Joshua E. Freeh, Anita D. Liang, Jeffrey J. Berton, and Timothy J. Wickenheiser

Glenn Research Center, Cleveland, Ohio

Electrical Systems Analysis at NASA Glenn

Research Center: Status and Prospects

NASA/TM—2003-212520

August 2003
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Joshua E. Freeh, Anita D. Liang, Jeffrey J. Berton, and Timothy J. Wickenheiser

Glenn Research Center, Cleveland, Ohio

Electrical Systems Analysis at NASA Glenn

Research Center: Status and Prospects

NASA/TM—2003-212520

August 2003

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NASA/TM—2003-212520 1 

Electrical Systems Analysis at NASA Glenn Research Center: 

Status and Prospects 

Joshua E. Freeh*

Anita Liang†

Jeffrey J. Berton*

Timothy J. Wickenheiser‡

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

An analysis of an electrical power and propulsion system for a 2-place general aviation aircraft is 

presented to provide a status of such modeling at NASA Glenn Research Center. The thermodynamic/electrical model and mass prediction tools are described and the resulting system power and 

mass are shown. Three technology levels are used to predict the effect of advancements in component technology. Methods of fuel storage are compared by mass and volume. Prospects for future 

model development and validation at NASA as well as possible applications are also summarized. 

Introduction

NASA aeronautics goals include reducing emissions and noise, and pioneering new technology innovation. Advancements in electrical power sources including fuel cells and electromechanical systems such as 

electric motors have shown promise in meeting these goals. The automobile and stationary power industries 

have embraced these technologies as a means to more efficient vehicles and power plants, as well as revolutionary new concepts. The resulting research and development effort has created lighter-weight, more compact and powerful fuel cells and electric motors. These improvements allow fuel cells and electric motors to 

begin to be considered for aeronautical applications. 

The appeal of the fuel cell begins with the potential of producing nearly emission-less electrical power. 

This idea is exciting and the effect far-reaching, but it must be portrayed with the caveat of a ‘cradle-tograve’ viewpoint for the fuel. Any claims for emissions reductions should include data for the lifespan of the 

fuel – from production and reformation to reaction within the fuel cell. With this statement in mind, the outlook is still very promising. Total emissions will likely be reduced and emissions from the fuel cell itself may 

be near-zero. A more practical advantage, compared to other electrical power sources, is that the fuel is contained external to the cell itself, unlike batteries and capacitors. Therefore, the total energy available is not 

directly limited by the cell or stack size, but by the ability to store fuel. Fuel cells are also modular and 

theoretically any voltage or power can be produced by a series and/or parallel configuration of stacks of 

cells. Furthermore, fuel cell energy conversion is electrochemical and not limited by the thermodynamic 

Carnot cycle. All thermodynamic power cycles, including gas turbines and intermittent combustion engines, 

are limited by this corollary restriction, where 

2

1

max 1

T

T

η = −

The lack of the Carnot limitation alone makes fuel cells and other electrochemical power sources appealing 

as a possible revolutionary change in power production. 

In addition, an electrically based power system may reduce noise by lowering internal powerplant noise 

and possibly further optimizing the propulsor and its performance. While this is of less concern for the automobile industry, the aviation industry is strongly regulated to established noise levels, especially near 

airports. While the propulsor and its noise would remain, the possible powerplant reductions make another 

argument for the technology. 
NASA/TM—2003-212520 2 

NASA has used fuel cells for every manned space flight. While a form of polymer electrolyte membrane 

(PEM) fuel cells was used for many of the Gemini missions, alkaline fuel cells have been used in the Apollo 

missions as well as the Space Shuttle. The fuel cells are supplied with pure H2 and O2 and power much of the 

vehicle electrical system. For the Apollo and Shuttle systems, the resulting water is potable and is an innovative way of producing the necessary drinking water for the crew. Interestingly, the specific power 

(power/mass) of Gemini and Apollo remained nearly constant, but the Shuttle specific power increased 

dramatically [1,2,3]. Currently, many transportation applications of fuel cells have returned to PEM designs 

because of new materials and other improvements. Compared to the space fuel cells, they are more compact 

with even more dramatic specific power and power density (power/volume) improvements in the last decade. 

The improvements in specific power and power density have enabled more than just space applications. 

Possible aeronautical applications include general aviation (GA) and unmanned aerial vehicle (UAV) propulsion and power production units for larger airplanes (replacing the current auxiliary power unit). Aside from 

reducing noise and emissions and improving efficiency, entirely new vehicles may become possible because 

of the change in power system. For example, a regenerative system based on a combined fuel 

cell/electrolyzer/solar array cycle may enable extremely long-range or -duration air vehicles for scientific, 

communication or other purposes [4]. 

