1 Regenerative Electric Flight Synergy and Integration of Dual-role Machines J. Philip Barnes AIAA Jan 2015 original 23 Feb 2015 Update

2 Presentation Contents Regenerative Electric-powered Flight J. Philip Barnes The visionaries Brushless MG M-G iGBT VMVM Power Electronics Brushed MG Synergy Integration Windprop Regenosoar

3 Hermann Glauert Regenerative Electric-powered Flight J. Philip Barnes “Consider the case of a windmill on an aeroplane”

4 Paul MacCready Regenerative Electric-powered Flight J. Philip Barnes Regenerative electric flight concept “with caution,” ‘99 Regenerative electric flight concept “with caution,” ‘99

5 Presentation Contents Regenerative Electric-powered Flight J. Philip Barnes The visionaries Brushless MG M-G iGBT VMVM Power Electronics Regenosoar Windprop Brushed MG

Angle of attack = 0, hub-to-tip  r tan  = V o Therefore: r tan  = V o /  = R tan  tip Approaches "Betz Condition“ Angle of attack = 0, hub-to-tip  r tan  = V o Therefore: r tan  = V o /  = R tan  tip Approaches "Betz Condition“ Blade section Looking outboard, Blade at 3 o’clock Chord line  Rotor velocity diagram - "Pinwheeling" & “Betz” conditions Axial wind VoVo VoVo Rotational wind,  r Relative wind W 1  V o W2W2 Helical wake  r Regenerative Electric-powered Flight J. Philip Barnes

7 Windprop Blade Angle and Operational Mode V  r  W Pinwheel V  r L  W Propeller V  r -L  W Turbine Define: “Speed ratio,”   v / v pinwheel = v / [  R tan  tip ] Similar to advance ratio (J) but meaningful for 3 modes Define: “Speed ratio,”   v / v pinwheel = v / [  R tan  tip ] Similar to advance ratio (J) but meaningful for 3 modes Regenerative Electric-powered Flight J. Philip Barnes

J. Philip Barnes Non-rotational (axial) inflow Axial velocity locally conserved Final swirl imparted suddenly Helical vortex wake, ea. blade Wake ~ aligned with meanline Wake-induced velocity (V i ) Glauert: 2V i  at "rotor out" Absolute velocity (V) increased Relative wind (W) decreased Immediate static pressure rise Propeller blade - comprehensive velocity diagram Relative wind W 1  W   r - V i   V 1  Zero-lift line Rotational wind Axial wind V 1  V o +V ix Helical wake vortex sheet W2W2 V 1  r - 2V i  V 2 Blade section Looking outboard Blade at 3 o’clock Chord line V i  V ix V i Prop/turbine flowfield is complex. Numerically integrate wake-induced velocities and apply the boundary conditions to solve for blade loading 

Speed Ratio,  ≡ v / (  R tan  t ) B=2 2 B=8 8 Force Coef., F ≡ f/(q  R 2 ) 9 Low-RPM 8 Blades  t = 30 o  Speed Ratio,  ≡ v / (  R tan  t ) Efficiency Turbine  / (f v) Turbine  / (f v) Propeller f v / (  ) Propeller f v / (  ) Pinwheel Regeneration Max efficiency Regeneration Max efficiency Windprop Efficiency and Thrust Regenerative Electric-powered Flight J. Philip Barnes Comparable efficiency by mode Eight blades spin slow & quiet Climb power ~ 7x cruise power Comparable efficiency by mode Eight blades spin slow & quiet Climb power ~ 7x cruise power Two windprops, same thrust and diameter Two windprops, same thrust and diameter High-RPM 2 Blades  t = 14 o 2 8 Propeller ~ cruise Propeller ~ cruise Propeller ~ climb Regen capacity Regen capacity

