Hydrogen is since long seen as an outstanding candidate for an environmentally acceptable, future aviation fuel. Since the first studies, the design of light yet highly insulated tanks for cryogenic liquid hydrogen has been identified as one of the key enabling technologies. Despite this early recognition, the design of the tanks is nowadays still seen as crucial as aircraft tanks differ significantly from existing tanks in the automotive or aerospace sector. To enable system level feasibility studies of hydrogen fueled aircraft, a preliminary design model for aircraft liquid hydrogen tanks is developed for both foam and multilayer insulations. This model is then used to design tanks for a small regional airliner as well as a large long range transport aircraft. Foam based and multilayer insulations are compared and the sensitivity of the tank weight to the fuselage diameter and the mission fuel load is assessed. The influence of a 'hold' period before take-off is analyzed too. As the developed model is intended for use in the preliminary aircraft design phase, structural design or attachment issues are not addressed. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.