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National Aeronautics and Space Administration
www.nasa.gov
Fundamental Aeronautics Program!
2012 Technical Conference March 13-15, 2012
Anita Abrego Aerospace Engineer Aeromechanics/ Ames Research
Center
Danny Barrows, Alpheus Burner, Larry Olson, Harriett Dismond,
Eduardo Solis, Larry Meyn, Ethan Romander
Subsonic Rotary Wing Project!Status of Blade Displacement
Measurements & Analysis
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Outline!
2
• Blade Displacement Measurements"• Data Reduction and
Validation"• Future Considerations"• Closing Remarks"
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Blade Displacement Measurements !
3
Setup/Hardware"• 8-cameras, 2 per rotor quadrant"•
4-Mega-pixel, 12-bit CCD progressive scan
digital cameras, with a pixel resolution of 2048 × 2048 pixels
"
• Nikon 10.5 mm f/2.8 DX (fish-eye) lenses "• Xenon flash-lamp
50 mJ strobes"
Blades"• Targets on the lower surface of each blade"• 48
retro-reflective targets, 2 inch dia."• 3 per radial station at
r/R from 0.2 to 0.97"
Ceiling"• 84 retro-reflective targets, 6 inch dia."• 84 coded
targets"
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Blade Displacement Measurements!
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Primary! Secondary!Blades per quadrant" 4" 1"
Azimuth positions" 40" 11"Images per camera" 60" 12"
Total acquisition time" 10 min" 1 min"
Primary data conditions!• 27 primary data conditions"•
Includes cases with all Airloads data types"• Matched conditions
with PIV and RBOS data"• Most images have been processed"•
Centroid inspections continue"Secondary data conditions!• Most
Airloads data points"• Image processing is underway"
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Long-exposure (~10ms) view of quadrant-1 from BD data camera
2
10 µ-sec data shot exposures
Data Reduction and Validation!
Camera Intersection Example Synchronously Captured Images for
Cameras 1, 2, 7, 8
Blade 1, ψ = 0°
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Camera Calibration Optimization • Currently under investigation
• Static test data, 0° shaft angle, 40
azimuth positions and 3 images/azimuth • Optimized the 3 camera
position
coordinates and 3 angles of each camera
Data Reduction and Validation!
Baseline Optimized
ψ = 120° and r/R = 0.85
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Static Precision and Bias • Static, wind-off measurements over
360° • 0° shaft angle • 40 azimuth positions,160 data points, 3
images each • Mean of 160 determinations of the standard deviation
at a single azimuth was used to
compute precision • Bias error was computed as the standard
deviation of the 160 samples over 360° after
removing the mean values of each blade
Data Reduction and Validation – Uncertainty Considerations!
r/R! Precision! Bias!Pitch" 0.007°" 0.267°"Flap" 0.007°"
0.372°"Lag" 0.002°" 0.366°"
Z"0.20" 0.002 in" 0.432 in"0.97" 0.066 in" 1.429 in"
Elastic Z"0.20" 0.002 in" 0.098 in"0.97" 0.038 in" 1.122 in"
Elastic Twist"0.20" 0.012°" 0.200°"0.97" 0.025°" 0.229°"
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Mean bias offset error • Static, wind-off measurements over
360° • 40 azimuth positions • 160 data points, 3 images each •
0° shaft angle • Collective pitch set to 0° • Lag angle and
elastic twist are expected to be near 0° • Mean offset from 0 can
be viewed as a bias offset error.
Data Reduction and Validation – Uncertainty Considerations!
r/R! Bias!Pitch" 0.97" 0.102°"Lag" 0.97" 2.253°"
Elastic Twist" 0.97" -0.023°"
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Bias Error vs Reference Transformation End r/R µ = 0.30, CT/σ =
0.10, Mtip = 0.65
Data Reduction and Validation!
0 0.2 0.4 0.6 0.8 12
1.5
1
0.5
0
0.5
1
1.5
2
Reference transformation end, r/R
Pitc
h, d
eg
tip bending 6 intip bending 0 intip bending 17 in
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 14
3
2
1
0
1
2
3
Reference transformation end, r/R
Flap
, deg
tip bending 6 intip bending 0 intip bending 17 in
0 0.2 0.4 0.6 0.8 11
0.8
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1
Reference transformation end, r/R
Lag,
deg
tip bending 6 intip bending 0 intip bending 17 in
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Bias Error vs Reference Transformation End r/R µ = 0.30, CT/σ =
0.10, Mtip = 0.65
Data Reduction and Validation!
0 0.2 0.4 0.6 0.8 110
5
0
5
10
15
20
Reference transformation end, r/R
Elas
ticZ,
inch
tip bending 6 intip bending 0 intip bending 17 in
0 0.2 0.4 0.6 0.8 10.5
0
0.5
1
Reference transformation end, r/REl
astic
twis
t, de
g
tip bending 6 intip bending 0 intip bending 17 in
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Pitch, Flap and Lag with NFAC measured and CFD µ = 0.30, CT/σ =
0.10, Mtip = 0.65
Data Reduction and Validation!
0 30 60 90 120 150 180 210 240 270 300 330 3600
2
4
6
8
10
12
14
16
Azimuth, deg
pitc
h An
gle,
deg
Blade 1Blade 2Blade 3Blade 4CFD/CSDCommandedNFAC meas
0 30 60 90 120 150 180 210 240 270 300 330 3603
4
5
6
7
8
Azimuth, deg
Flap
Ang
le, d
eg
Blade 1Blade 2Blade 3Blade 4CFD/CSDNFAC meas
0 30 60 90 120 150 180 210 240 270 300 330 3601
2
3
4
5
6
7
8
9
Azimuth, deg
Lag
Angl
e, d
eg
Blade 1Blade 2Blade 3Blade 4CFD/CSDNFAC meas
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Data Reduction and Validation!
