National Aeronautics and Space Administration
Electric Aircraft Technology Development
Overview Briefing
Barbara Esker, Advanced Air Vehicles Program
Mar. 14, 2018
www.nasa.gov
Outline
1. Brief review of terminology/systems to aid discussion
2. Missions and technology development – targeted vehicle classes
• Single-Aisle Transports
• Vertical Takeoff and Landing – Urban Air Mobility
• Thin Haul Conventional Takeoff and Landing
3. Enabling Test Capabilities
4. Concluding Remarks
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Electrified Aircraft Propulsion Concepts
Electrified Aircraft Propulsions systems use electrical
motors to provide some or all of the thrust for an aircraft
– Turboelectric systems use a turbine-driven generator as the power source. Partially turboelectric systems split
the thrust between a turbofan and the motor driven fans
– Hybrid-electric systems use a turbine-driven generator combined with electrical energy storage as the power
source. Many configurations exist with different ratios of turbine to electrical power and integration approaches.
– All-electric systems use electrical energy storage as the only power source.
3
Benefits of Electrified Aircraft Propulsion
Across Range of Missions
Improvements to highly optimized aircraft like single-aisle transports
– Potential fuel burn reduction estimated using turbo electric distribution to BLI
thruster in addition to other benefits from improved engine cores or airframe
efficiencies. Later developments could be more advanced electrical
distribution and power storage.
Enabling new configurations of VTOL aircraft
– The ability to widely distribute electric motor driven rotors/propulsors operating
from one or two battery or turbine power sources, enable new VTOL
configurations with potential to transform short and medium distance mobility
through 3x-4x speed improvement.
Revitalizing the economic case for small short range aircraft services
– The combination of battery powered aircraft with higher levels of autonomous
operation to reduce pilot requirements could reduce the operating costs of
small aircraft operating out of community airports resulting in economically
viable regional connectivity with direct, high-speed aircraft services.
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Subsonic Transport Technology Strategy
Ensuring U.S. technological leadership
Energy usage Harmful Objectionable
Prove out Prove out
reduced by more emissions reduced noise reduced
transformational transformational
than by more than by more than
propulsion technologies airframe technologies
Current Next Generation Future Generations 60% 90% 65%
Generation -Transitional- -Transformational-
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Transforming Propulsion – A Breakthrough Opportunity
Turbo-Electric Propulsion Architecture
Boundary-Layer Ultra-Efficient “Small
Ingesting Propulsor(s) Core” Turbofan
In whole or in part, transformational propulsion enables the next generation transitional subsonic
transport configuration and enables future generation transformational subsonic transports
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Electrified Aircraft Propulsion
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Studies Targeting Regional Jets & Single Aisle Markets
Partially and Fully Distributed Turboelectric Concepts
NASA STARC - ABL Boeing/NASA SUGAR - FREEZE
NASA N3-X
(twin aisle)
ECO-150
Parallel Hybrid Concepts
Low Spool
High Spool R-R LW EVE
Boeing/NASA SUGAR - VOLT UTRC hGTF
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Electrified Aircraft Propulsion Strategy
for Single Aisle Aircraft
Initial Focus on
Turboelectric Aircraft
Concept definition & system
analysis
Novel integration and BLI
Single aisle aircraft entry
MW flight-weight electrical Potential into service in 2035
component development Flight Demo timeframe
Integrated system testing
Advanced cores with large
power extraction
Hybrid electric option to be considered with advances in battery technology
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Development & Testing of MW Class Power System
High Power Density Electric Motor Development
16
14
NASA research (power density
at electromagnetic level), 1 – 3
Power Density, kW/kg
12 MW, >96 % efficiency
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Various claims
8 (100 – 200 kW)
6
Siemens (200 kW)
System level, 95 %
4 efficiency
Single-aisle Turboelectric Aircraft with Aft
2 Boundary Layer Ingestion (STARC – ABL)
Current electric vehicles
Current industrial • Conventional single aisle tube-and-wing
configuration
• Twin underwing mounted turbine engines with
NASA Electric Aircraft attached generators on fan shaft
Testbed (NEAT) for • Ducted, electrically driven, boundary layer
testing multi-MW level ingesting tailcone propulsor
power system • Projected fuel burn savings for single-aisle
missions
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MW-scale Electric Machines Research
• Motors and/or generators (electric machines) are needed on all
electrified aircraft.
• NASA is sponsoring or performing work to achieve power densities
2-3 times the state of the art for machines in the MW or larger class.
• Three major machine types are being developed: permanent
magnet, induction, and wound field
Continuous Specific Efficiency
Motor Nominal
power rating, power goal, goal, Speed
type dimensions
MW kW/kg %
Permanent
University of Illinois 1 13 >96 18,000 Cylinder 0.45 m by 0.12 m
magnet
Ohio State University 2.7 13 >96 Induction 2,500 Ring 1.0 m by 0.12 m
NASA Glenn Research
1.4 16 >98 Wound field 6,800 Cylinder 0.40 m by 0.12 m
Center
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MW-scale Converter Research
• Power converters are an essential component in most EAP aircraft
concepts, as they are used to convert from ac to dc power, or vice
versa
• NASA is sponsoring or performing work to achieve power densities 2-
3 times the state of the art for converters in the MW or larger class.
