Helicopters with Fuel Cells (IMAGE) Fraunhofer-Gesellschaft Caption A stack of lightweight fuel cells: The individual cells are held apart by plastic spacers. Measuring 2 x 5 x 4 centimeters, the structure is not much bigger than a matchbox. Credit © Fraunhofer IZM © 6/2008 Fraunhofer-Gesellschaft Usage Restrictions The picture may be used for editorial purposes only. It is protected by copyright. The use is free of charge if the reference is mentioned. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.