unmanned air vehile (uav) wing design and manufacture

7/31/2019 Unmanned Air Vehile (UAV) Wing Design and Manufacture

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Unmanned Air Vehicle (UAV) Wing Design

and Manufacture

Submitted by

Chong Shao Ming

Department of Mechanical Engineering

In partial fulf il lment of the requirements for

Degree of Bachelor of Engineering

National University of Singapore


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Summary

This paper documents the development of a UAV wing, encompassing the entire process

from design to manufacture, and finally its implementation on an aircraft. Beginning with

wing design and analysis, requirements are first identified and related concepts are

formulated. A literature survey is then conducted to establish focus for analysis.

Analysis is conducted for the four main design parameters. Firstly, airfoil selection is decided

using 2D CFD analysis. Verification of Xfoil is done by evaluating its results with available

wind tunnel data. It is subsequently used to extend the data library to incorporate a wider

selection. Reviewing the lift and stability requirements as well as stall patterns, GEMINI and

NACA0012 are the final selections for wing and tail airfoils respectively. Limitations of Xfoil

necessitate the use of 3D CFD analysis tool, Fluent, on planform selection. Justification is

first established for the choice of k-omega (Shear Stress Transportation) turbulent model.

Aerodynamic data is then generated for four different planforms with different

combinations of rectangular and tapered section. Their drag coefficients were found to be

lower than the baseline. However, they are not convincingly significant to justify their

selection over the rectangular baseline, which yields practical and aerodynamic benefits. For

dihedral and the sizing of control surfaces, practical data on stability and control derivatives

are derived from literature. Computations are subsequently carried out to determine the

design parameters.

To fabricate the wings, a computer numerical controlled system was developed. It

comprises of three sections. The mechanical parts were fabricated from scratch, while the

electronic components and the software were obtained from credible sources. To optimize

the performance of the system, mechanical calibrations were first carried out. The selection


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of wire heat and cutting speed has significant implications on the dimensional accuracy,

hence, empirical tests are conducted to derive the optimum values. Finally, the accuracy

and precision of the system is put the test through a detailed inspection of fabricated airfoils

cross section. The coordinates were registered and analyzed using Xfoil to yield

aerodynamic data. Differences were deemed acceptable.

With the established fabrication process, prototype aircrafts were assembled subsequently.

Other than demonstrating air worthiness, flight test is the most practical way to verify the

results from computational analysis. To achieve this, flight instruments and a data storage

device are mounted on the aircraft and flight data were collected. Analyses of the records

were carried out to derive the lift and glide ratio. Deviations from computational analysis

were justified and accounted for.


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Acknowledgements

The author wishes to express sincere appreciation to the supervisor, Assoc Prof Gerard Leng

for his patience and guidance throughout the course of project. His role as a mentor was

invaluable. Gratitude is also extended to the Staff and Technicians of the Dynamics Lab for

their administrative and technical support. Special appreciation also goes to Mr Anthony

Low, President of Radio Modellers Singapore, for his kind assistance in flight test.


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Table of Contents

List of Figures ....................................................................................................................... i

List of Tables ....................................................................................................................... iii

List of Symbols.....................................................................................................................iv

Introduction ........................................................................................................................ 1

Background and Overview ......................................................................................................... 1

Objectives .................................................................................................................................... 1

Design and Analysis ............................................................................................................. 2

Methodology............................................................................................................................... 2Requirements and Parameters .................................................................................................. 3

Mission Requirements ........................................................................................................... 3

Categorization of Parameters ................................................................................................ 3

Critical Performance parameters .......................................................................................... 4

Determining Stability Requirements ..................................................................................... 5

Literature Survey ........................................................................................................................ 5

Findings for Airfoil .................................................................................................................. 5

Findings for Planform ............................................................................................................. 6

Concept of Dihedral................................................................................................................ 7

Control Surfaces ..................................................................................................................... 8

Analysis ........................................................................................................................................ 8

Scope ....................................................................................................................................... 8

Airfoil Analysis and Selection .............................................................................................. 9

Planform Analysis and Selection ......................................................................................... 14

Dihedral Analysis and Computation .................................................................................... 18Control Surfaces Analysis and Computation ...................................................................... 18

Fabrication ........................................................................................................................ 20

Implementing CNC Solution ..................................................................................................... 20

Mot ivations ........................................................................................................................... 20

System Design, Manufacture and Assembly ...................................................................... 21

System Calibration and Optimization ................................................................................. 22


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Fabrication Precision Analysis.................................................................................................. 23

Mot ivation and Procedures ................................................................................................. 23Results ................................................................................................................................... 24

Fabrication and Assembly .................................................................................................... 26

Flight Test and Analysis ..................................................................................................... 27

Motivation ................................................................................................................................. 27

Deriving glide ratio ................................................................................................................... 27

Diagnosis of preliminary flights ............................................................................................... 28

Analysis of flight data ............................................................................................................... 28

Results and Evaluation ............................................................................................................. 29

Verifying Lift .......................................................................................................................... 30

Verifying CL/CD ..................................................................................................................... 30

Recommendations .................................................................................................................... 30

Conclusion ......................................................................................................................... 31

References ......................................................................................................................... 32

Appendices .......................................................................................................................... a

Requirements and Parameters .................................................................................................. a

Fabrication Design and Assembly ........................................................................................... b

Fabrication Calibration and precision check...................................................................... c

Fabrication Customisation and innovation in design ........................................................ d


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i

List of Figures

Figure 1: Project Overview ............................................................................................................. 1