This potential has caused NASA Glenn Research Center (NASA GRC) to begin investigating the technology at many levels including basic research in materials and chemical reformation, systems analysis, and 

CFD and other high-fidelity analyses. While the primary NASA goals are in aerospace, efforts have been 

made to coordinate with NASA counterparts in the Department of Energy, industry and universities to ensure 

the most beneficial outcomes for the research. The following is a description of current system analysis 

results for a GA propulsion system. It provides a detailed introduction into the modeling techniques as well 

as an idea of the state of fuel cell propulsion for aircraft. Another paper presents the overall results of this 

study for a specific GA airframe, the MCR01 [5]. 

NASA GRC has been involved in similar electrical systems studies in the past. For example, a 1994 

analysis examined the effects of various power system technology and mission requirements on the sizing of 

a solar/regenerative fuel cell-powered long endurance aircraft [6]. Another example is an exploration of Mars 

aircraft propulsion systems with an emphasis on the constraints of the Martian atmosphere [7]. NASA GRC 

was also involved in the development of the International Space Station (ISS) power system and the resulting 

experience has produced relevant work including a study to replace the ISS battery system with a group of 

flywheels [8]. The study includes detailed electrical models of a multi-component flywheel system. 

Current electrical systems modeling at NASA GRC includes analyses such as the electrical power production unit for larger aircraft and GA/UAV propulsion. Larger aircraft propulsion is being examined in less 

detail for critical technology identification. Work is continuing on flywheel applications and resurging in the 

long-duration aircraft missions because of new and improved technologies and different mission designs. 

There are also ongoing investigations into future manned space flight fuel cell power systems. 

Approach 

 

The propulsion system is simulated primarily through steady-state thermodynamic and physical models. 

The major components of the system, shown in Figure 1, include the PEM fuel cell, electric motor, compressor, fuel cell heat exchanger, and propeller. In addition, mass is estimated for each of the above components 

as well as other electric components and the electrical power distribution system. Various fuels, their distribution and storage are compared primarily by mass and volume and are included in the final airplane model. 

 System Design 

The system is designed to provide shaft power to a propeller. The electric motor converts the energy 

from electrical to mechanical power and the PEM fuel cell converts the energy from chemical to electrical 

power. The apparent ‘backwards’ description is meant to emphasize the simulation process that is used. The 

input shaft power therefore determines the fuel flow rate and air flow rate required. When modeled over a 

flight mission, these data establish the fuel required and therefore analytically size the airplane. 
NASA/TM—2003-212520 3 

Due to the altitude changes and resulting ambient pressure reduction, a radial compressor is used to 

maintain constant pressure at the inlet of the fuel cell. While the pressure change is relatively small at GA 

cruise altitudes, most fuel cells are currently designed for at least ambient pressure and may see a slight 

performance improvement at higher pressures [9]. For this study, a fuel cell inlet pressure of 2 atm is used to 

improve fuel cell performance and to be conservative in the compressor design. The final compressor design 

requirements, including flow rates and pressure ratio, are remarkably similar to that of a supercharger for a 

car. 

The fuel cell requires some form of heat removal such that it remains at the optimal temperature. 

Depending on the fuel cell type, different techniques can be used. For a PEM fuel cell, which operates at low 

temperatures (~80°C), the heat is low-grade and difficult to remove efficiently. While a detailed heat 

exchanger design is out of the scope of this study, the data based on simplified models are recorded. 

As noted in Figure 1, batteries are used in series with the fuel cell in the hybrid configuration. The hybrid 

motive is that by augmenting the fuel cell power during takeoff, a smaller fuel cell may be used, therefore 

reducing the mass and also requiring less fuel for the mission. During cruise, the fuel cell would recharge the 

battery in case of a missed approach or other emergency power surge requirement. 

 Thermodynamic Model

A common issue in electrical and electrochemical systems modeling is that there is no complete model 

package currently available. Chemical process codes typically lack fidelity in the mechanical and electrochemical subjects and similarly, electromechanical analysis codes lack a solid chemical and electrochemical 

background. When requiring propulsion codes such as a propeller performance model, the challenge of a 

universal tool becomes even more difficult. The software used in this analysis is the Numerical Propulsion 

Systems Simulation (NPSS), a NASA and U.S. aerospace industry-developed tool for gas turbine and rocket 

engine models [10]. 

NPSS is primarily a steady-state and transient nodal thermodynamic analysis code that was created so 

that the various organizations involved would have a similar tool for aerospace propulsion analysis. The code 

is object-oriented and therefore modular in that the code can be organized into portions analogous to gas 

turbine components, for example. The modularity also allows for higher-fidelity codes to be inserted into 

their respective section of the system model. A past example used a 1-dimensional mean-line compressor 

code external to NPSS, but accessed real-time by means of the CORBA software [11]. Higher fidelity examples such as CFD have also been demonstrated. NPSS also includes useful thermodynamic data and codes as 

built-in packages for the user. These include temperature and pressure data as a function of altitude, a form 

of the JANNAF data, and the CEA chemical equilibrium code [12]. 

