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Principles of Regenerative Electric-powered FlightJ. Philip Barnes 04 April 2014 Update
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
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Presentation Contents
• Nature’s “Regen” ~ the Great Frigate Bird• Regen aircraft elements & operating modes• “Windprop” aero design and performance• DC motor-generator, controller, and battery• “Regenosoar” vehicle & system performance • Summary & Recommendations
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Nature’s Regen Aircraft ~ the Great Frigate Bird
• Flight sustained by atmospheric vertical motion• Energy rate sensor ~ air temp, air pressure...?• Permeable plumage ~ no water landing or takeoff• Feed by surface plucking ~ Pterodactyl heritage?
• Self-contained takeoff• Emergency thrust • Sortie radius to 1800 km • Sortie duration up to 4 days
• Thermal day and night up to 2800 m• Lowest wing loading of any bird
Data: Henri Weimerskirch, et.al. Nature Jan 2003
Photography: Phil Barnes
30-year lifespan
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
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Windprop• Fixed rotation direction• Sign change with mode
• Thrust, Torque• Power, Current
• Self-contained takeoff • Emergency cruise/climb• Exploit vertical air motion
Optional solar panel
Energy Storage:• Battery• Ultra capacitor• Flywheel motor-generator
ESU
Regen Aircraft Elements and Operation
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
MotorGen
SpeedControl
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5
0
0
0
0
1
0
0
0
000
2
00
0
0
0
3
4
Radius from Centerline, m0 100 200 300 400 5000100200300400500
Elevation, zo ~ m
0
500
1000
1500
2000
2500
3000
3500
4000
u, m/s
Thermal Updraft Contours
Total Energy = Kinetic + Potential
Total Energy = Kinetic + Potential + Stored
• 1oC warmer-air column• 20-minute lifetime• ~ solar power x 10
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
U ~ m/s
Elevation, zo ~ m
12
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Dual-role Propeller andAirborne Wind Turbine
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Blade angle (b ) at radius (r)is measured from rotationplane to the chord line at (r)
Propeller Wake, Pitch, and Blade Angles
More blades at fixed thrust & diameter:• More wakes (one per blade)• Higher pitch ~ wakes farther aft / rotation• Lower rotational speed, lower tip Mach • Upshot: ~ similar efficiency, 2 to 8 blades
• Wake induces downwash (normal to local section) •Pitch:
helix length per rotation htip = 2 p R tan btip
• Uniform pitch: r tan b = R tan btip
• Blade tip angle (btip): 14o ~ low pitch 30o ~ high pitch
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
HorseshoeVortices
r
R
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Windprop Blade Angle and Operational Mode
v
wr
b
w
Pinwheel
• Pinwheeling: Zero angle of attack, root-to-tip- No thrust, no torque, small drag
v
wr
L b
w
Propeller
• Efficient prop: Rotate ~115% of “pinwheel RPM,” or fly at 87% of “pinwheel airspeed”
v w
r -L
b
w
Turbine
• Efficient turbine: Rotate ~ 87% of “pinwheel RPM,” or fly at 115% of “pinwheel airspeed”
• Define: “Speed ratio,” s v / vpinwheel = v / [ wr tan b ]
• Specify symmetrical sections & uniform pitch
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Speed Ratio, s ≡ v / ( w R tan btip) 0.5 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
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Force Coefficient, F ≡ f/(qpR2)
B=2
2
B=8
8
F
Low-RPM 8 Blades, btip = 30o
Pinwheel
F= -0.011 @ B=2
F= -0.008 @ B=8
Propeller ~ climb
Max efficiencyRegeneration Max capacity
Regeneration
Propeller ~ cruise
