Aircraft Design

AS5210: AERODYNAMIC DESIGN

DESIGN OF RC AIRCRAFT Submitted by, GROUP - M4 1. Debolina Dasgupta

(AE12M002)

2. Dharamendr Kumar Bhardwaj

(AE12M004)

3. Jadhav Krishna Balu

(AE12M005)

4. Jijo Unni K

(AE12M007)

5. Jitendra Kumar

(AE12M008)

Submitted to, Dr Luoyi Tao, Dr. G. Rajesh Department of Aerospace Engineering In Partial Fulfilment of the Requirements of AS5210 Aerodynamic Design Jan-May 2013 IIT Madras, Chennai

Contents LIST OF FIGURES............................................................................................ ix LIST OF TABLES ............................................................................................. xi LIST OF SYMBOLS ..........................................................................................xii CHAPTER 1: GOAL DETERMINATION AND MISSION SPECIFICATIONS ............. 1 1.1 INTRODUCTION ............................................................................................................................. 1 1.2 GOAL DETERMINATION................................................................................................................. 1 1.3 MISSION PROFILE .......................................................................................................................... 2 1.4 PRELIMINARY DESIGN CONSIDERATIONS ..................................................................................... 3

CHAPTER 2: LITERATURE SURVEY AND FIRST WEIGHT ESTIMATE ................... 4 2.1 INTRODUCTION ............................................................................................................................. 4 2.2 DATA COLLECTION ........................................................................................................................ 4 2.3 FIRST WEIGHT ESTIMATE .............................................................................................................. 6 2.4 CONCLUSION ................................................................................................................................. 7

CHAPTER 3: SECOND WEIGHT ESTIMATE........................................................ 9 3.1 INTRODUCTION ............................................................................................................................. 9 3.2 AIRFOIL .......................................................................................................................................... 9 3.2.1 Airfoil Data Collection ............................................................................................................ 9 3.2.2 Airfoil Selection .................................................................................................................... 10 3.2.3 Airfoil Operational Characteristics ....................................................................................... 11 3.3 WING DESIGN.............................................................................................................................. 12 3.3.1 Aspect ratio .......................................................................................................................... 12 3.3.2 Wing area (S) ........................................................................................................................ 14 3.3.3 Span Length (b) .................................................................................................................... 14 3.4 SECOND WEIGHT ESTIMATE ....................................................................................................... 15 3.4.1 Payload Weight Calculation ................................................................................................. 15 3.4.2 Power plant Weight Calculation .......................................................................................... 16 3.4.3 Weight Calculation ............................................................................................................... 21 3.5 CONCLUSION ............................................................................................................................... 21

CHAPTER 4: WING LOADING AND THRUST-TO-WEIGHT RATIO..................... 22 4.1 WING LOADING ........................................................................................................................... 22 4.1.1 Wing Loading for Stall Conditions ........................................................................................ 22 4.1.2 Wing Loading for Landing .................................................................................................... 23

i

4.1.3 Wing loading for Cruise conditions ...................................................................................... 25 4.1.4 Wing Loading for Loiter........................................................................................................ 26 4.2 WING LOADING SELECTION ........................................................................................................ 26 4.3 THRUST-TO-WEIGHT RATIO CALCULATION ................................................................................ 27 4.3.1. Thrust-to-Weight ratio for Take-Off conditions.................................................................. 27 4.3.2. Thrust-to-Weight calculation for Climb .............................................................................. 29 4.3.3. Thrust-to-Weight calculation for Vmax .............................................................................. 30 4.3.4. Thrust-to-Weight calculation for turning............................................................................ 31 4.4 SUMMARY OF THRUST-TO-WEIGHT AND SELECTION ................................................................ 31 4.5 WING LOADING FOR SEGMENTS DEPENDENT ON (T/W) ........................................................... 32 4.5.1. Wing Loading for Take-Off conditions ................................................................................ 32 4.5.2. Wing Loading calculation for Climb .................................................................................... 33 4.5.3 Wing Loading for Vmax ........................................................................................................ 33 4.5.4 Wing Loading for turning ..................................................................................................... 34 4.6 CONCLUSION ............................................................................................................................... 34 4.7 REFERENCES ................................................................................................................................ 34

CHAPTER 5: THIRD WEIGHT ESTIMATE AND INITIAL SIZING.......................... 35 5.1 THIRD WEIGHT ESTIMATE ........................................................................................................... 35 5.1.1 Material Selection ................................................................................................................ 35 5.1.2 Weight of the Wing .............................................................................................................. 36 5.1.3 Weight of the Fuselage ........................................................................................................ 41 5.1.4 Weight of Horizontal Tail ..................................................................................................... 42 5.1.5 Weight of Vertical Tail .......................................................................................................... 42 5.1.6 Weight of the Skin................................................................................................................ 43 5.1.7 Third Weight Estimate ......................................................................................................... 44 5.2 INITIAL GEOMETRIC SIZING ......................................................................................................... 45 5.2.1 Fuselage Sizing ..................................................................................................................... 45 5.2.2. Wing Sizing .......................................................................................................................... 45 5.2.3. Tail Sizing ............................................................................................................................. 45 5.3. SUMMARY OF MAJOR DIMENSIONS OF THE AIRCRAFT ............................................................ 48 5.4 REFERENCES ................................................................................................................................ 48

