Regenerative Electric-powered Flight J. Philip Barnes 1 Regenerative Electric Flight Synergy and...

Regenerative Electric-powered Flight J. Philip Barnes 1

Regenerative Electric FlightSynergy and Integration of Dual-role Machines

J. Philip Barnes 27 Dec 2014

Animated slides: F5 keyAlso: View ~ "Notes Page"

2Regenerative Electric-powered Flight J. Philip Barnes

Great theoreticians and experimentalists (all Ph.D.)

Ludwig Prandtl - Germany

Hermann Glauert - U.K.Royal Aeronautical Society

Albert Betz - Germany

Paul MacCready - USA

3

Presentation Contents

• Regen. elec. flight: Origin & Introduction

• Dual-role machines:– Propeller and wind turbine– DC motor-generator– Brushless motor-generator

• Integration: – Inverter-rectifier– DC boost converter– "Chop" Vs. "Boost" architecture

• “Regenosoar” aircraft concept

• Summary & Look Ahead

4

Exploit opportunities tostore Vs. expend energy

Energy Storage Unit:• Battery and/or:• Ultra capacitor• Flywheel w/M-G

Regen Aircraft Elements and Operation

Regenerative Electric-powered Flight J. Philip Barnes www.HowFliesTheAlbatross.com

PowerElectronics

Motor-Gen (M-G)

Windprop• Fixed rotation direction• Sign change with mode

• Thrust, Torque• Power, Current

5







6

Blade angle (b ) at radius (r)is measured from rotationplane to the chord line at (r)

Propeller Wake, Pitch, and Blade Angles

Effect of more blades (fixed T, R):• Steep blade angle, much lower RPM• Lower tip Mach, much-reduced noise • High torque → dual & counter rotation• Numerically integrate wake for loading

• 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


HorseshoeVortices

r

R

8Regenerative Electric-powered Flight J. Philip Barnes

Test data validating Glauert's rationale on induced velocity

Gradual buildup

F.E. Weick, Aircraft Propeller Design, McGraw-Hill, p. 102-103

Immediate swirl, as predicted by Glauert

J. Philip Barnes www.HowFliesTheAlbatross.com

• Propeller or wind turbine• Angle of attack = 0 • No change to flow direction• No change to relative wind• Helical drag wake (unloaded)• wr tanb = Vo (all sections)

• or, r tanb = const.= R tanbtip

Blade section Looking outboard,Blade at 3 o’clock

Cho

rd li

ne

b

Rotor blade velocity diagram - "Pinwheeling" condition

Pinwheeling sets up "Betz Condition"• Propeller or turbine at no load Perturb w or Vo to load rotor• Helical wake (drag and/or vortex)• Sets blade angle distribution b(r):

b = tan-1 [ Vo / (wr) ]• Says nothing about blade planform

Axial wind

Vo

Vo

Rotationalwind, w r

Rel

ativ

ew

ind

W1

b

Vo

W2

Hel

ical

wak

e

w r

J. Philip Barnes www.HowFliesTheAlbatross.com

• Non-rotational (axial) inflow• Axial velocity locally conserved • Final swirl imparted suddenly• Helical wake anchored at c/4• Wake ~ aligned with chordline• Wake-induced velocity (Vi)

• Glauert: 2Viq at "rotor out"• Absolute velocity (V) increased• Relative wind (W) decreased• Immediate static pressure rise

Propeller blade - comprehensive velocity diagram

Glauert: consistent physics & geometryVortex wake ~ aligned with chord lineBetz cond. (wake helix), prop or turbine,with or without rotor loading, provided:r tan b = const. and z=0 (sym. sections)

Relativewind W1

a

Wq w w r - Viq

f

V1

z Ze

ro-li

ft lin

e

Rotational wind

Axial wind

V1 w Vo+Vix

Hel

ical

wak

evo

rtex

shee

t

W2

V1

w r - 2Viq

V2

Blade section Looking outboardBlade at 3 o’clock

Chord line

b

Viq

Vix

Vi

11

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 w v / vpinwheel = v / [ wR tanbtip ]

• Symmetrical sections and r tan b = R tanbtip


12

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

High-RPM 2 Blades, btip = 14o

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)