Speed Ratio, s ≡ v / ( w R tan btip) 0.5 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
Efficiency
0.0
0.2
0.4
0.6
0.8
1.0
h Turbine t w / (f v)
Blades_btip
2_14o
8_30o
c l_minc l_max
Propellerf v / ( t w)
High-RPM 2 Blades, btip = 14o
Windprop Efficiency and Thrust
r / R 0.00 0.25 0.50 0.75 1.00
Blade Geometry
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Thickness
Chord, c/ R
Sym. Sectionsr tan b = R tan b tip
hub
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
sc
NF
DT
DD
sc
NF
vLDn
z
D
T
D
wp
D
wp
n
22
/
/1
)/(1
RR
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How Flow the ElectronsMotor-generator principles
Synergy: motor-gen & windpropDC Voltage conversion
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e
t
w
E
N turns
Generating
i
vi vq
Fp
Fq
B
i
Electromotive force, e= potential energy / charge= work / charge, (Fp / q) L= 2 N w (D/2) B L e = NDBL w ≡ k w
Change to generator mode:Same direction, rotation, wSame sign for EMF, e Sign change of torque, t Sign change of current, i
Torque, t = 2N (D/2) B (dx/dt) dq = 2N (D/2) B (dq/dt) dxt = NDBiL = NDBL i = k i
(+) Charge (q) with velocity, V in magnetic field of strength, B:Force vector, F = q V x B
e
t
w
E
N turns
Motoring
B
i
vi vq
Fp
Fq
B
i
L
Motor-generator Principles
=tw eiBoth
modes
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
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System Motoring and Regeneration Efficiencies
Pulse-width modulation (PWM) d ≡ “Duty cycle” ; h ≈ 0.99 d 0.25
(Refs 1,2)
"Ideal system efficiency" ignoring controller & torque lossesh system motor ≈ t w/(eb i) ≈ e i / (eb i) = e / eb = k w / eb h system regen ≈ eb i / (tw) ≈ eb i / (ei) = eb / =e eb / (k w)
Inverter(for brushless MG)
h ≈ 0.98 (Ref.3) Rm
Torque lossbrushes,iron loss,windage...
em
t+Dt
w
Vm
Rb
eb
Vb
ebQuote regen power here
Refs: (1) AiAA 2010-483, Lundstrom, p.8 ; (2) NASA CP 2282, Echolds, p.89 ; (3) Technical Soaring, Vol. xxi, No. 2, Rehmet, p. 39
i MotorRegen
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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Speed Ratio, kw/eb = EMF Ratio, emg/eb
Non-dimensional Characterization of Permanent-magnet DC Motor-generator-battery System Performance ~ Theory and Test Data
eb
Rt
em
Motor-generator & Battery ~ Performance Envelope and Data
REGENERATIONLMC "generator curve"48V / 3,600 RPMk = 0.16 N-m/ARt = 0.041 OhmLMCLTD.net
MOTORINGEEMCO 427D10024V / 15,000 RPMk = 0.015 N-m/ARt = 0.075 Ohm
THEORETICAL EFFICIENCY, kw/e bCURRENT GROUP, i R
t / eb
TORQUE GROUP, t Rt / (k e
b )
Phil
Barn
es A
pr-0
8-20
11
eb /(kw)
i
t
100% Duty Cycle
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
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Battery effectiveshuffled position
Takeoff / climb
Cruise
~Pinwheel
Best regen
Max regen
MotorGen
Periodic (about once per minute) battery shuffle via rotary switchensures equal time for all batteries at each “totem pole” position
Regeneration enjoys reduced active battery resistance
“Low-tech” Regen DC Electric Propulsion With Battery Shuffler
VoltageNode
Electrical Ground
4
5
3
2
1
Negativeterminalof batterynumber:
E D C BF
EDC
B
BATTERYSHUFFLESWITCH
1
5
Positiveterminal of battery number:
DCBAE
DCB
A2
3
4
Applicable: Brushed or Brushless, but no pulse-width modulation
Phil
Barn
es 0
7 Ap
r 201
1
F
E
D
C
B
A
Battery Series “Totem Pole” Voltage Node
Rotate 80o
Clockwise,then counter
clockwise
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
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• DCBC: Key enabler, efficient bi-directional power management– Only the motoring mode is shown in the introductory graphic above
