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Fabrication and aeroelastic analysis of silicone membrane micro air vehicle wings

Permanent Link: http://ufdc.ufl.edu/UFE0041333/00001

Material Information

Title: Fabrication and aeroelastic analysis of silicone membrane micro air vehicle wings
Physical Description: 1 online resource (68 p.)
Language: english
Creator: Lin, Albert
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: aeroelastic, deformation, fabrication, manufacturing, mav, membrane, silicone, uav, vic, wings
Mechanical and Aerospace Engineering -- Dissertations, Academic -- UF
Genre: Aerospace Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Flexible wing micro air vehicles (MAVs) have been developed at the University of Florida to improve adverse flying conditions. Typically, such MAVs display low Reynolds numbers and low aspect ratios. Current designs use elastic membranes bonded to a carbon fiber wing structure. A variety of materials are functional as integrated membranes, such as latex and polyester film. However, two design issues are presented with existing manufacturing procedures. First, membrane materials lack robustness as they are vulnerable to rupture, environmental conditions, and prolonged shelf-life. Second, uniform membrane pre-tension is essentially unattainable by current procedures, causing disparities which can significantly alter flight dynamics and create aeroelastic instabilities. A technique is developed which uses high performance platinum-cure silicone rubber to fabricate wing membranes exhibiting uniform pre-tension. Silicone rubber displays durability, high physical properties, and robustness in its function as an integrated MAV membrane. Visual image correlation is performed to validate silicone membrane displacements and pre-tensions of selected wing designs, as well as comparisons to latex membrane counterparts. Experimental data, including aerodynamic analysis, is further examined for aeroelastic topology optimized wings and compared with numerical models.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Albert Lin.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Ifju, Peter.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0041333:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041333/00001

Material Information

Title: Fabrication and aeroelastic analysis of silicone membrane micro air vehicle wings
Physical Description: 1 online resource (68 p.)
Language: english
Creator: Lin, Albert
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: aeroelastic, deformation, fabrication, manufacturing, mav, membrane, silicone, uav, vic, wings
Mechanical and Aerospace Engineering -- Dissertations, Academic -- UF
Genre: Aerospace Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Flexible wing micro air vehicles (MAVs) have been developed at the University of Florida to improve adverse flying conditions. Typically, such MAVs display low Reynolds numbers and low aspect ratios. Current designs use elastic membranes bonded to a carbon fiber wing structure. A variety of materials are functional as integrated membranes, such as latex and polyester film. However, two design issues are presented with existing manufacturing procedures. First, membrane materials lack robustness as they are vulnerable to rupture, environmental conditions, and prolonged shelf-life. Second, uniform membrane pre-tension is essentially unattainable by current procedures, causing disparities which can significantly alter flight dynamics and create aeroelastic instabilities. A technique is developed which uses high performance platinum-cure silicone rubber to fabricate wing membranes exhibiting uniform pre-tension. Silicone rubber displays durability, high physical properties, and robustness in its function as an integrated MAV membrane. Visual image correlation is performed to validate silicone membrane displacements and pre-tensions of selected wing designs, as well as comparisons to latex membrane counterparts. Experimental data, including aerodynamic analysis, is further examined for aeroelastic topology optimized wings and compared with numerical models.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Albert Lin.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Ifju, Peter.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0041333:00001


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1 FABRICATION AND AEROELASTIC ANALYSIS OF SILICONE MEMBRANE MICRO AIR VEHICLE WINGS By ALBERT Y. LIN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009

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2 2009 Albert Y. Lin

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3 To Mom

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4 ACKNOWLEDGMENTS I would like to take this opportunity to thank everyone who has contributed to my academics, research, and life throughout graduate school. Yaakov Abudaram, for your camaraderie throughout the MAV Lab, wind tunnel, and graduate school in general Mulugeta Haile Vijay Jagdale, for tea ching me the particulars of the VIC system. for your friendship and help with many lab experiments. Kyuho Lee, for your passion and talent in aircraft design. Dr. Bret Stanford, for teaching me the intricacies of the wind tunnel and your wealth of academic knowledge. Thank you for taking time to answer my qu estions. Pin Wu, for your conversations and generosity in sharing your laboratory. My family, for your love and constant support. Kim, Champ, Rhyley, and Lt. Dan, for your love and many happy memories. I owe many thanks to Dr. Peter Ifju, for giving me so many opportunities to succ eed. You are a patient, enthusiastic, and talented teacher and I enjoyed my time working with you. Thank you for everything that you have done for me

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...................................................................................................... 4 LIST OF TABLES ................................................................................................................. 7 LIST OF FIGURES ............................................................................................................... 8 LIST OF ABBREVIATIONS ............................................................................................... 11 ABSTRACT ........................................................................................................................ 12 CHAPTER 1 INTRODUCTION ......................................................................................................... 13 Motivation .................................................................................................................... 13 Objectives ..................................................................................................................... 15 Outline .......................................................................................................................... 15 2 LITERATURE REVIEW ............................................................................................... 16 3 EXPERIMENTAL DATA SYSTEMS ........................................................................... 20 Closed Loop Wind Tunnel ............................................................................................. 20 Visual Image Correlation ............................................................................................... 21 4 SILICONE MEMBRANE FABRICATION .................................................................... 23 Baseline Airfoil ............................................................................................................. 23 Design Process .............................................................................................................. 23 Step One: Construct Composite Airframe ................................................................ 24 Step Two: Mix Silicone Compound ......................................................................... 25 Step Three: Apply Silicone Compound .................................................................... 26 Step Four: Apply Vacuum Pressure ......................................................................... 26 Step Five: VIC Preparation ...................................................................................... 29 5 AEROELASTIC ANALYSIS ........................................................................................ 30 VIC Analysis ................................................................................................................ 30 Membrane Pre Tension Validatio n .......................................................................... 30 Topology Optimization Design Comparison ............................................................. 35 Aerodynamic Data ......................................................................................................... 41 6 RELATED CONCEPTS ................................................................................................ 46

