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Turboelectric and Hybrid Electric Aircraft Drive Key Perfomance Parameters
Dr. Kirsten P. Duffy – University of Toledo
Ralph H. Jansen – NASA Glenn Research Center
AIAA Electric Aircraft Technologies Symposium 1July 13, 2018
https://ntrs.nasa.gov/search.jsp?R=20180007414 2020-04-13T01:33:08+00:00Z
AIAA Electric Aircraft Technologies Symposium 2
BackgroundHybrid Electric and Turboelectric Aircraft Propulsion
Partially Turboelectric
NASA STARC-ABL
Fully Turboelectric
NASA N3-X
Hybrid Electric – NASA PEGASUS
July 13, 2018
• High Bypass Ratio (BPR)• Enabled by de-coupling the shaft speeds and inlet/outlet areas
• 4-8% improvement in propulsive efficiency expected for fully turboelectric propulsion (Felder, Brown)
• Boundary Layer Ingestion (BLI)• Reduces drag by reenergizing the wake
• 3-8% improvement in propulsive efficiency expected for fully turboelectric propulsion (Felder, Brown)
• Lift-to-Drag (L/D) Improvements• Distributed propulsion improves wing flow circulation control
• Up to 8% improvement expected (Wick)
AIAA Electric Aircraft Technologies Symposium 3
Electrified Aircraft Propulsion Benefits
July 13, 2018
Benefits ~
𝐿𝐷 𝜂prop E𝐿𝐷 𝜂prop AC
𝜂prop
𝐿
𝐷
• Electric Drive System• Electric machines
• Generators• Motors
• Power management and distribution• Rectifiers• Inverters• Distribution wiring• Fault protection
• Thermal system• Related to electric drive system losses
• Performance – STARC-ABL assumptions• MW-class motor and generator with at least 13 kW/kg and h = 96% • Rectifiers and inverters with 19 kW/kg and h = 99%• Stackup yields overall values of 2 kW/kg and h = 90%
• Input energy• Fuel energy density ~12,000 Wh/kg• Li-ion specific energy on the cell level of up to 200 Wh/kg• New battery technologies (Li-sulfur, Li-air) projected to be up to 750-1000 Wh/kg• Need to be de-rated from cell level to battery pack specific energy
AIAA Electric Aircraft Technologies Symposium 4
Electrified Aircraft Propulsion Costs
July 13, 2018
NASA HEMM Motor Conceptwith h > 98% (Jansen et al. 2018)
AIAA Electric Aircraft Technologies Symposium 5
BackgroundElectrified Aircraft Propulsion Systems
Baseline Turbofan Fully Turboelectric
Partially Turboelectric
July 13, 2018
Parallel Hybrid Electric
• Key Performance Parameters• Electric propulsion fraction x
• Electric drive efficiency helec
• Electric drive specific power Spelec
• Battery specific energy Sebatt
• Breakeven assumptions• Range is the same
• The input energy is the same
• Other assumptions• Payload weight is the same
• OEW/Initial weight is the same (OEW does not include electric drive system or battery weight)
AIAA Electric Aircraft Technologies Symposium 6
KPPs and Assumptions
July 13, 2018
AIAA Electric Aircraft Technologies Symposium 7
Range Equation
Set range of conventional aircraft and electrified aircraft equal
𝑅fuel =𝑆𝑒fuel𝑔
𝐿
𝐷𝜂o ln
𝑊i𝑊f
𝑅batt =𝑆𝑒batt𝑔
𝐿
𝐷𝜂o
𝑊batt𝑊i
July 13, 2018
AIAA Electric Aircraft Technologies Symposium 8
Range Equation
Set range of conventional aircraft and electrified aircraft equal
𝑅fuel =𝑆𝑒fuel𝑔
𝐿
𝐷𝜂o ln
𝑊i𝑊f
𝑅batt =𝑆𝑒batt𝑔
𝐿
𝐷𝜂o
𝑊batt𝑊i
July 13, 2018
~𝑊fuel𝑊i
For small Wfuel/Wi :
AIAA Electric Aircraft Technologies Symposium 9
Breakeven Analysis
July 13, 2018
Baseline Inputs:(L/D hprop htherm)AC
WfuelAC/WiAC
Electrified Aircraft Inputs:
(L/D hprop htherm)E
Equal RangeWfuelE/WiE Equal Input
Energy
WiE/WiAC Component Weights
Welec/WiE
Welec
Definition
Spelec
helec, x,
Sebatt WbattE/WiE
AIAA Electric Aircraft Technologies Symposium 10
Turboelectric Aircraft
July 13, 2018
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
hel
ec
Electric Drive Specific Power Spelec
(kW/kg)
Fuel Savings above this line
AIAA Electric Aircraft Technologies Symposium 11
Turboelectric Aircraft
July 13, 2018
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
hel
ec
Electric Drive Specific Power Spelec
(kW/kg)
Maximum Benefits
Medium Benefits
Minimum Benefits
7% aero/prop benefit
18% aero/prop benefit
29% aero/prop benefit
AIAA Electric Aircraft Technologies Symposium 12
NASA N3-X Turboelectric Example
Ref: Felder, Brown, Kim, and Chu, “Turboelectric distributed propulsion in a hybrid wing body aircraft” 2011
July 13, 2018
Parameter Baseline 777(tube and wing)
Baseline N3A (HWB)
Turboelectric N3-X (HWB)
L/D 19 22 22hprop 69.6% 72.2% 77.1%Spelec (kW/kg) 7.1
helec 98.54%
AIAA Electric Aircraft Technologies Symposium 13
NASA N3-X Turboelectric Example
July 13, 2018
