The Pennsylvania State University

Home , Adaptive compliant wing, Aileron

The Graduate School

ADDITIVELY MANUFACTURED COMPLIANT MECHANISM DESIGN AND

APPLICATION FOR SUAS CONTROL SURFACES

A Thesis in

Additive Manufacturing and Design

Thomas Jones

Submitted in Partial Fulfillment of the Requirements for the Degree of

Master of Science

May 2021

ii The thesis of Thomas Jones was reviewed and approved by the following:

Michael A Yukish Head, Manufacturing Systems Division Associate Professor of Aerospace Engineering Thesis Co-Advisor

Simon W Miller Assistant Research Professor Affiliate Professor of Architectural Engineering Thesis Co-Advisor

Timothy W Simpson Paul Morrow Professor in Engineering Design and Manufacturing Additive Manufacturing and Design Program Director

iii ABSTRACT

A design study was conducted to bridge the gap between conventional hinged aileron and compliant mechanism controlled morphing wing aileron designs for small unmanned aircraft systems using additive manufacturing methods. Taking advantage of the rapid prototyping capabilities of fused filament fabrication machines, several design options were created using multiple materials. Final design selection was determined by part usability and by metrics of reduced part count, weight, material use, assembly time, and other factors are enabled by additive manufacturing. The final compliant design was printed, tested and compared to a printed, conventional-style hinged aileron on a flying test-bed to look for aerodynamic benefits and to prove functionality. Data suggests there is some aerodynamic benefit to be gained with the compliant morphing wing aileron. Additional improvements include a reduction in total part count and time to assemble with improvements in final component weight and material usage possible using this design process. The use of additive manufacturing as a manufacturing process enabled rapid prototyping of concepts, greatly accelerating the design process and resulting in a novel design.

iv TABLE OF CONTENTS

LIST OF FIGURES ...... vi

LIST OF TABLES ...... ix

ACKNOWLEDGEMENTS ...... x

Chapter 1 Introduction ...... 1

Additive Manufacturing ...... 2 Small Unmanned Aircraft Systems ...... 3 Compliant Mechanisms ...... 5

Chapter 2 Literature Review ...... 7

Additively Manufactured Unmanned Aircraft ...... 7 Morphing Wing Technology ...... 13 AM with Morphing Wings ...... 16

Chapter 3 Design Process ...... 20

Design Considerations and Limitations ...... 20 Aircraft Design ...... 22 Aircraft Structure...... 23 Conventional Aileron Design ...... 26 Component Selection ...... 27 Initial Design Tests: TPU Arm Variants ...... 28 Secondary Design Tests: Compliant Shapes ...... 31 Final Design Tests: Sliding Skin ...... 36

Chapter 4 Testing and Analysis Methods ...... 44

Flight Campaign ...... 44 Experimental Data Collection ...... 45 Analytical Data Collection ...... 46 Additive Manufacturing Data ...... 47

Chapter 5 Results ...... 48

Hinged Aileron ...... 48 Morphing Aileron ...... 50 Analytical and Experimental Models ...... 52 Assembly Comparison ...... 54 Print Time and Material Usage ...... 55 Handling Qualities ...... 56

Chapter 6 Discussion and Conclusion ...... 57

References ...... 59

Appendix A Weather Data ...... 64

Appendix B Supplementary Materials ...... 65

vi LIST OF FIGURES

Figure 1: A schematic diagram of the FFF process (Gibson et al., 2014)...... 3

Figure 2: A typical fixed-wing aircraft control scheme (Flight Controls, n.d.)...... 5

Figure 3: The Southampton University Laser Sintered Aircraft (SULSA) in flight (Paulson et al., 2015)...... 8

Figure 4: The University of Virginia’s FFF printed sUAS (Easter et al., 2013)...... 9

Figure 5: The 3DAeroventures X-100 has a unique closed wing structure that is rarely seen made in balsawood or foam construction methods (Haddad, n.d.)...... 12

Figure 6: The morphing wing system developed by Flexsys on their test aircraft (Kota et al., 2016)...... 15

Figure 7: A schematic diagram of the morphing wing developed by Yokozeki et al. (2014)...... 16

Figure 8: A schematic diagram of the FishBAC design (a) and images comparing the deflections of the design (b) (Woods & Friswell, 2012)...... 17

Figure 9: A schematic diagram of the compliant morphing wing developed by Fasel et al. (2020)...... 19

Figure 10: A schematic diagram the Lulzbot Mini 2’s build volume (LulzBot Mini 2, n.d.)...... 23

Figure 11: An earlier iteration of the aircraft with a weaker landing gear design...... 24

Figure 12: The final design of the aircraft in flight, notice the wingtip covers...... 25

Figure 13: The conventionally hinged aileron design...... 27

Figure 14: The first TPU arm design (top) and the second (bottom), notice the significant stringing in the bottom design. This is undesirable due to added weight and interference with motion...... 28

Figure 15: The third TPU arm design (top, a) and the fourth (bottom, a). The unwanted form of the fourth design during the inward deflection is demonstrated in (b)...... 30

Figure 16: The CRAM test piece with PLA...... 31

Figure 17: A weight comparison of the Flex-16 pieces with the two modified Flex-16 pieces in PLA (a/c) and TPU (b/d)...... 32

vii Figure 18: The modified Flex-16 (a) and it rotated to about the maximum desired for an aileron (b)...... 33

Figure 19: A profile of the planned TPU aileron segment undeflected (a) and deflected by pulling on the lower arm and pushing with the top (b)...... 33

Figure 20: A side view of the full length first TPU arm design...... 34

Figure 21: The first TPU arm design without (a) and with (b) the planned PLA leading edge sheath...... 35

Figure 22: A side view of the full length second TPU arm design...... 36

Figure 23: The second TPU arm design without (a) and with (b) the PLA leading edge sheath. Note that this sheath would have been lengthened to cover the entire aileron section...... 36

Figure 24: The same surface-designed piece sliced in Simplify3D (a) and Cura (b)...... 37

Figure 25: Three initial sliding skin designs showing the difference between the pieces with no additional support and two different additional supports that connect to the same locations...... 38

Figure 26: A CAD model of the first full-length sliding skin model, with two trailing edge perimeters...... 40

Figure 27: A CAD model of the single-servo full-length sliding skin model...... 40

Figure 28: A top-down view of both ailerons...... 42

Figure 29: The top surface of the CM morphing wing aileron...... 42

Figure 30: The CM morphing aileron in the up position (a) and down position (b)...... 43

Figure 31: The final design of the aircraft with the morphing ailerons in flight...... 43

Figure 32: An onboard view looking back at the left wing while inverted during a 360° left roll with the morphing ailerons...... 45

Figure 33: A composite image of the morphing aileron at neutral, full up, and full down positions...... 46

Figure 34: The overall flight data for the hinge aileron...... 49

Figure 35: The roll rate tests for the hinge aileron with average value lines for left and right roll...... 49

Figure 36: The overall flight data for the second morphing aileron roll rate flight...... 50

viii Figure 37: The roll rate tests for the second morphing aileron flight with average value lines for left and right roll...... 51

Figure 38: Coefficient of lift versus the ratio of coefficient of drag for the morphing aileron (a) and hinge aileron (b)...... 53

Figure 39: A plot showing the amount of deflection from neutral measured at each aileron’s respective hinge point for a given control input percentage...... 54

ix LIST OF TABLES

Table 1: A comparison of AM technologies compared by Goh et al. (2017) for printed sUAS and their advantages and disadvantages...... 10

Table 2: A comparison of the same AM technologies compared by Goh et al. (2017) for printed sUAS and their advantages and disadvantages for compliant mechanism design...... 11

Table 3: A table adapted from Li et al. (2018) showing the development of morphing wing concepts over time...... 14

Table 4: Components used and their purposes...... 27

Table 5: Print parameters used for the flown versions of both the conventional hinge design as well as the CM...... 41

Table 6: Derived from experimental data for the hinged aileron...... 51

Table 7: Derived from experimental data for the first morphing aileron flight...... 51

Table 8: Derived from experimental data for the second morphing aileron flight...... 52

Table 9: Derived from experimental data for the full 360° rolls with the morphing ailerons...... 52

Table 10: Summary table of morphing versus hinged aileron performance...... 52

Table 11: A total parts list for both aileron types. Since some equipment varies on the components it comes with for a complete kit, parts for given items were noted but not counted toward the total part count. A complete kit is counted...... 55

Table 12: AM relevant parameters for the two aileron types as well as a comparison to the flight-ready weight...... 56

Table 13: Weather conditions for the hinge test flights...... 64

Table 14: Weather conditions for the morphing aileron test flights at the start of the day...... 64

Table 15: Weather conditions for the morphing aileron test flights at the end of the day...... 64

x ACKNOWLEDGEMENTS

I’d like to thank my advisors and colleagues that have provided extensive support and assistance along the way, not only with this thesis but other projects and activities in and out of school as well.

Chapter 1

Introduction

This study aims to design and demonstrate a fully 3D printed compliant mechanism morphing wing for the control of a 3D printed small unmanned aircraft, and culminated in a successful flight test of such a compliant mechanism. At the time of writing, no other example of such a mechanism that has been flown has been published. Examples in literature have either been of ground-based studies or of flight-tested examples that were partially 3D printed, e.g., only the internal structure with a non-printed skin.

This thesis first describes provides a brief overview on additive manufacturing, small unmanned aerial systems, and compliant mechanisms. A survey of previous research is then presented for state-of-the-art related fields that are combined in this effort to make a fully 3D printed control surface for an unmanned aircraft, as well as an account of the incremental steps taken to achieve this goal. This document will focus primarily on design for additive manufacturing principles and demonstrate a potential application for the technology where it has not yet been fully utilized. The design exploration is restricted to a material extrusion process due to its low-cost and simplicity that makes it attainable for an average designer or builder.