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6 7 CONCLUSION ............................................................................................................. 47 Conclusion .................................................................................................................... 47 Future Work .................................................................................................................. 47 APPENDIX A EXPERIMENTAL OUT OF -PLANE DISPLACEMENTS FOR BASELINE AND TOPOLOGY OPTIMIZED WING DESIGNS ................................................................ 49 B NUMERICAL OUT OF PLANE DISPLACEMENT MODELS FOR BASELINE AND TOPOLOGY OPTIMIZED WING DESIGNS, COURTESY OF STANFORD [4] ............ 60 LIST OF REFERENCES ...................................................................................................... 66 BIOGRAPHICAL SKETCH ................................................................................................ 68

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7 LIST OF TABLES Table page 2 1 Mechanical properties of silicone rubber .................................................................... 19 4 1 Properties of Dragon Skin ....................................................................................... 25 5 1 Maximum out -of plane displacements and locations, PR wing .................................... 30 5 2 Maximum membrane displacements, PR wing ............................................................ 35 5 3 Maximum out -of plane displacement comparisons ......................................... 40

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8 LIST OF FIGURES Figure page 1 1 Erosion of latex at the bonding surfaces of BR wing after 60 days. .............................. 14 2 1 Cornell University bat wing design with nylon fabric affixed to carbon fiber skeletal fingers [8]. ................................................................................................................ 17 2 2 Cornell University bat wing design with thin silic one sheets glued to a steel wire skeletal frame [8]. ..................................................................................................... 18 3 1 Schematic of the experimental test section. ................................................................. 20 3 2 Random speckling pattern for VIC analysis. ............................................................... 21 3 3 VIC system arrangement above wind tunnel test section. ............................................. 22 3 4 VIC cameras collect images throug h wind tunnel ceiling optical glass access. .............. 22 4 1 Types of wings construct ed using the baseline airfoil ................................................. 23 4 2 Cured carbon fi ber TOP wing structure placed onto wing tool for membrane preparation. .............................................................................................................. 24 4 3 Pigmented liquid silicone compound applied to TOP wing. ......................................... 26 4 4 Wing mold containing composite frame and silicone compound under vacuum pressure. ................................................................................................................... 27 4 5 Creating a reverse imprint for the cavity mold using slow curing epoxy. ...................... 28 4 6 Compression m old assembly for the baseline MAV wing. ........................................... 28 4 7 Compression m old assembly under 30 mm Hg vacuum pressure. ................................ 29 5 1 Experimental out of -plane displacement contour, silicone membrane PR 12 (refer Appendix A). ............................................................................................. 31 5 2 Normalized out -of -plane displacement (w/c), silicone membrane ..... 31 5 3 Out -of -plane displacement comparison of silicone membrane (top) and latex membrane ............................................................................... 32 5 4 Normalized out -of ................ 33 5 5 Out -of -plane displacement comparison, regular (top) and viscosity reduced (bottom) silicone membrane ......................................................................... 34

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9 5 6 Out -of ....... 3 5 5 7 Numerical (top) and experimental (bottom) out -of -plane displacements for baseline and topology optimized desig ................................................................... 36 5 8 Experimental (left) and numerical (right) out -of 12. .......................................................................................................................... 37 5 9 Experiment al (left) and numerical (right) out -of 12. .......................................................................................................................... 37 5 1 0 Experimental (left) and numerical (right) out -of -plane displacements, topology optimized wing for maximum lift (TOPmax lift ............................................... 38 5 11 Experimental (left) and numerical (right) out -of 12. .......................................................................................................................... 38 5 12 Experimental (left) and numerical (right) out -of -plane displacements, topology optimized wing for minimum lift slope (TOPmin lift slope ................................. 39 5 13 Experimental (left) and numerica l (right) out -of optimization wing for minimum lift slope (TOP ....................................... 39 5 14 Baseline and TOP design shapes compared in Figures 5 8 through 5 13, respectiv ely from left to right. ....................................................................................................... 40 5 15 Experimental (left) and numerical (right) out -of -plane displacements along 2y/b = .............................................................. 41 5 16 Experimental aerodynamic comparison, latex and silicone membrane PR wing, v = 30. ..................................................................................................... 42 5 17 Experimental aerodynamic comparison, latex and silicone membrane BR wing, v = 30. ..................................................................................................... 43 5 18 Experimental aerodynamic data for low -tensioned, latex membrane baseline and topology optimized designs by Stanford [4], v = 13 m/s 30. ........................... 44 5 19 Experimental aerodynamic data for uniform tensioned, silicone membrane baseline and topology optimized designs (from Figure 5 17), v 30. ................ 45 6 1 Fabrication of 24 inch BR piezoelectric concept wing membrane with pigmented liquid silicone compound. .......................................................................................... 46 6 2 24inch BR piezoelectric co ncept wing. ...................................................................... 46 A 1 Experimental out of ......................... 49

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10 A 2 Experimental out of -plane displacement contour, silicone membrane 12. .......................................................................................................................... 50 A 3 Experimental out of -plane displacement contour, viscosity reduced silicone membrane ..................................................................................... 51 A 4 Experimental out of -plane displacement contour, latex membrane ... 52 A 5 Experimental out of -plane displacement contour, silicone membrane 12. .......................................................................................................................... 53 A 6 Experimental out of -plane displacement contour, silicone membrane TOP wing optimized for maximum lift (TOPmax lift 10). .................... 54 A 7 Experimental out of -plane d isplacement contour, silicone membrane TOP wing optimized for minimum lift slope (TOPmin lift slope 10). ....... 55 A 8 Experimental out of -plane displacement contour, s ilicone membrane TOP wing optimized for minimum CL (TOPmin CL 15). ...................... 56 A 9 Experimental out of -plane displacement contour, silicone membrane TOP wing optimized fo r minimum CD (TOPmin CD 15). ..................... 57 A 10 Experimental out of -plane displacement contour, silicone membrane TOP wing optimized for minimum Cm (TOPmin Cm fer [4], Figure 7 15). .................... 58 A 11 Experimental out of -plane displacement contour, silicone membrane TOP wing, single r [4], Figure 7 18). ....................................................................................................... 59 B1 Numerical out of ................................ 60 B2 Numerical out of -plane displa .................................. 61 B3 Numerical out of -plane displacement model, silicone membrane TOP wing optimized for maximum lift (TOPmax lift 10). .................... 62 B4 Numerical out of .................................. 63 B5 Numerical out of -plane displacement model, silicone membrane TOP wing optimized for minimum lift slope (TOPmin lift slope 10). ....... 64 B6 Numerical out of -plane displacement model, silicone membrane TOP wing, single objective Figure 7 18). ............................................................................................................. 65

