time). For this lab experiments, 0.5mm and 1mm PVC are being

used for testing and manufacturing. The oven is set to 240 degrees for both two

materials, while 0.5mm PVC needs 1 minute to been heated to desire soft state and

2mm PVC need 3 minutes.

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4.1.2.2. Non-Uniform Wall Thickness

Secondly, it is Non-Uniform Wall Thickness that comes in during the experiments.

This is the number one disadvantage of the thermoforming process. Since

thermoforming is a “stretching” process, wall thickness of the product varies

depending on the amount of stretching that must occur to create the desired geometry.

There are many design rules as well as process variations to lessen the impact of

“stretching. Here drawing ratios are introduced.

Drawing ratios include Aerial Draw Ratios, Linear Draw Ratios and Height-to-

Dimension Ratios. Each has advantages but is only grossly representative of sheet

thinning, however they can be excellent instructional tools for comparing part designs

and processes.

4.1.2.2.1. Aerial Draw Ratio (ADR)

ADR is the overall measurement of stretch of the sheet. This is determined by

calculating the surface area of the formed part and dividing it by the surface area of

the sheet used to form the part.

ADR = Surface area of the formed section / Surface area of the sheet used to form the

part

In this part design, the surface area of the formed section is half a ellipse plus the rest

of area.

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L=18cm, R=9cm.

A=18, b=c=9, p=1.6075. S1=425cm^2

Ax2 + Bxy + Cy2 + 1 = 0, the area is .

S2=254cm^2

ADR=S1/S2=1.67

Maximum ADR’s are shown. This information is helpful to compare the stretching

properties of various materials.

Surface Area

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4.1.2.2.2. Linear Draw Ratio (LDR)

This the comparison of the length of a straight line drawn on the sheet before forming

as compared to the length of the same line after forming. Only the forming area is

included in this calculation.

LDR = Line length on formed part / Line length before forming

The drawing of this experiment is

The circumference of the ellipse is

For the special case where the minor axis is half the major axis, we can use:

So arc length C=21.8cm

So the LDR=21.8+918

= 1.71

The maximum LDR for various plastics is shown below.

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LINEAR DRAWRATIO(LDR)

Plastic Maximum LDR

ABS 3.4

Acrylic 2.1

HDPE 4.3

LDPE 4.5

PP 7.1

PVC 4.1

This experiment is within the range.

4.1.2.2.3. Height –To- Dimension Ratio

This ratio is simply the height of the formed part divided by the length of the greatest

opening of the part. The usefulness of this ratio is limited to simple symmetric parts

such as a drinking cup using straight vacuum forming process with a cavity mold.

H: D = Height of formed part / Greatest length of opening

H: D=9/18=0.5

PeterW. Klein (2009) stateD that the height-to-dimention ratio for PVC is 6.5. It

means that this experiment is within range.

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4.1.2.3. Size of the Station

Thirdly, the manufacture process is always restricted by the size of the station. At

first, it would the size of the vacuum table that has to be enlarged. Then it follows the

frame, and lastly the oven. In fact, by trying different cutting machine of the mould,

at last, the original oven is finally practical. The required size for the fuselage is

13.5cm nose length plus 18cm tail cone length. The shrinking rate for this process is

1:1.5, which mean the effective working area of the plastics should be more than

47.25cm. It was not possible for the vacuum table, frame and the oven! As shown

below, the frame is designed to have only 25*20cm effective working area. Vacuum

table has 20*15cm effective working area, and the oven has 30*25 effective working

areas. In order to continue this project with this method, some modifications have

been made. In order to make the whole piece of nose and cone at one time, two

identical parts had been divided and glued together.

This method is chosen to manufacture the UAV fuselage, not because it is the

requirement of this project, but mainly, it is the only way to manufacture fuselage by

plastics using the ideal design. Despite the disadvantages, vacuum forming, as a

commonly used industrial process, provide a practical way to the fuselage into reality.

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5. CONCLUSION

This UAV fuselage design and manufacture report has two main parts. The fuselage

design focus on aerodynamics, stress analysis and material selection. And the

manufacture part focuses on vacuum forming process.

Based on several researches on nose and tail cone fineness ratio as well as shape of

fuselage, this UAV fuselage is designed as ellipsoid, as the nose and tail cone ratio as

1:2.

Stress is calculated on mainly the steel plate attached to the engine and the carbon

fibre rod attached to wings. The max stress in the plate and rod is far less than the

yield strength, in fact, only 10% of which. So the fuselage structure is safe to use

these materials.

After comparing the properties of wood, Styrofoam, carbon fibre, plastics, and so on,

PVC is finally chosen for the main fuselage skin. Due to the stress requirement, as

well as the manufacturability, it is the desirable raw material.

In the manufacture part, vacuum forming is discussed. Several advantages and

disadvantages are listed as well. Solutions are provided as well.

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6. RECOMMENDATION

Since this fuselage design is restricted by the payloads, the fineness ratio cannot be

bigger than 2. In the future, one can try to increase the fineness ratio and better

improve the drag loss coefficient.