CHAPTER 6: THREE VIEW AND CONFIGURATION LAYOUT ............................ 49 6.1 INITIAL SIZING SUMMARY ........................................................................................................... 49 6.2 THREE-VIEW DRAWING............................................................................................................... 50 ii

6.3 WETTED AREA ESTIMATION........................................................................................................ 52 6.4 INTERNAL VOLUME ESTIMATION ............................................................................................... 53 6.5 CONCLUSION ............................................................................................................................... 53 6.6 REFERENCES ................................................................................................................................ 53

CHAPTER 7: PROPELLER SELECTION.............................................................. 54 7.1 INTRODUCTION ........................................................................................................................... 54 7.2 PROPELLER SIZING ...................................................................................................................... 55 7.3 SUMMARY OF PROPELLER SPECIFICATIONS ............................................................................... 57 7.4 PERFORMANCE RELATIONSHIPS ................................................................................................. 57 7.4.1 Propeller parameter calculation at take-off conditions ...................................................... 59 7.4.2 Propeller parameter calculation for climb conditions ......................................................... 60 7.4.3 Propeller parameter calculation for cruise conditions ........................................................ 61 7.4.4 Propeller parameter calculation for turning conditions ...................................................... 62 7.4.5 Propeller parameter calculation for landing conditions ...................................................... 63 7.5 CONCLUSION ............................................................................................................................... 64 7.6 REFERENCES ................................................................................................................................ 64

CHAPTER 8: IMPROVED DRAG POLAR AND POWER PLANT ESTIMATION...... 65 8.1 INTRODUCTION ........................................................................................................................... 65 8.2 LIFT .............................................................................................................................................. 65 8.2.1 Introduction ......................................................................................................................... 65 8.2.2 Calculation of CLα .................................................................................................................. 66 8.2.3 Calculation of CLmax ............................................................................................................... 66 8.2.4 Calculation of αCLmax ............................................................................................................. 69 8.3 PARASITE DRAG ESTIMATION ..................................................................................................... 70 8.3.1 Flat-plate Skin Friction Coefficient ....................................................................................... 70 8.3.2 Component Form Factor ...................................................................................................... 71 8.2.3 Component Interference Factor .......................................................................................... 71 8.3.4 Miscellaneous Drag .............................................................................................................. 71 8.3.5 Geometric Details ................................................................................................................ 71 8.3.6 Calculation and Summary Table of Parasite Drag ................................................................ 72 8.4 OSWALD SPAN EFFICIENCY FACTOR AND K ................................................................................ 74 8.5 MODIFIED DRAG POLAR .............................................................................................................. 75 8.6 CHECKING FOR WING LOADING IN SEGMENTS INDEPENDENT OF T/W .................................... 75 8.6.1 Wing Loading for Stall Conditions ........................................................................................ 76 iii

8.6.2 Wing Loading for Landing .................................................................................................... 76 8.6.3 Wing Loading for Cruise Conditions ..................................................................................... 76 8.6.4 Wing Loading for Loiter........................................................................................................ 77 8.7 WING LOADING SELECTION ........................................................................................................ 78 8.8 THRUST-TO-WEIGHT RATIO CALCULATION ................................................................................ 78 8.8.1. Thrust-to-Weight Ratio for Take-Off Conditions ................................................................ 78 8.8.2. Thrust-to-Weight calculation for Climb .............................................................................. 79 8.8.3. Thrust-to-Weight calculation for Vmax ................................................................................. 81 8.8.4. Thrust-to-Weight calculation for turning............................................................................ 81 8.9 SUMMARY OF THRUST-TO-WEIGHT AND SELECTION ................................................................ 82 8.10 WING LOADING FOR SEGMENTS DEPENDENT ON (T/W) ......................................................... 82 8.10.1. Wing Loading for Take-Off conditions .............................................................................. 82 8.10.2. Wing Loading calculation for Climb .................................................................................. 83 8.10.3 Wing Loading for Vmax ........................................................................................................ 83 8.10.4 Wing Loading for Turning................................................................................................... 84 8.11 SUMMARY OF POWER REQUIREMENTS ................................................................................... 84 8.12 CONCLUSION ............................................................................................................................. 85 8.13

REFERENCES .......................................................................................................................... 85

CHAPTER 9: ESTIMATION OF CENTRE OF GRAVITY OF AIRCRAFT .................. 86 9.1 INTRODUCTION ........................................................................................................................... 86 9.2 CG OF DIFFERENT COMPONENTS ............................................................................................... 86 9.2.1 Fuselage ............................................................................................................................... 87 9.2.2 Wing ..................................................................................................................................... 88 9.2.3 Horizontal Tail ...................................................................................................................... 89 9.2.4. Vertical Tail.......................................................................................................................... 91 9.2.5 Propeller ............................................................................................................................... 93 9.2.6. Motor .................................................................................................................................. 93 9.2.7. Battery................................................................................................................................. 93 9.2.8 Payload ................................................................................................................................. 94 9.2.9 Summary of the CG location of different components........................................................ 94 9.3 CG LOCATION OF AIRCRAFT ........................................................................................................ 95 9.4 CALCULATION OF CG OF LANDING GEAR ................................................................................... 96 9.4.1 Landing Gear Arrangement .................................................................................................. 96 9.4.2 Landing Gear Weight ........................................................................................................... 98

iv

9.4.3 Landing Gear CG................................................................................................................... 98 9.5 MODIFIED LOCATION OF CG ....................................................................................................... 99 9.6 CONCLUSION ............................................................................................................................. 100 9.7 REFERENCES .............................................................................................................................. 100