Figure 2: Methodology ................................................................................................................... 2

Figure 3: Dihedral Effects ............................................................................................................... 7

Figure 4: GEMINI (Cl vs alpha) ........................................................................................................ 9

Figure 5: GEMINI (Cl vs Cd)............................................................................................................. 9

Figure 6: ClarkY (Cl vs alpha) ........................................................................................................ 10

Figure 7: ClarkY (Cl vs cd) ............................................................................................................. 10

Figure 8: NACA64010 (Cl vs alpha) .............................................................................................. 10Figure 9: NACA64010 (Cl vs Cd) ................................................................................................... 10

Figure 10: SD8020 (Cl vs alpha).................................................................................................... 10

Figure 11: SD8020 (Cl vs Cd) ........................................................................................................ 10

Figure 12: Comparing Xfoil data .................................................................................................. 11

Figure 13: Comparing actual data ................................................................................................ 11

Figure 14: Cl vs alpha for short listed wing airfoils ...................................................................... 12

Figure 15: Cl/Cd vs alpha for short listed wing airfoils ................................................................ 12

Figure 16: Cl vs alpha for short listed tail airfoils......................................................................... 13

Figure 17: Cl / Cd vs alpha for short listed tail airfoils ................................................................. 13

Figure 18: ComparingTurbulence Models (Cl vs Cd) .................................................................. 15

Figure 19: ComparingTurbulence Models (Cl vs alpha) ............................................................. 15

Figure 20: Comparing Various Formulations .............................................................................. 15

Figure 21: Pressure Contour for Baseline ................................................................................... 16

Figure 22: Combination of Rectangular and Tapered Section ................................................... 16

Figure 23: CL vs CD for various planforms .................................................................................. 16

Figure 24: CL vs alpha for various planforms .............................................................................. 16

Figure 25: CL / CD vs alpha for various planforms ...................................................................... 17

Figure 26: Flap Effectiveness vs Surface Ratio ............................................................................ 20

Figure 27: Percentage deviation in Cut area vs Wire Current (for various cutt ing speeds) .... 23

Figure 28: Comparison between Actual and Fabricated Coordinates for GEMINI airfoil ........ 24

Figure 29: Comparison between Actual and Fabricated Coordinates for NACA0012 airfoil ... 24


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ii

Figure 30: Percentage deviation in dimension vs Position (GEMINI) ........................................ 24

Figure 31: Percentage deviation in dimension vs Position (NACA0012)................................... 24Figure 32: Comparing Cl vs alpha between Original and Fabricated GEMINI .......................... 25

Figure 33: Comparing Cl vs Cd between Original and Fabricated GEMINI ............................... 25

Figure 34: Comparing Cl vs alpha between Original and Fabricated NACA0012 ..................... 25

Figure 35: Comparing Cl vs Cd between Original and Fabricated NACA0012 .......................... 25

Figure 36: Assembly ...................................................................................................................... 26

Figure 37: Unpowered Glide ........................................................................................................ 27

Figure 38: 3D Flight path on map ................................................................................................ 29

Figure 39: Flight path - Altitude h (m) vs Distance R (m) ........................................................... 29

Figure 40: Assembled Units ............................................................................................................ c

Figure 41: Individual mechanical parts.......................................................................................... c

Figure 42: Soldered PCB ................................................................................................................. c

Figure 43: Individual Electronic Parts ............................................................................................ c

Figure 44: Wire Joint ....................................................................................................................... c

Figure 45: Markings for wire height .............................................................................................. c

Figure 46: Spirit level for horizontal alignment ............................................................................ c

Figure 47: Markings for parallel alignment ................................................................................... c

Figure 48: Set-up for Fabrication precision check ........................................................................ d

Figure 49: Close-up view to acquire coordinates ......................................................................... d

Figure 50: Flexibility in in adjusting tail position and angle ......................................................... d

Figure 52: Close-up view on control horns and rods.................................................................... d

Figure 51: Sleeve cuts to house structural reinforcements ......................................................... d


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iii

List of Tables

Table 1: Designated Objectives ...................................................................................................... 2

Table 2: Aircraft Specifications ...................................................................................................... 3

Table 3: Classification of Parameters ............................................................................................ 3

Table 4: Literature Survey Findings for Airfoil .............................................................................. 6

Table 5: Literature Survey Findings for Planform ......................................................................... 6

Table 6: Recommendation for Aileron .......................................................................................... 8

Table 7: Recommendations for Elevator and Rudder .................................................................. 8

Table 8: Scope of analysis............................................................................................................... 8Table 9: Selected Data for Wing airfoils ...................................................................................... 12

Table 10: Selected Data for Tail airfoils ....................................................................................... 13

Table 11: Short list of Turbulence Models from literature ......................................................... 14

Table 12: Planform Cases ............................................................................................................. 16

Table 13: Fluent results for various planforms ........................................................................... 17

Table 14: Computation results for various control surfaces...................................................... 20

Table 15: Innovation in mechanical design ................................................................................. 21

Table 16: Fabrication Procedures and Time taken ..................................................................... 26

Table 17: Diagnosis of Preliminary Flights .................................................................................. 28

Table 18: Selected Flight data ...................................................................................................... 29

Table 19: Parameters from optimization ...................................................................................... a

Table 20: Breakdown of Mechanical Parts.................................................................................... b

Table 21: Breakdown of Electronic parts ...................................................................................... b