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11 LIST OF ABBREVIATION S Al aluminum BR batten reinforced C Celsius cps centipoises Hg mercury hrs hours in inch KOH potassium h ydroxide lb pound m meter(s) MAV micro air vehicle MEMS microelectromechanical systems mm millimeter N Newton parylene C poly -monochloro -para -xylylene pli pounds per linear inch PR perimeter reinforced RTV room temperature vulcanizing s second Ti tita nium TOP topology optimized UAV unmanned aerial vehicle vVIC visual image correlation freestream velocity

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12 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science FABRICATION AND AEROELASTI C ANALYSIS OF SILICONE MEMBRANE MICRO AIR VEHICLE WINGS By Albert Y. Lin December 2009 Chair: Peter Ifju Major: Aerospace Engineering Flexible wing micro air vehicles (MAVs) have been developed at the University of Florida to improve adverse flying cond i tions. Typically, such MAVs display low Reynolds number s and low aspect ratios. Current designs use elastic membranes bonded to a carbon fiber wing structure. A variety of materials are functional as integrated membranes, such as latex and polyester fi lm. However, t wo design issues are presented with existing manufactu ring procedures. First, membrane materials lack robustness as they are vulnerable to rupture, environmental conditions, and prolonged shelf life. Second, uniform membrane pre -tension is essentially unattainable by current procedures, causing disparities which can significantly alter flight dynamics and create aeroelastic instabilities. A technique is developed which uses high performance platinum -cure silicone rubber t o fabricate wing m embranes exhibit ing uniform pre tension. Silicone rubber displays durability, high physical properties, and robustness in its function as an integrated MAV membrane. Visual image correlation is performed to validate silicone membrane displaceme nts and pr e tensions of selected wing designs, as well as comparison s to latex membrane counterparts. Experimental data including aerodynamic analysis, is further examined for aeroelastic topology optimized wings and c ompared with numerical models

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13 CHAPTER 1 INTRODUCTION Motivation Numerous micro air vehicles (MAVs) designed at the University of Florida are based on flexible wing structures due to fixed -wing aerodynamic challenges res ulting from low Reynolds number s (104105) [1]. The basic design is composed of a composite laminate frame with an affixed flexible membrane skin, which allows passive shape adaptio n [2 ]. Latex, mylar/polyester film, ecorex, and nylon are typical materials used as membrane skins, with latex being the most common. Perimeter reinforced (PR) wings have unconstrained interior membranes, bonded to a rigid composite perimeter. PR membranes allow for camber adaptation to varying flight conditions and wind gusts, translating load distributions on the wing which increases CL and decreases C [3 ]. Batten reinforced (BR) wings are designed with uni -directional strips of carbon fiber parallel to the chord line, extending from the leading edge to an unconstrained trailing edge. The battens are adhered to the membrane s kin, much like a bat wing, to provide flight load alleviation. Topology optimized (TOP) wings contain composite laminate distributions positioned in specific locations on the membrane. These shapes and locations correspond to specifically op timized aerod ynamic functions [4 ]. Latex of minimal thickness (on the order of 0.12 mm) is typically used because of billowing effects which aid in load distribution. After fabricating numerous latex membrane wings, two significant design issue s were observed. Latex membranes are not robust. They are not durable and are susceptible to tearing, punctures, and erosion due to heat, UV, and chemical agents. Figure 1 1 shows erosion of a latex membrane in contact with spray glue adhesive after 60 days. Degradation at the bonding points of the membrane inhibits flight performance consistency and is detrimental to shelf life.

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14 Figure 1 1. Erosion of latex at the bonding surfaces of BR wing after 60 days. Second, uniform membrane per tension is d ifficult to achieve and cannot be controlled by existing manufacturing methods. Adaptive cambering membranes differing in pre tension could cause instabilities, greatly affecting flight dynamics of the aircraft. Consider a PR wing designed for high lift, high drag which is manufactured with too much tension on one membrane. The higher pre tensioned membrane would require less drag, having more streamline shape. The lower pre tensioned membrane would have a larger deformation, thus higher drag. This sce nario could cause longitudinal and lateral instability of the wing, creating an adverse situation which defeats the purpose of the intended design. The purpose of this research is to develop a superior flexible membrane for incorporation onto composite MAV wings. This requires a fabrication process to address the aforementioned concerns, and silicone rubber will be introduced as the ideal material for this process.

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15 Objectives 1 Develop a method to fabricate MAV wing membranes using platinum -cure silicone rubber. 2 Develop a method to create silicone membranes with uniform pre tension. 3 Experimental validation of uniform membrane pre tension. 4 Experiment al comparison of latex and silicone membrane wings. 5 Experimental comparison and validation of topology optimi zed designs. 6 Fabricate conceptual wing designs using silicone rubber as the integration platform. Outline Chapter 2 is a literature review of bio inspired designs a silicone bat wing fabrication process developed at Cornell University, and advantages of s ilicone rubber as a flexible MAV membrane. Chapter 3 classifies experimental apparatus and data analysis procedures. This involves the visual image correlation system and closed loop low -speed wind tunnel. Chapter 4 details the silicone membrane fabricati on process. A step -by -step meth od is provided for co -curing ro om temperature vulcanizing silicone rubber to carbon fiber structures. This chapter also provides visual image correlation preparation. Chapter 5 analy zes experimental aeroelastic data. The P R design is used to validate pre tension uniformity of silicone membranes. A comparison is made between silicone membrane wings and their latex membrane counterparts. Selected optimal topology wing designs are evaluated an d compared to numerical models Chapter 6 pre sents concepts related to bio inspired wing designs and control surface integration with silicone membranes