CHAPTER 10: STABILITY AND TRIM ANALYSIS OF AIRCRAFT ....................... 101 10.1 INTRODUCTION ....................................................................................................................... 101 10.1.1 Longitudinal Stability........................................................................................................ 101 10.1.2 Lateral Stability ................................................................................................................ 101 10.1.3 Directional Stability .......................................................................................................... 101 10.2 LOCATION OF CENTRE OF GRAVITY ........................................................................................ 102 10.3 NEUTRAL POINT ...................................................................................................................... 102 10.4 PARAMETERS OF WING .......................................................................................................... 103

10.4.1
 ............................................................................................................................... 103

10.4.2 CLα ..................................................................................................................................... 103

10.5 PARAMETERS OF FUSELAGE.................................................................................................... 103 10.5.1 Cmαfus ................................................................................................................................. 103 10.6 HORIZONTAL TAIL PITCHING MOMENT .................................................................................. 105 10.6.1 Dynamic Pressure Ratio () ........................................................................................... 105 10.6.2 Planform Area Ratio () ........................................................................................... 105 10.6.3 Lift-Curve Slope of Horizontal Tail ( ) ...................................................................... 106 10.6.4 Tail Angle of Attack Derivative (  ) ......................................................................... 106 10.6.5 Non-Dimensional Aerodynamic Center x-location (
) ............................................. 107 10.6.6. Calculation of Cmh ............................................................................................................ 107 10.7 EFFECT OF POWER PLANT ON PITCHING MOMENT ............................................................... 107 10.8 LOCATION OF NEUTRAL POINT ............................................................................................... 108 10.9 STATIC MARGIN ...................................................................................................................... 108 10.10 Recalculation at new CG location: ........................................................................................ 109 10.10.1 (
 )New: .................................................................................................................... 109 10.10.2 (Cmαfus)new: ....................................................................................................................... 109 10.10.3 (  )new and (Cmh)new: ............................................................................................. 109 10.10.4 New location of neutral point: ....................................................................................... 110 10.11 MODIFIED VIEWS WITH NEW WING LOCATION ................................................................... 111 10.12 TRIM ANALYSIS...................................................................................................................... 112 10.13 CONCLUSION......................................................................................................................... 116

v

10.14 REFERENCES .......................................................................................................................... 116

CHAPTER 11: PARASITE DRAG ESTIMATION ............................................... 117 11.1 INTRODUCTION ....................................................................................................................... 117 11.2 FLAT PLATE SKIN FRICTION COEFFICIENT ............................................................................... 117 11.3 COMPONENT FORM FACTOR .................................................................................................. 118 11.3.1 Fuselage ........................................................................................................................... 118 11.3.2 Wing and tails................................................................................................................... 118 11.4 COMPONENT INTERFERENCE FACTOR.................................................................................... 118 11.5 LANDING GEAR DRAG ............................................................................................................. 118 11.6 GEOMETRIC DETAILS OF DIFFERENT COMPONENTS .............................................................. 121 11.7 CALCULATION AND SUMMARY OF PARASITE DRAG CALCULATION ....................................... 122 11.8 CONCLUSION ........................................................................................................................... 124 11.9

REFERENCES ........................................................................................................................ 124

CHAPTER 12: FLIGHT PERFORMANCE AND V-n DIAGRAM .......................... 125 12.1 INTRODUCTION ....................................................................................................................... 125 12.2 STALL CONDITIONS ................................................................................................................. 125 12.2.1. Stall Wing Loading........................................................................................................... 125 12.3 CRUISE CONDITIONS ............................................................................................................... 126 12.3.1 CD and CL ........................................................................................................................... 126 12.3.2 V min drag ............................................................................................................................. 126 12.3.3 Vcruise and CL ...................................................................................................................... 127 12.3.4 Cruise Wing Loading......................................................................................................... 127 12.3.5 CD ...................................................................................................................................... 127 12.3.6 Thrust for minimum drag ................................................................................................. 127 12.3.7 Power for minimum drag ................................................................................................. 127 12.3.8. Minimum power conditions............................................................................................ 128 12.3.9 Thrust for minimum power.............................................................................................. 128 12.3.7 Power for minimum power .............................................................................................. 128 12.4 CLIMB CONDITIONS ................................................................................................................ 128 12.4.1 CL and CD ........................................................................................................................... 128 12.4.2 Vclimb.................................................................................................................................. 129 12.4.3 Thrust for climb ................................................................................................................ 129 12.4.4 Power for climb ................................................................................................................ 129 12.4.5 Climb gradient .................................................................................................................. 129 vi

