NASADistributed Electric Propulsion

Research

E2 Fliegen

Stuttgart, Germany

Feb 27th, 2015

Mark Moore

Convergent Electric Propulsion Technology Demonstrator Principal Investigator

NASA Langley Research Center

mark.d.moore@nasa.gov

Many Electric Flight DemonstratorsHave Been Developed in Recent Years

2

Rui Xiang RX1EChina

E-FanEADS

FEATHERJAXA

E-GeniusEADS

Electric Cri-CriEADS

DA-36 E-StarEADS

Breuget Range Equation for Electric Aircraft

NASA Focus: Show Electric Flight

Relates to Higher Speed(While Still Achieving

High Efficiency)

But All are Low Speed

Range is Independent

of Speed

Electric Propulsion DifferencesCompared to Existing Propulsion Solutions

3

Electric Propulsion PenaltiesEnergy Storage Weight (50x worse than aviation fuel)

Energy Storage Cost (Tesla 65 kWhr battery is ~$25,000)Certification Uncertainties and Absence of Standards

Electric Propulsion Benefits~2x efficiency of turbine engines, 3-4x efficiency of piston engines

High efficiency across >50% rpm range6x the motor power to weight of piston engines

None air breathing - No power lapse with altitude or on hot daysExtremely Quiet

Zero vehicle emissions10x lower energy costs

Electric Propulsion Integration BenefitsScale independence of efficiency and power to weight

Power to weight and efficiency don’t degrade at smaller sizesExtremely compact

High reliability – few moving parts

The integration benefits suggest Distributed Electric Propulsion (DEP)approaches could achieve closely coupled, multi-disciplinary benefitsacross aerodynamics, propulsion, control, acoustics, and structures.

NASA Rapid Spiral DevelopmentResearch of Distributed Electric Propulsion

4

3m Span Small UAS

Scale

10m Span DEP Wing Only

Scale

11m Span Full General Aviation Aircraft

Scale

NASA Langley 1st DEP Spiral Sub-Scale 12’ Wind Tunnel Test

5

12’ NASA Langley Wind Tunnel Testing to Establish 1st DEP Controls Aerodynamic Database

Wind Tunnel Test Unpowered CL’s

NASA Langley 1st DEP Spiral Sub-Scale VTOL DEP Flight Demonstrator

6

7

General Aviation aircraft are only aerodynamically efficient at low speeds because the wing is oversized for 61 knot stall, 2000 ft field lengths.

Aerodynamic efficiency is very important for energy constrained electric aircraft.

Lift/DragRatio

Wing CL

Current General Aviation AircraftAerodynamic Efficiency

Cirrus SR-22

8

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1 1.2

Increase Wing Loading to AchieveHigh Aerodynamic Efficiency at High Speed

StallSpeed(knots)

Wing loading (lb/ft2)

DEP Clmax = 5

Stall Speed vs Wing Loading(General Aviation Aircraft)

Lift/Drag Ratio vs Cruise CL

(General Aviation Aircraft)

200 mphCruise

120 mphCruise

L/D

CLConventional GA aircraft

DEP GA aircraft

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1 1.2

DEPAircraft

200 mphCruise

00

9

Highly Coupled Aero-Propulsive DEP WingTo Achieve High Wing Loading

(18) .5m diameter propellers

distributed across wing span

with 12 kW per propeller

(220 kW total power)

0

1

2

3

4

5

6

-2 0 2 4 6 8 10

CL

α (º)

Lift Coefficient at 61 Knots (with and without 220 kW)

No Flap (STAR-CCM+) 40º Flap, No Power (STAR-CCM+)

40º Flap with Power (STAR-CCM+) 40º Flap with Power (Effective, STAR-CCM+)

40º Flap with Power (FUN3D) 40º Flap with Power (Effective, FUN3D)

10

• STAR-CCM+ uses SST

(Menter) k-ω turbulence

model with γ-Reθtransition model

• FUN3D runs use Spalart-

Allmaras

0

5

10

15

20

25

0 20 40 60 80

CL

max

Velocity (kts)

Unpowered

Constant Power (220 kW)

Lift Coefficient versus

Reference Speed

DEP Highlift Aero-PropulsiveAnalysis Results

11

NASA Langley 2nd SpiralDesign/Analyze/Build/Test 10m DEP Wing

12

NASA Langley 2nd SpiralDEP Wing Initial Testing

Low Speed Testing (40 mph) at Oceano Airport

Testing is Starting at NASA Armstrong Dry Lakebed

with Speeds of 70 mph

Air Bag System Dampens

Ground Vibration

13

Low Speed Taxi Testing Results

Instrumentation system is 75% complete; Air Data probe, wing surface pressures and GPS are not yet integrated, so we can’t account for winds on the airfield will increase/decrease effective airspeed (and measured lift)

With time averaging, the vibration levels from the ground are well managed.

