This project involved the design and development of a solar-powered unmanned aerial vehicle intended for long-endurance environmental monitoring missions. The concept was developed around applications such as forest-fire detection, weather observation, and large-area data collection. Solar energy was considered as a way to extend flight endurance while reducing dependence on conventional onboard energy sources. One of the main design challenges was balancing aerodynamic performance, aircraft weight, available solar-panel area, and the energy requirements of the propulsion and onboard systems. I worked on the aircraft configuration and evaluated design choices relevant to efficient long-duration flight. The geometry and mechanical configuration of the UAV were developed according to aerodynamic, structural, and operational requirements. Aerodynamic behaviour was investigated to evaluate and improve the performance of the aircraft configuration. Numerical analyses were performed to assess the system and its expected behaviour under different operating conditions. The placement of solar cells had to be considered together with aerodynamic and structural requirements rather than as an independent subsystem. Mission requirements were also considered when evaluating the aircraft's endurance and potential operating capabilities. The resulting design demonstrated how renewable-energy technologies could be incorporated into an unmanned aerial platform for scientific and environmental applications. This project developed my experience in aircraft design, aerodynamics, numerical analysis, energy management, and multidisciplinary UAV development.