Unmanned solar powered aircraft offer a unique set of advanced capabilities and have set general aviation records for longest continuous flight and greatest sustained altitude. However, the application of solar powered flight to small scale solar powered unmanned aerial vehicles (UAVs) has seen sparse research activity and is only partially explored. The use of solar power as an energy resource allows small scale UAVs to carry heavier, more powerful sensor payloads, and can extend flight times to over 24 hours, thereby achieving multi-day flight. This work focuses on recent developments by the Center for Distributed Robotics on a four meter wingspan solar UAV designed for low altitude aerial sensing applications. Highlighted in this paper are aspects of airframe, propulsion, and electronics hardware design as well as experiments that quantify the solar power system and airframe performance.