12.4.6 Climb Wing loading .......................................................................................................... 130 12.4.7. Rate of Climb ................................................................................................................... 130 12.5 TURN CONDITIONS.................................................................................................................. 130 12.5.1 Load factor (n) .................................................................................................................. 130 12.5.2 CL and CD ........................................................................................................................... 130 12.5.3 Thrust for turn.................................................................................................................. 131 12.5.4 Power for turn.................................................................................................................. 131 12.5.5. Turning wing loading....................................................................................................... 131 12.6 LANDING ................................................................................................................................. 131 12.6.1 Turn Radius (R) ................................................................................................................. 131 12.6.2. Approach Distance (Sa).................................................................................................... 132 12.6.3 Flare Distance (Sf) ............................................................................................................. 132 12.6.4. Ground roll distance (Sg) ................................................................................................. 132 12.6.5. Landing Wing Loading ..................................................................................................... 132 12.7. TAKE-OFF................................................................................................................................ 133 12.7.1 Static Thrust ..................................................................................................................... 133 12.7.2. Turn radius (R)................................................................................................................. 133 12.7.3 Airborne distance (Sa) ...................................................................................................... 133 12.7.4 Ground roll distance (Sg) .................................................................................................. 133 12.7.5 Take-off Wing Loading ..................................................................................................... 133 12.7.6 VTO .................................................................................................................................... 134 12.7.7. Power for take-off ........................................................................................................... 134 12.7.8 Maximum acceleration (a) ............................................................................................... 134 12.8 LOITER ..................................................................................................................................... 134 12.8.1 CL ...................................................................................................................................... 134 12.8.2 Loiter wing loading........................................................................................................... 135 12.9 SUMMARY AND SELECTION OF WING LOADING .................................................................... 135 12.10 THRUST-TO-WEIGHT ............................................................................................................. 135 12.10.1 Cruise ............................................................................................................................. 136 12.10.2 Climb .............................................................................................................................. 136 12.10.3 Turn ................................................................................................................................ 136 12.10.4 Take-Off.......................................................................................................................... 137 12.10.5 Vmax ................................................................................................................................. 137 12.11. SUMMARY AND SELECTION OF THRUST TO WEIGHT RATIO ............................................... 137

vii

12.12. V-n DIAGRAM ....................................................................................................................... 138 12.12.1 Introduction ................................................................................................................... 138 12.12.2 Load Factor..................................................................................................................... 139 12.12.3 V-n Diagram parameters calculation ............................................................................. 139 12.12.4 Limit load factor calculation........................................................................................... 140 12.12.5 Stall condition ................................................................................................................ 140 12.12.6 Manoeuvring point A ..................................................................................................... 141 12.12.7 Calculation of Velocity Vc ............................................................................................... 141 12.12.8 Diving velocity VD ........................................................................................................... 141 12.12.9 Velocity at negative limit load ....................................................................................... 141 12.12.10 Equations for the curves .............................................................................................. 142 12.12.11 Conclusion .................................................................................................................... 143 12.13 REFERENCES .......................................................................................................................... 144

Chapter 13: FINAL CONFIGURATION .......................................................... 145 13.1 INTRODUCTION ....................................................................................................................... 145 13.2 WEIGHT AND GEOMETRY ....................................................................................................... 145 13.3 PERFORMANCE CHARACTERISTICS ......................................................................................... 147 13.4 STABILITY PARAMTERS............................................................................................................ 148 13.5 FLIGHT ENVELOPE CHARACTERISTICS ..................................................................................... 148

viii

LIST OF FIGURES

Figure 1.1: Mission Profile ...................................................................................................................... 2 Figure 1.2 Sketch of the configuration.................................................................................................... 4 Figure 2.1. Structural or empty weight fraction plot .............................................................................. 5 Figure 2.2 Power plant fraction plot ....................................................................................................... 6 Figure 2.3 Mission leg weight fractions .................................................................................................. 8 Figure 3.2: NACA 2310 Airfoil Geometric Profile .................................................................................. 10 Figure 3.3: Lift Curve For NACA 2310 In The Operating Envelope ........................................................ 11 Figure 3.4: Drag Polar For NACA 2310 In The Operating Envelope ...................................................... 11 Figure 3.5: Aspect Ratio - Historical Data Plot ...................................................................................... 13 Figure 3.6: Wing Loading - Historical Data Plot .................................................................................... 13 Figure 3.7 Tau Camera .......................................................................................................................... 15 Figure 3.8 CL v/s CD for different velocities ........................................................................................... 18 Figure 3.9 Power v/s Velocity ............................................................................................................... 18 Figure 3.8 Rimfire 0.32 brushless Outrunner motor............................................................................. 19 Figure 3.9 Electrifly 4S 2200mAh LiPo .................................................................................................. 20 Figure 3.10 13 X 8 NEW APC Thin Electric Propeller ............................................................................. 20 Figure 3.11. Silver Series 45A Brushless ESC ......................................................................................... 20 Figure 4.1The Landing Path and Landing Distance[1]........................................................................... 23 Figure 4.2 Take-off analysis [2] ............................................................................................................... 27 Figure 6.1 Side View of the RC Model Airplane .................................................................................... 51 Figure 6.2 Top View of the RC Model Airplane ..................................................................................... 51 Figure 6.3 Front View of the RC Model Airplane .................................................................................. 52 Figure 7.1 Cross-section of a propeller[1]............................................................................................. 54 Figure 7.2 Fixed- Pitch propeller[1]....................................................................................................... 54 Figure 7.3 Variable- Pitch propeller[1] .................................................................................................. 55 Figure 7.4 Constant- speed propeller[1] ............................................................................................... 55 Figure 7.6. Variation of J with CT at different P/D ratios [5] ................................................................... 58 Figure 7.7. Variation of J with Cp at different P/D ratios [5] ................................................................... 58 Figure 8.1 Lift curve slope v/s Mach number ....................................................................................... 65 Figure 8.2 Taper ratio correction for low aspect ratio wings [1] ............................................................ 67 Figure 8.3 Airfoil leading edge sharpness parameter [1] ....................................................................... 67

