Wing Spars
-Aer E 423 Final Project-
By: Joe Rees
Outline
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Background
Theoretical Calculations
Predictions
Fabrication/Construction
Testing
Data Analysis
Failure Modes
Results/Conclusion
Background


Competing in the SAE-Advance Class R/C
plane competition in the spring.
Need to develop a strong, lightweight wing spar
Background

Actual R/C Plane:
NACA 4414 airfoil
 Chord of 18 inches
 12 foot span
 Max gross weight 55lbs

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Test Sections:
18 inch long beams
 2.5 inches tall
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Beam Types
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Rectangular

C-Channel
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I-Beam
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Sinusoidal
Theoretical Data
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From E-Glass Carpet Plots:
12 plies: 0.005”/ply x 12 plies = 0.06” total thickness
 [03/903]s
 Volume Fraction: 0.5 matrix and 0.5 fibers

Elastic Modulus (Ex)
Poisson's Ratio (νxy)
Shear Modulus (Gxy)
1st Ply Failure Tensile Strength
Tensile Strength at Fiber Failure
Compressive Strength at Fiber Failure
25 GPa
0.14
3.3 GPa
95 MPa
460 MPa
195 MPa
Theoretical Data

Moment of Inertia:
bd  h ( b  t )
3
I I  beam  I C  C hannel 
I rectangle 

3
12
bh
3
12
Maximum Displacement:
3
 1  PL
y

 48  E I
Beam
I-beam
C-Channel
Rectangular
Sinusoidal
Moment of Inertia (in4)
0.157
0.157
0.0781
0.0781
Force (lbs)
100
100
100
100
Max Displacement (in)
0.0260
0.0260
0.0495
0.0495
Predictions
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I-Beam and C-Channel will deflect half as much
as rectangular and sinusoidal beams
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No flanges = loss of strength
Failure Modes:
Rectangular – foam/composite interface
 C-Channel – crushing or foam/composite interface
 I-Beam – crushing
 Sinusoidal – foam/composite interface
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Fabrication/Construction
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Used hot wire to cut foam molds/cores
Cut fiber glass composite strips
Cured rectangular and sinusoidal beam under
room conditions with weights
Cured I-beam and C-channel with vacuum bag
Foam Core
Fibers
Testing
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MTS Machine
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Point load beam bending
Recorded displacement vs. load
Data Analysis
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Graphed theoretical data for various loads, P
vs. experimental data from MTS machine
3
 1  PL
y

 48  E I
P

Best fit line to experimental data:

Calculated and compared effective bending
stiffness:
 L  P 
 E I  eff
3

 
48

 y 
slope 
y
Data Analysis
- Rectangular Beam 
Effective Bending Stiffness, (EI)eff :
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Theoretical: 2.81x105 lb·in2
Experimental: 3.31x105 lb·in2
Error: 18%
Displacement (in)
-0.25
-0.2
-0.15
-0.1
-0.05
0
0
-50
-100
Experimental Data
-150
therotical
-200
-250
-300
y = 2726.3x + 26.931
-350
-400
-450
-500
Data Analysis
- C-Channel -
Effective Bending Stiffness, (EI)eff :
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Theoretical: 5.64x105 lb·in2
Experimental: 1.66x105 lb·in2
Error: 71%
Displacement (in)
-0.2
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0
-50
y = 1364.3x - 0.8696
Experimental Data
-100
Theoretical Data
-150
-200
-250
Force (lbs)
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Data Analysis
- I-beam -
Effective Bending Stiffness, (EI)eff:
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Theoretical: 5.64x105 lb·in2
Experimental: 2.28x105 lb·in2
Error: 60%
Displacement (in)
-0.55
-0.45
-0.35
-0.25
-0.15
-0.05
0
-100
-200
Experimental Data
Theoretical Data
-300
-400
-500
y = 1879.8x + 93.431
-600
-700
-800
-900
Force (lbs)
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Data Analysis
- Sinusoidal -
Effective Bending Stiffness, (EI)eff:
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Theoretical: 2.81x105 lb·in2
Experimental: 1.13x105 lb·in2
Error: 60%
Displacement (in)
-0.25
-0.2
-0.15
-0.1
-0.05
0
-5
Experimental Data
-15
Theoretical Data
-25
y = 195.7x - 3.9594
-35
-45
-55
Force (lbs)
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Failure Modes
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Foam/composite interface sheared
Sinusoidal
 Rectangular
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Failure Modes
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Matrix/fibers crushed
I-Beam
 C-Channel
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Results/Conclusion
I-beam
Theoretical EI
(lb·in2)
5.64x105
Experimental EI
(lb·in2)
2.28x105
C-Channel
5.64x105
Rectangular
Sinusoidal
Beam
Max Force (lb)
Max Displacement (in)
890
0.54
1.66x105
250
0.19
2.81x105
3.31x105
465
0.2
2.81x105
1.13x105
50
0.25
Observations:
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I-Beam held most weight
Max force held by sinusoidal was less then expected
C-Channel twisted out of MTS
More test samples needed
More experience using MTS
Questions?
Special Thanks To:
Dr. Dayal
Chunbai Wang
Peter Hodgell