In recent years, we have seen an uptrend in the popularity of UAVs driven by the desire to apply these aircraft to areas such as precision farming, infrastructure and environment monitoring, surveillance, surveying and mapping, search and rescue missions, weather forecasting, and more. The traditional approach for small size UAVs is to capture data on the aircraft, stream it to the ground through a high power data-link, process it remotely (potentially off-line), perform analysis, and then relay commands back to the aircraft as needed. All the mentioned application scenarios would benefit by carrying a high performance embedded computer system to minimize the need for data transmission. A major technical hurdle to overcome is that of drastically reducing the overall power consumption of these UAVs so that they can be powered by solar arrays. This paper describes the work done to date developing the 4.0 m (157 in) wingspan, UIUC Solar Flyer, which will be a long-endurance solar-powered unmanned aircraft capable of performing computationally-intensive on-board data processing. A mixture of aircraft requirements, trade studies, development work, and initial testing will be presented.