Advanced aerodynamic analysis is outside of the scope of this document; however, the method used will be briefly explained as it pertains to the flight test campaign evaluating the designs presented. The experimental portion of this work compares the performance of both a contemporary aileron with that of the designed compliant mechanism aileron on the same aircraft platform. The results of the design as well as areas for future improvement are also discussed.

2 Additive Manufacturing

Additive Manufacturing (AM) is a form of manufacturing that uses a layer-by-layer buildup of material to create an object from a 3D digital model. Whereas traditional manufacturing takes away material from a bulk shape (subtractive), AM adds material to a build plate or pre-existing structure in a process commonly referred to as 3D printing. This form of manufacturing can lead to the creation of more geometrically complex objects while producing less wasted material. The AM process is also typically quicker and more cost effective for small batch sizes since the production of dies or tooling is not required which makes it a very useful tool for rapidly prototyping new designs.

There are seven different types of additive manufacturing processes that have been standardized (ASTM Standard F2792, 2012). For the context of this study, a subprocess of material extrusion, fused filament fabrication (FFF), is the process used (Figure 1). FFF works by having a string of material, or filament, fed through a heater block where it is melted. This heat pipe is typically attached to a gantry-like system that moves it around a build platform. Some systems may have the build platform move instead. The melted material is fed from the heat pipe, through a nozzle where it is extruded layer-by-layer using specialized machine instructions and allowed to cool and solidify to create an object. Other material extrusion processes may use a chemical reaction to cure and bond material layers by use of a curing agent, the air, or otherwise

(Gibson et al., 2014).

Figure 1: A schematic diagram of the FFF process (Gibson et al., 2014).

Some popular FFF materials include polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate glycol (PETG). Prices for 1kg of material range from $15 up to over $60 for specialized material formulations.

In recent years, AM capable machines have come down in price considerably. This price reduction in material and the printers has made the technology more accessible to individuals and groups and has seen rapid growth in business and research opportunities as well as hobby-spaces

(Bourell, 2016).

Small Unmanned Aircraft Systems

A small Unmanned Aircraft System (sUAS) is the Federal Aviation Administration’s

(FAA) term for a remotely operated aerial vehicle, commonly referred to as an RC aircraft or drone, that weighs under 55 pounds (AC 107-2A - Small Unmanned Aircraft System (Small UAS),

2021). sUAS vary in type and design greatly but most are categorized as either a rotorcraft or

4 fixed-wing aircraft. A rotorcraft sUAS can take the form of a conventional helicopter or have multiple rotating blades or propellers in a pattern around an airframe to generate lift, e.g., a quadcopter. A fixed-wing aircraft sUAS is more akin to a conventional airplane where the wing is rigidly attached to the aircraft body, or fuselage, and moved through the air to generate lift. This study focuses on advancements for the latter.

Fixed-wing sUAS typically need at least four critical components to safely operate, a receiver, power supply, propulsion, and flight control surfaces. The receiver connects wirelessly to a ground-based controller that enables the operator to send commands to the aircraft. The power supply, typically a battery, will power the aircraft’s motor and onboard electronics. For sUAS using an internal combustion engine, the battery supplies power to the electronics while a liquid fuel powers the engine. The propulsion method can be an electrically driven motor, internal combustion engine, or for gliders, an upward air current.

The flight control surfaces for fixed-wing sUAS can come in many different configurations, a typical configuration is ailerons on wings that control the rolling action, elevator(s) on the horizontal tail(s) to control pitch, and rudder(s) on the vertical tail(s) to control yaw. Most fixed-wing sUAS require at least two control surfaces, though some are able to use less (e.g., a two-motor sUAS that uses differential and combined thrust to control direction and pitch) while others add additional devices (e.g., flaps, slats, spoilers). A schematic of a common fixed-wing aircraft layout is in Figure 2.

Figure 2: A typical fixed-wing aircraft control scheme (Flight Controls, n.d.).

As computer technology advanced and became more affordable, small autopilot systems and other sensor devices have found their way into sUAS. Thanks to this, it is now possible to capture real-time data, as well as obtain much more intricate sensor data from nearly any device placed on board, making sUAS an even more valuable research tool for a variety of applications.

For example, Pixhawks are an open-source, low cost autopilot system with data-logging capabilities (Open Source Autopilot for Drones, 2021).

Compliant Mechanisms

A compliant mechanism (CM) is a type of device that uses an input force or motion and translates it to an outward force or motion through the shape of the design itself. This is commonly achieved by having flexible members or joints within the device that allow its shape to change in accordance to the input (Howell, 2013).

6 CMs have several advantages that make their study interesting. One such advantage is the reduction of part count. Typical mechanisms have several pins, fasteners, hinges and other components to transfer motion and force. Through clever design, compliant mechanisms are able to replace hinges and connections with flexible joints while maintaining desired motion (Howell,

2013).

This decrease in part count, when coupled with 3D printing, can simplify the assembly process. By having this simplicity, costs associated with producing the mechanism can be reduced as well as operational costs as less lubrication is needed to reduce friction (Howell,

2013).

Brigham Young University’s (BYU) Compliant Mechanism Research Group (CMR) has stated that CMs also allow for a more precise component movement. Since there has been a reduction or elimination in fasteners, the locations that backlash can occur are also reduced or eliminated. Backlash is a usually unwanted movement caused by having gaps in interconnecting parts. The CMR also has shown that traditional mechanisms that have rubbing components will eventually wear due to friction which can lead to deviations from the original designed motion

(Howell, 2013). Conversely, their research shows that because of how CMs work, they are usually difficult to design. Many involve the use of non-linear equations to determine how they will respond and that their motion can change based on material used. There are also concerns of fatigue from the cyclical motions CMs undergo and the energy stored in certain states of operation (Dirksen et al., 2013).

7 Chapter 2

Literature Review

The chapter presents a brief overview of previous works done in AM sUAS literature, morphing wing technologies, and the combination of AM and morphing wings. The focus is on research performed in the sUAS and morphing wing spaces with highlights on factors that make certain designs more or less feasible for hobby-grade, inexpensive, desktop FFF systems. The review focuses primarily on printed sUAS made with the FFF system as this was the selected print process for the study, though one produced with SLS is discussed.

Additively Manufactured Unmanned Aircraft

A “fully printed aircraft” in this thesis describes an aircraft where all aerodynamic surfaces and the majority of internal structural members are printed. The design may use additional unprinted members, but it does not rely on them entirely to fly.

The first fully 3D printed sUAS was developed in 2011 (P. Marks, 2011). This aircraft, known as the SULSA, was made using the selective laser sintering (SLS) process with a nylon material. Other than being the first 3D printed sUAS, the aircraft achieved a number of impressive feats for a sUAS in general. It was able to be assembled within 10 minutes using a toolless process, flew for roughly 30 minutes, and used no fasteners in assembly (Paulson et al.,

2015). An image of the plane is shown in Figure 3. While impressive, the technology used to build the plane is not readily available to hobbyists or those without access to a SLS machine.

Figure 3: The Southampton University Laser Sintered Aircraft (SULSA) in flight (Paulson et al., 2015).

One of the first sUAS to be produced using the FFF process was created by a team at the

University of Virginia (Easter et al., 2013). As the FFF process is more accessible to the general public, this was an important step for printed sUAS. However, the aircraft (Figure 4) cannot make the claim of being fully printed. Its printed parts are lightened with holes throughout the external surfaces and the vehicle’s body is covered with a heat-shrunk film, similar to traditional balsawood style models, to cover these holes. Easter also claims that the aircraft’s ABS frame was said to withstand impact better than balsa designs and was more readily repairable due to being able to print identical parts within hours. With the often-volatile environment that sUAS operate in, impacts with obstacles and the ground are inevitable. An aircraft that is easier to repair will ideally spend less time in the repair shop and more time performing the mission. Designers later began creating models that were fully printed using FFF, apart from the necessary electronics or additional structural members like carbon fiber spars or fasteners.

Figure 4: The University of Virginia’s FFF printed sUAS (Easter et al., 2013).

Goh et al. (2017) extensively documents the recent history of sUAS and also shows that multiple other print processes have been used to create sUAS; however, many of these processes have certain disadvantages that outweigh their potential advantages for a robust flying platform.

A table summarizing the advantages and disadvantages for printed sUAS as a whole are listed by

Goh and displayed in a modified form in Table 1. Additional advantages and disadvantages for the same AM techniques but for compliant structures are discussed in Table 2. Observation of the hobbyist 3D printed sUAS community shows that FFF is the leading method for production of components, complete vehicles, and prototype vehicles with unconventional structures (Figure 5).

Table 1: A comparison of AM technologies compared by Goh et al. (2017) for printed sUAS and their advantages and disadvantages.

Technology Advantages Disadvantages Fused Filament • High strength material such as • Obvious stair stepping Fabrication (FFF, a Ultem is available effect in z-direction material extrusion • ABS plastic has higher survival rate process) compared to balsa during impacts • Ability to create functionally graded • Slow recovery rate from Polyjet, parts with multi-material printing high loading condition (A material jetting • Ability to print fine features • Strength of AM material is technology) • Good surface finish still inferior to that of the • Insignificant stair stepping effect biological bone • Ability to print fine feature size • Degradation of Stereolithography • Good surface finish photosensitive materials (SLA, a • Insignificant stair stepping effect leading to poor photopolymerization performance under load process) • Low tensile strength of material Selective Laser • Ability to print parts with good • Rough surface finish Sintering (SLS, a mechanical strength powder bed fusion • Large build area process) • Relatively low cost

Table 2: A comparison of the same AM technologies compared by Goh et al. (2017) for printed sUAS and their advantages and disadvantages for compliant mechanism design.