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16 CHAPTER 2 LITERATURE REVIEW Curre ntly, no manufacturing process exist s for co -curing silicone rubber onto composite MAV wings as fun ctional flexible membranes. Growing research interests in bio inspired skeletal -based designs have sparked intriguing innovations pursuing biologic al qualities and morphing features Pornsin -sirirak et al. [5] present a MEMS -base d wing technology which uses a titanium alloy metal (Ti6Al 4V) wingframe with a poly -monochloro para -xylylene (parylene C) membrane. Target MEMS wings include bioinspired designs such as beetles, dragonflies, butterflies, and bats. Early efforts utiliz ed silicon nitride pattern depositions and potassium hydroxide (KOH) etching to create wingframes. However, s ilicon wingframes were too fragile and abandoned in favor of the titanium alloy metal Thin, compliant skin membranes unique to flying and gliding animals (bats, flying squirrels, sugar gliders, etc.) exhibit maneuverability and agility unseen in other flying species of comparable size [6]. Bat wing research has been conducted for piezoelectric actuation of joints [7 ], various flight characterist ics to develop optimal shapes [8 ], and aerodynam ic effects of membraned -wings [9 ] Additionally, Waldman et al. [10] (Brown University) compares membrane airfoil behavior under aerodynamic loading with in vivo measurements of bat wings during flight. Bat membrane deformations are measured from recorded flight kinematics of a Cynopterus brachyotis in a wind tunnel, in which downstroke wing areas are observed to increase up to 100%. Callahan and Garcia [11] discuss a bio inspired bat wing fabrication method using a skeleton structure with various membrane materials incorporated at Cornell University. Initially, the skeleton was constructed with hollow carbon fiber rods, as it was light and strong enough to withstand pressure loads of an attached membrane. Due to in stability at the joints and weight

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17 concerns with epoxy adhe sives, the skeletal design was modified to s teel rods with composite fibers wrapped tightly around adjoining sections. Three membrane materials were tested: nylon fabric, spandex fabric, and sili cone sheets. Nylon and spandex fabrics were cut to desired wing shapes and fused to the skeleton joints with epoxy. Skeletal fingers, shown in Figure 2 1, were sewn securely to fabric material with needle and thread. Even so, t hin silicone sheets (also cut to desired wing shapes) were determined to be the most appropriate membrane material because it was sturdy, flexible, and stable under slight loading conditions. It also had a similar feel to live bats and was more rugged than latex. The main issue, however, was that silicone bonds only to itself. Wing assembly was therefore accomplished with a silicone -based glue to adhere the thin silicone sheets to the steel wire frame (Figure 2 2) Chapter 4 introduces an alternative silicone membrane fabrication method to [11 ]. Room temperature vulcanizing (RTV) silicone rubber as a liqu id compound is used to fabricate membranes i nst ead of thin silicone sheets. The compound is co -cured onto carbon fiber wing structures, hence eliminating the use of silicone -based adhesives. Figure 2 1. Cornell University bat wing design with nylon fabric affixed to carbon fiber skeletal fingers [8 ].

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18 Figure 2 2 Cornell University bat wing design with thin silicone sheets glued to a steel wire skeletal frame [8 ]. Silicone rubber is an ideal membrane mat erial because of its extremely elastic nature and favorable material properties. Normally, the compound requires heat to vulcanize. In this work, however, a high-purity pourable silicone rubber is used It is a platinum cured, RTV compound having liquid consistency [12]. The silicone compound is supplied in two parts which are mixed together, one of which contains the platinum catalyst. Additive agents such as pigments and viscosity reducers are also available if desired. The pot life is approximately 20 40 minutes. Typical mechanical properties of silicone rubber are listed in Table 2 1. Silicone rubber is an ideal material for UAV membranes because of these characteristics: Good resistance to extreme temperatures High resistance to ozone, radiation, and ageing factors Hydrophobic properties Efficient electrical insulation Exhibits flame retardant features Highly inert material It is superior to other elastomers with regard to thermal properties. At extreme temperatures, el asticity is sustained to 60C and exhibits a flash point of 750C. Recently, silicone rubber was even observed to have self -healing traits, as the material was capable of recovering almost all of its original tear stren gth [13].

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19 Table 2 1. Mechanical properties of silicone rubber Property Quantity Hardness, Shore A 10 90 Tensile strength 11 N/mm 2 Elongation at break 100 1100% Max. temperature +300C Min. temperature 120C

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20 CHAPTER 3 EXPERIMENTAL DATA SY STEMS Closed -Loo p Wind Tunnel Aerodynamic analysis is conducted in a closed loop wind tunnel manufactured by Engineering Laboratory Design, Inc (model 407B). A two-stage axial fan directs horizontal airflow up to a limit of 45 m/s through a 33 inch test section. Force a nd moment measurements are made by an internal AEROLAB strain gage sting balance, capable of six degrees -of -freedom and measuring loads on the order of 0.01 N [14 ]. It is supported by a U -shaped model arm connected to a motorized motion controller, rotating pitch rates at approximately 1/s. Wing models are bolted to the tip of the sting balance with a bracket mount, using an inclinometer to -swe ep of 0 30. Out -of Fig ure 3 1. Schematic of the experimental test section

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21 Visual Image Correlation The visual image correlation (VIC) system is a non intrusive method of obtaining full field, 3 D deformation measurements. In this work, out -of -plane displacements are considered for wings experiencing induced airflow by the wind tunnel. For 3D analysis, the optical arrangement includes two cameras to provide st ereo imaging capabilities [15 ]. Test specimens are prepared with a random speckling pattern, which is recognized by system. Each speckle represents a unique shape and intensity, serving as ideal targets (Figure 3 2). Figure 3 2. Random speckling pattern for VIC analysis. Digital images are taken before and after the surface deformation The correlation algorithm compares the intensity data from these two fields by mapping displacements, smoothing intensity data, and using a least squares correlation coeffic ient. Assuming target features are sufficient and calibration accurately performed, the displacement field can be established. Figures 3 3 and 34 show the VIC system setup in the wind tunnel test section.