• Silicon carbide and gallium nitride prototypes are being developed
with conventional cooling as well as a cryogenically cooled converter
Specific
Continuous Efficiency Switch
power goal, Topology Cooling
power rating, MW goal, % material
kW/kg
General Electric 1 19 99 3 level SiC/Si Liquid
University of Illinois 0.2 19 99 7 level GaN Liquid
Boeing 1 26 99.3 Si Cryogenic
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Materials for Electrified Aircraft Propulsion
• New soft magnetic materials – improve performance of converter filters and electric machines
• Insulation – electrical insulation with better thermal transfer to improve electric machine
performance
• High-Conductivity Copper/Carbon Nanotube Conductor – approach to reduce the mass of cables
• Superconducting Wire Development – AC superconductors which could be used for electric
machines or distribution
25-mm by 1.6-km
spin cast ribbon Hyper Tech produced multifilament
MgB2 superconducting wires
CAPS idealized magnetic field test
Transformer fabricated capability for wire segments
from spin cast ribbon
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Urban Air Mobility – Vertical Takeoff & Landing (VTOL)
Move people inside congested urban areas from point to point using a VTOL air vehicle
Technologies
• Electric & hybrid-electric distributed UberElevate
electric propulsion (~300-400 kw HEP) UberElevate
• Fault tolerant propulsion, flight Significant
systems commercial
• Low-noise/annoyance interest, initial
• Battery integration and safety commercial
• High-speed charging introduction
• Autonomous system capability Airbus - Vahana likely to be in
• Weather-tolerant operation 2022 timeframe
• High speed interoperable digital
communications network
• Higher efficiency small gas turbine for
hybrid electric
NASA strategy under development –
will influence initial & subsequent
generations
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Electrified Propulsion for Vertical Lift
Enable a broad expansion of vertical lift applications
Overarching
• Improve current configuration cost, speed, payload, safety, and noise
Vertical Lift
• Open new markets with new configurations and capability
Strategy
• Capitalize on convergence of technology in electric propulsion, autonomy and flight controls
FY17+ NASA technology emphasis
Very small Small Very Light Light Medium Med-heavy Heavy Ultra Heavy
<10 lbs <55lbs < 1500lbs <6000lbs <12,000lbs <25,000lbs <50,000lbs <100,000lbs
Technology applicability scales up
and down in many areas
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NASA-developed VTOL Concept Vehicles for UAM
NOT “BEST” DESIGNS; NO INTENT TO BUILD AND FLY 06 Feb 2018
Objective: Identify NASA Passengers 50 nm trips Market Type Propulsion
Quadrotor
concept vehicles that can be per full
charge/ “Air Taxi”
used to focus/guide NASA
refuel
research
1 1 x 50 nm Air Taxi Multicopter Battery
– Open, publicly-available
configurations 2 2 x 50 nm Commuter Side by Side Parallel
– Provide focus for trade Scheduled (no tilt) hybrid
studies and system analysis Side by Side
4 4 x 50 nm Mass Transit (multi-) Tilt Turboelectric
– Push farther than current wing “Vanpool”
market trends
6 8 x 50 nm Air Line (multi-) Tilt Turboshaft
– Provide a range of
rotor
configurations
– Cover a wide range of 15 Lift + cruise Hydrogen
technologies and missions fuel cell
that are being proposed 30 Vectored
thrust Tilt wing
Compound
“Airliner”
• Aircraft designed through use of NASA conceptual design and sizing tool
for vertical lift, NDARC.