Pinwheel

F= -0.011 @ B=2

F= -0.008 @ B=8

Propeller ~ climb

Max efficiencyRegeneration Max capacity

Regeneration

Propeller ~ cruise

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


• Comparable efficiency by mode• Eight blades quieter than two• Climb power ~ 7x cruise power

sc

NF

DT

DD

sc

NF

vLDn

z

D

T

D

wp

D

wp

n

22

/

/1

)/(1

RR

13







14

e

t

w

E

N turns

Generating

i

vi vq

Fp

Fq

B

iChange to generator mode:Same direction, rotation, wSame sign for EMF, e Sign change of torque, t Sign change of current, i

Electromotive force, e= potential energy / charge= work / charge, (Fp / q) L= 2 N w (D/2) B L e = NDBL w ≡ k w

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

= t w e iBoth

modes


k = "EMF constant"

15

System Motoring and Regeneration Efficiencies

"Ideal system efficiency" ignoring controller and all losseshsystem motor ≈ t w/(eb i) ≈ em i / (eb i) = em / eb = k w /

eb hsystem regen ≈ eb i / (tw) ≈ eb i / (emi) = eb / em = eb / (k

w)

Torque

em=kwt

w

Rt

eb

System total resistance

(*) AiAA 2010-483, Lundstrom, p.8

i MotorRegen


Typical controller pulse-widthmodulation (PWM) of duty cycle( ) d and efficiency h ≈ d 0.25 (*)

16

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

Rtem

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

CURRENT GROUP, i Rt / e

b

TORQUE GROUP, t Rt / (k e

b )

Phil

Barn

es A

pr-0

8-20

11

i

t

100% Duty Cycle


THEO. EFFICIENCY, kw/e b e

b /(kw)

Trends match theory

Windprop synergy

17








Brushless "DC" Motor-generator ~ "Y" configuration

Brushed Vs. BrushlessVirtues, features, & limits

Brushed:Theory foundation =tw ei ; =e kw ; =t ki

2-wire interfaceSimplified controlBrush maintenance~120V limit (arcing)Low-speed cogging

N

SBrushless:Inverter required3-wire interface>1000V capableMinimal coggingSame as brushed:

=tw ei ; =e kw ; =t ki

19

Equivalent DC machine

Brushless motor-gen. & inverter: Equivalent DC machine

Brushless machine with inverter/rectifier as a system follows brushed DC machine principles: tw = emi ; em = kw ; t = k iBoth systems have 2-wire interface with the power circuit

M-Geb

i


= t w em imotor or gen

Inverter-Rectifier

t

w

21








0

20

40

60

80

100

120

8 10 12 14 16 18

Collector current,

Amps

Base Voltage

Linearized transfer characteristic

Gate voltage, VGE

Transistor and flyback diode

Collector

Emitter

GateFlybackDiode

ICVCE

VGE

iGBTMOSFET

104

0

20

40

60

80

100

120

0.1 1 10 100 1000

Collector current, IC ~Amps

Collector-to-emitter Voltage drop, VCE

iGBT conduction characteristic"iGBT Basics," IXYS Corporation, IXAN0063

17

15

13

11

09

Gate voltage, VGE

• "High-tech, high-power light switch"• Inverter commutation & DCBC boost adjust• Lo-freq. (20-100 Hz) for commutation• Hi-freq. (>10 kHz) pulse-width-mod (PWM)• VGE (say 12 V) sets the collector current IC

• Collector voltage VCE (say 600 V) sets power• Flyback diode for switch energy dissipation• iGBT & diode unidirectional (via arrows)• Transistor ~ 2V loss ; Diode ~ 0.7V loss

Gate voltage (VGE) "opens the valve"


Inverter-rectifier ("inverter" for motoring mode)

• Each phase, per cycle: - Connect to battery voltage 120o

- Connect to ground 120o

- "Float" twice for 60o each float• Inverter converts 2-wire DC to 3-wire "AC"• Commutation toggles each phase 0-to-VB

• Switch pairs: one "upper" & one "lower“• Switch applies +15/-7V for iGBT on/off• Avoid short circuit: Always "diagonalize"

VB

VB

12

3

1

2

3-7V 15V S

N


DC-to-AC conversion ~ "inverter" commutation waveforms

AC basis

Inverter

"Dead time" avoids short

circuit


Inverter-rectifier ("inverter" for motoring mode) ~ Snapshots

VB

VB1

23

1

2

3

VB

VB1

23

1

2

3

VB

VB1

23

1

2

3

VB

VB1

23

1

2

3

"Upper" switch pairs diagonally with a lower switchTwo phases are operating; one phase is "floating"


Inverter-rectifier ("rectifier" for generating mode) - iGBT

EB

12

3

• Rectifier converts 3-wire AC to 2-wire DC• Battery is recharged via flyback diodes• Diodes enable only two phases at once• Commutation "ignored" (unidirect. iGBT)

SnapshotE1 - E3 > EB

1

2

3

Current to battery!