10 Presentation Contents Regenerative Electric-powered Flight J. Philip Barnes The visionaries Windprop Motor- Generators M-G iGBT VMVM Power Electronics Regenosoar

mm   bb N turns Generating i B i Change to generator mode: Same direction of rotation Same sign of EMF Same ratio, EMF/speed Same ratio, torque/current Torque & current reversed Change to generator mode: Same direction of rotation Same sign of EMF Same ratio, EMF/speed Same ratio, torque/current Torque & current reversed mm   bb N turns Motoring B i B i Motor-generator Principles 11 Regenerative Electric-powered Flight J. Philip Barnes Motoring mode: Any motor is a generator EMF proportional to RPM Torque propor. to current Motoring mode: Any motor is a generator EMF proportional to RPM Torque propor. to current  =  m i  m = k   = k i  =  m i  m = k   = k i

Motor-generator & Battery: Efficiency Envelope and Test Data REGENERATION LMCLTD.net MOTORING EEMCO 427D100 CURRENT GROUP, i R t /  b TORQUE GROUP,  R t / (k  b ) Phil Barnes Apr % Duty Cycle Regenerative Electric-powered Flight J. Philip Barnes THEO. EFFICIENCY, k  /  b  b /(k  ) Windprop synergy

“Equivalent brushed” machine 13 BLDC M-G & inverter-rectifier: Equivalent-brushed machine M-G & inverter/rectifier system has “brushed-DC” equivalent M-G bb i Regenerative Electric-powered Flight J. Philip Barnes Inverter- Rectifier   Brushless motor-gen: Electronically commutate 2 of 3 phases kk  =  m i  m = k   = k i  =  m i  m = k   = k i

14 Presentation Contents Regenerative Electric-powered Flight J. Philip Barnes The visionaries Windprop Brushless MG M-G iGBT VMVM Power Electronics Brushed MG Regenosoar

15 “Six-pack” inverter-rectifier ("inverting" for motoring) Inverter converts 2-wire DC to 3-wire "AC“ Alternating transistor “diagonal pairs” Commutation toggles each phase 0-to-V B Relatively low frequency at full power Inverter converts 2-wire DC to 3-wire "AC“ Alternating transistor “diagonal pairs” Commutation toggles each phase 0-to-V B Relatively low frequency at full power VBVB VBVB V 15V S N Regenerative Electric-powered Flight J. Philip Barnes

16 Six-pack inverter-rectifier (rectification for regeneration) BB 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 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 Snapshot  1 -  3 >  B Current to battery! Diodes provide "free" regen! Diodes provide "free" regen! Regenerative Electric-powered Flight J. Philip Barnes

17 Cruise efficiency penalty when “chopping” the main current 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 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 BLDC commutation voltage waveform (full power) has “relatively-low” frequency BLDC commutation voltage waveform (full power) has “relatively-low” frequency i on i av        Commutation with chopping PWM superimposed (cruise) has “very-high” frequency Commutation with chopping PWM superimposed (cruise) has “very-high” frequency Regenerative Electric-powered Flight J. Philip Barnes

18 DC boost converter - efficiency and regen application "Evaluation of 2004 Toyota Prius," Oakridge National Lab, U.S. Dept. of Energy 233 Vdc in kW Regen M-G Motor PWM iGBT C L VBVB 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 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 Climb Regen Cruise 97% power-conditioning efficiency for any mode Regenerative Electric-powered Flight J. Philip Barnes

19 “Chop” Vs. “boost” architectures compared "Chopper" architecture PWM main current chop 540V battery 10% loss at loiter Regen: none or inefficient "Chopper" architecture PWM main current chop 540V battery 10% loss at loiter Regen: none or inefficient Regenerative Electric-powered Flight J. Philip Barnes M-G i   PWM superimposed on commutation Inverter- Rectifier 540V batt. "Boost" architecture PWM sets DCBC boost 200V battery 03% loss at loiter Regen capable & efficient "Boost" architecture PWM sets DCBC boost 200V battery 03% loss at loiter Regen capable & efficient M-G i DC Boost Converter 2-way boost   PWM Inverter- Rectifier Commutation 200V batt.