ix

Figure 8.4 Subsonic maximum lift of high aspect ratio wings [1] ........................................................... 68 Figure 8.5 Mach number correction for subsonic maximum lift of high aspect ratio wings [1] ............ 68 Figure 8.6 Angle of attack increment for subsonic maximum lift of high aspect ratio wings [1]........... 69 Figure 8.7 Parasite Drag vs. Mach number ........................................................................................... 74 Figure 8.8 Modified drag polar ............................................................................................................. 75 Figure 9.1. Side view of the aircraft in cartesian coordinate system . .................................................. 86 Figure 9.2. Top view of the aircraft in cartesian system ....................................................................... 87 Figure9.3. CG location of fuselage ........................................................................................................ 88 Figure9.4. CG location of wing .............................................................................................................. 88 Figure 9.5 Schematic of the important geometric points for tail CG calculation [2] ............................. 89 Figure 9.6. CG location of horizontal tail .............................................................................................. 91 Figure9.7. CG location of vertical tail .................................................................................................... 92 Figure 9.8 Landing Gear Arrangement about Aircraft CG ..................................................................... 96 Figure 10.1. Position of ¼ root chord [1] .............................................................................................. 104 Figure 11.1 CD values for Landing Gear (Fixed Type) [2] ...................................................................... 119 Figure 11.2 CD values for Landing Gear (Fixed Type) [2] ...................................................................... 120 Figure 11.3 Parasite Drag vs. Mach number ....................................................................................... 124 Figure 12.1 V-n diagram for a general aviation aircraft ...................................................................... 139 Figure 12.2 V-n Diagram ..................................................................................................................... 143

x

LIST OF TABLES Table 1.1 Design Specifications ............................................................................................................... 2 Table 1.3 Preliminary design considerations .......................................................................................... 3 Table 2.1 Weight specification for RC airplanes ..................................................................................... 5 Table 2.2. Result table of iterative process............................................................................................. 7 Table 3.1 Airfoil Data .............................................................................................................................. 9 Table 3.2 Characteristics of NACA 2310................................................................................................ 10 Table 3.4 Wing Specifications ............................................................................................................... 14 Table 3.5 Parameter values at different velocities ............................................................................... 17 Table 4.1 Ground Rolling Resistance[1] .................................................................................................. 24 Table 4.2 Wing Loading at different flight conditions .......................................................................... 26 Table 4.3 Engine power at different flight conditions .......................................................................... 31 Table 4.4 Thrust-to-weight at different flight conditions ..................................................................... 31 Table 5.1 Weight of each component................................................................................................... 44 Table 6.1 Initial Sizing Summary ........................................................................................................... 49 Table 6.2 Wing and Empennage Wetted Area Calculation ................................................................... 52 Table 7.1. Historical Data for propeller selection of RC aircrafts [3] ...................................................... 56 Table 7.2 Propeller Parameters ............................................................................................................ 64 Table 7.3 Propeller performance in each segment............................................................................... 64 Table 8.1 RC Model Airplane (W0 = 1.98 kg) Component Geometric Data .......................................... 72 Table 8.2 Parasite Drag Calculation for design cruise speed of 20 m/s ................................................ 73 Table 8.3 Parasite Drag Coefficients for RC Model Airplane Speed Range........................................... 73 Table 8.4 Wing Loading at different flight conditions .......................................................................... 78 Table 8.5 Engine power at different flight conditions .......................................................................... 82 Table 9.1 CG location and weights of different components ............................................................... 94 Table 11.1 RC Model Airplane (W0 = 1.98 kg) Component Geometric Data ...................................... 121 Table 11.2 Parasite Drag Calculation for maximum cruise speed of 20m/s ....................................... 122 Table 11.3 Parasite Drag Coefficients for RC Model Airplane Speed Range....................................... 123 Table 12.1 Wing loading for different segments ................................................................................ 135 Table 12.2 Thrust-to-weight ratio of different segments ................................................................... 137 Table 12.3 Parameters required for V-n diagram ............................................................................... 140

xi

LIST OF SYMBOLS



AR

Aspect Ratio

BP

Balance Point

b

Wing span

c

Chord Maximum value of coefficient of lift for wing



 

Maximum value of coefficient of lift for airfoil CD

Coefficient of drag for wing Zero Lift Drag Coefficient

CL

Coefficient of lift for wing

Cp

Coefficient of Power

Croot

Root chord

CS

Speed Power Coefficient

CT

Coefficient of Thrust

Ctip

Root chord

D

Drag

e

Ostwald’s Efficiency Factor

hf

Flare Height

hob

Obstacle Height

HP

Engine Horsepower

J

Advance Ratio

k L

Parasite Drag Coefficient Lift

L

Propeller Blade Length

n

Load Factor

N

Increment time for free roll

xii

N

Speed in RPM

n

Speed in RPS

P P PTO

⁄

(⁄ )

Turn Radius Maximum Rate of Climb

S

Wing Area

Sa

Approach Distance

Sf

Flare Distance

Sg

Ground Roll Distance

STO

Take- Off Distance

SL

Landing Distance

T

Thrust

!"

