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National University of Singapore
10
UAV DESIGN AND MANUFACTURE U067782B
ZHANG XUETAO
2 | P a g e
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
3 | P a g e
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.
4 | P a g e
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.
7 | P a g e
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
8 | P a g e
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,
9 | P a g e
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.
10 | P a g e
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
11 | P a g e
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.
12 | P a g e
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
13 | P a g e
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.
14 | P a g e
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
15 | P a g e
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
16 | P a g e
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
17 | P a g e
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.
18 | P a g e
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
19 | P a g e
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.
22 | P a g e
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.
23 | P a g e
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.
24 | P a g e
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.
26 | P a g e
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
27 | P a g e
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
28 | P a g e
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.
29 | P a g e
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.
31 | P a g e
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.
32 | P a g e
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
33 | P a g e
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.
36 | P a g e
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