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22 Figure 3 3. VIC system arrangement above wind tunnel test section. Figure 3 4 VIC cameras collect images through wind tunnel ceiling optical glass access

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23 CHAPTER 4 SILICONE MEMBRANE FA BRICATION Baseline Airfoil Baseline airfoil characteristics used in this work are: 152 mm wingspan 124 mm root chord 1.25 aspect ratio 6.8% camber at the root (located at x/c = 0.22) 1.4% reflex at the root (located at x/c = 0.86) 7 dihedral (between 2y/b = 0.4 and the wingtip) 7 geometric twist (nose up) at the wingtips Figure 4 1 shows the different types of wings constructed using this airfoil: PR, BR, and TOP wings. Wings are constructed with two layers of carbon fiber (3000 fiber/tow, pre impregnated with thermoset epoxy) in a plain weave, bi -directional (0/90) orientation. The leading edge includes an extra layer of carbon fiber, adding stiffness to offset torsion. The battens of the BR wings consist of two layers of uni directional carbon fiber. Laminate shells of the TOP wings are made from one layer of bi -directional carbon fiber. A B C Figur e 4 1. Types of wings constructed using the baseline airfoil. A) PR wing. B) BR wing. C) TOP wing. Design Process A series of techniques were developed for fabricating silicone membrane wings with uniform membrane thickness and pre tension

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24 Step One: Cons truct Composite Airframe The first step is to construct the carbon fiber frame using standard manufacturing, vacuum bagging, and curing procedures. Figure 4 2. Cured carbon fiber TOP wing structure placed onto wing tool for membrane preparation. Initi ally, silicone was co -cured with the carbon fiber layup during the curing cycle. This was done under the premise that interaction with the thermoset epoxy during the curing cycle would promote adhesion to carbon fiber. Although the membrane successfully adhered to the wing, the carbon fiber layup occasionally warped during distribution of the pre vulcanized silicone rubber when vacuum pressure was applied. This occurred most often in TOP wing fabrication, as the silicone compound would shift laminate she lls from their desired locations. The process was repeated with a cured carbon fiber frame, yielding these observations: 1 Under vacuum pressure, silicone adhesion strength to carbon fiber is indistinguishable between the co -cured and cured process. 2 Under v acuum pressure, silicone adhesion to a cured carbon fiber frame is not temperature dependent.

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25 3 Both methods are successful, but it is much easier to fabricate silicone membrane wings using a cured carbon fiber frame. An increase in temperature accelerated the vulcanization rate of the silicone compound, but did not affect the bonding strength to carbon fiber. From a manufacturing standpoint, the best approach is to cure the carbon fiber structure first. It eliminates structural warping and prevents lamin ate shifting of TOP wings. However, future work is suggested to measure the adhesion strength between RTV and temperature accelerated silicone Step Two: Mix Silicone Compound The next step is to mix the silicone compound. Once the components are mixed, the liquid silicone is centrifuged (approximately 3 minutes) to eliminate air bubbles from the solution. The silicone rubber used is called Dragon Skin, manufactured by Smooth-On, Inc. It is a two component, platinum curing silicone elastomer composed of polyorganosiloxanes, amorphous silca, and platinum -siloxane complex. This material is extr emely flexible and yields a high tear strength. Table 4 1. Properties of Dragon Skin Property Quantity Elongation at break 1000% Mixed viscosity 23000 cps S hore A hardness 10 Tear strength 102 pli Weight 25.8 in 3 /lb Demold time 5 hrs Silicone additives may be applied to assist with membrane thickness and enhance VIC analysis. A thinning agent (SilcThin ) was used to reduce the viscosity of the mixture t o improve workability and prolong pot life. However, this additive does reduce material strength. The maximum amount allowed is 7.5% of the total mixture weight

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26 Step Three: Apply Silicone Compound Once air bubbles are removed, the silicone is applied to the wing tool. For releasing purposes, a layer of Teflon film is affixed to the wing tool with a thin coat of spray glue. It is essential to keep the wing tool smooth and free of defects as this surface directly translates to the surface of the membran e. At this point, the carbon fiber frame is placed onto the wing tool and silicone is poured onto the proper locations. Figure 4 3 Pigmented liquid silicone compound applied to TOP wing Step Four: Apply Vacuum Pressure The mold is placed in a vacuu m bag under a suction pressure of 30 mm Hg [16] Initially, the silicone was smoothed out by hand and rubber rollers through the vacuum bag (Figure 4 4). This method created two major setbacks. First, warping and shifting of the wing structure (expressed in Step One) occurred, primarily in un -cured carbon fiber frames and TOP wings. Second, the cured silicone membrane did not have consistent thickness. The thickness disparity

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27 was noticeable by eye, especially at the maximum win g camber where the silicone accumulated. There were also regions of the membrane which were extremely thin due to the inconsistent smoothing process. Figure 4 4. Wing mold containing composite frame and silicone compound under vacuum pressure. Creati ng a membrane of uniform thickness is critical because of the adaptive cambering and load alleviating nature of these wing designs. In addition, unnecessary weight is added to the wing due to the excess si licone. Manufacturing a compression mold for the wing was the most consistent way to fabricate silicone membranes of uniform thickness. This was done by using the origin al mold and generating a cavity mold using a slow -curing epoxy. Figure 4 5 shows the epoxy being cured in the wing tool, creating a r everse imprint for the cavity mold. The mold was bagged and put under vacuum pressure to create a smooth surface. Multiple coats of Frekote (mold release agent) was applied to the surface before adding epoxy. Screws were placed on either side to aid in removing the cured epoxy.

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28 Figure 4 5. Creating a reverse imprint for the cavity mold using slow -curing epoxy. Holes were dril led around the edge to create a vented cavity mold. This allow s for maximum amount of air to be vacuum ed out by the pump creat ing a smooth, thin membrane For releasing purposes, a layer of Teflon is affixed to the cavity mold with a thin mist of spray adhesive. T he composite frame and silicone compound is then sandwiched between the compression mold (Figure 4 6) before being p laced under vacuum pressure (Figure 4 7). It is important not to use too much spray adhesive because accumulation between the Teflon and mold surface will create deflects in the finished membrane. Figure 4 6. Compression m old assembly for the baselin e MAV wing.