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iv

List of Symbols

Angle of attack, deg Aspect ratio - Span, m Sidewash, deg Chord, m Mean chord, m Sectional drag coefficient Drag coefficient Aileron Control Power, deg-1 Sectional lift coeff icient Slope of sectional lift curve, deg-1 Lift coefficient Slope of sectional lift curve, deg-1 Slope of rolling moment coefficient due to sideslip

Slope of pitching moment coefficient, deg-1

Elevator Control Power, deg-1 Slope of yawing moment coefficent due to sideslip, deg-1 Rudder Control Power, deg-1 Aileron deflection, deg Elevator deflection, deg Rudder deflection, deg

Drag, N Downwash angle, deg Dihedral angle, deg Lift , N Tail efficiency Reynolds Number


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v

Density, kg/m3

Sidewash angle, deg Aileron surface area, m2 Elevator surface area, m2 Rudder surface area, m2 Horizontal tail surface area, m2 Vert ical tail surface area, m2 Flap effectiveness Freestream velocity, m/s Vertical tail volume ratio - Horizontal tail volume ratio - Weight, N Distance of centre of gravity from wing leading edge, m Distance of neutral point from wing leading edge, m


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1

Introduction

Background and Overview

The interest in Unmanned Air Vehicles has increased tremendously over the past decade

and a rise in its employment has been predicted (1) for the next twenty years to come.

Studies have been carried out on overall aspects of UAV design, such as cost-effectiveness

(2) and multidisciplinary optimization (3).

Currently, in the area of wing studies, majority of the work are dedicated the assessment of

novel concepts such as inflatable and retractable wings (4), (5). This paper focuses on the

development of conventional wings for a Class 1 (as defined in (1)) UAV. The entire process

will be covered, from the design and analysis to fabrication using a computer controlled

system. Finally, a flight evaluation was conducted to verify the design. Hence, this project

encompasses a larger intent, which is to assemble an actual UAV with mission capabilities.

Collaboration with three other team members is required, each handling an aspect of the

UAV. The diagram below depicts an overview.

Objectives

The project can be divided into three main components namely (1) Design and Analysis, (2)

Fabrication and (3) Flight Test. Each component comprises of designated objectives to be

fulfilled to complete the assignment.

Reference

Support

Wing and TailParameters

Optimization

UAV with capabilities

Project Requirements

ConstraintPropulsion

Structure

Establish objectives

Fulfill Objectives

Analysis

results

Figure 1: Project Overview


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2

Design and Analysis

Methodology

Basically, the task of designing involves the manipulation of physical parameters to alter the

aerodynamics. In turn, this will have direct influence over the aircraft performance and

stability, and hence, its mission capabilit ies.

The design process begins with identifying the desired performance and stability, as well as

the various design parameters to fulfill mission requirements. Subsequently, through

application of fundamental theory and literature reviews, a shortlist will be generated for

each parameter. Subsequently, a series of computational analyses will be performed to

justify the final selection. With the parameters generated, fabrication of the wing prototype

can then be carried out.

Components Designated Objectives

(1) Design and Analysis Designing solutions (i.e. selection of appropriateparameters) to meet mission requirements

Justification using computational analysis(2) Fabrication Development of a CNC solution to enable rapid and

precise production of 3D wings

Verification of equipment reliabilit y and worthiness(3) Flight Test and Analysis Demonstration of airworthiness

Evaluation of actual f light data

Requirements and

Parameters

Literature

SurveyAnalysis Parameters for

Fabrication

Table 1: Designated Objective

Figure 2: Methodolog


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3

Requirements and Parameters

Mission Requirements

The mission requirements of the UAV govern the design of wing. The table below shows the

general specifications of the aircraft modeled after typical UAVs available in the market.

Specifications

Designated Task short range surveillance

Payload Total aircraft weight < 1kg with Camera and data logger

Configuration Pusher, high-wing

Takeoff/ recovery Hand launched takeoff and Belly assisted landing

Maneuverability Turning radius of


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4

Critical Performance parameters

Lift for aircraft vsThe relationship between the lift coefficient and its corresponding angle of attack is the

most essential data for wing and tail design. It is primarily governed by the airfoil selection

and the planform. Aerodynamic concepts have been developed to link the sectional Cl of a

2D airfoil to 3D wings of finite span using Lifting line theory. It states that (6)

=

+ 2

LLT has proven to be reasonably accurate for straight wings in regions before stall .

Range and Endurance

vs and/Other than drag estimation, the relationship between drag and lift coefficient is crucial in

determining the range and endurance of the aircraft. In performance terms (7),

Range

=

1

=

1

Endurance

= 1

However, it must be noted that for radio controlled flight range is also limited by the radius

of the signal strength of transmitter and the endurance cannot last beyond its battery

duration.


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5

Determining Stability Requirements

Flight stability is a necessity for typical aircrafts. Conditions for static stability, which is the

tendency of the platform to return to its initial position after a disturbance (8), are shown

below.

Longitudinal Stability

Slope of aircraft pitching moment curve,

= + + Contribution to pitching moment from wing and tail

= ; = 1

Lateral Stability

Slope of aircraft pitching moment curve,

= + Contribution to yawing moment from vert ical tail,

= 1 +

Slope of aircraft rolling moment curve is largely dependent on the dihedral,

= .2 ()/

The criteria for static stability is given by

< 0, > 0, < 0Literature Survey

Findings for Airfoil

For considerations involving airfoil selection, literature review yields the following.