Baseline 777 vs Turboelectric N3-X
Baseline N3A HWB vs Turboelectric N3-X
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 5 10 15 20
Ele
ctr
ic D
rive E
ffic
ien
cy h
ele
c
Electric Drive Specific Power Spelec (kW/kg)
Break Even N3-X
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 5 10 15 20
Ele
ctr
ic D
rive E
ffic
ien
cy h
ele
c
Electric Drive Specific Power Spelec (kW/kg)
Break Even N3-X
AIAA Electric Aircraft Technologies Symposium 14
Partially Turboelectric STARC-ABL Example
Parameter Baseline N3CCPartially
Turboelectric STARC-ABL
x 45%
L/D 21.4 22.3
hprop 64% 75.1%
Spelec (kW/kg) 2.0 kW/kg
helec 90%
Ref: Welstead and Felder, “Conceptual design of a single-aisle turboelectric commercial transport with fuselage boundary layer ingestion”
July 13, 2018
AIAA Electric Aircraft Technologies Symposium 15
Partially Turboelectric STARC-ABL Example
July 13, 2018
75%
80%
85%
90%
95%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
hel
ec
Electric Drive Specific Power Spelec (kW/kg)
Break Even STARC-ABL
AIAA Electric Aircraft Technologies Symposium 16
Parallel Hybrid Electric PEGASUS Example
ParameterBaseline
TurbopropParallel Hybrid
Electric
x 25%, 50%, 75%
L/D 11 15
hprop 60% 72%
Sebatt (Wh/kg) 500, 750, 1000
Spelec (kW/kg) 7.3
helec 90%
Ref: Antcliff et al., “Mission analysis and aircraft sizing of a hybrid-electric regional aircraft,” 2016
July 13, 2018
AIAA Electric Aircraft Technologies Symposium 17
Parallel Hybrid Electric
July 13, 2018
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
Electric Drive Specific Power (kW/kg)
Design Range
Shorter Range
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
Electric Drive Specific Power (kW/kg)
1000 Wh/kg
750 Wh/kg
500 Wh/kg
Effect of Range Battery Specific Power
Electric Propulsion Fraction x = 25%
Shorter range
Sebatt = 750 Wh/kg
AIAA Electric Aircraft Technologies Symposium 18
Parallel Hybrid Electric
July 13, 2018
Constant Benefits:𝐿
𝐷𝜂𝑝𝑟𝑜𝑝
𝐻𝐸𝐿
𝐷𝜂𝑝𝑟𝑜𝑝
𝐴𝐶
= constant with x
Benefits Scale with x:𝐿
𝐷𝜂𝑝𝑟𝑜𝑝
𝐻𝐸𝐿
𝐷𝜂𝑝𝑟𝑜𝑝
𝐴𝐶
∝ x
Shorter Range, Sebatt = 750 Wh/kg
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
hel
ec
Electric Drive Specific Power Spelec (kW/kg)
75% Electric
50% Electric
25% Electric
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
hel
ec
Electric Drive Specific Power Spelec (kW/kg)
75% Electric
50% Electric
25% Electric
AIAA Electric Aircraft Technologies Symposium 19
Parallel Hybrid Electric
July 13, 2018
Constant BenefitsElectric Drive Weight Ratio
Constant BenefitsBattery Weight Ratio
Shorter Range, Sebatt = 750 Wh/kg
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
0 5 10 15 20
Wel
ecH
E/W
iHE
Electric Drive Specific Power Spelec (kW/kg)
75% Electric
50% Electric
25% Electric
0%
5%
10%
15%
20%
25%
0 5 10 15 20W
bat
tHE/W
iHE
Electric Drive Specific Power Spelec (kW/kg)
75% Electric
50% Electric
25% Electric
AIAA Electric Aircraft Technologies Symposium 20
Parallel Hybrid Electric
July 13, 2018
Constant BenefitsHybrid Electric to Baseline Weight Ratio
Shorter Range
0%
50%
100%
150%
200%
250%
300%
0 5 10 15 20
WiH
E/W
iAC
Electric Drive Specific Power Spelec (kW/kg)
75% Electric
50% Electric
25% Electric
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 5 10 15 20
Ele
ctri
c D
rive
Eff
icie
ncy
hel
ec
Electric Drive Specific Power Spelec (kW/kg)
750 Wh/kg
1000 Wh/kg
Electric Drive
AIAA Electric Aircraft Technologies Symposium 21
Parallel Hybrid Electric
July 13, 2018
x = 25%
• All Aircraft:• Higher electric drive specific power yields diminishing returns• Analysis is sensitive to propulsive benefit assumptions and to
component weight assumptions
• Parallel Hybrid Electric:• Dominated by the battery specific energy• Better suited to shorter range• Needs improvement in battery specific energy• Constant benefits – sensitive to electric propulsion fraction because of
battery weight• Scaled benefits – relaxes required electric drive performance
AIAA Electric Aircraft Technologies Symposium 22
Conclusions
July 13, 2018
AIAA Electric Aircraft Technologies Symposium 23
Acknowledgments
This work was funded by NASA:Advanced Air Vehicle Program
Advanced Air Transport Technology Project Hybrid Gas-Electric Propulsion Subproject
Amy Jankovsky subproject managerUS Government Contract NNC13TA85T
The methods used in this paper build on an analytical approach developed by Dr. Gerald Brown at NASA Glenn Research Center for preliminary analysis
of weights of electrical drive systems.
July 13, 2018