⁄

Thrust-to-Weight ratio for maximum Rate of Climb



Thrust-to-Weight ratio for Take-Off



#/

Engine Power for Take-Off

Engine power for Maximum Velocity R

!"

Pitch

Engine power for Maximum Rate of Climb

 

!"

Engine Power

Thrust-to-Weight ratio for maximum Velocity

Vf

Flare Velocity

VLO

Velocity at lift off

Vloiter

Loiter Velocity

Vmax

Maximum Velocity



Velocity at maximum Rate of Climb

VstallStall Velocity W

xiii

Weight

! % &'()*+

 " !

%" !

,-),.

Wing loading for Landing

⁄

Wing loading for maximum Rate of Climb

 " %

! % */

 " ! %

 " !

%"

0

Wing loading for stall conditions



Wing loading for Take-Off



Wing Sweep

XCG

Location of centre of gravity along X axis

YCG

Location of centre of gravity along Y axis

ZCG

Location of centre of gravity along Z axis Wing taper ratio Propeller efficiency

45

Density of air

6

Approach Angle

637

Obstacle Angle

8'

Λ

xiv

Wing loading for maximum Velocity

S

12'32

45

Wing loading for Cruise conditions

Coefficient of friction α

Angle of attack Density of air Sweep Angle

CHAPTER 1: GOAL DETERMINATION AND MISSION SPECIFICATIONS

1.1 INTRODUCTION Aircraft design is an iterative process. The design depends on many factors such as customer and manufacturer demand, safety protocols, physical and economic constraints etc. It is a compromise between many competing factors and constraints and accounts for existing designs and market requirements to produce the best aircraft. The design starts out in three phases: (a) Conceptual Design This involves sketching up a variety of possible configurations that meet the required design specifications. Fundamental aspects such as fuselage shape, wing configuration and location, engine size/power plant size and type are all determined at this stage. Constraints to design are all taken into account at this stage.

(b) Preliminary Design At this stage the design configuration arrived at in the conceptual design phase is then tweaked and remodelled to fit into the design parameters. Major structural and control analysis is also carried out in this phase. Aerodynamic flaws and structural instabilities if any are corrected and the final design is drawn and finalised.

(c) Detail Design This phase deals with the fabrication aspect of the aircraft. It determines the number, design and location of ribs, spars, sections and other structural elements. All aerodynamic, structural, propulsion, control and performance aspects have already been covered in the preliminary design phase.

1.2 GOAL DETERMINATION

The goal is to design a flying model of a miniature aircraft mainly intended to undertake missions viz. reconnaissance/ surveillance. The most common aircrafts i.e. the remote controlled aircraftshave multiple applications such as in military, weather forecast, topological survey, reconnaissance etc.

1

The team’s primary plan is to design for surveillance in forest areas to track the wildlife movements and to study their habitual patterns through the collected data. The surveillance aircraft can also be used to capture poacher activities within the reserve area.

1.3MISSION PROFILE The required mission profile for the RC model airplane to be designed is given in Figure 1.1 below.

LOITER CRUISE

CRUISE

Endurance ~15 min flight time CLIMB

DESCENT

Cruise Altitude 50m, TAKE-OFF

LANDING Figure 1.1: Mission Profile

Table 1.1 below enlists the design specifications for the aircraft to be designed. Table 1.1 Design Specifications S. No

PARAMETER

DESIGN VALUE

1.

Vstall

10 m/s

2.

Vcruise

20 m/s

3.

Vmax

25 m/s

4.

Take off distance

50 m

5.

Range / Endurance

~15 minutes of flight time (includes takeoff, climb to cruise altitude, descent and landing time)

6.

2

Landing distance

50 m

The data mentioned in Table 1.1provide a basis for the design. However, these are the initial specifications of the RC model airplane concept under consideration and may be altered based on the constraints imposed during the course of preliminary and detail design stages.

1.4 PRELIMINARY DESIGN CONSIDERATIONS

The preliminary design considerations arrived at, after literature survey, are enlisted in Table 1.3 below. These may be amended at a later stage after appropriate estimates and calculations. Table 1.3 Preliminary design considerations

3

S.NO.

PARAMETER

PRELIMINARY ESTIMATE

1.

Flying Weight

~1.0 - 2.0 kg

2.

Aspect Ratio (AR)

~6-8

3.

ARW/ARref

~4-5(1)

4.

(L/D)max

~9.5-12.5(2)

5.

Wing Type

High wing or low wing (to be decided)

6.

Power Plant

Electrical power plant inclusive of battery, motor, electronic speed control (ESC) and propeller

7.

Aerodynamic Control Surfaces

Ailerons, Elevators and Rudders

8.

Thrust to Weight Ratio

To be decided

9.

Range

~15 minutes of flight time

Propeller

Fuselage

Wing Planform – shape to be decided Vertical Tail Horizontal Tail

Figure 1.2 Sketch of the configuration

A conceptual configuration of the Radio-controlled Electrical powered model airplane has been shown in the Figure 1.2.

CHAPTER 2: LITERATURE SURVEY AND FIRST WEIGHT ESTIMATE

2.1 INTRODUCTION Literature survey of the available RC aircrafts is crucial for assuming initial specifications for the aircraft to be designed. These provide a basis for estimation of the weight of the aircraft as presented in this chapter.