• Concepts described in detail in publication “Concept Vehicles for Air Taxi
Operations,” by W. Johnson, C. Silva and E. Solis. AHS Aeromechanics
Design for Transformative Vertical Lift, San Francisco, Jan. 2018. 16
Potential Research Areas for
VTOL-enabled Urban Air Mobility
Passengers 50 nm trips Market Type Propulsion
per full
charge/ ROTOR-ROTOR INTERACTIONS
1
refuel
1 x 50 nm Air Taxi Multicopter Battery
PERFORMANCE • performance, vibration, handling qualities
2 2 x 50 nm Commuter Side by Side Parallel • aircraft optimization • aircraft arrangement
Scheduled (no tilt) hybrid • rotor shape optimization • vibration and load alleviation
4 4 x 50 nm Mass Transit (multi-) Tilt Turboelectric
wing • hub & support drag minimization
6 8 x 50 nm Air Line (multi-) Tilt Turboshaft • airframe drag minimization
rotor
15 Lift + cruise Hydrogen
fuel cell
30 Vectored
thrust ROTOR-WING INTERACTIONS
Compound • conversion/transition
• interactional aerodynamics
PROPULSION EFFICIENCY • flow control
• high power, lightweight battery Quadrotor + Electric
• light, efficient, high-speed electric motors
• power electronics and thermal management Tiltwing + TurboElectric
• light, efficient diesel engine
• light, efficient small turboshaft engine
• efficient powertrains SAFETY and AIRWORTHINESS
• FMECA (failure mode, effects, and criticality analysis)
• component reliability
AIRCRAFT DESIGN • crashworthiness
• weight, vibration Side-by-side + Hybrid • propulsion system failures
• handling qualities
• active control
NOISE & ANNOYANCE STRUCTURE & AEROELASTICITY
• structurally efficient wing and rotor support
• low tip speed
OPERATIONAL EFFECTIVENESS • rotor/airframe stability
• rotor shape optimization
• disturbance rejection (control bandwidth, control design) • crashworthiness
• aircraft arrangement/ interactions
• all-weather capability • durability and damage tolerance
• active noise control
• cost (purchase, maintenance, DOC) • metrics and requirements
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Thin Haul Commuter (Conventional Takeoff & Landing)
Commercial (9-10 passenger)
NASA Flight Testing – X57 Aircraft
X-57 “Maxwell”
• Cruise-sized wing: enabled by distributed electric
propulsion (DEP) system for takeoff/landing performance
• High-efficiency cruise propellers:
electric motors mounted at wingtips
Zunum Aero
• All-electric propulsion system: 40+ Current Effort:
kWh battery, 240 kW across 14
(Hybrid electric)
• Demonstration of technologies
motors & advanced concepts through
• Fully redundant powertrain flight tests
• Develop technologies to
extend the range
Eviation (all electric)
9-10 passenger, commercial
introduction planned for 2022 – 25
time frame
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Distributed Electric Propulsion (DEP)
Distributed Electric Propulsion:
Propellers
A system that distributes electric propulsion
Electric Motors
across the aircraft to yield significant benefits in
aerodynamics, control and reliability.
Motor
Controllers Challenges for DEP systems including:
High Current • Integration – Complex, highly distributed system
Wiring • Power Distribution – High voltage and current in very constrained areas
• Power Storage/Generation – Batteries or hybrid power plant
Battery • Command/Control – Motor commands & management of varying power
Systems demands
• Thermal – High power systems can generate significant heat loads
Simplified X-57 Mod III Configuration • Mechanical – Rotating motors/wings, folding propellers, interacting load paths
(typical DEP features) • Weight – Primarily energy storage and/or power generation system
• Acoustics – Multiple interacting noise sources (aero-propulsive, motors, props)
X-57 efforts will enable:
• Enhanced knowledge on interactions/integration including acoustics, power management, thermal loads, redundancy &
failure modes, folding propeller operations, and propulsion airframe interaction
• Critical source information for technology development, integration, flight test documentation, and lessons learned – will
inform/influence the development of certification standards (highly competitive industry not publishing their own work)
Essential Test Capabilities
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NASA Electric Aircraft Testbed (NEAT)
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NASA Electrified Aircraft Technology (NEAT)
Problem Results
Hybrid electric STARC-ABL powertrain design Completed the assembly of a STARC-
requires full-scale performance validation including ABL powertrain including turbo-
EMI mitigation, fault and thermal management, generation and tail-cone thruster
turbine surge/stall prevention, DC bus stability, machine pairs, ARINC 664
flight-efficiency, and high power, high voltage communication protocol, 600VDC
component verification. multi-bus, NPSS turbine and ducted
fan with closed loop torque feedback,
power regeneration, thermal
management system and facility
integration.
Successfully operated a 600VDC
STARC-ABL powertrain configuration
with approximately 460kW tail-cone
Aft boundary ingesting
electric motor thrust power with representative
turbine and ducted fan performance
maps through a representative flight
profile.
Objective Significance
Establish a 500kW STARC-ABL powertrain with This powertrain is the first operational powertrain that is representative of
COTS equipment and demonstrate operation of the the STARC-ABL vehicle and it enables model validation to establish
powertrain through a complete flight-profile with concept viability, demonstrates power/propulsion/communication/thermal
NPSS turbine and ducted fan emulation. integration at the MW scale, and guides the optimization of the powertrain
control dynamics.
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Hybrid Electric Integrated Systems Testbed (HEIST)
• Being developed to study power management and transition complexities, modular architectures, and flight control laws
for turboelectric distributed propulsion technologies using representative hardware and piloted simulations
• Configured in the fashion of an iron bird to provide realistic interactions, latencies, dynamic responses, fault conditions,
and other interdependencies for turboelectric distributed aircraft, but scaled to the 200 kW level.
• Power and voltage levels that would be considered subscale for a commercial transport, but test capability extends to
the entire airplane system and can exercise all aspects of flight control, including cockpit operations.
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Concluding Remarks
• Electrified propulsion technology development well underway.
• Specific technologies for development driven by the
integrated propulsion systems and the propulsion systems
driven by mission requirements
• Continuing to advance technologies and knowledge
applicable to variety of missions and systems as well as those
critical to enabling the systems
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