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29 Figure 4 7 Compression m old assembly under 30 mm Hg vacuum pressure Step Five: VIC Preparation This step is provided if VIC analysi s is desired. White pigment can be added to the silicone compound to enhance VIC pattern recognition. Cure d pigmented membranes have a glossy finish nonetheless, so a very light coat of flat white paint i s applied to the wing before the speckling pattern. Although paint does not adhere well to silicone, a minute coa t to dull the glossy features i s sufficient A random speckling pattern i s sprayed onto the wing with flat black paint. The nozzle of the spray paint was enlarged to create larger drops for the pattern instead of mist. Speckling patterns did not fail during wind tunnel testing under an applied lo ad

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30 CHAPTER 5 AEROELASTIC ANALYSIS VIC Analysis VIC analysis was conducted on baseline and topology optimized wing designs in the wind tunnel at v Validate uniform pre -tension of silicone membranes = 13 m/s and Objectives are to: Compare latex and silicone membrane designs Observe the effect s of reduced -viscosity silicone Compare exp erimental results with numerical models of topology optimized designs Membrane Pre -Tension Validation The PR wing was used as the baseline for validating uniform m embrane tension. Figure 5 1 shows the symmetry of out -of -plane displacements across both membranes. Inflation occurs at the consistent locations along spanwise sections. Maximum out -of -plane displace ment is 6.45 mm, measured at 2y/b = 0.70 for the left memb rane and 6.48 mm, measured at 2y/b = 0.68 for the right membrane (Figure 5 2). Figure 5 3 compares t he silicone membrane PR wing to its latex membrane counterpart. The same PR wingframe was used to construct both wings. Latex membranes were adhered with low -tension to promote maximum inflation for this comparison. Also, uniform pre tension was attempted when adhering the latex membranes. Although maximum out -of -plane displacements do not differ by much (Figure 5 4), Figure 5 3 is evidence that the latex membrane vastly underachieves in its attempt at membrane pre tension uniform ity. The contour also reveals inconsistent and decreased inflation surf ace area for the latex membranes. Maximum out -of -plane displacements are shown in Table 5 1. Table 5 1. Maximum out -of -plane displacements and locations, PR wing Membrane w [mm] Location (2y/b) Silicone, left 6.45 0.70 Silicone, right 6.48 0.68 Latex, left 6.43 0.58 Latex, right 5.76 0.68

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31 Figure 5 1 Experimental out -of -plane displacement contour, silicone membrane 12 (refer Appendix A) Figure 5 2. Normalized out -of -plane displacement (w/c), silicone membrane

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3 2 Figure 5 3. Out -of plane displacement comparison of silicone membrane (top) and latex membrane

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33 Figure 5 4. Normalized out -of Now that uniform pre tension across both membranes can be achieved, is it possible to control it? The ability to control membrane pre tension would allow flexible wings to be extremely versatile. Low -tensioned membranes could be used for applications requiring increased lift and st ability, while high tensioned membranes could be used for reduced drag. A silicone thinning agent was tested to reduce material viscosity in hopes of creating thinner, lower tensioned membranes. Figure 5 5 confirms increased billowing i n viscosity reduced membranes, as the membrane inflation is noticeably larger. The maximum out of -plane displacement increase is 23% (1.42 mm) due to the addi tion of the viscosity-reducing agent and 31% (1.80 mm) compared to the latex membrane. Figure 5 6 depicts not only a higher peak, but also an increase in inflation surface area. Displacements along the spanwise section 2y/b = 0.58 have maximum values shown in Table 5 2

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34 Figure 5 5 Out -of plane displacement comparison, regular (top) and viscosityreduced (botto m) silicone membrane

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35 Figure 5 6 Out -of The silicone thinning agent does reduce material strength, which could cause the increased inflation instead of a reduced membrane pre tension. A weaker membrane would be expected to inflate more under the same loads, and the distinction could not be clarified through these experiments. Future work is recommended to determine the effect of viscosityreducing agents on mater ial strength. A thermal test as well as a pressure test, is recommended to determine if pre tension can be controlled as a function of curing temperature or vacuum pressure, or both. Table 5 2 Maximum membrane displacement s, PR wing Membrane w [mm] Location (x/c) Latex 5.74 0.47 Silicone 6.12 0.50 Silicone Reduced Viscosity 7.54 0.50 Topology Optimization Design Comparison Stanford [4 ] formulates the computational framework for aeroelastic topology optimization of MAVs. Optimization of laminate topologies and locations is a function of flight condition,

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36 grid density, initial guess and design metric. Figure 5 7 presents baseline ( A, B, D) and topology optimized (C, E) wing designs. Wing C is a lift augmenting design optimized for maximum lift. Wing E is a liftalleviating design optimized for minimum lift s lope. The top row in Figure 5 7 represents defor mations predicted by Stan ford [4 ]. The bottom row depict s experimental out -of -plane deformation results of the same wing designs, fabricated with silicone membranes. Detailed experimental contours are listed in Appendix A. Appendix B lists numerical models gathered by Stanford [4 ]. Figure 5 7 Numerical (top) and experimental (bottom) out -of -plane displacements for baseline Figures 5 8 thru 5 13 illustrate comparisons between experimental results and numerical models generated by Stanford [4]. Comparisons are made between baseline and topology optimized designs for different cases. Figures show out -of -plane displacements contours in meters, with experimental resul ts on the left half and its corresponding numerical model on the right half. Since membrane pre tension parameters were not equal for the two models, a difference in maximum displacement values is expected (Table 5 3). It is more significant to note the shape similarities displayed in the following comparisons.

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37 Figure 5 8 Ex perimental (left) and numerical (right) out of 12. Figure 5 9 Ex perimental (left) and numerical (right) out of -plane displacements, PR win 12.

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38 Figure 5 10. Ex perimental (left) and numerical (right) out -of -plane displacements, topology optimized wing for maximum lift (TOPmax lift ) Figure 5 11. Ex perimental (left) and numerical (right) out -of -plane displacements, BR wing 12.

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39 Figure 5 12. Ex perimental (left) and numerical (right) out -of -plane displacements, topology optimized wing for minimum lift slope (TOPmin lift slope ) Figure 5 13. Ex perimental (left) and numerical (right) out -of -plane displacemen optimization wing for minimum lift slope (TOP)

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40 Figure 5 14. Baseline and TOP design shapes compared in Figure s 5 8 thr o u gh 5 13, respectively from left to right Table 5 3 shows differences in maximum out -of -plane displacements between the numerical model and experimental results. Displacement differences can be attributed to membrane pre tension inequalities between the two models. In other words, experimental membrane pre tensions and numerical solver input values were not eq ual, therefore causing inaccuracies in displacement measurements. A true comparison can only be made if both models have equal pre-tension inputs. Table 5 3 Maximum out -of -plane displacement Wing Numerical [mm] Experimental [mm] % Diff Rigid 0.49 1.56 218.37 PR 4.21 6.48 53.92 BR 1.89 2.59 37.04 TOP max lift 4.53 5.17 14.13 TOP min lift slope 4.25 4.79 12.71 TOP 1.68 1.61 4.17 In Figure 5 15, experimental results (le ft) are compared with numerical model s (right) for baseline and optimal to pology designs. Values are nor malized by the root chord and measured approximately along the spanwise section 2y/b = 0.58. Experimental displacements are reasonably consistent with predicted results. The PR wing did, however, outperform the wing optimized for maximum lift. The wing optimized for minimum lift also exceeded predicted results, but was within range compared to the other designs.