Technology Advantages Disadvantages • Wide variety of flexible filaments • Printed parts may have • Relatively inexpensive process “stringing” from flexible Fused Filament • Options for multi-material material Fabrication (FFF, a • Easy to start and stop process to • Bowden tube style designs material extrusion embed objects into the print have a more difficult time process) with flexible material • Relatively large feature size • Fastest print process within a 5” • UV cured materials can cube (Stereolithography vs. PolyJet: degrade from light and Top 4 Differences: Stratasys Direct, heat exposure over time n.d.) • Stratasys claims it isn’t Polyjet, • Parts print fully cured ideal for functional or (A material jetting • Multi-material capable rugged protoyping/testing technology) • Can print materials with shore (Stereolithography vs. hardness range of 20-90A in the PolyJet: Top 4 same build (Stereolithography vs. Differences: Stratasys PolyJet: Top 4 Differences: Direct, n.d.) Stratasys Direct, n.d.) • Can produce clear parts to observe • Parts require additional internal structures post processing to cure • Fine feature size resin, messy process • Flexible resins available • Requires filled vat of Stereolithography material, regardless of (SLA, a material amount used on photopolymerization part process) • Single material prints • Many parts not intended for long term (Gibson et al., 2014) • Often toxic resin • No need for support material • Requires personal (Gibson et al., 2014) protection equipment Selective Laser • Wide range of thermoplastics when dealing with Sintering (SLS, a available powdered material powder bed fusion • Parts require cooling time process) • Build volume is relatively large and multiple parts can be produced if (Gibson et al., 2014) sized appropriately

Figure 5: The 3DAeroventures X-100 has a unique closed wing structure that is rarely seen made in balsawood or foam construction methods (Haddad, n.d.).

Additively manufactured sUAS have since shown to have a wide versatility in research applications. Projects range from project lifecycle studies (Miller et al., 2019), experimental solutions, such as Ferraro et al.’s (2014) SLS printed sUAS fuel tank that was quickly designed and iterated upon, and components with specific shapes that are constructed with more geometric complexity compared to traditional building techniques like the SULSA’s elliptical wing (P.

Marks, 2011). Others have also taken advantage of being able to embed sensors and other electronics in printed sUAS components to monitor the overall health of the vehicle that may otherwise be undetectable to an operator on the ground (Stark et al., 2014). Many current designs in research, commercial, and hobbyist spaces are able to take advantage of faster prototyping, modularity in components, greater design intricacy that being fully printed allows compared to conventional balsawood or foam building techniques.

Generally, weight reduction is paramount when designing aircraft to decrease the power required to stay aloft and thus decrease fuel or battery consumption. AM sUAS are (typically)

13 heavier than their traditionally constructed counterparts (e.g., density of balsa wood is 0.11-

0.14g/cm3, PLA is ~1.24 g/cm3), but have many other advances over traditional designs (e.g., geometric complexity, manufacturability) that some users may not want to sacrifice, though this could change with material advancements.

Given that this material is heavier, designing for light-weight structures has even more importance. For example, a traditional aircraft aileron has multiple components that must be assembled to get a functional part. By reducing the amount of material per component, or even the number of components altogether, weight savings can accumulate.

Morphing Wing Technology

Morphing wing technology has been around since the dawn of heavier-than-air aviation.

Early designers saw a way to mimic the control mechanism of birds with the lightweight fabric and wood structures of the time (Barbarino et al., 2011). As aircraft became heavier and greater wing loadings developed, having warping wings for control that were strong enough to support the aircraft were not possible. The transition to hinged ailerons allowed designers to bulk up wings for strength and higher loading while maintaining controllability. This has been the standard ever since, with varying degrees of modification. Li et al. (2018) extensively documents the progression of morphing wing technology and Table 3 clearly highlights the multi-decade gap in morphing wing development. In some cases, morphing wings can take the form of a CM.

Table 3: A table adapted from Li et al. (2018) showing the development of morphing wing concepts over time.

Year Information Concept 1903 Wright Brothers’ flyer Twist morphing 1920 Parker variable-camber wing Variable camber 1979-1989 AFTI/F-111 MAW Variable sweep & camber 1995-1999 Smart Wing Program Phase I concepts Variable camber 1996-2001 Active aeroelastic wing Variable camber 1997-2001 Smart Wing Program Phase I concepts Variable camber 1999 Active hydrofoil Variable camber 1999 Finger concept by DLR Variable camber 2000 Belt-rib concept by DLR Variable camber 2000 FlexSys mission-adaptive compliant wing Variable camber 2003-2006 Lockheed Martin Z-wing concept Folding wing 2003-2006 NextGen aeronautics bat-wing concept Variable sweep 2003 SMA reconfigurable aerofoil Variable camber 2003 HECS wing Span morphing 2004 Multi-section variable-camber wing Variable camber 2004 Variable-gull-wing morphing aircraft Folding wing Virginia Polytechnic Institute and State 2004 Span morphing University telescoping-wing aircraft Variable camber & twist 2005 Morphing inflatable wing morphing 2006 Morphing HECS wing Span morphing 2007 Pneumatic telescoping wing Span morphing 2007 Supekar morphing wing Span morphing 2008 Antagonistic SMA-based morphing aerofoil Variable camber 2008 Bistable composite morphing-wing concepts Variable sweep 2008 Morphlet (morphing winglet) Folding wing 2009 Adaptive wing with SMA torsion actuators Variable camber 2010 Warp-controlled twist morphing wing Twist morphing 2011 Spa extending morphing wing Span morphing 2012 Multisegmented Folding Wing Folding wing 2012 SADE: seamless aeroelastic wing Variable camber 2013 Adaptive bending-twist coupling wing Twist morphing 2013 Bat-like morphing-wing Folding wing 2014 Compliant adaptive wing leading edge Variable camber 2015 Span-extending blade tip Span morphing 2015 Spanwise morphing trailing edge Variable camber 2016 GNATSpar wing Span morphing 2016 Twist morphing wing segments Twist morphing 2016 Morphing wing-tip Variable camber Compliant structures-based wing and 2016 Variable camber wingtip morphing devices 2017 Feathered wing Folding wing 2017 Aquatic micro air vehicle Variable sweep

Various design teams have been working to bring morphing wings back into the full- scale aviation space. The company Flexsys has partnered with the Air Force Research Laboratory

(AFRL) to develop what they claim is the “first seamless, hinge-free shape morphing wing”

(FlexFoil, n.d.). As stated in Kota et al. (2009), one of the key drivers behind the technology is reduced drag that leads to fuel savings. An image of the morphing wing system is in Figure 6.

Figure 6: The morphing wing system developed by Flexsys on their test aircraft (Kota et al., 2016).

Morphing wings could similarly by used for sUAS. Yokozeki et al. (2014) shows the development and aerodynamic data for one such possible morphing wing design. This design features a corrugated inner structure with a smooth outer skin and a wire that is tensioned to deflect the airfoil (Figure 7). Their study compared a hinged control surface with their morphing design and suggested improved performance in coefficient of lift. The design, however, is only able to deflect in a single direction and is a bit complicated to assemble, with wires that need to be a precise length and tension. The design was also not printed, but instead constructed of carbon

16 fiber reinforced plastics and plastic foam, though the generally monolithic form does lend well to the FFF process as no support material would be needed on the mechanism portion of the design.

Figure 7: A schematic diagram of the morphing wing developed by Yokozeki et al. (2014).

Montgomery et al. (2019) compared the aerodynamic results of morphing wings using numerical and analytical approaches to look at the roll control of a morphing wing aircraft. Their research shows that the analysis methods employed are “orders of magnitude faster than computational fluid dynamics” (CFD). They repeatedly emphasize that the methods used are not limited to the specific morphing aircraft observed in the study and can be used to analyze other designs.

AFRL created their own morphing wing called the Variable Camber Compliant Wing

(VCCW) (Joo et al., 2015). The VCCW was designed to change the wings camber by controlling both the leading and trailing edge of the wing using a single actuator. Different sizes of the wing section were constructed and wind tunnel testing performed. C.R. Marks et al. (2015) further explores the aerodynamics of the VCCW with a focus on airframe noise generation.

AM with Morphing Wings

There have been several advancements in recent years bringing morphing wings and additively manufactured aircraft together. Woods & Friswell (2012) created what is known as the

FishBone Active Camber (FishBAC) concept. This design, built in a HP DesignJet that uses the

17 FFF process, features a structure that mimics a fish’s spine and ribs with a trailing edge strip that holds two tendons that are actuated near the leading edge (Figure 8). The tendons are put into either tension or compression (one tendon opposite the other) and that pulls the solid piece in the trailing edge, but because of the spine it deflects in a smooth, curved shape to the tensioned side.

The external skin of the FishBAC is an Elastomeric Matrix Composite (EMC), so the design is not fully 3D printed. The design showed to have increases in the lift/drag ratio, similar to

Yokozeki et al. (2014), when compared to a regular hinged flap and standard airfoil. Moulton &

Hunsaker (2021) have also developed a slotted-skin printed morphing airfoil section that is made with AM, they performed some preliminary analysis, but it has not yet been flight tested.

(a) (b)

Figure 8: A schematic diagram of the FishBAC design (a) and images comparing the deflections of the design (b) (Woods & Friswell, 2012).

Acosta (2020) describes a later variant of the VCCW (discussed in previous section) and the VCCW’s flight verification and mentions that the structure makes use of 3D printed carbon fiber spars to connect the wing ribs. The VCCW model that was flown was tested on a sUAS and able to deflect both up and down and functioned as full-span ailerons with three points of

18 deflection in each wing-half. Acosta (2020) shows that the morphing wing structure is functional on an actual small-scale aircraft and that 3D printed components can be used, practically, in the design.