• “Boosts” DC voltage ~ 0-500 % with minor input/output ripple • Enables low-voltage battery to drive high-voltage LED lamp*• Enables reduced battery totem pole length, i.e. Toyota Prius* • DC voltage “boost” is controlled by PWM “duty cycle”• Power in ~ Power out: DC output current is thus reduced• Options: brushed-DC/low voltage or brushless/high voltage• Adjusts effective battery voltage to efficiently drive the M-G• Boosts motor-gen effective EMF for efficient battery recharge
* Wikipedia, “DC boost converter”
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014
DC boost converter enables efficient motoring & regen
CL
VB
M-GiGBTPWM
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16Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014
|-- --|dt t
d ≡ duty cycle ; t ≡ periodiGBT gate PWM
CL
VB
Mot-gen
iGBTPWM
VM
DC boost converter – Equivalent circuits
L diB /dt
C dVM/dtVB
iB
iM
VM
iGBT off
C dVM/dt
L diB /dt
iB
VB
iM
VM
iGBT on
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17Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014
DC boost converter – Voltage gain & conversion efficiency
L DiB2 /[(1-d)t]
C DVM2 /[(1-d)t]VB
iB
iM
VM
Segment 2: iGBT off for Dt = (1-d)t
C DVM1/(dt)L DiB1 /(dt)
iB
VB
iM
VM
Time segment 1: iGBT on for Dt = dt
[a] Voltage loop: VB - L DiB1 /(dt) = 0[c] Output current: iM - C DVM1 /(dt) = 0
[b] VB - L DiB2 /[(1-d)t] = VM
[d] iB - C DVM2 /[(1-d)t] = iM
[e] PWM cycle: DiB1 + DiB2 = 0 [f] DVM1 + DVM2 = 0
• Voltage & current gains set by duty cycle (d) alone [high-frequency assumed]• Efficiency is unity (resistance neglected) and is thus unaffected by L, C, d, t• “Deltas” (D) represent ripple applied to input current (iB) & outputs (iM, VM)
[g] Combine [a,b,e]: VM/VB = 1/(1-d) [h] via [c,d,f]: iM/iB = 1-d
Combine [g,h]: h ≡ iMVM /(iBVB) = 1
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18Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014
DC boost converter - efficiency and regen application
• 90o rotary mode selector switch for motoring or regeneration• Low-voltage option: Batteries in parallel, brushed-DC motor-gen• Hi-voltage option: Batteries in series, inverter & brushless DCMG
Regen
M-G
Motor
"Evaluation of 2004 Toyota Prius,"Oakridge National Lab, U.S. Dept. of Energy
233 Vdc in
5 10 15 20 kW
PWMiGBT
CL VB
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"RegenoSoar" Air Vehicle and System Performance
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RegenoSoar Design Rationale
Configuration Rationale• Maximum laminar airflow aero & counter-rotation props• Pusher avoids windprop helix downstream aero upset• One-person handling/steering (remote or in the cockpit)• Winglets include tip wheels (wings flex up under load)
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RegenoSoar ~ In Flight
Applications and Operations• Fleet broadcast energy rate• High-altitude earthwatch• Jet-stream rider• Storm rider
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Vehicle Performance ~ New Formulation, New Insight
L= nn w
T-D
w
v
f
g
Frigate Bird• T/D=0 (no thrust)• sink rate (-dz/dt) = nn(D/L)v
Frigate Bird and Regen• sink increases with g-load (nn)• sink increases with airspeed (v)
Regen T/D• climb: 6.3 • cruise: = 1.0 • solar-augmented glide: 0.5• pinwheel glide: -0.1• efficient regen (thermal): -0.4 • capacity regen (descent): -1.0
g
norientatio of regardless
1][(T/D)v(D/L)ndz/dt
Therefore,
γvsindz/dtrate,climb)3
(T/D)(D/w)/w)2
D/Ln(L/W)(D/L)/W)1
vsinγ(D/W)]v[(T/W)
/Wndefinev/W;bymultiply
state}{steadysinγT
n
n
n
T
D
L
WDDerive steady-climb Equation
Note: nn= cos g /cosf cL = nn w / (qs)
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Regenerative Flight Equation
“Total Climb”
Rate of change oftotal specific energy
Updraft “Total Sink”
Still-air “clean” sink rate
