Validated Modeling and Synthesis of Medium-scale Polymer Electrolyte Membrane Fuel Cell Aircraft

This paper describes a methodology for design and optimization of a polymer electrolyte membrane (PEM) fuel cell unmanned aerial vehicle (UAV). The focus of this paper is the optimization of the fuel cell propulsion system and hydrogen storage system for a baseline aircraft. Physics-based models, and experimentally-derived sub-system performance data are used to characterize the performance of each configuration within a design space. The results of aircraft synthesis and performance modeling routines are used to create response surface equations where tradeoffs among component specifications can be explored. Significant tradeoffs between fuel cell performance, hydrogen storage and aircraft aerodynamic and propulsion system design are presented. Validation and test results from a proof-of-concept fuel cell UAV propulsion system are presented. Validated models of the fuel cell and aircraft systems are used to predict the performance of fuel cell UAVs at the scale of the baseline aircraft. INTRODUCTION Proposed aircraft applications of fuel cells include auxiliary power units for conventionally powered aircraft or primary powerplants for low-power or long-endurance aircraft [1]. Fuel cell powerplants for UAVs are particularly attractive because of the fuel cell’s high energy density when compared to other rechargeable energy storage systems. Where advanced batteries can reach energy densities of 150Wh/kg at the module level [2], fuel cells can achieve >800Wh/kg at the system level [3]. This study is concerned with the design of fuel cell powerplants to serve as the primary method of propulsion in UAVs. A few researchers have proven the viability of small scale fuel cell powered UAVs by constructing demonstration aircraft [4, 5]. Ofoma and Wu, [6] and Soban and Upton [7] have performed conceptual design of larger-scale fuel cell aircraft. AeroVironment has designed and demonstrated a large-scale fuel cell UAV [8]. Despite these recent achievements, there exists a need for a documented and validated methodology for design and analysis of fuel cell UAVs. In order to begin developing tools and technologies for analysis of fuel cells as powerplants in aeronautical vehicles, a PEM fuel cell UAV demonstration project was started in 2005 as a collaboration between the Aerospace Systems Design Laboratory at the Georgia Institute of Technology Daniel Guggenheim School of Aerospace Engineering and the Georgia Tech Research Institute. The primary research objectives of this project are: the development of validated methodologies and tools for the fuel cell aircraft design, and the demonstration of a series of fuel cell UAVs. At present, a self-contained 500W fuel cell propulsion system has been designed, constructed and tested [9]. A full-scale baseline UAV shown in Figure 1 has also been designed, constructed and is undergoing battery-powered flight testing. The purpose of this study is to quantify important tradeoffs in propulsion system design for fuel cell aircraft and to define optimal fuel cell propulsion systems for a baseline UAV. For this study, the propulsion system is defined to include the PEM fuel cell, fuel cell balance of plant, compressed hydrogen storage system, electric motor system and propeller. A mathematical model of the fuel cell aircraft is constructed in the MATLAB programming environment where the fuel cell propulsion components can be scaled within a range of values. The scaling of the propulsion component models affects the