Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions - Michael Husemann, M.Sc. Christopher Glaser, B.Sc. Univ.-Prof. Dr.-Ing ...

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Assessment of a Fuel Cell Powered Air Taxi
in Urban Flight Conditions
Michael Husemann, M.Sc.
Christopher Glaser, B.Sc.
Univ.-Prof. Dr.-Ing. Eike Stumpf
Institute of Aerospace Systems (ILR)

Challenges of today’s mobility concepts
 Current Situation Requirements

 • Daily routine (commuting, free time) External Demands and Requirements
 • Travels (regional/ trans-regional)
 Mobility
 • Tendency towards ind. transport
 Needs Political Guidelines User Groups
 - benefits are cost-intensive
 - usage of cars not optimal
 • door-to-door-travel time Various requirements for a
 of max. 4 hours high level of comfort:
 (Flightpath 2050) • Punctuality/ Predict.
 • massive attrition/ poor condition Conflict
 • Environmental • Accessibility
 Infra- • frequent congestion/ limited parking requirements or health • 24/7 availability
 structure • complicated routings concerns • Individ. planning
 • Increasing oil prices (noise und pollutants) • Short travel times
 • Operating costs • comfortable
 • Internet access
 • inexpensive
 • Environmentally friendly
 new approaches: (noise und pollutants)
 • car and bike sharing
 Problem • driving services (Uber & Lyft) Mobility plays an important role in daily life
 • e-mobility
 important, but not sufficient Mobility that increases speed, decreases costs,
 more readily available

1 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Modern technologies enable new transportation possibilities
 Alternative Options
 Design Concepts
 I Use of the “third dimension”
 • Diversified mobility options
 • Opportunity of individualized mobility (on-
 demand)
 • Travel distance corresponds to approx. linear
 distance, which is why travel duration is shorter
 than with conventional mobility concepts
 • Bypassing areas at risk of congestion

 II Different application cases
 • Regional air transport
 for ranges between 50km < s < 500km
 • Suburban air transport
 for commuting purposes & feeder services
 • Urban air transport © Porsche Consulting

 daily transportation (leisure and commuting)

2 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Modern technologies enable new transportation possibilities
 Alternative Options
 Energy
 I Use of the “third dimension”
 • Diversified mobility options Batteries Fuel Cells
 • Opportunity of individualized mobility (on-
 demand)
 • • Short refueling times
 • Travel distance corresponds to approx. linear Rechargeable
 • No local emissions • High power density
 distance, which is why travel duration is shorter
 (noise and pollution) • High energy conversion
 than with conventional mobility concepts
 efficiency
 • Bypassing areas at risk of congestion
 • “No” local emissions
 (noise & pollution)
 II Different application cases • Long charging times
 • Regional air transport • Limited capacity (ranges)
 for ranges between 50km < s < 500km • Possible overheating risks • Complex design
 • Suburban air transport • Limited lifetimes • Thermo management
 for commuting purposes & feeder services (capacity < 80%) • Missing infrastructure
 • Urban air transport
 daily transportation (leisure and commuting)

 Does the application of fuel cells in air transportation offer operational benefits?

3 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Considerations are based on the initial battery powered Vahana concept
 A simplified version of the original design tool is available to the public

 Approach Parameter Studies

 Reference vehicle A
 Assumptions and highlighting of affected
 parameters

 • Characteristics Definition of study mission
 A B
 • Vahana concepts (mission profile)

 C Parameter studies: range and payload
 Principles of fuel cells

 D Effects on cost structure
 • Energy storage
 B
 • Equivalent specific energy

 E Conclusions

4 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Considerations are based on the initial battery powered Vahana concept
 A simplified version of the original design tool is available to the public

 Approach Parameter Studies

 Reference vehicle A
 Assumptions and highlighting of affected
 parameters

 • Characteristics Definition of study mission
 A B
 • Vahana concepts (mission profile)