40 mph, 6400 rpm α=10 deg, Full Flaps, Upwind with 4 kt wind

~2300 lbf Lift

NASA Langley 2nd SpiralDEP Wing Initial Testing

14

Data is matching CFD extremely well, with the vectored thrust

(effective lift) accounted.

40 mph, 6400 rpm α=10 deg, 40 Deg Flaps

Reference Speed (knots)

Current Validation

NASA Langley 2nd SpiralDEP Wing Initial Testing

15

Inner span propellers are fixed pitch and

fold conformal against the nacelle,

and are only active at low/slow flight.

Cruise Aero-Propulsive Effects

Wingtip Propulsors Increase Cruise Efficiency

Smaller diameter propeller

Higher Cruise Speed and/or

Lower tipspeed propeller

Lower Induced Drag

Aerodynamic Effects of Wingtip Mounted Propellers and Turbines,

Luis Miranda AIAA Paper 86-1802

Conventional GA Aircraft

DEP Aircraft

• Modifies existing General Aviation (GA) aircraft by removing the wingand engines, and replacing with a DEP wing system.

• Research provides rapid concept to flight of DEP technologies.• Complex high voltage electric power architectures and EMI mitigation• Multi-disciplinary high aspect ratio wing aeroelastics• Robust, reliable, Redundant distributed control• PAI design tools and validation, wingtip vortex propulsion• Spread frequency acoustics 16

Tecnam P2006T Baseline Light Twin Retrofit LEAPTech NASA DEP Demonstrator

NASA Langley 3rd SpiralDEP General Aviation X-Plane

17

DEP Community Noise Benefit

Conventional Single 3-Bladed Propeller Harmonics

(18) Asynchronous 5-bladed propellers that spread a

single blade passage harmonic across

30 harmonics instead of 1 that blends into the

broadband as ‘white noise’

Broadband noise

Conceptual Effects of Frequency Spreading

Cirrus SR-22

3rd Spiral DEP Flight DemonstratorSystem Level Impacts

18

Primary Objective• Goal: 5x Lower Energy Use (Comparative to Retrofit GA Baseline @ High

Speed Cruise)

• Minimum Threshold: 3.5x Lower Energy Use

Derivative Objectives• 30% Lower Total Operating Cost (Comparative to Retrofit GA Baseline)

• Zero In-flight Carbon Emissions

Secondary Objectives• 15 dB Lower community noise (with even lower true community annoyance) .

• Flight control redundancy, robustness, reliability, with improved ride quality.

• Certification basis for DEP technologies.

• Analytical scaling study to provide a basis for follow-on ARMD Hybrid-Electric

Propulsion (HEP) commuter and regional turbo-prop research investments.

Primary Objective Basis• Electric only conversion of the baseline aircraft results in a 2.9 - 3.3x efficiency

increase (i.e. 28% to 92% motor efficiency).

• Integrating DEP results in an additional 1.2 - 1.5x efficiency increase.

• Minimum threshold is 2.9 x 1.2 = 3.5, with goal of 3.3 x 1.5 = 5.0 goal.

19

Cirrus SR-22General Aviation Aircraft

3400 lb

200 Whr/kg batterieswith a 200 mile range

with reserves

400 Whr/kg battery energy density is critical to enable early adopter electric propulsion markets

Battery Specific Energy Sensitivity

Cirrus SR-22 with Retrofit Electric Propulsion

11,300 lb

Early Market Electric Propulsion MarketThin-Haul Commuter Mission

Example of dominant (green) and long-tail (yellow) market distribution (with each being 50% of the total market share)

0

2000

4000

6000

8000

10000

12000

14000

20

23

27

34

39

40

48

59

66

79

82

90

97

10

4

11

0

12

9

13

5

13

9

15

9

16

3

16

8

16

9

17

2

18

3

21

0

All Cape Air Operations 11.7M Seat Miles

~100 Cessna 402 9 passengerAircraft

Cape Air Commuter Trip Range Distribution

Trip Range (nm)

Numberof

Trips

Thin-Haul Commuters provide Essential Air Services to small communities with ‘thin’ passenger trip distributions. New business models and technologies are developing across many industries to capture ‘long-tail’ markets instead of focusing only on dominant markets.

