Aircraft Energy Gain From
an Atmosphere in Motion
J. Philip Barnes
15 June 2015 update
Part 2 of 2
J. Philip Barnes www.HowFliesTheAlbatross.com
Part 2 of 2:
Efficient Electric Flight
- The Regeneration Factor
28 June 2015
J. Philip Barnes
2
Presentation Contents
Windprop
Updrafts
The visionaries
VM
Regenosoar
iGBT
M-G
Brushless MG
Power Electronics
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Presentation Contents
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Hermann Glauert
“Consider the case of a
windmill on an aeroplane”
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J. Philip Barnes
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Paul MacCready
Regenerative electric flight
concept “with caution,” ‘99
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Presentation Contents
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Rotor velocity diagram - "Pinwheeling" & “Betz” conditions
wr
Blade section
Looking outboard,
Blade at 3 o’clock
Vo
Axial
wind
Vo
b
b
• Angle of attack = 0, hub-to-tip
• wr tanb = Vo Therefore:
• r tanb = Vo /w = R tan btip
• Approaches "Betz Condition“
Rotational
wind, w r
Vo
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J. Philip Barnes
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Windprop Blade Angle and Operational Mode
Propeller
b
L
Turbine
Pinwheel
b
b
V
V
V
wr
wr
wr
-L
W
W
W
Define: “Speed ratio,” s  v / vpinwheel = v / [ wR tanbtip ]
Similar to advance ratio (J) but meaningful for 3 modes
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Windprop Efficiency and Thrust
1.0
Efficiency
8
0.8
2
0.6
h
Low-RPM 8 Blades bt = 30o
Propeller
f v / (t w)
0.4
Turbine
t w / (f v)
0.2
Speed Ratio, s ≡ v / (w R tan bt)
0.0
0.5
1.0
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
0.9
Propeller ~ climb
0.8
B=8
0.7
• Comparable efficiency by mode
• Eight blades spin slow & quiet
• Climb power ~ 7x cruise power
B=2
0.6
0.5
0.4
Propeller
~ cruise
0.3
0.2
0.1
Force Coef.,
F ≡ f/(qpR2)
Regeneration
Max efficiency
Regen
capacity
0.0
-0.1
Pinwheel
High-RPM 2 Blades bt = 14o
2
-0.2
8
-0.3
-0.4
0.5
Two windprops, same
thrust and diameter
Speed Ratio, s ≡ v / (w R tan bt)
0.6
0.7
0.8
0.9
1.0
1.1
Regenerative Electric-powered Flight
1.2
1.3
1.4
J. Philip Barnes
1.5
1.6
1.7
1.8
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BLDC M-G & inverter-rectifier: System efficiency
kw
i
InverterRectifier
eb
t
M-G
w
tw = em i
em= k w
t=ki
Motoring efficiency = tw / (eb i) = em i / (eb i) = k w / eb
Regen. efficiency = eb i /(tw) = eb i / (em i) = eb /(k w)
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Motor-generator & Battery ~ Performance Envelope and Data
Non-dimensional Characterization of Permanent-magnet DC
Motor-generator-battery System Performance ~ Theory and Test Data
1.0
100% Duty Cycle
0.8
0.6
0.4
0.2
MOTORING
REGENERATION
EEMCO 427D100
24V / 15,000 RPM
k = 0.015 N-m/A
Rt = 0.075 Ohm
LMC "generator curve"
48V / 3,600 RPM
k = 0.16 N-m/A
Rt = 0.041 Ohm
LMCLTD.net
Windprop
synergy
i
eb
em
t
-0.2
Phil Barnes Apr-08-2011
Rt
0.0
-0.4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Speed Ratio, kw/eb = EMF Ratio, emg/eb
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J. Philip Barnes
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“Six-pack” inverter-rectifier ("inverting" for motoring)
VB
1
2
2
-7V 15V
VB
•
•
•
•
1
3
3
Inverter converts 2-wire DC to 3-wire "AC“
Alternating transistor “diagonal pairs”
Commutation toggles each phase 0-to-VB
Relatively low frequency at full power
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Six-pack inverter-rectifier (rectification for regeneration)
Snapshot
e1 - e3 > eB
1
1
eB
Diodes provide
"free" regen!
2
2
3
3
•
•
•
•
M-G max delta EMF exceeds battery EMF
Six-pack rectifies 3-wire AC into 2-wire DC
Battery recharged through flyback diodes
IGBTs unidirectional: commutation ignored
Regenerative Electric-powered Flight
J. Philip Barnes
Current to battery!
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Cruise efficiency penalty when “chopping” the main current
BLDC commutation voltage
waveform (full power) has
“relatively-low” frequency
Commutation with chopping
PWM superimposed (cruise)
has “very-high” frequency
ion
iav
| t | | | dt
• Typical PWM switching freq. f ≈ 20 kHz (inaudible)
• Per-iGBT switching energy loss S ≈ 20 mJ per cycle
• Chopping loss = f S = 0.4 kW ≈ 10% in loitering flight
DC boost converter eliminates part-power chopping loss
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J. Philip Barnes
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DC boost converter - efficiency and regen application
233 Vdc in
97% power-conditioning
efficiency for any mode
Cruise
Regen
Climb
Regen
5
Motor
VB
L
PWM
C
M-G
10
15
20 kW
"Evaluation of 2004 Toyota Prius,"
Oakridge National Lab, U.S. Dept. of Energy
iGBT
• DC boost converter efficiently integrates windprop & motor-gen
• IGBT gate PWM duty cycle adjusts battery or M-G voltage boost
• Efficient bi-directional power over the full operating range
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J. Philip Barnes
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“Chop” Vs. “boost” architectures compared
PWM superimposed
on commutation
i
540V
batt.
"Chopper" architecture
PWM main current chop
M-G
InverterRectifier
540V battery
10% loss at loiter
Regen: none or inefficient
w
t
Commutation
i
"Boost" architecture
PWM sets DCBC boost
200V battery
03% loss at loiter
Regen capable & efficient
Regenerative Electric-powered Flight
200V
batt.
DC Boost
Converter
PWM
J. Philip Barnes
M-G
InverterRectifier
2-way
boost
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t
w
19
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Regenosoar
8-blade rotors
Low RPM, quiet,
Low tip Mach
Counter rotors
Symmetric flow
Zero net torque
Pusher Config., laminar flow, no helix upset
Ground handling
No assistance req'd
Winglet tip wheels
Pod-air-cooled
MG & PE
Regenerative Electric-powered Flight J. Philip Barnes
Regen parked in
the wind with
safety perimeter
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Regenerative Electric-powered Flight J. Philip Barnes
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Regenerative Electric-powered Flight J. Philip Barnes
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Test data – Wind statistics (terrestrial)
Wind probability density data and approx. curve fit
0.18
Probability
Density, r
1/(m/s)
0.16
r ≈ (2.735 / Wmax ) [ sin { p (1 - W/Wmax) 2.5 } ] 1.6
0.12
0.10
J. Philip Barnes April 2015 www.HowFliesTheAlbatross.com
Dutch coast at 11m
Delabole England at 33m
Approx.fit, Vmax=25m/s
Effect of Vmax=20 m/s
Effect of Vmax=30 m/s
0.14
0.08
AGARD AG-243 Wind Energy, p. 2-14
ASME J. Solar Energy, V. 128, p. 533
0.06
0.04
Area = 1.0 for any Wmax
0.02
Wind speed, W, m/s
0.00
0
5
10
15
20
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June 2015
30
Ridge lift analysis ~ Courtesy of Hermann Glauert
U = 0.3 Wo
Wo
U = 0.5 Wo
Stream function study
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Regenerative Electric-powered Flight J. Philip Barnes
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1.75
1.45
1.15
Windprop
speed ratio
Regenerative Electric-powered Flight J. Philip Barnes
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Conditions for total energy gain with regeneration
“Physics” require:
• Updraft (or descent)
• High L/D, low sink
• High system efficiency
“Clean”
Updraft sink rate