Morphing wings are not limited to control surfaces. Vocke et al. (2011) created a span- morphing wing with sUAS integration in mind. Their wing skin is made from an EMC while the inside structure is a stereolithography (SLA) printed structure. With this structure, they were able to produce a wing section that could increase wing area up to 100%. Vocke et al. (2011) also makes note that further research would have to be conducted to see if their print method would be viable for a sUAS, but serves as a good ground-testing piece.

Fasel et al. (2020) made a significant leap in printed morphing wing technology. They designed and printed rib structures using continuous carbon fiber printing (an advancement of

FFF). These rib structures, however, each have their own servo that moves a rod that flexes the trailing edge. The compliant nature of the structure then flexes in a desired curve. A schematic of this design is in Figure 9. Several of these rib sections were assembled into a wing and covered with a thermoplastic skin. The rest of the aircraft was similarly constructed with the tail also having printed compliant structures. Fasel et al.’s (2020) greatest advancement is having brought the aircraft out of the wind tunnels and flown it in real world conditions, being one of the first to fly a sUAS where most of the control mechanisms are 3D printed. The design allowed them to have a continuous morphing wing where several segments along its span could differentially morph with a smooth transition from one to the next. This design, while advanced, does have the drawback of being complicated to assemble, having many parts, and still cannot claim to be a fully-3D printed morphing wing if that is a design goal.

Figure 9: A schematic diagram of the compliant morphing wing developed by Fasel et al. (2020).

In summary, the literature shows that much has been accomplished in the exploration of morphing wing technologies as well as the development of AM produced sUAS with a start to combining the two, however none of the fully-printed prototypes have a published test flight at the time of writing.

20 Chapter 3

Design Process

The design process was conducted in a largely trial-and-error manner with relevant research into other solutions in both additive and conventionally manufactured designs for inspiration. The relatively quick turnaround time of additive manufacturing allowed for physical prototyping of the design iterations, and is an example of how the technology has changed the design process itself.

Design Considerations and Limitations

Three categories of design considerations were taken into account in the design process, broken down into primary, secondary, and tertiary categories of importance. Primary considerations dealt with material selection and print processes limitations. Secondary considerations involved the overall mechanism shape and requirements to properly integrate it on a sUAS testbed, discussed in the Aircraft Design section. Tertiary design considerations were ease of assembly, material use, and print time; these are further discussed in the three Design Test sections as they pertain to each part.

The first step taken was to select a print process to work within. ASTM F42 group has developed standard terminology for seven different AM processes in F2792-12a. For the scope of this study, only desktop applications that are simple to use and widely available to the general public (via libraries, universities, makerspaces, personal use, etc.) were considered. This immediately eliminates binder jetting, material jetting, powder bed fusion, and direct energy deposition. Vat photopolymerization was eliminated due to the generally fragile nature of the parts produced by this method. It was also eliminated because complex geometries were

21 anticipated and the parts produced by this process require ultraviolet curing. It is challenging to properly cure the internal surfaces of thin, hollow parts and to do so properly would require additional design considerations. Sheet lamination was also another process that was considered, but it is one of the more wasteful AM processes, thus negating some of the reason to use AM for a sUAS (Gibson et al., 2014). The process also can have difficulty with hollow parts in some cases, which is a technique used by sUAS for weight savings (Mein, 2020). By far, the most popular method among those making 3D printed sUAS appears to be FFF. Many designs have become commercially and freely available that are designed for the FFF process (Šverko, 2019).

This process is also typically readily available in makerspace communities and as a desktop machine. For these reasons, FFF was the printing process selected for this study.

Material selection was the next step. As FFF was the selected process, a thermoplastic capable of being used on common FFF systems was needed. The most popular materials are PLA,

ABS, Ultem, PETG, and a foaming PLA variant. Goh et al. (2017) discusses the strengths and weaknesses of some of these materials for sUAS in further depth. Notably for FFF materials, they list ABS as the least dense material and polyphenylsulfone (PPSF) as the material with the highest elastic modulus. TPUs of 90A, 95A, and 98A were added to this list for consideration for the CM portion of the design because of their rubber-like flexibility and the potential use for such a material. Rejected materials are summarized in the following list, with all prices as of March

2021 for a 1kg spool1:

• Ultem and PPSF - high cost, $250 and $225, respectively.

• ABS - concern of potentially harmful fumes released during print and

requirement of additional print enclosures for a more controlled “chamber”

temperature to prevent thermal warping, $30.

1 www.3dxtech.com

• PETG – denser than PLA and lower elastic modulus (Wang et al., 2017 and

Durgashyam et al., 2019), $32.

• Foaming PLA – weak when compared to regular PLA and TPU and tends to

deform on hot days, $55 for 750g (LW-PLA NATURAL, n.d.).

Multi-material printing was considered, but ultimately decided against due to the added design complexity. Dual material extrusion is also a technology not as readily available to smaller makerspaces or individuals due to the higher cost. PLA and TPU were ultimately selected as the two materials of interest. PLA is one of the least expensive materials available with some spools being available for less than $20 and TPU provides flexibility which was a consideration for this project at a fairly low cost.

Aircraft Design

The requirements laid out for the aircraft design were driven by the considerations and limitations of the CM. To make things simple, a symmetric airfoil was be selected so that the final mechanism design could be mirrored about the chord line if needed for symmetric movement. To ensure that there was plenty of room within the wing structure for mechanism movement, a thicker airfoil was selected. The chord of the airfoil was limited to 200mm in length to fit within the diagonal build plate area of a Lulzbot Mini 2. The maximum length of a single aileron segment was set at 180mm to fit within the Mini 2’s Z-axis limits. Figure 10 shows a diagram of the Mini 2. The final imposed requirement was the ability to readily swap the outboard part of the wing between a conventional hinged aileron and the CM aileron. This feature was implemented to make it easier to rapidly test both designs in the field. The remaining aircraft dimensions were sized around the wing considerations.

Figure 10: A schematic diagram the Lulzbot Mini 2’s build volume (LulzBot Mini 2, n.d.).

An additional item to note on the design of AM sUAS is that the printed wing sections are orientated such that the Z (vertical) axis of the FFF printer is in line with the span of the wing.

This orientation allows for a smooth wing outer mold line, however, with this orientation there is greater chance of cracks or gaps appearing in the wing skin as layers separate. Care must be taken to adequately design the wing segments so that the skin is not overstressed.

Aircraft Structure

The aircraft was designed to be as simple and easy to work on as possible (Figure 11).

The selected design minimized time spent designing the plane and gave more time to the design

24 of the CM. The fuselage of the aircraft is a square carbon tube extending from the nose to tail. It has the motor and ESC mount, battery pod, wing, and tail surfaces screwed into it. The motor and

ESC mount, battery pod, landing gear, wing, tail, and electronics tray are all 3D printed out of

PLA. PLA was selected for these parts due to the earlier mentioned considerations in addition to the ability to rapidly prototype and change various aspects of the plane as seen fit during testing.

The wing attaches to the fuselage tube via a central pod that tilts it up at a fixed 3° angle of incidence. The tail pieces were basic flat plates with rounded leading and trailing edges with the vertical stabilizer having a curve to its leading edge. These structures used a simple piano-hinge style control surface attachment because they were not being tested. An early version of the aircraft is in Figure 11.

Figure 11: An earlier iteration of the aircraft with a weaker landing gear design.

The airfoil selected was a NACA 0018 due to its symmetry and thickness. The thickness allowed for sufficient internal volume to fit servos, the wing spars, wiring, and the CM. The symmetry was selected so as to have a mirrored design with symmetric movement. The wingspan

25 of the aircraft is 1280mm with the center fuselage pod being 80mm wide. The wing is a constant chord, rectangular planform wing with no twist or dihedral. A panel is fitted into the spars on each wingtip to cover the open gap of the wing structure, seen in Figure 12. The panels also notably gave improved yaw handling during initial prototype testing. The panels slide on and off without tools and allow the outer wing section, containing the aileron, to be removed quickly and easily. The ability to remove the aileron section easily was a key requirement to make the experimental comparison process of the two aileron types quicker in the field, if needed. It was also designed to make the ideation, print, build, time-to-fly cycle shorter.

The final design of the completed plane can be seen in Figure 12. The flying weight with the hinge ailerons is 1923g while with the morphing ailerons the weight is 2000g. Aerodynamic

“cleanliness” was not a factor in the design of the central body since the ailerons were the area of interest. Two pitot tubes were mounted in the wing equidistant from the aircraft centerline on opposite wing halves. This was both for redundancy and so extra data would be collected in the event that the prototype design caused significant yawing motion, which was not observed.

Figure 12: The final design of the aircraft in flight, notice the wingtip covers.

26 The aircraft underwent several modifications in its early design phases. AM promoted this since components were easy to redesign and produce within a day if needed. During initial testing, the landing gear broke several times as earlier versions were too weak. The tail originally had a wheel for steerability on the ground, but after a few landings broke off. A skid was instead printed and placed on the tail. It was designed to simply attach so that when it would slowly wear over continual use, another could be quickly printed and replaced. Figure 12 also shows the internal structure of the printed vertical stabilizer in silhouette.

