First Fuel-Cell Manned Aircraft

G IVEN the high efficiency and environmental advantages that fuel-cell technology could offer, along with the considerable improvements achieved in the automotive sector in the last 5– 10 years, the main airframe manufacturers have started to investigate their potential applications in aviation for both propulsion and onboard auxiliary power generation. In 2008, two important steps toward the implementation of fuel cells in aeronautical applications were met: the flight of the Boeing fuel-cell demonstrator airplane described in this paper and presented in Spain in February 2008 and the demonstration of a fuel-cell system generating auxiliary power for the hydraulic and electric systems of an Airbus 320, presented in France in February 2008 [1]. Although these programs will indubitably facilitate the integration of fuel-cell technology in aeronautical applications, there are still many technical challenges to be overcome before these systems can be integrated onboard commercial airplanes. However, fuel-cell technology could have a shortterm application (for example) in sport aviation or in specific missions of small manned or unmanned aircraft, in which fuel cells could offer improved mission endurances over those attained with current battery technology. The first challenge relates to increasing the specific energy density, a less serious concern for other industrial sectors but crucial in the aeronautical sector. Moreover, it is imperative to determine their reliability and performance in realflight conditions (for example, at high altitude, at different pitch and roll angles, etc.), since there are many requirements that are exclusive of aeronautical applications and for which no experience has been gained in other industrial sectors. Among these are, for example, variable pressure and temperature ranges and stringent safety requirements. Although limited in terms of different applications, there is a relatively long experience in the use of fuel-cell systems in the aerospace sector. Despite the fact that recent developments have centered on the automotive industry and in stationary power generation, in the 1960s, NASA (in collaboration with Pratt and Whitney and General Electric) developed fuel-cell systems for the Gemini and Apollo space missions [2]. Nowadays, considerably improved fuel-cell systems are employed onboard the space shuttles to produce water and electricity. A very innovative program that studied the use of fuel cells in the aeronautical sector was the Helios program, carried out in the United States between 1999 and 2003 [3]. The prototype, developed by AeroVironment, Inc., in collaboration with NASA, was a highaltitude (30,000 m) unmanned air platform with a flying wing configuration powered by electric motors. During the day, the Helios would use the energy provided by the photovoltaic cells for both propulsion and for generating hydrogen (throughwater electrolysis), and during the night, it would be powered by the fuel cell. Unfortunately, although they achieved an extremely impressive altitude record (30,000 m during 17 h) in 2001, the platform broke in flight in June 2003 and never flew with the fuel cells. In Arizona, on 26 May 2005, AeroVironment successfully completed the flight tests of one other unmanned platform with a similar aim to that of the Helios program but without using solar energy. It was a scaled prototype of theGlobalObserver [4]. The fuelcell-powered unmanned aerial vehicle (UAV) had a distributed electrical architecture in which liquid hydrogen fuel cells provided electricity to electric motors driving eight propellers. The Global Observer program continues with the aim of developing a platform able to stay aloft at high altitude (20,000 m) during at least 1 week, while carrying a 450 kg payload, to perform surveillance, reconnaissance, and frontier monitoring missions. NASA continues to be interested in high-altitude long-endurance unmanned platform surveillance missions. The Defense Advanced Research Projects Agency recently launched the Vulture program to develop new UAV concepts able to stay aloft at high altitudes during 5 years without interruptions for intelligence, communications, surveillance, and reconnaissance missions over areas of interest. Currently, the only systems able to cover fixed areas during several years are geosynchronic satellites orbiting at 35,780 km above the earth. The innovative platform would not only need to carry a payload of 454 kg, consuming 5 kW, but it would also need to maintain sufficient speed towithstand thewinds at 18,300–27,500m; that is, it should be able to operate like a satellite but covering larger areas (an almost futuristic challenge). Among other technologies, Received 17 November 2008; revision received 10 April 2009; accepted for publication 9 June 2009. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0021-8669/10 and $10.00 in correspondence with the CCC. ∗Research and Technology Europe, Environmentally Progressive Air Transport Team C/Canada Real de las Merinas 1-3, Building 4, Third Floor. Data available at http://www.boeing.com/news/releases/2008/q2/ 080403a_nr.html [retrieved April 2008]. Data available at http://www.boeing.com/news/releases/2008/q2/ 080421d_pr.html [retrieved April 2008]. JOURNAL OF AIRCRAFT Vol. 47, No. 6, November–December 2010

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