D
zt  u  nn V
L
“Total
Climb”
Trade 2% prop. efficiency
benefit of symmetric blades
for +TBD% range via regen
Windprop
Effect
T

1  (e  1) D 


“Total Sink”
Regen benefits include:
• Steep final descent
• Landing thrust reversal
• Ground wind recharge
Thermal Updraft Contours
Elevation, zo ~ m
• 1oC warmer-air column
• 20-minute lifetime
• ~ solar power x 10
U ~ m/s
0
1
2
3
4
Total Energy
= Kinetic
+ Potential
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5
J. Philip Barnes
Total Energy
= Kinetic
+ Potential
+ Stored
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Climb rate
Climb rate, m/s
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Energy rate
Energy rate, m/s
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Conclusions – Regenerative Electric Flight
Windprop
Updrafts
The visionaries
A regen is coming soon
to an airport near you!
VM
Regenosoar
iGBT
M-G
Brushless MG
Power Electronics
Regenerative Electric-powered Flight J. Philip Barnes
35
About the Author
Phil Barnes has a Master’s Degree in Aerospace
Engineering from Cal Poly Pomona. He is a
Principal Engineer and 34-year veteran of air
vehicle and subsystems performance analysis at
Northrop Grumman, where he presently
supports both mature and advanced tactical
aircraft programs. Author of several SAE and
AIAA technical papers, and often invited to
lecture at various universities, Phil is presently
leading several Northrop Grumman-sponsored
university research projects including an
autonomous thermal soaring demonstration,
passive bleed-and-blow airfoil wind-tunnel test,
and application of Blender 3D and Python for
parameterization and visualization of aircraft
geometry and flight simulation.
Outside of work, Phil is a leading expert on
dynamic soaring of the wandering albatross,
and he is pioneering the science of
regenerative-electric flight.
J. Philip Barnes
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