NPSS has several advantages that enabled its use for aerospace electrical systems analysis. Some of the 

most important include the built-in CEA code, the modularity, the design/off-design capabilities, and the 

aerospace industry familiarity. The CEA code provides a well-known basis for calculating equilibrium 

chemical mixtures that is valuable when analyzing fuel reformation as well as the fuel cell. The modularity 

allows for different users to supply their own fuel cell models or configurations without modifying the source 

code or the internal models. The design and off-design capabilities allow the user to set design point conditions and then evaluate that component at other, off-design conditions. An example is setting the compressor 

design pressure ratio and speed at sea-level static conditions and then evaluating the same compressor at 

cruise via an experimentally-correlated compressor map. This capability has proven to be useful in the fuel 

cell model. Finally, NASA is not the only interested party in analyzing possible aerospace electrical systems 

and a common tool among aerospace organizations may prove as valuable in this field as it has in the gas 

turbine and rocket industries. 
NASA/TM—2003-212520 4 

The thermodynamic PEM fuel cell model is a 0-dimensional model based on an ideal cell voltage and its 

losses. The losses are correlated using a multi-function curve-fit of a polarization curve of cell voltage vs. 

current density [13]. A small, conservative pressure effect is included based on data found in the DOE Fuel 

Cell Handbook [9]. This introduces a slight performance reduction for pressures below the design inlet pressure, a condition only seen at the extreme combinations of altitudes and flight speeds. Pressure increases are 

not seen in this study but are of interest. A more theoretical approach could be taken in which the Nernst 

equation would be used to evaluate partial pressure effects on the voltage, but experimental validation was 

lacking at the time of the analysis. The fuel cell characteristics, including design cell voltage, number of 

cells, stacks and their configuration, are set at the design point and then evaluated at off-design conditions 

using the polarization curve as the constant throughout the mission. An example is the difference between 

takeoff and cruise. If the fuel cell is designed at cruise, a relatively low power condition, then at takeoff, or 

higher power, the analysis would require a different current density and voltage based on the polarization 

curve. A similar approach was used in a thesis that designed a fuel cell scooter [14]. If designed correctly, the 

fuel cell can be more efficient at cruise and more current dense and therefore more powerful at takeoff. A 

related item to note is the difference between intermittent and continuous power. Because of the limits of 

heat removal, there is a power level above which the fuel cell will produce more heat than can be removed. 

This power level is known as the continuous power. Intermittent, or peak, power is typically the maximum 

allowable power produced for a short amount of time. For this application, cruise is limited to continuous 

power and the takeoff portion is able to use up to the peak power level. 

The electric motor model is simply a conversion of electrical to mechanical power via an experimentallycorrelated efficiency. The correlation is through a performance ‘map’ of shaft power vs. shaft rpm, with 

efficiency contours included. A map similar to that used in this analysis is shown in Figure 2. Two lines are 

shown: continuous and intermittent power, based on the same reasoning as described in the fuel cell section 

above. The motor continuous-power-to-peak-power ratio is found to be typically smaller than that of the fuel 

cell, and therefore more important in the final sizing and design. These maps are sometimes found in a technical specifications document for the motor. For this study, data for comparable motors are collected from 

four companies that currently design and manufacture electric motors for electric vehicles. All of the motors 

were designed to be compact and lightweight and therefore with the same design goals as with this study. 

Similar industrial motors are much heavier and larger in size. The four companies that are used are UQM 

Technologies, Solectria, AC Propulsion, and Ecostar [15-18]. The final performance map that was selected is 

the UQM Technologies data due to the quality and quantity of the data and its near-average performance 

(compared to the other three companies’ motors). The map is moderately scaled to the actual power required 

but the applicable speeds are nearly that of the optimum propeller, thus eliminating the need for a gearbox. 

The motor portrayed by the map is a liquid-cooled brushless DC permanent magnet machine. In addition, a 

lower-power motor is required to drive the compressor. Similar performance maps are used, with a lower 

efficiency due to the smaller size and possible gearbox because of the high compressor speed. 

The compressor model is the built-in NPSS 0-dimensional model again based on a performance map 

relating pressure ratio, air flow, speed and efficiency. As stated above, its primary design requirement is to 

deliver a constant fuel cell inlet pressure of 2 atm. The value is chosen to be a substantial requirement at 

some altitudes but also realistic for most PEM fuel cells. In addition, the required variation in pressure ratio 

is monitored to keep within a typical compressor performance regime. Based on the design specifications, 

single-stage, radial superchargers are found to be in the same range of values. Figure 3 shows an example of 

a performance map from Turbonetics, Inc., a manufacturer of high-performance car superchargers [19]. 

