In the framework of the European IMOTHEP project, a novel regional propeller-driven transport aircraft concept with distributed propulsion is investigated. A key feature of this aircraft design is the hybrid-electric approach allowing for fully electric flights on short range missions while extending the range with an integrated gas-turbine for longer range missions. Electrifying the powertrain allows to benefit from several advantages distributed propulsion promises such as reduced vertical tail size, reduced requirements for installed power, and potentially lower structural weight. Moreover, gains in overall aircraft efficiency may arise due to improved aero-propulsive efficiency. The present publication illustrates the comprehensive collaborative work of Safran Tech, CIRA, and DLR that was carried out within the IMOTHEP project with regard to aero-propulsive efficiency of the investigated aircraft design. Various numerical studies on basic aspects like propeller position as well as detailed design studies on propellers, propulsion integration, and high-lift devices were carried out. A wide range of numerical methods ranging from lifting line, over unsteady vortex-lattice and surface vorticity panel methods to Reynolds-averaged Navier-Stokes computations were thereby utilized and compared with each other. The studies led to important design parameter sensitivities and recommendations that were subsequently fed back to the overall aircraft design. Moreover, the design studies yielded an increase of 10% in aerodynamic performance (L/D) and a reduction of -6% in the required propulsive power. Considering the slipstream effect during the high-lift design indicated a potential for improved climb performance.