Vacuum forming is specially designed for thermoplastics forming process, with

simple procedure and lab-accessibility. During the experiments, two main problems

arise. Not only the size of the station restricts the whole experiments for more than a

month, the toxic gas is another main issue here as well. In the future, for next batch of

students, the vacuum station should be designed in the way that can be altered,

especially the size of oven and the vacuum table. Students want to do some vacuum

forming experiments before setting up the station, can approach SDE department to

get approve of accessing the design workshop in Department of Architecture. If the

oven is not available in the market within the budget, one can consider the furnace

available in the impact lab locates at EA-01-01 or the material lab locates at E3-04-1.

For construction of the vacuum forming table, please refer to the video from

YouTube:

http://www.youtube.com/watch?v=e5CGfoxnKaQ ,

http://www.youtube.com/watch?v=yhajk_IDTUo

http://www.youtube.com/watch?v=hGBRiYhxRTM

http://www.youtube.com/watch?v=Qc_FZcGzYn0&feature=related

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One can refer to

http://isites.harvard.edu/fs/docs/icb.topic604638.files/FormechVacuumGuide.pdf for

more details about industrial vacuum forming process.

Another problem arises during the experiments is the toxic gas. Since the vacuum

forming process requires the plastics to be very soft before put onto the mould and

vacuum table, so the time and temperature control during the heating process is

crucial. In fact, it is very hard to control the heating time so as to eliminate the toxic

gas. One should take note of this in the experiments and try to use a mask or do these

experiments in a clean room with air pump inside.

Instead of using clay as the ray material for the moulds, one can take wood or

Styrofoam into account. By using turning for wood block or foam cutter for

Styrofoam, a better surface finishing can be achieved.

In addition, besides vacuuming forming, stress analysis can be done using FEA.

During the design and experiment, it is inevitable that the models crashed. It

happened four times to this design. Also, during flight, accelerating and turning, the

structure would stand strong stress. If the material is wood or Styrofoam, it would be

necessary to use FEA to analysis the whole body FEA consists of a computer model

of a material or design that is stressed and analyzed for specific results. It is used in

new product design, and existing product refinement. In case of structural failure,

FEA may be used to help determine the design modifications to meet the new

condition.

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7. REFERENCE

1. Shu Xin-wei and Gu Chuan-gang (2006), “numerical simulation on the

aerodynamic performance of high-speed maglev train with streamlined

nose”, Shanghai Jiaotong University Press, China, Journal of Shanghai

Jiaotong University, v 40, n 6, 1034-7

2. Ota, Terukazu (1983), “nose shape effects on turbulence in the separated

and reattached flow over blunt flat plates”, : Zeitschrift fur

Flugwissenschaften und Weltraumforschung, v 7, n 5, p 316-321

3. Goodson, K. W (1958), “Effect of Nose Length, Fuselage Length, and

Nose Fineness Ratio on the Longitudinal Aerodynamic Characteristics of

Two Complete Models at High Subsonic Speeds”, National Aeronautics and

Space Administration, Hampton, VA, Langley Research Center, Journal of

Spacecraft and Rockets, v 9, n 2, 126-8

4. Campo, E. Alfredo(2008), “Polymeric Materials and Properties”,

William Andrew Publishing, ISBN-13: 9780815515517, 249 pp

5. Fagence, S.W. and Garvin, W.Barry (1973), “Large Size Vacuum

Forming”, Plast Inst, New Tech in Extrusion and Injection Moulding,

Conf, pp123-125

6. Wilhelm R (1971), “Vacuum forming of thermoplastics”, Plastvarlden, v

21, n 3, p 30-33

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7. Breuer, Heinz (1977), “Importance of Vacuum Technology for Extrusion

of Plastics as Exemplified by PVC Processing”, Plastverarbeiter, v 28, n

5, p 233-240

8. Ian C. McNeill, Livia Memetea and William J. Cole (1995), “products of

PVC thermal degradation”, Polymer Research, Chemistry Department,

University of Glasgow, Received 3 January 1995

9. Hemida, Hassan and Krajnovic, Siniša (2010), “LES study of the

influence of the nose shape and yaw angles on flow structures around

trains”, Elsevier, Journal of Wind Engineering and Industrial

Aerodynamics, v 98, n 1, p 34-46

10. Cui Degang (2008), “Structure technology development of large

commercial aircraft”, Press of Chinese Journal of Aeronautics, China,

Acta Aeronautica et Astronautica Sinica, v 29, n 3, 573-82, 25

11. PeterW. Klein (2009), “Fundamentals of Plastics Thermoforming”,

Morgan & Claypool, PP12-13

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APPENDIX 1 Historical Website about Aircraft Design

http://adg.stanford.edu/aa241/intro/history/history.html

http://www.boeing.com/history/

http://www.airbus.com/en/

http://invention.psychology.msstate.edu/

http://spicerweb.org/chanute/Cha_index.aspx

http://www.wrightflyer.org/

http://www.aero-web.org/history/wright/first.htm

http://en.wikipedia.org/wiki/History_of_the_aircraft_carrier

http://en.wikipedia.org/wiki/UAV

http://adg.stanford.edu/aa241/AircraftDesign.html

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APPENDIX 2 Aircraft Fuselage Nose Shape

3/4 Power

Cone

1/2 Power

Tangent ogive

Parabolic

Ellipsoid

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APPENDIX 3

moulds

Final product

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APPENDIX 4 Failed Prototypes

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APPENDIX 6 Processes

Mould building

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Prepare the plastics

Put into the oven

Temperature setting

240 degrees

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Turn on the vacuum cleaner; put the plastics on top of mould

Trimming-final product

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Assembly and paint