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6

Shape Key characteristics Applications

Heavily

CamberedHigh L, low D, low CM

Wings on high endurance UAVs, RC

sailplanes

Moderately

CamberedHigh L, low D, moderate CM

Wings on short range UAVs, RC

sports plane

Symmetrical Moderate L, Moderate D, low CMHorizontal and Vertical Tail,

Aerobatics

Empirical aerodynamic data is compiled in (9) for a selected number of airfoils in each

category. For the wing airfoil section, moderately cambered airfoil is highly recommended

for the assigned mission profile (10). The tail sections (horizontal and vertical), symmetrical

airfoils is the only intuitive option as provisions must be made for lift to be generated on

upper and lower surface.

Findings for Planform

The planform of a wing influences the lift distribution on it, and thus the flight performance.

Findings from (7), (10) are summarized below.

Profile Advantage Disadvantages

Elliptical1. Lowest induced drag

2. Stalls evenly across spans1. Difficult to fabricate

Rectangular1. Constant Re reduces risk of t ip stall

2. Easy to fabricate

1. Higher induced drag

2. Higher bending moments

Tapered

1. Lower induced drag than rectangular

planform

2. Smaller bending moment

1. Risk of t ip stall

Combined

Rect. &

tapered

1. Approach advantages of elliptical

2. Easier to fabricate

1. Hazards of t ip stall

remains

Table 4: Literature Survey Findings for Airfoi

Table 5: Literature Survey Findings for Planform


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7

Despite the advantages of elliptical planform, this option is eliminated due to complexities

involved in its production. Hence, only the feasibility of introducing taper will be explored.

Here, the optimum planform selection is a compromise between structural and lower drag

benefit of small and aerodynamic lift benefit of large (7)This prompts the investigation

of a combined rectangular and tapered planform.

Planform of tail sections are of secondary concerns. Their primary role is to provide stability

in the UAV and this has been resolved in the optimization process through the allocation of

dimensions. Horizontal tail will adopt a rectangular profile. Vertical tail will adopt a tapered

ratio of 0.8. To maximize rudder area, sweepback will also be introduced such that trailing

edges align vertically.

Concept of Dihedral

Dihedral is known to bring about rolling stability. A dihedral angle of can bring about

stabilizing effects by altering the resultant (positive will lead to higher lift) when

sideslip occurs. Given that the sideslip and dihedral angles are small,

= = .

The change in angle of attack will in turn alter the lift on both sides of the wing, hence

resulting in a restoring moment. Recommendations from (10) yield an angle of 2 degrees.

Figure 3: Dihedral Effect


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8

Control Surfaces

There are two main aspects to the design of control surfaces, i.e. their position and size.

Varying them will give different degrees of control effectiveness in terms of roll, pitch and

yaw. Findings from (10) yield preliminary guidelines for the various surfaces.

Type of aileron Strip aileron

/ 0.051 to 0.c / b 0.18c from trailing edge / 0.3b

Elevator Rudder

/ 0.3 to 0.35 / 0.3 to 0.5

Analysis

Scope

From the previous section, the tasks for the various parameters can now be allocated

Tasks

Airfoil Selection within the moderately cambered category

Planform Selection of the best combination of rectangular and taper

Dihedral Verifying the angle from literature with theoretical analysis

Control Surfaces Verifying the sizes from literature with theoretical analysis

Analysis will be focused on Wing. For tail sections, the scope of this project only requires

them to fulfill the function of pitch and yaw control, as well as to maintain flight stability.

Table 6: Recommendation for Aileron

Table : Recommendations for Elevator and Rudder

Table 8: Scope of analysi


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9

Airfoil Analysis and Selection

Validating Xfoil

Background and Motivation

Xfoil is an interactive program for the design and analysis of subsonic isolated airfoils. It is

widely received as a credible tool (11), (12) for analysis of airfoil by coupling viscous and

inviscid formulations. The main purpose of validating Xfoil is to extend the limited library of

airfoil data in the most efficient manner. Available literature (9) only have data of a few

airfoils and are limited to Re at intervals of 5 10. Besides this, incorporating a wider

range airfoil will improve the credibility of the final selection. Finally, given Xfoils relatively

short computation time, aerodynamic data can be generated quickly across different airfoils.

Execution and Evaluation

Data from available literature will be compiled and compared with the plots from Xfoil

under the same Re. This is carried out for 4 different airfoils at = 10 where real data isavailable from (9). They are Clark Y, GEMINI, NACA64-A-10 and SD8020.

Data accuracy

Figure 4: GEMINI (Cl vs alpha) Figure 5: GEMINI (Cl vs Cd)


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10

From the graphs, it is observed that the slope of the lift curves generated by Xfoil is fairly

accurate. The highest deviation belongs to Clark Y, with a percentage of 4.91%. Besides this,

the stall patterns for the wing candidates are well approximated too. With exceptions to

NACA0009 It can be seen also that viscous formulations are well documented in Xfoils

codes as drag estimations are accurate at values before stall.

Figure 6: ClarkY (Cl vs alpha) Figure : ClarkY (Cl vs cd)

Figure 8: NACA64010 (Cl vs alpha) Figure 9: NACA64010 (Cl vs Cd)

Figure 11: SD8020 (Cl v Cd)Figure 10: SD8020 (Cl v alpha)


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Data trends

To further justify the use of Xfoil to compare and contrast data of different airfoils, the

trends for the lift curves are examined. It is observed that in terms of stall angles, (),and (), the order is the same for both the actual and Xfoil data.