(see The Long-Tail: Why the Future of Business is Selling Less of More)

No Trips

with Range

> 220 nm

8

21

EADS has recently funded 4 electric propulsion integration flight demonstrators • To quickly become familiar with this new propulsion technology area through

hardware demonstrations that offer a solid engineering experience. • To quickly explore alternate integration approaches.• Companies have yet to flight demonstrated distributed electric architectures.

For each research effort spiral development was utilized to provide… • Experimentation that provides TRL advancement across vehicle sizes due to the

scale-free nature of electric technologies• Approach agility due to rapidly accelerating technologies• Provide early lessons learned with minimal consequence• Greater control of discrete costs and risks• Establish an early certification basis• “Fail early, Often”

Why Use Spiral Development?

Questions?

22

NASA

Convergent Aeronautic Solutions (CAS)

Distributed Electric Propulsion (DEP)

Tecnam P2006T Based X-PlaneEffect of Propeller Radius to Chord Ratio

Spanwise Lift Distribution with Propellers

α Lift Drag Thrust CL Effective CL CD

0º 3,377 lb 524 lb 853 lb 4.86 4.86 0.778

2º 3,471 lb 565 lb 853 lb 4.99 5.04 0.838

4º 3,535 lb 603 lb 853 lb 5.09 5.17 0.895

5º 3,589 lb 626 lb 853 lb 5.16 5.27 0.929

6º 3,617 lb 641 lb 853 lb 5.20 5.33 0.952

8º 3,645 lb 670 lb 853 lb 5.24 5.42 0.995

9º 3,648 lb 676 lb 853 lb 5.25 5.44 1.003

10º 3,662 lb 698 lb 853 lb 5.27 5.48 1.037

24

DEP Operating Cost BenefitWhile Achieving Zero In-Flight Emissions

Electricity based aircraft energy provide a decrease in price variability and cost riskas well as a true renewable energy path

(100LL fuel is ~2x higher cost than auto gas)

0

50

100

150

200

250

300

350

400

450

500

Energy

Insurance/Taxes

Personnel

Pilot

Acquisition

Facilities

Maintenance

General AviationTotal Operating Cost Comparison

SOA Baseline DEP Concept

$/Hr

0

1000

2000

3000

4000

5000

6000

Energy

Insurance

Flight Crew

Financing

Maintenance

Single Aisle CommercialDirect Operating Cost Comparison

SOA Baseline DEP Concept

System Impact of Applying Distributed Electric Propulsion

January 13–15, 2015 NASA Aeronautics Research Mission Directorate 2015 LEARN/Seedling Technical Seminar 25

Make Aircraft More Efficient, with Improved Emissions, Noise, Ride Quality, Safety, and Operating Costs

• Typically achieving an improvement in one aircraft capability requires taking penalties in other areas.• By leveraging this new integration technology, Distributed Electric Propulsion (DEP), dramatic

improvements are possible across these areas, while only absorbing penalties in range and weight (which penalties will become significantly reduced as battery specific energy improves).

• Applying DEP to a General Aviation aircraft enables these improvements, while limiting the range to 200 miles and increasing the vehicle weight from 2700 lb to 3400 lb.

Aerodynamic Efficiency: Lift/Drag ratio improved from 11 to 17Propulsive Efficiency: Energy conversion efficiency from 24% to 83%Emissions: Life cycle GHG decreased by 5x using U.S. average electricityCommunity Noise: Certification noise level from 85 to <65 dBSafety: Highly redundant propulsion system Ride Quality: Wing loading increased by >2.5xOperating Costs: Energy costs decrease from 45% to 12% of TOC

26

General Aviation: Cirrus SR-22

Gross Weight ~ 3400 lb

L/D cruise ~ 11

Wing loading = 25 lb/ft2

Commuters: Cessna Grand Caravan

Gross Weight ~ 6200 lb

L/D cruise ~ 10

Wing loading 22 lb/ft2

Regional Jets: Bombardier Q300

Gross Weight ~ 43,000 lb

L/D cruise ~ 16

Wing loading 71 lb/ft2

Single Aisle: Boeing 737

Gross Weight ~150,000 lb

L/D cruise ~ 18

Wing loading 111 lb/ft2

General Aviation SOA provides large benefit advantages for early market success with emerging electric propulsion technology adoption to provide more rapid tech acceleration for larger scale aircraft.

DEP Integration Application Across Aviation Markets

Electric propulsion integration benefitsdecrease with larger aircraft due to the far superior baseline metrics, but still offercompelling benefits across efficiency, emissions, noise, and operating costs.