20 Presentation Contents Regenerative Electric-powered Flight J. Philip Barnes The visionaries Windprop Brushless MG M-G iGBT VMVM Power Electronics Brushed MG Regenosoar

Regenerative Electric-powered Flight J. Philip Barnes 21 Counter rotors Symmetric flow Zero net torque Counter rotors Symmetric flow Zero net torque 8-blade rotors Low RPM, quiet, Low tip Mach 8-blade rotors Low RPM, quiet, Low tip Mach Compact power train Batt., M-G, ctrl, cables Compact power train Batt., M-G, ctrl, cables Regenosoar, 1 of 2

Regenerative Electric-powered Flight J. Philip Barnes 22 Ground handling No assistance req'd Winglet tip wheels Ground handling No assistance req'd Winglet tip wheels Pusher Config. Laminar flow, No helix upset Pusher Config. Laminar flow, No helix upset Pod-air-cooled MG & PE Regen parked in the wind With safety perimeter Regen parked in the wind With safety perimeter Regenosoar, 2 of 2

23 Steady-state climb or descent ~ New Formulation, New Insight Glider, soaring bird, or "clean" regen T/D = 0 (no thrust) Sink rate (-dz/dt) = n n (D/L)V With or without propulsion system Sink increases with g-load (n n ) D/L also increases with (n n ) Glider, soaring bird, or "clean" regen T/D = 0 (no thrust) Sink rate (-dz/dt) = n n (D/L)V With or without propulsion system Sink increases with g-load (n n ) D/L also increases with (n n ) Regen operating mode T/D climb  4.6 cruise= 1.0 pinwheel glide  -0.1 efficient regen (thermal)  -0.7 capacity regen (descent)  -2.0 Regen operating mode T/D climb  4.6 cruise= 1.0 pinwheel glide  -0.1 efficient regen (thermal)  -0.7 capacity regen (descent)  -2.0 L= n n W T-D  W  V  Derive steady-climb Equation: Note: n n = cos  /cos  c L = n n W/ (qS) Regenerative Electric-powered Flight J. Philip Barnes * SAE EQN 5.2, d  /dt = 0

“Total Sink” “Total Climb” “Total Climb” Windprop Effect Windprop Effect “ Clean ” sink rate “ Clean ” sink rate Updraft “Physics” require: Updraft (or descent) High L/D, low sink High system efficiency Regen “fallouts” incl. Steep final descent Landing thrust reversal Ground wind recharge Regenosoar: Physics and fallouts Based on weather & geography, potential for “flight without fuel”

25 Thermal Updraft Contours Total Energy = Kinetic + Potential Total Energy = Kinetic + Potential + Stored 1 o C warmer-air column 20-minute lifetime ~ solar power x 10 Regenerative Electric-powered Flight J. Philip Barnes U ~ m/s Elevation, z o ~ m

26 Climb & regeneration in the Thermal – Climb rate Regenerative Electric-powered Flight J. Philip Barnes Optimum Equilibrium Regeneration Climb rate, m/s

27 Regenerative Electric-powered Flight J. Philip Barnes Equilibrium Regeneration Optimum Climb & regeneration in the Thermal – Energy rate Energy rate, m/s

28 Regenosoar point performance Regenerative Electric-powered Flight J. Philip Barnes

29 Regenerative Electric-powered Flight J. Philip Barnes A "regen" is coming soon to an airport near you! A "regen" is coming soon to an airport near you! Conclusion – Regenerative Electric Flight M-G iGBT VMVM Synergy Integration inv. rect

30 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, aircraft parametric geometry modeling, and flight simulation with Blender 3D software. Outside of work, Phil is the world’s leading expert on dynamic soaring of the wandering albatross, and he is pioneering the science of regenerative-electric flight. About the Author J. Philip Barnes