ft The Investigation of an Inboard-Winglet
Application to a Roadable Aircraft
Nanyaporn Intaratep
Thesis submitted to the Faculty of the
Virginia Polytechnic Institute and State University
In partial fulfillment of the requirements for the degree of
Master of Science In Aerospace Engineering
James F. Marchman, III, Chair
William J. Devenport
Joseph A. Schetz
May 31, 2002
Blacksburg, Virginia
Keywords: Inboard winglet, Propeller-induced flow, Roadable aircraft,
Aerodynamics, Conceptual design
Copyright 2002, Nanyaporn Intaratep ii
The Investigation of an Inboard-Winglet Application to a Roadable Aircraft
Nanyaporn Intaratep
(Abstract)
The inboard-winglet concept was examined for its flow characteristics by testing
for pressure coefficients over the wing and winglet surface in the Virginia Tech Stability
Wind Tunnel over a range of freestream velocity and angle of attack. The results were
analytically applied to calculate aircraft performance of a roadable aircraft, Pegasus II,
which used the inboard-winglet concept in its design. The results proved that this concept
has the potential to increase a wing lift coefficient at the right combination of thrust setting
and freestream velocity better than a conventional wing-propeller arrangement. The lift
coefficient inside the winglet channel was approximated as 2D in behavior. It is also
shown that the winglets produce thrust at a positive-lift wing configuration. In the Pegasus
II, the vertical stabilizers act like inboard winglets and produce a thrust component from its
resultant force, giving 5.2% improvement in its effective aspect ratio and resulting in an
induced-drag decrease. With an application of the new wing concept, the Pegasus II
performance is comparable to other general aviation aircraft. iii
Acknowledgement
This work was partially supported by NASA Langley Research Center, Personal
Air Vehicle Evaluation Project, through NASA Grant NAG-1-001100.
The author greatly appreciates a precious guidance, support and patient from Dr.
James F. Marchman, III during these 2 years. Very special thanks to mother and friends. iv
Table of Contents
Abstract
ii
Acknowledgments
iii
Table of Contents
iv
List of Figures
vi
List of Tables
ix
Nomenclature
x
Chapter 1
Introduction
1
Chapter 2
Literature Review
4
2.1
Roadable Aircraft History
4
2.2
Wing Design for Roadable Aircraft
6
2.3
Channel Wing Concept
10
Chapter 3
Experimental and Theoretical Techniques
12
3.1
Wind Tunnel Testing
12
3.1.1
Pressure Model
12
3.1.2
Propeller and Drive System
17
3.1.3
Scannivalve System
20
3.1.4
Stability Wind Tunnel
21
3.1.5
Testing Conditions and Procedure
22
3.2
Resultant Force Approximation of the Experimental Model
24
3.3
Prediction of Lift Coefficient Augmentation from
Experimental Data
27
3.4
Pegasus II Design
31
3.5
Analytical Approximation of Thrust due to Inboard Winglets
35
3.6
Simplified Lift Coefficient Approximation for the Pegasus II
41
3.7
Performance Estimation of Comparator Aircraft and
Sensitivity Study
42
3.7.1
Takeoff Gross Weight and Fuel Weight Estimation
43
3.7.2
Takeoff Distance
46 v
3.7.3
Landing Distance
48
3.7.4
Maximum Cruise Velocity
49
3.7.5
Stall Velocity
50
3.7.6
Service and Absolute Ceiling
51
Chapter 4
Result and Discussion
52
4.1
Experimental Data Analysis
52
4.1.1
Pressure Coefficients at Power-Off Condition
52
4.1.2
Pressure Coefficients at Power-On Condition
64
4.1.3 Numerical Analysis of Experimental Data for Thrust on
the Winglets
78
4.1.4 Uncertainties
81
4.2
Discussion of the Inboard Winglet Application on the Pegasus II
83
4.2.1 Numerical Analysis of the Wing Lift Coefficient from
the Experimental Data
83
4.2.2
Results of Thrust Approximation from the Winglets
85
4.2.3
Result of the Simplify Lift Coefficient Approximation
for the Pegasus II
87
4.3
Comparator Aircraft Performance and Sensitivity Study
90
Chapter 5
Conclusions and Recommendations
96
5.1
Conclusions
96
5.2
Recommendations for Future Work
98
References
99
Appendix A 3D Lift Coefficient Approximation of the Pegasus II
103
Appendix B
Input Data of Comparator Aircraft
110
Appendix C
Performance Estimation Codes
111
Vita
145 vi
List of Figures
Figure 1.1 The Custer Channel Wing concept
3
Figure 1.2 View of the Pegasus in flight
3
Figure 2.1 Airphibian as in flying and roadable configurations
5
Figure 2.2 Drawing of Aerocar as in flying and roadable configurations
6
Figure 2.3 Telescopic wing in extended configuration
8
Figure 2.4 Synergy configuration in flying and driving mode
9
Figure 2.5 FSC-1 wing folding approach
9
Figure 2.6 Custer CCW-5 prototype at the Mid Atlantic Air Museum
11
Figure 3.1 Disassembly of pressure model of inboard-winglet concept
13
Figure 3.2 NACA0012 airfoil section
14
