This paper presents the design methodology developed by the academic aeromodeling group of the University of Stuttgart for the student UAV competition Air Cargo Challenge. The approach involves a multidisciplinary aircraft optimization considering aerodynamics, structural aspects, propulsion, and flight path optimization. A Python-based tool was created to calculate flight performance characteristics during a competition flight mission, enabling the evaluation of the design quality through the competition score, which serves as the single figure of merit for the design. The analysis of the wing is carried out using a combination of Avl and Xfoil, along with handbook methods calibrated through wind tunnel measurements for fuselage and landing gear. Additionally, a simplified propulsion and battery model is used. Extensive parameter studies are done to find a suitable synergetic parameter combination. For design optimization, an iterative optimization of the airfoil using Xoptfoil2 and resizing of the wing is described. The final design was then manufactured using lightweight composite materials and successfully deployed in the competition flights. A comparison of the measured flight performance with the calculated results shows good agreement.