The primary heat exchanger is used to maintain optimum average fuel cell temperature. It is modeled 

using the default NPSS gas-to-gas heat exchanger with an input effectiveness. Other heat exchangers are 

required for the system, including the motor heat regulation and the compressor aftercooler. The aftercooler 

is required to reduce the compressor exhaust heat to a manageable temperature for the fuel cell. The motor 

coolant loop is not modeled because it is a closed-loop system based on a liquid flow rate. The aftercooler is 

modeled to monitor the system requirements. 
NASA/TM—2003-212520 5 

Even though NPSS has propeller analysis capabilities, a more applicable model is used that is included in 

the airframe code, the NASA-developed Flight Optimization System (FLOPS) code [20]. For this analysis, 

the FLOPS propeller model is accessed real-time during the NPSS calculations to maximize thrust by varying propeller conditions. A detailed version of this method and its merits is described in [5]. 

Mass model 

The mass model is a spreadsheet-based tool. Each component is scaled based on best available data with 

conservative assumptions. The fuel cell system accounts for the balance-of-plant as well as the fuel cell 

stack. The components included are the stack itself, its control electronics, air and hydrogen humidifiers, 

water separator and the heat exchangers. The fuel cell stack is scaled based on the best-available industry 

data. At the time of analysis, a General Motors press release was announced that included a significant 

amount of data near the power levels required for this analysis [21]. Continuous and intermittent power 

levels were provided, as well as mass and volume. Because of the modular nature, the final mass is scaled 

linearly from the intermittent specific power, the most conservative method in this case. It is important to 

note that this power level is not the mechanical shaft power but the electrical power that is calculated to include the parasitic loss from the compressor as well as a smaller percentage for other electronic needs from 

the airframe and power system electronics. Fuel cell electronics are accounted for as a percentage of the fuel 

cell system mass due to the lack of tools available for such a calculation. The percentage is about 60% for 

most systems, but is increased for higher-power systems. General guidance was received from the NASA 

GRC Electrical Systems Development Branch and the inverter/controller data below. The other balance-ofplant correlations are based on data from the NASA GRC Electrochemistry Branch [22]. 

Electric motor mass is calculated based on the specific power scaling of the UQM product line of motors. 

It was found that the most accurate linear scaling was based on the continuous specific power and this is the 

method that is used. One of the benefits of all four motor manufacturers listed above is that a separate inverter/controller was included for each motor. The electronics were similarly designed for compact and 

lightweight power, as well as for the specific motors that are the baselines for this analysis. Likewise, a motor controller mass is scaled linearly based on continuous specific power. The values for the smaller compressor motor are scaled the same way, but with lower specific power values due to the smaller size. 

Another area that is difficult to assess at this level is the power distribution system, consisting of such 

hardware as the conductors and electrical connectors. While it is valuable to include some value as a placeholder and for conservatism, an accurate value is not known until a detailed design is complete. Therefore, a 

percentage of the fuel cell system mass is used, typically around 12%. 

Fuel system modeling 

 

The choice of fuel and its storage depends on many factors, both internal and external to the airplane. 

Internal examples include the type of fuel cell, mass and volume available and aircraft range desired. PEM 

fuel cells are extremely sensitive to impurities such as carbon monoxide and sulfur and therefore fuels other 

than pure hydrogen require extensive reformation. Mass and volume are two recurring design drivers in aircraft design and both severely limit the amount of fuel onboard, directly limiting the range of the aircraft. 

External factors for fuel selection include available fuel infrastructure and availability of the fuel itself. The 

lack of a pure hydrogen distribution infrastructure is a problem being actively addressed by the automobile 

industry and government research, though airport-specific issues may also be a factor. 

For this study, due to the mass, volume, and purity constraints listed above, only non-hydrocarbon 

hydrogen storage methods are analyzed. Ten different methods, including compressed and liquid hydrogen, 

metal hydrides, and carbon nanotubes, are compared by mass and volume using the best available industry 

and/or physical data. Storage methods that require heating, catalysis or other subsystems are penalized 

accordingly. The comparison is shown in Figure 4. Estimated error bars are included to show the uncertainty 

and the MCR01 takeoff gross weight (TOGW) is shown for a sense of scale for the mass axis. In addition, 

gasoline data is shown as an equivalent energy source, not as a possible fuel to reform into hydrogen. 
NASA/TM—2003-212520 6 

Fuel distribution is also considered in the overall mass estimate, but it has a high uncertainty in this early 

design stage, as is the power distribution. A constant value of 10% of the fuel cell system mass is used for 

conservatism. 