 C Parameter studies: range and payload
 Principles of fuel cells

 D Effects on cost structure
 • Energy storage
 B
 • Equivalent specific energy

 E Conclusions

4 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

A simple design tool provided by A³ is used to conduct parameter studies
 Vahana Alpha One
 Vehicle characteristics
 Characteristic Value
 PAX capacity 1
 Fuselage length 5.70 m
 Overall height 2.81 m
 3,5
 Wingspan 6.25 m
 3 300 kg Empty weight 475 kg
 600 kg MTOW 815 kg
 2,5 900 kg Payload 250 lbs
DOC [$/km]

 1200 kg
 2
 1500 kg © A³ Vahana
 Helicopter
 1,5
 Tilt-Wing
 1 Size of the dots represents the respective take-off mass

 0,5
 First results show a cost advantage of the tilt-wing
 configuration especially on longer distances (fixed-
 wings are used to generate lift during cruise flight)
 0 50 100 150 200
 Range [km]

 5 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Fuel cells contain higher energy densities than batteries
 Storage Equivalent

 Low volumetric density calls for special A fuel cell system requires several components
 storage technologies such as fuel tank, hydrogen and fuel cell

 © Hepperle
 © Hepperle
 Hydrogen is stored under pressure, liquid or in hybrids
 High pressure storage is considered most viable for small aerial Transformation of different parameters into one equivalent specific
 vehicles (350-700 bar, volumetric energy density improved) energy is necessary for proper comparison

6 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Considerations are based on the initial battery powered Vahana concept
 A simplified version of the original design tool is available to the public

 Approach Parameter Studies

 Reference vehicle A
 Assumptions and highlighting of affected
 parameters

 • Characteristics Definition of study mission
 A B
 • Vahana concepts (mission profile)

 C Parameter studies: range and payload
 Principles of fuel cells

 D Effects on cost structure
 • Energy storage
 B
 • Equivalent specific energy

 E Conclusions

7 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Initial assumptions are retained for comparability purposes
 General assumptions are based on a forecast predicting values in 2021 when Vahana is supposed to enter production
 1 2 3
 Performance and dimensions Manufacturing costs Operating costs

 Performance and efficiencies of electric Costs due to daily flight operations such
 powertrain unit and dimensions of the Material and production expenditures as replacement of individual wearing parts
 vehicle and personnel costs

 Parameter Value Unit Cost design Value Unit Maintenance Value Unit
 Battery specific energy 230 Wh/kg Material 220 $/kg Battery replacement 2000 Cycles
 Motor specific power 5 kW/kg Battery 161 $/kg Motor replacement 6000 FH
 Depth of discharge 95 % Motor 150 $/kg Servo replacement 6000 FH
 Fuselage width 1 m Servo 800 $/pcs Personnel costs 60 $/hrs
 Fuselage length 5 m Avionics 30,000 $ Periodic maintenance 0.05 MHR/FH
 Fuselage height 1.6 m Insurance 6.5 % aq. cost
 Gearbox efficiency 98 % Facility rental 2 $/ft²/month
 Motor efficiency 85 % Electricity 0.12 $/kWh

 Which parameters are affected by a propulsion modification?

8 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Two main design parameters must be adapted for the application of a fuel cell
 Affected Parameters

 The implementation of an equivalent fuel cell is carried out by adjusting the
 performance values of the previous battery.

 Mission study
 Cruise “X“ km
 Cruise ‘‘X“ km

 Battery specific energy Depth of discharge
 9090sec
 sec 90 sec
 90 sec
 Available energy provided for Unlike a battery, a fuel cell system hover +
 hover +
 transition
 hover +
 transition + hover
 propulsion (hydrogen instead of can use 100% of its available transition
 + +20
 20min buffer:
 minute buffer:
 transition
 electricity) energy (empty tank) •  33min
 min hover
 hover + transition
 + transition
  17 min at min. power
 • 17 min at min. power

 Engine, servo components and efficiencies remain unchanged (associated
 data can be adopted). Avionics, insurances, leasing and personnel costs
 are not affected by a modification
 Battery costs per mass unit (kg) and replacement cycle will change as the
 price of the fuel cell system will be different.

