National University of Singapore
UAV DESIGN AND MANUFACTURE U067782B ZHANG XUETAO
10
Table of content Summary
3
Introduction
4
UAV fuselage design
6
Aircraft shape and aerodynamics of fuselage Aircraft structure analysis
7 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 7|P a ge
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, prestretching, 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 twinhopper 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 2dimensional 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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R=4.5cm L=18cm
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.
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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 = 𝐼𝐼𝑦𝑦𝑦𝑦 =
𝑀𝑀𝑦𝑦 𝑧𝑧 𝐼𝐼𝑦𝑦𝑦𝑦
1 ∗ 40 ∗ 53 = 417𝑚𝑚𝑚𝑚4 12
Z=2.5mm
M=0.275N.m=275N.mm So 𝜎𝜎𝑥𝑥 =275*2.5/417=1.65N/mm^2=1.65× Γ=F/A=3.5×104 𝑃𝑃𝑃𝑃=0.035MPa
10 6 𝑁𝑁 𝑚𝑚 2
= 1.65𝑀𝑀𝑀𝑀𝑀𝑀
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 =
𝑀𝑀𝑦𝑦 𝑧𝑧 𝐼𝐼𝑦𝑦𝑦𝑦
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 viscoelastic 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
Cost
Formability Strength
Total
Ranking
time(S)
10%
40%
40%
Score
2.5
3
1.5
2.35
3
2
2
2
2.05
5
2.5
1
3
1.95
6
2.5
1
3
1.95
6
10% PS
60 3
ABS
80 2.5
PP
100 1
PE
100
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1 PETG
60
1
3
2
2.40
2
3
3
2
2.60
1
1
2
3
2.15
4
3
PVC
60 3
PC
120 0.5 •
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 Frame
Vacuum cleaner 25*20cm
Plastics
0.5mm for testing 1mm manufacturing
Oven
30*25cm
Temperature
240 degrees
Effective working
1:1.5
Time needed
1minutes for
ratio
0.5mm 3minutes for 1mm
Max mould length
18cm
Max mould
9cm
diameter
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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-toDimension 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.
Surface Area
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.
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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+9 18
= 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
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