Model Validation 

An electrical system designed for GA propulsion has never been assembled, so there is little available 

validation data. In addition, most electrical system and even component data for automobile-based systems 

have not been published due to the proprietary concerns. Therefore, component validation is the most realistic method for current and near-future studies. Most of the performance and mass data is empirical and based 

on current industry data and is hence validated to some extent. However, a true systems-level validation 

has not occurred and is a recognized weakness of such a model. Current efforts at NASA GRC include 

development of an electrical systems test-bed and also external partnerships with similar research-oriented 

organizations. 

Model Assumptions 

The primary assumptions that are used for the study are mainly due to NASA being a technology-driven 

government organization and not a business entity. The question asked for this study is not whether an electrically-driven airplane is financially justified, but whether the airplane is technically possible. Therefore the 

first assumption is to ignore cost. Though the costs are decreasing, fuel cells are still made in the laboratory, 

not on an assembly line and are therefore still very expensive per kilowatt. The other major assumption is 

that the required fuel infrastructure is also ignored as it is out of the scope of this systems study. It is a major 

issue that needs to be addressed for all possible applications of fuel cells. 

Three ‘technology levels’ are used to analyze the value of current research efforts and help direct future 

research: off-the-shelf, intermediate, and advanced technology. The assumptions that are used for each level 

are shown in Figure 5. As shown in the figure, the technology levels directly affect the component masses. 

More mature technology, such as compressors and power electronics are shown to improve slower than 

other, more actively-developed technologies such as the fuel cell. Not shown are the effects of efficiency 

improvement. These effects on the system will be addressed through a sensitivity analysis. 

Results and Discussion 

The powerplants are sized for two different GA airframes, the 2-place MCR01 [23] and the 4-place 

Cirrus SR-20 [24]. Both are composite airframes with the most current technology for their size classes. The 

MCR01 is powered by an 81 peak bhp Rotax 912 intermittent combustion (IC) engine [25] and the Cirrus is 

powered by a 200 peak bhp Teledyne Continental Motors IO360 IC engine [26]. In addition, propulsion 

systems for two larger commercial aircraft, the 50-passenger Embraer ERJ145 and the 100-passenger Boeing 

717, are analyzed at a less detailed level to assess the effects of scaling to much higher power levels. The 

following focuses on the MCR01 sizing to simplify this summary. Further information on the other analyses 

is available from the first author, if interested. Also, as stated in the introduction, a second paper focuses on 

the detailed results of the complete MCR01 analysis [5]. 

The initial modeling approach is to match the peak shaft power of the electric motor to the peak power of 

the Rotax engine, 81 hp. This does not imply that the continuous power of the motor and the engine are the 

same. In fact, the values are very different due to the nature of each system. The IC engine barely loses 

power, going from the peak 81 hp to a continuous value of 79 hp. For the electrical power system, the motor, 

rather than the fuel cell stack, is found to be the limiting component. Its continuous power is typically 

40% – 50% lower than the peak power, estimated at 40 hp for this case. 
NASA/TM—2003-212520 7 

The power and mass results are shown in Figures 6 and 7. The power charts show several interesting 

results. While producing 81 shaft hp, the electrical power requirement of the fuel cell is calculated to be 

about 15% higher due to the compression system and other auxiliary loads. Secondly, the cruise power percentages are different from the takeoff values because of the compressor operation. To deliver constant fuel 

cell inlet pressure at altitude, a higher percentage of compressor power is required. It should also be noted 

that based on the continuous power requirements, the actual cruise power levels drop from 98 hp to 61 hp. 

The mass charts also provide insight into the system. The fuel cell stack, for example, is typically 

considered to be the primary component in terms of mass. While it is calculated to be about 64% of the fuel 

cell system mass, it is only about 24% of the entire system mass. The electric motors and power management 

mass are both calculated to be larger portions of the total, at 28% and 31%, respectively. 

Matching the peak shaft power of the IC engine is successful in that the airplane model is able to analytically takeoff and cruise for a very short time [5]. However, a more realistic approach is to match a lower 

power level that is determined through minimum flight requirements such as takeoff field length and cruise 

speed. While this version of the MCR01 analytically flies slower and lower, it does fly longer and more 

appreciable distances. This concept was presented to NASA from Advanced Technology Products, a 

Massachusetts company attempting to actually build such an aircraft [27]. The lower power level is determined to be 49 peak shaft hp. This reduction in power dramatically lowers the system mass and volume such 

that more fuel and its storage can be included, enabling longer aircraft range. The actual mass is reduced 

from 487 lbm for the 81 hp case to 342 lbm for the 49 hp case, about a 30% improvement. The relative 

power percentages are similar to that of the 81 hp case. 

Much of the research for transportation applications of fuel cells is in mass reduction. Some of the possible advancements are listed in Figure 5 for the three technology levels and system mass totals are estimated 

for each level and compared in Figure 8. While the improvements are substantial, even the advanced technology case is heavier than a comparable IC engine. In order for the electrical system to earn its way onto the 

airplane, the remainder of the mass savings must come from improvement in efficiency. 