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41 Figure 5 15. Experimental (left) and numerical (right) out -of -plane displacements along 2y/b = 0.58, baseline and topology designs, Aerodynamic Results = 13 m/s. Experimental aerodynamic data was collected for two comparative studies. First, the performance of latex membrane and silicone membrane designs was measured usi ng PR and BR wings as baselines. Select aerodynamic coefficients for the PR wing are given in Figure 5 1 6 BR results are shown in Figure 5 1 7 The silicone membrane PR wing displayed a shallower lift slope and steeper pitching moment slope. It also had less dr ag at smaller angles of attack (less than 10), but higher the latex membrane Howev er, the silicone design outperformed the latex design according to drag and pitching moment.

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42 Figure 5 16. Experimental aerodynamic comparison, latex and silicone membrane PR wing, v 30.

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43 Figure 5 17. Experimental aerodynamic compa rison, latex and silicone membrane BR wing, v 30.

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44 Figure 5 18. Experimental aerodynamic data for low tensioned, latex membrane baseline and topology optimized designs by Stanford [4 ], vF igure 5 18 shows experi mental data taken by Stanford 30. [4] for baseline and topology optimized designs for CL, CD, and Cm. These wing s were constructed with low tension and latex membranes Experimental results for corresponding des igns are show n in Figure 5 19. All wings were manufactured with silicone membranes with comparable pre tension in both membranes The TOPmin Cm design was the most consistent, as it clearly displayed the steepest pitching moment. The TOPmin CL design ex hibited its optimization metric at higher angles of while the TOPmin CD 20). Overall, e xperimental results were reasonably consist ent with their expected behaviors.

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45 Figure 5 19. Experimental aerodynamic data for uniform tensioned, silicone membrane baseline and topology optimized designs (from Figure 5 17) v 30.

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46 CHAPTER 6 RELATED CONCEPTS Recently, there is heightened interest in developing bio inspired wings. Much effort has been dedicated to the study of natural flyers in hopes of mimicking benef icial flight characteristics Silicone membrane manufacturing techniques developed in this work may be helpful in creating designs along the bio inspiration front, i ncluding bat wing designs as expressed in Chapter 2. Composite skeletons could be co -cured with silicone membrane designs to develop very robust and realistic MAVs. Integrating control surfaces into these membranes is another concept which could further e volve future MAV designs. Figure 61 shows the fabrication of such a concept. A modified 24inch BR MAV wing is integrated with piezoelectric actuators on the wingtips. Pigmented silicone rubber serves as the fusing membrane. Wingtip deflections were observed and comparable with a 24 inch all -carbon fiber wing, also fused with wingtip actuators. Figure 6 1. Fabrication of 24-inch BR piezoelectric concept wing membrane with pigmented liquid silicone compound. Figure 6 2 24inch BR piezoelectric c oncept wing.

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47 CHAPTER 7 CONCLUSION Conclusion Flexible wing MAVs have two design issues that could be improved and should be addressed. First, current materials used for flexible wing membranes lack durability, robustness, and shelf life. Second, current manufacturing procedures are unable to create flexible wing membranes displaying consistent uniform pre tension. Silicone rubber was identified as an ideal membrane material because of its superior thermal properties, highly inert nature, and resistance t o environmental factors such as ozone, radiation, heat, and moisture. A manufacturing process was developed to cure liquid silicone rubber onto composite lamin ate wing structures, successfully fabricating membranes of uniform pre -tension. Experimental V IC data was gathered to validate this claim, using the PR design as the baseline. Furthermore, membrane inflation controllability was observed by adjusting the viscosity of the silicone solution (also validated with VIC). Aeroelastic comparisons with lat ex membrane platforms revealed the superiority of silicone membranes. Results indicated symmetric out of -plane displacements across both silicone membranes, unlik e those with latex membranes. Numerical models of selected t opology optimized designs were c ompared with experimental results, yielding similar displacement contours There was some variation in maximum membrane displacements, as pre tensions of the experimental models and numerical solver inputs were unequal. Future Work Future work should be carri ed out to perfect the silicone membrane co -curing manufacturing process of MAVs. Areas of focus should include: 1 Measuring silicone adhesion strength to composite structures over a range of curing temperatures.

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48 2 Develop ing a relationship between liqui d silicone viscosity and cured material strength. 3 Develop ing a relationship between membrane thickness and strength. 4 Conduct ing a thermal test to determine if pretension can be controlled as a function of silicone curing temperature. 5 Conduct ing a pressure test to determine if pre tension can be controlled as a function of vacuum pressure. 6 Creating precision -machined wing molds specifically for silicone membrane applications. 7 Develop ing bio -inspired wings using composite skeletons fused into silicone me mbranes. 8 Integrating control surfaces (such as piezoelectric actuators) into silicone membrane wings. 9 Build ing and fly ing prototype MAVs.

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49 APPENDIX A EXPERIMENTAL OUT OF -PLANE DISPLACEMENT C ONTOURS FOR BASELINE AND TOPOLOGY OPTIMIZED W ING DESIGNS Figur e A 1. Experimental out of

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50 Figure A 2. Experimental out of -plane displacement contour, silicone membrane 12.

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51 Figure A 3. Experimental out of -plane displacement contour, viscosity reduce d silicone membrane

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52 Figure A 4. Experimental out of -plane displacement contour, latex membrane

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53 Figure A 5. Experimental out of -plane displacement contour, silicone membrane 12.

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54 Figure A 6. Expe rimental out of -plane displacement contour, silicone membrane TOP wing optimized for maximum lift (TOPmax lift[4], Figure 7 10).

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55 Figure A 7. Experimental out of -plane displacement contour, silicone membrane TOP wing optimized for minimum lift slope (TOPmin lift slope), [4], Figure 7 10).

