Principles of Regenerative Electricpowered Flight J Philip Barnes

Principles of Regenerative Electric-powered Flight J. Philip Barnes 04 April 2014 Update 04 Apr 2014 www. How. Flies. The. Albatross. com 1

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 2

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? • Thermal day and night up to 2800 m • Lowest wing loading of any bird Self-contained takeoff Emergency thrust Sortie radius to 1800 km Sortie duration up to 4 days 30 -year lifespan Data: Henri Weimerskirch, et. al. Nature Jan 2003 Photography: Phil Barnes Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 3

Regen Aircraft Elements and Operation Speed Control Windprop • Fixed rotation direction Motor • Sign change with mode • Thrust, Torque • Power, Current Gen Optional solar panel ESU • Self-contained takeoff • Emergency cruise/climb • Exploit vertical air motion Regenerative Electric-powered Flight J. Philip Barnes Energy Storage: • Battery • Ultra capacitor • Flywheel motor-generator 04 Apr 2014 www. How. Flies. The. Albatross. com 4

Thermal Updraft Contours Elevation, zo ~ m • 1 o. C warmer-air column • 20 -minute lifetime • ~ solar power x 10 U ~ m/s 4 Total Energy = Kinetic + Potential Regenerative Electric-powered Flight J. Philip Barnes 3 04 Apr 2014 2 1 Total Energy = Kinetic + Potential + Stored www. How. Flies. The. Albatross. com 5

Dual-role Propeller and Airborne Wind Turbine 6

Propeller Wake, Pitch, and Blade Angles • Wake induces downwash (normal to local section) Horseshoe Vortices R • Pitch: helix length per rotation htip = 2 p R tan btip r • Uniform pitch: r tan b = R tan btip • Blade tip angle (btip): 14 o ~ low pitch 30 o ~ high pitch More blades at fixed thrust & diameter: Blade angle (b ) at radius (r) is measured from rotation plane to the chord line at (r) Regenerative Electric-powered Flight • • More wakes (one per blade) Higher pitch ~ wakes farther aft / rotation Lower rotational speed, lower tip Mach Upshot: ~ similar efficiency, 2 to 8 blades J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 7

Windprop Blade Angle and Operational Mode • Specify symmetrical sections & uniform pitch Propeller L Turbine Pinwheel b b b v v v wr wr wr -L w w w • Pinwheeling: Zero angle of attack, root-to-tip - No thrust, no torque, small drag • Efficient prop: Rotate ~115% of “pinwheel RPM, ” or fly at 87% of “pinwheel airspeed” • Efficient turbine: Rotate ~ 87% of “pinwheel RPM, ” or fly at 115% of “pinwheel airspeed” • Define: “Speed ratio, ” s v / vpinwheel = v / [ wr tanb ] Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 8

Windprop Efficiency and Thrust 1. 0 0. 8 Low-RPM 8 Blades, btip = 30 o High-RPM 2 Blades, btip = 14 o Efficiency 0. 6 0. 4 c l_max h Blades_btip 2_14 o 8_30 o Propeller f v / (t w) c l_min Turbine t w / (f v) 0. 2 Speed Ratio, s ≡ v / (w R tan btip) 0. 0 0. 5 1. 0 0. 6 0. 7 0. 9 0. 6 0. 9 1. 0 1. 1 Propeller ~ climb 0. 8 0. 7 0. 8 1. 2 1. 3 1. 4 1. 5 1. 6 1. 7 1. 8 Force Coefficient, F ≡ f/(qp. R 2) B=8 B=2 0. 5 0. 4 0. 3 0. 2 F Propeller ~ cruise Max efficiency Regeneration 0. 1 0. 0 -0. 1 -0. 2 -0. 3 -0. 4 0. 5 0. 30 Max capacity Regeneration Pinwheel F= -0. 011 @ B=2 0. 20 0. 8 0. 9 0. 10 8 1. 0 1. 1 Regenerative Electric-powered Flight 1. 2 1. 3 1. 4 J. Philip Barnes 1. 5 1. 6 04 Apr 2014 Chord, c/ R 0. 15 0. 05 Speed Ratio, s ≡ v / (w R tan btip) 0. 7 Blade Geometry 0. 25 2 F= -0. 008 @ B=8 0. 6 Sym. Sections r tan b = R tan btip 1. 7 1. 8 0. 00 Thickness hub r/ R 0. 25 www. How. Flies. The. Albatross. com 0. 50 0. 75 1. 00 9

How Flow the Electrons Motor-generator principles Synergy: motor-gen & windprop DC Voltage conversion 10

Motor-generator Principles (+) Charge (q) with velocity, V in magnetic field of strength, B: Force vector, F = q V x B L i E t Nt B urn e w s Fq i vi v q tw=ei Both modes Fp Nt urn s e i Regenerative Electric-powered Flight Torque, t = 2 N (D/2) B (dx/dt) dq = 2 N (D/2) B (dq/dt) dx t = NDBi. L = NDBL i = k i B Motoring Change to generator mode: Same direction, rotation, w Same 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 w Fq i vi v q E t Fp B Generating J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 11

System Motoring and Regeneration Efficiencies Pulse-width modulation (PWM) d ≡ “Duty cycle” ; h ≈ 0. 99 d 0. 25 (Refs 1, 2) Vb Inverter (for brushless MG) h ≈ 0. 98 (Ref. 3) Rb eb Quote regen power here eb i Motor Regen Vm Rm em t + Dt w Torque loss brushes, iron loss, windage. . . "Ideal system efficiency" ignoring controller & torque losses ≈ t w/(eb i) ≈ e i / (eb i) = e / eb = k w / eb hsystem regen ≈ eb i / (tw) ≈ eb i / (ei) = eb / e = eb / (k w) hsystem motor Refs: (1) Ai. AA 2010 -483, Lundstrom, p. 8 ; Regenerative Electric-powered Flight (2) NASA CP 2282, Echolds, p. 89 ; J. Philip Barnes 04 Apr 2014 (3) Technical Soaring, Vol. xxi, No. 2, Rehmet, p. 39 www. How. Flies. The. Albatross. com 12