Conclusions 

A systems analysis of an electrical power system for a 2-place general aviation airplane is reviewed to 

provide a status of such efforts at NASA Glenn Research Center. While basic lessons can be learned from 

such analysis, there is a need for more accurate models and validation of those models, especially at the systems level. Specific improvements include design of the power management system and its mass prediction, 

more detailed fuel cell and electric motor thermodynamic and mass modeling, and heat exchanger modeling. 

Most of these tools exist in some form, but the integration into a single, coherent systems model is not trivial. 

A dynamic model that investigates startup, takeoff, and other mission transients would also be valuable for 

such a system. Finally, further investigation into various hybrid configurations may be beneficial based on 

both the technical and financial success of battery/IC engine automobile hybrids currently in the market. 

Further analyses and model development are already underway at NASA GRC along with its partners. 

Equilibrium and kinetic hydrocarbon reformer models are being developed. The PEM fuel cell model is 

being improved and a solid oxide fuel cell model is being created. An electrical systems test-bed is being 

assembled that will be able to do much of the necessary validation of the models. 

While the potential for ultra-low emissions and very efficient flight is appealing, one must realistically 

assess such claims through all forms of modeling and hardware testing. There have been many predictions 

about fuel cell technology in the past [28] and it remains the authors’ goal to produce the most accurate 

results possible. 
NASA/TM—2003-212520 8 

References 

1. Russell, J.H.: Gemini Fuel Cell System, Proceedings of the 19th Power Sources Conference, Atlantic 

City, NJ, 1965. 

2. Morrill, C.C.: Apollo Fuel Cell System, Proceedings of the 19th Power Sources Conference, Atlantic City, 

NJ, 1965. 

3. NSTS 1988 News Reference Manual, Electrical Power System Section, NASA KSC, available at 

http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-eps.html, 1988. 

4. Burke, K.A.: High Energy Density Regenerative Fuel Cell Systems for Terrestrial Applications,

NASA/TM—1999-209429, 1999. 

5. Berton, J.J., Freeh, J.E., Wickenheiser, T.J.: An Analytical Performance Assessment of a Fuel CellPowered, Small Electric Airplane. To be presented at the Symposium on Novel and Emerging Vehicle 

and Vehicle Technology Concepts, organized by the Applied Vehicle Technology Panel of the NATO 

Research and Technology Agency, Brussels, Belgium, April 7–11, 2003.

6. Colozza, A.J.: Effect of power system technology and mission requirements on high altitude long 

endurance aircraft, NASA CR–194455, 1994. 

7. Colozza, A.J., Miller, C.J., Reed, B.D., Kohout, L.L., Loyselle, P.L.: Overview of Propulsion Systems for 

a Mars Aircraft, NASA/TM—2001-210575, 2001. 

8. Truong, L.V., Wolff, F.J., Dravid, N.V., Simulation of a Flywheel Electrical System for Aerospace 

Applications, NASA/TM—2000-210242, 2000. 

9. Department of Energy Fuel Cell Handbook, 5th ed., Federal Energy Technology Center, DOE, 2000. 

10. Numerical Propulsion System Simulation User Guide and Reference. NASA-Industry Cooperative 

Effort, Software Release NPSS 1.5.0, May 7, 2002. 

11. Follen, G., auBochon, M.: Numerical Zooming Between a NPSS Engine System Simulation and a OneDimensional High Compressor Analysis Code, NASA/TM—2000-209913.

12. Gordon, S., McBride, B.J.: Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications, NASA RP–1311, 1996. 

13. Colucci-Rios, J.A.: Fuel Cell Power Plant for Future Zero Emission Aircraft. Internal NASA Presentation, 2000. 

14. Lin, B.: Conceptual Design and Modeling of a Fuel Cell Scooter for Urban Asia, M.S. Thesis, Princeton 

University, Princeton, NJ, 1999. 

15. PowerPhase 100 performance data, courtesy UQM Technologies, Inc., Frederick, CO. 

16. AC90–C/DMOC645 performance data, courtesy Solectria Corp., Woburn, MA. 

17. AC–150 performance data, courtesy AC Propulsion Inc., San Dimas, CA. 

18. A 300V65 performance data, courtesy Ecostar/Ballard Power Systems Inc., Burnaby, B.C., Canada. 

19. Compressor model T3–40 performance data, courtesy Turbonetics, Inc., Simi Valley, CA. 

20. McCullers, L.: Aircraft Configuration Optimization Including Optimized Flight Profiles. Proceedings 

of the Symposium on Recent Experiences in Multidisciplinary Analysis and Optimization, NASA 

CP–2327, April 1984. 

21. General Motors Introduces World's Most Powerful Fuel Cell Stack. General Motors Corp. Press Release, 

Sept. 13, 2001.