Applying Lifting Line Theory to determine preliminary lift criteria

With Xfoil proven to be a credible data generator, data is generated for 8 airfoils, doubling

the size of data at hand. To begin, the required lift coefficient for the finite wing has to be

determined. For a 1 kg UAV cruising at a speed of 15m/s,

= 12 =

9.81

0.5 1.225 15 0.204 = 0.349

Using Lifting Line Theory earlier, as well as introducing a factor of 1.1, the minimum

sectional

was can be determined

= = 1.1 + 2 = 0.494Determining stability requirements

For Stability, the minimum criteria is < 0.017 as imposed by the opt imization process =

1

Figure 12: Comparing Xfoi dataFigure 13: Comparing actual data


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12

Substituting values from optimization, the minimum tail lift slope,

= 11 2 +

= 11 27.0180.687

(0.157) + 0.017

Where will be resolved after selection of wing airfoil

Results and Evaluation

Wing Lift Criteria and Stall Pattern

Table 9: Selected Data for Wing airfoils

Clark E197 GEMINI NACA 2415

Max 1.38 1.15 1.14 1.22Max/ 68 68 62 60 @=5o 0.82 0.76 0.8 0.75

/

@=5o 68 55 55 54

Stall angle 11 13 14 14

Stall pattern

Relatively

Sharp

Gentle over

range of 4

degrees

Gentle over

range of 5

degrees

Relatively

Sharp

Figure 14: Cl vs alpha for shortlisted wing airfoils Figure 15: Cl/ Cd vs alpha for shortlisted wing airfoil


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13

All of the airfoil fulfills the minimum sectional Cl. Comparing all aspects, GEMINI airfoil gives

the best overall result. E197 comes close however it loses out slightly over the stall pattern,

which is crucial for short range RC flight.

Cd follows a nearly vertical trend, constant drag for varying wing loadings which will aid in

the design of propulsion system (13).

Tail Stabili ty Criteria

Table 10: Selected Data for Tail airfoils

NACA64A-010 SD8020 NACA009 NACA0012

Max 0.7 0.92 0.84 1Max/ 35 45 42 45 @=5o 0.6 0.6 0.6 0.6@=5o 0.08 0.08 0.08 0.08/ @=5o 35 45 42 45Stall angle 6 10 10 10

Stall pattern Moderatelygentle

ModeratelySharp

ModeratelySharp

ModeratelySharp

With GEMINI selected as wing airfoil and applying the Lifting Line theory,

= + 2 = 0.0747 7

9= 0.0581

Figure 16: Cl vs alpha for shortlisted tail airfoil Figure 17: Cl / C vs alpha for shortlisted tail airfoil


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14

> 0.0123 For all the tail airfoils selected, they are able to fulfill the stability criteria above. SD8020 and

NACA0012 both present themselves to be feasible options for tail airfoil. NACA0012 is

selected.

Planform Analysis and Selection

Motivation

The selection of the planform requires analysis on the 3D profile of the wing. The theoretical

formulation of LLT is insufficient as it assumes an inviscid model. On the other hand,

although Xfoil accounts for viscous effects, it is only limited to 2D airfoil. The CFD software

Fluent provides the solution to this problem. The wing model will be created in Solidworks

and transferred to Gambit for meshing.

Turbulence model analysis

The current flow problem belongs to the low Re category. Findings from (14) have

shortlisted 3 suitable turbulence models, which will be assessed in this section.

Table 11: Shortlist of Turbulence Models from literature

Key Features

Spalart-Almaras Solves for eddy viscosity

K-Omega (standard) Calculates specific turbulence dissipation rate

K-Omega (Shear Stress Transportation) Account for transport of turbulent shear stress

Plotting the coefficients of lift and drag at various angles of attack yield the following


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15

From the graph, it can be observed that the standard version of k-omega model does not

agree with the other two especially in terms of drag estimation. Eliminating it leaves the

Spalart-Almaras model and the modified K-omega model. The latter emerged a better

option as it is able to model flow separation at high with a decline in lift coefficient unlike

the straight line trend in SA.

Further Justifications

To further justify the selection, results from 2D analysis and Lifting Line Theory are

compared with the SST model. A significant discrepancy can be observed between for the

LLT model due to its inability to account for viscous effect.

Figure 18: ComparingTurbulence Models (Cl vs Cd)Figure 19: ComparingTurbulence Models (Cl vs alpha)

Figure 20: Comparing Various Formulation


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16

In addition, the pressure contour plot of SST displays a realistic distribution, where losses

can be observed at the wing tips due to the trailing vortex.

Results and Discussion

With the best k-omega model selected, data is generated for 4 different permutations of

rectangular and taper planform.

Table 12: Planform Cases

Case 1 2 3 4

y 0.5 0.5 0.75 0.75

0.5 0.75 0.5 0.75

Results

y

Figure 21: Pressure Contour for Baseline

Figure 22: Combination of Rectangular

and Tapered Section

Figure 23: CL vs CD for various planformFigure 24: CL vs alpha for various planform


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17

Table 13: Fluent results for various planforms

Baseline 1 2 3 4

Max 0.9177 0.9780 0.9482 0.9551 0.9473Max/ 5.5702 5.7109 5.7330 5.7382 5.6803 0.0488 0.0502 0.0495 0.0485 0.0487 @=5o 0.3637 0.3881 0.3851 0.3817 0.3766 @=5o (N) 10.225 9.547 10.150 10.060 10.257

/ @=5o 5.2599 5.4538 5.4801 5.5051 5.4631

Verification for Lift

To calculate lift ,

= 12.

For baseline, the lift at 15 m/s at 5

o

L = 10.225 N. This further verifies that the airfoil

selection provides sufficient lift for the aircraft of 1 kg (9.81 N).