Conventional Aileron Design

The conventional aileron design used as a control in this study was also 3D printed, but the design was composed of multiple parts that required assembly (Figure 13). The inner structure used the same strut pattern as the main wing. It is 180mm in spanwise length and maintains the

200mm chord of the wing. The aileron itself is a separate piece from the wing segment, connected at three different hinge points. These hinge points are separately printed TPU tabs that are glued into channels on both pieces. On the top side of the wing section there is a servo pocket with a hole leading to the interior of the wing for the servo wire. A control horn is glued to the upper surface of the aileron and a pushrod linkage is attached. A linkage is also attached to the servo control horn and a carbon pushrod slotted through them and secured. Through flight testing, it was determined that the servo pocket was too large and was causing airflow separation from the wing. Flat pieces of scrap print material were glued over top with the edges sanded down. This pocket, ideally, would be on the bottom wing surface, but the manner in which the aircraft rocked while on the ground created concerns for the control horns striking the ground and detaching.

This extra material was not anticipated to affect the roll rate to a measurable degree.

Figure 13: The conventionally hinged aileron design.

Component Selection

The list of used components is in Table 4. The different servo used on the morphing wing was due to an identical servo to the one used in the hinge aileron not being available at the time of purchase.

Table 4: Components used and their purposes.

Brand Item Use E-Flite Power 10 motor Propulsion Aerostar 50A 2-6s ESC Motor speed controller APC 11 x 5.5-inch propeller Propulsion Holybro Power Module v3 Supplies power from battery to ESC and Pixhawk 3DR Pixhawk flight controller Flight controller, logs data and runs Ardupilot software 3DR 915MHz telemetry radio Provides real-time telemetry data 3DR GPS Module Logs position data and assists with automated flight modes 3DR Pitot Tube Gathers airspeed data YEP 20A 2-12s SBEC Supplies 5V to servo rail of Pixhawk FrSky X8R Control receiver Corona CS919MG Control servo (hinge aileron, rudder, elevator) Corona CS238MG Control servo (morphing aileron) Zippy 3s 2200mAh Battery

28 Initial Design Tests: TPU Arm Variants

The first design explored was a short spanwise section of aileron to gain initial impressions on the properties of the TPU used and to test the design creation process. Early tests fairly quickly ruled out the use of TPUs with a shore hardness value lower than 98A for any structural components or pieces requiring compression due to lack of stiffness; this also eliminated the 90A and 95A TPUs. The first model shown in the top of Figure 14 takes the profile of the airfoil with some basic structure to maintain the shape and arms attached to the interior of the trailing edge. The thought with this design was that the servo arms would have a push/pull motion on the TPU arms to deflect the trailing edge. At this time, cylindrical spars were planned to be used in the aircraft wing and the design tried to leverage this to be able to rotate around the spar. Manually pushing and pulling on the arms did produce a desirable movement of the trailing edge, however it also caused the skin to wrinkle and the airfoil shape to twist in front of the rear spar.

Figure 14: The first TPU arm design (top) and the second (bottom), notice the significant stringing in the bottom design. This is undesirable due to added weight and interference with motion.

29 The second design iteration (Figure 14 bottom) switched to square tube spars. This was to prevent rotation of the wing due to aerodynamic forces. Due to the lessons learned from the first variant, the second also saw two arms for a push/pull action but this time the arms ran mostly independent to the intended servo position from the trailing edge. A thicker section rigidly attached to the rear spar extends to the trailing edge to provide leverage and somewhat guide the trailing edge along the intended path. This design ended up having relatively little movement and wrinkling still occurred on the skin. It also showed, like version one, that the pushing motion was unreliable with the TPU 98A.

Design versions three and four began exploring what would happen if the trailing edge sections were printed in a way that biased them to spring outward. This action would mean that they would naturally want to push against the oncoming airflow and would only need to be pulled inward when a control deflection was not desired. This was partially inspired by a compliant grasper device that pulled a central rod to bring together two gripper arms (Diepens 2015).

Version three, Figure 15 (top), experimented shown with a triangular cut pattern in the interior of the arms to further promote a bending action. This worked well, however the rigidity to push against the airflow was lost. Design four (Figure 15, bottom) had thicker arms to compensate for this, but pulling them inward greatly distorted the airfoil outline. It is possible a combination of thicknesses and key cuts may have produced desirable results; however, this was not explored.

All four designs were also printed in PLA as a comparison point, but they all broke when subjected to the required deflections.

(a)

(b) Figure 15: The third TPU arm design (top, a) and the fourth (bottom, a). The unwanted form of the fourth design during the inward deflection is demonstrated in (b).

At this stage only 10mm long segments were being printed to save time and material, allowing for rapid prototyping and quick evaluation of any potential concept. Focus was primarily on the trailing edge so shortcuts were taken with the leading half of the parts by using standard infill patterns with no custom design.

31 Secondary Design Tests: Compliant Shapes

The fifth attempt at a CM came in the form of the Compliant Rolling-contact Architected

Materials (CRAM) piece. The CRAM makes use of compliant rolling-contact joints (CRJ) to have a single piece design that gets rolled or folded up and assembled into a mechanism with desired movement (Shaw et al., 2018). To assess the feasibility of this design, a basic two-roller, two-layer piece was printed in both PLA and TPU, shown in Figure 16. The PLA version was initially very stiff after initial assembly, but soon broke after a few rolling motions. The TPU version was much easier to assemble, however the bands connecting the two rollers also broke quickly due to how thin it was required to be for proper movement. The design requires the use of multiple fasteners which also increases overall weight and part count to undesirable levels.

Figure 16: The CRAM test piece with PLA.

32 The next design considered was a modified version of the Flex-16 (Figure 17, c and d) system developed by Fowler et al. (2014). The original design is a monolithic flexure device that can rotate 90° in both directions. The demonstration model was printed from titanium (Fowler et al., 2014). To start, the same design was modeled and scaled appropriately to fit within the airfoil section. This, however, proved to be too stiff for the given size if made from PLA and a modified version needed to be designed. The modified Flex-16 featured less arms than the original and allowed for movement. Roughly 0.3g was saved in the redesign with the PLA version (Figure

17c) and 0.2g with the TPU version (Figure 17d) for a 10mm tall section. With the Flex-16 TPU version, a significant amount of stringing was present and the modified version eliminated most of this without modifying printer parameters. The range of motion was not quite +/- 90° with the

PLA version, but roughly +/- 15-25° was achieved and is enough for an aileron. The TPU version was able to reach the full 90°, but this is unnecessary. After just a handful of deflections, the PLA version started experiencing fatigue in the corners where the arms meet the central circle. The

TPU version held up over several weeks of experiencing full deflections as a fidget toy.

(a) (b) (c) (d) Figure 17: A weight comparison of the Flex-16 pieces with the two modified Flex-16 pieces in PLA (a/c) and TPU (b/d).

With this information, a full-length segment of the modified Flex-16 was printed using

TPU to see what forces would be required to deflect it for an aileron. Figure 18 demonstrates the

33 deflection of a 10mm tall section. This 180mm segment proved to be too stiff for the size servo being used so the decision to use it in limited sections of an aileron hinge was made.

(a) (b) Figure 18: The modified Flex-16 (a) and it rotated to about the maximum desired for an aileron (b).

Development efforts then shifted to the creation of a full-length aileron section using the modified Flex-16 hinge. The first version was a mostly monolithic shape that had an attachment point to the rear wing-spar, the hinge connected to that, and the aileron on the other side. Coming from the aileron at both ends were two sets of arms meant to attach to a servo for the push/pull action. A 10mm tall section of this shape is in Figure 19.

(a) (b) Figure 19: A profile of the planned TPU aileron segment undeflected (a) and deflected by pulling on the lower arm and pushing with the top (b).

The hinge was placed in three 20mm long sections at each end of the aileron and in the middle spanwise. This design was not optimized for AM as it was just meant to be an initial test.

34 The print time ended up being 44 hours and 15 minutes using 111.5g of material neglecting the supports. A matching PLA sheath was printed with this part to be the leading edge and servo cover. It had a slightly inward biased skin to grip the TPU piece and minimize any gaps between the two. While the desired motion was possible, weight was still a major concern with this piece and so material reduction and manual optimization for printing was carried out. The part is shown in Figure 20 and Figure 21.

Figure 20: A side view of the full length first TPU arm design.

(a) (b)

Figure 21: The first TPU arm design without (a) and with (b) the planned PLA leading edge sheath.

The new piece (Figure 22 and Figure 23) had triangular cuts made in the trailing edge section to remove the bulk of material. Diagonal extensions were added to the hinge sections to allow the printer to build on the overhang rather than use support material. The arms were slightly shortened for a better fit. A test section at the trailing edge of the aileron was added as a type of slot to hold the PLA outer skin. The modified TPU piece now took 31 hours and 6 minutes to print and used 91.7g of material without supports. Very significant stringing occurred with this part and would require more post-processing time if print parameters cannot be adjusted to resolve this.

Figure 22: A side view of the full length second TPU arm design.

(a) (b) Figure 23: The second TPU arm design without (a) and with (b) the PLA leading edge sheath. Note that this sheath would have been lengthened to cover the entire aileron section.

Final Design Tests: Sliding Skin

All prototypes until this point used Simplify3D2 for slicing. Designs had to be compatible with the way this software processes slicing CAD models. As such, designs were made in a way that allowed the software to make complete loops with its toolpath planning. If a design was

2 www.simplify3d.com

37 created using surface modeling, instead of solid body modeling, it would have to use complete loops for Simplify3D to process it correctly. This limited some design options so the switch was made to Cura3 which supports surface models natively. With Cura, surface designs could be made without a completed loop and it handled single line extrusions properly. A comparison of the same part sliced in Simplify3D and Cura is shown in Figure 24. The part has two free ends on the outer loop that do not connect.

(a)

(b) Figure 24: The same surface-designed piece sliced in Simplify3D (a) and Cura (b).