9 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Parameter Studies: Effects on the range capacity
 Range Payload

 Payload is kept constant and all default Increasing range capacity is used to
 parameters are applied increase payload capacity

 800 1600
 Vahana

 700 battery 1400
 specific 60 km
 600 energy
 battery 1200 80 km

 maximum payload, lb
 maximum range, km

 specific energy
 until 20/30
 till 2020/30
 100 km
 500 1000 battery
 battery 120 km
 specific
 specificenergy
 400 800 till 2020/30
 energy
 equivalent
 equivalent
 300 specific energy 600 until 20/30
 specific energy
 PEMFC FC equivalent
 equivalent
 400 specific energy
 specific energy FC
 200 PEMFC
 200
 100
 0
 0

 energy density, Wh/kg energy density, Wh/kg
 Range increases nearly linearly with increasing energy density Buffer time increased
 60km from 20 min
 80km to 40 min
 100km due to heavier weights
 120km
 Strong correlation between both parameters since there are no Higher energy density results in a higher max. payload capacity
 real weight effects due to empty and lighter tanks Higher energy density for a certain range apparent for certain payload
 if a longer range is assumed for study mission

10 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Direct operating costs vary considerably due to different assumptions
 Lifetime of both power systems Battery Costs
 (30 min duration of flight) = ∗ ∗ ℎ 
 25000

 Energy Energy Battery Total battery
 Scenario
 density price weight costs
 20000
 High-price 230 Wh/kg 700 $/kWh 752.11 kg 121,250 $
 Low-price 400 Wh/kg 350 $/kWh 225.77 kg 31,607 $
 Durability [Cycles]

 15000

 Fuel Cell Costs
 10000
 = . ∗ + ℎ ∗ 

 Price per Hydrogen Energy Total FC
 5000 Scenario Max power
 power storage costs demand costs
 High-price 230 $/kW 200 kW 33 $/kWh 112.4 kWh 49,709 $
 0 Low-price 40 $/kW 200 kW 10 $/kWh 112.4 kWh 9,124 $
 Battery [16] Battery [13] Fuel Cell [2] Fuel Cell [13]

 Total costs fluctuate significantly due to deviating technological maturity
Range Max. power Energy Flight time
 Insights and uncertainty about future price developments of energy sources. More
100 km ~200 kW 112.4 kWh 1843.2 s detailed investigations necessary, which emphasize the costs

11 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Key takeaways and future work

 Today’s fuel cell technologies provide a higher energy density compared to batteries,
 which is why longer ranges can be achieved.
 The advantage of higher range capacities can be used for larger number of missions
 without having to refuel in between, which facilitates faster, smoother flight operations
 A higher range capacity can also be used to increase the max. payload capacity (up to
 six times the payload compared with standard configuration)

 Studies are based on a simplified design tool, which is why further investigations will be
 necessary to validate recent findings:
 • Required components for the application of fuel cells must be considered and included
 in future studies to optimize component weights
 • More detailed economic data in terms of acquisition and operating costs are necessary
 • External factors such as the distribution of hydrogen (i.e. infrastructure) must be
 included

12 Assessment of a Fuel Cell Powered Air Taxi in Urban Flight Conditions
 AIAA SciTech Forum 2019 | Michael Husemann, M.Sc. | San Diego, USA, January 10th 2019 |

Thank you.

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Michael Husemann 52062 Aachen | GERMANY
 M.Sc. Tel +49 241 80-96899
 Fax +49 241 80-92233
Research Assistant husemann@ilr.rwth-aachen.de
 www.ilr.rwth-aachen.de