The benefits of periodic cruise operation of flight vehicles have been known for three decades. Although a number of papers and doctoral dissertations have studied the periodic cruise phenomenon, they have not been systematically evaluated in any flight test program. The objective of the present research is the flight test evaluation of endurance-maximizing periodic cruise trajectories. Flight tests will be conducted in collaboration with the NASA Dryden Flight Research Center on a research UAV. A secondary objective of the proposed research effort is to investigate the use of dynamic soaring maneuvers for enhancing the UAV endurance performance. Phase I research will demonstrate the improvements in endurance performance using a UAV simulation model. Realistic UAV dynamics and atmospheric characteristics will be included in these simulations. Guidance algorithms for flying the periodic trajectories will also be developed. Based on the research findings of the Phase I research, Phase II work will refine the guidance algorithms and conduct flight test evaluation of endurance-maximizing periodic cruise trajectories. Development of periodic cruise flight control systems for production UAVs will be undertaken during the Phase III work.