Evaluation Drag Reduction vs Practicality

The results from various combinations do not exhibit data trends pertaining to variations in

taper ratio and the span of the rectangular section. The intent is to obtain the permutation

Figure 25: CL / CD vs alpha for various planforms


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18

which best approximates an elliptic planform, which is best approximated in case 3. This

combination gives the lowest drag coefficient and the highest glide ratio / at t rim flight.On the other hand, combinations which deviates from elliptical planform i.e. shorter

rectangular sections at y theis higher.

Although case 3 appears to be the best option, the rectangular planform is preferred. Firstly,

the savings on is rather insignificant (0.6147% reduction), with a penalty on its lift due

to its reduced surface area. In addition, the risk of incurring tip stall is higher for a tapered

planform, which will lead to loss of aileron control. Finally, with its ease of fabrication,

rectangular planform presents itself as the most practical option.

Dihedral Analysis and Computation

For a rectangular wing, the earlier formulation for roll stability due to sideslip becomes,

=

= From (15) and (16), the value of -0.125 is obtained for for Class 1 UAVs. This will give adihedral angle of 1.636. Available instrument for measurement is only accurate up to

1for fabrication. As such, the dihedral of 2will be adopted.

Control Surfaces Analysis and Computation

Concepts and Formulations

To quantify terms for analysis, the flap effectiveness parameter (8) is first introduced.

Generally, it can be expressed as the change in angle of attack due to the surface deflection,

=


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19

For each control surface, i.e. aileron, elevator and rudder, there is a required control power

which will govern their respective effectiveness parameter. From (8),

Aileron Control Power (for rolling), applying strip integration for a rectangular wing,

=2

= ( )

Elevator Control Power (for pitching),

= =

=

=

Rudder Control Power (for yawing),

=

=

=

=

Computation with data from literature

Typical values of control power for aircrafts similar to Class 1 UAVs can be obtained from

empirical findings in (15) and (16). Values of can be computed then. Finally, the control

surface area can be derived from the relationship between the surface ratios and

as

shown below (8).


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20

Figure 26: Flap Effectiveness vs Surface Ratio

Table 14: Computation results for various control surfaces

Ailerons Elevator Rudder

Control Power 0.181 -1.9 -0.12

0.1794 0.5366 0.6676 0.05 0.33 0.45

The values of the ratios fall well within the guidelines stated earlier in literature surveys, and

hence they will be employed in fabrication.

Fabrication

Implementing CNC Solution

Motivations

To meet the fabrication requirements, the process must involve a Computer Numerical

Control (CNC) method. Instead of adopting the method of arranging 2D precision cuts into

wingspan, the design of a 3D foam cutter is proposed. Despite the uncertainties in reliability,

the advantages are numerous.

1. Offers precision and accuracy in shaping complex geometries compared to manualmeans of arranging 2D sections

2. Capable of rapid prototyping, hence allowing extensive tests to be carried out


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3. Allows flexibility in re-configuration of wing for different mission profile4. DIY machine costs only a fraction (


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from PCB to motors. To ensure no errors in circuitry, voltage tests carried out using

mulitmeter.

Software

Research has found several CNC softwares. GMFC is justified to be the best option. It is

easily available online for free, with good reviews awarded. Besides this, there will not be

any compatibility issues as GMFC works seamlessly with FoamPro PCB.

System Calibration and Optimization

Synchronizing Software with Electronics

In preliminary testing, it was ensured that inputs into the PC results in a correct

corresponding response from the motor.

Carriage Positioning and Alignment

The positioning and alignment of carriages is important to ensure precision in cutting. Firstly,

using a spirit level, the entire setup is calibrated to the level position. Markings were also

placed at appropriate locations facilitate the parallel alignment of carriages and the

positioning of wire to the horizon. It is noted that markings are accurate up to 1 mm.

Optimization of Cutting

Motivation and Procedures

Before proceeding to the accuracy tests, it is necessary to determine the configuration for

optimum wire performance. A smooth cut depends on the cutting speed as wire heat

(controlled by varying current magnitude).

Issues with Underestimation Issues with Overestimation

Wire heat Unable to melt foam without contact Excessive kerf radius

Cutting Speed Prolonged heating Insufficient heat leading to contact


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As such, investigations are conducted on these two factors, current settings and cutting

speed. Trial cuts are carried out on scrap foam pieces of equal width of 2 cm, through a

same rectangular profile of 50.0 mm x 40.0 mm. Subsequently, deviations in the cut area

are tabulated in graphs below. Dimensions are measured using vernier calipers with

accuracy of 0.1Results

Figure 27: Percentage deviation in Cut area vs Wire Current (for various cutting speeds)

Cuts are carried out for 4 different current settings at 4 different speeds. At the cutting

speed of 1.25m/s and current output of 1.2 A, the deviation is the least among the trends,

hence establishing itself at the optimum point .

Fabrication Precision Analysis

Motivation and Procedures

With the system calibrated and optimized, the reliability can now be tested. To demonstrate

the precision of the foam cutter, investigations have to be carried out on the shape of the

airfoil. Samples cut sections of the wing and tail are fabricated and their coordinates are

plotted out using microscope magnifier and a X-Y table. The accuracy of the X-Y table is

0.001. The set-up is show in the appendix.


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Results

Deviations from input

Data coordinates obtained (in green) are scaled to the chord length and they are compared

with the original coordinate plot (red) which was uploaded to the foam cutter.

