As part of Clean Aviation's UPWING project, the present work aims at designing a hydrogenpowered transport aircraft for a Short-Medium Range mission (239 PAX, 2500 NM) while reducing its overall energy consumption compared to existing aircraft. From an aerodynamic point of view, one way to reduce drag is to use a higher aspect ratio wing. The present work focuses on the transonic aerodynamic design of a strut-braced high-aspect-ratio wing. The study begins with the overall aircraft study, which provides a preliminary design with the general shape of the aircraft (positions and dimensions of the horizontal and vertical stabilizers, wing and fuselage), based on conceptual design assumptions. Then the design process uses the ESP/CAPS CAD modeler and creates a geometry, which is used to assess the aerodynamic performance of the configuration (with automatic meshing, CFD RANS simulation and far-field drag analysis). The aerodynamic wing design also includes an airfoil optimization loop. The preliminary design takes into account structural considerations coming from low fidelity models. In the final paper, the aerodynamic performance of the optimized shape will be analyzed in cruise and off-design conditions.