Experimentation with the PLA sheath from the full-length TPU variants, showed that a thin wall of PLA may be stiff enough to withstand aerodynamic forces without requiring much extra internal support. Realizing that the main challenge of previous designs was the skin wrinkling, and with the switch to Cura, a new fully-PLA design was created (Figure 25). This

3 www.ultimaker.com/software/ultimaker-cura

38 design had a mostly standard structure for the leading-edge portion of the airfoil, but had the trailing edge mostly empty with just the airfoil profile printed as a single perimeter. A separation of this perimeter from the bottom skin of the airfoil was designed to avoid merging during the print process. This inward deflected tab would be pushed or pulled by an internal servo to deflect the remaining profile. An initial 10mm tall section was created, using a standard infill pattern for the leading edge. The design worked as a test piece to demonstrate if the desired movement could be achieved with the intended deflection. It was successful in this task, but the trailing edge was determined to still be too flimsy.

More iterations of the test piece were created using one to five perimeters on the trailing edge to add rigidity. These iterations also tested different potential methods of servo attachment as well as other changes to ensure proper motion. Two pieces were made to test additional supports leading from the servo attachment point to the location most susceptible to bending on the trailing edge skin (Figure 25). These additional supports did take away from the desired motion.

Figure 25: Three initial sliding skin designs showing the difference between the pieces with no additional support and two different additional supports that connect to the same locations.

39 Full-length pieces were created for the pieces that had two and five perimeters on the flexible trailing edge. These perimeters were designed on the surface-model side as opposed to slicer side. The five-perimeter piece proved to be too stiff for the servos used so a graded- perimeter piece was also made. This piece had the internal layers graded as they approached the tip of the trailing edge to see if that would help maintain the proper shape and ease issues with deflection. It was ultimately still too rigid. The two-perimeter piece showed promise as the aileron deflected easily from the servo attachment point and the deflected aileron took a considerable amount of force to deform out of the deflected position. It was decided to move forward with this design.

A full surface-modeled design was created for the aileron wing section (Figure 26). This would allow it to be lighter weight than the rest of the wing that had the internal structure designed primarily with solid bodies. This does come at the cost of strength as there is one less perimeter printed with the internal struts and each one is able to be a single extrusion width.

Strength in the structure is not as great of a concern in this part compared to the rest of the wing due to the wing loading being less on the wingtip, nonetheless, the part was overdesigned to ensure safety during testing. The same spacing in the structure pattern was used; different cutouts from this pattern were taken compared to the conventional aileron. A single-perimeter aileron version of the surface model was made to see if the two perimeters were actually necessary, but the large, unsupported single perimeter aileron warped too much during the build process.

Figure 26: A CAD model of the first full-length sliding skin model, with two trailing edge perimeters.

The piece used two servos at each end to fully support the aileron, both moving each end of a rod that connected to the aileron skin. A ledge was designed into the part to glue the servos to and the upper surface was given a curve to not impede the deflection of the aileron. With the servos attached and hooked up, the piece performed nicely and gave the desired motion. To get a more real-world sense of how much deflection would occur due to aerodynamic forces, the piece was held out of a car window traveling at 50 miles-per-hour, slightly higher than the maximum speed of the aircraft. The aileron did not appear to experience any significant adverse deflection due to aerodynamic forces in either the up or down position as well as the neutral position and felt very effective against the hand.

Figure 27: A CAD model of the single-servo full-length sliding skin model.

41 After determining the minimal effect of wind forces on the geometry, a single servo variant was created in an attempt to lighten the overall piece further and keep part count low

(Figure 27 and Figure 29). This servo was placed in the middle and a slot was created in the servo attachment bar for the servo arm. A thin metal rod was inserted in the rod and servo arm as an attachment and held in place by glue. Note that additional support material was required to print this slot, but it is roughly the same as that required for the two-servo variant. Two of these pieces were printed for testing on the aircraft. Relevant printer parameters for this piece and the conventional hinge are in Table 5 with an image comparing the two pieces in Figure 28.

Table 5: Print parameters used for the flown versions of both the conventional hinge design as well as the CM. Printing Parameter Value Nozzle diameter 0.4mm Layer height 0.2mm Flow rate 102% Extrusion width 0.42mm Perimeter shells 1 Top/bottom layers 0 Hot end temperature 230°C Build plate temperature 75°C for first layer, 70°C after Fan speed 0% Print speed 50mm/s, 42mm/s on walls Travel speed 130mm/s

Figure 28: A top-down view of both ailerons.

Figure 29: The top surface of the CM morphing wing aileron.

The final design met the requirement of fitting within the print volume of a Lulzbot Mini

2, used a single servo, minimal support material, and was a single piece that gave desired motion

(Figure 30). The design is seen in flight in Figure 31. With a design settled on, experimental validation could begin.

(a)

(b) Figure 30: The CM morphing aileron in the up position (a) and down position (b).

Figure 31: The final design of the aircraft with the morphing ailerons in flight.

44 Chapter 4

Testing and Analysis Methods

The following section details the procedures taken to gather experimental, analytical, and additive manufacturing data for the testing of the final design.

Flight Campaign

Each flight test campaign began with calibrating the aircraft accelerometers and compass.

When the aircraft was fully checked out and deemed ready for flight, weather conditions were recorded (temperature, pressure altitude, winds, humidity, and air pressure). If the flight events lasted an extended time, more weather was recorded partway through or at the end as well. Lists of weather conditions for the data gathering flights are in the Appendix.

To compare overall effectiveness of the new design when compared to the original, the parameter of interest for this study was the aircraft’s maximum sustained roll rate. The aircraft performance was first evaluated with the conventionally-designed hinged aileron described in

Chapter 3. Earlier testing with this aileron was done to ensure functionality and that no additional changes were required. After the aircraft was in a finalized state, flights were conducted to gather the roll rate data for both the hinge ailerons and morphing ailerons. All flights were conducted between 0 and 400 feet in altitude above the ground (AGL).

Figure 32: An onboard view looking back at the left wing while inverted during a 360° left roll with the morphing ailerons.

For the hinge ailerons, six total full-deflection events were conducted, rolling the aircraft side to side. These rolls were made within limits of where the aircraft felt safe to operate as far as handling (shy of approximately +/- 90° roll angle from wings-level). These rolls were made in rapid succession from one extreme to the opposite.

For the morphing ailerons, six full-deflection roll tests were conducted in each direction from level to the same limit as the hinge aileron. Two additional rolls were performed that did a full 360° rotation in each direction.

Experimental Data Collection

With the Pixhawk flight controller, airspeed and altitude data were collected at 10Hz, control output position data at 25Hz, and inertial measurement unit (IMU) data at 50Hz. For each test, the data was imported into MATLAB and the relevant data extracted. Since the Pixhawk has two different IMU data recordings (MPU-6000 and L3GD20 IMUs) and a recording from each of

46 the two pitot tubes, the average of the pair was taken for each. Data was filtered using a second- order Butterworth filter. Altitude data was not filtered as it was not required to get the roll data and mostly serves as a visual when plotting. The mean and standard deviation for each roll segment was found for airspeed and roll rate. Airspeed data was converted from indicated airspeed to true airspeed using the observed temperature and pressure on the relevant day of flight.

As the design of the morphing aileron seen in this document has no hinge point, a psudo- hinge point was determined based on where two lines from the trailing edge, at maximum deflections, are traced to corresponding symmetric points about the chord line intersect (Figure

33). Deflection angle and the aileron chord length are calculated from the point, giving a value of

82.8mm for the chord of the aileron. This value was compared to the actual hinge location on the conventional aileron for deflection values.

Figure 33: A composite image of the morphing aileron at neutral, full up, and full down positions.

Analytical Data Collection

Analysis was conducted with XFOIL to gain more aerodynamic data on the lift and drag of the deflected morphing aileron in comparison with the hinge aileron. For the morphing ailerons, a scanned profile of the aileron in deflected positions was used to generate the airfoil coordinates. XFOIL’s built in hinge function was used for the hinge aileron.

47 Additive Manufacturing Data

All additive manufacturing relevant analysis was done by comparing predicted material usage and print time and actual material usage and print time for both of the two hinge and two morphing ailerons. This data as well as part count and qualitative data, such as ease of assembly, are discussed further in Chapter 5.

48 Chapter 5

Results

This chapter displays the processed flight data and details the results of comparing the analytical and experimental models for the hinge and morphing ailerons. Key metrics considered are roll rate and handling qualities, with the key results being that the morphing ailerons worked well in both roll responsiveness and handling qualities. Additional aerodynamic factors and differences in AM qualities are also discussed.

Hinged Aileron

The hinge aileron was first tested to provide baseline data for comparison. Figure 34 shows the commanded signal given to the aircraft, the roll rate, true airspeed, and altitude for the test segment. Positive values for commanded signal and roll rate indicate a right roll. As shown in the plot, airspeed fluctuated at times which corresponds with changes in altitude. This change in airspeed does affect the roll rate to an extent, but the impact of rapid airspeed changes on roll is damped due to the aircraft’s inertia. Once a commanded input was given, there was a brief rise time while the aircraft’s roll rate accelerated before plateauing. The process repeats for each roll direction. Roll rate to the left was higher than rolls to the right even though all deflections and trim settings were equal. Figure 35 gives a larger view of the roll rate plot, with the yellow and purple lines representing the average roll rate for each direction.

Figure 34: The overall flight data for the hinge aileron.

Figure 35: The roll rate tests for the hinge aileron with average value lines for left and right roll.

50 Morphing Aileron

The morphing aileron received similar treatment for data analysis. As mentioned in

Chapter 4, the test method was modified to return to level before the next roll test instead of directly into the next roll. The “commanded signal” plot in Figure 36 shows this. In the roll rate plot and Figure 37 the same short rise time and plateaus can be seen, though shorter with the decreased time spent rolling. Average roll rates for each direction were more even than the hinged aileron, however the left roll continued to be higher.