Figure 28: Comparison between Actual and Fabricated Coordinates for GEMINI airfoil

Figure 29: Comparison between Actual and Fabricated Coordinates for NACA0012 airfoil

Through visual observation, one can hardly observe any difference. As such, graphs are

plotted to display the percentage deviations. It is shown that the leading and trailing edges

have the highest discrepancies due to the complications in fabrication.

Figure 31: Percentage deviation in dimension vs

Position (NACA0012)

Figure 30: Percentage deviation in dimension vs

Position (GEMINI)


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CFD verification

For an airfoil, the most practical form of precision check is to evaluate the aerodynamic

results rather than the dimensional differences. This calls for Xfoil analysis to be carried out

on the coordinates of fabricated samples.

Comparing the graphs for GEMINI, the fabricated sample has a higher lift curve slope,

before experiencing an earlier but gentler stall. This could be attributed to the onset of

separation as a result of the blunt trailing edge. However, applying the same analysis earlier,

the lift requirement is met as the Clat cruise=5o is the same. Lower drag is also observed.

Figure 32: Comparing Cl vs alpha between Original

and Fabricated GEMINI

Figure 33: Comparing Cl vs C between Original andFabricated GEMINI

Figure 34: Comparing Cl vs alpha between Original

and Fabricated NACA0012Figure 35: Comparing Cl vs C between Original andFabricated NACA0012


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For NACA0012, there are hardly any observable differences for both lift and drag curves. As

the effects on aerodynamics are not significantly critical, the fabrication precision is deemed

acceptable.

Fabrication and Assembly

Procedures

With the system optimized and its precision verified, the way is paved for fabrication. The

procedures are listed below. To demonstrate the capability of rapid prototyping, the time

taken for each step is tabulated as well. A set of wings and tail can be ready for assembly in

less than 100 minutes.

Table 16: Fabrication Procedures and Time taken

Steps Time taken (mins)

1 Cutting of core sections of Wing and tail 20

2 Cutting of control surfaces and joining to core sections 40

3 Attaching control horns and rods 40

Assembly

The manufactured set is finally assembled into an aircraft. To facilitate the process, several

modifications are introduced. Sleeve cuts customized to house skeletal support. The

innovative tail design also allows flexibility in adjustments of position and angle.

Figure 36: Assembl


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Flight Test and Analysis

Motivation

The best testament for the wing design is to demonstrate its airworthiness. Flight also

provides the most practical mean to verify results from computational analysis. By

equipping the UAV with a flight instruments and data logger, information on flight can be

collected. The aircraft is installed with a GPS tracker, which will record its altitude as well as

latitude-longitude. The air speed is also collected by means of a pitot tube. Evaluation can

then be carried out by comparing the results with the ones from earlier analysis.

Deriving glide ratio

The glide ratio presents itself as a credible indicator for evaluation to be made. Besides

being a representative figure for range and endurance, it can also be easily derived. For an

unpowered flight,

Figure 37: Unpowered Glide

= =

= = 1 = With the altitude (h) and ground distance (R) recorded, the glide ratio can be determined.


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Diagnosis of preliminary flights

Prior to the final flight tests, several unsuccessful prototypes were built. Although the main

issue lies in the lack of skill in flying RC models, there were other fundamental problems

which were addressed before a successful model was constructed.

Table 17: Diagnosis of Preliminary Flights

Problems Rectifications

Prototype 1 Excessive cross sectional arealeading to unnecessary drag

Weakness in tail boom

Replaced Fuselage with a smallerone

Prototype 2 Discovered the lack of thrust Replaced propeller with a larger onePrototype 3 Weakness in horizontal structure Replaced aluminium rods with

carbon fibre rods

Analysis of flight data

With the issues resolved, successful flights were carried out and the data were collected in

one of them. Coordinates of the flight path will be plotted on a map (Google Earth).

Representative flight profiles for cruise and glide will be examined. The flight angle of attack

is determined by considering the in-built incidence of 5o and flight path with respect to

the horizon. With this reference angle, comparisons can then be made with theoretical

analysis results.


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Results and Evaluation

Figure 38: 3D Flight path on map

Figure 39: Flight path - Altitude h (m) vs Distance R (m)

Table 18: Selected Flight data

Profile / Sector Powered Cruise Theory Unpowered Glide Theory

5o 5o 14o 14oAverage speed 15.4 15 13 15

0.331 0.3637 - -/ - - 3.97 4.549


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Verifying Lift

By demonstrating that aircraft could climb, the lift criterion is met. To further verify,

can be inferred from a straight and level flight (at the designated cruise speed andwhere L=W.

@ = 12 =

12 =

9,81

12

1,225 15.4 0.204= 0.331

It can be observed that the lif t coeff icient in real flight is only slightly lesser (9%). This could

be attributed to interference from the aircraft body.

Verifying CL/ CD

With data input from the glide section,

@ =

=

66 38702.4

591.3

= 3.97

Comparing the flight test result and the theoretical value, a 12.7% deviation is observed.

This is expected as it only represents the glide ratio of the wing and not the entire aircraft.

Addit ional drag contributions from other components will result in a lower glide ratio.

Recommendations

This flight test also highlights areas where improvements can be implemented. To conduct

an accurate measurement of aerodynamic forces, a wind tunnel analysis can be employed.

However, detailed cost-benefit analysis must be carried out to ensure its cost-effectiveness.

In terms of material usage, other types of foam can be explored to seek a stronger and

lighter option. Again, its cost-effectiveness must be weighed. Subsequently, sheeting can

also be used to strengthen the wing as well to ensure a smoother air f low.


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Conclusion

The designated objectives for each section were met. This completes the entire wing

development, from design and analysis, to the optimization and evaluation of fabrication

process, and finally to its implementation on a actual UAV where flight analysis is performed.