Diodes provide"free" regen!


Inverter-rectifier ("rectifier" for generating mode) - MOSFET

EB

12

3

• Rectifier converts 3-wire AC to 2-wire DC• Charge battery via MOSFETs & flyback diodes• Bi-directional: Comm. MOSFET assists diode

1

2

3

E1 - E3 > EB

Current to battery


Pulse-width modulation: Energy loss due to "chopping"

• At a given voltage, cruise current ≈ 15% of climb or accel current• Superimposed on commutation: PWM "chopping" at cruise• Typical switching frequency (f) for chopping ≈ 20 kHz (inaudible)• Reduce the duty cycle (d) to reduce average current (iav = d ion)• Energy is lost (iGBT & diode) with each on/off switching cycle• Per-iGBT switching energy loss (Sp) ≈ 20 mJ per switching cycle • Reduce chop losses: use PWM only on “upper” phase of 6-pack• Cruise chopping loss = f Sp = 0.4 kW = 20% @ 2 kW/phase

Remove PWM from commutation; Incorporate DC boost converter

• Commutation voltage cycle

• Comm. + PWM superimposed

ion

iav| |

dt| t |

29








• 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• Power conservation: doubling the voltage halves the current • Enables reduced battery totem pole length, i.e. Toyota Prius* • DC voltage gain or “boost” is controlled by PWM “duty cycle”• PWM used for DCBC gate current, not motor-gen main current

DC boost converter enables efficient motoring & regen

Boost battery voltage to efficiently drive the M-G as a motorBoost motor-generator EMF to efficiently recharge the battery

M-Gbrushed

or brushless

with inv.

CL

VM

VB PWM

+15/-7ViGBT


|-- --|dt t

d ≡ duty cycle ; t ≡ periodiGBT gate PWM

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

M-Gbrushed

or brushless

with inv.

CL

VM

VB

PWMiGBT


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 gain is set by duty cycle (d) • Efficiency = 1 (resistance neglected)

[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

dt |-- --|t

d ≡ duty cycle ; t ≡ periodiGBT gate PWM


DC boost converter - efficiency and regen application

"Evaluation of 2004 Toyota Prius,"Oakridge National Lab, U.S. Dept. of Energy

233 Vdc in

5 10 15 20 kW

Regen

M-G

Motor

PWMiGBT

CL VB

• DC boost converter integrates windprop and motor-generator• Adjust PWM duty cycle to hold voltage gain as RPM decreases• Efficient bi-directional power over a wide operating range

Climb Regen

Cruise


Circuit models, motor-generator efficiency, and current

ib /Gb

tw

Gb

Rh kw

eb

Rh

ib

a

Motoring

Gm ib

tw

Gm

Rh kw

eb

Rh

ib

a

Regenib = [eb Gb

2- Gb kw] / [Rh (1+Gb2)] motoring

ib = [kwGm - eb] / [Rh (1+Gm2)] regeneration

G ≡ DCBC voltage gain


0 10 20 30 40 50 60 70 80 90 1000

100

200

300

400

500

600

Voltage Map - Motoring and Regen with DC boost converter

Voltage

%RPM

Motor-gen EMF

M-G, gain 2.0

M-G

, gain

3.0

Battery, no boost

Batt, voltage gain 2.0

Batt, voltage gain 3.0

• Boost the battery for motoring• Boost the M-G to regenerate

Climb220 AmpsBatt: 540VM-G: 285V

Capacity Regen-8 Amps Optimal Regen

-11 Amps

Cruise35 Amps

36







37

Architectures compared

"Chopper" architecturePWM main current chopCruise: high chopping lossRegen: none or inefficient