0 30 60 90 120 150 180 210 240 270 300 330 3600
2
4
6
8
10
12
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Azimuth, deg
pitc
h An
gle,
deg
Blade 1Blade 2Blade 3Blade 4CFD/CSDCommandedNFAC meas
0 30 60 90 120 150 180 210 240 270 300 330 3604
3
2
1
0
1
2
3
Azimuth, deg
Pitc
h An
gle
Com
man
ded,
deg
Blade 1Blade 2Blade 3Blade 4CFD/CSDNFAC meas
Pitch vs Azimuth µ = 0.30, CT/σ = 0.10, Mtip = 0.65
Pitch − Commanded vs Azimuth µ = 0.30, CT/σ = 0.10, Mtip =
0.65
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Data Reduction and Validation!
0 30 60 90 120 150 180 210 240 270 300 330 3605
4
3
2
1
0
1
2
3
4
5
Azimuth, degEl
astic
Tw
ist,
deg
Blade 1Blade 2Blade 3Blade 4CFD/CSD
0 30 60 90 120 150 180 210 240 270 300 330 36020
15
10
5
0
5
10
Azimuth, deg
Elas
tic
Z, in
Blade 1Blade 2Blade 3Blade 4CFD/CSD
Elastic Bending and Elastic Twist with CFD µ = 0.30, CT/σ =
0.10, Mtip = 0.65, r/R = 0.97
Elastic Bending Elastic Twist
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0 0.2 0.4 0.6 0.8 120
15
10
5
0
5
Radial position, r/R
Elas
tic
Z, in
ch
Measured, RBM EstimatedPredicted, RBM ExactPredicted, RBM
Estimated
0 0.2 0.4 0.6 0.8 11
0
1
2
3
4
5
6
7
Radial position, r/R
Elas
tic
Z, in
ch
Measured, RBM EstimatedPredicted, RBM ExactPredicted, RBM
Estimated
0 0.2 0.4 0.6 0.8 11.5
1
0.5
0
0.5
1
1.5
Radial position, r/R
Elas
tic
Z, in
ch
Measured, RBM EstimatedPredicted, RBM ExactPredicted, RBM
Estimated
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Data Reduction and Validation!Elastic Bending with CFD
µ = 0.30, CT/σ = 0.10, Mtip = 0.65 ψ = 0° ψ = 150°
ψ = 255°
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Data Reduction and Validation!Elastic ΔZ Standard Deviation vs
r/R
µ = 0.30, CT/σ = 0.10, Mtip = 0.65
ψ = 150° ψ = 0°
ψ = 255°
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Data Reduction and Validation!Change in ¼-chord Elastic Bending
vs Revolution
µ = 0.30, CT/σ = 0.10, Mtip = 0.65
ψ = 0° ψ = 150°
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r/R = 0.20 r/R = 0.97 ψ = 255°
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Data Reduction and Validation!Elastic twist with CFD
µ = 0.30, CT/σ = 0.10, Mtip = 0.65
0 0.2 0.4 0.6 0.8 12
1.5
1
0.5
0
0.5
1
Radial position, r/R
Elas
tic tw
ist,
deg
ExperimentExperiment meanComputed
0 0.2 0.4 0.6 0.8 15
4
3
2
1
0
1
2
Radial position, r/R
Elas
tic tw
ist,
deg
ExperimentExperiment meanComputed
0 0.2 0.4 0.6 0.8 13
2.5
2
1.5
1
0.5
0
0.5
1
Radial position, r/R
Elas
tic tw
ist,
deg
ExperimentExperiment meanComputed
ψ = 0° ψ = 150°
ψ = 255°
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Data Reduction and Validation!Elastic twist standard deviation
vs r/R
µ = 0.30, CT/σ = 0.10, Mtip = 0.65 ψ = 0° ψ = 150°
ψ = 255°
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Data Reduction and Validation!Change in Elastic Twist vs
Revolution
µ = 0.30, CT/σ = 0.10, Mtip = 0.65
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ψ = 0° ψ = 150°
ψ = 255°
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Future Work!
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Data Processing!• Primary data point inspections"• Secondary
data point processing "• Continue efforts to automate image
processing and validation"• Data processing and validation
improvements continue,"
(1) optimization of camera calibrations"(2) alternate fish-eye
corrections based on equisolid angle projection"(3) weighting of
multiple intersection XYZ results by the variance to strengthen the
final
intersection results "
Collaboration!• Comparisons with computational results will
continue and assist with data
validation"• Comparisons with PIV and RBOS data"
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Closing Remarks !
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• The static precision of the photogrammetry technique for
pitch, flap, lag, were found from a static azimuth sweep to be less
than 0.01°. "
• Bias errors over the full range of azimuth can approach
0.4°. (All values are presented in terms of one standard
deviation.) "
• An additional mean bias offset error of 2.25° was discovered
for lag angle for the static sweep. "
• The static precision for elastic bending and twist were found
to be 0.002 inch and 0.012° respectively, with bias errors over the
full range of azimuth of 1.2 inch and 0.30° respectively."
• Comparisons of experimental and computational results for a
moderate advance ratio forward flight condition show good trend
agreements, but show significant mean discrepancies for lag and
elastic twist. "
• The experimental values of pitch agree well with the NFAC DAS
commanded pitch. "
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Closing Remarks!
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Preliminary results reported in the following publications,"–
Blade Displacement Measurements of the Full-Scale UH-60A
Airloads
Rotor, American Institute of Aeronautics and Astronautics
Applied Aerodynamics, June 2011."
– Blade Displacement Measurement Technique Applied to a
Full-Scale Rotor Test, American Helicopter Society 68th Annual
Forum, May 2012."
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