22. Personal communications with the Electrochemistry Branch at NASA GRC.

23. MCR Flight Manual, courtesy Dyn’Aéro S.A., Darois, France. 

24. Cirrus SR20 Specifications, courtesy Cirrus Design Corp., Duluth, MN. 

25. Rotax 912A performance data, courtesy Rotax Aircraft Engines, Bombardier-Rotax GmbH & Co. 

26. TCM IO360 performance data, courtesy Teledyne Continental Motors Co. 

27. Dunn, J., et al.: Electric Aircraft – Summary and Status. Advanced Technology Products Document 

001013-003, 2001. 

28. Warnock, D.R.: Megawatt Fuel Cells for Aerospace Applications. Proceedings of the 25th Power Sources 

Symposium, 1972. 

29. Colozza, A.J.: Hydrogen Storage for Aircraft Applications Overview. NASA/CR—2002-211867, 2002.

30. Dunn, M.E., Wehner, W., Stone, M.N.: Low-Pressure Automotive Hydrogen Storage Options, A Review.

Los Alamos National Laboratory, Department of Energy, 2001.
NASA/TM—2003-212520 9 

31. Bünger, U., Zittel, W.: Hydrogen storage in carbon nanostructures— still a long road from science to 

commerce?. Appl. Phys. A 72, 147, 2001.

32. Haaland, A.: High-Pressure Conformable Hydrogen Storage for Fuel Cell Vehicles. Proceedings of the 

2000 Hydrogen Program Review, NREL, 2000.

33. Sodium Borohydride data, courtesy Millennium Cell, Inc., Eatontown, NJ. 

Figure 1. A schematic of the propulsion and power system. Solid lines indicate a thermodynamic and a mass 

model while dashed lines indicate a mass model only. Batteries are present in the hybrid design. 

Figure 2. A motor performance map based on the UQM Technologies SR286. Efficiency contours are shown 

as percentages within the plot. 

C 

M 

PEM FC 

Batteries 

PMAD 

HX 

Hum 

Air M 

H2

Aux 

Air, H2O 

0

10

20

30

40

50

60

70

80

90

100

110

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Motor Speed (RPM)

Output Power (k

W)

0

20

40

60

80

100

120

140

Ouput Power (bhp)

Continuous

Intermittent (Takeoff)

90

90

84

84

87

93

93
NASA/TM—2003-212520 10 

Figure 3. A typical supercharger performance map from Turbonetics, Inc. 

Figure 4. Comparison by mass and volume of various hydrogen storage technologies and their estimated 

uncertainty. 15 kg of H2 is stored in each case. The takeoff gross weight of the MCR01 is included for 

scale for the mass axis. Also, gasoline is included not as a possible hydrocarbon source of hydrogen but as a 

comparison by energy (LHV). [29-33] 

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

0 5 10 15 20 25 30 35

Corrected Air Flow (lb/min)

Pressure Ratio

Corrected 

Speed (RPM)

153,500

143,500

132,800

122,800

109,700

96,500

79,500

56,400

75 70

65

700

200

600

500

400

300

100

0

2100

600

1800

1500

1200

900

300

0

gH2 , 3000 psi

gH2

, 5000 psi

gH2, 10000 psi

LH2

Slush H2

NH3

25% NaBH4

, aq. soln.

Metal Hydride

Carbon Nanotubes

Glass Microspheres

Gasoline

(energy equivalent

to 15 kg H2)

Mass (kg)

Volume (l)

Volume (l

Ma

)

ss (kg)

MCR01 TOGW

estimated

uncertainty

700

200

600

500

400

300

100

0

2100

600

1800

1500

1200

900

300

0

gH2 , 3000 psi

gH2

, 5000 psi

gH2, 10000 psi

LH2

Slush H2

NH3

25% NaBH4

, aq. soln.

Metal Hydride

Carbon Nanotubes

Glass Microspheres

Gasoline

(energy equivalent

to 15 kg H2)

Mass (kg)

Volume (l)

Volume (l

Ma

)

ss (kg)

MCR01 TOGW

estimated

uncertainty
NASA/TM—2003-212520 11 

Figure 5. Technology level assumptions with some estimated specific power values. 

Figure 6. Electrical power distribution for the 81 peak shaft hp case. The chart on the left is for takeoff 

conditions (0 ft. altitude and 0 knots) and the chart on the right is for typical cruise conditions (8,000 ft. 

altitude and 130 knots). 