Figure 36: The overall flight data for the second morphing aileron roll rate flight.

Figure 37: The roll rate tests for the second morphing aileron flight with average value lines for left and right roll.

The key takeaway for these plots is that a similar roll rate to the hinged aileron was achieved with the morphing aileron. The data for each flight conducted is summarized individually in Table 6 through Table 9 with all of the morphing aileron data combined in Table

10 and directly compared to the hinged aileron values from Table 6.

Table 6: Derived from experimental data for the hinged aileron.

Left Roll Right Roll Average Roll Rate (deg/s) -122.88 88.91 Standard Deviation (deg/s) 12.52 14.64 Average True Airspeed (m/s) 25.50 21.80 Standard Deviation (m/s) 1.94 1.60

Table 7: Derived from experimental data for the first morphing aileron flight.

Left Roll Right Roll Average Roll Rate (deg/s) -128.91 122.53 Standard Deviation (deg/s) 9.13 17.50 Average True Airspeed (m/s) 19.61 18.81 Standard Deviation (m/s) 1.16 4.96

Table 8: Derived from experimental data for the second morphing aileron flight.

Left Roll Right Roll Average Roll Rate (deg/s) -101.74 97.47 Standard Deviation (deg/s) 20.09 12.60 Average True Airspeed (m/s) 16.00 13.86 Standard Deviation (m/s) 2.16 0.85

Table 9: Derived from experimental data for the full 360° rolls with the morphing ailerons.

Left Roll Right Roll Average Roll Rate (deg/s) -124.44 121.64 Standard Deviation (deg/s) 13.60 26.58 Average True Airspeed (m/s) 19.38 19.46 Standard Deviation (m/s) 3.34 3.90

Table 10: Summary table of morphing versus hinged aileron performance.

Left Roll Left Roll Right Roll Right Roll (Morphing) (Hinge) (Morphing) (Hinge) Average Roll Rate (deg/s) -118.36 -122.88 113.88 88.91 Standard Deviation 15.87 12.52 18.54 14.64 (deg/s) Average True Airspeed 16.97 25.50 16.07 21.80 (m/s) Standard Deviation (m/s) 2.22 1.94 2.85 1.60

Analytical and Experimental Models

A key metric of performance is the drag induced by aileron deflection as compared to the lift generated. Through XFOIL analysis, a comparison of CL versus CD was developed. The plots show comparable increases in drag with respect to lift for both configurations. Note that 100% deflection with the morphing aileron corresponds to 70% on the hinge aileron to achieve the same deflection angle from their respective hinge points.

(a) (b) Figure 38: Coefficient of lift versus the ratio of coefficient of drag for the morphing aileron (a) and hinge aileron (b).

Figure 39 shows the amount of deflection per given control input. It can be seen that the hinge aileron follows a linear trend. The morphing aileron shows little extra input by the last positive 50% input, about 1.33° more. The last negative 50% range saw 4.8° of deflection in comparison. For the positive deflection, more skin surface is uncovered and does not have the additional support of the underside tab, causing it to bow outward more instead of deflect at the tip. The negative deflection is lessened due to the servo arm in this position causing the control bar to move up and down more than in and out. The deflection angles were taken from the hinge or psudo-hinge point and measured up or down from a neutral position.

Figure 39: A plot showing the amount of deflection from neutral measured at each aileron’s respective hinge point for a given control input percentage.

Assembly Comparison

Assembly for the hinged aileron is complex. There are many more components involved that need to be assembled when compared to the morphing aileron. Initially, the hinge tabs need to be glued into one of the two halves of the wing/aileron section. These tabs then need to aligned with and inserted into the corresponding slots on the mating piece while the have glue on them.

This task can be tedious with the design used since sometimes the tabs do not go into the slot immediately and require aligning while taking care to not accidentally glue them somewhere undesired. Then, a servo needs to be glued in place, control linkages need to be attached to control horns, a control rod needs to be cut to the required length and fit in place, and the aileron- side control horn needs to be aligned properly with the servo arm and glued in position. A component list for each aileron is in Table 11.

Two methods were created to assemble to morphing aileron. The first method involves a metal rod slightly longer than half the aileron section’s length, slotting it through the connection

55 bar with the servo in the middle, and gluing it in place. The second method saves some weight by using a shorter metal rod, but the print layers must be separated in the middle where the servo is located to allow for manipulation of the two halves for proper placement before gluing the metal rod and two skin halves back together. Both processes took less time than the conventional aileron and saw a reduction in part count.

Part Hinged Aileron Morphing Aileron Aileron/wing pieces 2 1 Servo (motor, screw, control horn) 1 1 Control horn 1 0 Pushrod 1 1 Control linkage (linkage, stopper, washer, hex nut) 2 0 Servo cover 1 0 Hinges 3 0 Total 11 3

Once the servo control rod is attached, CA glue can be applied to the side of the servo that will be in contact with the ledge and the connection bar with servo folded back under the underside skin tab. The servo wire is then fed through one side of the wing section.

Print Time and Material Usage

The overall printing time and material usage of this morphing wing design was increased in comparison to the hinge aileron. A table of the results is found below in Table 12. The raft is excluded from the material use columns, but support is not. It can also be noted from this data that the weight of components added to the hinge aileron is approximately 6.1g more than the morphing aileron. The servo used for the morphing aileron weighs 22g and the servo for the hinge aileron weighs 13g, model numbers are in Table 4. The reason for the dissimilar servos is

56 that due to the availability and time between testing prototypes, new servos needed to be ordered and an exact match could not be made. For the morphing wing servo, a higher torque servo was selected to ensure safety with the new aileron type, similar to having the wing structure overbuilt in this piece. Aerodynamic analysis was not affected by this decision.

Table 12: AM relevant parameters for the two aileron types as well as a comparison to the flight- ready weight.

Aileron Estimated Print Actual Print Estimated Material Flying Type Time (hr:min) Time (hr:min) Material Use (g) Use (g) Weight (g) Hinge 7:33 8:45 72 65.03 85.31 Morphing 9:54 10:18 120 101.83 124.01

Handling Qualities

The handling characteristics of the morphing aileron varied little from the hinge aileron, and not adversely. Response was snappy and had little slop when making sharp movements. The higher roll rate at lower airspeeds and increase in weight was not noticeable by feel. The performance felt like a hinge aileron in both manual and automated flight modes.

57 Chapter 6

Discussion and Conclusion

A morphing aileron design was designed, printed, and flown that shows promise for the

AM sUAS domain. Experimentally, it was shown that the morphing aileron can achieve higher max roll rates than a printed hinge aileron at both a slower airspeed and lower deflection angle from their respective hinge points. The morphing aileron showed strong controllability during flight and was indistinguishable from a hinged aileron from an operator’s perspective. The morphing aileron also was able to cut down part count from 11 to 3, but it also increased the assembled weight. The assembly process, while different than what sUAS builders may be used to, is simplified with the lower part count and one can make the conclusion that it can also take less time because of this.

In its current form, the morphing aileron weighs more than the hinge aileron. Due in part to a larger servo with higher torque being used as well as a more built up structure for safety purposes. The total weight and material usage are, however, within 40g of the hinge aileron and using the same servo would bring this within 30g. With additional refinements made to the overall design of the morphing aileron it is reasonable to expect the weight can be lowered to that of hinge aileron or less. Support material, while some consider an undesirable item in AM produced parts, is used in the central channel that the servo control horn slots into. The amount used is not enough to greatly increase the print time or material usage. With additional design optimizations this could be removed while simplifying the assembly process further.

While this paper does not focus on aerodynamics, a brief analysis was conducted. The

XFOIL analysis of both airfoils at differing degrees of deflections indicate that a maximum upward-deflected morphing aileron has slightly more lift and more drag than a hinge aileron at the same angle of deflection. The morphing aileron also has a tighter range of lift than the

58 conventional aileron. Overall, the aerodynamics of the morphing aileron are similar to the hinge aileron.

Future work can see a more robust aerodynamic analysis of the printed morphing aileron and how it compares to its hinged counterpart. The model could be modified to take into account different correction factors to use with the morphing aileron design. Different airfoils and sizes of wing sections containing the aileron can also be used. As this is the first iteration of the morphing aileron, it was not expected that it would fully improve upon the hinge aileron from an AM perspective. Rather it set out to prove that by taking advantage of certain AM capabilities, such a piece is possible and functional.

Future iterations of the morphing aileron could see an optimization of internal structure to further reduce weight while maintaining required strength. A possible way to eliminate the need for support structure could be to use a V-shaped channel instead of a rectangular one for the servo control horn slot. This could also eliminate the need to split the skin layers to insert the smaller control rod option. If the V-gap is large enough it could allow the rod to flex during insertion into one of the two guide holes in the connection bar, something not possible with the current design.

In summary, this study highlighted a gap in morphing wing technology that had not been filled yet. Through the use of AM technologies and leveraging the advantage of rapid prototyping, many different iterations of a potential solution to the gap were trialed before finally settling on a design. The design was tested experimentally and analytically to prove functionality and get a glimpse into what aerodynamic performance would be like. The design shows promise in several areas and with further iteration could surpass the current standard design for 3D printed sUAS ailerons.

59 References

AC 107-2A - Small Unmanned Aircraft System (Small UAS). (2021). Federal Aviation

Administration.

https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.info

rmation/documentID/1038977

Acosta, S. B. (2020). Flight Characteristic Verification of the Variable Camber Compliant Wing.

In Department of Electrical and Computer Engineering: Vol. Master of Science in

Electrical Engineering. Air Force Institute of Technology.