M-Geb

i

t w

PWM superimposed on commutation

Inverter-Rectifier

"Boost" architecturePWM sets DCBC boostEfficient motor & regen

M-Geb

i

DC BoostConverter

2-way boost t w

PWM

12V

Inverter-Rectifier

Commutation

38








Regenosoar - Features and Design Rationale

Counter rotorsSymmetric flowZero net torque

8-blade rotorsLow RPM, quiet, Low vibrationLow tip Mach

Ground handlingNo assistance req'dWinglet tip wheels

Pusher Config.Symmetry upstreamMax. laminar flow

Compact power trainBattery, motor-genand powertrain

Pod-air-cooled MG & PE

Regen parked in the windWith safety perimeter

40

Drag Coefficient, cD or cd

0.00 0.01 0.02 0.03 0.04 0.05

Lift Coefficient, c L or cl

0.00

0.25

0.50

0.75

1.00

1.25

1.50

Section and Vehicle Drag Polars

Max L/D

Min. Sink

"Clean configuration" ~ Windprop System Removed

Section

WindpropSystemRemoved


"Clean" aircr

aft

41

Load Factor and Turn Radius

Airspeed, v_km/h0 20 40 60 80 100 120 140

Turn Radius, m

0

50

100

150

200

250

300

350

400

nn

1.1

1.4

1.2

1.05

Thermaling1.6

r = v2 (cosg) / (g tanf)

Load Factor and Bank Angle

Load Factor, nn

1.0 1.1 1.2 1.3 1.4 1.5 1.6

Bank Anglefo

0

10

20

30

40

50

= f cos-1 [(cos )g /nn)]

Steady-state load factor (nn) ~ “g-load” and turn radius

nn w L / w = cos g / cos *f

Glide: nn w 1

Turn: nn w 1 / cosf

v L= nn w

w

g f


* SAE 2004-01-3088 EQN 5.2, dg/dt = 0

42

Airspeed, v ~ km/h

50 60 70 80 90 100 110 120 130 140 150

dz/dt ~m/s

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

g-Load, nn

1.0

1.2

Sea level25 kg / m 2

A = 16

1.4

1.6

Min SinkMax L/D

Load Factor and “Clean” Sink Rate

“Clean” REGENWindprop removed


cL = nn w / (qs)

43

Steady-state climb or descent ~ New Formulation, New Insight

L= nn w

T-Df

w

g

Glider, soaring bird, or "clean" regen• T/D=0 (no thrust)• Sink rate (-dz/dt) = nn(D/L)v

With or without propulsion system• Sink increases with g-load (nn)• D/L also increases with (nn)• Sink increases with airspeed (v)

Regen operating mode T/D• climb w 6.3 • cruise = 1.0 • pinwheel glide w -0.1• efficient regen (thermal) w -0.4 • capacity regen (descent) w -1.0

v

g

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

WD

Derive steady-climb Equation

Note: nn= cos g /cos *f cL = nn w / (qs)


* SAE 2004-01-3088 EQN 5.2, dg/dt = 0

“Total Sink”

e ≡ “Exchange Ratio,” as applicable:• turbine system efficiency ~71% • 1 / propeller system efficiency• 0 for pinwheeling (no exchange)

“TotalClimb”

WindpropEffect

“Clean” sink rateUpdraft

D

TV

L

Dnuz nt 11

Regen must have • Updraft - or final descent• High L/D, Low sink• High sys. efficiency

Regenerative Electric Flight Equation and Implications

45

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


U ~ m/s

Elevation, zo ~ m

12

34

46

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


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)


Climb rate Contours Energy rate Contours

Equilibrium Regeneration

Optimum

Total Specific Energy-gain Rate, m/sMax-capacity Regeneration in the Thermal


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

47

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

0.88

Regenerative Electric Flight Equation Applied for RegenoSoar


48







49

Regenerative Electric-powered Flight• Windprop: 8 blades spin slow, quiet, & efficient

• DC & BLDC machines: EMF proportional to RPM

• M-G & battery verify theoretical efficiency trends

• Synergy of windprop & MG: Efficiency Vs. RPM - Optimum “speed ratios” ~ 85% & 115% by mode

• Popular "chopper" control: inefficient at cruise

• DC boost converter: efficient climb, cruise, regen

• Regen applications:– Thermal, ridge, wave, final descent, ....– UAV fleet, storm rider, earth observer, ....

• Give up 2% prop efficiency w/symmetric sections to gain perhaps 5-15% range and/or flying time


M-GiGBT

VM

A "regen" is coming soon to an airport near you!

Regenerative Electric-powered Flight J. Philip Barnes 1 Regenerative Electric Flight Synergy and...

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