 Off-the-Shelf Technology Intermediate Technology Advanced Technology

Based on commerciallyavailable products

Based on current government and 

industry research and 

development

Based on government and 

university laboratory 

demonstrations

Fuel Cell 

Stack

Automotive-derivative PEM 

fuel cell stack (~1.0 hp/lb)

Higher operating temperature 

PEM fuel cell stack; higher power 

densities (~2.0 hp/lb)

New type of fuel cell with different 

chemistry, higher power 

densities, more efficient operation 

(~3.0 hp/lb)

Fuel Cell 

System

Automotive-derivative 

compressor, heat 

exchangers, humidifiers, 

separator (~0.6 hp/lb)

Integrated heat exchangers, 

humidifiers, separator into fuel 

cell; lightweight, more efficient 

compressor (~1.1 hp/lb)

Humidification, separation, 

extensive cooling not required 

(~1.6 hp/lb)

Electric 

Motor

Automotive-derivative 

permanent magnet electric 

motor (~0.7 hp/lb)

Electric motor with advanced 

cooling and more efficient design 

(~1.5 hp/lb)

Superconducting electric motor 

with very efficient and lightweight 

design (~5.0 hp/lb)

Power 

Electronics

Automotive-derivative power 

management and distribution 

(~0.5 hp/lb)

Higher temperature materials 

(SiC) and components; advanced 

cooling; more efficient design 

(~0.6 hp/lb)

Superconducting electronics for a 

very efficient and lightweight 

design (~0.9 hp/lb)

H2 Storage

Mid-pressure (5000 psi) 

compressed gas; liquid 

storage for long-duration 

missions 

Improved high pressure composite 

tanks; lightweight metal hydrides; 

lightweight, low-temperature 

chemical reformation

Liquid system design with low 

boiloff, high safety; or fuel cell 

able to use common liquid fuels 

directly

Batteries Currently available Li-Ion 

batteries

Advanced Li-Ion or similar 

chemistry batteries with higher 

power density

New battery chemistry with 

longer life and higher energy 

density

Propeller motor

83%

Fuel cell auxiliary 

power

Aircraft auxiliary 3%

power

5%

Compressor motor

9%

Propeller motor

66%

Fuel cell auxiliary 

power

5% Aircraft auxiliary 

power

8%

Compressor motor

21%

98 peak electrical hp 61 continuous electrical hp

Propeller motor

83%

Fuel cell auxiliary 

power

Aircraft auxiliary 3%

power

5%

Compressor motor

9%

Propeller motor

66%

Fuel cell auxiliary 

power

5% Aircraft auxiliary 

power

8%

Compressor motor

21%

98 peak electrical hp 61 continuous electrical hp
NASA/TM—2003-212520 12 

Figure 7. Mass distribution for the 81 peak shaft hp case. The chart on the left is the distribution for the 

fuel cell system and the chart on the right is the distribution for the entire electrical system. 

Figure 8. A representative chart of the effect of improved technology on electrical system mass. The data are 

for the 81 and 49 peak hp systems and the technology assumptions are based on Figure 5. The Rotax 912A 

IC engine mass is included for scale. 

Fuel cell stack

64%

Humidification / 

Seperation

19%

Compression

9%

Thermal 

management

8%

Fuel cell system

37%

Fuel distribution

4%

Electric motors

28%

Power 

management and 

distribution

31%

Fuel cell system mass: 178 lbm Electrical system mass: 487 lbm

Fuel cell stack

64%

Humidification / 

Seperation

19%

Compression

9%

Thermal 

management

8%

Fuel cell system

37%

Fuel distribution

4%

Electric motors

28%

Power 

management and 

distribution

31%

Fuel cell system mass: 178 lbm Electrical system mass: 487 lbm

0

50

100

150

200

250

300

350

400

450

500

Off-the-shelf Intermediate Advanced Off-the-shelf IC

engine

Mass (lbm)

81 peak shp

49 peak shp
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NASA TM—2003-212520

E–14082

WBS–22–706–88–03

18

Electrical Systems Analysis at NASA Glenn Research Center:

Status and Prospects

Joshua E. Freeh, Anita D. Liang, Jeffrey J. Berton, and Timothy J. Wickenheiser

Fuel cells; Systems analysis; Electric motors; Propulsion modeling

Unclassified -Unlimited

Subject Categories: 05 and 07 Distribution: Nonstandard

Prepared for the Novel Vehicle Concepts and Emerging Vehicle Technologies Symposium sponsored by the Applied

Vehicle Technology Panel of the North Atlantic Treaty Organization Research and Technology Agency, Brussels,

Belgium, April 7–10, 2003. Responsible person, Joshua E. Freeh, organization code 2400, 216–433–5014.

An analysis of an electrical power and propulsion system for a 2-place general aviation aircraft is presented to provide a

status of such modeling at NASA Glenn Research Center. The thermodynamic/electrical model and mass prediction

tools are described and the resulting system power and mass are shown. Three technology levels are used to predict the

effect of advancements in component technology. Methods of fuel storage are compared by mass and volume. Prospects

for future model development and validation at NASA as well as possible applications are also summarized.