ASTM Standard F2792. (2012). Standard Terminology for Additive Manufacturing Technologies.

ASTM International.

Barbarino, S., Bilgen, O., Ajaj, R. M., Friswell, M. I., & Inman, D. J. (2011). A Review of

Morphing Aircraft. Journal of Intelligent Material Systems and Structures, 22(9), 823–

877. https://doi.org/10.1177/1045389X11414084

Bourell, D. L. (2016). Perspectives on Additive Manufacturing. Annual Review of Materials

Research, 46(1), 1–18. https://doi.org/10.1146/annurev-matsci-070115-031606

Dirksen, F., Anselmann, M., Zohdi, T. I., & Lammering, R. (2013). Incorporation of flexural

hinge fatigue-life cycle criteria into the topological design of compliant small-scale

devices. Precision Engineering, 37(3), 531–541.

https://doi.org/10.1016/j.precisioneng.2012.12.005

Durgashyam, K., Indra Reddy, M., Balakrishna, A., & Satyanarayana, K. (2019). Experimental

investigation on mechanical properties of PETG material processed by fused deposition

modeling method. 2nd International Conference on Applied Sciences and Technology

(ICAST-2019): Material Science, 18, 2052–2059.

https://doi.org/10.1016/j.matpr.2019.06.082

60 Easter, S., Turman, J., Sheffler, D., Balazs, M., & Rotner, J. (2013). Using Advanced

Manufacturing to Produce Unmanned Aerial Vehicles: A Feasibility Study.

https://doi.org/10.1117/12.2027616

Fasel, U., Keidel, D., Baumann, L., Cavolina, G., Eichenhofer, M., & Ermanni, P. (2020).

Composite additive manufacturing of morphing aerospace structures. Manufacturing

Letters, 23, 85–88. https://doi.org/10.1016/j.mfglet.2019.12.004

Ferraro, M., Lock, A., Scanlan, J., & Keane, A. (2014). Design and flight test of a civil unmanned

aerial vehicle for maritime patrol: The use of 3D-printed structural components.

FlexFoil. (n.d.). FlexSys. www.flxsys.com/flexfoil

Flight Controls. (n.d.). L’avionnaire. www.lavionnaire.fr/VocableFlightControl.php

Fowler, R. M., Maselli, A., Pluimers, P., Magleby, S. P., & Howell, L. L. (2014). Flex-16: A

large-displacement monolithic compliant rotational hinge. Mechanism and Machine

Theory, 82, 203–217. https://doi.org/10.1016/j.mechmachtheory.2014.08.008

Gibson, I., Rosen, D., Stucker, B., & Khorasani, M. (2014). Additive Manufacturing

Technologies (3rd ed.). Springer International Publishing.

Goh, G. D., Agarwala, S., Goh, G. L., Dikshit, V., Sing, S. L., & Yeong, W. Y. (2017). Additive

manufacturing in unmanned aerial vehicles (UAVs): Challenges and potential. Aerospace

Science and Technology, 63, 140–151. https://doi.org/10.1016/j.ast.2016.12.019

Haddad, E. (n.d.). X-100 Infinity Wing 3D Printed RC Aircraft. 3DAeroventures.

www.3daeroventures.com/shop/infinitywing

Howell, L. L. (2013). Introduction to Compliant Mechanisms. In Handbook of Compliant

Mechanisms (pp. 1–13). John Wiley & Sons, Ltd.

https://doi.org/10.1002/9781118516485.ch1

61 Joo, J., Marks, C., Zientarski, L., & Culler, A. (2015). Variable Camber Compliant Wing –

Design. In 23rd AIAA/AHS Adaptive Structures Conference.

https://doi.org/10.2514/6.2015-1050

Kota, S., Flick, P., & Collier, F. S. (2016). Flight testing of flexfloiltm adaptive compliant trailing

edge. 54th AIAA Aerospace Sciences Meeting, 0036.

Kota, S., Osborn, R., Ervin, G., Maric, D., Flick, P., & Paul, D. (2009). Mission adaptive

compliant wing–design, fabrication and flight test. RTO Applied Vehicle Technology

Panel (AVT) Symposium, 18–1.

Li, D., Zhao, S., Da Ronch, A., Xiang, J., Drofelnik, J., Li, Y., Zhang, L., Wu, Y., Kintscher, M.,

Monner, H. P., Rudenko, A., Guo, S., Yin, W., Kirn, J., Storm, S., & Breuker, R. D.

(2018). A review of modelling and analysis of morphing wings. Progress in Aerospace

Sciences, 100, 46–62. https://doi.org/10.1016/j.paerosci.2018.06.002

LulzBot Mini 2. (n.d.). LulzBot. shop.lulzbot.com/lulzbot-mini-v2-0-boxed-for-retail-na-kt-

pr0047na?ref=KT-PR0047NA

LW-PLA NATURAL. (n.d.). ColorFabb. colorfabb.com/lw-pla-natural

Marks, C. R., Zientarski, L., Culler, A. J., Hagen, B., Smyers, B. M., & Joo, J. J. (2015). Variable

Camber Compliant Wing—Wind Tunnel Testing. In 23rd AIAA/AHS Adaptive Structures

Conference. https://doi.org/10.2514/6.2015-1051

Marks, P. (2011). 3D printing takes off with the world’s first printed plane. New Scientist,

211(2823), 17–18. https://doi.org/10.1016/S0262-4079(11)61817-4

Mein, S. (2020, January 24). Understanding the Seven Types of Additive Manufacturing. Firetrace

International. www.firetrace.com/fire-protection-blog/additive-manufacturing

Miller, S. W., Yukish, M. A., Hoskins, M. E., Bennett, L. A., & Little, E. J. (2019). A

Retrospective Analysis of System Engineering Data Collection Metrics for a 3D Printed

62 UAS Design. Procedia Computer Science, 153, 1–8.

https://doi.org/10.1016/j.procs.2019.05.049

Montgomery, Z. S., Hunsaker, D. F., & Joo, J. J. (2019). A Methodology for Roll Control of

Morphing Aircraft. In AIAA Scitech 2019 Forum. https://doi.org/10.2514/6.2019-2041

Moulton, B., & Hunsaker, D. F. (2021). 3D-Printed Wings with Morphing Trailing-Edge

Technology. In AIAA Scitech 2021 Forum. https://doi.org/10.2514/6.2021-0351

Open Source Autopilot for Drones. (2021, March 11). PX4 Autopilot. px4.io/

Paulson, C., Sobester, A., & Scanlan, J. (2015). Rapid Development of Bespoke Sensorcraft: A

Proposed Design Loop. In 56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics,

and Materials Conference (Vol. 1–0). American Institute of Aeronautics and

Astronautics. https://doi.org/10.2514/6.2015-0135

Shaw, L. A., Chizari, S., Dotson, M., Song, Y., & Hopkins, J. B. (2018). Compliant rolling-

contact architected materials for shape reconfigurability. Nature Communications, 9(1),

4594. https://doi.org/10.1038/s41467-018-07073-5

Stark, B., Stevenson, B., Stow-Parker, K., & Chen, Y. (2014). Embedded sensors for the health

monitoring of 3D printed unmanned aerial systems. 175–180.

https://doi.org/10.1109/ICUAS.2014.6842253

Stereolithography vs. PolyJet: Top 4 Differences: Stratasys Direct. (n.d.). Stratasys.

www.stratasysdirect.com/manufacturing-services/3d-printing/differences-between-

stereolithography-polyjet

Šverko, L. (2019, February 20). 3D Printed RC Plane: 10 Great Curated 3D Models. All3DP.

all3dp.com/2/3d-printed-rc-plane-best-curated-models/

Vocke, R. D., Kothera, C. S., Woods, B. K. S., & Wereley, N. M. (2011). Development and

Testing of a Span-Extending Morphing Wing. Journal of Intelligent Material Systems

and Structures, 22(9), 879–890. https://doi.org/10.1177/1045389x11411121

63 Wang, L., Gramlich, W. M., & Gardner, D. J. (2017). Improving the impact strength of

Poly(lactic acid) (PLA) in fused layer modeling (FLM). Polymer, 114, 242–248.

https://doi.org/10.1016/j.polymer.2017.03.011

Woods, B., & Friswell, M. (2012). Preliminary Investigation of a Fishbone Active Camber

Concept. In ASME 2012 Conference on Smart Materials, Adaptive Structures and

Intelligent Systems, SMASIS 2012 (Vol. 2). https://doi.org/10.1115/SMASIS2012-8058

Yokozeki, T., Sugiura, A., & Hirano, Y. (2014). Development and Wind Tunnel Test of Variable

Camber Morphing Wing. In 22nd AIAA/ASME/AHS Adaptive Structures Conference.

https://doi.org/10.2514/6.2014-1261

64 Appendix A

Weather Data

Table 13: Weather conditions for the hinge test flights.

Condition Value Wind speed (knots) 0-5 Temperature (°C) 24.1 Pressure altitude (m) 482 Humidity (%) 65.6 Air Pressure (inHg) 30.29

Table 14: Weather conditions for the morphing aileron test flights at the start of the day.

Condition Value Wind speed (knots) 8 Temperature (°C) -2.5 Pressure altitude (m) 485 Humidity (%) 87 Air Pressure (inHg) 30.30

Table 15: Weather conditions for the morphing aileron test flights at the end of the day.

Condition Value Wind speed (knots) 3 Temperature (°C) -1 Pressure altitude (m) 494 Humidity (%) 78 Air Pressure (inHg) 30.27

65 Appendix B

Supplementary Materials

• CM Aileron.stl o Design file for morphing aileron that was tested and shown in Chapter 4 • CM Aileron Flights.mp4 o Video for morphing aileron test flights