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56 Figure A 8. Experimental out of -plane displacement contour, silicone membrane TOP wing optimized for minimum CL (TOPmin CL(refer [4], Figure 7 15).

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57 Figure A 9. Experimental out of -plane displacement contour, silicone membrane TOP wing optimized for minimum CD (TOPmin CD)[4], Figure 7 15).

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58 Figure A 10. E xperimental out -of -plane displacement contour, silicone membrane TOP wing optimized for minimum Cm (TOPmin Cm [4], Figure 7 15).

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59 Figure A 11. Experimental out -of -plane displacement contour, silicone membrane TOP wing single um lift slope (TOP [4], Figure 7 18).

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60 APPENDIX B NUMERICAL O UT OF PLANE DISPLACEMENT M ODELS FOR BASELINE AND TOPOLOGY OPTIMIZED W ING DESIGNS, COURTES Y OF STANFORD [4] Figure B 1. Numerical o ut -of -plane displacement model

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61 Figure B 2. Numerical out -of -plane di splacement model

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62 Figure B 3. Numerical o ut -of -plane displacement model silico ne membrane TOP wing optimized for maximum lift (TOPmax lift[4], Figure 7 10).

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63 Figure B 4. Numerical out -of -plane displacement model

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64 Figure B 5. Numerical o ut -of -plane displacement model s ilicone membrane TOP wing optimized for minim um lift slope (TOPmin lift slope [4], Figure 7 10).

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65 Figure B 6 Numerical out -of -plane displacement model silicone membrane TOP wing, single objective ( ) opt imized for minimum lift slope (TOP), [4], Figure 7 18).

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66 LIST OF REFERENCES [1] Stanford, B., Ifju, P., A lbertani, R., Shyy, W., Fixed Membrane Wings for Micro Air Vehicles: Experimental C ha racterization, Numeri cal Modeling, and T ailoring, Progress in Aerospace Sciences Vol.44, No. 4 2008, pp. 258294. [2 ] Ifju, P., Jenkins, D., Ettinger, S., Lian, Y., Shyy, W., Waszak, M., Flexible -Wing Based Micro Air Vehicles, 40th AIAA Aerospace Sciences Meeting & Exhi bit, Reno, NV, AIAA Paper 20020705, 2002. [3 ] Stanford, B., Ifju, P., Membrane Micro Air Vehicles with Adaptive Aerodynamic Twist: Numerical Modeling, Journal of Aerospace Engineering, Vol. 22, No. 2, 2009, pp. 173184. [4 ] Stanford, B., Aeroelastic Analysis and Optimization of Membrane Micro Air Vehicle Wings, Ph.D. Dissertation, Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 2008. [5 ] Pornsin -sirirak, T., Tai, Y., Nassef, H ., Ho, C., Titanium alloy MEMS Wing Technology for a Micro Aerial Vehicle Application, Sensors and Actuators A: Physical Vol. 89, No. 1 2, 2000, pp. 95 103. [6 ] Song, A., Tian, X., Israeli, E., Galvao, R., Bishop, K., Swartz, S., Breuer, K., The Aero Mechanics of Low Aspect Ratio Compliant Membrane Wings, with Applications to Animal Flight, 46th AIAA Aerospace Sciences Meeting and Exhibit Reno, NV, AIAA Paper 2008517, 2008. [7 ] Leylek, E., Manzo, J., Garcia, E., A Bat -wing Aircraft Using the Smart Joint Mechanism, 3rd International Conference on Smart Materials, Structures, and Systems Acireale, Sicily, 2008. [8 ] Manzo, J., Leylek, E., Garcia, E., Drawing Insight from Nature: A Bat Wing for Morphing Aircraft, ASME Conference on Smart Material s, Adaptive Structures, and Intelligent Systems El licott City, MD, 2008. [9 ] Abdulrahim, M., Garcia, H., Lind, R., Flight Characteristics of Shaping the Membrane Wing of a Micro Air Vehicle, Journal of Aircraft Vol. 42, No.1, 2005, pp. 131137. [10 ] Waldman, R., Song, A., Riskin, D., Swartz, S., Breuer, K., Aerodynamic Behavior of Compliant Membranes as Related to Bat Flight, 38th Fluid Dynamics Conference and Exhibit, Seat tle, WA 2008. [11 ] Callahan, R., Garcia, E., Bio Inspired Bat Wing Des ign and Fabrication, AIAA Region INE Student Conference, Worcester, MA, 2009. [1 2 ] Fink, J., Reactive Polymers Fundamentals and Applications: A Concise Guide to Industrial Polymers William Andrew Publishing, Norwich, NY, 2005.

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67 [1 3 ] Keller, M., White, S., Sottos, N., A Self Healing Poly (Dimethyl Siloxane) Elastomer, Advanced Functional Materials Vol. 17, No. 14, 2007, pp. 23992404. [1 4 ] Boria, F., Optimization of a Morphing Wing Geometry Using a Genetic Algorithm with Wind Tunne l Hardware -in the -Loo p, M.S. Thesis, Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 2007. [1 5 ] Dally, J., Riley, W., Experimental Stress Analysis College House Enterprises, Knoxville, TN, 2005. [1 6 ] Lee, K., Development of Un manned Aerial Vehicle (UAV) for Wildlife Surveillance, M.S. Thesis, Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 2004.

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68 BIOGRAPHICAL SKETCH Albert Y. L in was born in Taipei, Taiwan in 1980. His f amil y m oved to the United States in 1983, where his fat her attended graduate school at Auburn University. He later grew up in Tallahassee, Florida and graduated from Lincoln High School in 1999. Lin enrolled at the University of Florida later that year and received a B achelor of S cience in Aerospace Engineering in 2004. After graduating, he worked as an airborne LiDAR operator/ a nalyst at the National Center for Airborne Laser Mapping (NCALM), conducting over 250 flight hours of aerial mapping across the United States in a Cessna 337 Skymaster Lin joined the Micro Air Vehicle (MAV) Laboratory in 2007 with hopes of pursuing a graduate degree under the advisement of Dr. Peter Ifju. During this time, he was a member of a talented team of MAV researchers who desig ned a number of state -of the art aircraft Lin received a Master of Science in Aerospace Engineering from the University of Florida in December 2009.