2.2 DATA COLLECTION The Table 2.1 below shows a compilation of the weight data collected using internet search of currently flying Radio Controlled (RC) electrically powered (EP) Model Airplanes.

4

Table 2.1 Weight specification for RC airplanes S.No.

RC AIRPLANE

Flying Wt, W0 (kg)

Structural Wt, We (kg)

Powerplant Wt, Wpp (kg)

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Revolution 3D trainer Foamtana Electrifly Yak 55M Electrifly Extra 330SC Hobbico Superstar EP Extra330 L Edge 540 Carbon Z Yak 54 Hawker Hurricane 25e F3A/Gadfly Nemesis Racer EP

0.430 0.450 1.700 0.234 1.230 0.620 1.650 1.730 2.100 2.350 2.100

0.282 0.280 1.187 0.178 0.918 0.427 1.157 1.139 1.528 1.713 1.390

0.148 0.170 0.513 0.056 0.312 0.193 0.493 0.591 0.572 0.637 0.710

Using Table 2.1, following two graphs, comparing the structural (also called empty weight) weight fraction and the powerplant weight fraction to the flying weight or AUW (i.e. AllAll-up weight termed as AUW, since for electric powered RC airplanes weight during the flight remains remains same), respectively have been plotted.

Figure 2.1. Structural or empty weight fraction plot

5

Figure 2.2 Power plant fraction plot

Figure 2.2 and Figure 2.3 also show the least square fitted linear regression equations, which has been used to do the preliminary weight estimate of the RC model airplane.

2.3 FIRST WEIGHT ESTIMATE

The weight of an RC EP model airplane can be estimated as,

W0 = WP / L + WE + WPP This can be rewritten as,

W W0 = WP / L + W0  E  W0

 W  + W0  PP   W0

  

which on simplification gives,

W0 =

6

WP / L W  W 1 −  E  −  PP  W0   W0

  

(2.1)

Following initial estimate has been used for the iterative process to arrive at the preliminary weight estimate of RC EP model airplane; From mission requirements;

WP/L = 0.15 kg

Starting guess value of AUW weight;

W0 = 1.1 kg

From Figure 2.2 and Figure 2.3, the powerplant and structural weight fractions have been used for the iterative estimation of AUW or flying weight. The intermediate results of the iterative process is compiled and shown in Table 2.2. The process was allowed to continue till an error of less than 0.5% had been achieved.

Table 2.2. Result table of iterative process Initial Guess

Fractional Weights

Estimated AUW

Error

W0

WP/L

We/W0

Wpp/W0

W0

%age

1.100

0.150

0.594

0.306

1.500

36.364

1.500

0.150

0.596

0.303

1.493

0.548

1.493

0.150

0.596

0.303

1.493

0.002

2.4 CONCLUSION

The first weight calculation estimates the flying weight of the aircraft to be 1.493 kg. However, this is a very preliminary estimate. Assuming a safe margin the initial weight of the aircraft is taken as 1.5 kg. The aircraft will be battery operated; hence all the weight fractions will be equal to the first weight estimate, WO. Thus, the final mission leg weight fractions are as follows:

7

2, W2

0, WO

3, W3

4, W4

1, W1 Figure 2.3 Mission leg weight fractions

8

5, W5

CHAPTER 3: SECOND WEIGHT ESTIMATE

3.1 INTRODUCTION The first weight estimate carried out in the previous chapter was completely based on historical data. In this chapter requirement specific airfoil and wing is chosen. Based on those, the power plant estimation is carried out.

3.2 AIRFOIL A considerable amount of airfoil data has been accumulated from windtunnel tests and in-flight tests over the years and the compilation is available in the airfoil catalogues. The selection of the airfoil from such a catalogue depends upon the design specifications that are required to be met, such as cruise and stall characteristics. A similar approach has been adopted to select an appropriate airfoil for the RC model airplane.

3.2.1 Airfoil Data Collection Following Table 3.1 shows a compilation of some of NACA 4-digit family of the airfoils considered for this work, as the RC model airplane has to operate at very low speed in surveillance operation. This set of airfoils has been selected based on the high stall angle, high maximum section lift coefficient, availability of thickness for structure and ease of manufacturability. At this stage of design a more rigorous approach of custom-designed airfoil based on computational analysis has been avoided. Table 3.1 Airfoil Data Zero lift Angle of Attack (AoA)

Cl,max

NACA 1408

-1.1

0.875

14

39.7

11

2.6

85.6%

NACA 1412

-1.11

1.417

15

54.2

16.5

3.5

64.9%

NACA 2310

-2.04

1.467

15

56.4

12.1

1.2

66.8%

NACA 2312

-2.05

1.377

15

56

14.5

1.7

48.2%

NACA 2414

-2.23

1.372

15

56.4

17.8

3

50.5%

Airfoil

9

αstall

(L/D)max

Trailing edge angle

Leading edge radius (%c)

(degrees)

Lower Flatness (%c)

3.2.2 Airfoil Selection

After thoroughly investigating the available airfoil dataset and based on the requirement of low stall speed, high maximum section lift coefficient and maximum aerodynamic efficiency the NACA 2310 airfoil has been chosen for the airplane design.

Figure 3.1, shows the profile of the selected airfoil designated as NACA 2310.