Motor-generator & Battery ~ Performance Envelope and Data Non-dimensional Characterization of Permanent-magnet DC Motor-generator-battery System Performance ~ Theory and Test Data TO CU RQ RR 0, 8 0, 6 UE EN GR OU 100% Duty Cycle TG P, t RO UP , i AL Rt / eb Rt / (k e b) TIC RE CIE I F EF EO TH i 0, 0 /e b eb /( k w) REGENERATION MOTORING LMC "generator curve" 48 V / 3, 600 RPM k = 0. 16 N-m/A Rt = 0. 041 Ohm LMCLTD. net EEMCO 427 D 100 24 V / 15, 000 RPM k = 0. 015 N-m/A Rt = 0. 075 Ohm 0, 4 0, 2 kw Y, C N Rt em eb t -0, 2 Phil Barnes Apr-08 -2011 1, 0 -0, 4 0, 0 0, 2 0, 4 0, 6 0, 8 1, 0 Speed Ratio, kw/eb = EMF Ratio, emg/eb Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 1, 2 www. How. Flies. The. Albatross. com 1, 4 13

“Low-tech” Regen DC Electric Propulsion With Battery Shuffler Positive BATTERY terminal SHUFFLE of battery SWITCH number: 1 3 4 5 B C D A F Voltage Node E A B C D B Battery Series “Totem Pole” Voltage Node A Takeoff / climb B 4 E D C Rotate 80 o Clockwise, then counter clockwise 3 2 1 Cruise C ~Pinwheel Phil Barnes 07 Apr 2011 2 E D C B Negative terminal of battery number: 5 D Best regen Motor Gen E Max regen F Electrical Ground Battery effective shuffled position Periodic (about once per minute) battery shuffle via rotary switch ensures equal time for all batteries at each “totem pole” position Applicable: Brushed or Brushless, but no pulse-width modulation Regeneration enjoys reduced active battery resistance Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 14

DC boost converter enables efficient motoring & regen VB L PWM i. GBT C M-G • 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 15

DC boost converter – Equivalent circuits VM L VB Mot-gen C i. GBT PWM i. GBT on i. GBT off i. B i. M L di. B /dt VB i. B VM VM C d. VM/dt VB dt i. M L di. B /dt C d. VM/dt |--t--| i. GBT gate PWM d ≡ duty cycle ; t ≡ period Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 16

DC boost converter – Voltage gain & conversion efficiency Time segment 1: i. GBT on for Dt = dt i. B VM L Di. B 1 /(dt) C DVM 1/(dt) Segment 2: i. GBT off for Dt = (1 -d)t i. B VM i. M VB L Di. B 2 /[(1 -d)t] i. M C DVM 2 /[(1 -d)t] VB [a] Voltage loop: VB - L Di. B 1 /(dt) = 0 [b] VB - L Di. B 2 /[(1 -d)t] = VM [c] Output current: i. M - C DVM 1 /(dt) = 0 [d] i. B - C DVM 2 /[(1 -d)t] = i. M [e] PWM cycle: Di. B 1 + Di. B 2 = 0 [f] DVM 1 + DVM 2 = 0 [g] Combine [a, b, e]: VM/VB = 1/(1 -d) [h] via [c, d, f]: i. M/i. B = 1 -d Combine [g, h]: h ≡ i. MVM /(i. BVB) = 1 • 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 (i. B) & outputs (i. M, VM) Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 17

DC boost converter - efficiency and regen application 233 Vdc in Regen 5 Motor VB L PWM i. GBT C M-G 10 15 20 k. W "Evaluation of 2004 Toyota Prius, " Oakridge National Lab, U. S. Dept. of Energy • 90 o 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 Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 18

"Regeno. Soar" Air Vehicle and System Performance 19

Regeno. Soar 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) Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 20

Regeno. Soar ~ In Flight Applications and Operations • • Fleet broadcast energy rate High-altitude earthwatch Jet-stream rider Storm rider Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 21

Vehicle Performance ~ New Formulation, New Insight Derive steady-climb Equation v L= nn w T-D f g g w Note: nn= cosg /cosf 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) Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 c. L = nn w / (qs) Regen • climb: • cruise: • solar-augmented glide: • pinwheel glide: • efficient regen (thermal): • capacity regen (descent): www. How. Flies. The. Albatross. com T/D 6. 3 = 1. 0 0. 5 -0. 1 -0. 4 -1. 0 25

Regenerative Flight Equation “Total Climb” Updraft “Total Sink” Rate of change of total specific energy Effect of windprop Still-air “clean” sink rate “Exchange Ratio, ” as applicable: • turbine system efficiency ~71% • 1 / propeller system efficiency • 0 for pinwheeling (no exchange) Regenerative Electric-powered Flight J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 26

Climb and Regeneration in the Thermal Elevation, m Climb rate Contours Elevation, m (minimum-sink airspeed) Energy rate Contours Op tim um Elevation, m Equilib rium Re Regenerative Electric-powered Flight genera tion J. Philip Barnes 04 Apr 2014 www. How. Flies. The. Albatross. com 27

Regenerative Flight Equation Applied for Regeno. Soar Regenerative Electric-powered Flight J. Philip Barnes 0. 82 0. 87 0. 88 04 Apr 2014 www. How. Flies. The. Albatross. com 28

Summary and Recommendations Regenerative Electric-powered Flight 29

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 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. How. Flies. The. Albatross. com 30