Figure 3.3 The pressure model in the wind tunnel
15
Figure 3.4 Pressure taps location and dimensions for various models
16
Figure 3.5 Propeller mounting inside the channel
18
Figure 3.6 Drawing of a motor-support structure
19
Figure 3.7 Diagram of the scanni valve system
20
Figure 3.8 General layout of Virginia Tech Stability Wind Tunnel
21
Figure 3.9 Flow characteristics at the model mounting station in
the Stability tunnel
22
Figure 3.10 Winglet pressure tap positions in x/c and paneling
25
Figure 3.11 Wing pressure tap positions in x/c and paneling
25
Figure 3.12 Diagram of resultant force component acting a wing section
26
Figure 3.13
Streamtube of an induced flow pass an actuator disk
27
Figure 3.14 Outboard wing stowage concept
33
Figure 3.15 Pegasus II three-view drawing
34
Figure 3.16 Diagrams of a wing-winglet interaction
36
Figure 3.17 Diagram of a relative velocity due to a change in wing circulation
38
Figure 3.18 Diagram of lift and drag of a winglet cross-section at r station
39
Figure 3.19 Mission profile of the comparator vehicles
42 vii
Figure 3.20 Geometry of Takeoff distances
46
Figure 3.21 Geometry of Landing Distances
48
Figure 3.22 Power-required and available curve
50
Figure 4.1 Pressure taps location for various models
53
Figure 4.2-4.9 The pressure distributions of the inboard-winglet wing
at -5 degree angle of attack
57
Figure 4.10-4.17 The pressure distributions of the inboard-winglet wing
at 0 degree angle of attack
58
Figure 4.18-4.25 The pressure distributions of the inboard-winglet wing
at 5 degree angle of attack
59
Figure 4.26-4.33 The pressure distributions of the inboard-winglet wing
at 10 degree angle of attack
60
Figure 4.34-4.37 Pressure distribution of the wing in the spanwise direction
61
Figure 4.38-4.41 The pressure distributions of the inboard winglet I
62
Figure 4.42-4.45 The pressure distributions of the inboard winglet II
63
Figure 4.46-4.49 The pressure distributions of the inboard wing sections
at static condition
68
Figure 4.50-4.53 The comparison of the pressure distributions
at a power-on and off condition
69
Figure 4.54-4.61 The power-on pressure distributions of the inboard-winglet
wing at -5 degree angle of attack
70
Figure 4.62-4.69 The power-on pressure distributions of the inboard-winglet
wing at 0 degree angle of attack
71
Figure 4.70-4.77 The power-on pressure distributions of the inboard-winglet
wing at 5degree angle of attack
72
Figure 4.78-4.85 The power-on pressure distributions of the inboard-winglet
wing at 10 degree angle of attack
73
Figure 4.86-4.89
The spanwise pressure distributions of the inboard-winglet
and conventional wing at the power-on condition
74
Figure 4.90-4.93 The comparison of the spanwise pressure distributions of the
inboard-winglet wing for the power-on and off condition
75 viii
Figure 4.94-4.97 The power-on pressure distributions of the inboard winglet I
76
Figure 4.94-4.97 The power-on pressure distributions of the inboard winglet II
77
Figure 4.102 Optimal twist angles of an inboard winglet relative to
the freestream velocity
86
Figure 4.103 Takeoff distance sensitivity
93
Figure 4.104 Stall speed sensitivity
93
Figure 4.105 Cruise speed sensitivity
94
Figure 4.106 Maximum rate of climb sensitivity
94 ix
List of Tables
Table 3.1 NACA0012 airfoil section coordinates
14
Table 3.2 Locations of chordwise pressure taps
17
Table 3.3 Locations of spanwise pressure taps
17
Table 3.4 Test velocities and corresponding Reynolds Numbers
23
Table 4.1 Drag coefficients of the winglets at the power-on condition
79
Table 4.2 Uncertainties in
p
C
for the different conditions at
c
x
/
=0.425 of

the mid-span section
81
Table 4.3
Lift coefficients of the mid-span section at
the power-off and on condition
84
Table 4.4 Calculation of the thrust coefficients for the experimental model
and the Pegasus II
85
Table 4.5 2D maximum lift coefficient of the GA(W)-2
87
Table 4.6 Maximum 3D lift coefficients and angles of attack for
various flap deflections
88
Table 4.7 2D lift coefficient of the GA(W)-1 at selected angles of attack
88
Table 4.8 Total maximum lift coefficients for different flight conditions
89
Table 4.9 Aircraft performance results of 4 comparator vehicles
91 x
Nomenclature
A
Propeller disk area (ft
2
)
AR
Geometric aspect ratio
e
AR
Effective aspect ratio
b
Wing span (ft)
b
Y-intercept
c
Chord length
p
c
Specific fuel consumption (lb/(hp.hr))
a
C
Section axial force coefficient
d
C
Section drag coefficient
0
D
C
Parasite drag coefficient
mp
D
C
,
Drag coefficient at minimum power
l
C
Section lift coefficient l
C
Section lift curve slop (per radian)
*
L
C
Power-off lift coefficient
A
L
C
,
Approached lift coefficient
max
L
C
Maximum lift coefficient
i
L
C
max,
Inboard maximum