Figure 3.2: NACA 2310 Airfoil Geometric Profile

The aerodynamic and geometric characteristics of NACA 2310 airfoil are as follows: Table 3.2 Characteristics of NACA 2310 Geometric Characteristics

Aerodynamic Characteristics

Camber

2% of chord

Clmax

1.467

Chord Length

0.25 m

αstall

15°

Location of maximum camber

30% of chord from LE

Stall Speed (m/s)

8.5

Maximum Thickness

10% of chord

(L/D)max

56.4

Trailing edge angle

12.1°

Lower flatness

66.80%

Leading edge radius

1.20%

10

3.2.3 Airfoil Operational Characteristics

As per design specification of stall speed of 10 m/s and cruise speed of 20 m/s, the operating Reynolds number envelope of airfoil has been estimated. Density of air(ρ) : 1.15 kg/m3 Viscosity of air: 1.983x10-5 N-sec/m sec/m2 Hence, Reynolds number (stall) = 1.67x105 Reynolds lds number (cruise) = 3.33x105 For the Reynolds number of 1.67x105 and 3.33x105, the airfoil lift-curve curve and drag as estimated using DESIGNFOIL Software are shown in Figure 3.3 and Figure 3.4 respectively.

Figure 3.3: Lift Curve For NACA 2310 In The Operating Envelope

Figure 3.4: Drag Polar For NACA 2310 In The Operating Envelope

11

3.3 WING DESIGN

3.3.1 Aspect ratio Table3.3 shows a compilation of the geometric data collected using internet search of currently flying Radio Controlled (RC) electrically powered (EP) Model Airplanes.

Table 3.3: Geometric Specification Of RC Airplanes Flying

Length

Span

Wing

Aspect

Wing Loading

Wt (kg)

(m)

(m)

Area (sq m)

Ratio

(kg/sq m)

W0

L

b

Sref

AR

W0/Sref

Revolution 3D trainer

0.430

0.965

0.864 0.245

3.04

1.754

Foamtana

0.450

0.978

0.991 0.254

3.86

1.770

Electrifly Yak 55M

1.700

1.194

1.283 0.328

5.02

5.187

Electrifly Extra 330SC

0.234

0.889

0.826 0.172

3.96

1.358

Hobbico Superstar EP

1.230

0.917

1.238 0.259

5.91

4.743

Extra330 L

0.620

0.889

0.925 0.170

5.03

3.647

Edge 540 25 45" RC EP

1.650

1.029

1.151 0.246

5.39

6.713

Carbon Z Yak 54

1.730

1.232

1.219 0.339

4.39

5.108

Hawker Hurricane 25e

2.100

1.067

1.359 0.310

5.96

6.781

Funster V2

2.350

1.346

1.842 0.546

6.21

4.306

Nemesis Racer EP

2.100

1.200

1.560 0.392

6.21

5.357

Using Table 3.3, the two comparison graphs of the aspect ratio of wing (AR) against the AUW and the wing loading to the flying weight or AUW have been plotted in Figure 3.5 and Figure 3.6 respectively.

12

Figure 3.5: Aspect Ratio - Historical Data Plot

Figure 3.6: Wing Loading - Historical Data Plot

13

Figure 3.5 and Figure 3.6 also show the least square fitted linear regression equations, using which following preliminary wing specifications have been estimated for AUW of 1.5 kg for RC model airplane. Table 3.4 Wing Specifications Wing Specification Aspect Ratio

5.35

Airfoil Chord Length (m)

0.25

Wing type

Rectangular high wing

All the RC Airplane considered in the historical dataset have high wing with rectangular planform. This allows designers to have high ground clearance as the height of the RC model airplane is very small and also gives more internal volume and stability to the airplane. Further, rectangular wings are easy to manufacture and integrate with the airplane fuselage. 3.3.2 Wing area (S) The design Vstall=10 m/S. We know that,

1 : = < = 45 #*/ ?  @ 2

where S= Projected area of the wing

From Chapter 1, W = 1.5 kg = 14.715 N and from section 3.2.2 CLmax= 1.467 Thus, @=

3.3.3 Span Length (b) We know,

2<

45 #*/  ?

=

@ = 0.174 I?

J = AR=5.35 and S=0.174 m2 Thus, b= 0.951 m

14

2 x 14.715 1.15 x 10? x 1.467

K? @

3.4 SECOND WEIGHT ESTIMATE

The weight of an RC EP model airplane during first estimate was estimated in Chapter 2 by,

W0 =

WP / L W 1 −  E  W0

  W PP  −    W0

  

Now, as we have more insight into the geometric and aerodynamic details of airplane components, we can revise the equation and arrive at a more accurate estimate using calculated payload and powerplant weight instead of using the powerplant weight fraction from historical data. Therefore, the revised equation becomes:

W0 =

W P / L + W PP W 1 −  E  W0

  

(3.1)

3.4.1 Payload Weight Calculation

The payload for the aircraft is chosen as an infra-red camera to serve the purpose of forest area surveillance. The camera best suited for the mission’s requirements is the Tau 320.

Figure 3.7 Tau Camera

The Tau is a long wavelength camera (8-14 microns) un-cooled micro-bolometer camera designed for infrared imaging applications with minimum size, weight and power consumption.

15

Specifications: (a) (b) (c) (d) (e) (f) (g) (h) (i)

320(H) x256 (V) un-cooled micro-bolometer sensor array, 25 X 25 micron pixels Spectral Band: 7.5-13.5 µm. NEdT Performance: