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Jornada de Nuevas Tecnologías Energéticas en el Sector Aeronáutico INTA - 3 octubre 2008

The Fuel Cell Demonstrator AirplaneBoeing Research & Technology Europe

N. Lapeña, J.Mosquera, E. Bataller, F. Ortí and C. Barberán*

Jornada de Nuevas Tecnologías Energéticas en el Sector Aeronáutico

INTA - 3 octubre 2008

Boeing Technology | Phantom Works Boeing Research & Technology Europe

BR&TE Brown Bag Seminar, March 14th 2008Jornada de Nuevas Tecnologías Energéticas en el Sector Aeronáutico INTA - 3 octubre 2008

Discussion Topics

Project objective

What is a fuel cell

The airplane

The systems

Bench tests

Ground tests

Flight tests with conventional aircraft & certification

Flight tests

Conclusions



The Fuel Cell Demonstrator Airplane

Project Objectives

The engine of a motor-glider (Diamond HK36TTC Superdimona) has been replaced by a PEM Fuel Cell/Li ion Battery hybrid power source that drives an electric motor rotating a variable pitch (constant speed) propeller

Benefits of Work: Develop capability for “hands on” integration of fuel cell systems in aerospace applications

Project aim: To demonstrate the feasibility of a straight and level manned flight with fuel cells as the only source of power

http://www.diamond-air.at/Pressebilder/HK36SuperDimona_Xtreme/MEDIUM/HK36i.JPG



In principle, a fuel cell operates like a battery but does not require recharging. It produces energy in the form of electricity and heat as long as fuel is supplied

What is a Fuel Cell ?

EnergyOHOH +→+ 222 21

Cell Components Single Cell Stack with End Platesand Connections

Cooling/Bipolar Element with Gas/Water Channels

Electrode &

Catalyst

PEM

Energy Carrier : H+

• Polymer Electrolyte: Nafion® (poly-perfluorosulphonic acid), needs humidification

• Anode Reaction: H2 (g) ⇒

2H+(aq) + 2e-

• Cathode Reaction: ½ O2 (g) + 2H+(aq) + 2e- ⇒ H2 O (l)• Temperature: < 80ºC

• Power Density: High ( 800 mA/cm2)



The Airframe

• 2 seater light-weight (all composite)• EASA CS 22 certified motor-glider• Max L/D of 27• MTOW of 770 kg• Engine: Rotax 914F 115 hp (other models with 80 hp or 100 hp)• TO roll (SL, standard): 182 m; • TO distance: 274 m• Landing roll (SL, standard): 195 m;• Landing distance: 395 m

432 kg

Original flight controls + propeller speed control + throttle control (electric motor torque command)



The Flight Mission

ROC > 1.5 m/sTO distance = 620 m MTOW = 870 kg

ROM Duration (min)

61 3 1 6 30 3 23

Flight Mission

PreflightStart-up

Taxi out @ around 20 km/hTake off (from 0 – 90 km/h)

Climb @ 97 km/h up to 1000 mCruise @ 100 km/h

ApproachLanding Taxi in

ROM brake power requirements (kW) *

5-20-

7-9 34.434.415.59-10 9-10 7-9

FC + Aux. Batteries

Power Requirements (Taking into account the weight increase due to new components (870 kg) & some EASA CS 22 requirements, such as ROC & T/O D)

•T/O & climb: 45 kWe, half from the Li ion battery & half from the fuel cell

• Cruise: 18 kWe, all from the fuel cell

01000200030004000

Ext

erna

l

Take

off

Cru

ise

Land

ing

Flight Mission

Alti

tude

(fee

t)

Motor eff ~ 89% cruise @ 2,000 rpmMotor eff ~ 86% climb @ 1,500 rpm



The Overall System

Propeller

Fuel

Electricity

Cooling

Control

Li-ion Batteries

PMAD

Motor Drive Fuel Cell

Controller

Pitch Control

Throttle

Fuel Cell Stacks

Air

Motor Radiator

Condenser + Intercooler

Propeller Adapter

SBC

M

Hyd

roge

n Ta

nk



The Airplane Layout



The Electrical System



• Control the start-up/shut-down sequences & the emergency stop

• Interface with the pilot through the instrumentation panel

• Generate the LV power supplies

• Distribute the electrical power

• Protect the different components (power sources & loads)

• Throttle conditioning

• Matches the propulsion motor power demand to the available power in normal/fault conditions

• Limits the max. allowable rate of power change per unit time to cope with the fuel cell response to step commands.

• Balance the power supply from FC & battery by means of the SBC

• Done as a function of the load to maximize the energy of the total hybrid power source • Achieved by regulating the output voltage of the SBC: it sets the bus voltage &, thus,

the current sharing between the sources• Regulated through a control loop• Works only during T/O & climb (45kW loads for 7 min)

The PMAD Functionalities

DISCONNECTED & USING NATURAL POWER DISTRIBUTION



Electrical architecture control, mainly initial battery connection to distribution bus:

crucial to ensure the power to the propulsion motor in normal & failure

modes

Control loops: correct operation of series boost converter and throttle

conditioning control loops at the same time

Electromagnetic interference: correct operation of components with a motor

system inducing perturbations

Electrical System Main Challenges



Motor (UQM) and water cooling system (IIC)• Power Phase 75 electric brushless DC motor from UQM Technologies Inc. • Experimental brushless permanent magnet electric motor (used in hybrid & fuel cell prototype cars)• The motor control variable is the torque• Motor tested with flight mission profile at UQM• Motor radiator & pump tested in the lab with forced air flow & with the propeller at the ground tests• Flight missions tested in the bench (with the motor coupled to a hydraulic brake) & in the ground tests(motor & propeller)

Propeller (MT) and adapter (TAM)• The motor rotates a variable pitch propeller, the MTV-1-A/175-05 model from MT Propeller• The rotational speed is controlled by the propeller pitch controller• Mechanical adapter to transmit the propeller thrust to the airframe structure rather than to the motor, which

is not prepared to transmit any axial loads.

The Propulsion System



- Manufactured by Intelligent Energy- Pressurized system (gross output power: 18kWe continuous, 25 kWe peak) - Auto controlled through a PLC- 2 stacks (with GORE MEAs) electrically connected in series- Thermal system & water recovery for cooling and humidification - Air system (filter, compressor, compressor motor & drive) - Hydrogen system - Max. dry weight 93kg, excluding mounts & wiring harnesses- Packaging within airplane nose cone available space & the co-pilot foot well

- System preliminarily tested in the bench with a load unit, and then with the batteries & the motor with the following objectives:

- To determine if the system can deliver max. power requirement & operate stably throughout the operative cycle

- To define acceptable limits to performance envelope - To determine H2 consumption & water mass required for operative cycle - To determine the system’s behaviour in steady state & in non-steady state - To characterise the fuel cell system controller’s behaviour under induced faults

- Flight missions successfully accomplished in the bench & in the ground tests with the propeller.

The Fuel Cell System



Fuel Cell System Acceptance Tests

Steady state testing/ Peak & continuous power output

0

40

80

120

160

200

240

280

320

360

0 20 40 60 80 100 120

I / A

Volts

0

5

10

15

20

25

Gro

ss p

ower

/ kW

SN554 / V SN550 / V total V gross Pwr / kW

0

10

20

30

40

50

60

70

80

90

100

10:48:0010:55:1211:02:2411:09:3611:16:4811:24:0011:31:1211:38:2411:45:3611:52:4812:00:00

Time [hh:mm:ss]

Pow

er [%

]

Gross Pow er Net Pow er

-20

-10

0

10

20

30

9:20 9:25 9:30 9:35 9:40 9:45 9:50

Time

Pow

er (k

W)

-200

-100

0

100

200

300

Pow

er (W

)

Gross Power /kW Net Power /kW Blower Power /kW Aux Power /W

0

50

100

150

200

250

300

8:44 9:14 9:44 10:14 10:44 11:14 11:44 12:14 12:44 13:14 13:44 14:14 14:44Time

Volta

ge (V

) & C

urre

nt (A

)

0

5

10

15

20

25

30

Pow

er (k

W)

Stack A Voltage /V Stack B Voltage /V Total Voltage /V Load Current /A Net Power /kW



Fuel Cell System Acceptance Tests

- Transient testing

- AC impedance tests -The UQM inverter induces a current ripple that the fuel cell delivers without errors.- Load transients

- Transient steps at low loadings do not cause any problems. - But large instantaneous transient steps at high loadings (75-100% load) would disconnect the battery.

- Tilt testing

-20

-10

0

10

20

30

9:21 9:23 9:26 9:28 9:31 9:33

Time

Pow

er (k

W)

-200

-100

0

100

200

300

Pow

er (W

)

Gross Power /kW Net Power /kW Blower Power /kW Aux Power /W



The Fuel System

EXHAUST

6mmx1

10mmx1.5

6mmx1 6mmx1

6mmx1

6mmx1

V01

V02 V03

V04

PRV01

PRV02

EV01

EV02

EV03 EV04

6mmx1

EXH

AUS

T

EXHAUST

EFV01

TT

PX01

PX02

PT

PSV00

PSV01

PSV02

GFI BLOCK

Stack B

REFUELING PORT

10mmx1.5

25mmx3

Stack A

EXHAUST

6mmx1

10mmx1.5

6mmx1 6mmx1

6mmx1

6mmx1

V01

V02 V03

V04

PRV01

PRV02

EV01

EV02

EV03 EV04

6mmx1

EXH

AUS

T

EXHAUST

EFV01

TT

PX01

PX02

PT

PSV00

PSV01

PSV02

GFI BLOCK

Stack B

REFUELING PORT

10mmx1.5

25mmx3

Stack A

Air Liquide Spain• High pressure composite tank, 2 pressure regulators, solenoid & manual valves, safety devices (EFV & PSV), sensors• Operations: purging, refueling & venting

Area classification: Sources of release, Release rate, Extent of zone, LEL, Ventilation

Zone 2 of Negligible Extent

Zone 1 of Negligible Extent



The Refueling Station

Air Liquide Spain

• External N2 & H2 @ 200 bar

• Pneumatic compressor to boost the pressure up to 350 bar in the on-board tank

• Purging & venting capability

• Depending on the cylinders pressure and ambient Temp refueling takes from 10-30 mins



The Auxiliary Batteries

SAFT Aviation

• 25 kWe to assist the fuel cell during the 7 min T/O & climb but sized for up to 50 kWe during 5 mins

• Components:• 66 VL20P cells electrically in series (11 blocks of 6 cells each) • Internal management unit to control the first level system cell

management & contains the centralized electronic system to manage the battery and the charge, discharge & state of charge algorithms.

• Sensors & contactors designed for battery protection in case of battery over-voltage, over-current in both directions, over-temperature & deep discharge.

• The cells, the battery management unit, all required protections (packing) & sensors are contained within a battery case compliant with the EASA CS 22 crash landing requirements (forward 9 g, upward 4,5 g, sideward 3 g, downward 4,5 g)

• No cooling requirements.

• Weight: 85 kg



The Auxiliary Batteries Acceptance Tests

• Normal operation: Battery static discharge @ constant current (100 A)

• Fuel Cell failure: • Battery static discharge @ constant current (200 A)• Transient tests • Single cell short-circuit

Boeing battery with 66 Li-ion VL20P cellsDischarge at 100A & 200A at +10°C

170

180

190

200

210

220

230

240

250

260

270

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00Time (mn)

Volta

ge (V

)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Ener

gy (W

h)

Voltage at 100A disch Voltage at 200A disch Energy at 100A disch Energy at 200A disch



Airplane Bench Tests

• First tests of the overall system

• Electric motor coupled to hydraulic brake to simulate the propeller

• Electrical integration thoroughly tested

• PMAD controls & protections successfully tested

• Flight missions successfully performed with the motor coupled to a hydraulic brake



Airplane Bench Tests

• Simulation of a flight mission with fuel cell failure during takeoff & climb - The battery provides the entire power required to takeoff & climb to ~ 450 ft, an altitude safe enough for a safe emergency landing.



Getting Ready for The Flight Tests

• Test pilot : involved in the project since 2003 and Head of Operations & Safety Procedures at the OCAÑA airfield for 5 years

• 3 flight test campaigns with original aircraft with the weight & power settings of the demonstrator aircraft at LOAN airport, Wiener-Neustadt (Austria)

• Verification of theoretical flight envelope estimations & reduced power performance:• Full power T/O• Flight with different flight regimes• Cabin configurations with and without motor• Take offs with Vx , Vy• Study of the different operating cruise speeds and stall speed Vs.

• Drafted the flight & emergency procedures for the demonstrator airplane test flights



Certification & Flight Readiness Review

• The experimental certification was granted by the Spanish CAA on 2/7/2008

• Airplane configuration review (airplane design review and subsystems, bench & ground test results review)

• Structural justifications review (W&B, overweight & mounting)

• Airworthiness limitations review

• Flight performance & flight path review (flight protocols, risk analysis, operations & maintenance manuals)

• Internal review by Boeing Flight Testing Team

• Experimental certificate issued for 6 months. Flights restricted to the airfield of Ocaña, within restricted airspace and special safety measures.



Airplane Ground & Flight Tests

• The propeller & its controller operate correctly

• The on-board hydrogen tank is re-fueled almost daily

• The motor inverter induces EMI but the electric system operates correctly

• The natural power distribution between the sources has proven to be as efficient as using the SBC control, while being more robust

• The ground tests have proved correct ventilation & cooling. During the entire flight mission both the motor temperatures & the PMAD electronics temperatures remain well below their thermal limits.

• The airplane is overweight but well balanced. No structural issues have been observed because the speed & load factors are reduced.

• No major vibration issues have been observed.



Flight Tests Results

• 4 flight missions successfully performed at OCAÑA airfield

• During the maiden flight the battery was not disconnected for safety reasons. Also there was a power reduction during T/O & climb so an altitude of only 350 ft AGL was reached

• During the 3 subsequent flights the airplane performed the entire flight mission and the battery was disconnected.

• T/O D: ~400 m• RoC: 300 Ft/min• Altitude achieved: 1000 ft AGL• Missions duration: over 25 mins (4 mins T/O & climb and the rest cruising)• Mission footprint recorded on the 3rd flight mission (altitude profile, vertical speed profile, ground speed profile) with an ICAO certified GPS system

The project objective (to maintain for the first time in aviation history a level manned flight with fuel cell power) was achieved!!




Altitude Profile




Vertical speed profile




Ground speed profile



Conclusions

The flight tests have been completed & the project objective (to maintain for the first time in aviation history a level manned flight with fuel cell power) has been achieved!!

Safety has been the team priority

The demonstrator flies well even with less power than the conventional aircraft and with 100Kg of overweight

We could have pushed it further!! At the end of the mission: 100 bar hydrogen pressure & over 35% battery charge



Conclusions

• The thrust delivery and the power transitions are smooth

• The noise and vibration levels are lower than in a conventional aircraft

• The fuel cell system shows itself as a reliable system when well conditioned

•The main barrier to implement currently available fuel cells in aviation is their low specific power density (high weight)



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