With a comprehensive coverage on the fundamentals of a conventional wing design and

manufacture, this project is provides an excellent platform for further studies to be

conducted. As demonstrated, the capability of rapid prototyping encourages extensive tests

to be conducted. Coupled with an established design process, this grants the ability to

customize wings to perform optimally for different missions. More design parameters e.g.

geometric twist can be introduced. External features which augment aerodynamics e.g.

winglets can also be tested by mounting them on the baseline.


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References

1. Defense, US Department of.Unmanned Systems Roadmap 20072032. 2007.

2. Hypothesis about cost-effective unmanned offensive airplane vehicles. Chiesa, Sergio, et

al. 2000, Aircraft Design.

3. Mulitdisciplinary Optimisation of Unmanned Aerial Vehicles (UAV) Using Multi-Criteria

Evolutionary Algorithms. Gonzalez, Luiz. F., et al. s.l. : 6th World Congress of Structural and

Multi-criteria Evolutionary Algorithms, 2005.

4. Inflatable and Rigidizable Wings for Unmanned Aerial Vehicle.Cadogan, David, Graham,

William and Smith, Tim. s.l. : AIAA, 2003. 2003-6630.

5. Design, development and testing of a morphing aspect ratio wing using an inflatable

telescopic spar. Blondeau, Julie, Richeson, Justin and Pines, Darryll J. s.l. : AIAA, 2003. 2003-

1718.

6. Bertin, John J.Aerodynamics for Engineers. 1997.

7. Anderson, John D.Aircraft Performance and Design. 1998.

8. Nelson, Robert C.Flight Stability and Automatic Control. 1998.

9. Selig, Michael S., et al.Summary of Low-Speed Airfoil Data Volume 1. 1995.

10. Stinton, Darroll.The Design of an Airplane.2001.

11. Multi-objective evolutionary optimization of subsonic airfoils by meta-modelling and

evolution control. Angelo, S D and Minisci, E.s.l. : Proceedings of the Institution of

Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2007, Vol. 221.

12. The aerodynamic shape optimization of airfoils using unconstrained trust region methods.

Lee, Jaehun, Jung, Kyungjin and Kwon, Jang Hyuk. s.l. : Engineering Optimization, 2009 , Vol.

41.

13. Aircraft Design: A Conceptual Approach. Raymer, D. 2006, AIAA.

14. Catalano, Pietro and Amato, Marcello.An evaluation of RANS turbulence modelling for

aerodynamic applications . s.l. : Aerospace Science and Technology, 2003.

15. Rapid Flight Test Prototyping System and the Fleet of UAVs and MAVs at the Naval

Postgraduate School. Kaminer, Isaac I., et al. s.l. : AIAA, 2000.


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16. UAV stability derivatives estimation for hardware-in-the-loop simulation of Piccolo

autopilot by qualitative flight testing. Garcia, Esteban Gonzalez and Becker, Jon. s.l. :

Aerodreams, 2000.

17. Weick, Fred E. and Jones, Robert T.Resume and analysis of NACA lateral control

research.s.l. : NASA, 1937.


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Appendices

Requirements and Parameters

Table 19: Parameters from optimization

Dimension Parameters Performance Parameters

wing aspect ratio 7 weight 10.8 N

horizontal tail aspect ratio 5 angle of attack 5 degree

vertical tail aspect ratio 2 velocity 14.8 m/s

fuselage diameter 0.10 m wing loading 5.4 kg/m2

fuselage length 0.26 m Cm0 0.086

CG distance from wing

leading edge0.05 m Cmalpha -0.982

wing leading edge distance

from fuselage tip0.09 m static margin 15.70%

CG to tail distance 0.68 m

tail incident angle -0.6


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Fabrication Design and Assembly

Table 20: Breakdown of Mechanical Parts

Section Component Section Component

Y axis carriageVert ical square stand

Motor

Housing

L Bracket Front Mount (X)

Drawer slide L Bracket Rear Mount (X)

X axis carriage

L bar L Bracket End Plate (X)

Drawer slide

Actuator /

Connectors /

Adaptors

Threaded rod

Threaded rod Motor Coupler

Wooden base L bracket Connector

X Housing

L bar Threaded Long Nut

Horizontal plate L flat Bracket

Vert ical plateCutter

Nichrome wire

Tensioning device

Table 21: Breakdown of Electronic parts

Component Specification Functions

Controller/ driver Unipolar chopper Connects to PC via parallel port

Stepper Motors 2.1A, 200 S/R Precision control of the lead screw

Power supplies 12, 14 VD Supply power to electronic parts and

timer module on PCB

Variable power supply 30V,7A Supply heat to cutter


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Fabrication Calibration and precision check

Figure 40: Assembled Unit

Figure 42: Soldered PCFigure 44: Wire Joint

Figure 43: IndividualElectronic Parts

Figure 45: Markings for wire heightFigure 46: Spirit level for horizontal

alignmentFigure 4 : Markings for parallel

alignment

Figure 41: Individual mechanical part


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Fabrication Customization and innovation in design

Coordinates display

Video Output

Magnifier

Sample Cut

X-Y table

Figure 48: Set-up for Fabrication precision check

Figure 49: Clos -up view on coordinates acquisition

Figure 50: Sleeve cuts to housestructural reinforcements

Figure 52: Close-up view on contro

horns and rods

Figure 51: Flexibility in in adjusting

tail position and angle

unmanned air vehile (uav) wing design and manufacture

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