Effect ofwindprop
D
Tv
L
Dnuz nt 11
“Exchange Ratio,” as applicable:• turbine system efficiency ~71% • 1 / propeller system efficiency• 0 for pinwheeling (no exchange)
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Ground-relative Climb Rate, m/sMax-capacity Regeneration in the Thermal
Normal Load Factor, Nn
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Elevation, m
0
500
1000
1500
2000
2500
3000
0.0
1.0
1.51.6
0.5
Ground-relative Climb Rate, m/sMax-efficiency Regeneration in the Thermal
Normal Load Factor, Nn1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Elevation, m
0
500
1000
1500
2000
2500
3000
3500
2.2
0.0
1.01.5
2.0
0.5
Total Specific Energy-gain Rate, m/sMax-efficiency Regeneration in the Thermal
Normal Load Factor, Nn
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Elevation, m
0
500
1000
1500
2000
2500
3000
3500
2.5
0.0
1.01.5
0.5
2.0
Climb and Regeneration in the Thermal (minimum-sink airspeed)
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com
Climb rate Contours Energy rate Contours
Equilibrium Regeneration
Optimum
Total Specific Energy-gain Rate, m/sMax-capacity Regeneration in the Thermal
Normal Load Factor, Nn
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.80
500
1000
1500
2000
2500
3000
0.0
1.01.5
2.0
0.5
2.1
Elevation, m Elevation, m
Elevation, m
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Item / mode ---> Climb max L/D Cruise max L/DPinwheel max L/D
Regen max efficiency, minimum sink,
zo=1480-m
Regen max capacity, minimum sink,
zo=1480-m
Airspeed, v ~ km/hr 85.0 85.0 85.0 77.2 77.2
Updraft, u ~ m/s 0.00 0.00 0.00 3.72 3.72
Turn radius, r ~ m n/a n/a n/a 56.5 56.5
Load factor, n ~ g 1.00 1.00 1.00 1.30 1.30
Lift coefficient, cL 0.64 0.64 0.64 1.12 1.12
Drag coefficient, cD (clean) 0.022 0.022 0.022 0.040 0.040
Installed thrust/drag ratio, T/D 6.33 1.00 -0.10 -0.40 -1.01
Installation penalty, D/D= -T/D 0.17 0.09 0.10 -0.03 -0.03
Clean sink rate, still air, n (D/L)v ~ m/s 0.75 0.75 0.75 1.03 1.03
Climb rate in still-air, dz/dt ~ m/s 4.00 0.00 -0.83 -1.43 -2.06
Total energy rate, dz t /dt ~ m/s -5.40 -1.05 -0.83 2.58 2.18
Ground-observed climb, dz o /dt ~ m/s 4.00 0.00 -0.83 2.29 1.66
Windprop speed ratio, s 0.57 0.85 1.00 1.15 1.75
Windprop speed ~ RPM 1096 735 625 494 324
Windprop Force group, F 0.92 0.14 -0.0070 -0.10 -0.26
Windprop efficiency, ht or hp 0.63 0.84 n/a 0.85 0.64
Powertrain efficiency (non-windprop) 0.80 0.85 n/a 0.85 0.8
System efficiency hst or hsp 0.50 0.71 n/a 0.72 0.51
Exch. ratio, 1/hsp : hst : 0 applic.) 1.98 1.40 0.0 0.72 0.51
Total Shaft power, tw ~ kW 29.5 3.50 0.00 -1.36 -2.58
Energy storage rate ~ kW -36.9 -4.12 0.00 1.16 2.07
0.82
0.870.82
0.88
Regenerative Flight Equation Applied for RegenoSoar
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Summary and Recommendations Regenerative Electric-powered Flight
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Regenerative Electric-powered Flight
• The Great Frigate Bird ~ nature’s “regen”– Self-contained takeoff & emergency thrust on demand– Energy extracted from vertical atmospheric motion– Energy rate sensor, flight sustained day-and-night
• “Energy Synergy” of the Windprop & Motor-Gen– Optimum “speed ratios” about 87% & 115% by mode
• Windprop: 8 blades spin slow, quiet, & efficient– Pinwheeling ~ imposes only minor performance penalty
• DC boost converter - efficient bi-directional power• Climb/sink rates, any mode, g-load, orientation• Climb in the thermal, even with maximum regen• Regen in ridge and wave lift to extend flight• Regenerative Flight Equation ~ total energy rate• We’re good to go ~ Let’s emulate the Frigate Bird
Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www.HowFliesTheAlbatross.com